No abstract

Background and aim: Changes in the physical properties of casts retrieved from disinfected impressions are a common problem in the fabrication of dental prostheses. However, there are limited data available about the effect of disinfecting solutions on the surface roughness of casts. This study aimed to assess the surface roughness of casts retrieved from addition silicone impressions disinfected by immersion in three different disinfectants for 5 and 30 minutes. Materials and methods: This in-vitro experimental study was conducted on 49 casts in 7 groups (n=7). A standard stainless steel die was used according to ANSI/ADA specification no. 25, and impressions were made using a low-viscosity addition silicone impression material. The impressions were disinfected by immersion in 1% sodium hypochlorite (NaOCl), 2.4% glutaraldehyde, or 5% povidone-iodine for 5 and 30 minutes. All impressions were poured with type IV dental stone, and their surface roughness (Ra) was measured using a digital hand-held roughness tester. Data were analyzed using two-way analysis of variance (ANOVA) and Tukey's test. Results: One-way ANOVA showed a statistically significant difference between the control group and the other 6 groups (P=0.004). 1% NaOCl/5 minutes was the only group which presented a different result from the control group (P=0.012). Two-way ANOVA showed that over time, the surface roughness of casts retrieved from silicone impressions disinfected by immersion in a disinfectant decreased (P=0.002), but no significant difference was noted between the disinfectant agents (P=0.243). Conclusion:The type of the disinfectant had no significant effect on surface roughness, although an increased duration of disinfection decreased the surface roughness of casts.

Background and Aim: Resin cements are used widely in restorative dentistry regardless of their biocompatibility. The aim of this study was to compare the cytotoxicity of two categories of dental cements consisting of three chemically set cements (Fuji I, Fuji PLUS and Harvard) and two dual curing cements (BisCem and Duo-Link) by use of MTT assay. Methods and Materials: In this experimental study, four round-shaped samples of each specimen were placed in DMEM culture medium for 24, 48 and 72 hours. The extracts from each sample were applied on L929 mouse fibroblasts. At the end of each period, MTT assay was carried out to estimate the mitochondrial respiration. Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey's post-hoc test. The degree of cytotoxicity for each sample was determined according to the reference value of the control group. Results: Fuji I cement showed the least cytotoxicity while Harvard and BisCem cements showed the highest cytotoxic effect. The differences were not significant compared to the positive control (distilled water). Conclusion: This study showed that dental cements are capable of eliciting biological response in gingival and pulpal cells. They present a potential risk of tissue damage which depends on the cement's brand and curing modes.

Background and Aim: High chipping rates of the veneering porcelain in zirconia ceramic restorations have been reported in many clinical studies. However, information on the bonding behavior of veneering porcelain to zirconia and lithium disilicate frameworks is limited. The purpose of this study was to evaluate the bonding strength of porcelain veneering to zirconia, lithium disilicate, nickel-chromium (Ni-Cr) and cobalt-chromium (Co-Cr) alloys. Materials and Methods: In this in vitro experimental study, core specimens were fabricated with 12 mm height and 11 mm diameter, and veneering specimens were fabricated with 7 mm height and 5 mm diameter according to the manufacturer's instructions in four groups (n=12) as follows: Group I: Ni-Cr alloy, group II: Co-Cr alloy, group III: lithium disilicate, and group IV: zirconia. The shear bond strength (SBS) test was performed in all samples with a universal testing machine with a crosshead speed of 0.5 mm/min. The fractured samples were examined under a stereomicroscope (×10) to determine the mode of failure. The results were analyzed by one-way ANOVA (P<0.05). Results: Maximum SBS was recorded in group IV (zirconia; 34.6 MPa) followed by groups II 30.66 MPa), 30.58 MPa), and III (lithium disilicate; 20.05 MPa). One-way ANOVA revealed no significant difference between the study groups (P=0.174). Conclusion:The SBS of porcelain veneering to zirconia, lithium disilicate, Ni-Cr, and Co-Cr alloys was not significantly different.

No abstract