Biomechanical Study Of Implant Restoration In The Posterior Maxillary Region With Atrophy Varying In Degrees

Owing to its comfortability, fine appearance and high success rate, implant restoration has become the optimal choice for edentulous patients. However, with the existence of maxillary sinus and decreasing height of residual alveolar bone, clinicians are frequently confronted with the insufficiency of vertical bone height in the posterior maxilla. Especially the poor bone quality of those who have lost their teeth for a long time makes it more difficult to perform implant restoration in this region. Thus primary stability of implant can hardly be realized, leaving implant restoration in the posterior maxilla less successful than any other regions.Nowadays, with the improvement of maxillary sinus augmentation, this technology effectively address the problem of insufficient bone volume, greatly widening the application of implant restoration. For those patients with obvious bone deficiency in the posterior maxilla, grafted maxillary sinus augmentation is conventionally carried out before implant insertion. Although this procedure has been approved by a wealth of previous studies, the optimal bone substitutes remain controversial. Autogenous bone is considered to be the preferable bone grafts because of its desirable osteoconduction, osteogenesis and osteoinduction. But there exist some evident drawbacks of autogenous bone, involving a second surgical site, tissue injury in donor sites and limited quantities of available bone, which restricts the clinical application of autogenous bone. Various kinds of new synthetic bone substitutes were invented thanks to the development of tissue engineering, as promotes a far-reaching progress in dental implant surgical technique. The ideal bone grafts should satisfy several standards, such as facilitating cell colonization, providing scaffold structure and so on, but the present graft materials are unable to attain all of the requirements. Moreover, successful cases of non-grafted maxillary sinus augmentation were constantly reported and this kind of surgical technique is gradually being accepted by clinicians. Some researchers pointed out that employing graft materials increased the risk of postoperative infection, resulting in the failure of implant restoration. Therefore, in order to avoid the trauma and complications ensuing from maxillary sinus augmentation, short implants are recommended for particular patients with an acceptable residual bone height. And quite a few clinical trials have confirmed the curative effect of short implant.To sum up, when it comes to the implant restoration in the posterior maxillary region, two major factors, the selection of implants and application of maxillary sinus augmentation, need further research. This study" utilize three-dimensional finite element method to evaluate the stress distribution in the implant-bone interface and analyze the corresponding biomechanical effects. The major parts of this study are listed as follows. Although finite element analysis is unable to realize a quantitative analysis of stress magnitude in maxilla, the results of qualitative analysis still possess certain value for clinical practice.1. Three-dimensional finite element analysis of influence of maxillary bone quality on implant stabilityPurpose:The present study evaluated the biomechanical effects induced by implant configuration and bone quality within an augmented posterior maxilla. The aim of this study was to ascertain the optimal choice of implant on the basis of actual bone conditions. Materials and methods:A couple of simplified maxillary segment models vary in bone quality (D2, D3 and D4 type) were constructed. Implants were embedded into the atrophic posterior maxilla with only 8 mm residual bone height. An oblique force of 150 N was applied to the occlusal surface of implant and maximal equivalent von-Mises stress was evaluated. Results:The standard implant with its apical part embedded in high-stiffness graft exhibited the best stress distribution pattern among all groups. The short wide implant could also realize a desirable stress allocation similar to high-stiffness group in D2 and D3 bone. Stress in supporting bone increased concomitantly with the reduction of bone quality. Conclusions:Bone quality should be one of the crucial factors taken into consideration before implant placement. Short wide implant could realize a similar stress distribution pattern as the standard does when bone quality was preferable. Grafted maxillary sinus augmentation was more recommended for implant rehabilitation in maxilla with poor quality.2. Three-dimensional finite element analysis of impact of residual bone volume of posterior maxilla on implant stabilityPurpose:The aim of this study was to explore the biomechanical impact induced by grafted and non-grafted maxillary sinus augmentation in a posterior maxillary model with different atrophy degrees. Materials and methods:A series of simplified maxillary segment models varying in residual bone height (10 mm,7 mm,5 mm,3 mm) and bone quality (D3 and D4) were established. Standard implants (10 mm) were integrated into the maxillary models. An oblique force of 150 N was applied to the occlusal surface of implant and maximal equivalent von-Mises stress was evaluated. Results:Bone quality had an enormous impact on stress magnitude of supporting bone. Applying sinus augmentation in combination with grafts was beneficial for stress distribution and high-stiffness graft performed better than low-stiffness one. For 7 mm and 5 mm atrophic maxilla, non-grafted maxillary sinus augmentation was feasible in D3 bone group. Conclusions:Poor bone quality was a negative factor for implant placement in the atrophic posterior maxilla, which could be improved by grafts to a certain extent. The choice of maxillary sinus augmentation approaches should be determined by the residual bone height and quality.