Investigation on primary stability of dental implants during compressive cyclic loading-unloading using µCT imaging, and digital volume correlation (DVC) method

Primary stability is the initial mechanical engagement of the implant with its neighboring bone, which is a prerequisite for successful implantation. Primary stability of dental implants can be investigated through in-vitro assessment of stiffness and the ultimate load of the bone-implant complex. Implantation and the following loading on an implant could cause mechanical damage in the peripheral bone, and subsequently, reduce the primary stability of the implant. This study aimed at finding the effects of damage induced in the bone through exerting compressive loading-unloading cycles on the primary stability of the bone-implant system. For this purpose, a dental implant was inserted into a bone sample extracted from the proximal part of a bovine tibia. The implant was undergone step-wise displacement-controlled loading-unloading cycles, and µCT images of the neighboring bone were obtained at each loading-unloading step. Then, the stiffness of the bone-implant structure was calculated after unloading the specimen in each step and the first maximum endured force during loading was considered as the ultimate load of the structure. The distribution of plastic stain in the bone due to loading-unloading of the construct was calculated using digital volume correlation, through correlating the µCT images after unloading in each step. Results of this work showed that increasing the step-wise displacement amplitude from zero to 0.96 mm caused a stiffness reduction of 40%, compared to the initial stiffness, and induced higher plastic strains in peri-implant bone. The results of this study can be used in optimizing the design of dental implants, with the approach of increasing primary stability.