Composite filling materials and сompomer. Technique filling cavities I and V classes in temporary and permanent teeth. Technique filling cavities II, III, IV classes in temporary and permanent teeth in children with different filling materials.

Composite filling materials and compomers. Technique filling cavities I and V classes in temporary and permanent teeth. Technique filling cavities II, III, IV classes in temporary and permanent teeth in children with different filling materials.

 Dental compomers are materials which are used in dentistry as restorative material. They were introduced in the early 1990s as a hybrid of two other dental materials: dental composites andglass ionomer cement. They are also known as polyacid-modified resin composites. They are used for restorations in low stress–bearing areas.

Compomers are dental restorative materials containing glass ionomer cement. Some features of compomers include fluoride release, radiopaque, quick cure time and good handling characteristics i.e. no slumping, easy to shape/polish, no sticking. Compomers can be light-cure or self-cure. Compomers are ideal restorative material for deciduous teeth and cervical defects. Packaging can be unit dose (capsule) or multi-dose (syringe) depending on designated use. Available shades can vary and can be complimentary or contradictory. Compomers are a popular choice among dentists, known for their good handling characteristics and fluoride release benefits. Choose a compomer that will best fit with your needs.

STEP-BY-STEP INSTRUCTIONS

1. Shade Selection

Shade selection should be made prior to the restorative procedure whilst the teeth are

hydrated. Remove any extraneous plaque or surface stain. Use the Dyract AP shade

guide provided which contains samples of original Dyract AP restorative. The colour

coding dot on the shade guide matches the coloured cap on the Compules Tip. Alternatively, a Vita Lumin Vacuum shade guide may be used. The Dyract AP shade

corresponds to the central part of the respective Vita tooth.

2. Cavity Preparation

In all classes of cavity this may be kept to the minimum required for caries removal.

3. Cleaning

Cavity cleanliness is paramount for the development of adhesion. In cases where no cavity preparation has been made, clean the tooth surface with a rubber cup and pumice or a prophy-paste like Nupro®. Preparing a fresh surface with a finishing bur will significantly increase bond strength to enamel. Wash surface thoroughly with air/water spray. Remove rinsing water by blowing gently with an air syringe or blot-dry with a cotton pellet. Do not desiccate the dentine structure.

4. Pulp Protection

For direct or indirect pulp-capping protect the dentine close to the pulp (< 1 mm) with a hard-setting calcium hydroxide liner (e. g. Dycal®), leaving the remaining cavity surface free for bonding with Prime&Bond NT.

5. Conditioning of dentine and enamel

For most restorative procedures with Dyract AP it is not necessary to condition the

prepared tooth. Only in the case of cavities with bevelled enamel margins or in situations which require maximum adhesion properties, acid conditioning is recommended. In this case, use a 36% phosphoric acid gel.

6. Application of Prime&Bond

1. Dispense Prime&Bond.

2. Immediately apply ample amounts of Prime&Bond to thoroughly wet all cavity

surfaces. This surface should be saturated which may necessitate additional application of Prime&Bond.

3. Leave the surface undisturbed for 20 seconds.

4. Remove solvent by softly blowing with air from a dental syringe for at least 5 seconds.

Surface should have a uniform, glossy appearance. If not, apply a second

layer of Prime&Bond repeating steps 2 to 4.

5. Light-cure for a minimum of 10 seconds3. Ensure uniform exposure of all cavity surfaces.

6. Immediately place Dyract AP compomer over the cured Prime&Bond NT.

7. Placement of Dyract AP

Insert Compules Tip into the notched opening of the applicator gun barrel.

Dispense Dyract AP directly into the cavity preparation. In deep cavities, incremental

placement and curing (in 3 mm layers or less) is recommended to minimise polymerization shrinkage.

8. Curing

Cure each increment separately with a VLC dental polymerisation unit for 40 seconds

or according to the table below. The tip of the light guide should be held as close as

possible to the restoration during curing. Important: Be sure to expose each area of the entire restoration to the curing light.

Additionally, the restoration should be cured through lingual or buccal enamel walls.

9. Finishing

Begin finishing immediately after curing. Gross excess material may be removed with fluted finishing burs or diamonds. Finishing is best achieved by using Enhanc Finishing and Polishing Discs and interproximal finishing and polishing strips. A high final lustre can be obtained by applying Prisma Gloss and Prisma Gloss Extrafine Polishing Pastes.

 

Dental composite resins are types of synthetic resins which are used in dentistry as restorative material or adhesives. Synthetic resins evolved as restorative materials since they were insoluble, aesthetic, insensitive to dehydration, easy to manipulate and reasonably inexpensive. Composite resins are most commonly composed of Bis-GMA and other dimethacrylate monomers (TEGMA, UDMA, HDDMA), a filler material such as silica and in most current applications, a photoinitiator. Dimethylglyoxime is also commonly added to achieve certain physical properties such as flow ability. Further tailoring of physical properties is achieved by formulating unique concentrations of each constituent. Many studies have compared the longevity of composite restorations to the longevity of silver-mercury amalgam restorations. Depending on the skill of the dentist, patient characteristics and the type and location of damage, composite restorations can have similar longevity to amalgam restorations. In comparison to amalgam, the aesthetics of composite restorations are far superior.

Today’s composite resins have low polymerization shrinkage and low coefficients of thermal shrinkage, which allows them to be placed in bulk while maintaining good adaptation to cavity walls. The placement of composite requires meticulous attention to procedure or it may fail prematurely. The tooth must be kept perfectly dry during placement or the resin will likely fail to adhere to the tooth. Composites are placed while still in a soft, dough-like state, but when exposed to light of a certain blue wavelength (typically 470 nm, with traces of UV), they polymerize and harden into the solid filling (for more information, see Light activated resin). It is challenging to harden all of the composite, since the light often does not penetrate more than 2–3 mm into the composite. If too thick an amount of composite is placed in the tooth, the composite will remain partially soft, and this soft unpolymerized composite could ultimately irritate or kill the tooth’s nerve. The dentist should place composite in a deep filling iumerous increments, curing each 2–3 mm section fully before adding the next. In addition, the clinician must be careful to adjust the bite of the composite filling, which can be tricky to do. If the filling is too high, even by a subtle amount, that could lead to chewing sensitivity on the tooth. A properly placed composite is comfortable, aesthetically pleasing, strong and durable, and could last 10 years or more.

The most desirable finish surface for a composite resin can be provided by aluminum oxide disks. Classically, Class III composite preparations were required to have retention points placed entirely in dentin. A syringe was used for placing composite resin because the possibility of trapping air in a restoration was minimized. Modern techniques vary, but conventional wisdom states that because there have been great increases in bonding strength due to the use of dentin primers in the late 1990s, physical retention is not needed except for the most extreme of cases. Primers allow the dentin’s collagen fibers to be “sandwiched” into the resin, resulting in a superior physical and chemical bond of the filling to the tooth. Indeed, composite usage was highly controversial in the dental field until primer technology was standardized in the mid to late 1990s. The enamel margin of a composite resin preparation should be beveled in order to improve aesthetics and expose the ends of the enamel rods for acid attack. The correct technique of enamel etching prior to placement of a composite resin restoration includes etching with 30%-50% phosphoric acid and rinsing thoroughly with water and drying with air only. In preparing a cavity for restoration with composite resin combined with an acid etch technique, all enamel cavosurface angles should be obtuse angles. Contraindications for composite include varnish and zinc oxide-eugenol. Composite resins for Class II restorations were not indicated because of excessive occlusal wear in the 1980s and early 1990s. Modern bonding techniques and the increasing unpopularity of amalgam filling material have made composites more attractive for Class II restorations. Opinions vary, but composite is regarded as having adequate longevity and wear characteristics to be used for permanent Class II restorations. Whether composite materials last as long or has the leakage and sensitivity properties when compared to Class II amalgam restorations was described as a matter of debate in 2008.

As with other composite materials, a dental composite typically consists of a resin-based oligomer matrix, such as a bisphenol A-glycidyl methacrylate (BISGMA) or urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide (silica). Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package (such as: camphorquinone (CQ), phenylpropanedione (PPD) or lucirin (TPO) begins thepolymerization reaction of the resins when external energy (light/heat, etc.) is applied. A catalyst package can control its speed.

Advantages of composites:

·        Aesthetics: The main advantage of a direct dental composite over traditional materials such as amalgam is improved aesthetics. Composites can be in a wide range of tooth colors allowing near invisible restoration of teeth. Composite fillings can be closely matched to the color of existing teeth.

·        Bonding to tooth structure: Composite fillings chemically bond to tooth structure. This strengthens the tooth’s structure and restores its original physical integrity. The discovery of acid etching (producing enamel irregularities ranging from 5-30 micrometers in depth) of teeth to allow a micromechanical bond to the tooth allows good adhesion of the restoration to the tooth. Very high bond strengths to tooth structure, both enamel and dentin, can be achieved with the current generation of dentin bonding agents.

·        Tooth-sparing preparation: The fact that composite fillings are glued (bonded) to the tooth means that unlike amalgam fillings, there is no need for the dentist to create retentive features destroying healthy tooth. Unlike amalgam, which just fills a hole and relies on the geometry of the hole to retain the filling, composite materials are bonded to the tooth. In order to achieve the necessary geometry to retain an amalgam filling, the dentist may need to drill out a significant amount of healthy tooth material. In the case of a composite restoration, the geometry of the hole (or “box”) is less important because a composite filling bonds to the tooth. Therefore less healthy tooth needs to be removed for a composite restoration.

·        Less-costly and more conservative alternative to dental crowns: In some situations, a composite restoration may be offered as a less-expensive (though possibly less durable) alternative to a dental crown, which can be a very expensive treatment. Installation of a dental crown usually requires removal of significant healthy tooth material so the crown can fit over or into the natural tooth. Composite restoration conserves more of the natural tooth.

·        Alternative to tooth removal: Because a composite restoration bonds to the tooth and can restore the original physical integrity of a damaged or decayed tooth, in some cases composite restoration can preserve a tooth that might not be salvageable with amalgam restoration. For example, depending on the location and extent of decay, it might not be possible to create a void (a “box”) of the geometry necessary to retain an amalgam filling.

·        Versatility: Composite fillings can be used to repair chipped, broken or worn teeth which would not be repairable using amalgam fillings.

·        Repairability: In many cases of minor damage to a composite filling, the damage can be easily repaired by adding additional composite. An amalgam filling might require complete replacement.

·        Reduced quantity of mercury released to the environment: Composites avoid mercury environmental contamination associated with dentistry. When amalgam fillings are drilled for height adjustment, repair or replacement, some mercury-containing amalgam is inevitably washed down drains.

·        When amalgam fillings are prepared by dentists, improperly disposed excess material may enter landfills or be incinerated. Cremation of bodies containing amalgam fillings releases mercury into the environment.

·        Reduced mercury exposure for dentists: Preparing new amalgam fillings and drilling into existing amalgam fillings exposes dentists to mercury vapor. Use of composite fillings avoids this risk, unless the procedure also involves removing an existing amalgam filling. A review article found studies indicating that dental work involving mercury may be an occupational hazard with respect to reproductive processes, glioblastoma (brain cancer), renal function changes, allergies and immunotoxicological effects. 

·        Lack of corrosion: Although corrosion is no longer a major problem with amalgam fillings, resin composites do not corrode at all. (Low-copper amalgams, prevalent before 1963, were more subject to corrosion than modern high-copper amalgams.

• Composite shrinkage and secondary caries: In the past, composite resins suffered significant shrinkage during curing, which led to inferior bonding interface.Shrinkage permits microleakage, which, if not caught early, can cause secondary caries (subsequent decay), the most significant dental disadvantage of composite restoration. In a study of 1,748 restorations, risk of secondary caries in the composite group was 3.5 times risk of secondary caries in the amalgam group. Good dental hygiene and regular checkups can mitigate this disadvantage. Most current microhybrid and nanohybrid composites have a polymerization shrinkage that ranges from 2% to 3.5%. Composite shrinkage can be reduced by altering the molecular and bulk composition of the resin. In the field of dental restorative materials, reduction of composite shrinkage has been achieved with some success. Among the newest materials, silorane resin exhibits lower polymerization shrinkage, compared to the dimethacrylates.

• Durability: In some situations, composite fillings may not last as long as amalgam fillings under the pressure of chewing, particularly if used for large cavities. Chipping: Composite materials can chip off the tooth.

• Skill and training required: Successful outcomes in direct composite fillings is related to the skills of the practitioner and technique of placement,. For example, a rubber dam is rated to be important to achieve low fracture rates and a longevity similar to amalgam in the more demanding proximal Class II cavities.

• Need to keep working area in mouth completely dry: The prepared tooth must be completely dry (free of saliva and blood) when the resin material is being applied and cured. Posterior teeth (molars) are difficult to keep dry. Keeping the prepared tooth completely dry can also be difficult for any work involving treatment of cavities below the gumline.

• Time and expense: Due to the sometimes complicated application procedures and the need to keep the prepared tooth absolutely dry, composite restorations may take up to 20 minutes longer than equivalent amalgam restorations.Longer time in the dental chair may test the patience of children, making the procedure more difficult for the dentist. Due to the longer time involved, the fee charged by a dentist for a composite restoration may be higher than for an amalgam restoration.

• Limited insurance coverage: Some dental insurance plans may provide reimbursement for composite restoration only on front teeth where amalgam restorations would be particularly objectionable on cosmetic grounds. Thus, patients may be required to pay the entire charge for composite restorations on posterior teeth. For example one dental insurer states that most of their plans will pay for resin (i.e. composite) fillings only “on the teeth where their cosmetic benefit is critical: the six front teeth (incisors and cuspids) and on the facial (cheek side) surfaces of the next two teeth (bicuspids).”Even if charges are paid by private insurance or government programs, the higher cost is incorporated in dental insurance premiums or tax rates.

Direct dental composites are placed by the dentist in a clinical setting. Polymerization is accomplished typically with a hand held curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved. When using a curing light, the light should be held as close to the resin surface as possible, a shield should be placed between the light tip and the operator’s eyes. Curing time should be increased for darker resin shades. Light cured resins provide denser restorations than self-cured resins because no mixing is required that might introduce air bubble porosity.

Direct dental composites can be used for:

·        Filling cavity preparations

·        Filling gaps (diastemas) between teeth using a shell-like veneer or

·        Minor reshaping of teeth

·        Partial crowns on single teeth

 History

Compomers were introduced in the early 1990s. Previous available restorative materials included dental amalgam, glass ionomer cement, resin modified glass ionomer cement and dental composites.

Composition

The composition of compomers is similar to that of a dental composite however it has been modified, making it a polyacid-modified composite. This results in compomers still requiring a bonding system to bond to tooth tissue. Compomer contains poly acid–modified monomers and fluoride-releasing silicate glasses. An acid-base reaction occurs as the compomer absorbs water after contact with saliva, which facilitats cross-linking structure and fluoride release.

Features

Fluoride release

Compomers do show a fluoride ion release, like a glass ionomer cement. The level of this fluoride release however is only around 10% of that released by a glass ionomer, and therefore its usefulness in preventing recurrent caries on primary tooth is questionable, and is shown to have no advantage over an amalgam restoration with F release bonding agent, which releases mercury and fluoride.^[1] Compomers also do not have the ability to ‘recharge’ with topically applied fluoride from toothpaste etc., like glass ionomer cements do which again will limit their efficacy. Compomers are recommended for patients at medium risk of developing caries.

Handling

Handling and ease of use of composites is generally seen as good by dental professionals.^[2] Compomers are available in both normal and flowable forms, with the manufacturers of the flowable compomers claiming that they have the ability to shape to the cavity without the ne

Aesthetics

Compomers are tooth coloured materials, and so their aesthetics can immediately be seen as better than that of dental amalgams. It has been shown that ratings in various aesthetic areas are better for compomers than resin modified glass ionomer cements.Compomers are also available in various non-natural colours from various dental companies for use in deciduous teeth.

A vast category of dental products, restorative direct filling materials are placed intraorally during numerous dental procedures including filling cavities, endodontic treatments and even prophy appointments. Direct filling materials include composites of all types, etchants, ceramic materials, sealants, glass ionomers, compomers, cavity liners and cleansers, fluoride varnishes, desensitizers opaque materials, and pre-fabricated veneers. Additionally, the category of Restorative Direct Filling Materials includes endodontic restorative materials such as core build-ups and endodontic posts, as well as systems used with direct restoratives such as composite fibers, matrices and interproximal wedges.           

Filling materials are used in the field of dentistry to restore teeth broken down by dental caries. Filling material are of various types, and they can be divided into two types on the basis of the indications of use: those that change over time (plastic materials) and those that do not change or barely change (technical materials).

 “Plastic materials” include composite, amalgam, cement, and glass ionomer cement (GIC). These materials are made up of various components that give the material very specific characteristics. First, the material is easy to manipulate or shape. Second, it must harden after a certain period of time. Third, it must be able to resist temperature and pressure fluctuations for as long as possible, thus remaining stable in shape and maintaining a tight seal. Dental materials fulfil these requirements with varying degrees of success. Most materials’ constantly change in chemical structure in the oral cavity, thus becoming loose after 2–10 years. Unfortunately, this is not immediately noticeable, and many patients only go to the dentist when they feel pain. By then, it’s usually too late because the secondary caries has reached the dental nerve (pulp), necessitating root canal treatment. This is why regular check-ups are so important. Fillings need to be changed as soon as they become loose, not when the tooth hurts.

“Technical filling” materials are manufactured by a technician and inserted into the mouth by a dentist, and these include gold, plastic, ceramics, and/or titanium. As a rule, these materials do not warp or change. Their disadvantage is the glue joint, i.e., the connection between the tooth and the material, as is seen with plastic materials. With good care and processing, most technical materials last from decades to a lifetime, with the processing and handling by the technician and the dentist playing a particularly important role.

Young patients should opt for technical materials because every time a tooth is drilled, there is a potential danger of damage to the dental pulp; in addition, a change of filling always results in some enamel removal, which can consequently lead to sensitivity. When a patient changes his/her cleaning routine and prevents the development of new plaque and secondary caries, technical materials remain sound for decades while plastic materials, even with optimal care, become loose with the passage of time.

Plastic Materials

Glass Ionomer Cements – Glass ionomer cements are special materials used for the purpose of restoring teeth. Although amalgam is now being used less frequently, glass ionomer cements are not a good alternative because of their instability, despite their ease of use. Glass ionomer cements were originally developed for use in the Third World, where a filling material that would not involve drilling of teeth was required. The introduction of high-viscosity glass ionomer cements in the mid-1990s further pushed the development of these cements. This class of glass ionomer cements was originally intended for atraumatic restorative treatment, which involved the insertion of fillings by individuals who were not dentists. The cement was simply pressed into the cavity; such procedures were performed during dental programmes organized in developing lands. Glass ionomer cements stick to the enamel and release fluorides into it, thus slowing the progress of caries. However, this fluoride release gradually slows down within the first few weeks following the filling, and if not supplemented by external means, the “battery effect” disappears completely. If the filling is coated with a fluoride paint, the filling is “recharged” with fluorides that are then transmitted to the enamel of the filled tooth.

Since glass ionomer cements can be used quickly and easily, they have now established themselves primarily in the field of pediatric dentistry. Both milk and permanent teeth can be successfully treated with these materials; however, they only last for 2–5 years because of rapid wear and limited resistance to distortion, making them unsuitable as permanent filling materials.

Glass ionomer fillings must be replaced after 2–5 years because they either distort or become loose. While removing the material with a drill, however, there is some inevitable loss of enamel, which equates to a larger filling and a smaller tooth. As a result, a root canal treatment becomes necessary sooner or later. If the root canal treatment is poorly done, the tooth may fall of within a few years, necessitating a prosthesis. This vicious cycle continues, and by the age of 60, a full prosthesis is required. Considering that even the best possible materials are useless if plaque is not efficiently removed from one’s teeth, investment in gold/ceramic/titanium inlays becomes worthwhile if you understand all the related factors and are willing to change your cleaning routines, because the teeth can then be maintained well for decades.

Compomers – Compomers are polyacid-modified composite materials. As the name suggests, they are a combination of glass ionomer cements and composites. Compomers form a subgroup of composite materials resulting in better hardening in a damp environment compared with pure composites. This also makes them easier to use.

 

 

Before getting too involved in the chemical properties of these materials, we will now discuss the indications for compomer use. Because of better tolerance toward damp environments compared wih pure glass ionomer cements, compomers are ideal for treating caries (cervical caries) or wedge-shaped defects (cervical abrasions) in the neck of the tooth (cervical region).

Composites – Composites are special plastics used in the field of dentistry as filling or restorative materials. They comprise three components: a composite matrix, a dispersive component, and a bonding component.

The composite matrix consists of monomers, co-monomers, initiators, stabilizers, and similar ingredients that give the composite its plasticity and make it shapeable. The monomers are tiny building blocks, like Lego bricks, and when the composite is exposed to halogen light, these monomers bind with the polymers to create bigger building blocks—a hardening process called polymerization.

 

 

During polymerization, unavoidable shrinkage of the material occurs. The amount of shrinkage is proportional to the volume of the filling. For this reason, large cavities should be filled and hardened in layers when composites are used in order to prevent the loss of a tight seal following polymerization shrinkage. In addition, because the polymerization process is very sensitive to humidity, composite fillings should be atempted only after isolating the tooth using a coffer dam.

Unfortunately, another disadvantage of the composite matrix is that it is not stable enough to withstand heavy occlusal forces, which break down the polymer and free the monomers. Monomers are poisonous and damage the tooth nerve, necessitating root canal treatment. They can also result in facial pain if the material is not used correctly.

To combat polymerization shrinkage and give the composite matrix better physical properties (stability against occlusal forces), fillers are added to the composite matrix. Fillers form the main part of the dispersal component and comprise tiny pieces of sand, glass, or quartz, and they are classified as macrofillers, microfillers, or complex microfillers according to particle size.

 

 

Macrofillers are created by a mechanical process. Glass, for example, is ground into dust that is added to the composite matrix. These composites are strong and can withstand excess load; however, they are not very polymerizable. Therefore, they may promote the development of plaque and increase the risk of caries.

Microfillers are produced chemically and added to the composite matrix. They are very polymerizable but not resistant to occusal forces.

Complex microfiller composites are prepared with both macro- and microfillers in an attempt to combine the positive features of both with varying degrees of success. Painstaking research is still being conducted to determine the ideal composition of composite restorative materials.

In order to combine inorganic fillers with organic composite matrices (monomers), we need a bonding component, which gives special features to the composite material.

 

 

Before we get into detailed chemistry, let’s sum up: composites should not be used for posterior teeth that are involved in mastication, and the use of a coffer dam and the insertion of a composite filling in increments decreases the risk of complications such as toothache and shrinkage. Many dentists specialize in composite fillings, and such work is very expensive. Opting for a ceramic inlay needs to be decided on an individual basis. While it is true that ceramic inlays are glued to the tooth with plastic glues, ceramics are resistant to occusal forces. In addition, the interface between the tooth and the filling is extremely fine if done well, thus minimizing polymerization shrinkage and monomer release.

 

 

The complications that arise when composite fillings are used incorrectly or in contraindicated areas are very harmful to the tooth. The tooth becomes sensitive to cold and heat for some time after the filling is done. The patient often experiences a sharp, acute pain in that tooth on stimulation. We call this acute pulpitis, that is, acute inflammation of the dental nerve (or pulp). The cold test will demonstrate a lingering response at this stage.

Eventually, the pulp dies completely, a process called necrosis. The tooth is now painless, even on cold stimulation, because necrosed pulp simply does not function. By this stage, a root canal treatment should be performed at the earliest.

 

If the root is not treated, the dead pulp tissue will cause an inflammatory reaction days, months, or even years later, and the tooth will suddenly become painful again. This time, it will be a blunt pressure pain, especially while chewing. The cause is inflammation of the bone surrounding the tip of the root (periapical infection), which arises from the necrotic pulp. You’re better off investing a bit more in gold, ceramic, or titanium inlays as these will spare you these complications.

A composite is any material that is composed of hard, pebble-like filler particles similar to sand or pebbles, surrounded by a hard matrix of a second material which binds the filler particles together.  The filler particles can be any coarseness varying from large rocks to microscopically fine powder or virtually any shape varying from spherical through fibers to flakes.  The matrix material generally starts out as a paste or liquid and begins to harden when it is activated, either by adding a catalyst (which may be mixed with the filler particles), or by adding water or another solvent to allow chemical reactions to take place.

 

Before it hardens, it can be pressed into a mold, or stuffed into a hole.  The most commonly understood composite material is concrete, or “Portland cement”.  It is composed of sand, sometimes mixed with pebbles, bound together by a matrix of lime, alumina and Iron.  This material can be formed into bricks, poured into molds, or used to “cement” iron rods into the ground. Composites are an increasingly important part of everyday life, from wooden particle board to Corian® countertops.

 

The image on the right shows the microscopic structure of a typical composite material.  The filler particles are the darker, irregular granules.  The matrix is the lighter material that surrounds them.  This particular composite is not highly “filled”, which means that there is a low density of filler particles compared to the amount of matrix material.  Compare that with the micrograph on the left.  This shows another composite material with differently shaped filler particles which are much more closely packed together.  This is a ” highly filled” composite.  Because the characteristics and relative volumes of both the matrix materials and the various filler particles can be manipulated by the manufacturer of the composite, it is obvious that these materials show an almost infinite range of physical properties.   

      In dentistry, The material commonly called “composite” is made of an acrylic matrix called BIS-GMA mixed with a finely ground glass particle filler.  The acrylic will harden with the addition of a catalyst, similar to the way fiber-glass hardens.  In the case of light cured composites, the catalyst is already mixed into the paste, but does not become active until illuminated with a strong light.  To ensure bonding between the filler and the matrix, the filler particles are coated with a silane-coupling agent that contain a methacrylic group able to co-polymerize with the matrix-forming dimethacrylate monomers and functional groups able to interact with the filler.

      Dental amalgam is also a composite, although it is not customary to refer to it as such.  It is made up of finely ground silver/tin metal powder mixed with mercury.  The mercury dissolves the outside layers of the metal powder particles to form a matrix of silver-tin-mercury which hardens around the unreacted metal powder particles to form the finished amalgam composite.  For much more on dental amalgam, please click here.

      Dental cements are all composite materials made from different  powders mixed with different liquids.  The liquid partially dissolves the powder particles and forms a matrix which becomes hard enough to act as a “glue” and is used to cement Crowns and Posts.  All non metallic composite filling materials are really just more highly filled versions of their respective cements.

      Porcelain is not generally thought of as a composite material, but it is in fact composed of a glass matrix filled with crystalline particles.  While ceramics are an extremely important part of dentistry, very few dental professionals really understand them.  For this reason, I have written a Beginners course in dental ceramics to help fill this void.

 

What is Bonding, and how is it done?

Prior to the age of bonding, dental restorations (fillings, crowns, onlays etc.) had to be attached to teeth mechanically.  This is still done in the case of most fillings by the use of undercuts placed inside the cavity preparation (the “hole” in the tooth). The filling material is condensed into the cavity preparation so that it flows into the undercuts.  When hardened, the filling will not be able to dislodge because it is larger at the bottom of the hole than it is at the top.  When placing a cast restoration such as a crown or an inlay, there can be no undercuts.  Otherwise, the casting would not be able to seat.  The vertical walls of the preparation are made nearly parallel, usually slightly tapered.  The space between the restoration and the tooth is filled with a waterproof cement such as zinc phosphate which hardens and “locks” the restoration onto or into the tooth.   The cement flows into the tiny imperfections in the sides of both the preparation and the restoration and acts as a “lock and key” to keep the restoration from sliding out or off the prepared tooth.  Bonding is a different process entirely.  Restorations that are bonded “stick” to the tooth without the aid of undercuts or “lock and key” cementation.  There are four types of bonding used in dentistry today.  

Acid etch enamel conditioning 

In this technique solution of phosphoric acid is placed on the enamel portions of the tooth and left in place for fifteen seconds.  When it is washed off, the formerly shiny enamel surface now looks like it is chalky, or frosted.  Under a microscope, the surface looks like a ragged landscape of jagged mountains and valleys (see micrograph to the right).  These microscopic irregularities are then filled with a liquid acrylic plastic which hardens in place.  Since the filling material is composed of the same sort of plastic, mixed with glass particles (see filled resins below) it will bond onto the plastic which becomes mechanically adhered to the conditioned enamel.  Click the image to learn more about the structure of enamel.

 

 

 

 

 

 

 

 

Dentinal bonding

The micrograph on the left shows what dentin looks like when it is sliced perpendicularly to the dentinal tubules.  The tubule openings are clearly visible, but the hard material between them is still fairly smooth and will not bond to a layer of liquid plastic in the same way as it does to etched enamel.  Etching the dentin dissolves a small amount of the hard dentin material around the tubules allowing the \strands of collagen that permeate the dentin to project beyond the cut surface, and partially opening up the the tubules (image to the right).  An aqueous solution of 2-hydroxyethyl methacrylate (HEMA)–a hydophylic (water soluble) polymer (plastic)–is applied to the conditioned dentin.  This material flows into the tubules and between the exposed collagen fibers.  This acts as a bridge between the otherwise hydophylic collagen fibers and a subsequent layer of hydrophobic (water insoluble) resin, allowing the resin to thoroughly infiltrate between the collagen fibers.  Once the resin hardens, it serves as the basis of dentinal bonding.   Click either image to learn more about the structure of dentin.

 

Chemical adhesion

Certain materials such as Glass Ionomer, and polycarboxylate cements may be applied directly to unconditioned enamel and dentin.  They are applied in a liquid form, and this liquid is fairly acidic.  Metallic polyalkenoate salts combine with the hydroxyapatite by replacing phosphate ions.  The carboxylic groups of the polyalkenoic chains can chelate (chemically combine with) the calcium of the hydroxyapatite to bond the cement to both dentin and enamel. This cross linking of restorative material and tooth structure gives excellent chemical bonding strength.

 

Amalgam bonding

The bonding of a dental amalgam to a tooth involves any or all three of the above mechanisms to bond a filled resin cement to the tooth structure and a mechanical mechanism to bind the amalgam to the resin.  The enamel and dentin are conditioned with 10% phosphoric acid, HEMA is applied to the dentin for dentinal bonding, and a layer of very loose filled resin is applied over the tooth structure.   Dental amalgam is condensed into the tooth while the resin is still unset.  This causes tags of amalgam and filled resin to intermingle at the interface, and when both materials set, they are securely mechanically locked together.  Thus the amalgam is locked to the resin, and the resin is bonded to the tooth. 

 

Types of resin composites

Macrofill Composites-This was the first type of resin composite marketed for filling front teeth.  As the name implies, the particles in a macrofill are fairly large.   Crystalline quartz was ground into a fine powder containing particles 8 to 12 microns in diameter.   As mentioned above, the acrylic matrix in a composite tends to shrink on setting.  Excessive shrinkage in a filling material is undesirable because it would either leave a gap between the tooth surface and the filling material, or, if well bonded, would cause cracks in the tooth structure as the filling contracts during setting.  The inclusion of glass particles reduces this problem because they reduce the volume of acrylic, and act as a mechanical “skeletal structure” within the composite to help maintain the original volume of the filling.  The advantage of large particle size is that more of them can be incorporated into the mixture without making it too stiff to work with.  Macrofills are 70% to 80% glass by weight.  Unfortunately, macrofill composites have two undesirable qualities:

Due to large particle size, macrofills are not very polishable.  The relatively soft acrylic polymer polishes below the level of the glass particles, which constantly pop out of the surface leaving holes in their place.  This leads to a surface which, on a microscopic level, looks like a series of craters interspersed with boulders.

Large particles are relatively easily dislodged from the surface of the restoration during function exposing the relatively soft acrylic polymer which wears away exposing more filler particles which again pop out ad infinitum.  This tendency to abrade away makes macrofils unsuitable for posterior restorations.

The first macrofill appeared on the market in the mid 1960’s.  Most older dentists affectionately remember it by its brand name, Adaptic.  Adaptic had the additional disadvantage of containing no radiopaque materials which made it hard to distinguish from decay on x-rays.

 Microfill composites – Microfill composites use particles of very small size as a filler, about .04-.5 microns in diameter.  The very small end of this range is called a colloidal silica and is produced by “burning” silica compounds in an oxygen and hydrogen atmosphere to form macromolecular structures which fall into this size range.  This type of composite was invented to overcome the esthetic liabilities of the macrofils.  Microfill composites polish beautifully and can be formulated to be quite translucent.

Unfortunately, the smaller the particle size, the fewer of them you can stuff into the composite because it becomes too stiff to work with.  A smaller particle has a relatively greater surface area in relationship to its volume than a bigger one.  In order to include many small particles in a composite mixture, their total surface area increases. As friction is a function of involved surface area, the increased surface increases internal friction and makes the composite so stiff that it cannot be manipulated.  According to Phillips Science of Dental Materials, “Colloidal silica particles, because of their extremely small size, have extremely large surface areas ranging from 50 to 400 square meters per gram.”

Therefore, due to its relatively low filler content,  this type of composite is weaker than composites with larger particle size, and has a relatively greater shrinkage during setting.  Microfills are only 35 to 50 percent by weight filler particles.  Microfils are used for small fillings in front teeth.  They are also used for direct veneers on front teeth because of their superior polishability.

Microfil composites have  three main disadvantages.

Due to the relatively low density of filler particles, microfils are not as strong as composites with larger particle size, especially on the incisal edges of front teeth where the bulk of material is likely to be fairly small.

Also due to low density of filler particles, microfils are more prone to shrinkage while setting, and this limits their use in large, bulky fillings.

Due to the relatively high level of acrylic matrix material, microfills tend to be quite translucent which gives them an overall tendency to cast a slightly gray hue. 

In order to overcome these limitations, it used to be common practice to use a layer of microfil composite over a bulk of macrofil in order to correct the hue problem and increase the strength of the structure to be built with it.  The microfil’s purpose in this case is to lend the restoration a more polishable finish, and a translucent enamel-like appearance.  The purpose of the underlying macrofil is to give the restoration strength and reduce shrinkage stresses.

Microfill composites are not generally used for posterior fillings because of the relatively unfilled nature of the material.  The relatively large amount of acrylic matrix wears too much when subjected to the stresses of grinding and chewing.

Hybrid composites – Hybrids contain a range of particle sizes ranging from 0.6 to 1 micrometers.  Developed in the late 1980’s, these composites achieve between 70 to 75 percent by weight of filler particles.  The first generation hybrids achieved excellent wear characteristics which made them acceptable as posterior filling materials.  They also had fair polishability.  The second generation of hybrids achieved greater polishability and superior color optics by using uniformly cut small filler particles between the larger particles, as well as resin hardeners which help to maintain a surface polish during prolonged function.  Hybrids also have unique color reflecting characteristics which gives them a chameleon-like appearance.  In other words, these materials are able to emit their own color as well as absorb color from the surrounding and underlying tooth structure.  Hybrid composites are today the workhorse of the modern dentist.  They are used iearly all anterior restorations, and are becoming commonplace in posterior restorations as well.

Microhybrid composites––Microhybrids are similar to regular hybrids except that they employ microfil particles  (very fine colloidal silica particles, approx 0.04 microns) to fill in between the larger particles.  The extremely small filler particles lend superior polishability and allow for finer color characterization, while the composite, as a whole, remains about 70% -75% filled.  This formulation comes closest to the surface characteristics of microfill composites while maintaining the durability and strength of standard hybrids.  Microhybrids are formulated to be layered, and some of the shades are opaque which mask the gray of the more translucent shades.  Microhybrids are stiffer than standard hybrids, and do not slump, so they are often more appropriate for rebuilding large areas of a tooth freehand.  On the downside, they do not flow as easily as standard hybrids, and it can be difficult to get them to flow into marginal areas and tight corners.  The availability of opaque shades allow for better masking of the gray color that is visible when microfill composites are used to close diastema (spaces between the teeth).  Microhybrids can also be used for posterior restorations.

Flowable composites -This composite restorative is formulated with a range of particle sizes about the same as hybrid composites.  The amount of filler is reduced and the amount of unfilled resin matrix material is increased.  This makes for a very loose mix.  It is delivered into a cavity using a syringe.  It flows freely over the inside surface of the cavity preparation.  This material has made it possible to fill small cavities in the tops of teeth without a shot since the area of decay is often small enough to be removed with little or no sensation in the tooth, and the flowable composite will bond even if there are no undercuts in the cavity preparation.  Flowable composites are often used to seal the dentin of a tooth prior to placing the filling material.  Due to the low level of filler particles, flowable composites are more prone to shrinkage, so they are generally not used by themselves to fill large cavities.

Resin (Composite) Cements –When formulated as loose, sticky, chemically cured substances (i.e. with a separate catalyst that is manually mixed into the base at the time of use), filled resins make remarkably strong cements for crowns, veneers, onlays, posts, Maryland bridges, orthodontic brackets and other bonded appliances. Since both porcelain and tooth structure can be etched with acids, the resin component can flow into the microscopic irregularities in the appliances to be cemented as well as the irregularities etched into the tooth structure.  This etched bond is, by itself, quite strong, however the presence of the filler particles adds a second “lock and key” type of mechanism to help cement the appliance as well.   

Resin modified glass ionomers

Resin modified glass ionomers are glass ionomer cements that contain a small quantity of a polymerizable resin component.  These  materials have most of the advantages of glass ionomer materials with the added advantage of water insolubility while setting. These materials are always dispensed in two component systems and begin hardening only when both components are mixed together.  The resins included in some systems have dual curing capability, which means that they will cure chemically once the pastes are mixed, but the curing can be accelerated by the use of high intensity light.  The ability to light cure the excess material reduces chair time. 

Resin modified glass ionomer cements

These are a real success story in dentistry.  Resin modified glass ionomer cements have become the standard material used to cement metal and zirconia based crowns and bridges onto prepared teeth.  They reduce post operative sensitivity and reduce the likelihood of cement washout.  They chemically bond to both the metal and the tooth structure.  They have much less shrinkage on setting than resin based composites.  They are also easy to use and simple to mix, unlike zinc phosphate cement which was the industry standard up until the introduction of these cements.

Resin modified glass ionomer restoratives

These are used mostly as bases under composite resin restorations.  They lack the ability to resist occlusal wear, but their major virtue is that they shrink very little while setting and thus reduce post operative sensitivity while reducing compressive stresses on the tooth.  They also release fluoride into the tooth structure.  They are also useful for filling cavities around the gum line.  In this capacity they leach fluoride into the tooth throughout their service life thus reducing the likelihood of recurrent decay.

The Compomers (polyacid-modified resin composites)

A compomer is really a modified composite resin.  These materials have two main constituents: A resin modified with dimethacrylate monomer(s) with two carboxylic groups present in their structure, and a filler that is similar to the ion-leachable glass present in glass ionomer cements. The filler particles are only partially silanated to help the adhesion of the resin to the glass particles, while at the same time allowing some of the soluble fluoride in the glass to leach out into the tooth structure.  When first marketed, it was claimed that the carboxylic groups in the resin would allow adhesion to tooth structure without the acid etch bonding technique, similar to glass ionomer cements.  This turned out to be a false assertion.  Even so, compomers are still popular with dentists for filling deciduous (baby) teeth, and, due to their high degree of translucency, they are highly esthetic when used for the repair of cervical (gum line) caries.  They confer a degree of fluoride release into the tooth, although less than that found in glass ionomer cements.  Thus, at least in the short term, they prevent recurrent decay while allaying parents’ concern about the presence of mercury in standard amalgam fillings.  They do not have the surface durability of standard composite resins, but will wear quite well for the life of a deciduous tooth.  Unlike glass ionomer restorations, they do NOT adhere to tooth structure without an acid etch bonding technique.   They are esthetically pleasing and seem to resist recurrent decay for several months after placement when used to fill cavities near the gum line.

Paste compomer restorative (filling) material; These materials are excellent tooth colored filling materials when used on front teeth ion stress bearing areas, such as for filling cavities at the gum line, or in larger restorations if they are fully supported by natural tooth structure and do not involve incisal or occlusal surfaces.  They are especially good on the buccal or labial (front) surfaces of teeth where esthetics is extra important.  They are often used to cover exposed, sensitive root structure on both front and back teeth.  

In spite of the fact that they are less wear resistant than regular composites, some dentists use light activated compomers to  fill baby teeth due to their extended fluoride release, and also to allay parents’ fears about the mercury in amalgam fillings.  The baby teeth generally exfoliate (fall out) before the wear becomes a problem.  Compomers are also useful in geriatric dentistry since oral hygiene is often poor in elderly patients, and they frequently suffer xerostomia (dry mouth).  The combination of poor oral hygiene and dry mouth causes rampant decay in these patients, and the constant release of fluoride at the tooth/restorative junction can be helpful to prevent recurrent decay.

Flowable compomers; These are like the paste compomer restorative, but they contain much more of the unfilled resin.  They are used in the same fashion as flowable composites, except they are rarely used in stress bearing areas such as the occlusal surfaces of adult teeth. 

A note on radiopacity of dental materials

X-rays are an essential part of dental diagnosis, and it is very important that any material that remains implanted in any part of the patient’s body, including his teeth, be radiographically distinguishable from natural structures or disease processes.  In other words, any material or device implanted in teeth or in any other part of the body must be visible on an x-ray.  Materials like amalgam, gold and titanium (for implants or posts) are made of metal and are naturally radiopaque (ie. they block x-rays and cast a white shadow on s-ray film).

Materials like restorative composites, porcelain, or various dental cements are not inherently radiopaque and without modification of their composition, would not be visible on an x-ray film except as a dark spot if deposited in bone or tooth structure.  Unfortunately, decay in teeth shows up as a dark area on an x-ray film, and in the early days of composite technology, before the addition of radiopacifiers, it was often difficult to distinguish between a composite filling or an area of decay in a tooth when looking at an x-ray.   The addition of zirconium dioxide, barium oxide or Ytterbium oxide to any radiolucent (the oposite of radiopaque) material will impart the property of radiopacity.  These three oxides are chosen for their compatibility with the chemistry of composites.  Note that Barium Sulfate is used as a “milkshake” or enema when taking medical x-rays for the observation of the gastro-intestinal tract. 

The addition of radiopacifiers is especially important in the production of dental cements used to lute crowns and bridges.  Even though the cement will spend its lifetime under the crown, excess cement will be forced out from between the crown and the tooth during placement, and often end up between the teeth or under the gums where it cannot be seen by direct observation.  When this happens, it can cause inflammation of the gums and even eventual loss of the tooth.  As long as the cement is visible on the x-ray, it will reveal the presence of the cement so that it can be removed. 

Technical Materials

Inlays – An inlay is a filling manufactured in a dental laboratory, and it is usually used to treat damage caused by caries. The joint between the tooth and inlay should be absolutely smooth. No irregularity should be detected on the surface of the inlay, even with the fine point of a dental probe. A gap between the inlay and tooth surface allows for plaque colonization in that area because it cannot be cleaned with a toothbrush, thus resulting in secondary caries.

A loose or projecting inlay can be observed by a dark line between the tooth and inlay and these are the regions where bacteria and plaque accumulate. The patient will feel pain only when the caries reaches the tooth nerve (pulp), and at this stage, a root canal treatment will be required. In order to prevent this, inlays should be checked yearly for a satisfactory fit.

Inlays can be made of plastic, ceramic, gold, or titanium. The technician manufactures the inlay on the basis of a plaster model fabricated using an impression of the teeth. The plaster model is a negative replica of the teeth, enabling the technician to prepare an exact-fitting inlay from the appropriate material.

Ceramic inlays are the most expensive type, but they are also the most frequently used. The main advantage of ceramic, apart from the excellent esthetic features, is that the filling is glued to the tooth. The joint is extremely strong, provided that the manufacturer’s instructions have been followed, including the use of a rubber dam (watertight compartment), appropriate tooth conditioning, etc (more about this in the videos Ceramic Inlays, Etching, and Bonding). Because of the complicated gluing procedure for ceramic inlays, gold inlays are often preferred by dentists.

In contrast with glued ceramic inlays, metal inlays are fixed simply by means of a tight fit. No glue is used, making this attachment weaker than a glued joint. In addition, the esthetic results with metal inlays are inferior when compared with those with ceramic inlays.

Indeed, attempts are sometimes made to cover gold inlays with a thin ceramic layer; unfortnately, this usually splinters after a short time because of occlusal forces, leading to exposure of the underlying gold.

Apart from the material used, fillings manufactured by technicians are differentiated into inlays, onlays, and overlays according to the size of the filling. Inlays do not have any contact with the corresponding tooth in the opposite jaw, whereas onlays do. If a cusp is covered by a filling, we call this an overlay.

The quality of tooth replacement depends less on the choice of material and more on the collaboration between the dentist, technician, and assistant and their experience in using the appropriate materials. Good inlays can, with appropriate care, last for decades or even a whole lifetime.

Alternatives to inlays include the well-known filling materials such as amalgam, cement, glass ionomer cements, etc. However, these materials are not as long-lasting; therefore, they may have to be changed every few years. This leads to the loss of healthy tooth material, which progresses to conditions requiring root canal treatments. Therefore, it is better to invest in more expensive materials for younger patients and instigate appropriate changes in their cleaning routines. While it’s true that the initial costs are higher, they will ultimately save suffering, time, and money.

With an experienced practitioner, the risks associated with tooth grinding for inlay placement are negligible. Nevertheless, complications occasionally occur, necessitating further measures. With every additional measure, there is a further possibility of complications that can even progress to becoming life-threatening. Complications specific to tooth preparation for inlays are described below:

·   Injury to neighboring structures such as the tongue, cheeks, nerves, blood vessels, and neighboring teeth and roots, with related consequences

·     Inflammation of the dental nerve (pulp), sometimes necessitating root canal treatment

·  A poor fit, which can result in secondary caries

In principle, every type of intervention on a tooth carries a danger of inflammation of the dental nerve (pulp). The dental professional should therefore ensure that the workmanship and materials employed will lead to durable and healthy results with good care.

Veneers – A veneer is a wafer-thin, translucent ceramic shell that is placed over the tooth and fixed with a special glue, which is usually a dental cement. Veneers are predominantly used on the front (anterior) teeth. A thin enamel layer (0.3–1 mm) is removed as required. This preparation is done according to anatomical conditions, and the goal is to achieve a cosmetically attractive, long-lasting result. Special depth marks show the dentist how much enamel needs to be removed; furthermore, they ensure uniform cutting. How much tooth substance needs to be removed depends on tooth alignment, existing fillings, and tooth color. In modern dentistry, teeth can be corrected through such minimally invasive procedures. However, such high quality esthetic work requires a well-established team (dentist, technician, and assistants).

Compomers” are recently introduced products marketed as a new class of dental materials. These materials are said to provide the combined benefits of composites (the “comp” in their name) and glass ionomers (“omer”). Based on a critical review of the literature, the author argues that “compomers” do not represent a new class of dental materials but are merely a marketing name given to a dentalcomposite.

 

TOOTH RESTORED USING COMPOMER

Shortly after the introduction of RMGICs, “compomers” were introduced to the market. They were marketed as a new class of dental materials that would provide the combined benefits of composites (the “comp” in their name) and glass ionomers (“omer”). These materials have two main constituents: dimethacrylate monomer(s) with two carboxylic groups present in their structure, and filler that is similar to the ion-leachable glass present in GICs. The ratio of carboxylic groups to backbone carbon atoms is approximately 1:8. There is no water in the composition of these materials, and the ion-leachable glass is partially silanized to ensure some bonding with the matrix.

 

These materials set via a free radical polymerization reaction, do not have the ability to bond to hard tooth tissues, and have significantly lower levels of fluoride release than GICs. Although low, the level of fluoride release has been reported to last at least 300 days. The delayed (post-cure and post-water-sorption) acid-base reaction between sparse carboxylic groups and areas of filler not contaminated by the silane coupling agents is speculative and is probably insignificant to the overall properties of these materials.

 

 

Based on their structure and properties, these materials belong to the class of dental composites. Often, they have been erroneously referred to as “hybrid glass ionomers”,“light-cured GICs” or “resin-modified glass ionomers” along with the “genuine” resin-modified GICs. The proposed nomenclature for these materials as polyacid-modified composite resins,a nomenclature that is widely used in the literature, may over-emphasize a structural characteristic of no or little consequence. Considering the low volume fraction filler and the incomplete silanization of the filler, it could be postulated that they are inferior composites. Both in vitro and in vivo investigations have confirmed this expectation. Lower flexural modulus of elasticity,compressive strength, flexural strength, fracture toughness and hardness, along with significantly higher wear rates compared to clinically proven hybrid composites, have been reported for these materials. Their clinical performance received mixed reviews in in vivo clinical trials^. With the exception of concerns about the release of HEMA from these materials, no other biocompatibility issues have been associated with their usage.Their applicability as orthodontic adhesives, amalgam bonding systems and veterinary restorative materials has also been reported.

Constant re-formulations of these types of materials may eventually lead to them being comparable or even superior to existing composites, but, as long as they do not set via an acid-base reaction and do not bond to hard-tooth tissues, they cannot and should not be classified with GICs. They are, after all, just another dental composite.

 

Dental composite resins are types of synthetic resins which are used in dentistry as restorative material or adhesives. Synthetic resins evolved as restorative materials since they were insoluble, aesthetic, insensitive to dehydration, easy to manipulate and reasonably inexpensive. Composite resins are most commonly composed of Bis-GMA monomers or some Bis-GMA analog, a filler material such as silica and in most current applications, aphotoinitiator. Dimethylglyoxime are also commonly added to achieve certain physical properties such as flow ability. Further tailoring of physical properties is achieved by formulating unique concentrations of each constituent. Unlike amalgam which essentially just fills a hole and requires retention features to hold the filling, composite cavity restorations when used with dentin and enamel bonding techniques restore the tooth back to near its original physical integrity. Nevertheless, time to failure is still longer for amalgam, and it has remained a superior restorative material over resin-base composites, but with poor aesthetic qualities. 

History of use

Initially, composite restorations in dentistry were very prone to leakage and breakage due to weak compressive strength. In the 1990s and 2000s, composites were greatly improved and are said to have a compression strength sufficient for use in posterior teeth. Today’s composite resins have low polymerization shrinkage and low coefficients of thermal shrinkage, which allows them to be placed in bulk while maintaining good adaptation to cavity walls. The placement of composite requires meticulous attention to procedure or it may fail prematurely. The tooth must be kept perfectly dry during placement or the resin will likely fail to adhere to the tooth. Composites are placed while still in a soft, dough-like state, but when exposed to light of a certain blue wavelength (typically 470 nm, with traces of UV, they polymerize and harden into the solid filling (for more information, see Light activated resin). It is challenging to harden all of the composite, since the light often does not penetrate more than 2–3 mm into the composite. If too thick an amount of composite is placed in the tooth, the composite will remain partially soft, and this soft unpolymerized composite could ultimately irritate or kill the tooth’s nerve. The dentist should place composite in a deep filling iumerous increments, curing each 2–3 mm section fully before adding the next. In addition, the clinician must be careful to adjust the bite of the composite filling, which can be tricky to do. If the filling is too high, even by a subtle amount, that could lead to chewing sensitivity on the tooth. A properly placed composite is comfortable, aesthetically pleasing, strong and durable, and could last 10 years or more. (By most North American insurance companies 2 years minimum)

The most desirable finish surface for a composite resin can be provided by aluminum oxide disks. Classically, Class III composite preparations were required to have retention points placed entirely in dentin. A syringe was used for placing composite resin because the possibility of trapping air in a restoration was minimized. Modern techniques vary, but conventional wisdom states that because there have been great increases in bonding strength due to the use of dentin primers in the late 1990s, physical retention is not needed except for the most extreme of cases. Primers allow the dentin’s collagen fibers to be “sandwiched” into the resin, resulting in a superior physical and chemical bond of the filling to the tooth. Indeed, composite usage was highly controversial in the dental field until primer technology was standardized in the mid to late 1990s. The enamel margin of a composite resin preparation should be beveled in order to improve aesthetics and expose the ends of the enamel rods for acid attack. The correct technique of enamel etching prior to placement of a composite resin restoration includes etching with 30%-50%phosphoric acid and rinsing thoroughly with water and drying with air only. In preparing a cavity for restoration with composite resin combined with an acid etch technique, all enamel cavosurface angles should be obtuse angles. Contraindications for composite include varnish and zinc oxide-eugenol. Composite resins for Class IIs were not indicated because of excessive occlusal wear in the 1980s and early 1990s. Modern bonding techniques and the increasing unpopularity of amalgam filling material have made composites more attractive for Class II restorations. Opinions vary, but composite is regarded as having adequate longevity and wear characteristics to be used for permanent Class II restorations (although amalgam has proved to last considerably longer and have reduced leakage and sensitivity when compared to Class II composite restorations).

Composition

Dental composite resin.

As with other composite materials, a dental composite typically consists of a resin-based oligomer matrix, such as a bisphenol A-glycidyl methacrylate(BISGMA) or urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide (silica). Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package (such as: camphorquinone (CQ),phenylpropanedione (PPD) or lucirin (TPO)) begins the polymerization reaction of the resins when external energy (light/heat, etc.) is applied. A catalystpackage can control its speed.

Advantages

The main advantage of a direct dental composite over traditional materials such as amalgam is improved aesthetics. Composites can be made in a wide range of tooth colors allowing near invisible restoration of teeth. Composites are glued into teeth and this strengthens the tooth’s structure. The discovery of acid etching (producing enamel irregularities ranging from 5-30 micrometers in depth) of teeth to allow a micromechanical bond to the tooth allows good adhesion of the restoration to the tooth. This means that unlike silver filling there is no need for the dentist to create retentive features destroying healthy tooth. The acid-etch adhesion prevents micro leakage; however, all white fillings will eventually leak slightly. Very high bond strengths to tooth structure, both enamel and dentin, can be achieved with the current generation of dentin bonding agents.

Disadvantages

Clinical survival of composite restorations placed in posterior teeth has been shown to be significantly lower than amalgam restorations.^[2] However, improvements in composite technology and techniques have improved their longevity.^[3]

Direct dental composites

A hand-held wand that emits primary blue light (λmax=450-470nm) is used to cure the resin within a dental patient’s mouth.

Direct dental composites are placed by the dentist in a clinical setting. Polymerization is accomplished typically with a hand held curing light that emits specific wavelengths keyed to the initiator and catalyst packages involved. When using a curing light, the light should be held as close to the resin surface as possible, a shield should be placed between the light tip and the operator’s eyes, and that curing time should be increased for darker resin shades. Light cured resins provide denser restorations than self-cured resins because no mixing is required that might introduce air bubble porosity.

 

 

Direct dental composites can be used for:

·                    Filling cavity preparations

·                    Filling gaps (diastemas) between teeth using a shell-like veneer or

·                    Minor reshaping of teeth

·                    Partial crowns on single teeth

Indirect dental composites

This type of composite is cured outside the mouth, in a processing unit that is capable of delivering higher intensities and levels of energy than handheld lights can. Indirect composites can have higher filler levels, and are cured for longer times. As a result, they have higher levels and depths of cure than direct composites. For example, an entire crown can be cured in a single process cycle in an extra-oral curing unit, compared to a millimeter layer of a filling.

As a result, full crowns and even bridges (replacing multiple teeth) can be fabricated with these systems. A stronger, tougher and more durable product is likely.

Indirect dental composites can be used for:

·                    Filling cavities in teeth, as fillings, inlays and/or onlays

·                    Filling gaps (diastemas) between teeth using a shell-like veneer or

·                    Reshaping of teeth

·                    Full or partial crowns on single teeth

·                    Bridges spanning 2-3 teeth

Composite shrinkage

Composite resins are notorious for shrinking upon curingHowever, their use as dental restorative materials focuses on low-shrinkage composites. Composite shrinkage can be reduced by altering the molecular and bulk composition of the resin. For example, UltraSeal XT Plus uses Bis-GMA without dimethacrylate and was found to have a shrinkage of 5.63%, 30 minutes after curing. On the other hand, this same study found that Heliomolar, which uses Bis-GMA, UDMA and decandiol dimethacrylate, had a shrinkage of 2.00%, 30 minutes after curing.In the field of dental restorative materials, reduction of composite shrinkage is a “hot topic”.

 

Composition

Although the original systems developed by Wilson and Kent (1971) have undergone several modifications, the essential components of this class of materials are unchanged and consist of water sol. of polycarboxylic acid, FAS glass, tartaric acid, pigments and radio-opacifiers. The polymeric components of most commercial embodiments are copolymers of acrylic acid with itaconic or maleic acid. Tartaric acid is added to the liquid to control the viscosity as well as the working and setting properties of the cement. The basic component is an acid-reactive FAS glass containing additional multivalent ions such as calcium, strontium and lanthanum, some of which are added to provide radiopacity to the set cement. The molar ratio of aluminum to silicon in the glass network has to be carefully controlled (usually 2 : 3 to 1 : 1) to provide the right balance of reactivity versus stability. These cements are supplied as bulk powder–liquid formulations as described for the zinc polycarboxylates. Both hydrous and anhydrous forms are available, depending upon the manufacturer. In the latter, the freeze-dried polyacid is mixed with the powder and water is supplied as the liquid.

In order to make it convenient for the dentist, manufacturers have developed unit-dose capsules, which are activated just before use by breaking a seal that allows the powder and liquid to come into contact. An amalgam triturator is then used to mix the components mechanically while specially designed delivery guns are provided to extrude the mixed paste directly into the oral cavity. The glass-ionomer luting cements contain a lower powder/liquid ratio, and hence are less viscous upon mixing than the restorative products. Furthermore, the particle size of the glass has to be quite small in order to meet the ISO specifications of film thickness.

Mechanism of action

Setting reaction

The essential constituents of glass ionomer cements are a poly-alkenoic acid and an ion-leachable glass. The glass particles can vary in size, and the size can determine the properties of the material, and are therefore graded for the various applications for glass ionomers. The acids involved, are originate from the polyalkenoic family of acids, which includes, amongst others, poly-acrylic acid, poly-itaconic acid and poly-maleic acid. The glass particles commonly are a calcium-alumino-silicate glass and contain calcium or strontium and fluoride. Restorative glass ionomers tend to contain larger particles than luting cements or lining materials; the setting reaction is, however, essentially similar. The setting reaction undergoes three main stages: dissolution, gelation and hardening. In the dissolution stage, the poly-alkenoic acid, in the presence of moisture, releases protons which attack the surface of the glass, causing the release of fluoride, calcium and aluminium ions. The outer surface of the glass becomes gel-like as the lost ions are replaced by hydrogen from the carboxylate groups from the poly-acid chains. The gelation reaction occurs over a few minutes, where the freed divalent calcium ions form ionic bonds with the negatively charged carboxyl ions on the poly-acid chains. They form cross-links if they connect to two adjacent chains or they may join two adjacent carboxyl groups on the same chain. During this stage, the material firms to the touch. Shaping of the restoration should be done quickly, as the material becomes friable as it hardens, making it very difficult to achieve a smooth shape. The hardening phase may take several days to complete, and only then does the material reach its final strength. During this phase, trivalentaluminium ions form more effective cross-links between adjacent chains.

Other components of the glass ionomer cement include tartaric acid, pigments and radio-opacifiers. The tartaric acid, when used in the correct concentration, will cause the setting to be improved; that is, the material remains workable for a sufficient amount of time to be placed and shaped, and then hardening occurs more rapidly. The final set material is porous enough to allow the free movement of small molecules, such as hydroxyl and fluoride ions, in and out of the material.

 

When the powder and liquid are combined, an acid–base reaction occurs between the FAS glass and the polycarboxylic acid in the presence of water eventually leading to a hardened mass. As with the zinc carboxylate cements, water plays several important roles in the overall setting of glass-ionomer cements.

 A very important by-product of the setting reaction is the release of fluoride ions from the glass matrix. This fluoride release process is sustained and occurs over a long period of time. It is important to realize that this fluoride ion release is a result of the setting reaction and the ion-exchange process in the cement. In this process, the fluoride from the glass is replaced by carboxylate groups and water. Hence, if properly formulated, there is little chance of the cement losing its strength with time. Considerable research has proved that no loss of strength of the glass-ionomer cement occurs over extended storage in water.

Role of tartaric acid

Tartaric acid is added to prolong the working time of the cement mix, improve the manipulative characteristics and narrow the range of the setting time. In the absence of this component, the mix becomes rubbery within a few seconds and is rather difficult to work with. The mechanism by which tartaric acid operates is believed to be a temporary suppression of the ionization of the polyacid as well as a preferential extraction of the cations from the glass so that polyacrylate complexes cannot form immediately, thus leading to an increased working time. Later, it sharpens the set and accelerates the hardening of the glass-ionomer mix.

 

Manipulation

Handling notes

The prepared cavity should first be conditioned with a dentine conditioner, the most common one being 10% polyacrylic acid. The conditioner removes the smear layer and debris from the prepared cavity walls, allowing a clean surface to bond to, but leaves smear plugs intact so as to prevent contamination of the cleaned dentine surface with dentinal tubular fluid. The acids used for the bonding of resin composite should not be used for conditioning prior to glass ionomer placement, as the low molecular weight of these acids would demineralize the dentine, leaving less calcium available for the ion-exchange bonding mechanism. The polyacrylic acid conditioning agent should only be applied for a short time, about 10 seconds, and should be washed off thoroughly before drying, without dehydrating the dentine.

 

Care must be taken when handling this class of materials since they are quite technique-sensitive and errors could lead to a potentially compromised clinical outcome.Manufacturers of these cements recommend that the powder and liquid are dispensed in defined ratios and then mixed rapidly with a spatula within 30–45 s. The general rule is to first incorporate half the amount of the powder into the liquid and then mix in the other half. The stainless steel cement spatula is most often used, although in some practices a plastic spatula is preferred to avoid potential discoloration. As with all powder–liquid formulations care must be taken to dispense the powder and liquid accurately so as to prevent operational variability. The working and set times are dependent on the powder/liquid ratio. The cement should be used immediately after mixing because the working time is only a few minutes at room temperature. If the ambient temperature is high, working time is even further decreased. If a skin forms over the cement, the mix should be discarded – otherwise adhesion will be compromised. The manipulation is easier for encapsulated versions although it is important to follow the manufacturers’ recommended speed and times for trituration of the capsules. Conventional glass ionomers are quite susceptible to moisture contamination. After initial set and removal of excess cement, it is often advisable to coat the cement margins with a sealing agent supplied by the manufacturer.

Setting and working time

The factors controlling the setting and working times are similar to those described for the polycarboxylate cements except that here the reactivity and the particle size of the FAS glass, rather than zinc oxide, are of relevance.

Physical properties

The conventional glass ionomers are rather brittle materials with high modulus of elasticity, low diametral tensile strength and low fracture toughness. They are susceptible to desiccation and hence must be protected with a varnish or a resin bonding agent during the setting process. Compressive strengths are similar to those of the zinc phosphate cements.

Fluoride release

Glass-ionomer materials exhibit a sustained release of fluoride over a long period of time. The uptake of the released fluoride ion in human saliva and its incorporation into human enamel have been reported. Although considerable debate exists about the ‘clinical proof’ of the benefits of fluoride, occurrence of recurrent caries in the teeth where these cements have been used is reported to be rare.

 This can be attributed to the ability of glass-ionomer cements to inhibit demineralization and enhance remineralization through release of fluoride to the adjacent tissue and surrounding fluid. The rate of fluoride release depends on a particular product brand. However, as a general class, glass ionomers release more fluoride than other types of fluoride-releasing materials.

Adhesion

Like the polycarboxylate cements, the conventional glass ionomers can bond to the calcium of hydroxyapatite of tooth tissue.

Post-operative sensitivity

In the past, one of the common complaints against conventional glass-ionomer cements has been the high incidence of post-operative sensitivity with greater incidence reported for the ‘anhydrous’ type. The most frequent reasons cited for post-operative dentinal hypersensitivity are as given below.

• Desiccation of the tooth. The glass ionomers require water for their setting and may absorb water from the dentinal tubules during this process. This phenomenon is thought to be more prevalent in the anhydrous cements where the dried polycarboxylic acid also needs water for rehydration.

•  Initial low pH of the material (although it increases rapidly during the setting process) may irritate the pulp.

•  Moisture contamination leading to poor sealing of the tooth and improper margins, hence leakage to bacteria and their by-products.

•  Too low a viscosity of the mix causing fluid to be forced down the dentinal tubules during seating of the prosthesis.

 Clinical usage

Although somewhat technique-sensitive, conventional glass-ionomer luting cements have a good clinical history and are employed primarily for the cementation of permanent metal and porcelain-fused-to-metal (PFM) crowns, for cementation of posts and as orthodontic band cement. The prolonged release of fluoride makes them particularly attractive for conditions where the risk of secondary caries is high. According to some manufacturers the use of polyacrylic acid conditioner is contraindicated in crown and bridge procedures so that the smear layer on the abutments remains to act as a protective layer. Their prolonged maturation time, however, allows for early water sensitivity and they are also more susceptible to hydrolytic degradation than the more insoluble RMGIs or composite luting cements. For this reason, it is advisable to use protective agents such as varnishes or resin-glazes along the crown margins or cover the fillings made from glass-ionomer with the varnish.

GICs as an adhesive cavity lining (the sandwich technique)

GICs have a number of advantages as a cavity lining as they bond to dentine and release fluoride which may help to reduce recurrent decay. They can be used beneath either a composite resin or an amalgam. The so called sandwich technique involves using a GIC as a dentine replacement and a composite to replace enamel.

 

 

 

 

Indications for glass ionomer cements

GICs generally are indicated for use in the following circumstances:

■ Liners and bases for direct and indirect restorations.

■ RMGICs are indicated for bonded-base restorations and temporary restorations, especially between appointments in endodontic therapy.

■ For rapid stabilisation of a dentition where there are multiple cavities in a patient with a high caries risk.

 ■ Atraumatic restorative technique (ART).

■ Cementation of cast indirect restorations.

■ Traditional GICs are useful for the restoration of root caries in the elderly patient.

Resin-modified glass ionomers

Resin-modified glass ionomers have a resin (monomer) component as well as the poly(alkenoic) acid and fluoro-aluminosilicate glass of conventional glass ionomers. They set by two mechanisms: acid–base reaction and curing of the monomer (chemically, by light or both).

They have improved appearance and physical properties compared with conventional glass ionomers. They are used in similar situations to glass ionomers and may also be used for small core build-ups.

RMGIs, developed in the late 1980s, are more recent entrants into the dental cement arena, having been first introduced commercially as a luting cement in 1994. This class of cements is less technique-sensitive than the conventional glass-ionomer materials and possesses some very favorable physicomechanical properties compared with conventional GI materials yet releases similar levels of fluoride. Since the RMGI luting cements also allow easy removal of excess cement, show minimal post-operative sensitivity and, so far, have exhibited good clinical performance and durability, this class of material has rapidly become one of the most popular materials for routine crown and bridge applications. Improvements in delivery format have now consolidated their use.

Composition

The first-generation materials were supplied as powder–liquid configurations and are available in hand-mix or encapsulated versions. Vast differences do exist between products from different manufacturers; hence care has to be taken in choosing a particular commercial product for clinical use. The essential components of a true RMGI are:

• polycarboxylic acid copolymer often modified with pendant methacrylate groups;

• FAS glass;

• water;

• water-compatible methacrylate monomers;

• free-radical initiators.

Setting and working time

The working time is typically greater than 2.5 min from the start of mix at ambient temperature of 23 °C. Higher temperatures and vigorous spatulation shorten the working time while lower temperatures prolong it. Excess material can be removed when the cement reaches a waxy stage after placement in the mouth (2–3 min at 37°C) using a suitable instrument. The restoration should be finished and the occlusion checked when the material has completely set (about 5 min from placement, depending on brand).

 Post-operative sensitivity

Perhaps the most attractive reason why this class of cements was readily adopted in clinical practice is because the users of RMGI luting cements observed remarkably low post-operative sensitivity in their patients (Christensen, 1995; Hilton et al., 2004). This is perhaps because these self-adhesive materials do not need the removal of the dentinal smear layer and are not as technique-sensitive as the conventional materials. The seal at the dentinal margin is very good; hence, hydrodynamic fluid flow or the ingress of bacteria do not appear to be a problem. Another factor that may play a role (though a minor one) is that the RMGIs start out at a higher pH (lower acidity) and, hence, do not cause an adverse reaction on the pulp.

Polyacid modified resin composites

 

 

Polyacid modified resin composites are also known as compomers.

*  Their properties are more like those of composites than glass ionomers.

* They have limited fluoride release but are stronger and have a better appearance than glass ionomers.

* Their wear resistance is less than that of composite restoratives.

*  They do not adhere directly to tooth substance, they require an adhesive agent to create a micromechanical bond to tooth structure.

* They may be utillised to restore cervical and anterior proximal cavities and for primary teeth.

Advantages

Compomers and resin composites share the same advantages. Additional advantages include fluoride release and ease of handling. The only situation where the use of a more hydrophilic resin system (i.e. a compomer) might be advantageous is in the restoration of non-carious and carious cervical lesions where moisture control can be problematical. The hydrophilic nature does not mean that the material can tolerate excess moisture in the form of saliva.

Steps to a Filling

When you visit your dentist to get a filling, you may be given local anesthesia to numb the area if necessary. Next, your dentist will remove decay from the tooth, using hand instruments or a drill. Air abrasion and lasers also can be used to remove decay.

A drill, which dentists call a handpiece, uses metal cones called burs to cut through the enamel and remove the decay. Burs come in many shapes and sizes. Your dentist will choose the ones that are right for the size and location of your decay.

At first, your dentist will use a high speed drill (the one with the familiar whining sound) to remove the decay and unsupported enamel of the tooth. Once the drill reaches thedentin, or second layer of the tooth, the dentist may use a lower speed drill. That’s because dentin is softer than enamel.

Once all the decay is removed, your dentist will shape the space to prepare it for the filling. Different types of fillings require different shaping procedures to make sure they will stay in place. Your dentist may put in a base or a liner to protect the tooth’s pulp(where the nerves are). The base or liner can be made of composite resin, glass ionomer, zinc oxide and eugenol, or another material.

Some of these materials release fluoride to protect the tooth from further decay.

If your dentist is placing a bonded filling, he or she will etch (prepare) the tooth with an acid gel before placing the filling. Etching makes tiny holes in the tooth’s enamel surface. This allows the filling to bond tightly to the tooth. Bonded fillings can reduce the risk of leakage or decay under the filling. That’s because the etched surface of the tooth and the filling material form a mechanical bond. Bonding is generally done with composite fillings.

Certain types of fillings get hardened by a special light. With these fillings, your dentist will stop several times to shine a bright light on the resin. This cures (hardens) the material and makes it strong.

Finally, after the filling is placed, your dentist will use burs to finish and polish the tooth.

After a Filling

Some people feel sensitivity after they receive a filling. The tooth may be sensitive to pressure, air, sweet foods or cold. Composite fillings often cause sensitivity, but other types of filling materials can, too.

In most cases, the sensitivity will subside over one to two weeks. Until then, try to avoid anything that causes it. If your tooth is extremely sensitive or your sensitivity does not decrease after two weeks, contact your dentist’s office.

It’s important to let your dentist know about any sensitivity you are feeling. The next time you need a filling, he or she may be able to use a different material and make changes to reduce sensitivity. People vary in their response to different materials. Your dentist has no way of predicting if your tooth will react to a particular material.

When you talk to your dentist about the sensitivity, try to describe it as precisely as possible. This information will help decide what should be done next. Your dentist may take out the filling and put in a new one. He or she may add a base, liner or desensitizing agent on the tooth as well. If the filling was very deep, you could need aroot canal treatment to solve the problem.

Besides sensitivity, some people feel discomfort when they bite down. There are two types of pain, each with a different cause.

·   The first type occurs when you bite, and worsens over time. This is caused by a filling that is too high and interferes with your bite. Once your anesthetic wears off, you would notice this right away. Contact your dentist. You will need to return to the office to have the filling reshaped.

·   The second type of discomfort is a very sharp shock that appears only when your teeth touch. This is called galvanic shock. It is caused by two metals (one in the newly filled tooth and one in the tooth it’s touching) producing an electric current in your mouth. This would happen, for example, if you had a new amalgam filling in a bottom tooth and had a gold crown in the tooth above it.

Your dentist polishes the filling after it is placed, but occasionally sharp edges may remain. You can’t detect this at first because of the anesthesia. If you find one, contact your dentist and arrange to have it smoothed as soon as possible to avoid injury to your tongue or mouth.

Temporary Fillings

You may receive a temporary filling (usually white, off-white or gray) if:

·  Your treatment requires more than one appointment.

·   Your dentist wants to wait a short period of time for the tooth to heal.

·   You have a deep cavity and the pulp (containing the nerve and blood vessels) becomes exposed during treatment.

·   You need emergency dental treatment.

A temporary filling may make your tooth feel better. This is because the filling seals the tooth, protecting the pulp from bacteria and reducing sensitivity.

Temporary fillings often contain eugenol, an ingredient in over-the-counter toothache remedies. Eugenol is also a component of oil of cloves, which people use for toothache pain.

Temporary fillings are not meant to last. Usually, they fall out, fracture or wear out within a month or two. If you get a temporary filling, make sure you visit your dentist to get a permanent one. If you don’t, your tooth could become infected or you could have other problems.

Why Replace a Filling?

Fillings don’t last forever. They can become discolored. Composite, tooth-colored fillings pick up stains, and yellow or darken over time. When you chew, your teeth and any fillings in them are subjected to tremendous pressures. Even if no other problems develop, some fillings will wear out over time and will need to be replaced. A filling will need to be replaced earlier if it falls out, leaks or cracks.

Food debris and bacteria can seep down under a filling that is cracked or leaking. Since you can’t clean there, the bacteria feed on the food debris and form the acid that causes tooth decay. Decay under a filling can become extensive before you notice it or it causes you pain. This is why you should have your fillings checked regularly and get them replaced when problems are found.

Fillings That Fall Out

Fillings can fall out for several reasons:

·  You bite down too hard on a tooth that has a large filling, and break the filling or the tooth.

·     The filling material that was used cannot withstand the forces placed upon it. For example, if you have broken a large piece of your front tooth, a porcelain (tooth-colored) crown is probably a good treatment choice. In some cases, a dentist may place a composite filling instead. This may look good or acceptable. However, if the composite is too large, a strong biting motion may break the plastic material.

·   The cavity is contaminated with saliva when the filling is placed. For composite resins, this will disrupt the bonding of the material. As a result, the bond will not stick well to the tooth and it may fall out.

Cracked Fillings

Both amalgam and composite fillings can crack, either soon after they are placed or after the fillings have been in place for some time.

Cracks can occur soon after a filling is placed if the filling is higher than the rest of the tooth surface, and must bear most of the force of biting. Cracks also can occur over time, as the forces from chewing and biting affect the filling.

Small cracks also can occur at the edges of a filling. These usually are caused by wear over time. These cracks often can be repaired.

Leaking Fillings

A filling is said to be leaking when the side of the filling doesn’t fit tightly against the tooth. Debris and saliva can seep down between the filling and the tooth. This can lead to decay, discoloration or sensitivity.

Both amalgam and composite fillings can leak. An amalgam filling sometimes leaks slightly after it is placed. You would notice this as sensitivity to cold. This sensitivity decreases for the next two to three weeks. Then it disappears altogether. Over that period, the amalgam filling naturally corrodes. The corrosion seals the edges of the filling and stops any leaks.

A composite filling could be contaminated with saliva. This would weaken the bond between the filling and the tooth and allow for leaks. Other times, there may be small gaps where the tooth and filling meet. These gaps are caused by shrinkage when your dentist places the filling. Sensitivity after receiving a composite filling may disappear over time. If it doesn’t, the filling may need to be replaced.

Fillings also can leak as a result of wear over time. These fillings should be replaced.

Worn-Out Fillings

Some fillings can last for 15 years or longer. Others, however, will have to be replaced in as little as five years. Your dentist can determine if your fillings are worn enough that they need to be replaced.

Clenching and Grinding 

If you clench or grind your teeth, you may have more problems with your fillings. The forces placed on your teeth can lead to tooth sensitivity and extra wear on your fillings. Clenching or grinding also can cause your teeth and fillings to crack or develop small craze lines. These are fine cracks you can see if you shine a light on your tooth.

Keeping Your Fillings

Although some fillings can last for many years, the average life of an amalgam filling is about 12 years. Composite fillings may not last this long.

Your dentist will examine your fillings at your checkup visits. You may need X-rays if your dentist thinks a filling might be cracked or leaking, or to see whether decay is occurring under the filling. Make an appointment with your dentist:

· If a tooth is sensitive

· If you see a crack

· If part of a filling appears to be missing

You should visit your dentist regularly for cleanings, brush with a fluoride toothpaste, and floss once a day. If you have many fillings or very large fillings, your dentist may prescribe a fluoride gel you can use at home. The fluoride will help strengthen the enamel of your teeth and help to prevent future cavities. Your dentist or hygienist also can apply a fluoride varnish around the edges of these teeth at your checkup visits.

Replacing a Filling

Before removing your old filling, your dentist will discuss treatment options with you. It is often possible to repair an old filling instead of removing it and replacing it completely. However, if the entire filling has to be replaced, the dentist may reevaluate what filling material to use. Talk with your dentist about how you would like the filling to look. Then he or she can select the material that is best for you.