PROBABILITY OF FAILURE OF ORTHODONTIC BRACKETS BONDED WITH DIFFERENT CEMENTING AGENTS

Objectives. The aim of this study was to compare the maximum loads at failure and the probability of failure of three glass ionomer cements and a composite cement bonding orthodontic brackets to human premolar teeth. Methods. The cements studied included a conventional glass iono mer cement, two resin-modified glass ionomer cements and a composite c ement. The roots of 200 human premolar teeth were embedded in acrylic resin and the buccal enamel surface of the crown prepared as required. Each cement used to bond the bracket to the enamel was weighed, and l ight-cured where required. The specimens were stored for 10 min or 24 h at 37 degrees C and 100% humidity. A tensile shear force was applied via a wire loop placed under the wings of the bracket. The maximum lo ad at failure was noted and subjected to Weibull analysis to compare p robabilities of survival for each cement. The data obtained was also a nalyzed using a Kruskal-Wallis lest followed by comparison of the grou ps using Mann-Whitney tests. Results. Comparison of the loads at failu re revealed that the composite cement was significantly stronger than the glass ionomer cements at 10 min and 24 h (p < 0.05). Weibull analy sis of the results gave values for the Weibull moduli and probabilitie s of survival for an orthodontic bracket under a given load for each c ement at 10 min and 24 h. Significance. Glass ionomer cements give a n umber of clinically significant advantages over composite cement in th e retention of brackets. The resin-modified glass ionomer cements test ed had a higher probability of survival than the conventional cement t ested at 24 h. However, further improvements in their early bond stren gth would be clinically beneficial.