Three-dimensional analysis of initial biofilm formation on polytetrafluoroethylene in the oral cavity.

AIM: There is published evidence that polytetrafluoroethylene (PTFE) exhibits beneficial surface characteristics by means of long-term biofilm accumulation. The purpose of this study was to investigate and compare early biofilm formation on polytetrafluoroethylene, ceramic-reinforced polytetrafluoroethylene and as the control group, stainless steel. MATERIALS AND METHODS: This study comprised 10 healthy volunteers (5 females and 5 males) with a mean age of 27.3 ± 3.7 years. Three different slabs (two PTFE coatings: one pure and one ceramic-reinforced polytetrafluoroethylene, and stainless steel) were placed in random order on a splint in the mandibular molar region. Intraoral splints were inserted for 48 h. After 48 h, we removed the slabs from the splints and stained the biofilm with a two-color fluorescence assay for bacterial viability (LIVE/DEAD BacLight-Bacterial Viability Kit 7012, Invitrogen, Mount Waverley, Australia). The amount of biofilm accumulation was assessed using confocal laser scanning microscopy (CLSM). RESULTS: The biofilm surface coverage was 55.8 ± 39.8% on pure PTFE-coated probes, 55.9 ± 35.0% on ceramic-reinforced PTFE-coated probes, and 33.3 ± 37.8% on stainless steel. The differences among the three groups were not significant (p = 0.301). Biofilm depth was 5.6 ± 5.4 µm on pure PTFE-coated probes, 5.2 ± 3.8 µm on ceramic-reinforced PTFE-coated probes, and 2.4 ± 2.9 µm on stainless steel. The Friedman test revealed a significant difference in biofilm depth (p = 0.002). Pairwise comparison of biofilm accumulation yielded a significant difference between pure PTFE and ceramic-reinforced PTFE compared to stainless steel (p = 0.017; p = 0.005). CONCLUSION: Our results indicate that the beneficial surface characteristics of PTFE coatings by reducing long-term biofilm are not a result of inhibiting initial bacterial adhesion.

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.