Influence of Different Composite Materials on Gap Formation

Objectives: A numerical material model for finite element analysis to describe the change of volume, of mechanical characteristics and of flow during polymerisation of dental composite fillings, together with new measurement techniques, had been developed by Fraunhofer Institute (Freiburg, D). After import of this model in a FE-software, it was supposed to be possible to determine certain conditions to avoid the development of marginal gaps. The aim of the present study was the verification of the material model by investigating the influence of using different composite materials and different filling procedures on gap formation in a clinically oriented experiment. Methods: Bovine teeth were randomly distributed into ten groups (n=8). In the first part of the study, class V cavities were prepared into enamel and dentin, and filled with a nano-composite, with and without using a self-etching bonding agent (BA). In the second part, all class V cavities were prepared into dentin, and then were filled with three different composite resins, with and without BA. The marginal adaptation of the specimens (length, width and surface area) was evaluated after thermocycling under 500 x magnification (light microscope). Results: Artificial aging showed no significant influence on marginal quality (p>0.0.5). As clinically expected, gap formation was significantly smaller at the enamel margins compared to the dentin margins (p=0.005), and with BA than without BA (p=0.029). The range of the three composites concerning marginal gap formation was: 78 wt% nano-fillers and pre-polymerized matrix < 78w% nano-fillers < 61wt% fine-particle-fillers (p=0.04). These data confirm the results of the FE-calculation concerning expected influences on gap formation. Conclusions: According to the present results the transfer of the newly developed material model to the clinically oriented research is possible, and should be the next step. Study supported by DFG, project No HA 2432/1-1, 2432/1-3.