Magnitude and Direction of Mechanical Stress at the Osseointegrated Interface of the Microthread Implant

Background: The mechanism by which the microthread implant preserves peri-implant crestal bone is not known. The objective of this research is to assess the effect of microthreads on the magnitude and direction of the stress at the bone-implant interface using finite element analysis modeling. Methods: Three-dimensional finite element models representing the microthreaded implant (microthread model) and smooth surface implant (smooth model) installed in the mandibular premolar region were created based on microscopic and computed tomography images. The mesh size was determined based on convergence tests. Average maximum bite force of adults was used with four loading angles on the occlusal surface of the prosthesis. Results: Regardless of the loading angle, principal stresses at the bone-implant interface of the microthread model were always perpendicular to the lower flank of each microthread. In the smooth model, stresses were affected by the loading angle and directed obliquely to the smooth interface, resulting in higher shear stress. The interfacial stresses decreased gradually in the apical direction in both models but with wavy pattern in the microthread model and smooth curve for the smooth model. Although peak principal stress values were higher around the microthread implant, peri-implant bone volume exhibiting a high strain level >4,000 mu was smaller around the microthread implant compared to the smooth implant. Conclusion: Stress-transferring mechanism at the bone-implant interface characterized by the direction and profile of interfacial stresses, which leads to more compressive and less shear stress, may clarify the biomechanical aspect of microthread dental implants. J Periodontol 2011;82:1061-1070.