Effect of molar mass of an experimental primer on shear bond strength to dentin

A novel oligomer was synthesized in different molecular masses and used as a primer in dentin bonding. The hypothesis was that an intermediate molecular mass would optimize the conflicting needs for diffusion into etched dentin (low M(w)) and high mechanical properties (high M(w)). The initial oligomer synthesized was tert butylmethacrylate-co-maleic anhydride, which was further reacted to add hyrdoxyethyl methacrylate (HEMA) across the anhydride. The oligomer was synthesized in a series of molecular masses from approximately 800-6000 amu. The oligomer with an average M(w) of approximately 1000 amu provided the highest bond strength (16 MPa), with both lower and higher molar mass oligomers producing lower bond strengths. A polynomial model was fitted to the data with an R(2) = 0.606, while a linear model only had an R(2) = 0.534. This implies that the graph of molar mass to bond strength has a maximum in the range of molar masses examined, and that an optimum molar mass can be found between 800 and 6000 amu.