Recent reports indicate that shorter etching times than 60 seconds can be adopted without affecting the bond strength and clinical disadvantages. The purpose of this in vitro study was to compare the shear bone strength and to measure depth of
etch
at
different etching time length.
One hundred and eight extracted bovine lower central incisors were embedded each in a tooth cup with cold-cure acrylic resin, The facial surfaces of the teeth were ground wet with 600-, 800-, 1000-, and 1200- grit Sic papers, and finally polished
with a
water slurry of extrafine silicon carbide power, washed with tap water, and dried with hot air.
Nine groups of none prepared teeth were etched with a commercial(38% phosphoric acid solution for 0, 5, 10, 15, 20, 30, 60, 90, and 120 seconds, respecitively, rinsed with tap water, and dried with hot air. One conditioned teeth from every group
was
selected randomly for the scanning electron microscopic examination, and the remaining eight teeth of the groups were used for measuring the push shear bond strengh after bonding brackets and immensing them in the 36.5℃water for 24 hours.
Another nine groups of three teeth were used for measuring the depth of etch and surface roughness with a surface profilometer, after pieces of adhesive tape of 3mm inner diameter positiomed on the ground enamel surfaces, and etched with the
above
mentioned.
The data obtained form the above expeiments were analysed statistically with one way ANOVA and Dunkan's multiple range test with the 95% confidence level.
@ES The results and conclusiion of the study were as follows ;
@EN 1. The results of shear bond strength for the given experimental etching times were not statistically different, but showed the tendency of decreasing stear bone strength after over 60 seconds etching times.
2. On the scanning election microscopic examination, it was observed that the morphological patterns of etched enamel surface for 5 to 20 seconds were similar and consitent, and those for 30 to 120 seconds showed increasing over-etched patterns
depending on the length of etching times.
3. The depth of etch was increased almost proportionally by the length of etching times, but it was not assocated with the shear bond strength.
4. The surface roughness increased depending on the length of etching times, but it was not associated with the shear bond strength.
5. This experiment indicated that proper etching time with 38% phosphoric acid solution is in the range of 5 to 30 seconds.
KOREA J ORTHOD 1993 ; 23(1) : 75-88.
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