[ effect of the number of clinical bracket points on the accuracy of curve fitted to dental arch form by 3D method]

Adjustment of an accurate curve to the dental arch is an important part of orthodontic treatment. Our goal was comparing the fitting accuracy of two curves constructed by different numbers of clinical bracket points [CBP] to the dental arch form using 4[th] degree polynomial function. A mathematical formula associated with a polynomial function was used to reconstruct the dental arch forms of 18 adolescents [18 casts] with normal occlusion. CBPs were marked on every tooth present in each maxillary and mandibular model [second molar to second molar] using an orthodontic bracket positioning gauge. A coordinate measuring machine [CMM] was used to record the coordinates of each CBP [x, y]. Then a curve fitting software was used to obtain the best 4[th] degree polynomial function and the associated curve fitted to all 14 CBPs. Another polynomial 4[th] degree function curve was obtained for the same models using CBPs only on central incisors, canines and second molars. Curves for each model were compared using statistical values including correlation coefficient, standard error, sum of residuals and R[2]. The mean root squares for curves fitted to 14 points in all samples were 0.8855 and it was 0.9629 when 6 points were compared with 14 points. The intraclass correlation coefficient [ICC] between curves fitted to 6 and 14 points was 0.946 in mandible, 0.983 in maxilla and 0.969 for both. Six CBPs were enough for proper fitting of 4th degree polynomial function to dental arch forms of both jaws

[ effect ofpremolar extraction on lips' curvatures in borderline orthodontic patients]

Although orthodontists have long recognized that the extraction [Ext] of premolars often is accompanied by changes in the soft tissue profile, investigations indicate that the soft tissue does not always respond favorably to hard-tissue retraction. This study was designed to evaluate the effects of treatment, with and without premolar Ext. on the lateral facial profiles of borderline patients with particular reference to the curvature of the upper and lower lips. Eighty-nine border line patients were included in this study. 41 patients were treated with a non-extraction [Non-Ext] protocol, 16 patients were treated with extractions of 5/5, 18 patients with 4/4 and 14 patients with 4/5. All pre-and posttreatment lateral cephalograms were traced and analysis by one examiner. To quantify the soft tissue effects of growth and treatment, the depths of the upper and lower lip curves were calculated in two ways relative to the PM reference line and anterior soft tissue reference line.The changes in depth of upper and lower lip curves were statistically significant [P < 0.001]. The Non-Ext group showed an increase in depth of upper and lower lip curves, whereas the Ext group showed a decrease in depth of tipper and lower lip curves. No significant differences were found between the various extraction sequences [5/5. 4/4. 4/5] for depth of the upper and lower lip curves changes. The upper and lower lip changes were significant; more retrusivc in the Ext group and more protrusive in the Non-Ext group 2] There were no significant post treatment differences in the depths of upper and lower lip curves between premolar extraction sequences