In vitro comparison of primary incisor enamel surfaces etched with an acid solution or acid gel.

This study compared the effectiveness of an acid solution and an acid gel in etching the facial surfaces of primary anterior teeth. Comparisons included: (1) microscopic examination of the quality of etched enamel surfaces, (2) microscopic examination of the formation and penetration of resin tags into the etched surface, and (3) mechanical tests of the shear strength of the enamelresin bond. The acid solution yielded a more uniform etch. Depth of resin tag penetration was about the same on surfaces prepared with either etchant; however, surfaces treated with acid solution exhibited a greater number of tags that were distributed more uniformly along the entire resin surface. Shear strength of the enamel-resin bond was the same on surfaces prepared with either etchant. Previous research on acid etching has focused primarily on acid solutions. Over the past several years, gels for etching enamel have appeared on the market and have replaced acid solutions as the etchant of choice of many clinicians. Some of the newer gels are thixotropic in nature. This property permits the gel to become less viscous when subjected to forces encountered during the application of the gel to the tooth surface and to return to its original viscosity upon standing. Because of this property, gels allow for increased control in placement and thus offer a distinct technical advantage to the clinician in terms of convenience. With gels it is possible to reduce or eliminate acid overflow to gingival tissues and to avoid accidental etching of hard tissues adjacent to the desired site. Despite these apparent advantages, there has been contradictory documentation in the literature on whether gels are as effective as acid solutions. Some have noted that due to the viscous nature of gels, their ability to wet the enamel surface effectively may be reduced.1 Others have stated that by-products from the etching reaction form at the enamel-gel interface and reduce the effect of the acid; they contend that these by-products are eliminated only when flesh acid is applied continuously. 2 It also has been stated that a longer wash time is necessary to remove gel residues from the etched enamel surface. 1,3 However, reported data on wash times for gels are inconclusive. Some have reported that microscopic remnants and by-products were left on the surface even after copious amounts of water were used. 1 Another study found that a 2-second wash left acid residue but a 5-second wash provided a clean surface. 4 Laboratory studies comparing solution and gel etchants have been contradictory. When Brannstrom et al. s etched the buccal surfaces of young permanent teeth for 60 seconds with either 50% phosphoric acid gel or 37% phosphoric acid solution, resulting etched enamel surfaces were similar. In a later study, they found that a 15-second etch with 50% phosphoric acid gel provided a more retentive surface on young permanent teeth than a 60-second etch using the same gel. 6 Yet, Diedrich4 found that etching permanent teeth with 50% phosphoric acid gel for 30 seconds left the surface relatively unaffected; in his tests, a 60or 120second etch produced the most desirable etching pattern. In a clinical study by Hardison,7 sealant retention on the occlusal surfaces of permanent molars was compared when the etchant was either a 33% phosphoric acid gel or 35% phosphoric acid solution; the results showed no significant difference in retention after six months. In summary, only a few studies have compared the etching abilities of acid gels for conditioning permanent tooth enamel and the findings are inconclusive. Moreover, because there is clear evidence that primary and permanent enamel respond differently to acid etching, s,9 findings for etching characteristics of permanent teeth cannot be generalized to include primary teeth. To date no studies have been reported that compared acid gels and acid solutions for etching PEDIATRIC DENTISTRY: December 1984/Vol. 6 No. 4 209 primary tooth enamel. Therefore, the present study was undertaken to compare the effectiveness of an acid gel and an acid solution for etching primary teeth. Methods and Materials This study consisted of three parts: 1. Evaluation of etched enamel surfaces with a scanning electron microscope (SEM) 2. Measurement of tag length as an indication of etch depth 3. Measurement of shear strength of the enamelresin bond.