An improvement in the adhesion between polymers and hard tooth tissues would be an important advance in preventive and restorative dentistry.' To achieve this improvement, there is a great need to study the molecular level interactions that take place between polymers and the tooth surface. In order to elucidate the nature and mechanism of this interaction, Misra and Bowen2 have studied the adsorption behavior of the adduct of the diglycidyl ether of bisphenol A with N-phenylglycine, on synthetic hydroxyapatite from methylene chloride solution using the BET method and attenuated total reflection infrared spectroscopy. This adduct is useful in providing improved adhesion to dentin. A rate law, based on an increasingly difficult gradual folding of the adsorbed molecules with an eventual fixation of the two chelating rings side by side, was suggested to explain all the kinetic features of the adsorption process.
The purpose of this Note is to report some detailed aspects of the adsorption behavior of PMMA on materials of human teeth, dentin, and enamel, and synthetic hydroxyapatite. We believe that this is the first application of the ESR method with the spin-labeling technique to study the molecular interaction between polymers and human teeth. This method gives us unique and useful information on the interaction.
The enamel and dentin samples were obtained from dried human teeth. The synthetic hydroxyapatite Cal&' O&(OH)2 was purchased.* Spin-labeled PMMA was prepared by the method described in our previous article? The solid powder, 0.2 g, was added to 5 mL of the CC14 polymer solution and stirred for 4 h a t 25°C f 2°C. The adsorbents were centrifuged after the adsorption equilibrium had been attained and separated from the supernatant solutions. The solids were rinsed with pure CC14, and 0.1 g of the each sample was placed in a quartz sample tube. The ESR spectra from the adsorbed polymer were measured with a JEOL JES FE 3-X spectrometer at 25°C. Figure 1 shows the ESR spectrum (a) of the spin-labeled PMMA adsorbed on hydroxyapatite from CC14 solution at 25"C, together with the calculated spectrum (b). The observed * Seikagaku Kogyo Co., Ltd