Faculty Bibliography

PURPOSE: The objective of this study was to evaluate the bone response to a nanothickness bioceramic ion beam-assisted deposition (IBAD) on endosteal implants in a canine model. MATERIALS AND METHODS: Alumina-blasted/acid-etched (control) and IBAD-modified (test) implants were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy + ion beam milling, thin-film mode X-ray diffraction, and atomic force microscope. The implants were surgically placed in four dogs' proximal tibiae and remained for 2 and 4 weeks in vivo. Oxytetracycline (10 mg/kg) was administered for bone labeling 48 hours prior to euthanization. Following euthanization, nondecalcified thin sections were prepared for UV and transmitted light microscopy. The amount of bone labeling was evaluated along the length and away from the implant surface by means of a computer software. The % bone-to-implant contact (BIC) was determined for each specimen. One-way analysis of variance at 95% level of significance along with Tukey's post hoc multiple comparisons were utilized for statistical evaluation. The characterization showed Ca- and P-based amorphous coatings with a 20- to 50-nm thickness. RESULTS: In vivo results showed a significant increase in general and site-specific (to 0.5 mm from the implant surface) bone activity for the 4-week test implants compared with the control implants. Bone activity levels decreased as a function of distance from the implant surface for all groups. No significant differences in BIC were observed between groups. CONCLUSIONS: This study showed that both surfaces were biocompatible and osteoconductive and that a time-dependent increase in osteoactivity occurred around the test implants.

The objective of this study was to evaluate the morphology and integration status of 30 human retrieved plateau root form implants. Thirty plateau design root form implants that were in function from 8 to 13 years were retrieved from patients due to prosthetic reasons. Following surgical removal, the samples remained in 10% buffered formaline for 7 days. Bone morphology was evaluated by transmitted and polarized light microscopy, and bone-to-implant contact (BIC) histomorphometric assessment was determined through computer software. Irrespective of time in vivo, lamellar bone was observed in close contact with the implant surface and between plateaus. BIC ranged from approximately 20 to approximately 80%. Polarized light microscopy showed a highly directional osteonic morphology between plateaus for most implants. A haversian-like microstructure running perpendicular to and along with the implants' long axis (between plateaus) was observed in regions of cortical and trabecular bone, revealing a unique bone microstructural evolution over time around functionally loaded plateau root form implants.

OBJECTIVE: To evaluate the mouth-motion step-stress fatigue behavior of two porcelain-zirconia all-ceramic crown systems. METHODS: The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based tooth preparation was made by rapid prototyping and used as a master die to fabricate all-ceramic crowns with 1.0 mm porcelain veneered on 0.5 mm Y-TZP cores (LAVA veneer+LAVA frame, 3M/ESPE, and Vita veneer+CERCON frame, Dentsply). Crowns were cemented on aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Three crowns from the LAVA group were subjected to single cycle load to failure for stress profile design; remainder subjected to step-stress mouth-motion fatigue (three step-stress profiles). All mechanical testing was performed by sliding a WC indenter of 6.25 mm diameter 0.7 mm lingually down the mesio-distal cusp. Master Weibull curves and reliability for missions of 50,000 cycles at 200 N load were calculated (Alta Pro 7, Reliasoft). RESULTS: Single load to failure showed fractures through the zirconia core. Reliability for a 200 N x 50K cycle mission was not significantly different between systems. In fatigue, failure occurred by formation of large chips within the veneer originating from the contact area without core exposure. CONCLUSIONS: LAVA and CERCON ceramic systems present similar fatigue behavior; fatigue loading of both systems reproduces clinically observed failure modes

This study aimed to physico/chemically characterize and evaluate the in vivo performance of a beta-TCP particulate grafting material. SEM/TEM, and EDS and XPS were used for morphology and chemistry assessment, respectively. FTIR was used to determine Ca-P phases characteristic bands. Rietveld refinement/XRD spectra was performed for secondary phase detection. Particle size distribution and specific surface were assessed by a scattering-laser based technique and BET, respectively. Mercury porosimetry was employed to determine pore-size distribution. For in vivo evaluation, the grafting material was used in 12 patients' sinus lifts, and biopsies were obtained at post-operative times of 3, 6, and 9 months. SEM/TEM revealed multigrained particles with interconnected pores. EDS showed Ca, P, and O, with stoichiometry close to theoretical values. XRD/Rietveld showed that the material presented crystalline beta-TCP with similar to 9% beta-Ca(2)O(7) secondary phase. FTIR did not detect the presence of bands related to alpha-TCR Human histologic assessment showed that newly formed bone was present at 3 months, and degrees of bone organization increased as time elapsed in vivo. Human histology showed that the material is suitable for bone regeneration in a maxillofacial complex region. (C) 2009 Elsevier B.V. All rights reserved.

PURPOSE: The present study assessed damage to the inferior alveolar nerve (IAN) following nerve lateralization and implant placement surgery through optical and transmission electron microscopy (TEM). MATERIALS AND METHODS: IAN lateralization was performed in 16 adult female rabbits (Oryctolagus cuniculus). During the nerve lateralization procedure, one implant was placed through the mandibular canal, and the IAN was replaced in direct contact with the implant. The implant was placed in the right mandible, and the left side was used as a control (no surgical procedure). After 8 weeks, the animals were sacrificed and samples were prepared for optical and TEM analysis of IAN structural damage. Histomorphometric analysis was performed to determine the number and cross-sectional dimensions of nerve fascicles and myelin sheath thickness between experimental and control groups. The different parameters were compared by one-way analysis of variance at the 95% significance level. RESULTS: Alterations in the perineural and endoneural regions of the IAN, with higher degrees of vascularization, were observed in the experimental group. TEM showed that the majority of the myelinated nerve fibers were not affected in the experimental samples. No significant variation in the number of fascicles was observed, significantly larger fascicle height and width were observed in the control group, and significantly thicker myelin sheaths were observed in the experimental samples. CONCLUSION: IAN lateralization resulted in substantial degrees of tissue disorganization at the microstructural level because of the presence of edema. However, at the ultrastructural level, small amounts of fiber degeneration were observed.

The objective of this study was to physico/chemically characterize and evaluate the in vivo performance of two nanothickness ion beam assisted depositions (IBAD) of bioceramic coatings on implants in a beagle model. Alumina-blasted/acid-etched (AB/AE) Ti-6Al-4V implants were subjected to two different IBAD depositions (IBAD I and IBAD II), which were physico/chemically characterized by SEM, EDS, XPS, XPS + ion-beam milling (depth profiling), XRD, AFM, and ToF-SIMS. A beagle dog tibia model was utilized for histomorphometric and biomechanical (torque) comparison between AB/AE, IBAD I, IBAD II, and plasma-sprayed hydroxyapatite (PSHA) coated implants that remained in vivo for 3 and 5 weeks. The coatings were characterized as amorphous Ca-P with high Ca/P stoichiometries with thicknesses of an order of magnitude difference (IBAD I = 30-50 nm and IBAD II = 300-500 nm). The histomorphometric and biomechanical testing results showed that the 300-500 nm thickness deposition (IBAD II) and PSHA positively modulated bone healing at early implantation times.

The aim of this study was to evaluate the biomechanical fixation, bone-to-implant contact, and bone morphology of an ion beam assisted deposition of a 300-500 nm thick Ca- and P-based bioceramic surface on a previously alumina-blasted/acid-etched Ti-6Al-4V implant surface in a dog model. MATERIALS AND METHODS: Thirty-six 4.5 x 11 mm plateau root form implants, control (alumina-blasted/acid-etched-AB/AE) and test groups (AB/AE+300-500 nm bioceramic coating, Nanotite) were placed along a proximal tibia of six beagle dogs remaining for 2 and 4 weeks (n = 3 animals per implantation time). Following euthanization, the implants were torqued to interface fracture at approximately 0.196 radians/sec until a 10% maximum load drop was detected. The implants in bone were nondecalcified processed to approximately 30 microm thickness slides for histomorphologic and bone-to-implant contact (BIC) assessment. Statistical analyses for torque to interface fracture were performed using a mixed model ANOVA, and BIC was evaluated by the chi2 test at 95% level of significance. RESULTS: At 4 weeks, significantly higher torque to interface fracture was observed for the Test implant surface. Histomorphologic analysis showed higher degrees of bone organization for test implants compared to control at 2 and 4 weeks. Significantly higher BIC was observed at 4 weeks compared to 2 weeks (no statistical differences between control and test implants). CONCLUSION: The higher torque to interface fracture and increased bone maturity obtained in this study support that the surface modification comprising a 300-500 nm Ca- and P-based bioceramic coating positively influenced healing around pleateau root form implants.

In this work, a three-dimensional model for bone remodeling is presented, taking into account the hierarchical structure of bone. The process of bone tissue adaptation is mathematically described with respect to functional demands, both mechanical and biological, to obtain the bone apparent density distribution (at the macroscale) and the trabecular structure (at the microscale). At global scale bone is assumed as a continuum material characterized by equivalent (homogenized) mechanical properties. At local scale a periodic cellular material model approaches bone trabecular anisotropy as well as bone surface area density. For each scale there is a material distribution problem governed by density-based design variables which at the global level can be identified with bone relative density. In order to show the potential of the model, a three-dimensional example of the proximal femur illustrates the distribution of bone apparent density as well as microstructural designs characterizing both anisotropy and bone surface area density. The bone apparent density numerical results show a good agreement with Dual-energy X-ray Absorptiometry (DXA) exams. The material symmetry distributions obtained are comparable to real bone microstructures depending on the local stress field. Furthermore, the compact bone porosity is modeled giving a transversal isotropic behavior close to the experimental data. Since, some computed microstructures have no permeability one concludes that bone tissue arrangement is not a simple stiffness maximization issue but biological factors also play an important role.

OBJECTIVE: The purpose of this study was to determine the microtensile bond strength of various resin composite/adhesive systems to alumina particle abraded Ti-6Al-4V substrate after aging for 24h, 10 days, and 30 days in distilled water at 37 degrees C. METHODS: Four laboratory resin composite veneering systems (Gradia, GR; Solidex, SOL; Ceramage, CER; and Sinfony, SF) were bonded to 25 mm diameter machined disks of Ti-6Al-4V with their respective adhesive and methodology, according to the manufacturer's instructions. Microtensile bars of approximate dimensions 1 mm x 1 mm x 6 mm were prepared for each resin composite/adhesive system. After cutting, groups (n=12) from each adhesive system were separated and either stored in water at 37 degrees C for 24h (baseline) or aged for 10 or 30 days prior to loading to failure under tension at a cross head speed of 1.0mm/min. Failure modes were determined by means of scanning electron microscopy (SEM). Statistical analysis was performed through one-way ANOVA and Tukey's test at 95% level of significance. RESULTS: Significant variation in microtensile bond strength was observed for the different systems and aging times. SOL and GR showed the highest mean bond strength values followed by SF and CER at baseline. Aging specimens in water had an adverse effect on bond strength for SOL and CER but not for the SF and GR groups. SIGNIFICANCE: In vitro bond strength of laboratory resin composites to Ti-6Al-4V suggests that strong bonds can be achieved and are stable for certain systems, making them useful as an alternative for esthetic fixed prosthetic restorations

Clinically, zirconia-supported all-ceramic restorations are failing by veneer-chipping without exposing the zirconia interface. We hypothesized that mouth motion step-stress-accelerated fatigue testing of standardized dental crowns would permit this previously unrecognized failure mode to be investigated. Using CAD software, we imported the average dimensions of a mandibular first molar crown and modeled tooth preparation. The CAD-based tooth preparation was rapid-prototyped as a die for fabrication of zirconia core porcelain-veneered crowns. Crowns were bonded to aged composite reproductions of the preparation and aged 14 days in water. Crowns were single-cycle-loaded to failure or mouth-motion step-stress- fatigue-tested. Finite element analysis indicated high stress levels below the load and at margins, in agreement with only single-cycle fracture origins. As hypothesized, the mouth motion sliding contact fatigue resulted in veneer chipping, reproducing clinical findings allowing for investigations into the underlying causes of such failures