[ effect of addition of calcium hypochlorite disinfectant on setting expansion and surface hardness of dental stone]

Addition of disinfectants to dental stones is one method to prevent cross-contamination between patients and laboratory personnel. This study aimed to evaluate the effect of addition of calcium hypochlorite disinfectant on setting expansion and surface hardness of dental stone. In this experimental study, calcium hypochlorite aqueous solution with 0.5% concentration was added to type V dental stone. Setting expansion was measured by extensometer in millimeter and surface hardness was measured by Rockwell hardness test machine. Data were statistically analyzed using t-test with 0.05 level of significance. The mean setting expansion values were 2.49 +/- 0.0017 mm and 0.27 +/- 0.0094 mm in the test and control groups, respectively and had a statistically significant difference. The mean Rockwell hardness number was 74 +/- 1.93 and 85 +/- 3.09 in the test and control groups, respectively with no statistically significant difference. Setting expansion and surface hardness of type V dental stone increased and decreased, respectively by the addition of 0.5% calcium hypochlorite. Thus, this disinfection method needs modification for routine use in the laboratory setting

Comparison of physical properties of an iranian and a german dental stone type iv according to ada specifications

Dental stone type IV and V are predominantly used for construction of cast and die in fixed prosthodontics and must have some special properties. The aim of this study was to compare the three physical properties of an Iranian a German dental stone type IV. In this experimental study, setting time, setting expansion and compressive strength properties were evaluated according to ADA specification No.25for Iranian Tara and German Gildand type IV dental stone. For setting time, setting expansion and compressive strength tests, Vicat apparatus, extensometer and universal testing machine were used, respectively. Data were compared to ADA specification No.25 for dental stone type IV and statistically analyzed using t-test with a 0.05 level of significance. Mean of setting expansion for Iranian and German dental stone were 0.024 +/- 0.011 and 0.0245 +/- 0.009, respectively and were within the limits of ADA specification and there was no statistically significant difference between them [P=0.966]. Mean of setting time for Iranian and German dental stone were 44.5 +/- 0.70 and 17. +/- 0.41 and mean of compressive strength for Iranian and German dental stone were 16.17 +/- 0.97 and 20.15 +/- 1.96 and both specifications were not within the limits of ADA specification, but statistically significant differences were found between groups [P<0.001]. Iranian dental stone type IV could not fulfill 2 out of 3 tested ADA specification and modification of this stone is necessary for use in fixed prosthodontics laboratory processes

effect of 15% carbamide peroxide bleaching on the shear bond strength of composite to enamel

Carbamide peroxide bleaching has been implicated to adversely affect the bond strength of composite to enamel. The purpose of this study was to evaluate the effect of carbamide peroxide bleaching on the shear bond strength of composite to bleached enamel bonded with a three step total etch system; Scotchbond Multipurpose [SBMP], and two simplified all-in-one systems; Prompt L-Pop [PLP] and i bond. Seventy two human molar teeth were randomly assigned to three control and three experimental groups. The experimental groups were subjected to a%15 carbamide peroxide bleaching system. Twenty four hours later, all the control and experimental groups were bonded with cylinders of composite, using three dental bonding agents. After thermocycling, shear bond strengths were determined by a universal testing machine. The data were evaluated using one way ANOVA and Duncan tests [P < 0.05]. The composite bond strengths of SBMP were 19.52 +/- 15.21 MPa to the unbleached and 7.95 +/- 4.16 MPa to the bleached enamel. For PLP, the unbleached enamel exhibited bond strengths of 9.6612.89 MPa and, the bleached one showed a bond strength value of 5.3910.66 MPa. For i-bond the composite bond strengths were 11.46 +/- 4.31 MPa to the unbleached and 6.41 +/- 2.01 MPa to the bleached enamel. There was a statistically significant difference between the shear bond strength of the control and experimental groups of each dental bonding agent [SBMP, P < 0.001, PLP, P < 0.001, i bond: P = 0.002]. Bleaching with 15% carbamide peroxide used in this study reduced the bond strengths of the composite to the enamel bonded with a three step total etch and two simplified one step all-in-one dental bonding agents