Biomechanical Response of Class II MOD Restorations Con-Sidering Polymerization Shrinkage and Transient Occlusal Loading: A Finite Element Study

Class II mesio-occluso-distal (MOD) restorations are routinely used to rehabilitate molars with extensive structural loss, where cavitary bases are commonly applied to protect dentine and modulate stress transfer. Nevertheless, polymer-based restorative materials undergo polymerisation shrinkage during curing, generating residual stresses that subsequently superimpose on functional masticatory loads—a coupled effect that is rarely addressed explicitly in finite element analyses of Class II MOD restorations and may increase stress concentrations and mechanical failure risk. This study investigates the biomechanical influence of cavitary base type and the absence of a cavitary base in Class II MOD restorations through three-dimensional finite element analysis. A patient-based three-dimensional human molar model was reconstructed from cone-beam computed tomography (CBCT) data. A transient occlusal loading cycle from 0 to 0.25 s was simulated, reaching a peak load of 600 N. Restorations incorporating cavitary bases were modelled using ceramic and glass–ceramic restorative materials combined with different base materials, while restorations without bases employed composite materials with varying silica content. Mechanical behaviour was evaluated using von Mises stress and maximum principal stress distributions. The results indicate that restorations without cavitary bases exhibit a more uniform stress distribution and reduced stress concentrations compared with restorations incorporating cavitary bases under transient occlusal loading. These findings suggest that, when polymerisation shrinkage and functional loading are considered simultaneously, the absence of a cavitary base may offer biomechanical advantages in stress transfer and structural integrity for Class II MOD restorations.