The Influence of Connection on the Microleakage Development of Implant- Supported Fixed Bridges.

PURPOSE: If bacteria penetrate through the implant-abutment connection, they may initiate inflammatory reactions in the peri-implant tissue. It seems that the type of connection plays a key role in the development of peri-implantitis. The aim of the present in vitro study was to compare the microleakage of implant-supported fixed complete arch bridges at the levels of abutment and implant. METHODS: Ten identical polyurethane model bases containing six implants each were produced using an edentulous model of the upper jaw. These models were prepared with two types of implant-supported complete arch prostheses. Five specimens were fixed at implant level and five at abutment level. The inner parts implants were inoculated with Escherichia coli (E.coli). Each implant was surrounded with closed bacteria-proof vessels to observe bacterial migration from the inner parts of implants to the nutrient solution. Samples of nutrient solution were taken at different time points up to 2 to 10 days and colony forming units were determined. RESULTS: The bacterial accumulation in the implant-supported bridges at the implant level was significantly lower than at the abutment-level (p=0.00953). CONCLUSION: For implant-supported fixed complete arch prostheses, bacterial accumulation was lower at the implant level than at the abutment-level.

Stress analysis of an all-ceramic FDP loaded according to different occlusal concepts.

The aim of this study was to investigate the influence of four different occlusal concepts on stress distribution in a four-unit fixed dental prosthesis (FDP) made of zirconia. A three-dimensional finite element (FE) model was created and four model versions with between 15 and 42 contact points were developed. A force of 300 N was distributed over the chewing surface according to the different occlusal concepts and virtually applied perpendicularly to the occlusal plane in each version. Then, FE analysis was performed and stress distribution evaluated. Generally, highest tensile stresses were located at the point of load application within the veneering layer and ranged from 104 to 204 MPa. The highest tensile stresses within the framework were located at the basal side of the connectors and ranged between 12 and 39 MPa. This study shows that the distribution of occlusal contact points significantly influences the stresses induced by occlusal forces in four-unit all-ceramic fixed dental prostheses and strongly suggests that the number and distribution of occlusal contacts may be important to minimise fatigue effects caused by cycling.

Influence of the veneering process on the marginal fit of zirconia fixed dental prostheses.

Distortions in the marginal region during manufacture are detrimental to the long-term success of fixed dental prostheses (FDPs). The aim of the present in vitro study was to evaluate changes in marginal fit because of the veneering process of four-unit FDPs made from different zirconia materials. Two groups of FDPs with 10 specimens each were machined from white body zirconia blanks (VITA In-Ceram YZ Cubes, KaVo Everest ZS-Blanks) by means of computer-aided design/computer-aided manufacturing systems and subsequently sintered to their final density. The marginal and internal gaps of the frameworks were determined using a replica technique. Afterwards, frameworks were veneered with the recommended ceramics (VITA VM9, GC Initial Zr), and fitting accuracy was evaluated again. Statistical analyses were performed by Student's t-test with the level of significance chosen at 0.05. With one framework/veneering system (Everest ZS-Blanks/Initial Zr), both marginal gap (P = 0.019) and internal gap (P = 0.001) at the premolar retainer were significantly affected by the veneering process. The resulting distortions were directed towards the lumina of the retainers and the mean values of the measured gaps decreased by about 23.8 mum (marginal gap) and 27.3 mum (internal gap). For the other system (In-Ceram YZ Cubes/VM9), no distortions because of the veneering were found. The veneering of zirconia restorations may lead to significant changes in the marginal fit, while the combination of core and veneering material used influences the resulting distortions.