Environmental damage and occlusal contact area wear of composite restoratives.

The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in-vivo degradation of composite resins. The resin matrix can be softened and fillers constituents can be leached out when composites are exposed to certain chemicals/food-simulating liquids (FSLs). A reciprocal compression sliding wear device was used to study the effects of the chemical environment on occlusal contact area (OCA) wear of four composite restoratives (Silux Plus, Z100, Ariston pHc and Surefil). The effects of FSL on hardness was also investigated and correlated to wear. Thirty-six hardness/wear specimens of each material were made and stored in artificial saliva at 37 degrees C for 24 h. The specimens were then divided into six groups of six specimens and stored in the following FSL for 1 week at 37 degrees C: distilled water (W), 0.02 N citric acid (C), 0.02 N lactic acid (L), heptane (H) and 75-25% ethanol-water solution (E). Conditioning in artificial saliva (S) was used as control. After conditioning, the specimens were wear tested at 20 MPa contact stress against SS304 counter-bodies in the respective FSL/artificial saliva up to 20 000 cycles. Wear depth (lm, n=6) was measured using profilometry. Change in hardness (DeltaKHN, Knoop hardness number) was determined by microhardness testing pre- and post-conditioning. Results of statistical analyses (ANOVA/Scheffe's at significance level 0.05) of wear data were as follows: Silux - S, W > L, H, E and C, L > H; Z100 - S, W > all other mediums and E > H; Ariston - all other mediums > H; Surefil - W, C > S, L, H, E (> indicates significantly more wear). With the exception of Surefil, the greatest wear was observed with conditioning and wear testing in water. This ranged from 93.18 +/- 21.96 lm for Z100 to 31.43 +/- 2.80 lm for Surefil. For all materials, conditioning in heptane resulted in the least wear. This ranged from 8.9 +/- 2.2 microm for Ariston to 16.5 +/- 5.9 lm for Silux. The effects of the different FSL on OCA wear were material dependent. No correlation was observed between DeltaKHN and wear.

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator. Part II. An SEM evaluation.

The qualitative wear of amalgam alloys and composite resins opposing cast chromium alloys after impact-sliding wear simulation with the BIOMAT wear simulator was assessed. An impact stress of 28 MPa was adopted to allow for stresses generated during parafunctional activities. The worn specimens were examined using SEM at both impact sites and region of sliding wear. For amalgam alloys, ranking from the smoothest to the roughest surface under SEM observation was as follows: unicompositional alloy>admixed alloy>gallium alloy. For composite resins the ranking was: microfilled composite>small particle composite>hybrid composite. The qualitative SEM assessment results were consistent with our earlier volumetric wear results and supports the hypothesis that surface microstructure affects wear. Composite selection for teeth opposing cast chrome prostheses should be done with caution and knowledge of the composition of the material as three-body wear may occur.

Effect of food-simulating liquids on surface characteristics of composite and polyacid-modified composite restoratives.

The chemical environment is one aspect of the oral environment that could have an appreciable influence on the in vivo degradation of composite resins. The effects of food-simulating liquids on the surface roughness and hardness of composite (Silux Plus, Z100, Spectrum TPH, and P50) and polyacid-modified composite resins (F2000 and Dyract AP) were thus investigated and compared. Sixty disks of each material were made. Half were used for microhardness testing and the remaining half for studying surface roughness using profilometry. Each group of 30 disks was subdivided into six groups of five and conditioned for one week as follows--Group 1 (control): air at 37 degrees C; Group 2: distilled water at 37 degrees C; Group 3: 0.02 N citric acid at 37 degrees C; Group 4: 0.02 N lactic acid at 37 degrees C Group 5: heptane at 37 degrees C; Group 6: 50% ethanol-water solution at 37 degrees C. Data were analyzed using one-way ANOVA and Scheffé's test at a significance level of 0.05. Results showed that the surface roughness of all restoratives evaluated was not significantly affected by food-simulating liquids. No significant change in surface hardness was noted with conditioning of Spectrum TPH, Dyract AP, and F2000 in the various food-simulating liquids. The BIS-GMA-based composites Silux Plus, Z100, and P50 appeared to be more susceptible to the softening effects of some food-simulating liquids.

Comparative wear ranking of dental restoratives with the BIOMAT wear simulator.

Fundamental in vitro wear tests are important for the study of wear mechanisms, provision of data during material development and screening of materials prior to clinical trials. The aim of this project was to compare the wear of six dental restoratives using the BIOMAT wear simulator which was developed to simulate jaw movements and stresses generated in the occlusal contact areas during the chewing process. The correlation of wear to hardness of the restoratives was also assessed. Wear ranking from the least to the most volumetric wear was as follows: high copper unicompositional alloy, Tytin (T) < high copper admixed alloy, Valiant PhD (V) < microfilled composite resin, Silux Plus (S) < gallium alloy, Galloy (G) < heavily filled composite resin, Z100 (Z) < hybrid composite resin, P50 (P). The high copper amalgam alloys had significantly greater wear resistance when compared with all the composite resins. The gallium alloy, microfilled and heavily filled composite resins also exhibited significantly less wear than the hybrid resin. Wear ranking with the BIOMAT simulator was similar to that obtained in vivo. Ranking from the hardest to softest material: high copper unicompositional alloy, T < gallium alloy, G < high copper admixed alloy, V < hybrid composite resin, P < heavily filled composite resin, Z < microfilled composite resin, S. The amalgam alloys were significantly harder than the heavily filled and microfilled composite resins. There was no apparent correlation between wear performance and material hardness.

Bruxing-type dental wear simulator for ranking of dental restorative materials.

An instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.