A Comprehensive in Vitro and in Vivo Failure Analysis of Titanium Dental Implant Systems

This dissertation provides a novel approach to understand failure modes and evaluate the surface performance of commercially pure (cp) titanium (Ti) dental implants (DI). It is based on the hypothesis that multiple oral factors can damage the titanium oxide (TiO2) layer leading to peri-implant dissolution of metal ions. This study is comprised of three aims to understand the effect of (i) surgical insertion in different bone qualities; (ii) bacteria colonization; (iii) occlusal forces on the surface of DI. In the aim 1, DI were inserted following surgical procedure in simulated bone materials of different densities to check the possibility of surface exfoliation and corrosion behavior. Powder x-ray diffraction (XRD) of ground specimen from the insertion site was performed to detect particle release. ASTM standard electrochemical corrosion tests were performed to evaluate the corrosion behavior of DI post-insertion. In the aim 2, surface analyses of in vivo failed retrievals were performed. DI were immersed in in vitro polyculture of early colonizers (Stretptococcus mutans, S. salivarius, S. sanguinis), and late colonizers (Aggregatibacter actinomycetemcomitans, Porphyromonas gingivalis) for 30 days. In the aim 3, cyclic occlusal forces were employed on DI immersed in (i) phosphate buffered saline (PBS) and in (ii) bacterial polyculture. Optical microscope, x-ray photoelectron spectroscopy (XPS), and electrochemical corrosion tests were performed to evaluate the surface-morphology, chemistry, and potential of (i) failed explanted retrievals, and (ii) DI obtained post-in vitro tests. Powder XRD results post-insertion test confirmed that particles were not released due to the insertion procedure irrespective of bone density. Electrochemical corrosion results post-insertion further corroborated that the surface integrity was not compromised due to insertion irrespective of bone quality. In vivo retrieval analyses suggested that both early- and late-colonizers degraded the surface- morphology (discoloration, pitting, scratches, and fractures) and chemistry (thinning/depletion of TiO2 layer with respect to the control). However, in vitro bacteria immersion tests showed that late- colonizers inflicted more damage to the surface chemistry compared to the early colonizers. Electrochemical corrosion results also indicated higher corrosion rate (not statistically significant) for DI immersed in late colonizers compared to early colonizers and their respective controls. The surface degradation due to bacteria adhesion was aggravated in the presence of mechanical forces. XPS analysis illustrated depleted TiO2 layer for DI exposed to cyclic loading in circulating broth containing bacteria compared to DI subjected to fatigue test in PBS. The overall findings of this study indicated that bacteria could degrade the surface which would be exacerbated by mechanical loading. This dissertation highlights the need to focus on the material surface, as particle release into the peri-implant tissue might trigger osteolysis and affect biological integration.