Abstract
BackgroundContrary to buccal orthodontics, lingual orthodontics has no reference for vertical bracket positioning on the maxillary central incisor. The aim of this study was to provide a reference point in relation to torque for lingual bracket positioning on the palatal surface curvature (PSC) of the maxillary central incisor.MethodsCone beam computed tomography (CBCT) radiographs of 50 right maxillary central incisors from archives of a dental radiographic center were transferred to Photoshop, where their PSC was traced using pen-tool. The PSC torque angle values of the incisors were calculated in Excel using cubic poly-Bezier curves at 0.5-mm increments and at the inflection point of PSC. Descriptive statistics for the torque angle values of the increments and for the inflection point for the 50 incisors were then calculated. One-way ANOVA test was used to detect systematic differences between the increments, and Tukey test was used post-hoc.ResultsFor all incisors, increments incisal to inflection point exhibited progressive decrease in torque angle values from the first-calculated increment to inflection point while increments cervical to inflection point exhibited progressive increase from inflection point to last-calculated increment. Mean torque angle values of all the increments and inflection point showed high standard deviations and vast range of values. One-way ANOVA test was highly statistically significant (p < 0.0001) and most pairwise comparisons of the increments using Tukey test were significant.ConclusionsInflection point can be used as a reference for bracket positioning on PSC. Cervically oriented shifts in vertical bracket position cause crown labial/root palatal movement cervical to inflection point and crown palatal/root labial movement incisal to it. A scientific mathematical justification for customized bracket torque prescriptions on PSC of maxillary central incisor was also provided.
Highlights
Contrary to buccal orthodontics, lingual orthodontics has no reference for vertical bracket positioning on the maxillary central incisor
As there is no reference in lingual orthodontics for bracket positioning on palatal surface curvature (PSC), the aim of this study was to find if the inflection point of PSC can be used as a torque reference for lingual bracket positioning
To fulfill the aim of the study, 50 right maxillary central incisors (RMCI) were selected from Cone beam computed tomography (CBCT) archives of a dental radiographic center and the TorqueAVnalgulees of their Photoshop-traced PSC were calculated at 0.5-mm increments and at the inflection point using the first derivative of their cubic poly-Bezier curve
Summary
Lingual orthodontics has no reference for vertical bracket positioning on the maxillary central incisor. The aim of this study was to provide a reference point in relation to torque for lingual bracket positioning on the palatal surface curvature (PSC) of the maxillary central incisor. TorqueAVnalgulee of only one bracket site on the lingual surfaces of a set of maxillary and mandibular dentition, while Bryant et al [4] with a mathematical equation of a parametric survival model could only calculate the maximum slope found at the inflection point of the palatal surface curvature (PSC) of the maxillary central incisor. The pen-tool in Adobe Photoshop Creative Cloud 2013 (Adobe Systems Inc., San Francisco, CA) can create cubic Bezier curves, which are parametric mathematical equations where the tangent at any point on these curves could be calculated by using the curve’s first derivative [15]. The initial and terminal control points of the cubic Bezier curve lie on the curve and are always its endpoints while the other two intermediate control points which determine its curvature do not generally lie on the curve [16]
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