Browsing by Author "Wang, Frederick"
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Item Can Oral Bacteria and Mechanical Fatigue Degrade Zirconia Dental Implants in Vitro?(American Chemical Society, 2019-05-15) Siddiqui, Danyal A.; Sridhar, Sathyanarayanan; Wang, Frederick; Jacob, Joel J.; Rodrigues, Danieli C.; 0000-0002-2398-5979 (Siddiqui, DA); 0000-0002-0389-0833 (Rodrigues, DC); Siddiqui, Danyal A.; Sridhar, Sathyanarayanan; Wang, Frederick; Jacob, Joel J.; Rodrigues, Danieli C.Zirconia (ZrO₂) is an emerging alternative to titanium for dental implant systems due to its material properties including high mechanical strength and chemical stability. However, oral environmental factors such as bacterial adhesion and mechanical fatigue may trigger low-temperature degradation of ZrO₂, leading to reduced mechanical strength and potential implant fracture. Although failure modes of ZrO₂ in orthopedic applications have been studied, they have yet to be thoroughly investigated in the context of dental implant systems. Thus, the goal of the present study was to assess the surface of ZrO₂ dental implants for signs of degradation after exposure to oral bacteria and oral bacteria in combination with mechanical fatigue. ZrO₂ dental implants were subjected to 30-day immersion in (i) early or (ii) late colonizing oral bacteria or (iii) were mechanically loaded for 2 × 106 cycles with oral bacteria in circulation. Optical microscopy, Raman microscopy, and X-ray photoelectron spectroscopy (XPS) were used to evaluate the surface morphology, phase composition, and chemical composition, respectively. Post-immersion, all implants exhibited minimal changes in surface features, and all loaded implants survived cyclic fatigue tests. All implants had <1% monoclinic phase at the collar, junction, and screw regions, excluding the screw threads, for which monoclinic phase was significantly higher but <10%. XPS revealed an increase in carbon- and nitrogen-based organic debris on the implants exposed to early colonizers as compared to those immersed in late colonizers or synergistically with mechanical loading. Within the limitations of the present study, ZrO₂ is a suitable alternative material for dental implant systems based on its ability to resist both physical and chemical degradation imposed by oral bacteria and applied cyclic loads. © 2019 American Chemical Society.Item Multifaceted Roles of Environmental Factors toward Dental Implant Performance: Observations from Clinical Retrievals and In Vitro Testing(Elsevier Inc.) Sridhar, Sathyanarayanan; Wang, Frederick; Wilson, T. G., Jr.; Valderrama, P.; Palmer, Kelli; Rodrigues, Danieli C.; Sridhar, Sathyanarayanan; Wang, Frederick; Palmer, Kelli; Rodrigues, Danieli C.Objective: Oral bacteria and periodontal pathogen have been predominantly linked with early- and late- stage failures of titanium (Ti) dental implants (DI) respectively. This study is based on the hypothesis that bacterial colonization can damage the surface oxide (TiO₂) layer. Early-failed DI were compared with DI post-in vitro immersion in early colonizing oral bacteria; late failed DI were weighed against DI immersed in late colonizing anaerobic pathogens. Methods: Retrieval analysis: Seven early- stage failed implants with five of them connected to healing abutments (HAs), and ten late- stage failed retrievals were subjected to surface analysis. Bacteria immersion test: Three dental implants each were immersed in polycultures containing (i) early colonizers (Streptococcus mutans, S. salivarius, S. sanguinis) (ii) late colonizers (Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans). The implants were immersed for 30 days to simulate the healing period and bacterial biofilm adhesion. Optical microscope, x-ray photoelectron spectroscopy (XPS), and electrochemical test were performed to analyze the surface- morphology, chemistry, and potential respectively. Results: Early colonizers inflicted surface morphological damage (discoloration and pitting). Even though, XPS detected thinner oxide layer in 2/3 early retrievals, XPS and electrochemical tests illustrated that the TiO₂ layer was intact in HAs, and in DI post- immersion. Late colonizers also caused similar morphological damage (discoloration and pitting), while mechanical wear was evident with scratches, cracks, and mechanical fracture observed in late-stage retrievals. XPS indicated thinner oxide layer in late-stage retrievals (3/4), and in DI post-immersion in late colonizers. This was reflected in electrochemical test results post-immersion but not in the late-stage retrievals, which suggested an intact surface with corrosion resistance. Significance: This study concluded that bacteria could negatively affect implant surface with late colonizers demonstrating more pronounced damage on the surface morphology and chemistry. ©2018 The Academy of Dental Materials