Composite Resins:A Review of the Types, Propertiesand Restoration Techniques

Abstract: The history, composition, properties and typesof composite resins were reviewed. Clinical restorativetechniques using composite resins as the filling materialare different from those using amalgam. Specific cavitypreparation designs, filling techniques, and finishing andpolishing procedures are reviewed and discussed. Com-posite resins should be used with full awareness of theiradvantages as well as their short-comings and limitations.

'Stephen H.Y. Wei, BDS(Hon.), MDS, DDS,MS, FRACDS, FICO, FACDProfessor and Head, Department of Children'sDentistry & OrthodonticsDean, Faculty of Dentistry

and

Endarra L.K. Tang, BOS, MOSDepartment of ChildrensDentistry & OrthodonticsFaculty of Dentistry

Introduction

According to McLean, the first attempt to develop plasticrestorative materials was revealed in the Allied FieldInformation Technical Report No. 1185, published in1947. A cold-cured acrylic resin for use in restortivedentistry was developed in Germany(1). The self-cured,unfilled acrylic materials could be placed directly into theprepared tooth. The polymer and monomer were com-bined and inserted into the cavity where it polymerized.However, these amine-containing resins were not colourstable and turned dark on exposure to sunlight. They alsohad problems of excessive working time for initial set(1.5 minutes), poor compressive strength, low abrasiveresistance, low modulus of elasticity, high water absorp-tion and a polymerization shrinkage of 7% by volume.Their high coefficient of thermal expansion also predis-posed them to micro leakage and the problems associatedwith microleakage(2).

In 1958, the first composite resin material, P-Cadwrit,was made available in Germany. In 1959, Bowen filed hisfirst patent in the U.S.A. on the famous Bis-GMA resin.The advantages of composite resins based on Bis-GMAresin over an acrylic resin include: lower polymerizationshrinkage, non-volatile, lower exothermic properties, greatercompressive strength and less toxic to the pulp(3)·

Knight et al developed the urethane dimethacrylatesin 1973. A resin was made for use in composite dentalmaterials subsequently which have advantages of higher

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University of Hong Kong2/F., Prince Philip Dental Hospital34 Hospital RoadSai Ying PunHong Kong

'Corresponding author:

Key word: Composite Resins, Types,Properties, Restorative Techniques

molecular weight, lower viscosity and less in vivo stain-ing with use than Bis-GMA(l) resins.

Composition of Resins

According to Lutz et al(4), filled restorative resins con-sist of three-dimensional combinations of a minimum oftwo chemically different materials with a surface interfa-cial phase. The 3 phases are: the matrix phase, the surfaceinterfacial phase, and the dispersed phase. Each resin"must also include an accelerator-initiator system to beginand complete polymerization. The chemically cured com-posites generally use an amine-peroxide system, whereasthe light-cured resins use a diketone-amine system whichis activated by the intense blue light. In addition, pig-ments and opaquers are added to control transluency andshade.

The resin matrix is a dimethacrylate oligomer suchBis-GMA or urethane-diacrylate. The surface interfacialphase consists of either a bipolar coupling agent to bindthe organic resin matrix to the inorganic fillers, or a

copolymeric of homopolymeric bond between the organicmatrix and partial organic filler. The degree of interfacialadhesion and chemical stability is critical for successfulclinical use of any composite resin(5).

Lutz et al( 4) classified the dispersed phase based onthe three major classes of filler particles used. Traditionalmacrofillers consist of quartz, glass, borosilicate, andground or crushed ceramic. The diameter of macrofillersparticles range from 0.1 to 100A.055/lm. Microfillers areusually pyrogenic silica which are amorphous, finelydispersed particles of about 0.04A.05.5/lm in size. Themicrofiller-based complexes are usually one of threetypes : (l) splintered prepolymerized particles of I to200A.05 5/lm in size, (2) spherical pripolymerized parti-cles of 20 to 30A.055/lm in diameter, and (3) agglomer-ated microfiller complexes of I to 25A.055/lm in diam-eter.

Self-cured resins are advantageous where compos-ite-resins need to be placed in areas of the mouth wherelight cannot reach adequatly(2). However, the visiblelight-cured resins have many advantages, including: con-trol over the working time, immediate finishing of arestoration and control over the depth of cure. Since nomixing is required, it means easier handling and minimalporosity, The major benefit is that the restoration will bemuch more colour stable compared to self cured resins.Therefore, the majority of the composite resins nowavailable are light-cured resins(2,6).

Types and Characteristics of Composite Resins

Traditional (large particle-size) composities

Traditional compsite resins were widely used in the late1960's and early 1970's. The best known resins of thistype are Adaptic (Johnson & Johnson) and Concise (3M).They were chemically cured and were about 70% filledwith particles of glass or quartz. The average diameter ofthese filler particles was about 15/lm. The major weak-ness of these resins was the bond between the dispersedpurely inorganic large particles and the organic ma-trix(5). Clinically the macrofillers fracture and are dis-lodged selectively from the faster wearing resin matrix.Hence, with clinical wear, they have a poor wear resist-ance and develop a rough surface which trapped plaque.Colour stability was also poor which caused staining ofthe restoration.

Although the traditional large particle sized com-posite resins had served as an acceptable restorativematerial for Class III and IV restorations for 2 decades,they are now basically obsolete.

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Fine-Particle size Composite Resins

This type of comp osite resins contain glass or other fillerparticles of 1 to 5/lm in diameter(2.6) which comprise70% to 80% of the material by weight(2) Some productsmay contain a small amount of silica to improve theircondensability(6,7). The increased filler content in vol-ume percentage improves the clinical handling character-istics and wear resistance. Most of these resins are visiblelight cured. Compared to the large-particle compositeresins, they provide a smoother restorative surface withless surface degeneration, better color stability and higherstrength(5). However, they are still not ideal for the mostaesthetic anterior restorations. The relatively large fillerparticle size limit the degree of polishability and the mosthighly lusterous surface cannot be obtained. Also, even ifan acceptable smoothness is achieved initially, chemicaldegeneration at the filler-matrix interface would stillcause some degree of surface degeneration(5).

Examples of fine-particle anterior composite resinsinclude Prisma-fil (L.D. Caulk), Visio-fil (ESPE - Pre-mier) and Aurafill (Johnson & Johnson) and examples ofposterior composite resins include: Estilux posterior (Kulzer),Fulfil (L.D. Caulk and Marathon (Den-mat).

Fine-particle type of composite resins are indicatedfor use in Classes I, II or IV cavities, and incisal edgerestorations in mandibular incisors(2).

Hybrid (Blended) Composite Resins

These are the most recently developed group of compos-ite resins. They contain a blend of microfill and smallparticles in the range of 0.04 to 5.0/lm(6). In addition tocolloidal silica, different particles such as barium silicateand borosilicate glasses may also be' added as fillers tothe hybride composite resins, so as to improve theirworking properties(5). Well-controlled particle size dis-tribution allow increased filler loading (70% to 87%) forhigher strength. The high filler content also results inlower thermal expansion and less polymerization shrink-age. The increase in smaller particles allows improvedpolishability so that this group of composite resins can befinished to give surface smoothness approaching that ofmicrofilled composites.

Examples of hybrid anterior composite resins in-clude: Command Ultrafine (Sybron/Kerr) and Valux OM).Examples of hybrid posterior resins include: Occlusin(lCI) and P-50 (3M).

Some companies have claimed that the hybridecomposite resins they produce can be used for bothanterior and posterior restorations. Examples of these so

called 'all-purpose composite resins' include: HerculiteXR (Sybron/Kerr); Prisma AP.H (L.D.Caulk) and Bril-liant (Coltene). One of the characteristics of these com-posite resins is that they have expanded shade ranges.E.g. the Brilliant (Coltene) resins have 8 dentine shades,6 enamel shades and a grey/blue incisal shade. HercluteXR (Sybron/Kerr), on the other hand, have 6 dentineshades, 6 enamel shades and 2 incisal shades. PrismaAP.H (L.D. Caulk) have a total of 16 shades, including 8normal shades and 8 accessory shades.

Hybrid composite resins can be used in a wide rangeof cavities including Classes I, II, III and IV cavities,except where the restoration involves a large labial sur-face on the anterior and a highly polished smooth surfaceis required for aesthetic reasons. In those cases, hybridecomposite resins may not give the best esthetic results.

Microfilled Composite Resins

Homogeneous microfilled composite resins contain 0.02to 0.071lm pyrogenic silica particles in an organic matrixto obtain a filler content of 38% to 65%(5). To increasefiller loading, the resin containing the colloidal silicamay be pre-polymerized, ground into particle and incor-porated as fillers( 6).

Microfilled composite resins can be finished to ahigh degree of smoothness, and their surface actuallybecome smoother with time. Microfilled resins are veryhard and therefore difficult to finish in areas of pooraccess. However, their tensile strenght is low, they arebrittle and should not be used in Class IV stress bearingareas. They are excellent for use in cases where anaesthetic and smooth finish restoration of moderate strengthis required. They can be used as a veneering material overcores built-up using fine-particle size composite resins orhybrid resin in large anterior restoration, so that bothstrength and aesthetics can be optimised. The thermalexpansivity and water absorption of microfilled resins areusually higher than those of hybrid and small-particlecomposite resins, and they norma'ny cannot be syringed(6).

Examples of anterior microfilled resins include :Durafill VS (Kulzer), Heliosit (Vivadent) and Silux-Plus(3M). One example of posterior microfilled resins isHeliomolar (Vivadent) although the manufacturer claimsthat this product can be used for anterior restorations aswell.

Properties Composite Resins

Polymerization Shrinkage

All composite resins contract during polymerization, suchcontracti on is termed polymerization shrinkage. Polym-erization shrinkage of composite resin is important be-

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cause of its effect on cavosurface margins. It causeseparation between a composite resin mass and the adja-cent tooth structure. Marginal adaptation of a compositeresin restoration is dependent on several factors includ-ing: polymerization shrinkage, hygroscopic properties,bonding between restoration material and the cavity walls.coefficient of thermal expansion of the material, and thefinishing methods(8-11). It has been demonstrated thatdespite acid etching of enamel walls, hygroscopic expan-sion of composite resin, careful finishing procedures, anduse of material with thermal expanxivity similar to that ofenamel, marginal gaps will still result from polymeriza-tion shrink age. Such shrinkage may cause marginal gapformation, or when the enamel - resin bond remainsintact, it may result in damage within the composite resinin the form of microcracks which may in turn will dausepremature failure of the restoration(12).

The shrinkage properties of a composite resin aredependent on both the physical components of the mate-rials and how the materials are cured and handled clini-cally. Various composite materials have been shown toexhibit polymerization shrinkage from about 1.5 - 5.5%by vo lume(8). Recent studies report shrinkage of about1-2% volume for posterior composite resins compared toabout 4-5% volume for early conventional composites(13).Incorporation of a high fraction of filler particles alongwith an appropriate composition of the monomer matrixtheoretically would give a composite resin the lowestpossible polymerization shrinkage. The amount of volu-metric ch ange in posterior composite resins when curedhas been stated as one of the main determinants of thelongevity of the composite resin restoration.

Water Absorption

The technical properties of composite resins are affectedby absorption of water, which acts as a plasticizer and astress corrosion agent, weakening the particle matrixinterface.

Localized swelling occurs at the filler-matrix inter-face causing debonding, which may lead to hydrolyticbreakdown. Break down on the surface of compositeresins may also be facilitated by temperature changes andsolvent effects. The higher the temperature, the morerapid the water absorption(14). The amount of waterabsorption in posterior composite resins used today isabout 0.2 - 0.6% by weight. Water absorption will lead tobreakdown of the composite resin with use.

Wear

Wear may be defined as the unwanted removal of solidmaterial from surface as a result of mechanical action(15).The traditional large-particle size composite resins con-

tain large filler particles which are considerably harderthan the resin matrix. During mastication, stresses aretransmitted onto the restoration surface and particularlythe particles projecting from the occlusal surface. Sincethe particles ae harder than the resin matrix in which theyare embedded, much of the stress is transmitted throughthe particle into the resin itself. Stress will concentrateand become excessively high where the submerged por-tion of the particle is angulated or irregular in shape.Such a condition tends to generate small cracks arroundthe particle, thereby weakening the matrix locally(16). Anew generation of composite resins has therefore beendeveloped which contain filler particles of reduced sizesbut increased filler loading. The amount of stress aroundeach particle is reduced which result in a significantreduction in loss of anatomical form.

In some composite resins, softer filler particleshave been incorporated in order to decrease the differ-ence in hardness between the filler and the matrix. Whensofter filler particles are used, the masticatory stressesare partially absorbed by the particle, rather than beingtotally transmitted into the surrounding matrix(12). Theuse of softer filler particles therefore reduce the likeli-hood of generating small cracks around the filler andweakening the matrix locally. Scanning electron micro-scopic examinations of the stress-bearing area revealsthat the softer particles actually become worn and pol-ished with wear.

Restorative Techniques

In the past decade, several alternative preparations to thetraditional G.V. Black's cavity preparations have beensuggested. These alternative preparations are much smallerthan the conventional cavity preparation and are termed'microconservative'(l7). The reasons for modifying thecavity design is because the conventional cavity requiresunnecessary extension. Extension for prevention is in-creasingly questioned and this seems unnecessary sincefissure sealants are now available. Extention for retentionhad also become unnecessary since adhesive restorationmaterials are available. Extension to remove weakenedtooth structure is unnecessary since materials like com-posite resins can provide reinforcement.

With increasing concern about microleakage, thereis a desire to reduce the perimeter of a restoration,because the longer the margin, the greater the potentialfor marginal breakdown and leakage. Futhermore, thenewer restorative materials like glass ionomer cementsand composite resins require a different approach fromthat use for amalgam restorations. It is difficult to ma-nipulate composite resins to produce a successful resultin the conventional cavity designed for amalgam restora-tions. It is therefore logical to design a preparation that

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best suits the restorative material being used._ Hunt(17) proposed an "internal" preparation tech-

nique which involved access to the carious lesion form anocclusal approach just inside the marginal ridge, removalof the carious dentine via this occlusal cavity and finallyhandling the proximal enamel lesion. There are threemethods of handling the enamel lesion: (i) punching ordrilling out the weakened or porous enamel; (ii) enamalporosity is left intact to avoid trauma to the enamal walland to retain a shell of porous enamel, allowing forremineralization; and (iii) cut a minibox to remove theporous enamal, at the same time removing the overlyingenamal up to and including a portion of the enamal ridge.

Covey et al(18) measured the resistance to fractureof the marginal ridge in teeth prepared with a modifiedClass II cavity proparation (the internal tunnel technique)which is considered to be weaker than the 'internal'preparation. It was found that teeth prepared with tunnelcavities were understandably weaker than unpreparedteeth. However, once the teeth were restored they becameno weaker than the unprepared teeth. Covey et al(18),therefore suggested that the restorative materials are-capable of re-establishing most of the fracture resistanceof the marginal ridge.

Filling Techniques

To mini mise the effect of polymerization shrinkage andcontraction stresses, there are specific filling techniquesproposed for composite resin restorations. Studies haveshown that ligh-cured composite resins shrink in thedirection of the polymerization light source(12). Contrac-tion towards the light source causes the resin to shrinkfrom margins of the preparation.

Fisbein et al(19) investigated the effect of anincremental filling technique on microleakage aroundClass II composite restorations in vitro. They believedthat curing an increment of a filling gives rise to a smallercontraction th an curing of an entire filling placed in bulk.Part of the space resulting from contraction of the firstincrement will be filled by the second increment. Inaddition, if the first increment is placed on the dentinebonding agent at the cavity floor without being anchoredon other surfaces, it may be expected to contract towarddentine and not away from it. Asumssen and Munksgaard(20)described a two-step filling technique involving inclininglayers. After curing the first inclining layer, a secondlayer is added and polymerized. It was found that thewidth and occurence of the marginal gaps was reducedwhen this technique was used with a variety of dentineadhesi ves.

Lutz et al(21) proposed the 'three-sited light curingtechnique' which was used in conjunciton with light -reflicting wedges (Figure 1). It was found that this tech-

Fig. 1 Three-sited curing technique. The first incre-ment is cured through the light-reflecting wedge;the large second and the smaller third from thebuccal and lingual directions in order to ensurethat the shrinkage vectors run towards the ca-vity margins. Afourth increment is added to theocclusal surface. [From Quint Int 1986; 17(2):778.]

nique, though complex, can minimise the adverse effectsof composite resin polymerization shrinkage. Therefore,this was recommended for use in Class II restorations.

It was generally believed that multiple small incre-ments of resins would reduce the polymerization shrink-age stress, minimize post-operative sensitivity or discom-fort, and increase the longevity of service of the restora-tion. However a recent research published by Eakle andIto(22) showed that although the diagonal insertion tech-nique used in filling mesio:occluso distal cavities pro-duced less microleakage than if fillings were placed inone single increment or in horizontal layer increments,the difference was not satistically significant. They alsofound that cervical margins that ended on the root surfacehad extensive microleakage regardless of the filling tech-nique employed. Another study was published by Ciucchiet al(23) which compared the proximal adaptation and themarginal seal of different types of posterior compositeresin restorations employing different filling techniques.The three filling techniques they employed included: thethree-sited light-curing technique, the multilayer tech-nique and the indirect composite inlay technique. Theresults did not show statistically significant differencesin adaptation or marginal seal among the three composite

32

resin techniques used. They also found that adaptationand seal in composite resin restorations were inferior tothose of the amalgam restorations.

Although there are some encouraging research re-sults on the success rates of posterior composite restora-tions(24), a study using scanning electron micrographicevaluation of the posterior composite revealed that mod-erate to medium marginal degradation occurred duringthe first two years of clinical service(25). The later studytested four different light cured posterior composite res-ins, including: two hybrid composite resins (P - 30, 3MDental Products Div; Ful-fail, LD Caulk / Dentsply InL),one microfilled composite resin (Heliomolar, VivadentInc.), and a two-component system with a hybride baseand a macrofill occlusal material (Estilux-Posterior, KulzerCo). It was concluded that the use of these productsshould be limited to selected cases in which esthetics is ofprimary concern.

Finishing and Polishing

According to Farah et al(26), initial reduction should bedone using 25-4511m diamonds (e.g. MFl/MF2, PremierDental Products Co.; ET fine diamonds, Brasseler USA,Inc.), in a high-speed handpiece running at 1/3 to 1/2 fullspeed with water/air coolant spray and light sweepingmotion. A 10 - 25A.055m diamond bur (e.g. MF3, Pre-mier Dental Products Co.; E T extra fine diamonds,Brasseler USA, Inc.; and T & F Hybrid Points, ShofuDental Corp.) should then be used again in a high-speedand piece running at 1/3 to 1/2/ full speed with water / aircoolant spray and a light sweeping motion. Sof-lex OMDental Products) medium, fine and superfine disks shouldbe used where access permits, and finally Quasite Midi-Points (Shoufu Dental Corp.) used to obtain a final luster.

Pratten and Johnson(27) evaluated the various fin-ishing instruments used on a highly-filled posterior com-posite and a blend anterior composite. They found thatthe same finishing instruments and techniques revealedno significant differences in the surface roughness of theanterior and posterior composite resins. The smoothestsurface was achieved with Mylar matrix strips; and thesmoothest instrumented surface was achieved with aseries of abrasive disks. Although a fine diamond burwith 25A.05511m particles produced the roughest surface,and estra-fine diamond with I5A.05511m particles pro-duced a surface smoothness superior to that producedwith a white stone and similar to the smoothness pro-duced with a carbide bur and rubber points.

It has been speculated that the wear rate of acomposite resin restoration may, in part, be attributed tothe mechnaical finishing procedures done after insertionand polymerization(28). Specifically, it was postulated

that the rapid rotating blades of the finishing instrumentgene rated numerous microcracks in the subsurface. Sucha condition would weaken the surface superficially, mak-ing it less resistant to wear. Ratanapridakul et al24investigated clinically the effect of finishing on the wearrate of a posterior composite resin. They found that theelimination .of conventional finishing procedures on theocclusal surface resulted in a substantial reduction inwear. Therefore, careful contouring of the compositeresin before light-curing, so as to minimise the need offinishing and polishing, would help to reduce wear to therestoration during service.

Conclusions

The types and characteristics of composite resins andtheir properties, and the modified cavity preparations,filling techniques and finishing and polishing proceduresof composite resin restorations have been reviewed andbriefly discussed. During the last decade, composite res-ins have been used more frequently in the posteriorregion of the mouth. More and more patients are nowdemanding nonmetallic restorations for esthetic reasonsand because 9f concerns about alleged but unsubstanti-ated mercury toxicity. At present, they do not completelyreplace amalgam and other metallic fillings. However,with proper selection of cases and the exercise of due carein their manipulation and placement they should help toprovide aesthetic and functional restorations for both theanterior and posterior teeth.

References

1. McLean JW. Limitations of posterior composite resins andextending their use with glass ionomer cements. Quint Int1987; 18(8): 517-528.

2. Valentine CWo Composite resin restoration in esthetic den-tistry. J Am Dent Assoc 1987; Special Issue 55E-6IE.

3. Branden M. Selection and properties of some new dentalmaterials. Dent Update 1974; 1(10): 489-501.

4. Lutz F et al. Dental restorative resins: types and character-istics. Dent Clin North Am 1983; 27(4): 697-712.

5. Wei SHY & Jensen M. Composite Resin Restoration.Chapter 12 In : Paediatic dentistry - total patient care, WeiSHY ed. Lea & Febiger, Philadelphia, 1988. P 199-223.

6. Farah JW & Powers JM. The Dental Advisor. 1987; Vol. 4,No. 4.BB7. Farah JW & Powers JM. The Dental Advisor.1986; Vol. 3, No.2.

8. Goldman M. Polymerization Shrinkage of resin base re-storative materials. Aust Dent J 1983; 28(3) : 156-161.

9. Jorgensen KD, Asmussen E & Shimokobe H. EnamalDamages caused by contracting restorative resins. Scand JDent Res 1975; 83 (2) : 120-122

10. Ehrnford L & Derand T. Cervical gap formation in Class IIcomposite resin restorations. Swed Dent J 1984; 8: 15-19.

II. Braden M, Caauston BE & Clarke RL. Diffusion of waterin composite filling materials. J Dent Res 1976; 55(5) :730-732.

12. Bausch lR, DeLange C & Davidson CL, et al. The Cinicalsignificance of polymerization shrinkage of composite resinrestorative materials. J Prosthet Dent 1982; 48(1): 59-67.

13. Rees IS & lacobson PH. The polymerization shrinkage ofcomposite resins. Dent Mater 1989; 5(1): 41-44.

14. Lundin S-A. Studies on Posterior composite resins withspecial reference to Class II restorations. Swed Dent 1Supplement 73, 1990.

15. Roulet IF. A material scientist's view: assessment of wearand marginal intergrity. Quint Int 1987; 18(8) : 543-552.

16. Leinfelder KF. Current development in posterior com-posite resins. Adv Res 1988; 2(1): 115-121

17. Hunt PRo Microconservative restorations for approximalcarious lesions. J Am Dent Assoc 1990; 120( 1) : 37-40.

18. Covey D, Schulein TM & Kohont Fl. Marginal ridgestrength of restored teeth with modified Class II cavitypreparations. 1 Am Dent Assoc 1989; 118(2) : 199-202.

19. Fisbein S, Holan G, Grajower R & Fuks A. The effect ofVLC Scotch bond and an incremental filling technique onleakage around Class II composite restorations. 1 DentChild 1988; 55(1) : 29-33.

20. Asmussen R & Munksgaard EC. Bonding of restorativeresins to dentine: status of dentin adhesives and impact oncavity design and filling techniques. Int Dent J 1988; 38:97-104.

21. Lutz F, Krejci I & Oldenburg TR. Elimination of polymeri-zation stresses at the margins of posterior composite resinrestorations: a new restorative technique. Quint Int 1986;17(2) : 777-784.

22. Eakle WS & Ito RK. Effect of insertion techniques onmicro leakage in mesio-occlusodistal composite resin resto-rations. Quint Int 1990; 21(5) : 369-373.

23. Ciucchi B, Bouillagnet S & Holz 1. Proximal adaptationand marginal seal of posterior composite resinrestorations placed with direct and indirect techniques.Quint Int 1990; 21(8): 663-669.

24. Barnes DM, Blank LW, Thompson VP, Hol ston AM &Gingell lC. A 5- and 8- year clinical evaluation of aposterior composite resin. Quint Int 1991; 22(2): 143-151.

25. Dietschi D & Holz J. A clinical trial of four light-curingposterior composite resins: two-year report. Quint Int 1990;21(2) : 965-975 .

26. Farah JW Powers 1M. The Dental Advisor 1988 Vol. 5. No.3.

27. Pratten DH & 10hnson GH. An evaluation of finishinginstruments for an anterior and a posterior composite. 1Prosthet Dent 1988; 60(2) : 154-158.

28. Ratanapridakul K, Leinfelder KF & Thomas 1 . Effect offinishing on the in vivo wear rate of a posterior compositeresin. 1 Am Dent Assoc 1989; 118(3) : 33-335.

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References:

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Journals:I) Massier M, Barber T K. Action of amalgam on den-

tine. J Am Dent Assoc 1953; 47: 415-22.2) Murray A J, Nanos J A, Fontenot R E. Compressive

strength of glass ionomer with and without silveralloy. J Dent Res (Abstract no: 215) 1986; 65: 193.

3) Kato Y, Okawa A, Hayashi S, eL al. Studies onmarginal leakage of composite resin resLorations.Part 2: On the leakage properties of various compos-ite resin restorations. Jpn J Conserv Dent 1976; 19:281-9.

Books:(Cite edition and page nos; chapters in books whererelevent.)1) Zinner I D. Esthetic considerations in restorative

dentistry. In Seide L J, ed. A dynamic approach torestorative dentistry. 1st edn. W.B. Saunders Com-pany, 1980; 10. 520-58.

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Monographs:Tay W M. Physio-chemical properties of alumino silicatebased dental cements. University of London, 1988. PhDthesis.

Tables:Each table, should be typed on a separate sheet, numberedconsecutively in Roman numerals ( eg Table 1V ), andtitled with a descriptive but concise heading. Perpendicu-lar dividing lines should not be used. Explanatory notes ifany shoul.d be placed below the Table

Illustrations:Must be of good quality usually 127 by 173mm [5 by 7ins] but no larger than 203 by 254 mm [8 by 10 ins].Submit 3 copies in a heavy-paper envelope. N.B.Authorsmust keep copies of everything submitted. At the back ofeach illustration label the appropriate Figure numbercorresponding to the order of appearance as citied in thetext. Use a soft pencil to indicate the the top of theillustration and lightly write in the fUnning title. Theauthors name should not be added. Original drawings,figures, charts, and graphs should be professionally drawnand lettered in Indian Ink large enough to be read afterreduction. High quality computer generated line diagramsor glossy prints are also acceptable. Photographs, ingeneral should be clear black-and-white prints on glossypaper. Colour illustrations may be submitted if theycontribute to the value of the article but the full cost ofprinting must be born by the author(s). Prints of radio-graphs should be sharp and clear. Photomicrographs mustinclude a scale and the magnification should be clearlystated. If full facial photographs are used, patients writtenconsent must be submitted with the manuscript.

Legends:Each figure must have a legend that is clear withoutreference to the text. All legends should be typed underthe corresponding figure with the figure number clearlyindicated.