Objective: The purpose of this study was to investigate the influence of cavity preparation of MOD inlays on interfacial stresses between the restoration and tooth under static loading by finite element analysis.
Materials and Methods: 3D finite element analyses were employed to calculate the interfacial stresses with the use of contact elements. Four types of MOD cavity restorations in mandibular first molars were modeled (1) occlusal box extended to mesial and distal margins, (2) occlusal box extended to the proximal sides with 30 degrees widening, (3) proximal box extended gingivally (4) proximal box extended buccal-lingually. In each group, two kinds of restorative materials, ceramic and composite, were applied. The Young's modulus of the ceramic and composite were assumed to be 65GPa and 19GPa, respectively. A 400N compressive force was applied at an angle of 45 degrees from the vertical with a 10mm diameter steel ball. The contact stresses along the external margin of the restorations were compared.
Results: The configuration of Group (3) showed the lowest interfacial tensile stress regardless of the restorative material. With the same configuration, the interfacial tensile stress of the ceramic model was much higher than the composite model, although the stress distributions within the restorations were similar. The maximum interfacial tensile stresses of the 4 groups were listed in Table1.
Conclusions: The results indicate that a proper preparation of MOD inlays can reduce the interfacial stress, and hence improve the failure resistance of the restoration. In general, an inlay configuration with the proximal box extended gingivally, without proximal side widening and with a more compliant restoration will give lower interfacial stress between the tooth and restoration.
Table 1. The maximum tensile stress of each model (MPa)
| Group (1) | Group (2) | Group (3) | Group (4) |
Composite resin | 32.01 | 27.77 | 19.98 | 29.53 |
Ceramic | 58.75 | 56.87 | 32.82 | 46.58 |