Patient demand for durable, esthetic, anti-cariogenic dental materials that requires minimal tooth preparation for placement has led to renewed interest in glass ionomers. Glass ionomer has low polymerization shrinkage, has coefficient of thermal expansion similar to that of tooth structures and can minimize microleakage by chemical adhesion to tooth structures and metal. Sustained fluoride release allows site-specific caries control. Unfortunately, the presently available glass ionomer formulation suffers from having poor tensile strength, low modulus of elasticity and solubility. One of the problems lies in the polyacrylic acid structure of the glass ionomer. The carboxylic acid groups reside in direct attachment to the polymer backbone resulting in a very rigid structure. Due to steric hindrance, some carboxyl groups become inaccessible, preventing their participation in cross-linking with Ca+ + and Al+ + + from glass fillers and Ca+ + from tooth structures. The objective of this proposal is to develop an ionomer formulation through the incorporation of amino acid derived monomers with carboxylic acid groups at various distances away from the polymer backbone, to allow for greater flexibility, less rigid ionic cluster, better filler dispersion and physicochemicaI adhesion to tooth structures. This concept and technique have been substantiated in polymer chemistry literature and were supported by our preliminary data where significant increases in tensile and flexural strengths in such flexible polymers were found. The formulation of monomers and polymers will be analyzed and characterized. The optimal monomer ratios and the molecular weights of the polymers will be determined to maximize their physical properties. Selected mechanical properties (diametral tensile strength, compressive strength, flexural strength, abrasion resistance) of the new polymer will be tested; acid solubility, bond strength to enamel and dentin, and the microstructures of the improved ionomers will be tested and examined. The micromechanisms for ionomer failure remains unclear. Accomplishing the goals for eliminating the weak links in the microstructures that governs fracture propagation and for improving the physical properties through modification of basic polymer structures are crucial to the further development of reinforced visible light cured ionomer systems.
