Abstract
Titanium implants have been used from the last four decades to replace missing teeth. Recently, there have been concerns by some patients about using titanium in the body as these metals may induce allergic reactions. This research is designed to develop a metal-free approach by using one-piece titanium (Ti) and zirconia (Zr) implants to anchor overdentures.
Aims: The research aimed to investigate soft and hard tissue response to Ti and Zr implants in edentulous patients. Additionally, median-palatal bone was investigated as a novel implant site to anchor maxillary-overdenture. The aim of the microbial analysis was to see if the type of biomaterial has an influence on the oral environment.
Methods: The current thesis is based on five experiments involving human cadavers, sheep (animal model) and a randomised controlled clinical trial. The thesis has investigated novel implant site in the maxilla of 16 human cadavers. Bone specimens from the cadavers were harvested from the maxillary premolar and median palatine region and a Micro Computed Tomography (Micro-CT) and histomorphometric analysis was conducted. To supplement human clinical trial, a preclinical in vivo animal trial was also conducted that investigated osseointegration around the Ti and Zr implants. Histomorphometry was used to evaluate bone implant contact around 40 implants (Ti = 20, Zr = 20) in the jaw and femur of ten sheep. Additionally, a quantitative real time reverse-transcriptase polymerase chain reaction (qRT-PCR) technology was used to analyse bacterial biofilms associated with the tongue and implants (Ti and Zr) placed in patients. The human trial investigated surgical and peri-implant outcomes of 24 participants (Ti =12, Zr =12) with implant overdentures.
Results: Higher values for bone volume fraction and trabecular number were found in the median palatine region although the differences were not statistically significant (Bone volume-fraction, p = 0.06 and Trabecular-thickness, p = 0.07). Trabeculae in the median palatine region were less separated then the premolar region (Trabecular-Separation, p = 0.04). In the animal study, all femur implants survived the healing period and a statistically significant difference was observed between the %BIC for Zr and Ti implants (p = 0.002). In the mandible, 5/10 Zr implants and 2/10 Ti implant failed to osseointegrate. The human clinical trial presented somewhat similar results with high failure rates of one-piece Ti and Zr implants. A low success rate of 67.9% was noted in the crestal implants while a survival rate of 50% was noted for the palatal implants.
Conclusions: The major implication of this research project is to acknowledge the relationship between implant design (morphology), surgical implant site and successful long-term osseointegration. Further studies are needed to investigate median palatine bone as an implant site to anchor an implant overdenture. In vivo animal trials have documented favourable outcomes of Zr implants. Two-piece Zr implant design should be investigated to eliminate the one-piece design factor, a probable feature responsible for Zr implant failure in most of the reported studies. Within the limitations of the research, Zr implants presented in this trial cannot be recommended for routine use, and further RCTs with larger cohorts and improved implant designs are needed.