In this study, we evaluated the effects of shrinkage correction values (50, 100, 150 μm) and the firing temperature (1450, 1500, 1550℃) on the machining accuracy of semi-sintered zirconia blocks (Y-TZP) to investigate the machining accuracy of CAD/CAM fabricated zirconia frames. The results showed that the machining accuracy was significantly higher both for the shrinkage correction values and firing temperature in the occlusal area, with lower shrinkage correction values at each measurement point of 1.2, 2.0, 3.0, 4.0 and 5.0 mm from the occlusal surface, but these were higher than in the die model. Shrinkage correction values for the firing of semi-sintered zirconia will enable the precise fabrication of zirconia frames for clinical application.

View full abstract

The objective of this study was to evaluate the change in color and glossiness of four types of titanium alloy immersed in an alkaline denture cleanser containing peroxide, and to clarify the surface properties. After immersion in the denture cleanser, commercially pure titanium discolored with prolonged immersion, and this reduced the glossiness. The Ti-6Al-4V and Ti-6Al-7Nb alloys showed more marked discoloration than pure titanium. The Ti-20Cr alloy showed slight discoloration. After the immersion of titanium alloys, the dissolution of the elements from the tested alloys was confirmed. According to surface analysis, the surface of the markedly discolored Ti-6Al-4V and Ti-6Al-7Nb alloys consisted of a four-fold thicker titanium oxide film than that of pure titanium, and the slightly discolored Ti-20Cr alloys had an oxide film with only a one-third thickness. These results suggest that titanium alloys in an alkaline denture cleanser containing peroxide are oxidized by the oxidation reaction of peroxide, and Ti-20Cr alloy has less of an influence regarding oxidation by peroxide on the alloys.

View full abstract

The aim of this study was to evaluate the influence of peroxide type, enzyme type, and Ag⁺-apatite type denture cleansers on the color stability of four commercial metallic materials : cobalt-chromium alloy (Co-Cr), nickel-chromium alloy (Ni-Cr), pure titanium (CpTi), and titanium alloy (Ti-alloy). Color changes were examined with a colorimeter and visual observation during 90 days of denture cleanser immersion. Surface observation of discolored samples was also performed using a scanning electron microscope (SEM). In the samples of Co-Cr and Ni-Cr, no noticeable discoloration was observed. The samples of Ti-alloy immersed in peroxide type and Ag⁺-apatite type denture cleansers, and sample of CpTi immersed in Ag⁺-apatite type denture cleanser showed discoloration after 90 days of immersion. SEM images showed roughness caused by corrosion of the metal surface. These results suggest that the color stability of metallic material is influenced by the metal type and type of denture cleanser used.

View full abstract

The finite element method involves a series of computational procedures to calculate the properties of elements, which requires a model solution. Such a structural analysis allows the determination of stress and strain resulting from external forces. This paper aims to summarize the applications of the finite element method in dental research, and to describe the recent technological advances, with emphasis on the use of non-linear finite element solutions. The literature review focused on the current status and challenges of the use of the finite element method for individual study targets, such as: 1) Non-linear tooth movement, 2) Tooth-to-tooth contact, 3) Implant-abutment contact, 4) Bonded interface, 5) Viscoelastic soft tissue, 6) Fatigue of dental materials, and 7) Bone-implant complex. The further advancement of the non-linear analysis of human oral structures consisting of soft and hard tissues is strongly encouraged to create a wide range of mechanical solutions that would be beneficial for dental and oral health science.

View full abstract