This study was performed to evaluate suitability as orhtodontic band cement by measuring the retentive bond strengths, change of retentive bond strengths by time and failure patterns of cements after removal of bands cemented with each two brands of zinc phosphate cements and glass ionomer cements using universal testing machine.
Orthodontic bands were cemented with two brands of zinc phosphate cements and two brands of glass ionomer cements to the cervical line of crown portion in specimens involving forty extracted human molar teeth embedded in resin blocks. After the specimens were then stored in artificial saliva at 371C during 24 hours, tensile bond strength on bands of specimens using universal testing machine was measured. The retentive bond strength of cements was defined the strength required to initially fracture the cement bond holding the orthodontic bands to the tooth and cement failure pattern was assessed with the quantity of cement remaining on enamel. Prior to recementation, both the tooth and the inside of the band were carefully cleaned. Recemented specimens were subjected to 3000 thermocycles at a temperature differential of 50C . Two temperature baths, one at 51C and the other at 55C, were used. The dwell time in each bath was 15 seconds. The specimens were then stored in artificial saliva at 37C. Retentive bond strength was tested on band cemented after 2 weeks. Cement failure pattern was also assessed.
The results were as follows:
1. No significant difference in retentive bond strength was found among all cements.
2. The effect of time on retentive strength of the zinc phosphate cements was not appeared.
3. ´rhe retentive strength of the glass ionomer cements was increased with time(p<0.01).
4. In cement failure patterns, zinc phosphate cement was below 30 percent and glass ionomer cement was about 50 percent(p,<0.01).
The above results suggest that retentive bond strength between zinc phosphate cements and glass ionomer cements is similar. It is suggested that in fluoride releasing glass ionomer cements, cement failure pattern reduce the possibility of enamel decalcification. Thus, this results suggest that glass ionomer cement can be regarded as more effective enamel protective orthodontic cement comparing to zinc phosphate cement.
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