single_composite can serve all purposes

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BRITISH DENTAL JOURNAL VOLUME 199 NO. 2 JULY 23 2005 73

Can a single composite resin serve all purposes? J. J. M. Roeters,1 A. C. C. Shortall2 and N. J. M. Opdam3

The consensus view less than a decade ago was that direct posterior composites should be restricted to small restorations,preferably in premolar teeth with little, if any, occlusal function. Major advances in adhesive systems, materials andrestorative techniques have combined to allow us to question this view and our increased clinical evidence base makes itappropriate to reconsider this viewpoint.

1Associate Professor, Department of Cariology andEndodontology, Radboud University Nijmegen, TheNetherlands; 2*Reader in Restorative Dentistry, TheUniversity of Birmingham, School of Dentistry, St Chad’sQueensway, Birmingham, B4 6NN; 3Department ofCariology and Endodontology, Radboud UniversityNijmegen, The Netherlands*Correspondence to: Dr Adrian Shortall Email: [email protected]

Refereed PaperReceived 06.10.04; Accepted 22.02.05doi: 10.1038/sj.bdj.4812520© British Dental Journal 2005; 199: 73–79

INTRODUCTIONIn 1996 an article was published whichstated that the indications for compositesare all types of restorations (includingcusp-capping and crowns).1 According tothe author the only limiting factor was theskill of the operator.1 The following year amulti-author paper stated that the consen-sus view from the current literature wasthat posterior composites should be limitedto small class I and II restorations, prefer-ably in premolar teeth with little, if any,occlusal function, in young adult patientswho have benefited from advances in pre-ventive dentistry and maintain a high stan-dard of oral hygiene.2 The authors consid-ered that the use of composite remainedlimited in the restoration of deciduous

molar teeth, given the resurgence in the useof glass polyalkenoate (ionomer) cements(GIC) and the introduction of resin-modi-fied GICs. These authors considered thatdespite the inherent limitations in compo-sition and construction of current compos-ites, their technique sensitivity, relativelyhigh cost and uncertain long term (> 10year) performance, they may be consideredas the material of choice for the restorationof ultra-conservative and small Class I andClass II preparations in posterior teeth.

Much has changed since this paper waspublished and new knowledge, coupled toour increased clinical evidence base makesit appropriate to reconsider this positionstatement. Since then, the number of den-tal practitioners skilled in posterior com-posite use has increased as in most Euro-pean dental schools students learn aboutadhesive restorative techniques and aretaught placement of composite restora-tions in Class I and II situations. Also ingeneral dental practice the use of dentalamalgam as a restorative is decliningwhile the number of composite restora-tions increases.3 It has been pointed outthat many dentists remain reluctant to useresin composites in posterior teeth, eitherbecause of their mediocre reputation or

because the confusion over restorativeconcepts and techniques makes their suc-cessful application doubtful.4 Theseauthors go on to explain that majoradvances in adhesive systems, materialsand restorative techniques have combinedto generate significant new restorativeopportunities for direct posterior compos-ites thus making them an essential materi-al for practitioners. They also remind usthat successful clinical application reliesupon appropriate materials selection for agiven situation, coupled with a soundunderstanding and implementation ofeffective application techniques. In addi-tion a certain, minimum case specific levelof operator competence (proficiency) isrequired. While the clinical performancehistory of amalgam restorations is stillgenerally superior to that of posteriorcomposites when correctly indicated andexecuted the annual failure rate for com-posites may match or even surpass that ofmodern dental amalgam.5-8

It is safe to assume that amalgam hasalready reached its zenith in terms of clini-cal performance while the longevity ofposterior composites is set to increase,albeit at an unknown rate. This will occuras more practitioners become proficient in

Points out that the use of dental amalgam as a restorative is declining. Explains that many practitioners remain reluctant to use resin composites in posterior teeth

but attitudes vary internationally. Suggests that the longevity of composites is set to increase while amalgam has reached its

zenith. Defines specific requirements for choosing composite materials for anterior and posterior

situations.

I N B R I E FVERIFIABLE CPD PAPER

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74 BRITISH DENTAL JOURNAL VOLUME 199 NO. 2 JULY 23 2005

the correct selection and application ofthese materials through personal clinicalexperience and evidence based learningand as the materials and bonding agentsare improved.

Longevity should not be the only wayto look at a restorative material thoughthis has always been the case with dentalamalgam. Using dental amalgam the cavi-ty preparation needed to be adjusted tomeet the requirements of the material.Instead of this one should question in whatway the tooth can be preserved as long aspossible. Composite resin, glass ionomercements and compomers do not require themore traditional preparation required foramalgam and adhesive restorative materi-als and techniques can be adjusted to allkinds of cavity shapes. As a consequencemuch less sound tooth tissue will be sacri-ficed. An in vivo study showed that whenprimary caries lesions in the occlusal surfaces of first molars were restored withamalgam the surface occupied by therestoration was five times larger thanwhen a composite resin was used.9 Thismeans that a composite restoration can bereplaced several times before the sameamount of tooth material as with amalgamis lost. However, when composite resinrestorations fail on the long term, there isno need to replace them completely asthey can be repaired.10 By doing this the‘tooth countdown’ repeat restorative cycleis halted.11 The total removal of bondedtooth coloured posterior restorations ismore technically demanding and timeconsuming than for amalgam removal.12

In addition, in vitro studies show thatremoval of bonded composite from class Iand II cavities frequently results in signifi-cant sound tooth tissue loss which increaseswith increasing cavity depth.12-15 Anotherimportant advantage of the adhesivelybonded composite restoration is thereduced chance for cusp fracture compared to dental amalgam.16 Completecusp fracture or incomplete cusp fracture(cracked-tooth syndrome) is a commonoccurrence in clinical practice.17,18 Whiledifferent opinions exist as to whetherdirect or indirect adhesive and cusp-cover-age restorations are best suited for restor-ing wide cavities in weakened posteriorteeth19,20 the effectiveness of using directbonded composite in the immediate treat-ment of painful cracked teeth has beenwell documented.20

Manufacturers will hopefully optimisetheir materials/bonding systems inresponse to reliable clinical research data,which is the final arbiter of success. Unfor-tunately manufacturers are often drivenby market forces to launch new productsprematurely with exaggerated perform-ance claims. By the time reliable inde-

pendent research evidence is publishedshowing that the product is inferior to itspredecessor the manufacturer has usuallydiscontinued it for a replacement material.This is not a ‘practice builder’ for the den-tist who is left with the consequences ofthe under-performing product. Manufac-turers may be driven to launch productsprematurely in order to maintain orimprove market share. This approach canprove to be shortsighted, as dentists haveto rationalise the short-term failures oftheir restorations to an increasingly den-tally aware public.

Expert group meetings have been pro-posed as one means of bridging the dividebetween the need for good evidence andthe relentless challenge of the introductionof new products and concepts in the fieldof direct adhesive restorative materials.21

In addition, the vast majority of clinicallong-term published studies of direct pos-terior resin-based composite restorationsare found lacking in their description ofdetailed operative techniques employed.22

As reliable evidence about the clinical per-formance of new materials is generally notavailable as soon as required, it is the pur-pose of this multi-author paper to reflectinternational opinion from two countrieswhere the uptake of posterior compositesby the vast majority of practitioners iswidely divergent. Composite is the mostfrequently used direct posterior restorativein the Netherlands3 whereas in the UK theconverse applies.23 A 1999 survey of thework of vocational dental practitioners andtheir trainers revealed that amalgam wasthe most frequently used restorative with >5 fold and > 10 fold the number of amal-gams used for Class I and II restorationsrespectively in comparison to compos-ites.24 Also, a more recent survey conclud-ed that 49% of respondents from GreatBritain seldom place large compositerestorations in molar teeth.23 Differences inthe system for health care remuneration inthe two countries account, at least in part,for this difference. In addition, the UK datain question compared unfavourably, interms of restoration longevity, in compari-son to data from other European countriesand Australia. It is hoped that the consen-sus view expressed in this paper, based onshared information and a collective inter-pretation of contemporary literature, willallow the reader to apply the knowledge inan informed fashion in order to allowhim/her to choose appropriate materialsand techniques for clinical practice.

Though all the indications can be cov-ered with composite resin it is not obviousthat this is achievable with a single material.Depending on the indication the restorativematerial should meet specific requirements.Composites vary in composition and han-

dling characteristics and each of these factors will influence their clinical per-formance. Composite resins are composedof a resin matrix and filler particles. Thetype of resin will affect the viscosity of theresin and the amount of cross-linking butwhen properly polymerised it will not havea great effect on the mechanical propertiesof the material. Additions of filler particlesto the resin improve the strength and wearresistance of the material while the poly-merisation shrinkage of the restoration willbe reduced. Based on the filler, compositescan be classified in various ways. A classi-fication based on filler size and loadingwas introduced in 1983:25

• Conventional composites with a fillerparticle size of 1 to 15 micrometer andfiller content up to 60% by volume

• Microfilled composites with a filler sizebetween 0.04 to 0.15 micrometer (or 40to 150 nanometer) and filler contentbetween 20 and 50% by volume

• Hybrid composites with a combinationof microfillers and particles up to 5micrometer and filler content between50 to 70% by volume.

A classification based on the size ofthe largest particles has been presented asfollows:26

• Microfills with a particle size between0.01 to 0.1 micrometer.

• Minifills with a particle size between 0.1and 1 micrometer.

• Midifills with a particle size of 1 to 10micrometer.

Resin composites have also been classi-fied to give more information about theirfiller content and filler distribution:27

• Traditional or conventional composites.• Microfine composites• Densified composites which can be mid-

way-filled (< 60 vol.%) or compact-filled (> 60vol.%) while the filler size isdescribed as ultrafine (< 3 micrometer)or fine (> 3 micrometer)

• Miscellaneous composites are a mixtureof densified and microfine composites.

Recently ‘nanofilled’ composites com-prising of nanomers (5-75nm particles) andnanocluster agglomerates have been mar-keted for dental use with different optical,mechanical and chemical properties to themore traditional micron-scale composites.Nanoclusters in all but translucent shadesare agglomerates (0.6-1.4 micron size) ofprimary zirconia/silica nanoparticles (5-20nm size) fused together at points of con-tact and the resulting porous structure isinfiltrated with silane. While initial short-term clinical findings appear promising28

questions have been raised about the sta-bility of the filler-matrix interface on the

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basis of short term immersion and in vitrofatigue stress testing.29,30 The filler parti-cles should be well bonded to the resinmatrix as otherwise the material will besubject to deterioration and fatigue in thelong term. Long-term clinical studies arerequired to assess fatigue resistance.

Another way to classify composites isaccording to the intended indication.There are anterior composites, posteriorcomposites or universal composites thatshould be suitable for application in ante-rior and posterior teeth. Depending on thefiller content, filler size, type of filler andtype of resin, composites will vary in con-sistency or viscosity and rankings havebeen made of a number of compositesbased on their consistency.31-33 In recentyears composites with special handlingproperties have been marketed:• Packable (‘condensable’) composites or

ceromers are highly viscous materialsdesigned to mimic the handling of adental amalgam

• Flowable composites are materials that arelow viscous or relatively fluid composites

• Conventional composites are materialsthat lie in between these two extremes.The materials in this group can be easilyinjected out of a compule and will readi-ly adapt to the surface they are applied.

With the extensive range of currentlyavailable types (hybrid, microfilled,nanofilled, ‘smart’, fluoride releasing, etc)viscosities, shades, opacities and presenta-tion formats (syringes, compules, completsetc) of composites it becomes difficult forthe dentist to make a logical choice. Today,there is a tendency to bring highly viscousuniversal composites onto the market. Atthe same time several composites notbelonging to this category but demon-strating excellent long term clinical per-formance (P30 and P50, 3M/ESPE) havebeen withdrawn from the market.34-37

The aim of this article is to define thespecific requirements for each indicationand to describe which material character-istics are needed to fulfil these. Further-more, the influence of specific handlingcharacteristics on the clinical performancewill be discussed.

SPECIFIC REQUIREMENTS There is a difference in the requirements aresin composite should meet to performwell in anterior or posterior teeth.

Restorations in anterior teethIn the anterior region of the mouthrestorations may fall inside the smile lineand therefore the aesthetic properties ofthe resin composite will be of majorimportance. Resin composites can be usedfor class III, IV and V restorations, full

veneers and complete crowns. Dependingon the location on the tooth, restorationsmay be subjected to different forces.

The ideal anterior composite shouldmeet the following demands:• Must be available in a sufficient number

of shades and degrees of translucency.To get a natural looking restoration, lostdentine should be replaced by an opaquecomposite while a more translucentmaterial best mimics enamel. For opti-mal aesthetics under every condition thecomposite should also be able to exhibitfluorescence

• Capable of being readily polished to a lus-trous finish. A smooth surface will be morecomfortable and less vulnerable to extrin-sic pigmentation. The polish should alsobe readily maintained in the long term.

• Colour stability must be good• Should have sufficient strength to resist

the forces of occlusion and articulationwhen class IV restorations or fullveneers are made

• Easy to adapt to the tooth cavity andcontour to shape.

Both hybrid and microfilled compositescan be selected for anterior restorations.Traditionally microfilled composites arepopular for anterior restorations. Due tothe small size of the filler particles (0.04-1.5 micrometer) these composites have thesmoothest surface. Due to the structure ofthe material the polish is readily main-tained. Nevertheless microfilled compos-ites also have some drawbacks. Due to thesmall size of the filler particles the fillercontent is rather low. As a result theresistance against fracture is low and thematerial is sensitive to fatigue.38 Class IVmicrofill composite restorations frequentlyexhibit chip fractures at the incisal edge(Fig. 1).39,40 Furthermore, the colour sta-bility of microfilled composites is not sogood. The high resin content of thesematerials is responsible for a continuouswater absorption that not only affects thephysical properties but also the colour stability.41-42 In the case of a restorationthat is subjected to heavy loads, a combi-nation of a microfill with a backing of astronger composite should be consideredif aesthetic demands are critical.

Whether hybrid composites are suitablefor anterior restorations largely dependson the size of the filler particles. The smallerthe average filler particle size is, the betterthe polish that may be obtained. When theaverage filler particle size is below 1micrometer, the surface lustre (polish) thatmay be obtained is considered to beacceptable and these are the so-called submicron hybrid composites.

Especially for anterior teeth, the surfacewill not become smoother due to wear.Thus, appropriate finishing techniques areimportant. Wear will make the surfacerougher in time and periodically polishingmay be required. Advantages of the hybridcomposites are the improved fractureresistance and good colour stability as theresin content is low compared with amicrofill (Figs 2a, 2b, 2c, 2d).43

Restorations in posterior teethMost restorations in the occlusal surfaces ofposterior teeth will be loaded directly andindirectly by occlusion and/or articulation.The resulting forces can be much higher

Fig. 1 Chip fracture of a large class IV restoration

Fig. 2a Patient with an oblique incisal line and apalatally inclined upper right canine

Fig. 2b The canine was built up in a buccaldirection and tooth 12 was lengthened with ahybrid anterior composite resin (ClearfilPhotoBright, Kuraray)

Fig. 2c Occlusal view after restoration

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than in anterior teeth. In general, restora-tions in molars are more stressed than inpremolars. The critical requirements a resincomposite for posterior restorations mustmeet are high fracture strength and wearresistance coupled with good radiopacitywhile the aesthetic properties are lessimportant than in the anterior region. Thevisibility of restorations in occlusal surfacesis usually limited and in most cases a toothcoloured restoration will meet the aestheticneeds of the patient even when the toothcolour is not optimally reproduced. A slightshade mismatch between the restorativematerial and tooth can even be an advan-tage as margin finishing and recall inspec-tion are simplified. A posterior compositeavailable in a limited number of shades willsatisfy most dentists and patients.

The ideal posterior composite shouldmeet the following demands:• Should be strong enough to prevent bulk

fracture as this will require repair orreplacement of the restoration. Thestrength of a resin composite will mainlydepend on the filler content assuming astable filler/matrix coupling. Compositeswith a filler content in excess of 65% byvolume have high fracture resistance.43 Ahigh filler content will be accompanied bya relatively large average filler particlesize as the smaller the filler particles arethe more resin is needed to wet the parti-cle surfaces. In an in vitro study evaluat-ing the abrasion and attrition wear of avariety of composite materials the authorsstated that the trend towards compositeswith smaller filler particles will result inmaterials with reduced mechanical prop-erties.44 Such materials will be prone toattrition and fracture. This statement issubstantiated by clinical studies. An invivo evaluation of indirect inlays andonlays made of a microfill compositeshowed that failure due to fatigue becameevident after two to three years.45 Aneight year evaluation of class II restora-tions (Fig. 3) showed a significantly high-er failure rate for a microfilled composite(Heliomolar) and a submicron hybridcomposite (Herculite) than a heavily filledhybrid composite (P30).46 In addition to

the filler content, the modulus of elasticitycan be used as an indicator for the frac-ture resistance of a resin composite. Themodulus of elasticity reflects the ability toresist deformation and correlates wellwith filler load.47 For a composite likeSolitaire using a porous filler, high valuesare reported for the filler content — 90%by volume.48 Then the modulus of elastic-ity can be used as an indication for thereal filler content as an increase in fillercontent is accompanied by an increase inthe modulus of elasticity. The modulus ofelasticity of Solitaire I is lower than that ofdentine and clinical and laboratory stud-ies report a low fracture resistance for thismaterial.49 Restorations in posterior teethare repeatedly loaded and the resultingdeformation may lead to fatigue. Thoughit is often stated that composites shouldhave a modulus of elasticity comparablewith dentine (15-18 GPa) this can be ques-tioned. Natural teeth are also composed ofenamel that has a modulus of elasticity ofabout 80 GPa. Compared with enamelevery resin composite resin can be consid-ered as an elastic material. Heavily filledhybrid composites can have a modulus ofelasticity of up to 25 GPa. The fractureresistance of such composites is the high-est of all resin composites (Fig. 4).43

• Must not be sensitive to long term mar-ginal breakdown. Many dentists considermarginal breakdown as a minor problem.However, according to at least one studythere is a relationship between the quali-

ty of the marginal adaptation of posteri-or composite restorations and the risk offuture failure.50 The failure rates forrestorations with marginal deteriorationwere generally higher than either theoverall failure rates or the failure rates ofrestorations with sound margins.Restorations with marginal deteriorationwere between two to five times morelikely to have failed five years afterplacement than restorations with soundmargins. The incorporation of largerfiller particles is advantageous for pre-venting marginal breakdown. When themargins of composite restorations aresubjected to attrition wear, microfills(Heliomolar and Silux) and minifills(Z100 and Herculite) showed significant-ly more marginal breakdown than twomidifills (Fulfil and Clearfil Posterior).51

Marginal breakdown showed an excel-lent inverse correlation with fracturetoughness for these composites. Themidifills have an average particle size inexcess of 1µm. Despite of the fact thatthey are hybrid composites the twominifills with an average filler particlesize less than 1µm (in particular Z100)demonstrated large chip fractures paral-lel to the margins (Fig. 5).

Another possible explanation for thepoor marginal behaviour of Z100 found inone study51 is its sensitivity to hydrolytic

degradation.52,53 Other workers have stud-ied the effect of chemical media on surfacehardness of four composite restoratives.53

Z100 appeared to be the most susceptibleto softening after water storage. Z100 usessynthetic zirconia/silica fillers, which likeother silica fillers have irregularly distrib-uted Si-O-Si bonds. Swelling from watersorption by the resin matrix could inducestress around the stiff filler inclusions as aresult of matrix expansion. The high energylevel resulting from strained Si-O-Sibonds, makes the fillers more susceptibleto stress corrosion attack causing completeor partial debonding of fillers whichdecreases hardness. These in vitro findingsare supported by clinical studies. A three-year clinical evaluation of Z-100 in poste-

Fig. 2d The same restorations after 14 years. Therestorations demonstrate less darkening than thenatural dentition

Fig. 3 Fracture and marginal breakdown of a two-year-old class II restoration of a low E-moduluscomposite resin containing a polyglass filler(Quadrant Posterior Dense; Cavex)

Fig. 4 13-year-old MOD restorations in thepremolars made with an ultrafine compact-filledcomposite resin (P30, 3M). Despite bulkdiscolouration there is little evidence of wear andmarginal breakdown

Fig. 5 Bulk fracture in a six-years-old large MODrestoration in tooth 24 restored with the ultrafinecompact-filled composite resin (Z100, 3M)

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rior restorations demonstrated marginalbreakdown to be present in half of therestorations.54 It is interesting to note thatits successor Z250, while sharing the samefiller type, but featuring a lower elasticmodulus and a less hydrophilic resinmatrix system has been reported as show-ing a failure rate of only 4% at four yearrecall in one clinical study of molar toothrestorations.55 It will be interesting to seewhat longer term investigations reveal. Intwo clinical studies heavily filled hybridcomposites (P50 and Clearfil Ray Posteri-or) showed better marginal adaptationafter two years in service than a submi-cron hybrid composite (Herculite).56,57 Athree year clinical and indirect evaluationof three composites in class I and IIrestorations showed significantly moremarginal breakdown for the microfillHeliomolar and the small particle hybridHerculite than for the heavily filled parti-cle P30 APC.58,59

• Should be wear resistant and not be tooabrasive (‘wear kind’) to the antagonisticteeth. Some of the earliest posterior com-posites showed average occlusal wear of100 to 150 microns per year.59,60 Somecurrent materials now exhibit at least 10fold lower mean occlusal wear rates peryear in contact-free occlusal areas (three-body wear) and appear to approach ormatch the wear resistance of dental amal-gam at five year recall. However, wearrates increase three to five fold in occlusalcontact (centric stops; two-body wear)areas and may be much higher still inbruxing patients.61,62 While loss of proxi-mal contacts was identified as the majorcause for the high failure rate of Occlusinrestorations at 10 year recall62 no suchfailure pattern was noticed in a 10 yearstudy of Visio-Molar radiopaque restora-tions.63 These authors reasonably con-cluded that differences in materialsand/or restoration cavity design mayhave accounted for the large differenceseen in the failure rates/patterns. Wear ofresin composites may result from abra-sion and attrition. The wear resistance willincrease with the filler content and whenthe filler is bonded to the resin phase bysilanisation.64 Wear is not only affectedby the makeup of the restorative materialbut also by its union to tooth tissues. Theavailable evidence suggests that wear isreduced when the restoration is bonded tothe cavity walls.65 Abrasive wear for dif-ferent types of composite is not statistical-ly different while attrition wear is higherfor microfills and submicron hybrid com-posites than for heavily filled hybrids(Figs 6a, 6b).44 Enamel wear will be lesswhen the filler particles are silanised.64

However, the opposing enamel will wearmore against quartz and zirconium con-

taining composites than against micro-filled composites.44 Another in vitro studydemonstrated significantly more wear onthe enamel side when the opposing mate-rial was a quartz-containing conventionalhybrid than with submicron hybrid com-posites.66 A 10-year clinical study on classII restorations demonstrated more wearfor a submicron hybrid composite thanfor a heavily filled hybrid composites.36

Indirectly assessed wear of the heavilyfilled hybrid composite Clearfil PhotoPos-terior appeared to be very low after threeyears of clinical service.67 The same mate-rial also had a high survival rate in a 10-year clincal evaluation.37 In a study eval-uating direct in- and onlays of asubmicron hybrid composite the failurerate was higher in molars than in premo-lars but wear was not considered to be aproblem.68 Unacceptable wear was onlyrecorded in patients who were bruxers.When extensive restorations are plannedattention should also be paid to the possi-bility of abrading antagonistic teeth.

The lower the polymerisation shrink-age the better it is as the shrinkageresults in stress that may affect the bond.

• Must have good radiopacity to enable thediagnosis of dental caries on radiographs.

Handling characteristicsResin composites are available in variousconsistencies and packages. Every dentistshould select a material which s/he is com-fortable with handling. In the last fewyears there is a tendency to bring materialson the market with an increased viscosity.Some materials are very stiff in consistency

and are called packable composites orceromers. In non-scientific articles basedon information from the manufacturers,packables are seen as materials withimproved handling and as the ideal alter-native for dental amalgam in posteriorteeth. The idea is given that these materialsare not much different in handling fromdental amalgam and that packing thecomposite results in good adaptation and atight approximal contact.69 Whether allpackables are suitable alternatives for dental amalgam is questionable. It hasbeen suggested that increased viscosityhas been achieved by adding additionalincrements of filler or by using highmolecular weight resins.70

Packable dental composites do not havea significantly higher filler loading thannon-packable composites. Rather, thehigher viscosity and handling characteris-tics that are unique to this class of resincomposites result principally from alter-ations of filler shape, size, or distribution.71

Large differences in mechanical propertiessuch as flexural strength, flexural modulus,fracture toughness and wear resistanceappear to exist between various packablecomposites.72 Other in vitro studies haveconcluded that packable composites appearto offer inferior or at best only equivalentproperties compared to a conventionalhybrid.73-75 Finally, it has been concludedthat packable composites are unlikely tooffer improved clinical performance overwell-placed non-packable composites.75

Furthermore, they question the ability ofclinicians to readily achieve tight inter-proximal contacts using packable compos-ites. The quality of the approximal contactis determined by the matrix system and notby the consistency of the resin composite.76

For some packables the manufacturerclaims that the material is suitable forapplication and curing in bulk. In vitrostudies have demonstrated that this is notthe case and the requirement for effectivepolymerisation does not differ from conventional composites.75,77 Most light-curing composites taken from a syringecontain some small porosities. For mostcomposites these porosities become lessafter injecting.78-80

When using highly viscous compositesporosities will increase due to a poor adap-tation of such materials to the tooth sur-face and previously applied layers of com-posite.81 In class I composite restorationssignificantly more voids and an imperfectwall adaptation were found for stiff com-posites and for composites applied bysmearing and condensing instead of by aninjection technique. The study was repeatedwith a group of six operators filling asmall and a large class I cavity with a realpackable or a medium viscosity composite

Fig. 6a A large MOD preparation in tooth 36 wasrestored with an ultrafine midway-filledcomposite resin (Prodigy, Kerr)

Fig. 6b The 4-year-old restoration demonstratesgeneralised wear, discolouration and marginalbreakdown

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that was injected.82 Restorations werefilled in two increments. All operatorsappeared to have more problems with han-dling the packable composite resin.Restorations made with the packable com-posite showed significantly more porosi-ties and voids along the cavity wall andbetween the increments. Restoring smallcavities without porosities appeared to bemore difficult than restoring large cavities.Such porosities and voids can be sites formicroleakage or may weaken the restora-tion. In an in vitro study simulating clini-cal handling samples were made with astiff composite (Herculite) or a low viscouscomposite (P50).83 Samples were made inbulk or in two layers. The layering tech-nique resulted in a significantly lowerflexural strength compared with the bulksamples. However, the decrease in flexuralstrength was significantly more for Her-culite than for P50. Adaptation betweenlayers appeared to be better for P50 thanfor Herculite where lines and voids wereobserved between increments. It is likelythat such defects will reduce the resistanceof a restoration against fatigue afterrepeated loading. The adaptation to thecavity wall of the highly viscous compos-ites is a point of concern seeing the numer-ous studies in which flowables are used toimprove the adaptation and to reducemicroleakage. Whether the flowable willhave a beneficial effect depends on thetype of composite with which it is com-bined. When the resin composite is a verystiff packable a positive effect can befound on microleakage. Nevertheless, themicroleakage is still more than for a con-ventional hybrid resin composite.84 Some-times the use of a flowable composite isadvised to compensate for the poor per-formance of an adhesive system that pro-duces a very thin layer that does not cureby itself due to oxygen inhibition.85

Application of a flowable is always anadditional step in the restorative procedure,which can be avoided when a resin com-posite of lower viscosity and a good adhe-sive system is selected. Despite the generalbelief that flowable composite resins areeasy to apply, several studies prove theopposite and report porosities and voids inthe flowable composite.84,86-87

What the effect of a layer of flowable willhave on margins under load is still unknown(Fig. 7). Loaded margins are prone to tensilefatigue and the physical properties of theflowables with their low filler content maybe insufficient in the long term.

For anterior restorations a highly viscouscomposite will be more difficult to apply onthe tooth surface. When building up therestoration in various shades there is anincreased risk of porosities between the por-tions of composite. Marginal discolouration

and surface porosity will have a negativeeffect on the aesthetics.

The consistency of a composite alsodefines the mode of delivery. Compositescan be available in a syringe or a pre-dosed capsule or compule. Injecting thecomposite into the preparation will resultin a reduction of porosities and voids. Aprerequisite is the ability to place the endof the compule close to the bottom of thecavity. Stiff composites require a specialdesign of the tip to be able to squeeze thematerial out. Therefore, the end of the tipmust have a large diameter and this willprevent good access to small-sized cavi-ties. Inserting the composite with a handinstrument will introduce even moreimperfections in the restoration.81

DISCUSSIONDuring the last 10 years many new com-posites have been introduced. Most ofthese materials are marketed as universalcomposites. The first time such materialswere introduced the argument that it waseasy to work with just one material wasvalid. In those days composites were hardlyused in stress-bearing restorations in pos-terior teeth, and if so, the size of therestorations was most of the time small tomoderate. With the low frequency of pos-terior restorations there was a risk thatposterior composites would have passedtheir shelf life before being used. Today,things have changed as composites are fre-quently applied in posterior teeth and arenot limited to small restorations. Due totheir filler content, universal compositeswill always be a compromise either to theaesthetics or strength. For the dentist whoalso wants to make long-lasting largecomposite restorations in posterior teeththey can be advised to choose a specialposterior composite. Such a materialshould have a high filler content (65 to 70vol%) and must have an average filler par-ticle size larger than 1 micrometer. Prefer-ably, such a material should be available ina well-designed compule to allow goodaccess to small cavities. As compules are

designed for single use only, compulescontaining various volumes of compositesshould be available to avoid wasting muchmaterial when small cavities are restored.As an alternative the dentist can decide tofill his/her own compules.

As the number of composite resinsmeeting these requirements has decreasedover the last years, there is an importanttask for the manufacturers. Only with special resin composites for restorations inanterior and posterior teeth can the indica-tions as mentioned a decade ago be opti-mally covered.1

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Fig. 7 A DO cavity in tooth 24 where flowablecomposite lining has pooled at the cervical cavitymargin

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single_composite can serve all purposes

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