Typescript. Bibliography: leaves 131-167.

Objectives: The present work was under taken to compare osseointegration of immediately and delayed restored implants in a sheep model, and to compare methods of assessing osseointegration. Methods: Twenty wide-platform implants were placed in the posterior mandibles of 10 sheep, 3 months after premolar extractions. Ten were control implants placed and restored after 3 months of submerged healing. Ten were test implants placed contralaterally and immediately restored. Animals were sacrificed after a further 3 months of healing. At each experimental stage implant stability was measured with resonance frequency analysis (RFA) and standardized radiographs were taken. Tissue blocks with the implants were embedded in acrylic resin. The specimens were analysed by three-dimensional micro tomogram (micro-CT) images. Ground sections of the tissue blocks were then prepared for light microscopy and quantitative morphometry. Morphometric parameters computed by both methods were mean percent bone-to-implant contact (BIC) and mean percent bone density (BD). Radiographic, stability and morphometric measurements were compared statistically. Results: The survival rate was 60% (controls) versus 40% (test) (p=0.28). Mean crestal bone levels after three months restoration did not differ significantly between control (5.54 � 0.92) and test groups (4.35 � 1.61) (p=0.56). All surviving implants were stable at stage three and RFA values in implant stability quotient (ISQ) did not differ significantly between the two groups (test 82.3 � 3.9 versus control 78.8 � 4.3, p=0.36). No correlation was found between crestal bone loss and RFA (Spearman�s rho =-0.27, p=0.46). Histomorphometric analysis found no statistical difference (%BIC test 65.65 � 12.7%, control 53.36 � 6.41%, p=0.18; and %BD test 54.84 � 8.45%, control 64.69 � 13.57%, p=0.11). A similar trend was observed for mean micro-CT (%BIC test 65.72 � 72, control 50.84 � 4.19, p=0.11). Histology revealed high density inflammatory infiltrates beneath the sulcular and pocket epithelium. No significant difference was found between histomorphometric (HMA) and microCT analysis (%BIC p=0.08, %BD p=0.08). A statistically significant correlation was observed between HMA and microCT for %BIC (Spearman�s rho = 0.89, p=0.02) but not %BD (Spearman�s rho = 0.51, p=0.30). Conclusions: The results suggest that the sheep mandibular model has limited potential for evaluation of implants designed for poor quality bone and for the assessment of implant loading protocols. This thesis does highlight the potential for the use of this model in peri-implantitis studies. The results suggest that morphometric variables determined by HMA and microCT analysis are comparable, however further studies are required to standardize the microCT protocol to reduce metal artifacts and enhance bone-implant contrast.

This inquiry investigated the suitability of the jaw of domestic sheep as an animal model for dental implantology research. Initially, parameters for osseous healing of critical size defects (CSD) in the sheep mandible were established. Pilot studies were conducted using machined-surface implants and a surgical protocol established for dental implant placement in ovine mandibular sites. Subsequent experiments considered the utility of this animal model for examination of techniques designed to enhance osseointegration. Hydroxyapatite-coated implants were compared with titanium plasma-sprayed (TPS) implants, either alone or combined with autogenous bone grafts or a bone graft/collagen vehicle loaded with transforming growth factor-beta (TGF-β). Immunofluorescent bone labelling gave information on the mineral apposition rate (MAR). Implant survival and "acceptability" (likelihood of clinical success) were major output variables, along with histomorphometric analysis of percent bone-implant contact (%BIC) and percent peri-implant bone density (%density). Naturally-occurring "broken-mouth" periodontitis in sheep was identified as a potential confounder. Subsequent experiments considered implants with different surfaces. The model was also extended from a two-stage surgical protocol to include single-stage implants. The effect of pre-existing ovine peridontitis was also examined. A systematic review and meta-analysis of published animal implant experiments was conducted in order to validate the candidate sheep model. Major findings were as follows. The size of non-healing sheep mandibular unicortical CSD is >12mm. Attempts to establish a chronic non-healing CSD were unsuccessful. The sheep diastema proved unsuitable for implant placement. The model was modified to a post-extraction protocol. Implant "acceptability" rates after 3 months integration in the sheep mandible (defined as implant survival with %BIC >10%) ranged from 50% - 100% for different implant surface treatments and placement protocols. Histomorphometriic analyses revealed that %BIC ranged from 11 � 17% to 81 � 29 % for different titanium surfaces and up to 85 � 11% for hydroxyapatite surfaces. Implants with TGF-β plus autogenous bone grafts had %BIC of 36 � 30% compared with 43 � 30% for implants with grafts alone. Bone per unit area (%density) adjacent to, but outside of the implant threads, ranged from 63 � 16% to 86 � 3% and was markedly lower for titanium plasma-sprayed surfaces and for one-stage implants. Within the implant threads, %density varied from 31 � 33% to 73.4 � 8.3%, and was markedly lower for machined titanium surfaces. Sheep periodontitis had little effect on the protocols investigated. The sheep mandibular model was found to be comparable to similar models in other species and merits further development.

Interbody fusion cages are increasingly used in the treatment of spinal disease and injury in order to stabilize movement and promote arthrodesis of the vertebral bodies, but the micro-mechanics of the interaction between the cage and the adjacent host bone is not fully understood. This information has bearing on post-surgical therapy protocols, prediction of long-term bone tissue changes, and optimization of cage design. In order to gain insight into this problem, functional microCT imaging was used to directly evaluate implant micromotion and full-field vertebral body strains in an animal model implemented with various configurations of BAK interbody cages. It is believed that variations in cage design will produce variable implant success, functional fusion will be related to the extent of implant fixation, and specific strain fields will be associated with fused and unfused samples. We found that samples ranged from completely unfused (implant motion) to fully fused with organized trabecular bone (no motion). Strains concentrated at the implant interface in unfused samples, while fully fused samples exhibited uniformly distributed strains. / Graduation date: 2004

Dental and orthopaedic implants are currently the solutions of choice for teeth and joint replacements with success rates continually improving, but they still have undesirable failure rates in patients who are compromised by disease or age, and who in many cases are the ones most in need. The success of titanium (Ti) implants depends on their ability to osseointegrate with the surrounding bone and this, in turn, is greatly dependent on the surface characteristics of the device. Advancements in surface analysis and surface modification techniques have improved the biological performance of metallic implants by mimicking the hierarchical structure of bone associated with regular bone remodeling. In this process, damaged bone is resorbed by osteoclasts, which produce resorption lacunae containing high microroughness generated after mineral dissolution under the ruffled border, as well as superimposed nanoscale features created by the collagen fibers left at the surface. Indeed, increasing Ti surface roughness at the micro and sub-microscale level has been shown to increase osteoblast differentiation in vitro, increase bone-to-implant contact in vivo, and accelerate healing times clinically. Recently, the clinical application of surface nanomodification of implants has been evaluated. Still, most clinically-available devices remain smooth at the nanoscale and fundamental questions remain to be elucidated about the effect of nanoroughness on the initial response of osteoblast lineage cells. Another property that could be used to control osteoblast development and the process of osseointegration is the electrical surface charge of implants. The presence of endogenous electrical signals in bone has been implicated in the processes of bone remodeling and repair. The existence of these native signals has prompted the use of external electrical stimulation to enhance bone growth in cases of fractures with delayed union or nonunion, with several in vitro and in vivo reports confirming its beneficial effects on bone formation. However, the use of electrical stimulation on Ti implants to enhance osseointegration is less understood, in part because of the lack of in vitro models that truly represent the in vivo environment. In addition, an aspect that has not been thoroughly examined is the electrical implication of implant corrosion and its effect on the surrounding tissue. Implants are exposed to extreme conditions in the body such as high pH during inflammation, and cyclic loads. These circumstances may lead to corrosion events that generate large electrochemical currents and potentials, and may cause abnormal cell and tissue responses that could be partly responsible for complications such as aseptic loosening of implants. Consequently, Ti implants with tailored surface characteristics such as nanotopography and electrical polarization, could promote bone healing and osseointegration to ensure successful outcomes for patients by mimicking the biological environment of bone without the use of systemic drugs. The objective of this thesis is to understand how surface nanostructural and electrical characteristics of Ti and Ti alloy surfaces may affect osteoblast lineage cell response in vitro for normal tissue regeneration and repair. Our central hypothesis is that combined micro/nanostructured surfaces, as well as direct stimulation of Ti surfaces with fixed direct current (DC) potentials, can enhance osteoblast differentiation.

This study evaluated differences in dental implant outcomes in patients with osteoporosis and their matched controls. Twenty-four patients, who received dental implants at the University of Toronto, were 60+ yrs and had osteoporosis at the time of implant placement, and their controls matched for age, sex and implant related features were examined clinically and radiographically. Clinical and demographic variables recorded at implant placement and follow-up examination, were analyzed. Implant survival rates of 95.1% and 100%, and success rates of 91.4% and 100% were noted in the osteoporosis and control samples respectively. All failures in the osteoporosis sample occurred in the maxilla of a single subject, raising suspicion that these were related to individual problems specific to this subject. Due to the paucity of adverse outcomes and with all the implant failures having occurred in one subject, no relationship of adverse outcomes with clinical and demographic variables could be analyzed.

This study evaluated differences in dental implant outcomes in patients with osteoporosis and their matched controls. Twenty-four patients, who received dental implants at the University of Toronto, were 60+ yrs and had osteoporosis at the time of implant placement, and their controls matched for age, sex and implant related features were examined clinically and radiographically. Clinical and demographic variables recorded at implant placement and follow-up examination, were analyzed. Implant survival rates of 95.1% and 100%, and success rates of 91.4% and 100% were noted in the osteoporosis and control samples respectively. All failures in the osteoporosis sample occurred in the maxilla of a single subject, raising suspicion that these were related to individual problems specific to this subject. Due to the paucity of adverse outcomes and with all the implant failures having occurred in one subject, no relationship of adverse outcomes with clinical and demographic variables could be analyzed.

Reproduction de : Thèse de doctorat : Psychologie : Lyon 2 : 2002. / Titre provenant de l'écran-titre. Bibliogr.

Thèse d'exercice : Chirurgie dentaire : Université de Nantes : 2005. / Bibliogr. f. 131-139 [104 réf.].

Thèse d'exercice : Chirurgie dentaire : Université de Nantes : 2004. / Bibliogr. f. 110-118 [97 réf.].