[Durability of protective effect of resin-based coating material on root surface]

To compare the durability of resin-based root-surface coating material and all-in-one self-etching adhesive on root surface in vitro.

Human extracted premolars or molars with intact roots were selected. The cementum was removed using a periodontal scaler to expose root dentin. The root surface was coated with an acid-resistant nail varnish, leaving a window of 3 mm×3 mm on the exposed dentin.The window was covered with either PRG Barrier Coat (PRG) or Clearfil S3 Bond (CS3). After water aging for 14 d, specimens were immersed in acid buffer at pH 4.5 for 4 d and the demineralization buffer was changed every 24 h. Then the specimen was split longitudinally through the center of the 'window' and the cross-sectional surface was observed with scanning electron microscope (SEM). After fixed and dehydrated, the prepared samples were coated with platinum. The coating material, root dentin and the interface was observed by scanning electron microscope (SEM). The thickness of the coating material was measured on the SEM images. Regarding toothbrush wear test, coronal dentindisks were prepared and covered with PRG and CS3, respectively. After storage in water for 24 h, the specimen was subjected to the toothbrush wear tester for 100, 200, 300, 500, 700, 1 500 brushing cycles. A slurry of fluoride toothpaste (1:2 ratio of toothpaste and deionized water by weight) was used and the brushing load was 300 N. The surface microstructure of remaining coating material was analyzed using SEM. The wear depths were determined by a profilometer. Statistical analysis was performed with SPSS 20.0 by one-way ANOVA. The level of significance was at 0.05.

Application of PRG Barrier Coat produced a coating layer of (47.1±27.3) μm, while CS3 presented a thin film of (5.7±2.1) μm in thickness. The exposed dentin was hermetically sealed and no obvious gap was observed at the interface in both PRG and CS3 groups. There was no dentin demineralization observed in both groups after water aging. The wear depths of PRG and CS3 increased along with the numbers of brushing cycles. PRG wore at a significant lower pace than CS3 did (P<0.05).

PRG coating resin had similar performances as CS3 on protecting root dentin from demineralization after water aging. What's more, PRG demonstrated a higher toothbrush wear resistance than CS3. We concluded that PRG Barrier Coat contained S-PRG filler may be an effective coating material for protecting exposed root from both chemical and mechanical challenges. Further studies should be carried out to evaluate the long-term reliability of the rootsurface coating materials under the clinical setting.