Yasuko Nakaoki

Effect of remaining dentin thickness on microtensile bond strength of current adhesive systems

The purpose of this study was to evaluate the effect of remaining dentin thickness (RDT) on the bond strength of current adhesive systems. Third molars were randomly allocated among four groups depending on the adhesive system used: Clearfil SE Bond ONE (SE1), G-Bond PLUS (GB), BeautiBond (BB), and Clearfil Mega Bond (MB). Bonded specimens were stored in water at 37°C for 24 h. Teeth were then sectioned perpendicular to the adhesive interface to produce beams. After measuring RDT of each beam, microtensile bond strength test was carried out using a universal testing machine at a crosshead speed of 1 mm/min. All data were analyzed by linear regression analysis. Bond strengths of one-step self-etch materials used in this study increased with an increase in RDT. In contrast, that of two-step self-etch adhesive system was not affected by RDT.

Colloidal platinum nanoparticles increase mitochondrial stress induced by resin composite components

Components of dental composites have been implicated as metabolic and oxidative stressors in cells. Antioxidant colloidal platinum nanoparticles (CPtN) could be useful as nanofillers that reduce cellular stress caused during placement and exposure to unpolymerized composite components. Yet, CPtN may have pro- or anti-oxidative properties depending on the chemical environment in which they are used. This study investigated the ability of CPtN to mitigate mitochondrial or oxidative stress induced by camphorquinone (CQ) and dimethylaminoethyl methacrylate (DMAEM), two components of dental composites that initiate light-activated addition polymerization. THP-1 human monocytic cells were exposed to subtoxic concentrations of CQ and DMAEM, then blue light for 0-60 s. Mitochondrial and oxidative stress were estimated 0, 6, or 24 h after irradiation by measuring cellular ATP or GSH levels, respectively. CPtN (0-20 ppm) were added prior to blue light irradiation. Statistically significant effects were determined by ANOVA with Tukey post-hoc analysis (α = 0.05). Light alone did not alter THP-1 activity, but CQ and DMAEM induced 120% increases in cell ATP levels, which was increased further (50%) by CPtN. Blue light irradiation caused a 50% drop in ATP levels, which increased to 75% when CPtN were added. GSH levels were suppressed by CQ/DMAEM and blue light, and CPtN increased suppression by 20-30%. CPtN did not mitigate mitochondrial or oxidative stress in THP-1, but amplified these stresses under the conditions tested.

Microtensile bond strength of a newly developed resin cement to dentin

The purpose of this study was to evaluate the microtensile bond strength (µTBS) of a newly developed resin cement, ECD-89 (ECD, Tokuyama Dental, Tokyo, Japan) to dentin and to observe the interfacial micromorphology by comparing with two commercial resin cements, Multilink Automix (MA, Ivoclar Vivadent AG, Schaan, Liechtenstein) and Panavia F2.0 (PF, Kuraray Noritake Dental, Tokyo, Japan). Flat dentin surfaces of human third molars were exposed using #600 SiC. After application of primer and cement to the dentin surface, each cement was applied and cured with light (light condition) or without light (dark condition). The teeth were sectioned to obtain beams (1 mm×1 mm) after 24 h of water storage. The mean bond strengths and SDs (MPa) were: ECD: 68.6±14.9, MA: 39.2±18.9, PF: 39.4±18.5 and ECD: 54.5±22.4, MA: 36.7±15.6, PF: 13.4±4.46 when cured in light and dark condition, respectively. In both conditions, ECD-89 showed statistically higher µTBS than the others.