Biomechanical optimisation of the length ratio of the two endosseous portions in distraction implants: a three-dimensional finite element analysis

Insufficient alveolar height is one of the most common problems in oral implantation, and it may preclude placement of an implant or compromise the final aesthetic outcome of the restoration. To solve this problem, distraction implants (DIs) have been introduced because they can fulfill the functions of bony augmentation and implantation simultaneously and facilitate the operation, minimise the trauma, and shorten the duration of treatment. However, the high risk of complications such as device fracture from uneven distribution of stress or transport bone resorption from insufficient blood supply, has impeded their clinical use. As the cortical transport portion of the DI is more important for bearing occlusal force than the apical support portion, and the length of the transport portion is normally the height of the transport bone segment, lengthening the transport portion may help to obtain a rational distribution of stress and increase the blood supply to the transport bone. For those cases in which alveolar height is limited, the dimension of the DI must be minimised to be applicable, so it is important to find an optimised balance between the lengths of the transport and support portions for a better performance. We have made a finite element analysis to optimise the length ratio of transport:support portions. The effects of the length ratios on the stress distribution in the jawbones were evaluated. A ratio of 8:2 showed the minimum stress and most resistance to displacement. These results provide a valuable reference for further improvement of designs of DI and help to promote its clinical application.