THE EFFECTS OF PH OF N-METHACRYLOYL GLYCINE PRIMER ON BOND STRENGTH TO ACID-ETCHED DENTIN

To develop a more effective adhesive primer, it is imperative to under stand the adhesion mechanisms of the resin to the demineralized dentin through a dentin primer. When the bonding agent was directly applied to the dentin etched by 40 wt % phosphoric acid without a primer pretr eatment, the bond strength of the resin to the dentin was 5 MPa. Conve rsely, when the demineralized dentin was pretreated with the N-methacr yloyl glycine (NM alpha A) primer solution with a pH value of 1.5, the bond strength increased considerably to 15 MPa. However, the bond str ength dropped dramatically from 15 to 3 MPa when the sodium salt of NM alpha A was added, thereby increasing the pH value of the NM alpha A primer solution from 3.2 to 5.0. When the pH value was increased above 3.5 (pKa value), the number of ionized NM alpha A species increased i n the solution. As a result, the bond strength of the resin fell to ap proximately 3 MPa. This result was obtained despite the 5-mu m-thick h ybrid layer that was created in the subsurface of the intertubular den tin. The number of unionized NM alpha A species increased by lowering the pH value below 3.5. As a result, the NM alpha A primer provided a higher bond strength of the resin to the demineralized dentin. In cont rast, when 10 wt % citric acid containing 3 wt % ferric chloride was a pplied to the dentin, maximum bond strength was obtained when the pH v alue of the NM alpha A primer solution was 3.5. The pH dependency of t he bond strength obtained following 10 wt % citric acid containing 3 w t % ferric chloride etching is different from the results obtained fro m 40 wt % phosphoric acid etching. This can be attributed to the diffe rence in the characteristics of the demineralized collageous layer. (C ) 1996 John Wiley & Sons, Inc.