The aim of this study was to examine defect depths and volumes at the resin composite-dentin (R/D) interface after air polishing with different particles and spray angles. Samples were 54 dentin specimens that were formed in saucer-shaped cavities filled with resin composite. Each specimen was air polished with either sodium bicarbonate (NaHCO3) or one of two glycine (Gly) powders. The air polisher was set at angles of 90° to the interface and at 45° to the interface from both the dentin and resin composite sides. Air polishing with Gly powder produced defects with less depth and volume than NaHCO3 powder (p < 0.05). Air polishing with a spray angle of 45° to the interface from the resin composite side produced fewer defects (p < 0.05) than polishing from the dentin side. Air polishing to the R/D interface from the resin composite side produced fewer defects to the interface because the hardness of the resin composite was higher than that of dentin.

In the early stages of biofilm accumulation, the electric charge of the dental enamel and pellicle surfaces is known to be involved. We therefore investigated the relationship between oral hygiene and intraoral electric potential (IoP) in 45 male participants using a double-blind study. IoP, but not body surface electric potential, was loosely correlated with oral hygiene condition (Oral Hygiene Index; OHI). IoP was also loosely correlated with smartphone use; however, there was no significant correlation between smartphone use and OHI. IoP elevation might be caused by OHI elevation resulting from biofilm formation as an internal factor, with smartphone use as an external factor. This in vitro study revealed the generating capacity of Streptococcus mutans accompanied by biofilm accumulation using a microbial fuel cell. These results suggest that IoP elevation is caused by biofilm accumulation induced by power generation of oral bacteria, resulting in elevation of OHI.

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Abstract：The purpose of this study was to evaluate the plaque removal effects of an electric interdental toothbrush and a conventional manual interdental toothbrush at the proximal surfaces of model teeth. The electric interdental toothbrush was composed of a main body with a motor that generated the vibrations and a PROSPEC ® interdental toothbrush attachment. The manual interdental toothbrush did not vibrate. The mean plaque removal rate of the electric interdental toothbrush was 26％ and 32％ after 5 and 10 cleanings, respectively, and these removal rates were significantly higher(p＜0.01)than those for the manual interdental toothbrush. Based on these findings, it is concluded that the plaque removal effect of the electric interdental toothbrush was greater than that of the manual interdental toothbrush.