Efficacy of polyphasic calcium phosphates as a direct pulp capping material.

OBJECTIVES: Polyphasic calcium phosphates (Poly-CaP), a complex of hydroxyapatite (HAp) and soluble calcium phosphates including alpha-tricalcium phosphate and tetracalcium phosphate, demonstrate promoting effects on hard tissue formation by osteoblasts. We hypothesized that a Poly-CaP block with a soluble calcium phosphates phase on one side and an insoluble HAp phase on the other side is useful for vital pulp therapy as it may promote dentin regeneration and provide the surface effective to achieve sealing. The purpose of this study was to investigate the efficacy of Poly-CaP as a direct pulp capping material by examining the Ca-release profile, the in vivo ability to induce reparative dentinogenesis, and the bonding of HAp surface with adhesive systems. METHODS: Poly-CaP prepared by annealing crude HAp disc was immersed in buffer solution at pH 7.4 or 4.0, and the concentration of Ca released was measured until 15 days. The pulp of 9-week-old Wister rat molar was exposed and capped with Poly-CaP or HAp block, and dentin bridge formation and pulpal inflammation was evaluated histopathologically after 2 or 4 weeks. Etch & rinse or self-etching adhesive was bonded to HAp surface, and the interface was observed using SEM. RESULTS: Poly-CaP exhibited continuous release of Ca with significantly greater amount than HAp at both pH conditions (P<0.05, Student's t-test). Animal tests demonstrated formation of complete dentin bridge at higher rate for Poly-CaP compared with HAp after 4 weeks (P<0.05, Steel-Dwass test). Impregnation of resin into etched HAp surface, with production of intimate contact at the bonding interface, was seen for all adhesives. CONCLUSIONS: Poly-CaP is a potentially useful material for direct pulp capping with the advantages to promote dentin bridge formation and to provide tight sealing by adhesives.

Polymerization contraction stresses of resin-based composite restorations within beveled cavity preparations of Class I restorations.

PURPOSE: To evaluate internal stresses resulting from polymerization of resin-based composite materials in cavity preparations beveled at the internal line angles or the cavosurface margin, compared with those in conventional butt-joint box-shaped cavity preparations. MATERIALS AND METHODS: Contraction stress generated in resin-based composite restorations placed in an experimental cavity preparation model was determined using micro-photoelastic analysis. Three types of cavity preparations simulating Class I restorations with bevels at internal line angles (1 mm and 2 mm deep), and at the cavosurface margin (2 mm deep) were prepared in a posterior composite model in order to obtain no marginal defect with the restorative composite. The transparent restorative composite was bulk-filled into the preparations and light-cured for 80 seconds. Specimens 2 mm thick for micro-photoelastic analysis were cut perpendicular to the long axis of the preparation. Fringe patterns for directions and magnitudes of stresses were obtained using transmitted and reflected polarized light. Then, the photoelastic stress analysis was performed to examine stresses in the preparations. The data were statistically compared with the previous data in conventional butt-joint box-shaped preparations by ANOVA and Scheffé's F test (P < 0.05). RESULTS: In 1 and 2 mm deep internal beveled cavity preparations, the maximum principal stress lines were parallel to the wall at the straight internal bevels. In the preparation with a round bevel at the cavosurface margin, the stress distribution in the bulk of the preparation was similar to that in the butt-joint preparation. Maximum stress values in 1 and 2 mm deep internal beveled preparations were 12.2 +/- 0.2 MPa and 18.8 +/- 2.8 MPa, respectively. For 2 mm-deep preparation, the maximum stress values in the internal beveled preparations were significantly lower than those values in butt-joint box-shaped cavity preparations. Maximum stress values in the preparations with the bevel at the cavosurface margin were 22.7 +/- 1.0 MPa, and were not significantly different from those values observed in the butt-joint preparations.