The purpose of this study was to compare shear bonding strengths and debonding patterns of the ceramic brackets attached on the crystal which were grown on the enamel surface of a tooth with different concentrations of lithium sulphate-contained polyacrylic acid in different application times. Four kinds of concentrations of mixed solutions were made and applied to the enamel surface on extracted human premolars. The solutions were made by adding 0.3M or 0.6M of lithium sulfate to 50% or 65% of polyacrylic acid with 0.3M sulfuric acid. The solutions were applied for 30 or 60 seconds. After bonding, a universal testing machine was used to measure the shear bond strength, and then observations were made of debonding patterns through the stereoscope. And the enamel surface was observed through the scanning electron microscope to examine the pattern of crystal growth and debonding. The results were as follows: 1, Shear bond strength in the enamel surface treated with 50% polyacrylic acid was higher than that with 65% polyacrylic acid. 2. There were no statistical differences in shear bond strength according to concentration of lithium sulfate and application time of solutions. 3. Enamel surface was almost free of resin debris after debonding. 4. Enamel surface treated with 50% polyacrylic acid showed higher density of crystal growth than that with 65% polyacrylic acid under scanning electron microscope.
Bicuspid ; Ceramics ; Crystallization* ; Dental Enamel ; Humans ; Lithium* ; Sulfur ; Tooth

The purpose of this study was to compare in vitro shear bonding strength with three different enamel surface preparations: (1) 30% sulfated polyacrylic acid with 0.3M lithium sulfate (2) 40% sulfated polyacrylic acid with 0.3M lithium sulfate (3) 37% phosphoric acid. 105 extracted human premolar teeth were divided into each three groups of 35. Metal brackets were bonded to teeth in the three groups. The same self curing resin was used for all groups. A shearing force was applied to the teeth. After debonding, bases of bracket and enamel surfaces were examined under steroscopic microscope to determine the failure modes. Statistical analysis of the data was carried out with one way ANOVA and Student t-test. The results were as follows. 1. Shear bond strength values for the 30% polyacrylic acid and 40% polyacrylic acid group were approximately two thirds of the phosphoric acid group. It maintains clinically acceptable but not enough bond strength. 2. There was no statistically significant difference in shear bond strengths between 30% and 40% polyacrylic acid group. 3. The failure modes of brackets had some differences. In polyacrylic acid groups, the percentage of adhesive/enamel failure was higher than that of adhesive/bracket interface failure. On the contrary in phosphoric acid groups, the results were reversed. Further study of bond strength could be required. If polyacrylic acid enamel conditioning is used clinically.
Bicuspid ; Dental Enamel* ; Humans ; Lithium ; Tooth