Relationship between crown-root angulation (collum angle) of maxillary central incisors in Class II, division 2 malocclusion and lower lip line.

AIM: The present study aimed to measure the magnitude of the collum angle (crown-root angulation) of maxillary central incisors present in Class II, division 2 malocclusion and to relate the changes in its magnitude with variations in the lower lip line. METHODS: A set of 120 conventional lateral cephalograms were selected and divided into three groups of 40 each based on the type of malocclusion presented: Class II, division 2 (group 1); Class II, division 1 (group 2); and Class I (group 3). The collum angle of the maxillary central incisor was measured, and the lower lip line was recorded. RESULTS: Analysis of variance (ANOVA) revealed that the mean collum angle was statistically significantly different in the three groups. The mean collum angle was greatest in Class II, division 2 malocclusion (group 1). The mean collum angles were 3.24 ± 4.69 degrees, 0.95 ± 1.06 degrees, and 1.05 ± 1.50 degrees in groups 1, 2, and 3 respectively. In χ ² test comparison of the location of the lower lip line (incisal, middle, or apical third of the central incisor) among the three groups, the lower lip line was found to contact the middle third of the central incisor most frequently in Class II, division 2 malocclusion. ANOVA followed by Tukey honestly significant difference (HSD) test showed that the mean collum angle is significantly increased when the lower lip is in the middle third (P < .05) of the central incisor. CONCLUSION: Variations in magnitude of the collum angle with the change in the lower lip line suggest a probable etiologic role of the lower lip line in the development of the collum angle.

The effect of topical fluoride agents on the physical and mechanical properties of NiTi and copper NiTi archwires. An in vivo study.

AIM: The aim of this in vivo study was to determine the effect of topical fluoride agents on the mechanical properties of NiTi and copper NiTi archwires. METHODS: Thirty patients with fixed appliances were randomly divided into three groups: Group I (Control group) used no topical fluoride agents; Group II used a fluoride rinse; Group III applied a fluoride gel to the teeth. After 30 days, the archwires were retrieved and the moduli of elasticity and yield strengths measured. The groups were compared with the oneway ANOVA, and Tukey's HSD test was used to identify the significant groups. One wire was randomly selected from each group and the surface examined with a scanning electron microscope. RESULTS: During unloading the modulus of elasticity of the NiTi archwire fell significantly in the gel group. The moduli of elasticity and yield strengths of the NiTi archwires during loading, and the copper NiTi archwires during loading and unloading, were not affected by either the gel or the rinse. Scanning electron microscopic analysis revealed that the copper NiTi archwires in the gel group had the most pitting. CONCLUSIONS: Topical fluoride agents alter the mechanical properties of NiTi wires and, hence, may prolong orthodontic treatment.