Shear bond strength of orthodontic brackets cemented with a zinc oxide-polyvinyl cement.

The purpose of this study was to compare the shear bond strengths and enamel surface structure after debonding a conventional metal bracket and a polycrystalline ceramic bracket bonded with a bipolar zinc oxide-polyvinyl cement (F-21) or a light-cured resin cement (Transbond). Forty extracted human premolars were used. The buccal enamel surfaces were used, and the teeth randomly divided into four groups of 10 teeth each: group 1: conventional metal bracket (Unitek) bonded with Transbond; group 2: metal bracket bonded with F-21; group 3: ceramic bracket (Transcend 2000) bonded with Transbond; and group 4: ceramic bracket bonded with F-21. The brackets were bonded to the etched enamel surfaces according to manufacturer's instructions. All specimens were stored in distilled water for 24 hours and then thermocycled for 300 cycles between 5 degrees C and 55 degrees C. The specimens were mounted in dental stone and placed in the Instron at a crosshead speed of 0.5 mm/min with a knife-edged blade. Immediately after debonding, the enamel surface and bracket-enamel interface were evaluated visually and with a stereomicroscope. Representative samples were then examined with the scanning electron microscope. The analysis of variance and Student-Newman-Keuls tests were performed. The results in megapascals were Group 1: 19,6 (+/- 9,6); group 2: 14,3 (+/- 4,6); group 3: 28,8 (+/- 12,6); and group 4: 18,5 (+/- 7,5). Group 3 was statistically significantly different (P < 0.008) from all other groups. Groups 1, 2, and 4 were not significantly different.(ABSTRACT TRUNCATED AT 250 WORDS)