Faculty Bibliography

The objective of this study was to evaluate the in vitro degradation of pellet and powder forms of a poly-L-D-lactic acid material used to produce plates and screws for orthopedic, oral, and maxillofacial applications. MATERIALS AND METHODS: In order to produce the powder form the as-received pellets were milled in a cryogenic chamber. Particles size distribution (PSD) histograms were developed for both forms. The materials were then characterized by Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) before and after immersion in simulated body fluid for 30, 60, and 90 days. RESULTS: SEM showed that for both forms material degradation started after 30 days of immersion in SBF and evolved until 90 days. Degradation started at the amorphous zones of the polymer and exposed of deeper crystalline layers. The pellet and powder samples PSD showed polydispersed patterns with mean diameters of 673.98 microm and 259.55 microm. Thermal onset degradation temperatures were 365.64 degrees C and 360.30 degrees C, and of 363.49 degrees C and 359.83 degrees C before immersion and after 90 days in SBF for the pellet and powder forms, respectively. The Tg's of the pellets and the powder were approximately 61.5 degrees C and 66 degrees C, and their respective endothermic peaks were observed at approximately 125 degrees C and 120 degrees C. The specific heat (c) was approximately 8.5 J/g and 6.2 J/g for the pellet and powder material, respectively. CONCLUSION: According to the results obtained, cryogenic milling resulted in particle plastic deformation, and alterations in glass transition temperature, melting temperature, and specific heat of the material.

OBJECTIVE: To test the hypothesis that dentin Hertzian contact response varies with loading rate and tubule orientation. DESIGN: Sound teeth (n=12) were cut either parallel or perpendicular to the axial direction to expose dentin (n=6 each). The cut specimens were embedded (poly-methyl-methacrylate (PMMA) and divided into two groups: (GL) load applied parallel to dentin tubule direction and (GP) load applied perpendicular to tubule direction. A 1.5mm diameter tungsten-carbide ball was used for Hertzian contact testing with a maximum load of 150 N load and loading rates of 0.1, 1, 100, and 1000 N/s on each specimen. Indented specimens were observed microscopically and photomicrographs acquired. Hertzian contact diameter and modulus were analysed (p<0.05) by one-way ANOVA and Tukey test. RESULTS: There were significant differences (p<0.05) in Hertzian response with respect to loading rate for GL (0.1N/s versus 1000 N/s, 0.1N/s versus 100 N/s, 1N/s versus 1000 N/s, and 1N/s versus 100 N/s), and GP (0.1N/s versus 1000 N/s, 0.1N/s versus 100 N/s, and 1N/s versus 1000 N/s). Contact modulus was higher for GL compared to GP at all loading rates (p<0.05). CONCLUSION: The results suggest that dentin contact modulus is loading rate dependent. Tubule orientation of dentin did not influence contact modulus values (p>0.05)

PURPOSE: The purpose of this study was to evaluate the bone healing kinetics around commercially pure titanium implants following inferior alveolar nerve (IAN) lateralization in a rabbit model. MATERIALS AND METHODS: Inferior alveolar nerve lateralization was performed in 16 adult female rabbits (Oryctolagus cuniculus). During the nerve lateralization procedure, 1 implant was placed through the mandibular canal, and the IAN was replaced in direct contact with the implant. During the 8-week healing period, various bone labels were administered for fluorescent microscopy analysis. The animals were euthanized by anesthesia overdose, and the mandibular blocks were exposed by sharp dissection. Nondecalcified samples were prepared for optical light and scanning electron microscopy (SEM) evaluation. RESULTS: SEM evaluation showed bone modeling/remodeling between the IAN and implant surface. Fluorochrome area fraction labeling at different times during the healing period showed that bone apposition mainly occurred during the first 2 weeks after implantation. CONCLUSIONS: The results obtained showed that bone healing/deposition occurred between the alveolar nerves in contact with a commercially pure titanium implant. No interaction between the nerve and the implant was detected after the 8-week healing period. Appositional bone healing occurred around the nerve bundle structure, restoring the mandibular canal integrity and morphology.

The aim of this study was to qualitatively demonstrate surface micro-morphological changes after the employment of different surface conditioning methods on high-alumina and glassy-matrix dental ceramics. Three disc-shaped high-alumina specimens (In-Ceram Alumina, INC) and 4 glassy-matrix ceramic specimens (Vitadur Alpha, V) (diameter: 5 mm and height: 5 mm) were manufactured. INC specimens were submitted to 3 different surface conditioning methods: INC1--Polishing with silicon carbide papers (SiC); INC2--Chairside air-borne particle abrasion (50 microm Al2O3); INC3 - Chairside silica coating (CoJet; 30 microm SiOx). Vitadur Alpha (V) specimens were subjected to 4 different surface conditioning methods: V1--Polishing with SiC papers; V2 - HF acid etching; V3--Chairside air-borne particle abrasion (50 microm Al2O3); V4--Chairside silica coating (30 microm SiOx). Following completion of the surface conditioning methods, the specimens were analyzed using SEM. After polishing with SiC, the surfaces of V specimens remained relatively smooth while those of INC exhibited topographic irregularities. Chairside air-abrasion with either aluminum oxide or silica particles produced retentive patterns on both INC and V specimens, with smoother patterns observed after silica coating. V specimens etched with HF presented a highly porous surface. Chairside tribochemical silica coating resulted in smoother surfaces with particles embedded on the surface even after air-blasting. Surface conditioning using air-borne particle abrasion with either 50 microm alumina or 30 microm silica particles exhibited qualitatively comparable rough surfaces for both INC and V. HF acid gel created the most micro-retentive surface for the glassy-matrix ceramic tested.

This study presents the in-vivo evaluation of Ti-13Nb-13Zr alloy implants obtained by the hydride route via powder metallurgy. The cylindrical implants were processed at different sintering and holding times. The implants' were characterized for density, microstructure (SEM), crystalline phases (XRD), and bulk (EDS) and surface composition (XPS). The implants were then sterilized and surgically placed in the central region of the rabbit's tibiae. Two double fluorescent markers were applied at 2 and 3 weeks, and 6 and 7 weeks after implantation. After an 8-week healing period, the implants were retrieved, non-decalcified section processed, and evaluated by electron, UV light (fluorescent labeling), and light microscopy (toluidine blue). BSE-SEM showed close contact between bone and implants. Fluorescent labeling assessment showed high bone activity levels at regions close to the implant surface. Toluidine blue staining revealed regions comprising osteoblasts at regions of newly forming/formed bone close to the implant surface. The results obtained in this study support biocompatible and osseoconductive properties of Ti-13Nb-13Zr processed through the hydride powder route. © 2007.

INTRODUCTION: Understanding how teeth move in response to mechanical loads is an important aspect of orthodontic treatment. Treatment planning should include consideration of the appliances that will meet the desired loading of the teeth to result in optimized treatment outcomes. The purpose of this study was to evaluate the use of computer simulation to predict the force and the torsion obtained after the activation of tear drop loops of 3 heights. METHODS: Seventy-five retraction loops were divided into 3 groups according to height (6, 7, and 8 mm). The loops were subjected to tensile load through displacements of 0.5, 1.0, 1.5, and 2.0 mm, and the resulting forces and torques were recorded. The loops were designed in AutoCAD software(2005; Autodesk Systems, Alpharetta, GA), and finite element analysis was performed with Ansys software(version 7.0; Swanson Analysis System, Canonsburg, PA). Statistical analysis of the mechanical experiment results was obtained by ANOVA and the Tukey post-hoc test (P < .01). The correlation test and the paired t test (P < .05) were used to compare the computer simulation with the mechanical experiment. RESULTS AND CONCLUSIONS: The computer simulation accurately predicted the experimentally determined mechanical behavior of tear drop loops of different heights and should be considered an alternative for designing orthodontic appliances before treatment.

Objective: This series of laboratorial and in-vivo studies describe the characterization, evolution, and in-vivo performance of various Ca- and P-based nanothicknesses and microstructures ion beam assisted depositions (IBAD) onto Ti-6Al-4V implants. Materials and Methods: Characterization- The 4 mm in diameter and 10 mm in length implant rods (Ti-6Al-4V) with IBAD 1, IBAD 11, and control (alumina-blasted/acid-etched, AB/AE) surfaces were provided by an implant manufacturer. The in-vitro characterization comprised the following techniques: (1) SEM/EDS, (2) XPS/Depth Profiling (3) Thin-film XRD (4) AFM + ToF-SIMS for coating thickness determination (5) AFM- Ra determination. In-vivo- Three animal experiments were carried out for evaluation of the nanothickness bioceramic coatings. All experiments comprised a proximal tibia model with 4-6 implants placed along the bones. Times in-vivo ranged from 2-5 weeks. Static (bioactivity, bone to implant contact) and dynamic (mineral apposition rates- MAR) histomorphometric measurements were recorded. Biomechanical testing was performed by pullout and torque to interfacial failure testing. Results. Combination of the characterization techniques showed that all bioceramic coatings were Ca- and P-based bioceramics of amorphous microstructure. AFM +ToF-SIMS showed that IBAD 11 coatings were thicker (300-500 nm) compared to IBAD I coatings (30-50 nm). Surface roughness did not change significantly for the IBAD implant groups compared to control. The in-vivo results showed higher degrees of osseoactivity, torque to failure, and MAR for the coated implants at different times in-vivo. [BAD 11 had higher biomechanical fixation at early implantation times compared to other groups. Conclusions: The results obtained in the in-vitro part this study support that both IBAD I and IBAD 11 coatings are Ca- and P- based amorphous bioceramics in the nanothickness range with theoretical high dissolution rates. The increased osseoactivity observed for [BAD coated and the high MAR v allies observed for IBAD coated compared to AB/AE implants support the effect of the bioceramic coating presence in the overall bone healing. A thickness effect was reveled through biomechanical testing where IBAD 11 (300-500nm thickness) presented higher performance.

AIM: Static Hertzian contact tests of monolayer glass-ceramics in trilayer configurations (glass-ceramic/cement/composite) have shown that thick cement layers lower strength. This study sought to test the hypothesis that thick resin cement layers lower mouth motion fatigue reliability for flat glass-ceramic/cement/composite trilayer systems and that aging in water reduces reliability. METHODS: Dicor plates (n > or = 12 per group) (10 x 10 x 0.8 mm(3)) were aluminum-oxide abraded (50 microm), etched (60 s), silanized, and bonded (Rely X ARC) to water aged (30 days) Z100 resin blocks (10 x 10 x 4 mm(3)). Four groups were prepared: (1) thick cement layer (>100 microm) stored in water for 24-48 h, (2) thick cement layer stored for 60 days, (3) thin cement layer (< or =100 microm) stored for 24-48 h, and (4) thin cement layer stored for 60 days. The layered structures were fatigued (2 Hz) utilizing mouth motion loading with a step-stress acceleration method. A master Weibull distribution was calculated and reliability determined (with 90% confidence intervals) at a given number of cycles and load. RESULTS: The aged group (60 d) with thick cement layer had statistically lower reliability for 20,000 cycles at 150 N peak load (0.11) compared with both nonaged groups (24-48 h) (thin layer = 0.90 and thick layer = 0.82) and aged group with thin cement layer (0.89). CONCLUSION: Trilayer specimens with thick cement layers exhibited significantly lower reliability under fatigue testing only when stored for 60 days in water. The hypothesis was accepted. These results suggest that diffusion of water into the resin cement and also to the glass-ceramic interface is delayed in the thick cement specimens at 24-48 h.

The purpose of this study was to develop a technique to evaluate the implant-abutment gap of an external hexagon implant system as a function of radius. Six implants of 3.75 mm in diameter (Conexao Sistema de Protese Ltda, Sao Paulo, Brazil) and their respective abutments were screw connected and torqued to 20 N cm(-1). The implants were mounted in epoxy assuring an implant long-axis position perpendicular to the vertical axis. Each implant was grounded through its thickness parallel to implant long-axis at six different distance interval. Implant-abutment gap distances were recorded along the implant-abutment region for each section. Individual measurements were related to their radial position through trigonometric inferences. A sixth degree polynomial line fit approach determined radial adaptation patterns for each implant. Micrographs along implant sections showed a approximately 300 mum length implant-abutment engagement region. All implants presented communication between external and internal regions through connection gaps and inaccurate implant-abutment alignment. Average gap distances were not significantly different between implants (P > 0.086). Polynomial lines showed implant-abutment gap values below 10 mum from 0 mum to approximately 250 mum of the implant-abutment engagement region. Gap distances significantly increased from approximately 250 mum to the outer radius of the implant-abutment engagement region. The technique described provided a broader scenario of the implant-abutment gap adaptation compared with previous work concerning implant-abutment gap determination, and should be considered for better understanding mechanical aspects or biological effects of implant-abutment adaptation on peri-implant tissues.

INTRODUCTION: The purpose of this study was to evaluate the bone response to statically loaded 2.5-mm diameter mini-implants of 6 and 10 mm lengths activated after various healing periods in a dog model. METHODS: Seventy-eight machined-surface Ti-6Al-4V mini-implants were bilaterally placed in the mandibular premolar and molar regions of 6 beagle dogs. The left (experimental) and the right (control) hemi-arches received 6 and 7 mini-implants, respectively. Experimental mini-implants healing periods of 0 days (immediately activated), 1 week, and 3 weeks were followed by a 12-week load activation period (250 g between parallel implant pairs). Control (nonloaded) mini-implant groups were placed for 12 weeks, 3 weeks, and 1 week before the dogs were killed they provided data concerning the experimental groups' bone to mini-implant scenarios at load activation times. The mandibles were exposed by sharp dissection, and decalcified specimens were prepared for histomorphologic and histomorphometric (bone to mini-implant contact) assessment. RESULTS: Survival rates were 100% and 77.78% for the control and the experimental groups, respectively. Survival rates were 88.89% for the 10-mm and 66.67% for the 6-mm experimental groups. All failed devices had tissue inflammation and were lost after spring placement. The control groups showed classic bone-healing events, and the experimental groups showed mature bone morphology after 12 weeks in vivo regardless of placement time before load activation. Bone to implant contact values were not significantly different between the experimental and the control groups that remained 12 weeks in vivo. CONCLUSIONS: These results showed that low-intensity immediate or early orthodontic static loads did not affect mini-implant performance.