The goals of the proposed research are to develop a pulp-capping material that can also serve as a base/lining cement, consisting of tetra- and dicalcium phosphates (TTCP and DCPA), hydroxyapatite (HAp) and carboxylated monomers/polymers. The cement combines the advantages of light-curing, pulp-capping and glass ionomer cements. The cement is termed """"""""Synthetic Dentin"""""""" (SD) because it is composed of calcium phosphates and a polymer.
The specific aims of the proposal are: (1) to formulate cements with sufficient pH levels of 8-10 and 10-12 and diametral tensile strength (DTS) of 16 MPa, (2) to make a two-paste system of SD with physical properties that do not decline more than 20% within 6 months of storage, (3) to develop SD with adhesiveness to dentin while maintaining ideal pH and high strength by adjusting the composition of resin, fillers, (4) to introduce anticariogenicity, (5) to evaluate SD in vivo, by studying the stimulation of dentin bridging over exposed pulps in animal teeth, (5) to evaluate a dentin substitute for instrumental and/or toxicity analyses. The experimental design intends to optimize pH and strengths, which will be measured for two resin systems and four concentrations of TTCP with the two Ca/P ratios of 1.96 and 2.05. The resin systems consist of pyromellitic glycerol dimethacrylate and two carboxylated and one carboxyl-free diluent resin. To facilitate the use of SD, a two-paste system will be tested by 24 h DTS after 1, 3, and 6 months of storage. Factors influencing the adhesiveness of SD to dentin are: (i) the type of resin, (ii) the presence of water in the liquid phase, (iii) the filler type and (iv) concentration, and (v) the presence of internal stresses in the cured cement. A 2/5-1 fractional factorial design will be used to evaluate the effect of factors i-v on pH, DTS and the shear bond strength. Two selected formulations of SD will be tested in vivo on exposed pulps in dogs (7 teeth per formulation). Reproducibility of material properties of the dentin substitute will be assessed by permeability, XPS and IR spectroscopy.
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