Comparative analysis of the amount of dental structure loss during cavity preparations for direct and indirect restorations and its relation to tooth fracture strenght

Objectives: This study evaluated, in vitro, the amount of dental structure loss after cavity preparations for direct and indirect restorations and its relationship with the fracture strengthof the tooth. Methods: Six groups of 10 specimes were obtained by preparing MOD cavities for direct resin composite (groups I, II and III) and indirect inlay restorations (groups IV, V and VI) in 60 first sound-human premolars with standardized dimensions: pulpal floor 2mm in depth, gingival wall 1.5mm in width and axial wall 2mm in heigth. The bucco-lingual width of the occlusal box were performed in 1/4, 1/3 and 1/2 of the intercuspid distance; the proximal boxes were 1/4, 1/3 and 1/2 of the tooth bucco-lingual dimension. The difference between the teeth weighted before and after preparation (digital scale - 0,001g precision) was calculated in order to assess the amount of dental tissue lost. Fracture strengths were recorded in a Universal Testing Machine (Instron). A compressive load was applied with a 6mm diameter stainless steel bar at a crosshead speed of 0.5mm/min. The data were analyzed by two-way ANOVA and TUKEY test. Results: Cavity preparations for inlay with 1/4 width removed 41,2% more dental structure when compared to those for direct resin composite restorations with the same width. Cavity preparations for inlay with 1/3 width removed 53,7% more dental structure than 1/3 width for resin composite restorations; cavity preparations for inlay with 1/2 width removed 39,7% more dental structure than 1/2 width for resin composite. The values of fracture strenght were: GI: 187,65kgf; GII: 143,62kgf; GIII: 74,10kgf; GIV: 164,22kgf; GV: 101,92kgf; GVI; 50,35kgf. Statistical differences were observed between groups I and IV, II and V, III and VI. Conclusions: Inlay cavity preparations caused the greatest amount of dental tissue loss in all widths and the lowest fracture strength for all groups tested.