[Effect of pit and groove retention form with different depths on stress distribution of mandibular first molar occlusal veneers: three-dimensional finite element and Weibull analysis].

Objective

To determine the effect of the occlusal veneer with pit and groove retention form (PGRF) design on the stress distribution and failure probability in the mandibular first molar.

Methods

A standard resin molar model of the mandibular first molar was selected to establish three-dimensional finite element models simulating two levels of occlusal wear (0.5 and 1.0 mm), each with 10 groups. Two different restoration designs (common occlusal veneer and PGRF occlusal veneer) were simulated; PGRF was set at four different pit and groove depths (0.25, 0.50, 0.75 and 1.00 mm), and two different computer-aided design and computer-aided manufacturing (CAD/CAM) materials (lithium disilicate glass ceramic with high elastic modulus and resin-matrix ceramic with low elastic modulus) were used. Apply a 241 N load at a 45° angle to the long axis of the tooth, directed at the lingual incline of the buccal cusp of the mandibular first molar. The maximum principal stress (σmax) and maximum displacement of the occlusal veneer restoration models were calculated. Weibull analysis was used to evaluate the failure probability of the models.

Results

The σmax values of the PGRF occlusal veneer were slightly higher than those of the common occlusal veneer, while those of the dental tissue were lower. With the increase in the PGRF depth, the maximum displacement peak value of the occlusal veneer and cement layer decreased significantly. Compared to a conventional occlusal veneer, preparing a 1 mm deep pit-and-fissure retention form on a 0.5 mm thick occlusal veneer reduces the maximum displacement peak by 44.00 μm for the veneer and 41.37 μm for the adhesive layer. For a 1.0 mm thick occlusal veneer, the same retention form reduces the maximum displacement peak by 43.82 μm for the veneer and 39.89 μm for the adhesive layer. The overall failure probability of the model tended to decrease.

Conclusions

This numerical study shows that the design of PGRF on the occlusal veneer may be a favorable restoration strategy that can significantly reduce the debonding tendency of occlusal veneer, and this can improve the clinical longevity of occlusal veneer prostheses.