8. Therapeutic lining: groups, composition, properties, indications, overlay technique. Isolative lining: their type, purpose and features. Overlay technique in cavities of different classes. Silver and copper amalgam: composition, properties, positive and negative qualities, indications and rules of application. Polishing features of the amalgam fillings.

8. Therapeutic lining: groups, composition, properties, indications, overlay technique. Isolative lining: their type, purpose and features. Overlay technique in cavities of different classes. Silver and copper amalgam: composition, properties, positive and negative qualities, indications and rules of application. Polishing features of the amalgam fillings.

 

Dental amalgam

Dental amalgam is a mixture of mercury and an alloy containing silver and tin with added copper and zinc. The alloy and mercury are held together in a capsule, with the two components separated by a plastic diaphragm. When the diaphragm is broken and the capsule is placed in the mixing machine (amalgamator), the two components are mixed together (triturated) to form a silver-coloured paste. This paste is then condensed into the cavity. This is a very important stage: well-condensed amalgams are stronger than poorly condensed ones, as more of the weaker, mercury-rich γ2-phase is removed during carving. The final set material should contain 45–50% mercury; however, when there is less than 50% mercury in the amalgam mix it can prove too dry and difficult to work with. The more mercury in the mixed material, the softer the material is and the easier it is to pack and carve, but the set restoration will be weaker and more prone to corrosion. To reduce the amount of mercury in the final restoration, the amalgam should be vigorously condensed, as this causes excess mercury to rise to the surface where it can be carved away and discarded in a safe manner. For this reason amalgam should always be placed to overfill a cavity.

Amalgam is weak in thin section so cavities have to be cut suitably deep (2 mm) and because amalgam does not adhere to tooth tissue, the cavity must be undercut. Dental amalgam continues to be used despite concerns about health and the environment because it has high clinical success, known performance, relatively low cost and is easy to manipulate. Despite the high usage of this material it is not ideal and suffers from several problems including marginal breakdown, fracture and poor appearance. Secondary caries is the most common reason given for the replacement of amalgam restorations but this diagnosis may not necessarily always be correct.

There is a well-recognized need for effective alternatives, not only because of its less than ideal properties but also because of public and political concerns about its use, the changing patterns of dental disease and patient expectations of dental care.

 

 

Composition

Mercury used in dental amalgam is purified by distillation. This ensures the elimination of impurities which would adversely affect the setting characteristics and physical properties of the set amalgam.

Typical composition of a modern amalgam powder are given in Table 1. It can be seen that the major components of the alloy are silver, tin and copper. Small quantities of zinc, mercury and other metals such as indium or palladium may be present in some alloys.

 

 

After the discovery in the 1960s that some of the properties of ‘conventional’ amalgam materials could be improved by the inclusion of great quantities of copper (in place of silver) a new class of materials was developed and became available for use by the dentist. The ISO Standard finally recognized this change in composition when the 1986 version of ISO 1559 was published. These newer alloy powders have the same basic ingredients as the conventional products but they contain much greater concentrations of copper, typically 10–30% compared with less than 6% in the conventional materials. These newer alloys are referred to as copper-enriched alloys. In addition to the increased copper levels some alloys also contain small quantities of other metals such as palladium. Higher copper levels in alloy powders may be produced by the manufacturer in one of several ways. Lathe-cut, spherical or spheroidal powders can be produced in which the manufacturer alters the ratio of metals at the melting stage. Hence the resulting alloy particles are similar in shape and size to conventional alloys but simply contain a higher copper content. These are single-composition, copper-enriched alloys. An alternative approach is to blend particles of conventional alloy with those of, for example, a silver–copper alloy in order to achieve a higher overall copper content. Such blends are called dispersion-modified, copper-enriched alloys and one widely used product contains two parts by weight of a lathe-cut alloy of  conventional composition (less than 6% copper) and one part by weight of spherical silver–copper eutectic particles. The latter particles contain 72 parts silver and 28 parts copper and the overall copper content in the blended alloy is 12%.

Types of amalgam

Amalgam may be classified by the shape of the particles that make up the powder, or the constituent metals of the particles. The particles of alloy that make up the powder can either be spherical in shape or an irregular shape known as lathe-cut (Fig. 2).

 

 

The shape of the particles determines how the material handles. Spherical particles are formed by spraying molten alloy into an inert atmosphere. As it falls spheres form and solidify. The other method of creating the powder is to grind small particles from a solid block of alloy, hence the name lathe-cut. It gives more resistance when packing into cavities than spherical amalgam, but is not as prone to slump when building up a large restoration. One of the most popular types of amalgam in current usage is dispersed phase or admixed amalgam, consisting of spherical silver/copper particles and lathe cut silver/tin particles. Combined together, they give good handling characteristics. With spherical amalgams being more easily condensed, less mercury is needed to wet the particles, which in turn leads to a final material with lower mercury content and better physical properties.

 Setting reactions

The reaction which takes place when alloy powder and mercury are mixed is complex. Mercury diffuses into the alloy particles; very small particles may become totally dissolved in mercury. The alloy structure of the surface layers is broken down and the constituent metals undergo amalgamation with mercury. The reaction products crystallize to give new phases in the set amalgam. A considerable quantity of the initial alloy remains unreacted at the completion of setting.

The structure of the set material is such that the unreacted cores of alloy particles remain embedded in a matrix of reaction products.

The set material contains unchanged particle cores consisting of the gamma (γ) phase, surrounded by a matrix of γ1 and γ2. The γ2 phase is associated with increased corrosion, creep (plastic change over time) and lower strength. Modern amalgams have low γ2 content due to the presence of higher amounts of copper. The copper acts to convert the γ2 phase to γ1 and the formation of a silver–copper alloy, Cu6Sn5, by the reaction: Ag + Cu +γ2 ⇒γ1 + Cu6Sn5

The copper can either be mixed with the alloy powder, so that the particles contain silver, tin and copper, or silver–copper particles can be added to a traditional amalgam powder. For this reason modern amalgams are known as ‘high copper’ amalgams or ‘non gamma-2’. On initial set, the material is quite weak and prone to fracture if heavy occlusal forces bear down on it, and it takes up to 24 hours for the material to reach its optimal strength. The presence of zinc in an amalgam can cause it to expand in the presence of moisture; this could lead to the fracture of teeth. Zinc used to be added during the manufacture of the alloy powder to act as a scavenger for oxygen which would otherwise form oxides of tin and silver. It is usual these days to produce the alloy powder without the need for zinc by manufacturing the powder in an oxygen-free, inert environment.

The essential difference between this and the reaction for conventional alloys is the replacement of the tin–mercury, γ2 phase in the reaction product with a copper–tin phase. The copper–tin phase may exist in the form of Cu6 Sn5 (η phase) or Cu3 Sn (ε phase) depending on the precise formulation of the alloy. In either case, the elimination of the γ2 phase has a profound effect on the properties of the set material.

Properties

Dimensional changes: The setting reaction for amalgam involves a dimensional change.

Strength: The strength of dental amalgam is developed slowly. It may take up to 24 hours to reach a reasonably high value and continues to increase slightly for some time after that. At the time when the patient is dismissed from the surgery, typically some 15–20 minutes after placing the filling, the amalgam is relatively weak. It is necessary, therefore, to instruct patients not to apply undue stress to their freshly placed amalgam fillings.

Plastic deformation (creep): Amalgam undergoes a certain amount of plastic deformation or creep when subjected to dynamic intra-oral stresses.

Corrosion: The term corrosion should be distinguished from the often misused term tarnish. Tarnishing simply involves the loss of luster from the surface of a metal or alloy due to the formation of a surface coating. The integrity of the alloy is not affected and no change in mechanical properties would be expected. Amalgam readily tarnishes due to the formation of a sulphide layer on the surface.

Corrosion is a more serious matter which may significantly affects the structure and mechanical properties. The heterogeneous, multiphase structure of dental amalgam makes it prone to corrosion. Electrolytic cells are readily set up in which different phases form the anode and cathode and saliva provides the electrolytes. Corrosion produces a restoration with poor appearance and may significantly affect mechanical properties.

Copper-enriched amalgams contain little or no γ2 phase. The copper–tin phase, which replaces γ2 in these materials, is still the most corrosion-prone phase in the amalgam. The corrosion currents produced, however, are lower than those for conventional amalgams.

Thermal properties: Amalgam has a relatively high value of thermal diffusivity, as would be expected for a metallic restorative material. Thus, in constructing an amalgam restoration, an insulating material, dentine, is replaced by a good thermal conductor. In large cavities it is necessary to line the base of the cavity with an insulating cavity lining material prior to condensing the amalgam. This reduces the harmful effects of thermal stimuli on the pulp.

The coefficient of thermal expansion value for amalgam is about three times greater than that for dentine. This, coupled with the greater diffusivity of amalgam, results in considerably more expansion and contraction in the restoration than in the surrounding tooth when a patient takes hot or cold food or drink. Such a mismatch of thermal expansion behavior may cause microleakage around the filling since there is no adhesion between amalgam and tooth substance. However, one must take care not to overstate the effects of thermal expansion and shrinkage since the transient nature of intra-oral thermal stimuli indicates that only the surface layers of exposed materials will be affected. The occurrence of decay in the dentine which surrounds an amalgam filling is the major cause for replacement of such restorations. It is likely that microleakage plays an important part in initiating such lesions.

 Biological properties: Certain mercury compounds are known to have a harmful effect on the central nervous system. The patient is briefly subjected to relatively high doses of mercury during placement, contouring and removal of amalgam fillings.  A lower, but continuing, dose results from ingestion of corrosion products.

Another potential problem concerns allergic reactions to mercury in dental amalgam. Such allergic reactions, usually manifested as a contact dermatitis or lichenoid reaction, are well documented and caormally be explained by previous sensitization of the patient with mercury-containing medicaments.

Serious problems can be avoided by ensuring that the surgery is well ventilated and that flooring  of a suitable type is chosen such that accidental spillages can be readily dealt with. Excess, waste or scrap amalgam should be stored, under water or chemical fixative solution, in a sealed container in order to prevent another possible source of contamination. Mercury or freshly mixed amalgam should never be touched by hand. Mercury is readily absorbed by the skin, a fact which was obviously not appreciated in the days when it was normal practice to ‘mull’ the material in the hand before condensation. In addition to being hazardous this practice leads to contamination of the amalgam.

Despite the increased exposure of dental personnel to mercury vapour, examinations of the health, mortality and morbidity rates for dentists have shown that they are not significantly different from those of the general population, a fact which should go a long way towards reassuring those who harbor fears over mercury toxicity.

Clinical handling notes for dental amalgam

Cavity design: Many designs of cavity have been used for amalgam restorations, starting with modification of Black’s design for cavities for gold restorations. Over the years the cavity design has been refined to minimize destruction of healthy tooth tissue and to give an appropriate form to the restoration to ensure that the physical properties of the material are optimized in the end product.

Amalgam does not chemically bond to tooth surface but requires tooth preparation to create a shape of cavity that contains both retention and resistance forms to prevent dislodging of the restoration. This is carried out by creating undercuts, dovetails, pits and grooves in the dentine of the tooth, in large cavities dentine pins are used. This inevitably requires more tooth tissue to be removed than is necessary to remove the caries alone and can lead to unnecessary destruction of precious tooth tissue. A proper prepared cavity should be wider within the structure of the tooth than at its surface, in order that the material should be mechanically retained.  At all times the cavity should be no wider than is compatible with removal of caries from the dentine, removal of any unsupported enamel and adequate access to pack the amalgam into the cavity should be provided. All internal line angles should be rounded to minimize internal stresses within the restoration and to facilitate adaptation of the material to the cavity walls. The floor of the cavity, both that overlying the pulp and at the gingival extent of any box, should be flat to permit condensation of amalgam.

The cavo-surface margin is of particular importance for amalgam restorations. Amalgam is weak in thin section and hence a cavo-surface angle of  approaching 90^o is desirable. This can be difficult to achieve, particularly on a cusp slope, while retaining a reasonable quantity of tooth tissue (Fig. 3). Local modifications to the cavity margin, in enamel, may help to surmount this problem. It is always necessary to remove unsupported enamel once any carious dentine has been removed.

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Fig.3  Cavity shape for amalgam restoration

This is relatively easy to achieve on the clearly visible cavity surface, but it should be remembered that the enamel prism orientation close to the gingival margins is apical. Hence this area of the tooth needs to be finished using a gingival margin trimmer. Failure to remove unsupported enamel will result in an intrinsic weakness at the margins of the restoration. The unsupported tissue could fail either during function or under the pressure applied by a steel matrix band while the restoration is being packed. Such failure would result in very rapid marginal ditch formation and probable early failure of the restoration through recurrent decay.

Small cavities rely upon the undercut between opposing walls of the tooth for retention. If one or more cusps have fractured off a tooth it may be necessary to use an alternative form of retention for the amalgam. One method is to prepare pits and grooves in the remaining dentine into which the amalgam can be condensed. These act as retentive features if positioned correctly in relation to the remaining tooth tissues.

Matrices: If an external wall of a tooth is breached by a cavity a steel matrix band needs to be applied to the tooth to provide a surface against which the amalgam can be condensed. In addition to forming the external wall of the cavity the matrix should adapt very closely to the gingival margin of the cavity to prevent the production of ledges of amalgam outside the cavity during packing.

 Trituration: The mixing or trituration of amalgam may be carried out by hand, using a mortar and pestle, or in an electrically powered machine which vibrates a capsule containing the mercury and alloy.

 Condensation: Following trituration, the material is packed or condensed into the prepared cavity. A variety of methods have been suggested to condense amalgam including ultrasonic vibration and mechanical condensing tools. The mechanical tools apply quite high loads with reasonably large amplitude of movement of the condensing tool. As a consequence they may be associated with damage to teeth, notably cuspal fracture during condensation.

Ultrasonic condensers tend to produce local heating of the amalgam with detrimental effects both in terms of mercury vapour release and modification in the setting reaction of the material. The most widely used method of condensation is with a hand instrument called an amalgam condenser. These are flat-ended and come in a variety of styles. The shape and size of the condenser should be chosen with the size of the cavity in mind. The condenser must be able to fit within the cavity outline and should be able to get reasonably close to the peripheral margin of the restoration.

 Carving:  The objectives of carving an amalgam restoration are to remove the mercury-rich layer on the amalgam surface and to rebuild the anatomy of the tooth, re-establishing contact with the opposing dentition. Obviously, the knowledge of normal tooth anatomy is necessary for this purpose.

 Polishing:  Polishing is carried out in order to achieve a lustrous surface, having a more acceptable appearance and better corrosion resistance. The fillings should not be polished until the material has achieved a certain level of mechanical strength, otherwise there is a danger of fracture, particularly at the margins.

Indications for amalgam restorations

Amalgam has a high compressive strength, but offers poor aesthetics and so is best suited to restorations of premolar and molar teeth where heavy occlusal forces are experienced and where the cavities are not suitable for composite resins. Due to their durability, amalgam restorations are often used to rebuild badly broken down teeth prior to final restoration with crowning.

 

Pulp protection. Linings

Insulating linings

To prevent noxious stimuli reaching the pulp it has been custom and practice to apply protective materials to the floor and/or the pulpo-axial wall of preparations (Fig. 4). These materials were commonly placed under amalgams and resin composites to prevent thermal stimulation of the pulp and acid contamination of dentine respectively. Insulating lining (zinc-phosphate cement “Adhesor” SpofaDental – (Fig. 5) ) usually is used to separate root canal filling material (i.e. – zinc-eugenol cement “DEXODENT” AlphaBeta) from the crown filling (e.g.- composite material).

 

 

It has been demonstrated that thermal stimulation of dentine is not normally a problem clinically and that routine basing of preparations for amalgams, to prevent thermal stimulation, inherently weakens the restoration without benefit to the continuing vitality of the tooth. It is also accepted that dentine can be etched without harmful pulpal effects and therefore routine lining of preparations for resin composites is now contraindicated.

It is currently suggested that the routine placement of a preparation liner or base for all restorations is contraindicated. All preparations should, however, have some form of sealer applied and some preparations (usually deep) will require a liner and/or base. There is some merit in etching preparations prior to placing a sealer, liner or base, as etching will remove the smear layer which is contaminated with bacteria. Removal of the smear layer in this way affords gross debridement of the preparation and will also improve the quality of the interface between the sealer/liner and the dentine substrate.

Liners

Preparation liners also seal freshly cut dentine but have additional functions, such as adhesion to tooth structure, fluoride release and/or antibacterial action. Preparation liners are applied in thin section (<0.5 mm) and materials currently used include RMGICs, dentine adhesive systems, flowable resin composites and hard-setting calcium hydroxide cements. It has been suggested that RMGICs(resin modified glasss ionomers cements) have greater resistance to microleakage than dentine adhesive systems. This feature can be used to good advantage when planning to place an amalgam in a deep preparation.

 

Therapeutic (Treatment) linings

In the case of deep dental caries partial necrectomy is allowed, when the bottom of the cavity is very thin and there is a danger of the pulp horn disclosure, necrectomy is conducted with excavator. In this case is permitted to leave on the bottom of the cavity a layer of dense pigmented dentin, but in the course of acute deep caries – it is allowed to leave a small layer of softened dentin with the next remineralizing influence on it. In such cases it is recommended to use calcium hydroxide paste (“Life” KERR) as a treatment lining, it is placed for 14 days, with the subsequent filling of carious cavity with permanent filling material.

Indications for use:

For deeper cavities where there is less than 2 mm of remaining dentine, an insulating liner should be placed in the deepest aspects of the preparation. It is usual to place a small increment of hard-setting calcium hydroxide cement in the deepest aspects (but only if a pulp exposure is evident or a micro-exposure suspected). This is termed ‘direct pulp capping’. In very deep cavities in which the pulp is nearly exposed, hard-setting calcium hydroxide cement is applied to this area only. This is termed ‘indirect pulp capping’. It is important to minimise the extent and thickness of the hard-setting calcium hydroxide cement, as the material is weak and prone to fracture under restorations. The thickness of calcium hydroxide lining is should be no more than 0,3 mm.

                                                              

Life –is a calcium hydroxide cement. The material is provided as two pastes. Approximately equal amounts of each paste are dispensed onto the mixing pad and mixed with a spatula. One of the active ingredients is a salicylate compound which has a very distinctive ‘medicated’ odour. Life is a hard-set calcium-hydroxide base indicated for use as a direct and indirect pulp-capping material and as a cement base for all restorative filling materials.

Dycal – possesses a quick, convenient and easy paste to paste mixing system. This system prevents small variations in the base to catalyst ratio, affecting the working and setting times of the material. The material sets hard quickly and withstanding amalgam condensation, allowing for the immediate placement of restorative material or an intermediary base. Dycal has high compressive strength, low solubility and a hard setting, resisting the forces of amalgam condensation. It does not inhibit the setting of acrylic and composite restorations and has no negative effect on the aesthetic result of translucent composite materials.

 

A lining material may also act as a therapeutic agent by providing active protection of the dentine. Objectives of pulp protection are as follows:

■ Therapeutic:

1.    Stimulate odontoblasts to lay down reparative dentine.

2.    Encourage remineralisation of dentine.

3.    Act against any remaining bacteria.

■ Protect from chemicals. These may come from the oral cavity, bacteria or from the restorative material.

■ Protect from temperature. Metal restorative materials, such as amalgam and gold, will transmit changes in temperature from the oral cavity and, in the absence of a suitable layer of dentine in deep cavities, additional protection must be provided.

■ Seal the dentinal tubules. This will prevent fluids containing bacteria, molecules and ions entering the dentinal tubules, and as a result prevent pain and possible further caries.

Methods of pulp protection with insulating lining

This method depends upon the type of cavity.

The modern concept of insulating lining usage is as follows:

■ Minimal cavities: either a dental adhesive is used to seal the dentinal tubules or no pulp protection + filling material

■ Moderately deep cavities: a layer of a resin-modified glass ionomer is used to give thermal and chemical protection + filling material

■ Deep cavities: a thin layer of setting calcium hydroxide as a therapeutic lining is applied, followed by a layer of resin-modified glass ionomers + filling material

 

Techniques for placement:

A small ball-ended instrument is used to place the setting calcium hydroxide material (Fig. 7). The calcium hydroxide should be placed in a thin layer on the deepest part of the cavity. For the glass ionomer, a flat plastic or ball-ended plastic is used and the material is applied to the pulpal floor and/or pulpal wall, depending on the cavity shape.

The lining material should not extend to the cavity margins.

 

 

CALCIUM HYDROXIDE CEMENTS

Composition: Some calcium hydroxide preparations consist simply of a suspension of calcium hydroxide in water. This is applied to the base of the cavity and dries out to give a layer of calcium hydroxide. These materials are both difficult to manipulate and form a very friable cavity lining which is easily fractured. A solution of methyl cellulose in water or of a synthetic polymer in a volatile organic solvent can be used instead of water. These additives produce more cohesive cement but the compressive strength remains very low at about 8 MPa. This is well below the value of strength required to withstand amalgam condensation and when this filling material is to be used the calcium hydroxide preparation must be overlaid with a layer of stronger cement. Most calcium hydroxide products in current use are supplied in the form of two components, normally pastes, which set following mixing to form a more substantial cavity lining. The composition of a typical commercial product is given in Table 2.

 

 

The structural formula of butylene glycol disalicylate, a glycol salicylate commonly used in one of the pastes, is given in. This is a difunctional chelating agent having two aromatic groups with reactive groups in ortho positions. On mixing this with a paste containing zinc oxide and calcium hydroxide, chelate compounds. It is thought that zinc ions are primarily responsible for chelation, with calcium being largely unreacted.

The sulphonamide compound used in the zinc oxide/calcium hydroxide paste is present merely as a carrier and is not thought to have any therapeutic effect. Some cements contain paraffinic oils instead of sulphonamides. These cements are more hydrophobic and release their calcium hydroxide more slowly. This may have an adverse effect on the antibacterial properties of the cement.

Light-activated calcium hydroxide cements are available. They carry brand names which suggest that they are chemically similar to the two-paste products. They are, however, based on a totally different setting reaction involving light-activated polymerisation of a modified methacrylate monomer of the type used in resin based filling materials. A typical material contains dimethacrylate (e.g. Bis GMA) hydroxyethylmethacrylate (HEMA), polymerisation activators and calcium hydroxide. The purpose of the HEMA is to produce a relatively hydrophilic polymer which can absorb water and release calcium hydroxide to create an alkaline environment.

 

 

Properties: The mixed materials have very low viscosity and setting can be relatively slow for some products. Moisture has a dramatic effect on the rate of setting however, and the materials set within a few seconds of being placed in the cavity, even when the cavity has been ‘dried’. Setting of the light-activated materials is more under the control of the operator and residual moisture in the cavity does not have the same influence on setting time. An exposure to activating light for only a few seconds is required to activate polymerisation of the thin layer of cement. One characteristic of these cements which has been largely ignored is the relatively high temperature rise produced on setting. This results from the heating effect of the light source and the exothermic setting reaction. The set material is relatively weak compared to other cements, having a compressive strength.

 

The set materials have a relatively high solubility in aqueous media. Calcium hydroxide is readily leached out, generating an alkaline environment in the area surrounding the cement. This is thought to be responsible for the demonstrated antibacterial properties of these materials. This characteristic is utilized in very deep carious lesions, sometimes involving exposure of the pulp, or occasionally in cases of traumatic exposure of the pulp during cavity preparation. The calcium hydroxide cement is used as a pulp capping agent in such situations.

It is sufficiently biocompatible to be placed adjacent to the pulp and capable of destroying any remaining bacteria.

The material is also able to initiate calcification and formation of a secondary dentine layer at the base of the cavity. This calcification process is a product of irritation of the pulp tissues by the cement, possibly mediated by the activation of TGFβ, a cellular growth factor. Calcium from the cement does not become bound into the mineralized tissues of the calcific barrier/secondary dentine.

In pulp capping procedures the calcium hydroxide material is generally overlaid with a strong cement base material such as zinc phosphate cement before completing the restoration of the tooth with amalgam. The resin-based calcium hydroxide materials are far less soluble than the conventional products. This is advantageous providing that the rate of calcium hydroxide release remains great enough to maintain the antibacterial and dentine regeneration properties of the material. One problem with the resin-based materials is that the unreacted methacrylate groups can become attached to a freshly placed composite resin restoration.

The composite shrinks during its setting reaction and this can pull the calcium hydroxide material away from the tooth, leaving a void.

Calcium hydroxide cements are routinely used as lining materials beneath silicate and resin-based composite filling materials. Unlike the eugenol-containing cements they have no adverse effect on these filling materials and form an effective chemical barrier against acids and monomers. The need for a lining material beneath a composite is controversial. As stated previously, some authorities would suggest that with modern dentine adhesives there is no need for a lining as the cavity margins are sealed by the adhesive, making microleakage unlikely. Obviously any lining that is placed will act as a barrier between the bonding agent and the dentine, reducing the potential area available for bonding. Indeed, it has been suggested that even exposed pulps can simply be etched and then coated with a resin adhesive to give a primary seal.

 

ZINC OXIDE/EUGENOL CEMENTS

 Composition and setting: These products may be supplied as a powder and liquid or as two pastes.( Table 3.)

 

 

Zinc oxide/eugenol cements may be used as linings in deep cavities without causing harm to the pulp. Unconsumed eugenol is able to leach from the set material and although this substance has been shown to be irritant under certain conditions, it appears to have an obtundant effect on the pulp. The free eugenol is also bacteriocidal which helps to minimize the effects of bacterial ingress and the production of exotoxins causing pulpal damage as a consequence of microleakage.

 The materials form an effective thermal barrier under metallic restorations having a value of thermal diffusivity similar to that for dentine. The main uses of these cements are for linings under amalgam restorations, either used alone or as a sublining overlaid with a zinc phosphate material. They are also used as temporary luting cements and as temporary filling materials.

At the time of writing the consensus view is:

•  That exposed pulps should be capped with a proprietary calcium hydroxide material before attempting to bond composite to the adjacent dentine.

•  That where the dentine at the base of the cavity is superficial (judged to be some distance from the pulp) then a lining is not required beneath an adhesive restoration.

•  That where a cavity is very deep and the dentine at the base of the cavity is judged to be ‘close to the pulp’, then it may be prudent to place a lining over that area alone. This final point gives problems clinically as it can only be based on a dentist’s subjective assessment of the depth of the cavity.

Information was prepared by Levkiv M.O.