Quality of dental restorations. FDI Commission Pro... - ResearchGate

130marginal degradation compared tothe other tooth groups. Osborneand Gale 130 reported that themarginal fracture of high-copperamalgam restorations could not berelated to the intraoral locationafter fourteen years service. Interactionsbetween tooth position andwidth indicated that lowerpremolars with conservative restorationsexhibited the least fractureat the margins, and upperpremolars with a wide preparationexhibited the most. Osborne andGale 131 reported that the marginaldegradation of 429 Class II amalgamsafter two years was less inlower premolars than in the otherposterior teeth.Goldberg et al. 132 studied 475restorations over 1.5 years. UsingANOVA analyses, these investigatorscompared marginal fracturescores among different subgroups,categorised by intraoral location andfound more fractures in molars thanin premolars.Oral environmentDerand 133 assessed restorations offour amalgam alloys in 163 teethafter 2.5 years. The patients weredivided into three levels of bitingforce. It was found that marginalfractures increased with increasingbite force for the conventionalalloys, but that the relationship wasnot significant for the three nongamma-2alloys.Restoration failure andclinical factorsTechnical excellence of restorationsdeteriorates in clinical service andmay or may not be linked to restorationfailure. Certain investigators,including those of Harris 134 andOwens 135 , reflect a common opinionthat materials themselves areoften the least of the problems andthat most restoration failures canbe attributed to poor attention todetail in cavity preparation andmaterial handling. However, thisview can at best be regarded asexpert opinion, and is linked to thefailure criteria. In a survey of 571International Dental Journal (2001) Vol. 51/No.3dentists, perceived causes of restorationfailure were ranked bypatient-related factors (45 per cent),dentist-related (35 per cent) andmaterial choices (20 per cent) 136 . Anamusing secondary finding was thatthese estimates were for restorationsin general, while the percentageswere 48, 26 and 26 per centrespectively when dentists addressedthe causes of failure of the restorationsthey had made themselves.The following sections presentthe effects of the numerousdependent and independent variablesinfluencing the quality ofrestorations, notably the operator;the operative techniques and instrumentused; the material; the location;type; size; initial and short-termtechnical excellence of the restorationand patient factors.General performanceMaterial factorsDifferences in composition andphysical propertiesSubtle differences in physical propertieswithin specific materialgroups may be considered to havea small effect on clinical performancein general practice settings. Aparticular exception is perhaps compositeresin cements for indirectrestorations, where the microfilledcements seem to be superior tocements with larger fillers 14,136 ,although conflicting results havebeen reported 138 . Two longitudinalmulticentre studies involving 24dentists in seven clinics revealed onlyminor differences amongst sixcomposite resins after three andfive years 139,140 . Dunne and Millar 141reported the evaluation of 315porcelain labial veneers in 96patients, fitted up to five yearspreviously in two teaching hospitals.Increased problems and failurerates were associated with veneerswhere inappropriate luting agentswere employed, that is, lutingcements not dedicated to veneercementation. In studying over 1,544amalgam restorations, 1,213 restorationsremained after 15 fifteenyears. The conclusions from thisstudy was that the type of amalgamalloy used had no associationwith restoration survival 108,109 . VanNoort and Davis 142 observed in afive-year prospective study thesurvival of 2,399 Class III and 1,093Class V chemically-activated anteriorcomposite resin restorations in26 general dental practices, that thedifferences in clinical performancesbetween six materials was small. Ina cross-sectional study, 75 privatepractitioners evaluated 1,147 twoto-fouryears old anterior restorationsof 25 different materialsaccording to the CDA system. Withthe exception of one compositeresin, no obvious differences in thequality of dental restorations wereobserved 33 .Operator factorsAmong various clinical factorsaffecting restoration performance,an operator association is frequentlydetected in multicentre and crosssectionalstudies (Table 1). Controlledclinical studies are usually designedto avoid such operator effects, anddifferent research groups haveemployed various strategies (seesection on statistical issues) tocontrol these effects.Most of the relevant papersoffer no explanation of theobserved variation in operatoreffect, although some authors stressthe necessity of specific training fordental personnel using new materials.It is also possible that anindirect patient association may haveinfluenced an apparent operatorassociation. Whether the experienceof the operator can be associatedwith technical excellence is uncertain.For example, Hawthorne andSmales 150 reported that the survivalfor composite resin restorationswas best for the most recent graduates.By contrast, Shaini et al. 151commented that the poorestresults were seen in relation to theinexperienced operators. Of course,appropriate clinical training andexperience are necessary prerequisitesfor favourable clinical outcomes.