Efeito da contração de polimerização em restaurações diretas em resinas compostas em dentes posteriores

Abstract

The composite resins have been widely used over years in posterior restorations. However, the composite resins have an inherent characteristic called polymerization shrinkage which may be associated with undesirable clinical manifestations such as post-operative sensitivity, microleakage and recurrent caries. The aim of this study was to investigate the influence of some factors such as occlusal loading, restorative technique, mechanical properties of materials, use of liner and environment conditions on the biomechanical behavior of direct composite resin restorations in posterior teeth through laboratory and computational studies. This study was divided into five specific objectives; objective 1: To investigate the effect of occlusal loading and mechanical properties of composites on shrinkage stress in premolars; objective 2: To investigate the effect of environmental conditions, such as temperature and humidity, mechanical properties on biomechanical behavior of molars with class II MOD; objective 3: to investigate the effect of glass ionomer resin liner and filling technique on biomechanical behavior of class II MOD composite resin restoration, specifically analysing cuspal strain by strain gage test, termal and mechanical fatigue and fracture resistance; objective 4: to investigate the effect of the same parameters of objective 3 on mechanical properties of restorative materials, marginal adaptation and shrinkage stress distribution; objetivo 5: To generate an article with all conclusions about shrinkage and posterior restorations by the Brazilian clinical communication contributing with the social function of knowledge generation. The methods used on the all studies were cuspal strain by strain gage test, post-gel measurments by strain gage test, thermal and mechanical fatigue, fracture resistance, marginal adaptation and fracture mode under scanning electron microscopy, dynamic indentation test for calculation of Vickers Hardness and elastic modulus, indentation test for hardness Knoop calculation, finite element analysis 2D and 3D. After data analysis it can be concluded that materials with higher elastic modulus cause greater shrinkage stress; occlusal loading on the margin of restoration cause great stress concentration at interface; occlusal stable contact in the center of restoration cause low stress concentration; high temperature and humidity affect the post-gel shrinkage, elastic modulus, cuspal strain, bond strength and stress shrinkage in the teeth restored with direct composite resins; the simulation of oral environment should be performed in laboratory tests to evaluate the shrinkage and cuspal strain; the order of filling technique, represented by sequence of the oblique increments, had no influence the cuspal strain, fracture resistance, fracture mode, marginal adaptation and stress distribution in molars restored with composite resin; cuspal strain and shrinkage stress decreased significantly with the presence of resin modified glass ionomer resin liner in direct posterior composite resin restorations; the fracture resistance and fracture mode was not influenced by the presence of liner in molars restored with composite resin; gingival margin had higher gap formation than proximal margins in molar restored with direct composite resin restoration.