[ vitro comparison of solubility of resin modified glass ionomer and a base containing hydroxyapatite in water, acid and artificial saliva]

Solubility is one of the shortcomings of dental materials that causes decreased physical and mechanical properties and longevity of the restoration. The aim of this in vitro study was to compare the solubility of the resin modified glass ionomer cement and a base containing hydroxyapatite. This experimental study was carried out according to ISO4049:2000[E] and ISO 9917-1:2007[E]. Ten samples of each of the two materials including resin modified glass ionomer and a base containing hydroxyapatite were evaluated for solubility in distilled water and artificial saliva. Evaluation of acid solubility was performed in lactic acid with pH=2.7 +/- 0.02 for 24 hrs. The data were analyzed by two-way ANOVA test. The mean values of solubility in distilled water for RMGIC and base containing hydroxyapatite were 0.6 [ +/- 0.3] and -1.6 [ +/- 1.4], respectively. The means of saliva solubility were 0.007 [ +/- 0.8] and 1.07 [ +/- 1.4], respectively for the mentioned materials. The mean value of acid solubility was 0.000474 [ +/- 0.000784] for RMGIC and 0.000334 [ +/- 0.000221] for Lime-lite. There was no significant difference between values of water sorption and solubility of the two materials [p>0.05]. The solubility of the two tested materials in distilled water, artificial saliva and acid was very little and there was no significant difference between them in this regard

Effect of 10% carbamide proxide on mercury release from two types of dental amalgam

The chemical reactions occur at the amalgam surface when exposed to bleaching agents. Mercury ion is released from dental amalgam when bleached. The aim of this in vitro study was to investigate the effect of carbamide peroxide [CP] on the release of mercury ion from two types of spherical dental amalgam. Two commercial brands of dental amalgam, Cinalux and GS-80, were selected. 18 amalgam discs o any brand were prepared in silicon moulds according to the manufacturer's instructions. After 60 minutes, the discs were removed and individually immersed in artificial salvia [AS] for 24 h at 37°C. Then, the discs of any amalgam were divided into two equal test group [A] and control group [B]. Each specimen in the test group was treated in eight-hour cycles with 10% of CP. The specimens of the control group was treated in similar cycles with AS. All of the solutions were taken for Hg ion release determination, using cold-vapor atomic absorption mercury analyzer system. The data were analyzed using General Linear Model followed by Repeated Measures ANOVA. The results indicated that the bleaching agent significantly caused more mercury ion to be released into the solutions [p<0.05] but artificial salvia did not show this effect. The release rate of mercury from the Cinalux during the two weeks of treatment period with 10% CP showed an increase from 11.63 micro g/lit in the first day to 228.85 micro g/lit in the last day. The release rate from GS-80 showed a decrease from 130.96 micro g/lit in the first day to 80.68 micro g/lit in the last day. Treatment with 10% carbamide peroxide increased mercury release from dental amalgam in comparison with the artificial salvia. The release of Hg from 2 brands of dental amalgam was in a safe range

Evaluation of the effect of polishing on flexural strength of feldspathic porcelain and its comparison with autoglazing and over glazing

Ceramic restorations are popular because they can provide the most natural replacement for teeth. However, the brittleness of ceramics is a primary disadvantage. There are various methods for strengthening ceramics such as metal framework, ceramic cores, and surface strengthening mechanisms through glazing, work hardening and ion exchange. The purpose of this study was to evaluate the effect of polish on flexural strength of feldspathic porcelain and to compare it with overglaze and autoglaze. In this experimental study, one brand of feldspathic porcelain [colorlogic, Ceramco] was used and forty bars [25x6x3 mm] were prepared according to ISO 6872 and ADA No. 69. The specimens were randomly divided into four groups: overglazed, auto glazed, fine polish and coarse polish [clinic polish]. Flexural strength of each specimen was determined by three point bending test [Universal Testing Machine, Zwick 1494, Germany]. Collected data was analyzed by ANOVA and post-hoc test with P<0.05 as the limit of significance. A significant difference was observed among the studied groups [P<0.0001]. According to post-hoc test, flexural strength in overglaze and fine polish group were significantly stronger than clinic polish and autoglaze group [P<0.001]. Although the mean value for overglazed group was higher than fine polish group, this was not statistically significant [P=0.9]. Also no statistical difference was seen between autoglazed and coarse polish group [P=0.2]. Based on the findings of this study, flexural strength achieved by fine polish [used in this study] can compete with overglazing the feldespathic porcelains. It also can be concluded that a final finishing procedure that involves fine polishing may be preferred to simple staining followed by self-glazing