Retention of orthodontic bands with new fluoride-re leasing cements

The prevalence of enamel decalcification beneath orthodontic bands has indicated the need for a fluoride-releasing, enamel-adhesive orthodontic luting cement. The purpose of this study was to compare the retentive bond strengths of orthodontic bands cemented with two new fluoride-releasing cements, a zinc polycarboxylate and a glass ionomer, with the retentive bond strength of bands cemented with the standard orthodontic cement zinc phosphate. The site of cement failure was also evaluated. One hundred eighty extracted human molar teeth were embedded in resin blocks and randomly assigned to three cement groups. Adapted bands were cemented by a clinically acceptable technique. The cemented teeth were then assigned to one of three time intervals-24 hours, 7 days, and 60 days-and thermocycled in synthetic saliva. The force required to initially fracture the cement bond was used as a measure of cement retention. By means of the Instron, a tensile load was applied to each cemented band. The maximum retentive strength (cement failure) was interpreted from the stress-strain curve at the point where linearity deviated. The failure site was judged subjectively: between cement and enamel, within the cement, or between cement and the band. Using stress at failure, an analysis of variance showed no significant differences among the retentive strengths of the three cements. The chi-square test revealed a significant difference (P < 0.01) between failure sites of the zinc phosphate and glass ionomer cements. Significantly more bands cemented with the glass ionomer failed at the cement/band interface, leaving the cement adhered to the tooth. Both the glass ionomer and zinc polycarboxylate cements tested were found to be suitable as orthodontic luting agents. In addition, the favorable failure site of the glass ionomer (cement adhered to enamel) may offer clinical protection against decalcification under loose bands.