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.

Reliability of Different Bending Test Methods for Dental Press Ceramics.

OBJECTIVE: This study investigates the reliability of different flexural tests such as three-point-bending, four-point bending, and biaxial tests, in strengthening the dental pressed ceramics (DPCs) frequently used in clinical applications. METHODS: The correlations between the three types of bending tests for DPCs were investigated. Plate-shaped specimens for the three-point and four-point bending tests and a disc-shaped specimen for the biaxial bending test were prepared. Each bending test was conducted using a universal testing machine. RESULTS: The results for six DPCs showed that the flexural strength in descending order were the three-point flexural strength, biaxial flexural strength, and four-point flexural strength, respectively. Then, a regression analysis showed a strong correlation between each of the three test methods, with the combination of four-point and biaxial flexural strength showing the highest values. The biaxial flexural strength was not significantly different in the Weibull coefficient (m) compared to the other tests, with the narrowest range considering the 95% interval. The biaxial bending test was found to be suitable for materials with small plastic deformation from the yield point to the breaking point, such as DPCs.

Mechanical Properties of Selective Laser Sintering Pure Titanium and Ti-6Al-4V, and Its Anisotropy.

Selective laser sintering (SLS) is being developed for dental applications. This study aimed to investigate the properties of Ti-6Al-4V and pure titanium specimens fabricated using the SLS process and compare them with casting specimens. Besides, the effect of the building direction on the properties of the SLS specimens was also investigated. Specimens were prepared by SLS using Ti-6Al-4V powder or pure titanium powder. Casting specimens were also prepared using Ti-6Al-4V alloys and pure titanium. The mechanical properties (tensile strength and elongation), physical properties (surface roughness, contact angle, and Vickers hardness); corrosion resistors (color difference and corrosion), and surface properties (chemical composition and surface observation) were examined. Both Ti-6Al-4V and pure titanium specimens produced using the SLS process had comparable or superior properties compared with casting specimens. In comparing the building directions, specimens fabricated horizontally to the printing platform showed the greatest tensile strength, and the surface roughness scanned in the horizontal direction to the platform showed the smallest. However, there was no significant effect on other properties. Thus, the SLS process with Ti-6Al-4V powder and pure titanium powder has great performance for the fabrication of dental prosthesis, and there is a possibility for it to take the place of conventional methods.

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.

Color change capacity of dental resin mixed with silver methacrylate caused by light irradiation and heating.

We synthesized silver methacrylate, added it to resin for dental use, and observed color changes in the resin from colorless to red-purple following light irradiation. Therefore, 0.01-0.10 wt% silver methacrylate was added to two types of resin powder, i.e., self-curing resin produced by the polymerization of a barbituric acid derivative, quaternary ammonium, and an organometallic compound (Type I), and BPO-tertiary amine resin (Type II), and samples were produced by polymerization with the attached monomer. Changes with time in the color of samples from 3 hours (new samples) to 16 days (old samples) after polymerization and also color changes of old and new samples after heating were evaluated. Subsequently, changes in color with variations in the light intensity, irradiation time, and wavelength were evaluated in terms of color differences.