The Effect of Mandibular Flexure on Stress Distribution in the All-on-4 Treated Edentulous Mandible: A Comparative Finite-Element Study Based on Mechanostat Theory.

The All-on-4 treatment concept is a felicitous approach for treatment of edentulous mandible. Mandibular flexure plays a decisive role in several restorative failures-for instance, screw loosening, particularly in widely separated implant supports such as those utilized in All-on-4 treatment methods. We investigated the effect of mandibular flexure on stress distribution and likelihood of bone loss or growth in the implanted mandible using two frequently used All-on-4 methods of implantation: parallel and tilted. Three-dimensional finite-element models of mandible and dental implants together with their compartments were developed. Assuming sagittal symmetry for the mandible, only half of the full geometry was considered. In the parallel model, two dental implants were inserted into the mandible perpendicular to the occlusal plane. In the tilted model, the posterior implant was rotated 30° around the buccal-lingual axis. In both models, maximum stress was detected at the neck region of the posterior implant. This maximum stress was greater in the tilted model than in the parallel model. However, since the corresponding strain was considerably lower in the parallel model, according to mechanostat theory several elements in the parallel model were at risk of bone loss. In contrast, the greater strain in the tilted model decreased the likelihood of bone loss. These findings suggest that use of tilted implants in the treatment of edentulous mandible would reduce the probability of bone loss in vulnerable parts of the osseous tissue surrounding dental implants.