An evaluation on the effects of 37% phosphoric acid and self – etching primer on shear bond strength of enamel Dr. A. Davari* - Dr. H. Hajizadeh* - Dr. H. Sharifikhatoonabadi** *- Assistant Professor of Operative Dentistry Dept. - Faculty of Dentistry - Yazd University of Medical Sciences. **- Dentist. Background and Aim: The goal of this study was to evaluate the effects of 37% phosphoric acid and self – etching primer on the bond strength of composite resin to enamel. Materials and Methods: Twenty bovine mandibular incisors were mounted in self – curing acrylic resin, and facial enamel surfaces were ground wet on 600 – grit disc paper. Then specimens were divided into three groups of ten. Different enamel surface treatments were applied as follows: Group A: Etching with 37% phosphoric acid and enamel bonding agent (Colten). Group B: Self – etching bonding agent (Prompt – LP). Group C: Etching with 37% phosphoric acid and self – etching bonding agent (Prompt – LP). After adhesive curing, a column of composite of 2 mm diameter was cured on the surface. After one – week storage and thermocycling, specimens were debonded at a cross – head speed of 1mm/min using an Instron machine. The teeth were examined stereomicroscopically to assess the site of debonding. The data were subjected to one – way ANOVA and LSD test at 0.05 level of significance. Results: The mean shear bond strength values were 15.4±6.5, 24.8±9.7 and 25.4±11 MPa for groups A, B and C, respectively. The enamel – resin interface was the most common site for bond failure in group A. Cohesive failure, in composite or enamel was more common in groups B and C, respectively. The differences between groups B and C with A was significant but no statistically significant difference was found between groups B and C. Conclusion: Self – etching agents can be used as alternatives for conventional phosphoric acid enamel treatment. Key words: Enamel bonding – Self etch – Shear strength | 
