Influence of different indirect composite materials and cavity preparation design on the fracture resistance of MOD inlay restoration

Objectives: Evaluate the fracture resistance of indirect composite materials on the three different MOD inlay cavity designs.
Methods: 80 mandibular third molar selected and divided into 4 groups. (1) intact teeth as control group, (2) non-proximal box, (3) 2mm proximal box, (4) 4mm proximal box. Each cavity design received two different indirect composite materials: Estenia (Kuraray) or Epricord (Kuraray) (n=8). The inlay restorations were adhesively cemented with dual cure resin cement (Panavia, Kuraray, Japan). After storing 24h distilled water, specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5mm/min. Statistical analysis was performed using the One Way analysis of variance and Tukey Post Hoc Test (p<0.05).
Results: The highest fracture strength values were obtained from non-proximal box cavity design (significantly, 3060.1±654.8); it was followed by 2mm proximal box (2033.7±356.4) and 4 mm proximal box (1564±635.1) for Estenia. There was no significant difference between three inlay cavity design for Epricord (2150.3±553.4; 2191.6±642.3; 2006.9±531.5 respectively, (p>0.05)). Estenia exhibited significantly higher fracture strength than Epricord only for the non-proximal cavity design (p<0.05). The fracture strength values of non-proximal box cavity design inlays restored with Estenia and 2mm proximal box cavity design inlays restored with Epricord were similar to those of the intact teeth (2805.2±640.7).
Conclusions: Using a non-proximal box design for the cavity may further improve the fracture resistance of the inlay restoration. The fracture strength of indirect composites can show variability according to the design of the cavity.