Faculty Bibliography

This study evaluated the effect of core-design modification on the characteristic strength and failure modes of glass-infiltrated alumina (In-Ceram) (ICA) compared with porcelain fused to metal (PFM). Premolar crowns of a standard design (PFMs and ICAs) or with a modified framework design (PFMm and ICAm) were fabricated, cemented on dies, and loaded until failure. The crowns were loaded at 0.5 mm min(-1) using a 6.25 mm tungsten-carbide ball at the central fossa. Fracture load values were recorded and fracture analysis of representative samples were evaluated using scanning electron microscopy. Probability Weibull curves with two-sided 90% confidence limits were calculated for each group and a contour plot of the characteristic strength was obtained. Design modification showed an increase in the characteristic strength of the PFMm and ICAm groups, with PFM groups showing higher characteristic strength than ICA groups. The PFMm group showed the highest characteristic strength among all groups. Fracture modes of PFMs and of PFMm frequently reached the core interface at the lingual cusp, whereas ICA exhibited bulk fracture through the alumina core. Core-design modification significantly improved the characteristic strength for PFM and for ICA. The PFM groups demonstrated higher characteristic strength than both ICA groups combined

This article presents details of processing, characterization and in vitro as well as in vivo evaluations of powder metallurgy processed Ti-13Nb-13Zr samples with different levels of porosity. Sintered samples were characterized for density, crystalline phases (XRD), and microstructure (SEM and EDX). Samples sintered at 1000 degrees C showed the highest porosity level ( approximately 30%), featuring open and interconnected pores ranging from 50 to 100 mum in diameter but incomplete densification. In contrast, samples sintered at 1300 and 1500 degrees C demonstrated high densification with 10% porosity level distributed in a homogeneous microstructure. The different sintering conditions used in this study demonstrated a coherent trend that is increase in temperature lead to higher sample densification, even though densification represents a drawback for bone ingrowth. Cytotoxicity tests did not reveal any toxic effects of the starting and processed materials on surviving cell percentage. After an 8-week healing period in rabbit tibias, the implants were retrieved, processed for nondecalcified histological evaluation, and then assessed by backscattered electron images (BSEI-SEM) and EDX. Bone growth into the microstructure was observed only in samples sintered at 1000 degrees C. Overall, a close relation between newly formed bone and all processed samples was observed.

PURPOSE: In an attempt to overcome the potential long-term limitations observed with plasma-sprayed hydroxyapatite-coated implants, nanothickness bioceramic coatings have been processed onto previously grit-blasted/acid-etched surfaces. Our objective was to evaluate the bone response to alumina-blasted/acid-etched and a thin ion beam-deposited bioceramic (Test) implant surfaces at 2 and 4 weeks in vivo with a dog tibia model. MATERIALS AND METHODS: Plateau root form implants (5 x 6 mm) were placed bilaterally along the proximal tibia of 6 Doberman dogs and remained for 2 and 4 weeks in vivo (n=6 per implant type and time in vivo). After euthanization, the implants were processed in a nondecalcified form and reduced to approximately 30 mum-thickness plates. Transmitted light optical microscopy at various magnifications was used to qualitatively evaluate the bone healing patterns. Bone-to-implant contact (BIC) was determined and 1-way ANOVA at 95% level of significance with Tukey's post-hoc multiple comparisons was used for statistical analysis. RESULTS: Histomorphology showed new bone formation filling the spaces between the plateaus at both in vivo time intervals through large quantities of woven bone formation. A higher degree of bone organization was observed between the plateaus of Test implants at 4 weeks in vivo than the alumina-blasted/acid-etched implants. No significant differences in BIC were observed for the different groups (P> .86). CONCLUSION: Despite nonsignificant differences between BIC for the different implant surfaces and times in vivo, higher degrees of bone organization were observed for the Test implants at 4 weeks, and biomechanical testing is suggested to verify its biomechanical fixation effectiveness.

OBJECTIVE: This study was designed to compare the bone healing process around plateau root from (PRF) and screw root from (SRF) titanium dental implants over the immediate 12 week healing period post implant placement. MATERIAL AND METHODS: 32PRF and 32SRF implants were placed in 8 beagle dogs at 12, 8, 5 and 3 weeks prior to enthanisation using a bilaterally balanced distribution. Undecalcified ground sections were prepared from the biopsies taken and histometric measurements of bone implant contact (BIC) and bone area fraction occupancy (BAFO) were made on the middle 5 mm portion of each 8 mm implant root length. RESULTS: The analysis showed that although measurements of bone to implant contact (BIC) and bone area fraction occupancy (BAFO) tended to be greater for the SRF implants at all four time points, the differences in measurements between implant types did not reach statistical significance (P=0.07, P=0.06). The effect of time on BIC and BAFO was found to be strongly significant for both implant types thus indicating a statistically significant increase in BIC and BAFO overall with time (P=0.004, P=0.002). Furthermore, both PRF and SRF implants behaved similarly over time with measurements of BIC and BAFO progressing in parallel. Histomorphologic analysis of these sections demonstrated the prominent role of woven bone (callus) in the bone healing process around PRF implants. CONCLUSION: The results can be interpreted to indicate a comparable development of secondary stability for both PRF and SRF implant designs. However, as these parameters reflect the structural connection between implant and bone and not the functional properties of the bone to implant interface, they cannot be regarded as comprehensive measures of osseointegration. This particularly relevant given the reduced load bearing capacity of woven bone.

The complex and patient-unique geometry of posterior all-ceramic dental crowns represents a particularly interesting set of challenges to understanding stress concentration and fracture evolution in response to loading. A series of numerical and physical experiments, with both single cycle and fatigue loading, show that geometry profoundly influences the stress concentration and fracture initiation and propagation. In stylized crowns with uniform axial wall height, stresses concentrate beneath the indenter. As the height of the axial wall increases, loads to cause failure increase linearly. In crowns with variation in axial wall height around the periphery, stresses concentrate both beneath the indenter and at the margin of the core ceramic. The magnitude of the stress concentration at the margin is directly related to the amount of variation in axial wall height around the periphery of the crown. Anatomically correct veneered zirconia core crowns subjected to single-cycle loads, fracture in areas of greatest stress concentration identified by finite element models. Fractures and stress concentrations that occur in response to single-cycle loading are important indicators of initiation sites for fatigue failure. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008

The fundamental aspects of damage initiation and accumulation in one-piece zirconium oxide endosseous dental implants remain to be investigated. Aims: This study tested the null hypothesis that there is no influence on mouth-motion fatigue reliability and failure modes between as-received and after full crown preparation on one-piece ceramic implants. Methods: Forty-eight one-piece Y-TZP ceramic implants (Nobel Biocare, Goteborg, Sweden) were utilized. All specimens were embedded in acrylic resin exposing the first two threads at 30 degrees angulation with respect to the vertical axis (as per ISO specification 14801). Full crown preparations were performed following prosthodontic guidelines for half of the specimens. As-received and prepared specimens were distributed among three step-stress profiles based on the specimens ultimate fracture strength. Specimens were step-stress fatigued until failure or survival. A master Weibull curve was generated from the data and the reliability for completion of a mission of 50,000 cycles at 600 N load calculated. Results: No differences between the groups' reliability was observed. Failure mode for both groups was similar, where cracks initiated mainly at the tensile bending side of the second thread's internal diameter. The low Weibull modulus (<1) indicates that fatigue (<150,000 cycles) did not influence failure. Failure depended upon the applied load. Conclusion: Crown preparation did not influence the reliability of the one-piece ceramic implant. The null hypothesis was accepted. Fatigue did not influence the life time of ceramic implants at loads under 600 N. (c) 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008

Among dental implant design alterations, surface modifications have been by far the most investigated topic. Regarding implant surface research, the lack of hierarchical approaches relating in vitro, in vivo, clinical trials, and ex vivo analyses has hindered biomaterials scientists with clear informed rationale guidelines for implant surface design. This manuscript provides a critical hierarchical overview of the in vitro, laboratory in vivo, clinical, and ex vivo methodologies used to investigate the performance of novel biomaterials aiming to allow dental professionals to better evaluate the past, present, and future dental implant surface research. This manuscript also contains an overview of the commercially available surface texture and chemistry modifications including novel nanotechnology-based fabrication processes. Over the last decade, surface texturing has been the most utilized parameter for increasing the host-to-implant response. Recently, dental implant surfaces utilizing reduced length scale physico/chemical features (atomic and nanometric) have shown the potential to synergistically use both texture and the inclusion of bioactive ceramic components on the surface. Although surface modifications have been shown to enhance osseointegration at early implantation times, information concerning its long-term benefit to peri-implant tissues is lacking due to the reduced number of controlled clinical trials. Given the various implants/surfaces under study, the clinician should ask, founded on the basic hierarchical approach described for the in vitro, laboratory in vivo data, as well as the results of clinical studies to effectiveness before use of any dental implant

Thick bioceramic coatings like plasma sprayed hydroxyapatite have been shown to increase the overall tissue response and biomechanical fixation of dental implants. However, the presence and potential fracture of a bone-coating-metallic substrate interface at long times after implantation led these implants to fall from favor in clinical practice. The purpose of this study was to evaluate the biomechanical fixation and biological response of Ca- and P-based, 20-50 nm thickness bioceramic deposition on a previously alumina-blasted/acid-etched Ti-6Al-4V implant surface in a dog model. Cylindrical alumina-blasted/acid-etched (AB/AE) (Control, n = 16), and Nanothickness bioceramic coated AB/AE(Nano, n = 16) implant surfaces were surgically placed in dogs proximal tibia and remained for 2 and 4 weeks in vivo. Following euthanization, the implants-in-bone were mounted in epoxy and pullout at a 0.5 mm/min rate. Following mechanical testing, the specimens were decalcified and processed (Hematoxylin and Eosin) for standard transmitted light microscopy evaluation. Percent bone-to-implant contact (BIC) to the pulled out implant surface was determined through computer software. Statistical analyses were performed by one-way ANOVA at 95% level of significance and Tukey's post-hoc multiple comparisons. No significant differences in pullout force were observed (p > 0.88): 2W Control (212.08 +/- 42.96 N), 2W Nano (224.35 +/- 42.97 N), 4W Control (207.07 +/- 42.97 N), and 4W Nano (190.15 +/- 45.94 N). No significant differences in %BIC were observed (p > 0.94): 2W Control (72.66 +/- 8.51), 2W Nano (69.44 +/- 8.51), 4W Control (70.44 +/- 8.51), and 4W Nano (69.11 +/- 9.09). It is shown that 20-50 nm thickness bioceramic depositions onto previously alumina-blasted/acid-etched substrates did not improve the biomechanical fixation and the BIC at early implantation times, and studies concerning shorter and longer implantation times are recommended for confirmation or before a conclusion can be made.

The objective of this study was to physico/chemically characterize a commercially available and a newly developed Bioglass and also to evaluate their degradation properties. Materials and Method: Two bioresorbable glasses were utilized, a bioglass synthesized at Chemical Engineering College (University of Sao Paulo, Lorena, Sao Paulo) (BG1), and the other bioglass utilized was Biogran (BG2) (3i Implant Innovations, Brazil). Particles size distribution histograms were developed for both materials, and then they were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XR-D) and Fourier Transform Infrared (FTIR) before and after immersion in simulated body fluid (SBF) for 30, 60, and 90 days. Results: The particle size distribution showed that the mean particle diameters at 10%, 50%, and 90% of the total volume were 17.65, 66.18, and 114.71 mu m for BG1, and 354.54, 437.5, 525.00 mu m for BG2. SEM images of BG1 showed that the as-received material had a rough Surface and as the time of degradation elapsed, this surface became smooth. The images of BG2 showed that the as-received material also had a rough surface, and after immersion in SBF, the material's crystalline content/morphology could be observed. The X-ray diffraction recorded that BG1 showed a silica peak, not seen at BG2. FTIR revealed that both bioglasses were of similar composition, except for the CO3-carbonate minor peak, present at the BG2 sample. Conclusions: 1. The particle size distribution showed a polydispersed pattern for both materials. 2. The material Suffered degradation, and the decomposition increased as a function of immersion in SBF. 3. Both bioglasses had similar composition.