Comparison of shear bond strengths of orthodontic brackets bonded to deciduous and permanent teeth.

INTRODUCTION: This study was conducted (1) to compare the bond strengths of identical orthodontic brackets bonded to deciduous and permanent teeth with either of 2 primer/adhesive systems and (2) to evaluate the modes of bracket/adhesive failure. METHODS: Thirty-four permanent teeth and 34 deciduous teeth were collected. To these freshly extracted teeth, metal brackets were bonded with 2 primer/adhesive systems. These specimens were divided into 4 groups. In group I, consisting of 17 permanent teeth, the brackets were bonded with an acid-etching adhesive system; in group II, the self-etching adhesive system was used for bonding the brackets to 17 permanent teeth; in group III, consisting of 17 deciduous teeth, the acid-etching adhesive system was used; and in group IV, the self-etching adhesive system was used for bonding the brackets to 17 deciduous teeth. Shear bond strength was measured with a universal testing machine, and the mode of bracket/adhesive failure was determined according to the adhesive remnant index. RESULTS: The shear bond strengths of all 4 groups exceeded what is believed to be clinically sufficient strength of 6 to 8 MPa. Whether deciduous or permanent teeth, there were no significant differences in shear bond strength between the acid-etching and self-etching adhesive systems. The shear bond strengths of the brackets bonded to the deciduous teeth with either adhesive system were lower than those to the permanent teeth. Bond failure occurred at the enamel-adhesive interface more frequently in the self-etching adhesive system than in the acid-etching adhesive system. CONCLUSIONS: Bond strengths of brackets were lower with deciduous teeth but were high enough for clinical purposes.

Anterior crossbite in the primary dentition: proposal for a new analytical method in children.

The aim of this study was to clarify the features of profiles of patients with anterior crossbite in early childhood, using a new method of analysis. Lateral cephalograms of 139 (68 males; 71 females) untreated child patients with anterior crossbite in the primary dentition were assessed. The patients were aged from 3 to 5 years. To evaluate disharmony between the maxilla and the mandible, a proprietary calculating system, the Theoretical Individualized Profile drawing System (TIPS), was applied. Using this system, individualized standard cephalometric values were obtained for normal occlusion. This standard profile, which was harmonized with the cranial base structure of each patient, was compared with the child's original profile. The sizes of the mandibles in the children with anterior crossbite, subclassified into three age groups (3, 4, and 5 years) were greater, both horizontally and vertically, than those in the mean profiles derived from TIPS. The vertical size of the maxilla was smaller than that derived from TIPS in the patients aged 3 years. In contrast, in the patients aged 5 years, the vertical size of the maxilla was larger than that derived from TIPS. These results suggest that, in children with anterior crossbite, the vertical growth of the maxilla is closely related to the variation of morphological conditions with development.