PubMed · 6919997
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1982-06-23. Postbasic nursing procedures. 10. Plaster cast 1.. https://pubmed.ncbi.nlm.nih.gov/6919997/
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AIM: To evaluate the sealing ability of calcium sulphate when used under composite resin for the repair of furcation perforations having different diameters. METHODOLOGY: Perforations of different diameter were created in the floors of pulp chambers in 60 extracted human molar teeth with either a number 3 (1 mm diameter) or 5 (1.5 mm diameter) round bur. The specimens of each group were divided into four sub-groups which were repaired with composite resin either alone or in combination with calcium sulphate that created an artificial floor (15 teeth group(-1)). Eight teeth without furcation perforations served as negative controls. In the leakage detection device, 1 mol L(-1) glucose solution was forced under a pressure of 1.5 KPa from the crown towards the pulp chamber floor. The concentration of leaked glucose was measured at 1, 2, 4, 7, 10, 15 and 20 days using a glucose oxidase method and the data evaluated using the rank sum test. RESULTS: The specimens with larger perforations repaired with composite resin alone had significantly more leakage (P < 0.05). Using calcium sulphate as an artificial floor significantly decreased leakage of smaller perforations (P < 0.05). In groups repaired with calcium sulphate under composite resin, leakage in smaller perforations was markedly lower than that in larger ones (P < 0.05). No significant difference was found between the specimens with 1 or 1.5 mm perforations repaired with resin alone (P > 0.05). CONCLUSIONS: Calcium sulphate significantly improved the sealing ability of 1 mm perforations repaired with composite resin but not for 1.5 mm perforations.
Thermal effects produced in a laser-irradiated sample were studied by micro-X-ray diffraction and micro-Fourier transform infrared spectroscopy (FTIR). Gypsum, transformed into bassanite at 124 degrees C and into anhydrite at 147 degrees C, was used as a thermal indicator. Pit formation by a wavelength-tunable free electron laser (FEL) irradiation on the gypsum pellet maximized at a wavelength of 3.0 microm, 2 mJ/shot, and pits were not detected in those irradiated at 2.6 or 3.8 microm compared with the maximum at 3.0 microm and diminished at 2.0 or 4.0 microm in the human tooth case. Micro-X-ray diffraction and micro-FTIR did not reveal any appreciable bassanite or anhydrite in the irradiated regions. From the laser ablation viewpoint, these results allow the FEL ablation to be considered as plasma or evaporative ones. This study indicated that the micro-pulse of laser was effective to prevent thermal damages of laser irradiation.
AIM: Gypsum products are used for the preparation of stone casts of oral and maxillofacial structures and as important adjuncts to dental laboratory operations involved in the production of dental prostheses. The aim of this study was to determine the effect on the dimensional accuracy of a working cast of adding a stone base using different stone products. METHODS AND MATERIALS: A total of forty impressions of a mandibular dentoform were made. The impressions were dried with compressed air and stored at room temperature for 24 hours before pouring stone casts. The forty impressions were randomly divided into four groups of ten each. All forty impressions were poured once using one pre-weighed 140 Gm package of Silky Rock (SR) Type IV improved stone (Whip Mix Corporation, Louisville, KY, USA ) per impression. All working casts and the die setups were prepared according to the manufacturer's recommendations for pin placement (M.R. Dual pin and sleeve). Four different types of dental stone (II, III, and IV) and Flow Stone (FS) were used as bases for the working models. They were mixed according to the manufacturer's recommendations. The lower posterior teeth were flattened on the dentoform prior to taking the impressions. All were indexed using a mounted abrasive disc. Four teeth were selected as follows: 21, 28, 30, and 18. These represented A, B, C, and D landmarks, respectively. All measurements (five times for each specimen) were made with a Universal measuring microscope (Unitron Instruments, Inc., Bohemia, NY, USA). After the pre-sectioned measurements were recorded, the stone base was poured. A manual hand saw was used to section and fabricate removable dies for the mandibular landmarks A, B, C, and D. The dies were later seated and removed ten times to simulate the average amount of handling during laboratory procedures. Each die was carefully seated and measurements were made using the same technique as for the master model and unsectioned casts. Multivariate repeated measures analysis of variance (MANOVA) was used to test the difference in three different landmark distances (AB, AC, and AD) among the master model before and after sectioning of the working dies and among the four different base materials. Univariate analysis of variance (ANOVA) was conducted for each measurement, AB, AC, and AD to test the difference in landmark distances on the master model at pre sectioning and then at post sectioning using four different base materials. When there was a significant main effect (p < .05), the Student-Newman-Keul's (SNK) were used to test for pair wise comparison of means (P<0.05). RESULTS: The results of the MANOVA indicated there was a significant difference in three landmark measurements on the master model before and after sectioning of the working dies for the four different base materials (F = 6.60, p = 0.0001). In addition there was a significant difference in three landmark measurements on the master model at: (1) pre sectioning (p = 0.0001), (2) between the master model and SR material (p = 0.0002), (3) between the master model and Laboratory Plaster (LP) material (p = 0.0001), (4) between the master model and Quick Stone (QS) material (p = 0.0001), and (5) between the master model and FS material (p = 0.0001).