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Effects of Cantilever Length and Implant Inclination on the Stress Distribution of Mandibular Prosthetic Restorations Constructed from Monolithic Zirconia Ceramic.

PURPOSE
This study aimed to biomechanically evaluate the effects of cantilever length and implant inclination on the stress distribution of mandibular prosthetic restorations constructed from monolithic zirconia ceramic.


MATERIALS AND METHODS
Mandibular full-arch prostheses supported by four implants constructed from monolithic zirconia were designed using either a 5-mm or 9-mm cantilever length and a 15-degree or 30-degree distal tilt for the posterior implants. A simulated static load of 600 N was applied from the right side at a 45-degree angle. Von Mises and principal stress values in superstructures were analyzed using the Mesh VR Studio program.


RESULTS
When the effects of cantilever length were examined, in the models with the 15-degree implant tilt, stress values for posterior implants, porcelain, and cortical bone were lower when the cantilever length was shorter (5 mm). In the models with the 30-degree implant tilt, stress values in all implants (except for the anterior implant on the right) and in the porcelain superstructure were lower when the cantilever length was shorter; however, stress values for cortical and spongious bone were lower with the longer (9 mm) cantilever. When the effects of implant inclination were examined, in the models with a 5-mm cantilever, stress values for posterior implants and cortical bone were lower when the implant tilt was more severe (30 degrees). In the models with a 9-mm cantilever length, stress values for the right anterior implant, posterior implants, and cortical bone were lower when the implant tilt was less severe (15 degrees).


CONCLUSION
Cantilever length and posterior implant inclination affected the distribution of force. Increasing the cantilever length led to a reduction in stress values in distally tilted posterior implants. Moreover, increasing the distal inclination led to a reduction in stress values in both the distally tilted posterior implants and cortical bone tissue in the model with a short cantilever. The monolithic zirconia full-arch porcelain superstructure was not affected by implant angulation, but was affected by cantilever length, with lower stress values observed with a longer cantilever.