Dental resins with reduced shrinkage during hardening

Unsaturated spiro-orthocarbonates are monomers that expand on polymerization and will co-polymerize with conventional BIS-GMA based resins. This combination has good physical properties and bonding to enamel with some polymerization expansion evident at 50 C. Dispersion of the carbonate in microcrystalline form in liquid monomer appears to be a method to allow its reaction in the initial polymerization.

[Studies on dental self-curing resins. (17). Adhesion of PMMA with bovine enamel or dental alloys (author's transl)]

We synthesized 4-methacryloxyethyl trimellite acid (4-MET) and anhydride (4-META), and tried them as a reactive comonomer for adhesives to bovine enamel. In the case of non-etched enamel, tensile adhesive strength was 40-50 Kg/cm2 after one day immersion in 37 degrees C water, but it decreased below 10 Kg/cm2 after a month immersion in 37 degrees C water. It could be concluded that this adhesion was not sufficient for practical usage. Then we applied this method to an etched enamel. After a series of experiments we concluded that it was necessary to etch bovine enamel surface with 30% citric acid for practical usage. Adhesion of some dental alloys with a PMMA rod was also studied and adhesive strength in Co-Cr alloy was over 150 Kg/cm2 either after one month immersion in 37 degrees C water or 60 times thermal cycles between 4 degrees C and 60 degrees C.