Abstract :
[en] Dental implants are nowadays a reliable solution to replace missing teeth and have been widely documented. However, they require a minimal bone quantity (in height and thickness). But alveolar bone defects are very frequent, for instance due to periodontitis, traumatism or acute dental infection. Moreover, a simple tooth extraction leads to significant bone resorption. Therefore, alveolar bone regeneration is often necessary in order to place implants and to restore the patient's dentition with implant-supported prosthesis. Even though alveolar bone reconstructions have been considered as traumatic, especially due to the need of a second surgical site for bone harvesting, techniques have evolved with the introduction of biomaterials. However, it is difficult to compare the influences of such biomaterials on osteogenesis and to elaborate on the advantages of one product over another.
The overall objective of this thesis is to contribute to the understanding of the biological concept of alveolar bone regeneration, in particular sinus lift and socket preservation procedures. The influence of biomaterials on bone regeneration has been emphasized through preclinical and clinical studies.
The number of commercially available biomaterials for bone regeneration is growing every day and some materials are not supported by strong scientific data in the literature. The first part of this thesis (Chapter 1) is dedicated to the characterization of several biomaterials often used in dentistry. The impact of their various characteristics on osteogenesis has been reviewed, from chemical aspect to micro- and macromorphology. Furthermore, a data sheet integrating the physico-chemical and morphological properties of each studied biomaterial has been developed as a tool for clinicians.
Sinus floor elevation has often been considered as a bone graft. In 1996, a consensus conference on “sinus lift” took place and the procedure was qualified as “sinus bone-graft”. But new scientific evidence has shown that this qualification is not justified. Chapter 2 aims at understanding the physiology and the biological model of sub-sinusal bone augmentation by using either a simple blood clot, autogenous bone chips or biomaterials (BHA) as space fillers under the lifted sinusal membrane. If bone formation did occur with the 3 types of space fillers, the augmented volumes significantly dropped with the blood clot or the autogenous bone chips but remained stable with BHA. Therefore, a slowly resorbable biomaterial such as BHA might be suitable in sub-sinusal bone augmentation to prevent the re-expansion process.
Understanding the biological concept of sinus lift procedures, several authors demonstrated the clinical efficacy of biomaterials when used alone in this specific model. Nevertheless, biomaterials known to be resorbable led to a lamellar bone architecture that might not be able to maintain the volume of the regenerated tissue over time. Moreover, many types of biomaterials are available and scientific evidence of short and long-term performance of newly introduced biomaterials is still poor. Chapter 3 aims at comparing the performances, in terms of bone formation, resorption rate and 3-D stability, of four calcium phosphate-based biomaterials often used for sub-sinusal bone augmentation, in a rabbit model. Particulated space-filling biomaterials seemed to be more efficient to promote osteogenesis compared to paste-like biomaterials. Highly resorbable biomaterials appeared to withstand intrasinusal pressure after a period of six months in rabbits.
Non- or slowly resorbable biomaterials are of great interest in the dental field because the long-term stability of 3-D bone augmentation is a key factor for dental implant and aesthetic outcomes. Therefore, the mechanical and non-resorbable properties of titanium, known to be highly compatible in vivo and highly resistant to body fluid corrosion, are potential advantages for bone augmentation prior to dental implantation. Nevertheless, the use of titanium particles as space fillers in bone regeneration was weakly reported in the literature from a histological point of view. Thus, Chapter 4 compares the behavior and the effect of porous titanium particles versus the well-documented BHA. Even though both biomaterials allowed osteogenesis and adequate 3-D stability, the bone architecture, and more specifically the amount of bone-to-material contact (BMC), was significantly different.
Inclusion of the particles in a carrier or in binding agents such as a collagen gel or fibers might be of interest in order to ease surgical handling. However, the possible influence of those collagen carriers on bone tissue responses remains poorly investigated. The objective of Chapter 5 was to investigate the effect of collagen at different stages of the osteogenesis process, still in the same rabbit model. The findings clearly showed the presence of inflammatory cells at an early stage of bone regeneration when collagenated xenogenic biomaterials were used compared to collagen-free xenogenic granules. Nevertheless, despite the transient inflammation, the final quantity of newly formed bone was similar in the various groups.
The last two chapters of this thesis take some of the preclinical findings of the previous chapters to the clinical field.
The objective of Chapter 6 was to assess the clinical outcome of a minimalized sub-sinusal bone augmentation procedure using only biomaterials, simultaneously with the placement of 102 non-submerged implants in 40 patients. Implant and prosthodontic survival rates as well as complications were evaluated after a follow-up period of 2 to 6 years. This clinical trial emphasized that, if the amount of remaining bone height is sufficient to ensure implant primary stability, their placement can be performed simultaneously with sinus lifting, even in a non-submerged fashion. This procedure reduces the number of surgeries and the time before prosthetic rehabilitation.
The objective of Chapter 7 was to to develop a new method to objectively evaluate in humans the 3-D volume variation of alveolar socket preservation over time by means of computed tomography and 3-D image analysis.
Short summary:
Before placing dental implants, alveolar bone regeneration is often required due to bone defects caused by periodontitis, traumatism or even a simple tooth extraction. Bone augmentation surgical procedures have very much evolved thanks to a better understanding of biological processes and to the introduction of biomaterials.
The overall objective of this thesis is to bring a contribution to the understanding of the biological concept of alveolar bone regeneration, and in particular sinus lift and socket preservation procedures. The influence of biomaterials on bone regeneration has been emphasized through preclinical and clinical studies.
