Fixing dental prosthesis. Complications and errors in fabrication bridges.

Fixing dental prosthesis. Complications and errors in fabrication bridges.

Dental Bridge Complications

A dental bridge is a permanent artificial implant used to replace one or more missing teeth, according to the University of Maryland Medical Center. The bridge consists of three pieces that fit into the open space in the mouth, bridging or closing the gap. Bridges usually consist of a porcelain false tooth joined together by two crowns or a cap that surrounds the teeth. Complications are rare, but it is important to know any risks associated with the procedure.

Sensitivity

A common complication associated with a dental bridge is tooth sensitivity, according to the website AboutCosmeticDenistry.com. Many people experience mild tooth sensitivity to extreme heat, coldness or touch following a dental bridge procedure. A dull ache in the gums usually accompanies the sensitivity. The discomfort usually subsides in a few weeks.

Decay and Infection

Decay is a common long-term complication associated with a dental bridge. Decay can occur when food and other particles get stuck in between the teeth as a result of natural wear and tear or a poorly fitted bridge. The Cosmetic Dentistry Guide states that approximately 10 to 15 years after receiving the bridge, the cement that holds the teeth together usually cracks, allowing food particles to accumulate in the small holes and resulting in decay. In addition, decay can lead to infection when bacteria from the food particles that accumulate between the teeth enter the bloodstream and spread to various parts of the body.

Pain

Some people may experience mild to moderate pain after receiving a dental bridge, according to the website Dental-Implants.com. It is normal to have minor pain, inflammation and/or bruising around the gums after the procedure. The discomfort usually subsides after a few days. Severe pain that persists for a week or more may signal an infection or an ill-fitting bridge.

Breakage

People who have a dental bridge may experience broken teeth, according to the website My Dental Health. Stress can weaken, break or cause pulp death in the teeth that support the dental bridge. During the bridge implantation, the natural supporting teeth are ground down so the bridge can attach to them. The pressure from the grinding can cause weakened or fragile teeth to crack. The website SmileGuys.com states that low-quality dental bridges can also cause the surrounding teeth to break or fracture during chewing or biting

Dental Bridge Risks

Recurrent Decay

Preparation for a dental bridge requires shaving down teeth on either side of the empty space. This is so that the crowns can fit down over the teeth in order to retain the false tooth. If the margin of the crown does not fit exactly onto the prepared tooth, there is a chance for bacteria to contact the tooth surface beneath the crown. Without correction, the teeth can become decayed to the point of being lost, and the bridge must be removed. Before the bridge is cemented into place, the dentist should check thoroughly to be sure that all margins are closed.

Pain

The dentist must take the existing bite into consideration when fabricating a dental bridge. Teeth produce strong biting forces, and the synthetic material used to fabricate the bridge does not absorb these forces as well as the natural teeth. If the new bridge does not properly reproduce the bite of the patient, moderate to severe pain can result. This can often be corrected with minor adjustments to the bite, performed by the dentist.

Periodontal Disease

If a patient is at risk for periodontal disease, placement of a dental bridge can make the condition worse. Biting forces on a bridge can cause strain on the ligament surrounding the tooth, leading to bone loss over time, according to H.T. Shillingburg in “Fundamentals of Fixed Prosthodontics.” Also, if the bridge ends beneath the gum line, irritation can occur, leading to gingival recession. Proper oral hygiene is essential to prevent periodontal disease from starting or progressing.

Limited Options

Once the teeth on either side of the bridge have been shaved down to fabricate the bridge, there is no way to get the tooth structure back. If there is a reason to remove the bridge once it is cemented, there will be limited options for restoring the space other than fabricating a new bridge.

Potential Risks and Complications of Dental Bridges

Tooth Decay for Anchor Teeth

The dental bridges will fill a gap in your mouth and the bridges will be placed on the tooth before and after the gap, which are also known as anchor teeth. These neighboring teeth will have to be adjusted, so as to be able to place a crown on them. This means that the dentist will peel off a few millimeters from each tooth, even if these teeth are perfectly healthy. The enamel will be affected, so these teeth will be more susceptible to tooth decay. Plaque can gather in the crown area and may be difficult to clean.

It is essential to floss and use an interdental brush that can remove the plaque.

Gum Disease

Dental bridges will increase the risk of gum disease. The bridges are made up of two crowns on the anchor teeth and the false teeth. All these will gather plaque, which is problematic to clean and in time, the plaque will harm the gum, so gum disease or gingivitis may develop. Prevent these problems with regular teeth brushing and periodical professional cleaning.

Lose the Bridges

The crowns on the anchor teeth may become loose and they may fall off while you chew. This may be dangerous, as you may swallow the false teeth and the crowns, which are quite large and can lead to severe digestive problems.

If you see that the bridges are loose, you have to make an appointment with your dentist to fix the problem and prevent the ingestion or losing the bridges.

The crowns will be cemented back and they should be stable.

The consumption of high amounts of alcohol can dissolve the cement that holds the dental crowns on the anchor teeth, so try to avoid alcohol as much as possible. Check out the labels of mouth rinse, most products contain alcohol; ask your dentist to recommend you a special mouth rinse or avoid mouth rinse altogether.

Fractures

As the crowns on the anchor teeth are made of all ceramic materials or ceramic material fused on metal, the crowns may be fragile and can fracture while chewing on hard textured food. The false teeth may also break or get chipped.

You should avoid eating rough textured foods such as nuts or ice. If you notice that the bridges are fractured, try not to swallow and visit your dentist right away.

Minimal fractures may be repaired, but in some cases, you may need to replace the bridges or crowns.

Damage Neighboring Teeth

Bridges made of ceramic materials may become rough in time and a rough surface that constantly presses against your natural teeth can damage the enamel of these teeth.

In case you notice that the bridges have a rough surface, visit your dentist. The bridges will be polished to have a smooth surface.

 

Dental Cements
dental cement  any of various bonding substances that are placed in the mouth as a viscous liquid and set to a hard mass; used in restorative and orthodontic dental procedures as luting (cementing) agents, as protective, insulating, or sedative bases, and as restorative materials
Introduction

Although dental cements are used only in small quantities, they are perhaps the most important materials in clinical dentistry because of their application as (1) luting agents to bond preformed restorations and orthodontic attachments in or on the tooth, (2) cavity liners and bases to protect the pulp and foundations and anchors for restorations, and (3) restorative materials. This multiplicity of applications requires more than one type of cement because no one material has yet been developed that can fulfill the varying requirements.

Over the last two decades, the emphasis has been on materials for luting in view of the increased use of fixed partial dentures. More recently, with the advent of glass-ionomer cements, interest in restorative applications has revived also. These different applications require different physical properties and appropriate clinical manipulative characteristics, and so, in response to the changing situation, new international standards are being developed (International Standards Organization [ISO]), as are various national standards (American National Standards Institute/American Dental Association [ANSI/ ADA]) based on performance criteria rather than specific composition.

For acceptable performance in luting and restorative applications, the cement must have adequate resistance to dissolution in the oral environment. It must also develop an adequately strong bond through mechanical interlocking and adhesion. High strength in tension, shear, and compression is required, as is good fracture toughness to resist stresses at the restoration-tooth interface. Good manipulation properties, such as adequate working and setting times, are essential for successful use. The manipulation, including dispensation of the ingredients, should allow for some margin of error in practice. The material must be biologically acceptable.

Most cements are powder-liquid materials that may be dispensed and mixed manually or predispensed in capsules that are mixed mechanically. Some recent materials are composed of two pastes. Cements set by chemical reaction between the ingredients (often an acid-base reaction) or involve polymerization of a monomeric component.

In the early 20th century zinc oxide-phosphoric acid, zinc oxide-eugenol (clove oil 85%), and silicate glass-phosphoric acid cements were discovered. These zinc phosphate, zinc eugenate, and silicate cements were widely used until the 1970s, wheew cements began to be developed.

The introduction of new types of cements was prompted by the emphasis on improved biocompatibility and bonding to the tooth that began to develop 20 years ago. New information on pulpal histopathology resulting from particular clinical techniques and materials, as well as the demonstration of marginal leakage involving penetration of bacteria to the dentin interface and a reduction in retention of restorations, led to the realization that new materials possessing good wetting and bonding to enamel and dentin and low toxicity were needed.

These concepts were the basis of the development of cements based on polyacrylic acid: first the zinc polyacrylate (polycarboxylate) cements, then the glass-ionomer cements, and more recently the resin cements and hybrid ionomer cements. The newer cements have gradually become established as alternatives to zinc phosphate cement because of their minimal effects on pulp, similar strength and solubility characteristics, and adhesive properties.

The advent of the acrylic resins led to the development of poly(methyl methacrylate) in the mid-1950s. These materials had limitations such as lack of adhesion, leakage, and toxicity that terminated their use for routine cementation. In the last 15 years, polymerizable bis-GMA and other dimethacrylate monomer cements have become available in various forms for attachment of cast restorations and orthodontic brackets to enamel. More recently, similar systems containing (potentially) adhesive monomers have been marketed for fixed partial denture cementation.

 

The cements based on the reaction between calcium hydroxide and a liquid salicylate also originated 25 years ago. They were primarily fluid, two-paste materials intended for the lining of deep cavities that had actual or potential exposure, thus providing an antibacterial sealing action to facilitate the formation of reparative dentin. The susceptibility to acid erosion of the original formulations, both through marginal leakage of restorations and exposure to phosphoric acid during acid-etch techniques, has resulted in more resistant compositions and, quite recently, to a light-cured, resin-based material.

As a result of the research of the last 15 years, cements of five basic types are available, classified according to the matrix-forming species:

1. Phosphate bonded

2. Phenolate bonded

3. Polycarboxylate bonded

4. Dimethylacrylate bonded

5. Polycarboxylate and dimethylacrylate combinations

 

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 Classification of dental cements according to bonding mechanism.

 

 

 

Numerous brands of each type are available, and there is some overlap between properties. Since clinical and in vivo evaluation of cements is still very limited, the predictive value of laboratory data for assessment of clinical performance requires knowledgeable interpretation, especially because generalizations on specific types of cement cannot be made on the basis of the behavior of one or two brands.

 

“Permanent” luting cements
Product	Type	Manufacturer
Fuji Plus	Hybrid ionomer	GC America
Vitremer Luting	Hybrid ionomer	3M/Espe
Fleck’s Extraordinary	Zinc phosphate	Mizzy
Fuji I	Glass ionomer	GC America
Fynal	Zinc oxide-eugenol	L.D. Caulk
Hy-Bond Polycarboxylate Cement	Zinc carboxylate	Shofu Dental
Hy-Bond Zinc Phosphate Cement	Zinc phosphate	Shofu Dental
Ketac-Cem	Glass ionomer	3M/Espe
Advance	Hybrid ionomer	L.D. Caulk
Modern Tenacin	Zinc phosphate	L.D. Caulk
Super EBA	Zinc oxide-eugenol	Bosworth
Tylok Plus	Zinc carboxylate	L.D. Caulk
Zinc Cement Improved	Zinc phosphate	Mission White Dental

 

 

 

Phosphate-Based Cements

Zinc phosphate cement

Applications

Because of their long history, these materials have the widest range of applications, from the cementation (luting) of fixed cast alloy and porcelain restorations and orthodontic bands to their use as a cavity liner or base to protect pulp from mechanical, thermal, or electrical stimuli.

Composition and setting

The powder is mainly zinc oxide with up to 10% magnesium oxide and small amounts of pigments. It is fired at high temperature ( 1,000C) for several hours to reduce its reactivity. The liquid is an aqueous solution of phosphoric acid containing 45% to 64% H₃PO₄ and 30% to 55% water. The liquid also contains 2% to 3% aluminum and 0% to 9% zinc. Aluminum is essential to the cement-forming reaction, whereas zinc is a moderator of the reaction between powder and liquid, allowing adequate working time and permitting a sufficient quantity of powder to be added for optimum properties in the cement.

Some zinc phosphate cements have modified compositions. One material, widely used as a cavity liner, has 8% aluminum and only 25% H₃PO₄ in the liquid and a powder that contains calcium hydroxide. Others may contain fluoride and have as much as 10% stannous fluoride.

The amorphous zinc phosphate formed binds together the unreacted zinc oxide and other components of the cement. The set cement consists of a cored structure of residual zinc oxide particles in a phosphate matrix:

Manipulation

The measurement of components and the timing of mixing are essential to consistent success. The mixing slab must be thoroughly dried before use. The powder is added to the liquid in small portions to achieve the desired consistency. Dissipation of the heat of reaction by mixing over a large area on a cooled slab will allow a greater incorporation of powder in a given amount of liquid. The cement must be undisturbed until the end of the setting time. The cement liquid is kept sealed with a stopper to prevent changes in the water content. Cloudy liquid should be discarded. Increasing the powder/liquid ratio gives a more viscous mix, shorter setting time, higher strength, lower solubility, and less free acidity. Use of a chilled (5C) thick glass slab slows the initial reaction and allows incorporation of more powder, giving superior properties in the set cement.

Properties

The long persistence of zinc phosphates in clinical practice indicates that reasonable performance is obtained. Although the properties are far from ideal, they are usually regarded as a standard against which to compare newer cements. The principal reasons for their satisfactory performance under routine conditions are that they can be easily manipulated and that they set sharply to a relatively strong mass from a fluid consistency.

Properties of dental luting cements
				Strength (MPa)
Material	Film thickness (mm)	Setting time (min)	Solubility (wt%)	Compressive	Tensile	Modulus of elasticity (GPa)
Zinc phosphate	25-35	5-14	0.2 max	80-100	5-7	13
Zinc oxide-eugenol
Unmodified	25-35	2-10	1.5	2-25	1-2	
Polymer reinforced	35-45	7-9	1	35-55	5-8	2-3
EBA-alumina	40-60	7-13	1	55-70	3-6	3-6
Zinc polycarboxylate	20-25	6-9	0.06	55-85	8-12	5-6
Glass ionomer	25-35	6-9	1	90-140	6-7	7-8
Polymer based	20-60	3-7	0.05	70-200	25-40	4-6

For a given brand of material, the properties are a function of the powder/liquid ratio. For a given cementing consistency, the higher the powder/liquid ratio, the better the strength properties and the lower the solubility and free acidity.

At room temperature (21C to 23C) the working time for most brands at luting consistency is 3 to 6 minutes; the setting time is 5 to 14 minutes. Extended working times and shorter setting times can be achieved by use of a cold mixing slab, which permits up to an approximate 50% increase in the amount of powder, improving both strength and resistance to dissolution.

The cement must have the ability to wet the tooth and restoration, flow into the irregularities on the surfaces it is joining, and fill in and seal the gaps between the restoration and the tooth. The minimum value of film thickness is a function of powder particle size, powder/liquid ratio, and mix viscosity. As measured by ISO and ANSI/ADA specifications, acceptable cements give film thicknesses of less than 25 um. In practice, the cement fills in the inaccuracies between the restoration and the tooth and allows most castings to seat satisfactorily. Unless escapeways or vents are provided with full crowns, separation of powder and liquid may occur, with marginal defects in the cement film.

At the recommended powder/liquid ratio (2.5 to 3.5 g/mL), the compressive strength of the set zinc phosphate cement is 80 to 110 MPa (11,000 to 16,000 psi) after 24 hours. The minimum strength for adequate retention of restorations is about 60 MPa (8,500 psi). The strength is strongly and almost linearly dependent on powder/liquid ratio. The tensile strength is much lower than the compressive strength, 5 to 7 MPa (700 to 900 psi), and the cement shows brittle characteristics. The modulus of elasticity (stiffness) is about 13 GPa (1.8  10⁶ psi).

According to the standard method, the solubility and disintegration in distilled water after 23 hours may range from 0.04% to 3.3% for inferior material. The standard limit is 0.2%. The fluoride-containing cements give a figure of about 0.7% to 1.0% because of the leaching of fluoride. The solubility in organic acid solutions, such as lactic or citric acid, is 20 to 30 times higher. These data are only a rough guide to solubility under oral conditions. The comparative evaluation of cement solubility under clinical conditions has shown significant loss but conflicting results. Dissolution contributes to marginal leakage around restorations and bacterial penetration. This may be facilitated by dimensional change. The cement has been found to contract about 0.5% linearly, giving rise to slits at the tooth-cement and cement-restoration interfaces.

Biologic effects

The freshly mixed zinc phosphate is highly acidic with a pH of between 1 and 2 after mixing. Even after setting 1 hour, the pH may still be below 4. After 24 hours, the pH is usually 6 to 7. Pain on cementation is due not only to the free acidity of the mix but also to osmotic movement of fluid through the dentinal tubules. Hydraulic pressure developed during seating of the restoration may also contribute to pulpal damage. Prolonged pulpal irritation, especially in deep cavities that necessitate some form of pulpal protection, may be associated with the extended duration of the set material’s low pH. This is minimized by a high powder/liquid ratio and rapid setting. One material that has a low acid content and incorporates calcium hydroxide has little effect on pulp when used as a liner. Very thin mixes will also lead to etching of the enamel.

Advantages and Disadvantages

The main advantages of zinc phosphate cements are that they can be mixed easily and that they set sharply to a relatively strong mass from a fluid consistency. Unless the mix is extremely thin (for instance, with a very low powder/liquid ratio), the set cement has a strength that is adequate for clinical service, so manipulation is less critical than with other cements.

However, zinc phosphates’ distinct Disadvantages include pulpal irritation, lack of antibacterial action, brittleness, lack of adhesion, and solubility in oral fluids.

Modified zinc phosphate cements

Copper and silver cements

Black copper cements contain cupric oxide (CuO); red copper cements contain cuprous oxide (Cu₂O). Others may contain cuprous iodide or silicate. Since a much lower powder/liquid ratio is necessary to obtain satisfactory manipulation characteristics with these cements, the mix is highly acidic, resulting in much greater pulpal irritation. Their solubility is higher and their strength is lower than zinc phosphate cements. Their bacteriostatic or anticariogenic properties seem to be slight. Silver cements generally contain a small percentage of a salt such as silver phosphate. Their advantages over zinc phosphate cement have not been substantiated.

Fluoride cements

Stannous fluoride (1% to 3%) is present in some orthodontic cements. These materials have a higher solubility and lower strength than zinc phosphate cement due to dissolution of the fluoride-containing material. Fluoride uptake by enamel from such cements results in reduced enamel solubility and potentially anticariogenic effects.

Silicophosphate cements

These materials have been available for many years as a combination of zinc phosphate and silicate cements. The presence of the silicate glass provides a degree of translucency, improved strength, and fluoride release.

Applications

Their principal applications have been for the cementation of fixed restorations and orthodontic bands (Type I), as a provisional posterior restorative material (Type II), and as a dual-purpose material (Type III).

Composition and setting

The powder in these materials consists of a blend of 10% to 20% zinc oxide (zinc phosphate cement powder) and silicate glass (silicate cement powder) mechanically mixed or fused and reground. The silicate glass usually contains 12% to 25% fluoride. Some materials have been labeled “germicidal” because of the presence of small amounts of mercury or silver compounds. The liquid is a concentrated orthophosphoric acid solution containing about 45% water and 2% to 5% aluminum and zinc salts.

The setting reaction has not been fully investigated, but may be represented as follows:

The set cement consists of unreacted glass and zinc oxide particles bonded together by the aluminosilico-phosphate gel matrix.

Manipulation

The mixing is analogous to that for a phosphate cement; a nonabradable spatula and a cooled mixing slab should be used. The filling mix should be glossy, with puttylike consistency.

Properties

At cementing consistency, the setting time is 5 to 7 minutes; working time is about 4 minutes and may be increased by using a cold mixing slab.

These cements generally have shorter working times and a coarser grain size, leading to a higher film thickness than with zinc phosphate cements. One material is improved in these respects, and film thickness is adequate for cementation of cast gold and porcelain restorations.

The compressive strength of the set cement is in the range from 140 to 170 MPa (20,000 to 25,000 psi); the tensile strength is considerably lower at 7 MPa (1,000 psi). The toughness and abrasion resistance are higher than those of phosphate cements.

The solubility in distilled water after 7 days is about 1% by weight. Solubility in organic acids and in the mouth is less than for phosphate cements. Fluoride is leached out and may contribute to anticariogenic action. The durability in bonding orthodontic bands to teeth is greater, and less decalcification is observed.

The glass content gives considerably greater translucency than phosphate cements, making silicophosphate cements useful for cementation of porcelain restorations.

Biologic effects

Because of the acidity of the mix and the prolonged low pH (4 to 5) after setting, pulpal protection is necessary on all vital teeth. Fluoride and other ions are leached out from the set cement by oral fluids, resulting in increased enamel fluoride and probable anticariogenic action.

Advantages and Disadvantages

Silicophosphate cements have better strength, toughness, and abrasion resistance properties than zinc phosphate cements, and show considerable fluoride release, translucency, and, under clinical conditions, lower solubility and better bonding.

Disadvantages include an initial pH and total acidity that are greater than those for zinc phosphate cements. Pulpal sensitivity may be of longer duration, and pulpal protection is essential. Manipulation is more critical than with zinc phosphate cements.

Phenolate-Based Cements

Introduction

There are three main types of cement under this classification:

1. The simple zinc oxide-eugenol combination that may contain setting accelerators

2. The reinforced zinc oxide-eugenol materials

3. The ortho-ethoxybenzoic acid (EBA) cements

Cements have also been formulated using other phenolic liquids, but these have seen little use except for those containing calcium hydroxide and a salicylate.

Zinc oxide-eugenol cements

Applications

The basic combination of zinc oxide and eugenol finds its principal applications in the provisional cementation of crowns and fixed partial dentures, in the provisional restoration of teeth, and as a cavity liner in deep cavity preparations.

Composition and setting

The powder is essentially pure zinc oxide (United States Pharmacopeia [USP] or equivalent, arsenic free). Commercial materials may contain small amounts of fillers, such as silica. About 1% of zinc salts, such as acetate or sulfate, may be present to accelerate the setting. The liquid is purified eugenol or, in some commercial materials, oil of cloves (85% eugenol). One percent or less of alcohol or acetic acid may be present to accelerate setting together with small amounts of water, which is essential to the setting reaction.

A chemical reaction occurs between zinc oxide and eugenol, with the formation of zinc eugenolate (eugenate):

The precise mechanism is not fully understood, but the set mass contains residual zinc oxide particles bonded by a matrix of zinc eugenolate and some free eugenol. Water is essential to the reaction, which is accelerated also by zinc ions. The reaction is reversible because the zinc eugenolate is easily hydrolyzed by moisture to eugenol and zinc hydroxide. Thus, the cement disintegrates rapidly when exposed to oral conditions. The rate of reaction between the zinc oxide and the eugenol is dependent on the nature, source, reactivity, and moisture content of the zinc oxide and on the purity and moisture content of the eugenol.

Manipulation

The zinc oxide is slowly wetted by the eugenol; therefore, prolonged and vigorous spatulation is required, especially for a thick mix. A powder/liquid ratio of 3:1 or 4:1 must be used for maximum strength.

Properties

The working time is long because moisture is required for setting. Variable results are obtained with different samples of zinc oxide, depending on their mode of preparation and reactivity. For a given oxide, set time is controlled by moisture availability, accelerators, and the powder/liquid ratio. Mixes of cementing consistency set very slowly unless accelerators are used and/or a drop of water is added. Commercial materials set in the range of 2 to 10 minutes, resulting in adequate strengths at 10 minutes for amalgam restorations to be placed.

The particle size of the zinc oxide and the viscosity of the mix govern the film thickness. Use of a fluid mix gives values of about 40 um.

Because of the weak nature of the binding agent, the compressive strength is low, in the range of 7 to 40 MPa (1,000 to 6,000 psi). The tensile strength is very low also.

The solubility is high, about 1.5% by weight in distilled water after 24 hours. Eugenol is extracted from the set cement by the hydrolytic decomposition of the zinc eugenolate/eugenate. The cement disintegrates rapidly when exposed to oral conditions.

Biologic effect

The presence of eugenol in the set cement under clinical conditions appears to lead to an anodyne and obtundent effect on the pulp in deep cavities. When exposed directly to oral conditions, the material maintains good sealing characteristics despite a volumetric shrinkage of 0.9% and a thermal expansion of 35  10^-6/C. The sealing capacity and antibacterial action appear to facilitate pulpal healing; however, when in direct contact with connective tissue, the material is an irritant. Reparative dentin formation in exposed pulp is variable. Eugenol is a potential allergen.

Advantages and Disadvantages

The main advantage of these materials is their bland and obtundent effect on the pulpal tissues, together with their good sealing ability and resistance to marginal penetration.

Disadvantages include low strength and abrasion resistance, solubility and disintegration in oral fluids, and little anticariogenic action.

Reinforced zinc oxide-eugenol cements

Applications

These materials have been used as cementing agents for crowns and fixed partial dentures, cavity liners and base materials, and provisional restorative materials.

Composition and setting

The powder consists of zinc oxide with 10% to 40% finely divided natural or synthetic resins (eg, colophony [pine resin], poly[methyl methacrylate], polystyrene, or polycarbonate) together with accelerators. The liquid is eugenol, which may also contain dissolved resins as mentioned earlier and accelerators such as acetic acid, as well as antimicrobial agents such as thymol or 8-hydroxyquinoline.

The setting reaction is similar to zinc oxide-eugenol cements. Acidic resins such as colophony (abietic acid) may react with the zinc oxide, strengthening the matrix.

Manipulation

More powder is required for a cementing mix than with other cements. The proper ratio must be adhered to for adequate strength properties. Measures are provided for some commercial materials. The mixing pad or slab should be thoroughly dry. The powder is mixed into the liquid in small portions with vigorous spatulation until the correct amount has been incorporated. Adequate time should be allowed for setting without disturbance of the cement. Both powder and liquid containers should be kept closed and stored under dry conditions.

Properties

These cements may have a long working time because moisture is needed for setting. Some commercial materials contain moisture and, therefore, have working and setting times in the same range as zinc phosphate cements, that is, 7 to 9 minutes in oral conditions. Setting time is also lengthened by reducing the powder/liquid ratio.

At cementing consistency, values of film thickness from 35 to 75 um have been obtained with commercial materials. Clinical trials have shown satisfactory performance in seating castings for cements with the lowest values.

These materials have compressive strengths in the range from 35 to 55 MPa (5,000 to 8,000 psi). The tensile strength is 5 to 8 MPa (700 to 1,000 psi). The strength is adequate as a lining material and for luting single restorations and retainers with good retention form. The modulus of elasticity is 2 to 3 GPa (300,000 to 400,000 psi). The mechanical properties of these cements are reduced by immersion in water, which results in loss of eugenol, although this appears to be slower than with simple zinc oxide-eugenol materials. This tendency seems less pronounced with the polymer-reinforced materials.

Because of the presence of the resin, the solubility of these cements appears to be somewhat lower than that of zinc oxide-eugenol materials.

Biologic effects

Polymer-reinforced zinc oxide-eugenol cements have biologic effects similar to basic materials, although there is some variation in inflammatory reaction in connective tissue with the brand of material. There may be softening and discoloration of some resin restorative materials.

Advantages and Disadvantages

The main advantages of these materials are the minimal biologic effects, good initial sealing properties, and adequate strength for final cementation of restorations.

The principal Disadvantages are the lower strength, higher solubility, and higher disintegration compared to zinc phosphate cements; hydrolytic instability; and the softening and discoloration of some resin restorative materials.

EBA and other chelate cements

To further improve on the basic zinc oxide-eugenol system, many researchers have investigated mixtures of zinc and other oxides with various liquid chelating agents. The only system that has received extensive commercial exploitation for luting and lining is that containing ortho-ethoxybenzoic acid.*

*Noneugenol cements have also been developed in which fatty acids or low-odor phenolic derivatives are used to overcome the smell and taste of eugenol.

Applications

These materials have been used for the cementation of inlays, crowns, and fixed partial dentures, for provisional restorations, and as base or lining materials.

Composition and setting

In EBA materials the powder is mainly zinc oxide containing 20% to 30% aluminum oxide or other mineral fillers. Polymeric reinforcing agents, such as poly(methyl methacrylate), may also be present. The liquid consists of 50% to 66% ethoxybenzoic acid with the remainder eugenol.

The setting mechanism has not been fully elucidated. It appears to involve chelate salt formation between the EBA, eugenol, and zinc oxide. The setting is accelerated by the same factors that are operative for zinc oxide-eugenol cements.

Manipulation

In general, the manipulation is similar to that of reinforced zinc oxide-eugenol cements. The cement mixes readily to a very fluid consistency even at a high powder/liquid ratio. In order to obtain optimal properties, it is important to use as high a powder/liquid ratio as possible; this is about 3.5 g/mL for cementation and 5 to 6 g/mL for liners or bases. Vigorous spatulation is required for about 2 minutes to incorporate all the required powder. The correct mix flows readily under pressure because of the long working time. Adequate setting time in the mouth should be allowed. Several days may be required to reach maximum strength.

Properties

The working time at room temperature is long because of the dependence on moisture. The setting time ranges between 7 and 13 minutes under oral conditions .

The film thickness appears to be in the range of 40 to 70 um for the different brands and seems adequate for permanent cementation of restorations at the lower level.

At cementing consistency, the compressive strength of these materials is in the range of 55 to 70 MPa (8,000 to 10,000 psi); higher values, similar to those of zinc phosphate cements, can be obtained by increasing the powder/liquid ratio. The tensile strength is considerably lower, about 3 to 6 MPa (500 to 900 psi). The modulus of elasticity is about 5 GPa (700,000 psi). The EBA cements show viscoelastic properties with very low strength and large plastic deformation at slow (0.1 mm/min) rates of deformation and at oral temperature (37C). This may explain why the retention values for crowns and orthodontic bands are considerably below those obtained using zinc phosphate cements.

The solubility is similar to that of the polymer-reinforced zinc oxide-eugenol materials in distilled water, although loss of eugenol also occurs. The resistance to solubility in organic acids appears to be greater than that of the zinc phosphate cements. When exposed to moisture, greater oral dissolution occurs than for other cements. However, a clinical survey by Silvey and Myers (1978) of the performance of an EBA-alumina cement over 3 years showed only very slightly worse results than for zinc phosphate and polycarboxylate cements. Oral breakdown may thus depend on the precise brand and manipulation.

Biologic effects

The biologic properties of these materials appear to be similar to those of zinc oxide-eugenol materials.

Advantages and Disadvantages

The principal advantages of EBA cements are their easy mixing, long working time, good flow characteristics, and low irritation to pulp. Strength and film thickness can be comparable to those of zinc phosphate cements.

The main Disadvantages are the critical proportioning, hydrolytic breakdown in oral fluids, liability to plastic deformation, and poorer retention than zinc phosphate cements. These materials seem best suited for luting restorations with good fit and retention where there is no undue stress and as cavity bases.

Calcium hydroxide chelate cements

The value of calcium hydroxide as a pulp-capping material that facilitates the formation of reparative dentin has long been recognized. This action appears to be largely attributable to its alkaline pH and consequent antibacterial and protein-lyzing effect. Although a number of aqueous paste materials based on calcium hydroxide are available, they are not easy to manipulate and the dried films tend to crack. In the early 1960s, phenolate-type cements based on the setting reaction between calcium hydroxide and other oxides and salicylate esters were introduced.

Applications

These materials are used as liners in deep cavity preparations.

Composition and setting

These materials are usually formulated as two pastes: One paste contains calcium hydroxide, zinc oxide, and zinc salts in ethylene toluene sulphonamide; the other contains calcium sulfate, titanium dioxide, and calcium tungstate (a radiopacifying agent) in a liquid disalicylate ester of butane-1,3-diol. The calcium hydroxide is intended to be in excess to produce an alkaline pH that will effect an antibacterial and remineralization action. There is some variation among the materials in this respect. At least one material contains fluoride.

Calcium and zinc oxide react with the salicylate ester to form a chelate similar to the zinc oxide- eugenol reaction. Likewise the reaction is greatly accelerated by moisture and accelerators.

Manipulation

Equal lengths of the two pastes are mixed to a uniform color.

Properties

Working time may be 3 to 5 minutes, depending on the availability of moisture. In the mouth, setting is rapid, about 1 or 2 minutes.

The compressive strength at 7 minutes is about 6 MPa (900 psi), and the tensile strength 1.5 MPa (200 psi); at 1 hour the corresponding values are about 10 MPa (1,500 psi) and 1.5 MPa (200 psi); and at 24 hours the values are 14 to 20 MPa (2,000 to 3,000 psi) and 1.7 to 2 MPa (250 to 300 psi). Thin films become resistant to 8 MPa (1,100 psi) penetration force in 90 seconds. At 37C plastic flow without fracture occurs.

The solubility in 50% phosphoric acid during acid-etching procedures is significant. These cements seem to be subject to hydrolytic breakdown. When continued marginal leakage takes place, complete dissolution of the linings of these materials can occur.

Biologic effects

These cements appear to exert a strong antibacterial action when free calcium hydroxide is available and to assist in remineralization of carious dentin. They facilitate the formation of dentin bridges when used for pulp capping on exposures. Their effect on exposed pulp is superior to that of zinc oxide-eugenol materials. These materials can also exert a pulpal protective action by neutralizing and preventing the passage of acid and by acting as a barrier to the penetration of other agents such as methyl methacrylate.

Advantages and Disadvantages

The advantages of these materials include their easy manipulation, rapid hardening in thin layers, good sealing characteristics, and beneficial effects on carious dentin and exposed pulp.

Their Disadvantages are that they show low strength even when fully set, exhibit plastic deformation, are weakened by exposure to moisture, and will dissolve under acidic conditions and if marginal leakage occurs. The data on physical properties and clinical experience suggest that further improvements in these materials are required before they can be utilized as the sole liner in deep cavity preparations.

More recently polymerizable resin compositions containing calcium hydroxide have been introduced as alternatives to these materials.

Polycarboxylate (Carboxylate)- Based Cements

Zinc polycarboxylate cements

The polycarboxylate cements were developed in the late 1960s as adhesive dental cements that would combine the strength properties of the phosphate system with the biologic acceptability of the zinc oxide- eugenol materials.

Applications

Zinc polycarboxylates are used for the cementation of cast alloy and porcelain restorations and orthodontic bands, as cavity liners or base materials, and as provisional restorative materials.

Composition and setting

The powder in these cements is zinc oxide with, in some cases, 1% to 5% tin or magnesium oxide; 10% to 40% aluminum oxide or other reinforcing filler may be present in some brands. A small percentage of stannous or other fluoride may also be included to improve mechanical properties and provide leachable fluoride. The liquid is approximately a 40% aqueous solution of polyacrylic acid or an acrylic acid copolymer with other organic acids, such as itaconic acid. The molecular weight of the polymer is generally in the range of 30,000 to 50,000, which accounts for the viscous nature of the solution. In some brands of the material the polyacrylic acid component is dried and added to the powder. In a brand that is encapsulated the liquid is a weak solution of NaH₂PO₄, which both reduces the viscosity of the polyacrylic acid and retards the setting of the cement. In other brands water is simply added to the powdered ingredients.

The zinc oxide reacts with the polyacrylic acid, forming a cross-linked structure of zinc polyacrylate. The set cement consists of the residual zinc oxide particles bonded together by this amorphous gel-like matrix:

Manipulation

The material should be carefully proportioned and the freshly dispensed components mixed rapidly in 30 to 40 seconds. The mix should be used while it is still glossy, before the onset of cobwebbing. The correct cementing mix is more viscous than a zinc phosphate mix, but because of its different rheology it flows adequately under pressure. The water mix materials are more fluid initially. The interior of restorations and tooth surfaces should be clean and free of saliva. The powder and liquid should be stored under cool conditions and kept sealed with a stopper. Prolonged or cold storage may cause the liquid to gel; to reverse this, it must be warmed to 50C. Loss of moisture from the liquid will lead to thickening.

 

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 Typical consistency for water mix polycarboxylate and glass-ionomer cements. The mix is comparable to zinc phosphate cements.

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Properties

The rate of setting is affected by the powder/liquid ratio, the reactivity of the zinc oxide, the particle size, the presence of additives, and the molecular weight and concentration of the polyacrylic acid. At luting consistency the recommended powder/liquid ratio for most materials is about 1.5:1 by weight. The working time is 2.5 to 3.5 minutes at room temperature, and the setting time is 6 to 9 minutes at 37C; the water mix materials tend to give slightly longer setting times. As with other cements, working time can be substantially increased by mixing the material on a cold slab and by refrigerating the powder. The liquid should not be chilled, as this encourages gelation due to hydrogen bonding.

The freshly mixed cement shows shear thinning. Contrary to the subjective impression that the correct mix for a zinc polycarboxylate cement is much thicker than that of a luting zinc phosphate mix, under pressure they flow out to the same degree to a film thickness of 25 to 35 um. In fact, the zinc phosphate mix tends to thicken more quickly than the zinc polycarboxylate mix. One of the most common errors made with the polycarboxylate cements is to make a mix that appears to be as fluid as a zinc phosphate mix; this will result in a low powder/liquid ratio with consequent poor properties in the cement. Measuring devices for these materials will ensure correct proportions.

At cementing consistency, the compressive strength of these materials is in the range of 55 to 85 MPa (8,000 to 12,000 psi), and the tensile strength is 8 to 12 MPa (1,100 to 1,700 psi). Strength increases with the powder/liquid ratio, reaching a maximum at about 2:1 by weight, and it is increased also by additives such as alumina and stannous fluoride. In general these cements have somewhat lower compressive strengths than zinc phosphate cements but are significantly stronger in tension. The cement gains strength rapidly after the initial setting period; the strength at 1 hour is about 80% of the 24-hour value. The modulus of elasticity is about 6 GPa (850,000 psi).

In distilled water, the solubility ranges from less than 0.1% to 0.6%. The latter high value relates particularly to cements that contain stannous fluoride. However, as in the zinc phosphate system, the solubility is appreciably higher in acids such as lactic and citric acid. In vivo solubility is similar to or less than that for zinc phosphate cements.

Bonding to clean enamel and dentin surfaces can occur through calcium complexation. In practice, adhesion to dentin may be limited because of debris and contamination. The material also sticks to clean stainless steel, amalgam, chromium-cobalt, and other alloys. Bond strength is related to the strength of the cement.

Biologic effects

The effect of zinc polycarboxylate cements on pulp is comparable to or less than that of zinc oxide-eugenol. The formation of reparative dentin in exposed pulp is variable. The generally good biocompatibility appears to be primarily due to the low intrinsic toxicity and also to (1) the rapid rise of the cement pH toward neutrality; (2) localization of the polyacrylic acid and limitation of diffusion by its molecular size and ion binding to dentinal fluid and proteins; and (3) the minimal movement of fluid in the dentinal tubules in response to the cement. The presence of stannous fluoride does not appear to affect the mild response. The fluoride-containing cements release fluoride, which is taken up by neighboring enamel and which presumably will exert anticariogenic effects.

Advantages and Disadvantages

The main advantages of these materials are the low irritation, adhesion to tooth substance and alloys, easy manipulation, strength, solubility, and film thickness properties comparable to those of zinc phosphate cements.

The Disadvantages are the need for accurate proportioning for optimal properties and thus more critical manipulation, the lower compressive strength and greater viscoelasticity than zinc phosphate cements, the short working time of some materials, and the need for clean surfaces to utilize the adhesion potential.

 

Polymer-Based Cements

Introduction

The majority of the materials in this group are polymethacrylates of two types: (1) materials based on methyl methacrylate and (2) materials based on aromatic dimethacrylates of the bis-GMA type. The closely related cyanoacrylate monomers, notably ethyl and isobutyl, have found some limited use for the attachment of facings and for pin cementation. However, the hydrolytic stability and biologic effects in this situation are suspect and little use is made of them.

Acrylic resin cements

Applications

Acrylic resin cements are used for the cementation of restorations, facings, and provisional crowns.

Composition and setting

The powder in these materials is a finely divided methyl methacrylate polymer or copolymer containing benzoyl peroxide as the initiator. Mineral filler and pigments may also be present. The liquid is a methyl methacrylate monomer containing an amine accelerator.

The monomer dissolves and softens the polymer particles and concurrently polymerizes through the action of free radicals from the peroxide-amine interaction. The set mass consists of the new polymer matrix uniting the undissolved but swollen original polymer granules.

Manipulation

The liquid is added to the powder with minimal spatulation to avoid an incorporation of air. The mix must be used immediately because working time is short. Excess material must be removed at the final set, hard stage and not when the material is rubbery, otherwise marginal deficiencies will be created.

Properties

The properties of these materials are comparable to those of the cold-curing acrylic resin filling materials. They are stronger and less soluble than other types of cement but display low rigidity and viscoelastic properties. They have no effective bond to tooth structure in the presence of moisture; thus they permit marginal leakage, although they may show better bonding than other cements to resin facings and polycarbonate crowns.

Biologic effects

As with acrylic resin filling materials, marked pulpal reaction may occur and pulpal protection is necessary.

Advantages and Disadvantages

The advantages of these materials include relatively high strength and toughness and low solubility.

Disadvantages include a short working time, deleterious effects on pulp, and difficulty in removal of excess cement from margins.

Adhesive resin cements

Adhesive acrylic materials have been formulated by adding an adhesion promoter, 4-methyloxy ethyl trimelletic anhydride (4-META), to the methyl methacrylate monomer as well as an additional polymerization initiator, tributyl boron, which is also believed to aid chemical bonding to dentin. Such materials have been developed as cements for metal fixed partial dentures especially of base metal (Superbond, Parkell) and for bonding amalgam to dentin and composites (Amalgambond, Parkell). In vitro tests have shown high bond strengths for the luting cement to oxidized, etched, or silica-coated casting alloy surfaces. Shear bond strength to amalgam is significantly less than the bond strength to dentin, which is comparable to other dentin bonding systems in the region of 20 MPa. Since these materials have only low ( 10%) filler content, the physical properties are typical of acrylic resins, that is, moderate strength with high deformation under load. Although the materials have been widely used for cementation of fixed partial dentures, there is little clinical data on longevity, and the cements are said to be technique sensitive.

Dimethacrylate cements

Dimethacrylate cements are usually based on the bis-GMA system: They are combinations of an aromatic dimethacrylate with other monomers containing various amounts of ceramic filler. They are basically similar to composite restorative materials.

Applications

Dimethacrylate cements are used for bonding crowns (usually porcelain), fixed partial dentures, inlays, veneers, and indirect resin restorations.

Composition and setting

These cements are classified according to the following methods of curing:

1. Chemically (or auto-) cured: These are usually paste-paste systems and are used to cement metal and opaque ceramic core (eg, Procera, In-Ceram) restorations.Working…

 × 
Chemically cured resin cement for use under opaque restorations (Panavia 21, Kurarary/J. Morita).

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2. Dual cured: These cements start curing with light and continue with chemical curing. The chemical cure will polymerize more thoroughly than light curing alone . These are used to cement translucent restorations (eg, porcelain, indirect resin restorations).

Working…

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 Dual-cured resin cement in syringe form for use when light may not penetrate enough for complete curing (Dual Cement, Vivadent).

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3. Light cured/dual cured: These can be used for light curing only or can be dual cured when dual-cure catalysts are added to the light-cure base. These products are used for both light-cure applications (eg, thin porcelain veneers) and dual-cure applications.

Working…

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 Light-cured/dual-cured cements may be cured with light or with addition of dual-cure catalyst, which will allow setting to continue after light is turned off (Variolink II, Vivadent).

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In the powder-liquid materials, the powder is generally a finely divided borosilicate or silica glass together with fine polymer powder and an organic peroxide initiator. The liquid is a mixture of bis-GMA and/or other dimethacrylate monomers containing an amine promoter for polymerization. Some materials contain monomers with potentially adhesive groups, such as phosphate or carboxyl, similar to dentin bonding materials. The two-paste materials are of similar overall composition but with the monomers and fillers combined into two pastes. In light-cured and dual-cured materials, light-sensitive polymerization systems such as diketones (eg, camphorquinone) and amine promoters are present, respectively, in the two cement components in addition to the chemical-initiator systems.

On mixing the components, polymerization of the monomers occurs, leading to a highly cross-linked resin composite structure.

Manipulation

Correct proportioning of powder and liquid components using measures is important. Paste materials are usually proportioned 1:1 (equal lengths). Rapid, thorough mixing, minimizing air inclusion, until uniform is critical.

Properties

As with resin composite restorative materials, monomer conversion is incomplete, even under optimum cure conditions, and thus manipulation is critical to optimum physical properties. For light- and dual-cured materials, the maximum light exposure is desirable. Maximum properties are generally reached about 10 minutes after polymerization; only small changes occur over the ensuing 24 hours.

Since polymerization systems vary and filler contents range between 20% and 80% for the various products, physical properties vary widely and the solubility of a specific material for a particular clinical application should be checked individually. Compressive strengths have been reported to range between 100 and 200 MPa (14,000 and 28,000 psi), and diametral tensile strengths from 20 to 50 MPa (3,000 to 7,000 psi) with corresponding differences in microhardness. These values are considerably higher than traditional cements, and therefore high values can be obtained for retention of well-fitting crowns. However, optimum luting performance is very dependent on fluidity, seating capability, and film thickness. Many resin cements tend to show unacceptably high values for film thickness. Recently, to improve wetting of the tooth, preparation, seating, and bond strength, some resin cements have been used with dentin bonding primers, thus increasing the clinical complexity of the system. Although these materials have been used widely in adhesive techniques, especially for ceramic restorations, there are comparatively few clinical reports of their longevity. Aside from failures induced by material and technique shortcomings during the critical clinical manipulation, studies indicate that resin cement bonds will most likely fail through cyclic fatigue stresses. Some studies on etched metal restorations cemented with chemically cured cements have indicated a median survival time of about 8 years.

Biologic effects

The materials themselves appear to pose few problems, although some patients experience objectionable odors. Cases of allergy among dental personnel have occurred, especially where reactive dentin bonding systems have been used. Skin contact should be avoided.

Pulpal pathology may be due to poor seating, polymerization contraction, and consequent microleakage. All systems show some microleakage that may contribute to tooth sensitivity and clinical failure. Microleakage appears to occur least with systems employing dentin bonding agents, but there are no long-term studies on this aspect.

Advantages and Disadvantages

The advantages of these cements include high strength; low oral solubility; and high micromechanical (and possible chemical) bonding to prepared enamel, dentin, alloys, and ceramic surfaces.

Disadvantages include the need for a meticulous and critical technique, more difficult sealing and higher film thickness than traditional cements, possible leakage and pulpal sensitivity, and difficulty in removal of excess cement.

 

 

Glass-Ionomer Cements

Introduction

These materials were formulated in the 1970s by bringing together the silicate and polyacrylate systems. The use of an acid-reactive glass powder together with polyacrylic acid solution leads to a translucent, stronger cement that can be used for luting and restorative materials.

Applications

Glass-ionomer cements are used for the cementation of cast-alloy and porcelain restorations and orthodontic bands, as cavity liners or base materials, and as restorative materials, especially for erosion lesions. They are being replaced by hybrid ionomer cements, which allow better handling.

Composition and setting

The powder in these materials is finely ground calcium aluminum fluorosilicate glass with a particle size around 40 um for the filling materials and less than 25 um for the luting materials. One brand (Zionomer Liner, Den-Mat) also contains zinc oxide. Silver powder is fused into the glass in Ketac-Silver (3M/ESPE) for improved physical properties. The liquid is a 50% aqueous solution of a polyacrylic-itaconic acid or other polycarboxylic acid copolymer that contains about 5% tartaric acid. Some other materials contain 10% to 20% added silver, silver alloy, or stainless steel. In some materials the solid copolymer is added to the powder, and the solution contains tartaric acid; in others, all the ingredients are in the powder, and the liquid is water.

On mixing, the polyacrylic and tartaric acids react with the glass, leaching calcium and aluminum ions from the surface, which cross-link the polyacid molecules into a gel. The tartaric acid serves to increase working time and gives a sharp setting by forming metal ion complexes. Differences in composition between brands affect the hardening rate and properties. Some recent evidence suggests that a polysilicate matrix may also form within the polygel over time.

Manipulation

The material should be carefully proportioned and the freshly dispensed components mixed rapidly in 30 to 40 seconds. Some brands are encapsulated, mechanically mixed, and injected. The powder/liquid ratio for luting is about 1.3:1 for the conventional types of glass-ionomer cement. This ratio appears to be critical with these cements to obtain optimal cementation properties. Best results are obtained by mixing the chilled powder with the liquid on a chilled slab. The correct cementing mix is fluid, similar to zinc phosphate. The lining mix is somewhat more viscous, depending on the brand. The restorative mix should have a puttylike consistency and a glossy surface. Tooth surfaces should be clean and free from saliva but not dehydrated. Restoration surfaces should be free from debris and contamination. The cement hardens slowly and should be protected from loss or gain of moisture when set clinically. Restoration margins or filling surfaces should be protected with a varnish or a light-curing sealant. This is less important with light-cured materials.

Properties

For the luting materials, the setting time is in the range of 6 to 9 minutes. The lining materials set in 4 to 5 minutes, and the restorative materials set in 3 to 4 minutes.

Materials that are light-cured set in approximately 30 seconds when exposed to a visible light source. The acid-base reaction continues slowly and properties improve over time.

Film thickness is in the range of 25 to 35 um, which is adequate to seat castings satisfactorily, although the flow properties are quite dependent on the powder/liquid ratio.

For the luting cements, the compressive strength increases over 24 hours to 90 to 140 MPa (13,000 to 20,000 psi) depending on the brand. The tensile strength increases similarly to 6 to 8 MPa (900 to 1,100 psi). The compressive modulus of elasticity is about 7 GPa (900,000 psi). The lining materials have compressive and tensile strengths in the same range with some light-cured materials at the higher end of the range reaching 150 to 160 MPa (21,000 to 23,000 psi) in compression and 10 to 12 MPa (1,400 to 1,700 psi) in tension. The light-cured materials are significantly tougher in some brands, with a lower modulus. The restorative materials range from 140 to 180 MPa (20,000 to 26,000 psi) in compression and 12 to 15 MPa (1,700 to 2,100 psi) in tension. The light-cured restorative materials may have strengths as high as 200 MPa in compression and 20 MPa in tension. Some silver-containing materials are in this range, and even higher strengths have been achieved in recent materials.

In general, with light-cured materials, properties are dependent on the depth of cure.

The solubility of the cements in water is about 1% for a luting material, and this is higher in lactic acid. Good resistance to dissolution is observed under oral conditions. Resistance to dissolution and disintegration is improved by varnish protection for conventional cements.

Erosion of clinical restorations of conventional cements by acid phosphate fluoride preventive-treatment solutions has been observed, making these solutions contraindicated.

Some studies show that light-cured glass-ionomer materials continue to absorb water over several months, with swelling and reductions in strength and stiffness. The clinical significance of this behavior is not yet clear.

Glass-ionomer cements exhibit bonding to enamel, dentin, and alloys in a manner similar to zinc polycarboxylates. In vitro and in vivo the adhesion is variable and is affected by surface conditions. Slight and variable marginal leakage has been observed. Bonding to dentin for conventional materials is not improved by pretreatment with polyacrylic acid solutions, whereas with light-cured materials it is dependent on the use of dentin primers.

Biologic effects

Pulpal response to the lining and restorative materials appears generally favorable. Variable behavior has been reported for the various luting materials with instances of postoperative sensitivity. This has been attributed to a prolonged initially low pH coupled with the effects of the toxic ions. This may be accentuated by dehydration of dentin and marginal leakage of bacteria. Leaching of fluoride and uptake by adjacent enamel occurs with these cements, and this continues for at least a year with potentially cariostatic effects. Antibacterial action has been attributed to low initial pH, leaching, release of silver and other ions, or a combination of these. Light-cured materials have been observed to show greater cytotoxicity.

Advantages and Disadvantages

The advantages of glass-ionomer cement materials include easy mixing, high strength and stiffness, leachable fluoride, good resistance to acid dissolution, potentially adhesive characteristics, and translucency.

The Disadvantages include initial slow setting and moisture sensitivity, variable adhesive characteristics, radiolucency, and possible pulpal sensitivity.

Resin-modified glass-ionomer cements

Applications

A recent addition to the spectrum of materials, these versatile cements, sometimes also called hybrid ionomers, have many uses: cavity liners, bases, core buildups, and luting cements. One hybrid ionomer is used for permanent cementation of crowns, orthodontic appliances, and core buildups.

 

 

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Continuum of glass-ionomer and composite restorative materials. (After Albers, 1996).

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 A hybrid ionomer (Vitremer, 3M).

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Composition and setting

In hybrid ionomers, the acid-base setting reaction in glass-ionomer cements has been modified by the introduction of water-soluble polymers and polymerizable monomers into the composition. The use of copolymers of acrylic acid and methacrylate monomers in the liquid leads to materials that undergo the customary acid-base reaction on setting and can also be light cured via the methacrylate groups. This gives improved lining and restorative materials with an immediate command set and thus higher early strength and water resistance. Some commercial materials contain a preponderance of polymeric components with minimal acid-base reaction.

The classification of these materials as glass-ionomer cements is controversial. Some light-cured restorative glass-ionomer cements are used with a dentin primer similar to dentin bonding resin composite systems and thus depend on surface infiltration for bonding in addition to chemical interaction.

Resin-modified glass ionomers are available in hand-mixed and predosed capsules. The resin monomers in the liquid depend on the product and include bis-GMA, hydroxyethylmethacrylate, and methacrylate-modified polyacrylates along with photoinitiators.

 

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 A simple hybrid ionomer luting cement for hand mixing or automix with capsules and gun (Fuji I, GC America).

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Manipulation

For hand-mixed compositions, the powder should be fluffed before dispensing. The powder and liquid should be mixed quickly, within 30 seconds, on the pad. These cements have a working time of about 2.5 minutes. For luting, the cement is applied to the undesiccated tooth to avoid possible postoperative sensitivity.

Properties

 The strength properties of the two types of cements are similar, with considerable variations among brands. There is a major difference in flexibility, with the hybrid ionomers being twice as flexible, as indicated by lower modulus of elasticity values. Also, many of the hybrid ionomers have been found to expand on setting, possibly due to the absorption of water, which is more than for resin cements. Therefore, hybrid ionomers are not recommended for luting all-ceramic crowns, to avoid possible expansion stresses and crown fracture.

Mechanical properties of glass-ionomer and hybrid ionomer cements*
	Glass ionomers	Resin-modified glass ionomers
Flexural strength (MPa)	25	35-70
Flexural modulus (GPa)	8	4
Compressive strength (MPa)	180-200	170-200
Diametral tensile strength (MPa)	22-25	35-40
Shrinkage (% vol)	3	3.5-expansion
*Data from Burgess et al (1996). Used with permission from The Compendium of Continuing Education in Dentistry.

 

Biologic effects

Hybrid ionomers release fluoride from the glass component, which is favorable for caries prevention. Long-term, large-scale clinical data are not available for an overall assessment of their biologic effects.

Advantages and Disadvantages

Their advantages include dual cure, fluoride release, higher flexural strength than glass-ionomer cements, and ease of handling. Also, they are capable of bonding to composite materials.

One problem is a possible setting expansion that may lead to cracking of all-ceramic crowns. Therefore, resin cements, zinc phosphate, and glass-ionomer cements are still recommended for metal-free crowns.

Selection and Use of Cements
None of the cements available is free from deficiencies in the required clinical characteristics, such as biocompatibility, ease of manipulation, satisfactory sealing, retentive properties, and long-term stability. A proportion of clinical failures is inevitable, but this can be minimized by proper selection and manipulation of the cement. The following factors should be kept under review:

1. Rapid uniform and reproducible dispensing of the components

2. Rapid, thorough mixing

3. Moisture isolation where practical

4. An undisturbed setting

5. Careful removal of excess

6. Avoidance of excessive drying of dentin

Factors within the clinician’s control, such as the design and execution of the preparation, adequate isolation, proper seating of the restoration, and finishing of the margins, are also important determinants of success as is the manipulation of the cement.

These considerations may influence cement selection and use, but a governing factor is the biological state of the tooth tissue. The selection of particular cements for specific clinical situations is limited both by the preparation and the properties of the cement.

Clinical Decision Scenarios for Dental Cements
This section presents one approach for choosing dental cements for specific situations. Advantages and Disadvantages of each material are prioritized using the following codes: * = of minor importance, ** = important, and *** = very important.

Materials  Zinc phosphate vs resin cement for crown cementation

Description  A dentist has finished preparation of a full gold crown for a maxillary left permanent second molar and is ready to cement the crown. This is a routine crown cementation. The preparation is normal, the tooth is vital, and there is no known pulpal pathology. The dentist may choose between a resin cement and zinc phosphate cement.

Critical Factors

  Ease of use, cost, effectiveness

Zinc phosphate

Advantages

*** Low cost

     Long clinical history

     High rigidity

     Long working time

*** Easy to use

Disadvantages

*** No bond to tooth

     Slow setting time

     Moisture sensitivity during mixing

Resin

Advantage

*** Bonds to tooth

     Fast setting time

     Higher strength

*** Easy to use

Disadvantages

*** High cost

     Short working time

     Film thickness varies widely among brands

     Difficult to remove excess

Analysis/Decision  Comparing the properties of the two cements reveals they are balanced in advantages and Disadvantages for this situation. The choice finally rests in the personal preference of the dentist. Since this dentist had more experience with zinc phosphate, she chose to use that material.

Materials  Glass ionomers vs zinc phosphate cement for crown cementation

Description  An older gentlemen with a history of periodontal surgery to correct bony defects has broken the cusps off a previously restored mandibular first molar. The patient’s plaque control is only fair, and he is taking medications that could result in some degree of “dry mouth.” He has had a slightly increased level of caries activity since the surgery and since beginning the medication. The dentist has elected to restore the tooth with a cast crown, which has now been returned from the laboratory and is ready for cementation. The dentist has both zinc phosphate and glass-ionomer luting cements available and must decide which to use.

Critical Factors  Caries resistance, good seal

Zinc phosphate

Advantages

*** Good seal

 ** Reasonable cost

 ** Adequate strength

 ** Little sensitivity

Disadvantages

*** No fluoride release

Glass ionomer

Advantages

*** Good seal

*** Fluoride release

 ** Adequate strength

 ** Reasonable cost

Disadvantages

 ** Occasional sensitivity

Analysis/Decision  Both cements have a good seal, but only the glass ionomer releases fluoride after cementation. Fluoride is generally accepted to reduce caries and seems to do so in individuals such as this patient. For this reason, the glass ionomer was selected. Careful attention to instructions allowed cementation without the sensitivity sometimes experienced with glass-ionomer cements. The dentist was satisfied with this treatment choice.

Materials  Glass ionomers vs zinc phosphate for bases under amalgam restorations

Description  A patient has a mandibular molar that exhibits extensive carious destruction. Due to the patient’s finances, a large, pin-retained amalgam restoration is selected. Following caries removal and preparation, it is determined that the cavity needs a base prior to placement of the amalgam restoration. The dentist has zinc phosphate and glass-ionomer cements available and must choose between them for a base material.

Critical Factors  Strength, modulus of elasticity

Zinc phosphate

Advantages

*** Adequate modulus of elasticity

*** Adequate strength

 ** Ease of use

 ** No sensitivity

Disadvantages

 ** No fluoride release

Glass ionomer

Advantages

*** Adequate modulus of elasticity

*** Adequate strength

 ** Fluoride release

 ** Ease of use

Disadvantages

 ** Occasional sensitivity

Analysis/Decision  Since the advantages and Disadvantages were essentially balanced for this situation, neither cement had a clear advantage. The highly significant modulus of elasticity, essential for a good base, was roughly equivalent. In this case, the dentist chose glass ionomer because of the added advantage of fluoride release, which is thought to reduce recurrent decay. However, because that was not a problem with this patient, either cement would have been an acceptable choice.

Materials  Zinc oxide-eugenol vs calcium hydroxide as liners under amalgam restorations

Description  A patient ieed of a slightly deep mesio-occlusodistal amalgam on a mandibular left first molar was seen by the dentist. The patient reported that the last two amalgams the dentist placed had been quite sensitive for several weeks following placement. They had finally lost their sensitivity, but the patient felt they had hurt unusually long for new restorations. Upon preparation, the dentist decided that a base was indicated. Both calcium hydroxide and zinc oxide-eugenol base materials were available.

Critical Factors  Strength, modulus of elasticity, reduction of sensitivity

Zinc oxide-eugenol

Advantages

 ** Ease of use

 ** Decreased sensitivity

 ** Low cost

Disadvantages

*** Low strength

*** Low modulus of elasticity

Calcium hydroxide

Advantages

 ** Ease of use

 ** Stimulates secondary dentin

 ** Low cost

Disadvantages

*** Low strength

*** Low modulus of elasticity

Analysis/Decision  In this situation, again, there is no clear advantage for either base. Both have low strength and low modulus of elasticity, necessitating that they be applied as very thin layers. The zinc oxide-eugenol has the advantage of the anodyne eugenol, which is known to reduce tooth sensitivity. The calcium hydroxide, on the other hand, will stimulate the formation of secondary dentin and thus is good if the restoration is near the pulp. This was true in the situation described, but the patient also had a history of sensitive teeth following placement of amalgam restorations. Therefore, the dentist selected the zinc oxide-eugenol as the liner of choice. Had the cavity preparation been deeper and the pulp visible through the dentin, calcium hydroxide would have been selected due to its ability to stimulate formation of secondary dentin.

Materials  Flowable resin composite vs hybrid ionomer for Class 5 restorations in high-caries-risk patient

Description  An older patient has recurrent caries around the margins of a few old Class 5 amalgam restorations, probably due to poor hygiene and a mild xerostomia resulting from a cholesterol-lowering drug. The patient requested that the replacement restorations be more esthetic. The dentist considers flowable composites and hybrid ionomers.

Critical Factors  Ease of placement, prevention of recurrent decay, reasonable esthetics

Flowable composite

Advantages

*** Very simple placement

*** Excellent esthetics

   * Less soluble

Disadvantages

*** Higher incidence of recurrent decay

 ** Higher sensitivity to moisture contamination during placement

Hybrid ionomer

Advantages

*** Ease of placement

*** Less recurrent decay

*** Reasonable esthetics

 ** Less sensitivity to moisture during placement

Disadvantages

   * More soluble than flowables

Analysis/Decision  Due to the patient’s high risk of recurrent decay, the dentist decided to use the hybrid ionomer restorative material. She chose a dual-cure hybrid ionomer for its ease of use and potential to be recharged with fluoride at future visits.

Materials  All-purpose adhesives vs cavity varnish under amalgam restorations

Description  A patient is seen and diagnosed as needing numerous amalgam restorations, some large. Upon preparation, the cavities turn out to be normal in size and depth. There is little remarkable about the patient or the restorations. The dentist has both cavity varnish and new all-purpose adhesives to use under the amalgam restorations. The all-purpose adhesives are reported by the manufacturer to bond the amalgam to the teeth, but the dentist knows that such claims are as yet probably exaggerated.

Critical Factors  Marginal leakage, bond to tooth, cost, time required for application

Varnish

Advantages

*** Low cost

*** Easy placement

Disadvantages

*** No bond to tooth

*** Mediocre seal

Adhesives

Advantages

*** Superior marginal seal

*** Bond to tooth

Disadvantages

 ** High cost

*** Complex placement

Analysis/Decision  Since there is no evidence of excessively weakened cusps, the possible bonding of the new adhesives is not significant in this case. The superior seal makes them desirable, but their high cost and complex placement process complicates the choice. The dentist had been to a recent lecture on dental materials in which the speaker claimed the new materials should be a standard of practice, so he chose to place the adhesives. The patient reported a complete lack of postoperative sensitivity in the new restorations.

Materials  Dentin adhesives vs glass-ionomer liners under composite restorations

Description  A patient has several Class 5 toothbrush abrasion lesions on his maxillary and mandibular premolars. At first, they were no problem, but over the years they have become sensitive, and the patient wants the discomfort relieved. The lesions are not carious but are somewhat deep. The occlusal, mesial, and distal margins are on enamel, but the cervical margin is on cementum. The dentist decides against glass-ionomer restorations because she feels a better esthetic result can be obtained with a composite material. In addition, she feels the composite will better resist further toothbrush abrasion. She is uncertain whether to use a dentin bonding agent alone or a glass-ionomer lining cement under the cervical margin to prevent leakage. She has heard that composites often leak on margins that are on cementum.

Critical Factors  Marginal seal, bond strength

Dentin adhesives

Advantages

 ** Good seal

*** Adequate bond strength

 ** Lower cost

Disadvantages

*** Poorer marginal seal

Glass ionomer

Advantages

*** Better marginal seal

*** Adequate bond strength

Disadvantages

 ** Additional cost

 ** Additional procedure

Analysis/Decision  Although there are more advantages for the bonding agent, the most significant advantagebetter marginal sealfavors the glass-ionomer liner. It adds to the cost and the time to do the procedure, but it provides a significantly better seal. The better seal results in a superior restoration that justifies the extra cost and time. The glass-ionomer liner was selected.

Materials  Hybrid ionomer vs glass ionomer for treatment of recurrent caries at gold crown margins

Description  During a dental hygiene appointment, patient examination revealed recurrent caries around the margins of a few gold crowns. Replacement of the crowns is not feasible due to the patient’s lack of funds. Normally, the dentist would use a glass-ionomer material to restore the marginal areas after the decay has been removed. However, he is considering the use of the newer hybrid ionomers due to their dual-curing ability.

Critical Factors  Prevention of recurrent caries, ease of placement, bond to tooth structure

Hybrid ionomer

Advantages

*** Easy to place

*** Tooth colored

   * Low cost

*** Fluoride release

 ** Bonds to tooth

   * Smoother finish

 ** Light/dual cure

Disadvantages

   * Less durable

   * Isolation is critical

Glass ionomer

Advantages

*** Resonably easy to place

*** Tooth colored

   * Low cost

*** Fluoride release

*** Bonds to tooth

Disadvantages

   * Less durable

 ** More plaque retentive

   * Isolation is critical

 ** Chemical cure only
Most definitive indirect dental restorations today are luted to the preparations using one of 4 types of dental cements: (1) glass ionomer (GI) cements, (2) resin-modified glass ionomer (RGMI) cements, (3) self-etching resin cements, or (4) resin cements, requiring the use of total-etch technique and placement of dentin adhesives on the preparation prior to luting the definitive restoration.
First, it is important to note that no cement will perform to its optimal level clinically without an adequate preparation that includes good resistance and retention form. Total-etch adhesives and resin cements by virtue of higher bond strengths can help compensate for minor issues of exaggerated axial taper and/or lack of axial height of the preparation. However, no cement will hold a restoration in place long-term when the preparation is grossly inadequate. New metal and ceramic primers have been developed that have been reported to enhance bond strengths of cements to nonetchable substrates, such as zirconia and m

 

 

Radiopaque Glass Ionomer Luting Cement for permanent fixation of:

Cementation of metal-based inlays, onlays, crowns, bridges and posts

Cementation of high strength (zirconia based) all ceramic crowns and bridges

Radiopaque Glass Ionomer Luting Cement

 

Glass ionomer based Luting cement self cure in handmix version for restoration of primary teeth,core build up.

 

Used for fixing permanently caps, crowns, bridges, inlays & onlays

Indications:

 

Permanent fixation of veneers

 

Permanent fixation of crowns & bridges

 

Primary teeth fillings

 

Fissure sealing

 

Fillings of cervical erosions

Packaging:

Powder – 10g jar

Liquid -8ml bottle

Measuring spoon

Mixing Pad