A New Technique With Sodium Hypochlorite to Increase Bracket Shear Bond Strength of Fluoride-releasing Resin-modified Glass Ionomer Cements: Comparing Shear Bond Strength of Two Adhesive Systems With Enamel Surface Deproteinization Before Etching

By eliminating the organic substances from the enamel surface before etching (deproteinization), orthodontic bond strength can theoretically be increased because the resulting etch-pattern is predominantly type 1 and 2, instead of type 3. Fluoride-releasing resin-modified glass ionomer cements (RMGIs) might then routinely be used to bond brackets, instead of composite resins. Reducing the incidence of white spot lesions, a major current iatrogenic effect of orthodontic treatment, is a worthy cause which might be achieved due to the fluoride-releasing properties of RMGIs. The objective of this study was to determine whether deproteinization of human dental enamel surfaces, with 5.25% sodium hypochlorite (NaOCl) before etching, increases orthodontic bracket shear bond strength (SBS) of 2 adhesive systems: a composite resin and a RMGI.Seventy-six extracted human premolars were cleaned, and randomly divided into 4 groups (2 experimental and 2 control), with 19 premolars in each group. In group 1 (experimental) and group 2 (control), brackets were bonded to the teeth using Transbond XT (3M Unitek Orthodontic Products, Monrovia, CA) and in group 3 (experimental) and group 4 (control), Fuji Ortho LC (GC America, Inc., Alsip, IL) was used. The buccal surfaces of the premolars in experimental groups 1 and 3 were deproteinized with 5.25% NaOCl for 1 minute followed by rinsing, drying, and acid etching for 30 seconds. Subsequently, the acid was rinsed off, the enamel was dried (and remoistened in the Fuji Ortho LC groups), and orthodontic brackets were bonded, either with primer and composite resin, or with RMGI. The same protocol was used in the 2 control groups (2 and 4), except that NaOCl was not used. The teeth were then stored in distilled water at room temperature for a maximum of 24 hours, thermo-cycled 500 times, between 5°C and 55°C, placed in a controlled Water Bath, at 37°C for 24 hours, mounted on acrylic rings, and debonded using a universal testing machine. The enamel surfaces were examined at 10× magnification to determine the amount of residual adhesive remaining on the tooth. An analysis of variance was used to determine whether there was a significant difference in SBSs between the 4 test groups, together with a post hoc test to determine possible significant differences among the pair of means; a χ2 test was used to compare the adhesive remnant index (ARI) scores. There were no significant differences in the SBS (P = 0.05) between the Transbond XT groups. There were significant differences in the SBS (P = 0.05) between the Fuji Ortho LC groups. The mean SBS for Transbond XT with NaOCl was 9.41 ± 4.46 megapascals (MPa); for Transbond XT without NaOCl, 8.12 ± 3.10 MPa; for Fuji Ortho LC with NaOCl, 9.64 ± 5.01 MPa; and for Fuji Ortho LC without NaOCl, 5.71 ± 3.87 MPa. The comparisons of the adhesive remnant index scores between the 2 Transbond groups (χ2 = 6.41) indicated that bracket failure mode was not significantly different (P < 0.05), and for the Fuji Ortho LC groups (χ2 = 24.08) indicated that bracket failure mode was significantly different (P < 0.05), with more adhesive remaining on the enamel bonded using Fuji Ortho LC with NaOCl. SBS was significantly increased from 5.7 to 9.6 MPa using NaOCl in the Fuji Ortho LC group (compared with 9.4 MPa in the transbond XT group with NaOCl). The Fuji Ortho LC experimental group, in which NaOCL was used, had a significantly greater amount of adhesive remaining on the enamel than the control group. It was concluded from this in vitro study that with NaOCl use, bracket bond strength with Fuji Ortho LC is similar to Transbond XT, so that fluoride-releasing RMGIs may possibly be used to bond brackets to reduce the incidence of white spot lesions.