Evaluation of thermal conductivity and flexural strength properties of poly(methyl methacrylate) denture base material reinforced with different fillers.

STATEMENT OF PROBLEM: Poly(methyl methacrylate) (PMMA) is widely used in prosthodontics as a denture base material. However, it has several disadvantages, including low strength and low thermal conductivity. PURPOSE: The purpose of this in vitro study was to evaluate thermal conductivity and flexural strength after adding powdered Ag, TiO2, ZrO2, Al2O3, SiC, SiC-nano, Si3N4, and HA-nano in ratios of 10 wt% to PMMA. MATERIAL AND METHODS: A total of 144 specimens were fabricated and divided into 18 groups. Specimens were left in water for 30 days. Thermal conductivity values were measured using a heat flowmeter, flexural strength was measured with a 3-point bend test, and specimens were investigated with environmental scanning electron microscopy. One-way ANOVA was used to compare means followed by using Duncan multiple range test (α=.05). RESULTS: The thermal conductivity value of PMMA increased significantly after the addition of Si3N4, SiC, Al2O3, SiC-nano, TiO2, ZrO2, HA-nano, and Ag. Progressive increases in thermal conductivity were observed in Si3N4, SiC, and Al2O3 fillers. Flexural strength values of the control group were not significantly different from those of the SiC, Al2O3, or Ag group (P>.05). In the other groups, flexural strength values decreased significantly (P<.05). On the basis of electron microscopy, we observed that Si3N4, SiC, and Al2O3 powders had higher thermal conductivity values that are dissipated more homogeneously in PMMA. CONCLUSIONS: Although the addition of 10 wt% SiC, Al2O3, and Ag powder to PMMA significantly increased thermal conductivity, the flexural strength values of PMMA were not significantly changed.

Effect of different post space irrigation procedures on the bond strength of a fiber post attached with a self-adhesive resin cement.

STATEMENT OF PROBLEM: The effects of different post space irrigation procedures on the bond strength of a self-adhesive resin cement to the root canal dentin are still unclear. PURPOSE: The purpose of this in vitro study was to evaluate the effects of alternative post space irrigation procedures on the cement strengths of posts attached with a self-adhesive resin cement. MATERIAL AND METHODS: Forty single-rooted teeth were selected, and after root canal preparation and obturation, post spaces were prepared. The teeth were divided into 4 groups corresponding to the post space irrigation procedure and treated as follows: the distilled water (DW) group (control) received 15 mL of distilled water; the NaOCl+ethylenediaminetetraacetic acid (EDTA) group was treated with 5 mL of 5.25% NaOCl, 5 mL of 17% EDTA, and 5 mL of distilled water; the chlorhexidine (CHX) group was treated with 15 mL of 2% chlorhexidine solution; and the phosphoric acid (PA) group treatment consisted of etching the walls of the prepared post holes with 35% phosphoric acid. Fiber posts were attached with a self-adhesive resin cement, and specimens were cut horizontally for push-out testing. The statistical evaluation consisted of 1-way ANOVA with the post hoc Tukey honest significant differences test (α=.05). RESULTS: The NaOCl+EDTA treatment yielded a significantly higher bond strength than those used in the other 3 groups (P=.003). No statistically significant differences were found among any of the other groups, as different root regions showed similar bond strength values (P>.05). CONCLUSIONS: The results showed that EDTA in combination with NaOCl could be advantageous for post space irrigation when fiber posts are bonded with a self-adhesive resin cement.

Comparison of the metal-ceramic bond after recasting and after laser sintering.

STATEMENT OF PROBLEM: Failure of the bond between metal and ceramic is common with metal ceramic prostheses. PURPOSE: The purpose of this in vitro study was to investigate how recasting affects the metal-ceramic bond strength for 1 base metal and 1 noble alloy compared with laser-sintered Co-Cr alloy by using a procedure based on ANSI/ADA Specification No. 38. MATERIAL AND METHODS: One laser-sintered (Co-Cr) and 2 metal (Co-Cr, Pd-Ag) alloys were used. Metal strips (25 × 3 × 0.5 mm) were obtained with 2 different methods: torch melting and laser sintering. Twelve alloy specimens were processed for each group. Vita VM13 porcelain layers (8 × 3 × 1.1 mm) were fabricated at the centers of the metal frameworks. Specimens containing 100% fresh alloy were used in the first casting group (control). Metal ceramic specimens were prepared for each alloy, and no new metal was added to the second and third castings. The findings were statistically analyzed and compared with a 2-way analysis of variance (ANOVA). RESULTS: The second casting of the noble alloy-ceramic specimen had the highest mean metal-ceramic bond strength in flexure. No significant differences were found between the laser-sintered Co-Cr and the Pd-Ag metal ceramic specimens after the first and third castings. CONCLUSION: All groups had adequate porcelain bond strength, except C2 (second casting of Co-Cr alloy) and C3 (third casting of Co-Cr alloy). Co-Cr alloy fabricated with new laser-sintering techniques is a promising alternative for metal ceramic restorations. Further research is needed before its use can be advocated in the dental laboratory.