Bone Stress Analysis of Various Angulations of Mesiodistal Implants with Splinted Crowns in the Posterior Mandible: A Three-Dimensional Finite Element Study

Purpose: Ideally, implants for dental prostheses should be placed parallel to each other. However, anatomic limitations sometimes make nonparallel implants necessary. The purpose of this study was to determine the bone stresses on implants tilted at various angles and to determine what arrangements might carry a higher risk of failure. Materials and Methods: Three-dimensional finite element models were constructed using the mean values measured for the Asian mandible in the first and second molar areas. Eight implants were divided into three tilting types: parallel implants (P1PP, P2MM, and P3DD), convergent implant apices (C1PD and C2MP), and divergent implant apices (D1DP, D2DM, and D3PM). A biting load of 200 N was applied vertically and obliquely on the occlusal central fossa of the splinted crowns. The main effects of each level of the three investigated factors (loading type, relationship of implant apices, and distal tilting of one or both implants) in terms of the stress values were computed for all models. Results: The loading type was the main factor affecting the stress in bone when comparing implant apices and distal tilting of the implant body. When loading was combined with distal tilting, the stress values were significantly increased, especially in models P3DD and C1PD. Conclusion: The loading type is the main factor affecting the stress distribution for different implantation arrangement. Moreover, placement of the implants with distal tilting should be avoided in the posterior mandible. Keywords: convergent implant apices, divergent implant apices, finite element analysis, implant axis, implant loading