Effectiveness of nitric-NPG as a conditioning agent for enamel

This in vitro study was designed to measure the bond strength of composite resin to enamel treated with various regimes of HNO3-NPG (N-phenylglycine and glycidylmethacrylate) followed by application of PMDM (pyromellitic dianhydride and 2-hydroxyethyl methacrylate). Forty freshly extracted human teeth were prepared with a flat area entirely in enamel on the proximal surface and then divided into five groups. Group 1 was treated with 37% H3PO4, Group 2 with 2.5% HNO3-NPG while rubbing the enamel with the solution, Group 3 with 2.5% HNO3-NPG without rubbing, Group 4 with 37% H3PO4 plus 2.5% HNO3-NPG with rubbing, and Group 5 with 5% HNO3-NPG without rubbing. After drying, PMDM solution was applied to each specimen for 60 seconds. Unfilled resin was applied, cured for 20 seconds, and the composite resin was placed and cured from all sides for a total of 120 seconds. After water bath storage for 7 days, specimens were tested on an Instron machine at a crosshead speed of 2.0mm/min. The highest shear bond strengths measured were for Group 1 (22.7 MPa), followed by Group 2 (20.92 MPa). The lowest bond strength recorded was for Group 3 (14.43 MPa). The results of this study indicate that enamel surfaces treated with 2.5% HNO3-NPG solution, if the solution is rubbed during application, produce a bond strength comparable to that achieved by H3PO4 conditioning.