Influence of restorative material and proximal cavity design on the fracture resistance of MOD inlay restoration

Objective This study aimed to evaluate the effects of the restorative material and cavity design on the facture resistance of inlay restorations under a compressive load using acoustic emission (AE) measurement. Materials and methods Two restorative materials, a composite resin (MZ100, 3M ESPE) and a ceramic (IPS Empress CAD, Ivoclar Vivadent), and two cavity designs, non-proximal box and proximal box, were studied. Thirty-two extracted human third molars were selected and divided into 4 groups. The restorative materials and cavity designs used for the four groups were: (1) composite and non-proximal box; (2) ceramic and non-proximal box; (3) composite and proximal box; (4) ceramic and proximal box. The restored molars were loaded in a MTS machine via a loading head of diameter 10 mm. The rate of loading was 0.1 mm/min. During loading, an AE system was used to monitor the debonding and fracture of the specimens. The load corresponding to the first AE event, the final maximum load sustained, as well as the total number of AE events recorded were used to evaluate the fracture resistance of the restored teeth. Results For the initial fracture load, Group 2 (236.15 N) < Group 1 (428.14 N) < Group 4 (441.24 N) < Group 3 (540.06 N). The same trend was found for the final load, i.e., Group 2 (1594.68 N) < Group 1 (2003.82 N) < Group 4 (2004.89 N) < Group 3 (2057.53 N). For the total number of AE events, Group 4 (2135) > Group 2 (1685) > Group 3 (239) > Group 1 (221). The differences from pairwise comparisons in the initial fracture load and final load were mostly insignificant statistically (p > 0.05), the only exception being that between Groups 2 and 3 in the initial fracture load (p = 0.039). For the total number of AE events, statistically significant differences (p < 0.05) were found between all group pairs that involved different materials, with the composite groups giving much fewer AE events than the ceramic groups. Conversely, no statistically significant difference in the AE results was found between groups with the same material, irrespective of the cavity design. Significance For teeth restored with MOD inlays, the use of composite resin as the restorative material may provide higher fracture resistance than using ceramic. Using a proximal box design for the cavity may further improve the fracture resistance of the inlay restoration, although the improvement was not statistically significant under axial compression.