Browsing by Author "Sridhar, Sathyanarayanan"
Now showing 1 - 5 of 5
- Results Per Page
- Sort Options
Item A Comprehensive in Vitro and in Vivo Failure Analysis of Titanium Dental Implant Systems(2018-08) Sridhar, Sathyanarayanan; Rodrigues, Danieli C.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.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 Corrosion Behavior of Zirconia in Acidulated Phosphate Fluoride(Faculdade De Odontologia De Bauru) Thomas, Anie; Sridhar, Sathyanarayanan; Aghyarian, Shant; Watkins-Curry, P.; Chan, J. Y.; Pozzi, A.; Rodrigues, Danielli C.; Thomas, Anie; Sridhar, Sathyanarayanan; Aghyarian, Shant; Rodrigues, Danielli C.Objective: The corrosion behavior of zirconia in acidulated phosphate fluoride (APF) representing acidic environments and fluoride treatments was studied. Material and Methods: Zirconia rods were immersed in 1.23% and 0.123% APF solutions and maintained at 37°C for determined periods of time. Surfaces of all specimens were imaged using digital microscopy and scanning electron microscopy (SEM). Sample mass and dimensions were measured for mass loss determination. Samples were characterized by powder X-ray diffraction (XRD) to detect changes in crystallinity. A biosensor based on electrochemical impedance spectroscopy (EIS) was used to detect ion dissolution of material into the immersion media. Results: Digital microscopy revealed diminishing luster of the materials and SEM showed increased superficial corrosion of zirconia submerged in 1.23% APF. Although no structural change was found, the absorption of salts (sodium phosphate) onto the surface of the materials bathed in 0.123% APF was significant. EIS indicated a greater change of impedance for the immersion solutions with increasing bathing time. Conclusion: Immersion of zirconia in APF solutions showed deterioration limited to the surface, not extending to the bulk of the material. Inferences on zirconia performance in acidic oral environment can be elucidated from the study. ©2016, Journal of Applied Oral Science. All rights reserved.Item Evaluation of Oral Microbial Corrosion on the Surface Degradation of Dental Implant Materials(Wiley, 2018-08-13) Siddiqui, Danyal A.; Guida, Lidia; Sridhar, Sathyanarayanan; Valderrama, Pilar; Wilson, Thomas G., Jr.; Rodrigues, Danieli C.; 0000-0002-0389-0833 (Rodrigues, DC); Rodrigues, Danieli C.; Siddiqui, Danyal A.; Guida, Lidia; Sridhar, SathyanarayananBackground: Titanium (Ti) dominates as the material of choice for dental implant systems. Recently, titanium-zirconium alloy (TiZr) and zirconia (ZrO₂) have emerged as alternative materials due to higher mechanical strength and lower corrosion susceptibility. Oral pathogenic bacteria can colonize Ti surfaces, leading to surface degradation, which has yet to be investigated on TiZr and ZrO₂. The aim of this study was to compare in vitro oral bacterial adhesion and subsequent surface degradation on commercial Ti, TiZr, and ZrO₂ implants. Methods: Ti, TiZr, and ZrO₂ implants with sandblasted, acid-etched (SLA) surfaces in addition to modified SLA-treated (modSLA) Ti implants (n = 3) were immersed for 30 consecutive days in Streptococcus polyculture. Post-immersion, adherent bacterial count was quantified. Optical microscopy was used to assess qualitative degradation and score Ti-based implants based on degree of surface damage while electrochemical testing quantified corrosion behavior. Analysis of variance followed by post-hoc Tukey test was used to statistically compare quantitative results (alpha = 0.05). Results: Ti-SLA, Ti-modSLA, and TiZr-SLA implants exhibited localized features characteristic of corrosion attack while ZrO₂-SLA implants experienced minimal changes in surface morphology as compared to non-immersed control. Corrosion features were more numerous on Ti-modSLA implants but smaller in size as compared with those on Ti-SLA and TiZr-SLA implants. No significant differences in corrosion resistance (polarization resistance and corrosion rate) were observed between Ti-SLA, Ti-modSLA, and TiZr-SLA implants. Conclusion: TiZr and ZrO₂ dental implant surfaces were not more susceptible to colonization and surface degradation by oral Streptococcus species than commercially pure Ti implants.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