[Effect of acid etching on the primary enamel smooth surfaces. (3) A study of the etching times].

The purpose of this study was to investigate the influence of etching times for the effect of acid etching on the primary enamel smooth surfaces. Fifty labial surfaces of the extracted or exfoliated caries-free primary anterior teeth were used. The cleaning and polishing pretreatment used in this study was polishing with a brush cone (Howe-Neos-Dental Co.) with water at a low speed (600-6000 r.p.m.). The etchant used in this study was 40% phospholic acid gel and the etching times were 10, 30, 60, 90 and 120 seconds. All specimens were washed with an air water spray for 30 seconds after etching. The following observations were obtained using the SEM. 1. The shorter the etching time, the higher was the rate of the cases which did not show any prism structure. 2. The numbers of the cases which did not show any prism structure were: 4 (40%) out of the 10 in 10 seconds etching, 2 (20%) out of the 10 in 30 seconds etching and 1 (10%) out of the 10 in 60 seconds etching. All cases showed prism structure in 90 seconds and 120 seconds etching. 3. The most common etching patterns in all etching times were poorly structured etching patterns. 4. The longer the etching time, the higher was the rate of the cases which showed peripheral etching patterns. 5. Tooth to tooth differences in the etching effects and patterns were observed under the same etching times. Various etching effects and patterns on the same enamel surface were observed. 6. Among the etching times used in this study, 90 seconds was an adequate time for etching on the unground primary enamel smooth surfaces polished with a brush cone.