Effects of cortical bone thickness on an immediate-load implant

Objectives: This study used rapid prototyping (RP) and non-linear finite element (FE) models to investigate the effects of cortical bone thickness on the bone strains, and the interfacial conditions between the bone and implant interfaces (BII) on an immediate-load implant. Methods: From computer tomography images of a human mandible, RP models with 0, 1.7 and 3.4 mm cortical bone thicknesses were created by Zprinter 310. The self tapping brass implants and temporary hexed cylindrical abutments (3i Implant Innovations, FL, USA) were inserted into the RP models. Two loading conditions (130N of vertical and 45 degree of lateral forces) were applied to the implant, and then the strains on crestal region were measured by rosette strain gauges (KYOWA, Tokyo, Japan) and data acquisition system (NI, Texas, USA). In addition, all corresponding non-linear contact FE models were generated by ANSYS Workbench 10.0 to study the bone strains, and interfacial sliding and gap distances between the immediate-load implant and bone. Results: The bone strains among three models with non-, 1.7, and 3.4 mm cortical bone thicknesses were indiscriminate on the vertical loading mode. However, on the lateral load the model without cortex increased the strain and the sliding distance between BII obviously (more than 50%) as compared with the 1.7 mm cortical bone thickness of model. Raising the cortex thickness from 1.7 mm to 3.4 mm would decrease the bone strain and the sliding and gap distances by 17%-28% and 13%, respectively. Conclusions: Without the cortical bone, immediate implant loading would induce the extreme bone strain at crestal region, and the sliding and gap distances between BII. Thicker cortical bone shows a benefit to reduce the bone strain, sliding and gap distances especially on the lateral load. Acknowledgement: This research was supported by China Medical University and Metal Industries Research & Development Centre.