Development of a topologically optimized patient-specific mandibular reconstruction implant for a Brown class II defect

Abstract

Segmental defects affecting the continuity of the mandible have a profound impact on a patient's quality of life. Adequate reconstruction of such continuity defects is essential to restore aesthetics and function. While reconstruction using an autologous bone transplant supported by a stock reconstruction plate is the gold standard treatment, it has various drawbacks that can be attested to the plates’ off-the-shelf nature.

To mitigate these drawbacks, this study develops a patient-specific implant for the reconstruction of Brown class II defects with a high ramal osteotomy. The implant is intended to be additively manufactured in Ti6Al4V grade 23 ELI and features porous scaffold zones at the symphyseal and condylar sides which can induce bone ingrowth.

Finite element (FE) analyses were used to assess the implants’ performance in terms of failure, stability and stress shielding by simulating four clenching tasks. In addition, the implant was topologically optimized and re-evaluated.

The results showed that the implant experienced stress below its yield strength and fatigue limit. Relative micromotions between the implant and the bone indicated adequate stability to allow bone ingrowth to occur. Strains in the bone indicated limited stress shielding should occur between screw connections and around the osteotomy planes.

Finally, topological optimization reduced implant volume by 49% compared to the initial design, while FE analyses showed similar performance to the original design. The resulting implant is a promising first prototype that is numerically evaluated and can be optimized further in terms of fixation, surgical approach and dental restoration by in situ testing.