[ 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

[ comparison of solubility of zinc phosphate and polycarboxilate based on Iranian standard No 2725 and 2726]

Zinc phosphate and polycarboxilate cement have wide application in operative, pedodontics dentistry and fixed prosthodontics. The Ariadent zinc phosphate and polycarboxilate cements are manufactured in Iran. One of the important and necessary properties of each cement to be used in oral cavity is its low solubility. The purpose of the present study was to determine and compare the solubility of Harvared zinc phosphate and polycarboxilate cement with Ariadent. In this experimental study that was based on specification No 2725 and 2726 of Iranian standard, ten discs shaped samples with 1 +/- 0.03 mm width and 10 +/- 0.3 mm diameter was constructed for each cement. Zinc phosphate solubility with spectrophotometry and polycarboxilate solubility with conductivity evaluation was measured. The data were analyzed with T test. Statistical analysis was significant [p<0.05]. The mean value of solubility for Harvard and Ariadent zinc phosphate cement was in order 1.23 +/- 0.24 and 0.86 +/- 0.15 mgr P205 per gr. There was statistically significant difference between the two above cements [p=0.001]. The mean value of solubility for Harvard and Ariadent polycarboxilate cement was in order 39.27 +/- 4.40 and 37.85 +/- 3.05 simence on the meter per kg. There was no statistically significant difference between the two above cements [p=0.4]. In accordance to determined values from Iranian standard No 2725 and 2726, the mean value of solubility of 4 experimental cements in this study was within standard limits

Comparing the retention of two luting agents with common core type materials

A major part of dental work is associated with fixed prosthodontics. The permanence of cemented restorations is based on different factors for instance, retention, appropriate cement and applying the correct way of use. The aim of this study was to compare the retention of zinc phosphate and polycarboxylate cements with the common core build up materials such as amalgam, composite, casting alloy and coremax II. In this experimental study twenty 6x6 mm cylinders were produced from every core build-up material. The teeth were prepared by means of mounting and cutting by high speed h and piece. To build - up a substitutionary crown cylinder, 100 cylinders were made by means of based metal casting alloy ingut with external diameter of 12 mm, height of 6 mm and a 6.1 mm hole in the center. 10 samples were cemented with zinc phosphate and the other 10 with polycarboxylate. The samples were placed under the dartec machine and the neccessary power for egress of piston from cylinder was measured by the dartec. The data were analyzed by SPSS software, factorial ANOVA and Duncan tests. The retention mean value of zincphosphate cement to casting alloy, Amalgam, Composite, Coremax II and the tooth sample was respectively as follows: 77 +/- 5, 71 +/- 5, 37 +/- 4, 32 +/- 2 and 24 +/- 2 MPa. The retention mean value of polycarboxylate cement to tooth, Amalgam, casting alloy, Composite and Coremax II was respectively as follows: 37 +/- 3, 32 +/- 6, 22 +/- 4, 10 +/- 1 and 8 +/- 1 MPa. ANOVA test demonstrated statistically significant differences between retention mean value of zinc phosphate and polycarboxylate cement with 5 core build-up materials [P<0.001]. The reason of more retention in polycarboylate cement to tooth structure can be related to chemical bonding between tooth and cement. The results of this study revealed that the casting alloy provided more retention than amalgam. The more retention of amalgam in comparison with composite and coremax II can be related to a more powerful compressive strength of amalgam

comparison of the accuracy and dimensional stability between two silicon impression materials [Speedex and Irasil]

Condensation silicons are more commonly used in fixed Prosthodontics than other elastomers. The aim of this study was to compare the accuracy and dimensional stability of two condensation silicons: Speedex and Irasil. A metal master model containing two abutments representing two prepared teeth with definite dimensions was prepared and a metal tray was made. 40 impressions were taken [20 of each impression material] and 10 of them were poured with die stone [Prevest] after 30 minutes and the other IC were poured after 120 minutes, according to the manufacturer's instructions. Using a steriomicroscope M6c-l 0 and Digital camera motican-480 the following dimensions were measured three times on the metal and stone models: [1] x = distance between the center of the abutments [2] y1 = height of the abutment with an undercut [3] y2 = height of the abutment without an undercut [4] z1 width of the abutment with an undercut, and [5] z2 = width of the abutment without an undercut. The difference between the dimensions of the main and stone models was assessed, Multivariance and T-tests were used for statistical analysis. There was no significant difference in dimensional stability between groups I and 4 [Speedex, 30' and Speedex, 120'] and between groups 2 and 3 [Irasil, 30'-120']. A significant difference was observed between Speedex and Irasil in both time periods [30 and 120 minutes]. The difference between the die stone and the master model was significant in mesiodistal [x] and buccolingual [H] dimensions for both materials. A significant difference was also found between Irasil and the main model in occlusogingival [y1] and buccolingual [z2] dimensions in both time periods, but Speedex failed to show a significant difference in the same dimensions and time periods. In the y2 dimension in contrast to Irasil, Speedex demonstrated a significant decrease of dimensional stability. Timing did not affect the dimensions of the two impression materials. The mesiodistal dimensions [x] of both Speedex and Irasil increased on the casts. A significant difference was found in dimensional stability between Speedex and Irasil impression materials

[ comparison of the film thickness and compressive strength between Ariadent and Harvard zinc phosphate cement]

Recently, the Ariadent Zinc phosphate cement has been introduced to market with low cost. Some dentists purchase this product because of low cost and others avoid buying it because of unreliable quality. The two important properties of ideal dental cement are to have the minimum film thickness [less than 25 micron] and to have favorable compressive strength. The purpose of this study was to determine the mean and to compare the film thickness and compressive strength of Ariadent and Harvard Zinc phosphate cement.In this experimental study evaluation was made based on Iranian standard number 2725. To measure film thickness of each cement, the first step was to prepare two glass slabs and their thickness was measured with micrometer, then each cement was prepared according to standard procedure and was put between the glass slabs. The difference between glass slabs with and without cement was measured. This procedure was repeated 3 times and average of three measurements were obtained and determined as mean of cement film thickness. To determine the compressive strength of each cement at first a mold was fabricated according to standard procedures. Then each prepared cement was poured in to the mold. After 24 hours each of five prepared specimens was Put under load and the average compressive strength was calculated. The mean film thickness for Arident Zinc phosphate was 42.33 +/- 4.50 micron and for Harvard cement was 24.3 3 +/- 5.70. The mean compressive strength of Ariadent Zinc phosphate cement was 44.90 +/- 4.11 MPa and for Harvard cement was 62.85 +/- 5.19 MPa. The statistical analysis [t-student] revealed significant difference between two phosphate cement. In this study mean film thickness of Iranian Ariadent Zinc phosphate cement was more than standard level [25 micron] and the mean compressive strength was less than standard level [70 MPa]. These results indicated that Ariadent cement was of low quality and below standard. But Harvard Zinc phosphate cement had a standard film thickness and its compressive strength was close to standard and this is a reason for acceptable quality of Harvard Zinc phosphate cement