Faculty Bibliography

Bone remodeling, along with tissue biomechanics, is critical for the clinical success of endosseous implants. This study evaluated the long-term evolution of the elastic modulus (GPa) and hardness (GPa) of cortical bone around human retrieved plateau root form implants. Thirty implant-in-bone specimens showing no clinical failure were retrieved from patients at different in-vivo times (0.3 to approximately 24 years) due to retreatment needs. After dehydration, specimens were embedded in methacrylate-based resin, sectioned along the bucco-lingual long axis and fixed to acrylic plates and nondecalcified processed to slides with approximately 50 mum in thickness. Nanoindentation testing was carried out under wet conditions on bone areas within the first three plateaus. Indentations (n = 120 per implant total) were performed with a maximum load of 300 muN (loading rate: 60 muN/s) followed by a holding and unloading time of 10 s and 2 s, respectively. Elastic modulus (E, GPa) and hardness (H, GPa) were computed. Both E and H values presented increased values as time in vivo elapsed (E: r = 0.84; H: r = 0.78). Significantly higher values for E and H were found after 5 years in vivo (p < 0.001). Maxillary or mandibulary arches or positioning did not affect mechanical properties, nor did implant surface treatment on the long-term bone biomechanical response (E: p >/= 0.09; H: p >/= 0.3). This work suggests that human cortical bone around plateau root form implants presents an increase in elastic modulus and hardness during the first 5 years following implantation and presents stable mechanical properties thereafter. (c) 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.

This study evaluated the early biomechanical fixation and bone-to-implant contact (BIC) of an alumina-blasted/acid-etched (AB/AE) compared with an experimental resorbable blasting media (RBM) surface in a canine model. Higher texturization was observed for the RBM than for the AB/AE surface, and the presence of calcium and phosphorus was only observed for the RBM surface. Time in vivo and implant surface did not influence torque. For both surfaces, BIC significantly increased from 2 to 4 weeks.

PURPOSE: Failures of implant-abutment connections have been observed clinically, especially in single-tooth replacements. This study sought to evaluate the reliability and failure modes of implant-supported anterior crowns restored with different implant systems. MATERIALS AND METHODS: Forty-two Ti-6Al-4V dental implants (~4 mm diameter) were used for single anterior crown replacement and divided into two groups according to tested system: (NB) Replace Select system, Nobel Biocare (n = 21); and (IL) Internal connection system, Intra-Lock International (n = 21). Proprietary abutments were screwed to the implants and anatomically correct maxillary central incisor metal crowns were cemented and subjected to step-stress-accelerated life testing in water. Use-level probability Weibull curves and reliability for a mission of 50,000 cycles at 200 N (95% 2-sided confidence intervals) were calculated. Polarized-light and scanning electron microscopes were used for failure analyses. RESULTS: The Beta values for NB and IL (2.09 and 2.05, respectively) indicated that fatigue accelerated the failure of both groups. The calculated reliability for the NB system (0.81) was lower than for the IL system (0.96), but no significant difference was observed between groups. Screw and abutment fracture was the chief failure mode in group NB, while screw fracture was most representative in specimens of group IL. CONCLUSIONS: Reliability of implant-supported maxillary central incisor crowns was not significantly different between NB and IL abutments. Failure modes differed between implant systems

OBJECTIVES: To evaluate the reliability and failure modes of regular and horizontal mismatched platforms for implant-abutment connection varying the implant diameter. MATERIAL AND METHODS: Regular (REG, n = 21, 4.0-mm-diameter implant) and horizontal mismatched (HM, n = 21, 4.6-mm-diameter implant) platform Ti-6Al-4V implants were restored with proprietary identical Ti-6Al-4V abutments and metal crowns (cobalt-chrome, Wirobond((R)) 280, BEGO, Bremen, Germany) cemented. Mechanical testing comprised step-stress accelerated-life testing, where crowns were distributed in three loading profiles for fatigue in water, producing timely and clinically relevant fractures. The probability of failure vs. cycles (95% two-sided confidence intervals) was calculated and plotted using a powerlaw relationship for damage accumulation, Weibull modulus (95% two-sided confidence intervals) and then the reliability for a mission of 50,000 cycles at 125 N load (95% two-sided confidence interval) were calculated. Fractography was performed in the scanning electron microscope. RESULTS: The beta-value for group REG (beta = 1.37) indicated that fatigue was a factor accelerating the failure, whereas load alone dictated the failure for group HM (beta = 0.71). The Weibull parameter contour plot showed no significantly different Weibull modulus for REG (10.24) compared to HM (10.20) and characteristic strength of 162.6 and 166.8 N, respectively (P > 0.91). The calculated reliability for a mission of 50,000 cycles at 125 N load was not significantly different (0.71 for REG and 0.73 for HM). Abutment screw failure was the chief failure mode. CONCLUSIONS: Reliability was not significantly different between groups and failure modes were similar

Purpose: The purpose of this study was to test the hypothesis that all-ceramic crown core-veneer system reliability is improved by modifying the core design and as a result is comparable in reliability to metal-ceramic retainers (MCR). Finite element analysis (FEA) was performed to verify maximum principal stress distribution in the systems. Materials and Methods: A first lower molar full crown preparation was modeled by reducing the height of proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based preparation was replicated and positioned in a dental articulator for specimen fabrication. Conventional (0.5 mm uniform thickness) and modified (2.5 mm height, 1 mm thickness at the lingual extending to proximals) zirconia (Y-TZP) core designs were produced with 1.5 mm veneer porcelain. MCR controls were fabricated following conventional design. All crowns were resin cemented to 30-day aged composite dies, aged 14 days in water and either single-loaded to failure or step-stress fatigue tested. The loads were positioned either on the mesiobuccal or mesiolingual cusp (n = 21 for each ceramic system and cusp). Probability Weibull and use level probability curves were calculated. Crack evolution was followed, and postmortem specimens were analyzed and compared to clinical failures. Results: Compared to conventional and MCRs, increased levels of stress were observed in the core region for the modified Y-TZP core design. The reliability was higher in the Y-TZP-lingual-modified group at 100,000 cycles and 200 N, but not significantly different from the MCR-mesiolingual group. The MCR-distobuccal group showed the highest reliability. Fracture modes for Y-TZP groups were veneer chipping not exposing the core for the conventional design groups, and exposing the veneer-core interface for the modified group. MCR fractures were mostly chipping combined with metal coping exposure. Conclusions: FEA showed higher levels of stress for both Y-TZP core designs and veneer layers compared to MCR. Core design modification resulted in fatigue reliability response of Y-TZP comparable to MCR at 100,000 cycles and 200 N. Fracture modes observed matched with clinical scenarios.

OBJECTIVES:: To evaluate a novel implant design for immediate implantation. This implant presents a specially designed expanded diameter midcrestal "wing" thread, which is aimed to provide added bone contact for greater insertion torque and primary stability. METHODS:: Mandibular premolars were extracted in 2 mongrel dogs, and immediate dental implants were inserted into the fresh extraction sockets. Implants were evaluated for stability using a resonance frequency analysis device immediately after insertion and after 4 and 8 weeks. Removal torque of 1 randomly selected implant in each hemimandible was measured as well. At 8 weeks, the remaining 6 implants were processed histologically. RESULTS:: Mean implant stability quotient at implant placement was 64.38 (5.03) and 74.5 (3.08) at 8 weeks. Average removal torque immediately after implant placement was 49.65 (20.3) N.cm and 98.33 (12.34) N.cm at 8 weeks. The mean bone-to-implant contact value at 8 weeks was 38.89% (7.65%). CONCLUSIONS:: The examined implant with the expanded diameter midcrestal "wing" thread showed good results of resonance frequency analysis and removal torque during the initial healing phase, and as such, it might be used for immediate implantation and loading.

Laser metal sintering has shown promising results, but no comparison with other commercially available surface has been performed. This study sought to evaluate the biomechanical and histological early bone response to laser sintered implants relative to alumina-blasted/acid-etched (AB/AE). Surface topography was characterized by scanning electron microscopy and optical interferometry. Surface chemistry was assessed by x-ray photoelectron spectroscopy. Beagle dogs (n = 18) received 4 Ti-6Al-4V implants (one per surface) in each radius, remaining for 1, 3, and 6 weeks (n = 6 dogs per evaluation time) in vivo. Bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO) were evaluated. Biomechanical evaluation comprised torque-to-interface failure. The laser sintered surface presented higher S(a) and S(q) than AB/AE. Chemistry assessment showed the alloy metallic components along with adsorbed carbon species. Significantly higher torque was observed at 1 (p < 0.02) and 6 week (p < 0.02) for the laser sintered, whereas at 3 week no significant differences were observed. Significantly higher BIC and BAFO was observed for the Laser Sintered (p < 0.04, and p < 0.03, respectively) only at 1 week, whereas no significant differences were observed at 3 and 6 weeks. The laser sintered implants presented biocompatible and osseoconductive properties and improved biomechanical response compared with the AB/AE surface only at 1 and 6 weeks in vivo.

This study investigated the effect of an Argon-based atmospheric pressure plasma (APP) surface treatment operated chairside at atmospheric pressure conditions applied immediately prior to dental implant placement in a canine model. Surfaces investigated comprised: rough titanium surface (Ti) and rough titanium surface + Argon-based APP (Ti-Plasma). Surface energy was characterized by the Owens-Wendt-Rabel-Kaelble method and chemistry by X-ray photoelectron spectroscopy (XPS). Six adult beagles dogs received two plateau-root form implants (n = 1 each surface) in each radii, providing implants that remained 1 and 3 weeks in vivo. Histometric parameters assessed were bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Statistical analysis was performed by Kruskall-Wallis (95% level of significance) and Dunn's post-hoc test. The XPS analysis showed peaks of Ti, C, and O for the Ti and Ti- Plasma surfaces. Both surfaces presented carbon primarily as hydrocarbon (C-C, C-H) with lower levels of oxidized carbon forms. The Ti-Plasma presented large increase in the Ti (+11%) and O (+16%) elements for the Ti- Plasma group along with a decrease of 23% in surface-adsorbed C content. At 1 week no difference was found in histometric parameters between groups. At 3 weeks significantly higher BIC (>300%) and mean BAFO (>30%) were observed for Ti-Plasma treated surfaces. From a morphologic standpoint, improved interaction between connective tissue was observed at 1 week, likely leading to more uniform and higher bone formation at 3 weeks for the Ti-Plasma treated implants was observed.

Summary Titanium or zirconium computer-aided design/computer-aided manufacturing abutments are now widely used for aesthetic implant treatments; however, information regarding microscopic structural differences that may influence the biological and mechanical outcomes of different implant systems is limited. Therefore, the characteristics of different connection systems were investigated. Optical microscopic observation and scanning electron microscopy showed different characteristics of two internal systems, namely the Astra Tech and the Replace Select system, and for different materials. The scanning electron microscopic observation showed for the Astra Tech that the implant-abutment interface seemed to be completely sealed for both titanium and zirconium abutments, both horizontally and sagittally; however, the first implant-abutment contact was below the fixture top, creating a microgap, and fixtures connected with titanium abutments showed significantly larger values (23.56 mum +/- 5.44 in width, and 168.78 mum +/- 30.39 in depth, P < 0.001). For Replace Select, scanning electron microscopy in the sagittal direction showed that the sealing of titanium and zirconium abutments differed. The seal between the implant-titanium and implant-zirconium abutments seemed to be complete at the butt-joint interface; however, the displacement of the abutment in relation to the fixture in the lateral direction was evident for both abutments with no statistical differences (P > 0.70), creating an inverted microgap. Thus, microscopy evaluation of two commonly used internal systems connected to titanium or zirconium abutments showed that the implant-abutment interface was perfectly sealed under no-loading conditions. However, an inverted microgap was seen in both systems, which may result in bacterial accumulation as well as alteration of stress distribution at the implant-abutment interface.

The biomechanical effects of a non-thermal plasma (NTP) treatment, suitable for use in a dental office, on the surface character and integration of a textured dental implant surface in a beagle dog model were evaluated. The experiment compared a control treatment, which presented an alumina-blasted/acid-etched (AB/AE) surface, to two experimental treatments, in which the same AB/AE surface also received NTP treatment for a period of 20 or 60 s per implant quadrant (PLASMA 20' and PLASMA 60' groups, respectively). The surface of each specimen was characterized by electron microscopy and optical interferometry, and surface energy and surface chemistry were determined prior to and after plasma treatment. Two implants of each type were then placed at six bilateral locations in 6 dogs, and allowed to heal for 2 or 4 weeks. Following sacrifice, removal torque was evaluated as a function of animal, implant surface and time in vivo in a mixed model ANOVA. Compared to the CONTROL group, PLASMA 20' and 60' groups presented substantially higher surface energy levels, lower amounts of adsorbed C species and significantly higher torque levels (p=.001). Result indicated that the NTP treatment increased the surface energy and the biomechanical fixation of textured-surface dental implants at early times in vivo.