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Solubility Parameters, Fractional Polarities, and Bond Strengths of Some Intermediary Resins Used in Dentin Bonding

An effective bonding of resin composites to dentin is generally preceded by a conditioning of the surface of the dentin. Previous studies have indicated that the intermediary or adhesive resin should have specific wetting characteristics matching those of the conditioned dentin, in order that optimum bonding can be ensured. The wetting characteristics may be expressed in terms of solubility parameter (8) and polarity (p) of the resin. The aims of the present study were to determine these variables for a number of compounds used in adhesive resins and to investigate the effects of 8 and p on the shear bond strength to dentin. Solubility parameters were obtained according to the method of Small. Fractional polarities were calculated on the basis of measurements of refractive index and dielectric constant of the resins. In the measurements of bond strength, Scotchprep, EDTA+Gluma, or Al 2Ox3/glycine were used as dentin conditioners in combination with intermediary resins having various 8 and p. For each conditioner, the shear bond strength (BS) could be "explained" by an exponential expression of the form BS = ea+bx, where x = (8+cp+d)2, and where a-d are constants depending on the conditioned dentin. It may be concluded that solubility parameter and polarity of the intermediary resins are important variables in the process of bonding to dentin.