Alrabeah, Ghada O.; (2019) The Effect of Different Implant-Abutment Connection Geometry and Abutment Alloy on Corrosion Product Release and Cell Response. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Problem: The observed positive effect of the platform-switching concept on peri- implant bone level is not well understood. Dental implants may be prone to tribocorrosion leading to the release of metal ions and particles which may disrupt bone homeostasis Objectives: The aim of this project was to compare the amount of corrosion products released from different implant-abutment couplings with different connection geometries under accelerated corrosion tests, and to evaluate different osteoblastic cell responses to the released products. Materials and methods: Part I: Titanium cylinders were connected to titanium alloy (Ti-6Al-4V) and cobalt– chrome alloy abutments forming either platform-switched or platform-matched groups. Samples were subjected to static immersion in 1% lactic acid for 1 week. Metal ions released were measured and microscopic analyses were performed pre- and post- immersion to assess corrosion at the interface. Part II: Osteoblasts were treated with culture media containing different concentrations of metal ions obtained from the results of part I. Osteoblasts treated with ion-free culture medium served as the controls. Osteoblastic viability, apoptosis and expression of genes related to bone resorption were analysed. Part III: The samples used in part I were incubated with osteoblasts. Viability, apoptosis and expression of the genes tested in part II were investigated. Part IV: Titanium implants were coupled with either titanium, gold, cobalt-chrome, or zirconia abutments forming either platform-switched or platform-matched groups. The specimens were subjected to cyclic loading under wet acidic environment. Metal ions released were measured and microscopic evaluations were performed pre- and post- immersion for tribocorrosion assessment and wear particle characterization. Results: Part I: The implant–abutment couplings underwent an active corrosion process resulting in metal ions released into the surrounding environment. The platform- matched groups demonstrated higher amount of metal ion release. Part II and Part III: Osteoblastic cell viability, apoptosis, and regulation of bone resorbing mediators were significantly altered in the presence of both the metal ions and the different implant-abutment couplings. The observed changes in some of the biological responses tested were more pronounced in groups representing the platform-matched implant-abutment couplings. Part IV: The implant–abutment couplings underwent an active tribocorrosion processes resulting in metal ions and wear particles released into the surrounding environment. The platform-matched groups demonstrated higher amount of metal ion release and more surface damage Conclusion: Platform-switching concept had a positive effect in reducing metal ion release and wear features from dental implants which in turn minimised the adverse osteoblastic biologic responses related to peri-implant bone loss, therefore highlighting the possible role of corrosion products in the mediation of crestal bone loss around dental implants

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