We have developed calcium phosphate electrets. The term electret indicates a solid material with high dense surface charges introduced by electric poling. Electrets can spontaneously irradiate surfaces of surrounding substances such as organic and inorganic molecules, and cells and tissues in vivo. We have confirmed the validity of those electrets for manipulation of cells and tissues. The fundamental properties of electrets will be introduced with “biomanipulation” characteristics.

This study evaluated the effect of contamination by handpiece lubricant spray on the microtensile bond strength (μTBS) of bonded denture base resins. We also investigated the effects of various surface pre-treatments on the recovery of μTBS. Denture-based MMA resin was polymerized and shaped into 12 x 12 x 7 mm blocks. One side of the cut surfaces was abraded using #120 SiC paper and contaminated with lubricant spray. After applying 14 different surface treatments to each contaminated surface, blocks were bonded using auto-cured MMA resin and compared with an uncontaminated control. The lubricant spray-contaminated group showed significantly lower μTBS (23.4±5.3 MPa) than the uncontaminated control (58.3±5.4 MPa；p＜0.05). Only groups with soaking or ultrasonic cleansing in aqueous solution of sodium bicarbonate or ultrasonic cleansing in commercial denture cleaner showed recovery of μTBS to the same level as or higher than the uncontaminated control.

In this study, the mechanical properties of single shade composites resins (CRs) with color-matching ability were evaluated by surface hardness tests using a dynamic ultra-micro hardness tester and bending tests using a universal testing machine. These tests were performed on four single shade CRs and their four corresponding blockers. Also, six conventional CRs as a control group were examined, leading to a total of 14 different CRs to compare mechanical properties.As a result, dynamic hardness, indentation elastic modulus, and flexural modulus showed a positive correlation with the filler content. On the other hand, flexural strength showed no correlation with the filler content. In addition, no difference in mechanical properties was observed between the single shade and conventional CRs. Therefore, these new materials are considered to be clinically applicable in the same way as conventional materials.