Effects of Removal Conditions on Mercury Amount Remaining in the Oral Cavity and inside Drainage System after Removing Dental Amalgams.

Mercury is produced and drained into the environment by removing dental amalgams, which may cause mercury pollution. This study aimed to clarify the mercury amount remaining in the oral cavity and inside the drain system after removal. The effects of the removal conditions and differences in drainage systems were also investigated. Dental amalgams filled in the tooth and placed in a phantom head were removed using an air turbine under several conditions (two removal methods, absence of cooling water, and intraoral suction). Then, the oral cavity was rinsed with 100 mL of water (oral rinse water), and 500 mL of water was suctioned to wash the inside of the drainage system (system rinse water). Both water samples were collected in two ways (amalgam separator and gas-liquid separator), and their mercury amounts were measured. It was found that the amount of mercury left in the oral cavity and drainage system after dental amalgams removal could be reduced when the amalgams were removed by being cut into fragments as well as using cooling water and intraoral suction. In addition, using amalgam separators can significantly reduce the amount of mercury in the discharge water and prevent the draining of mercury into the environment.

Effect of resin composite filler on digital imaging fiber-optic transillumination.

Using a trans-illumination device that applies digital imaging fiber-optic transillumination (DIFOTI) technology, which involves the use of transmitted near-infrared laser light for inspection, the effect of composite resin (CR) restoration of a tooth on caries detection was evaluated. A cavity was formed in a tooth of the lower jaw cut from the specimen, experimental CRs with various filler rates were filled, and the influence of the filler on the obtained image was investigated. On the near-infrared images, the lightness differences between the CR-restored portion and the tooth portion were measured. The translucency parameter (TP) value and the correlation between the lightness differences and TP value of the CRs were investigated. The experimental results showed that the greater rate of macro-filler is, the lighter image and larger TP value. In other words, CR with hybrid filler to increase the TP value is less likely to affect caries detection by DIFOTI.

Correlations among bending test methods for dental hard resins.

Three types of bending tests -the 3-point bending test, 4-point bending test and biaxial flexural test- were performed to examine the correlations among the testing methods for dental hard resins (HRs). The results for 5 HRs showed that the bending strengths in descending order were: biaxial flexural strength>3-point bending strength>4-point bending strength. Regression analysis of the test methods indicated that the coefficients of determination were large for all test methods; the largest was for the combination of the 4-point bending test and biaxial flexural tests. The Weibull moduli ranged from 5.42 to 10.61, and a similar descending-order trend was found in the Weibull characteristic strength (S0) of the test methods. The biaxial flexural test method is thus a valid test of the flexural strength of dental hard resins.

Application of noble metal cluster to PMMA resin and influence on mechanical properties and color.

To improve the mechanical strength of denture base resin, several types of noble metal cluster were introduced into PMMA, and the mechanical properties and color changes were evaluated. Complex salts of gold, silver, platinum, and palladium were used as the raw materials of noble metal clusters, and after adding each cluster to MMA, polymerization and thermal treatment were performed to produce PMMA-noble metal cluster complexes. Bending deflection, bending strength, and Vickers hardness were measured, and the formation conditions of metal clusters were investigated using EPMA, SEM, and TEM. Furthermore, color changes between before and after metal cluster creation were measured. The bending deflection increased with the addition of silver and platinum, and decreased with the addition of palladium. The bending strength was lowest with the addition of gold, highest with the addition of palladium. Vickers hardness increased with the addition of palladium. Color differences increased with increasing thermal treatment temperature.