The Influence of Mineralizing Solutions on the Bonding of Composite Restorations to Dentin: Pre-treatment with N-phenylglycine-glycidyl Methacrylate Adduct

B.E. CAUSTON,* M. DAYMON,* and N.W. JOHNSON** J Dent Res 60(7): 1321- 1324, July 1981 Departments of *Materials Science in Dentistry and **Oral Pathology, The London Hospital Medical College, University of London, London, El 2AD, England

The effect of surface treatment by acids or mineralizing solutions prior to the application of a primer (NPG-GAlA) has been studied. The reproducibility of results and the number of bond failures occurring during storage in water for seven dare reported. Mineralizing solutions are shown to be capable of improving the efficacy of primers. Introduction. The cavity primer supplied with Cervidentt is an alcoholic solution of Nphenylglycineglycidyl methacrylate (NPG-GMA). Bowenl,2 has described the synthesis and chemical action of this adduct. He has shown that it chelates with surface calcium in both dentin and enamel and can act as a primer between hydroxyapatite and additioncuring resin systems. Cervident cavity primer is a practical system based on Bowen's work and was chosen for this study in preference to preparing pure adducts in our own laboratory. Bowen proposed that the N-phenylglycine moiety chelates with calcium in the surface,1 and spectroscopic evidence of Ca/carboxylate bond formation has been published.3'4 Views differ as to whether the NPG-GMA adduct is of clinical importance or not, possibly because of difficulties in obtaining reproducible data from laboratory models. Our first impression of the material was that very high bond strengths were recorded generally, interspersed with complete failures. Hence, we felt a need to find a method of reducing the number of failures while at the same time increasing the mean bond strength. Etching of dentin has been suggested as a method of improving retention despite the dangers of pulpal irritation. Removal of the smear layer of collagenous debris by the use of mild acids such as citric acid5 has also been suggested. Because the NPG-GMA adduct chelates with calcium, we felt pre-treatment of dentin with a mineralizing solution could provide an alternative approach. Based on earlier work with the use of such solutions for the improvement of bond strength between dentin and both polycarboxylate cements and composite resins,6 we felt solutions such as Sat-SnCI2 and 1M CaC12, which leave deposits of crystals firmly attached to the dentin surface, might be successful. Furthermore, a new formulation which we have termed "ITS"§ has shown promise. It is the influence of such surface treatments and their sequence of application on both the mean bond strength and the scatter of data that are reported here. Materials and methods. One acid etchant, 37% phosphoric acid, and one cleanser, 50% citric acid, were tested, each being applied for 30 s only. Four mineralizing solutions were tested, 1M CaC12, 1M SnF2, Sat-SnCl2, and "ITS, Conclusions. The performance of etchants as adhesion promoters in combination with a chelating primer can be improved by a ten-minute application of ITS mineralizing solution prior to etching. Mineralizing solutions are only effective in improving the performance of chelating primers if the mineral layer they produce is stable. The application time of ITS when used to improve the performance of NPG-GMA must be about ten min. Acknowledgments. The authors wish to thank the staff of The London Hospital Medical College Oral Surgery Department for their co-operation in the collection of teeth for this experiment.