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

129recommended that non-gamma-2amalgams should be used.Cavity designStratis and Bryant 111 carried out atwo-year study of 111 Class I andII amalgam restorations placed byone operator, and reported that acombination of modification of theocclusal cavo-surface angle andfinishing of the restoration had aninfluence on the marginal fractureat two years.Kreulen et al. 112 reported a photographicevaluation of the marginsof 245 Class II amalgam restorationsplaced by three dentists. Theprinciple variable influencingmarginal adaptation was the dentist.In addition, improvement of themarginal adaptation by an occlusalbevel was discussed compared withnon-bevelled margins.Investigations published before1992 on the possible relationshipbetween marginal fracture andClass I and Class II cavity preparationsfor amalgam has beenreported in a previous paper, andwill not be discussed further 113 .Fukushima et al. 114 reported astudy on the early marginal breakdownof 432 posterior compositeresin restorations. It was determinedthat smaller cavities, greaterbulk of material at the margin(especially in functional cusp areas),and well-finished margins withoutoverfilling seem to reduce theoccurrence of marginal fracture.Material handling and proceduresSuccessful bonding is associatedwith several technique-relatedfactors. The use of adhesives istechnique sensitive because ofcomplex multi-step applicationtechniques 38,115 . Careful managementof the status of the collagenmeshwork is important to preventit from disintegration or collapseand thereby ensuring optimal resinpenetration 116 .A clinical technique, commonlyreferred to as ‘wet bonding’, hasbeen recommended especially foradhesive systems that utilise waterfree,acetone-containing primers.However, recent research hasrevealed that bonding systems thatutilise water-based primers appearto bond with equal effectiveness todry and wet dentine 117 . Adhesivesystems using acetone-based primersrevealed a higher techniquesensitivity 118 , whereas adhesivesystems containing water-basedprimers appear to be less techniquesensitive,as far as the remainingwetness of the acid-etched dentinesurface is concerned 119 .Clinically, the exact timing ofthe different stages of bonding asrecommended by the manufactureris often very difficult. For example,parts of the dentine may beetched for the same amount oftime as the enamel because theprecise differentiation between thetwo substrates is not always possible.Excessive etching may result indemineralisation depths that aregreater than monomers can effectivelypenetrate 115,119 , and causesevere collapse of the collagenmeshwork 119 . The depth of demineralisationis dependent on etchingtime and phosphoric acid concentration120 , while the thickness of themonomer penetration, or ‘hybrid’,layer is a function of conditioningtime 121 . However, the implicationsof these variables on long-termclinical outcomes remain uncertain.IsolationDesiccation of the demineraliseddentine causes collapse of thecollagen meshwork, which impedesthe proper infiltration of theprimer 121 . Therefore, a wet bondingtechnique is recommended 122,123 .However, there is a wide range ofinterpretations of ‘wet’ 124,125 , withno clear guidelines in manufacturers’directions for use. While thenegative consequences of excessiveair-drying are well documented foracetone-based systems 122,123 , theresults for water-based systems arevariable 125 .Contamination of the etchedenamel surface with saliva prior tothe placement of a resin-basedmaterial significantly reduces thebond strength to enamel. Studieson the influence of saliva contaminationon dentine bonding arevariable. Although the tolerance ofmodern adhesives to saliva contaminationhas improved, reductionsin bond strengths may be anticipatedafter saliva contamination. Itis therefore important to preventsaliva contamination after applicationof the primer 126 .The effect of using rubber damremains uncertain. In an experimentalstudy comparing shear bondstrength of 36 composite resinrestorations placed either withcotton rolls or under rubber dam,no significant differences werenoted between the two groups 127 .In another study using the sameprotocol, microleakage was assessed.This study concluded that the useof rubber dam isolation resulted inless microleakage at the enamelresininterface 128 .Patient factorsIntraoral locationAs for wear, bite force is probablya significant aetiological factorregarding the extent of materialdeterioration. As a result of relativelyhigh bite forces in the firstmolar region, it can be assumedthat more marginal fractures willoccur in this location.In a study of 88 composite resinrestorations placed by nine dentalstudents, it was observed after twoand three years that marginal integritywas significantly better inpremolars compared to that inmolars 100,101 .Berg and Derand 129 reporteddata on 51 out of originally 115porcelain inlays made with theCerec technique after five years in46 patients. No significant differencesin marginal ditching weredetected between molars andpremolars.Jokstad 29 did not find any strongrelationship between marginaldegradation and intraoral locationafter five years observation of ClassII amalgam restorations. Only thelower premolars showed lessFDI Commission, Jokstad et al.: Quality of dental restorations