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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 52  |  Issue : 1  |  Page : 3-11

A comparative computed tomographic evaluation of expression of angulation and inclination in self ligating brackets


1 PG Student, Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
2 Prof, Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
3 Reader, Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
4 Senior Lecturer, Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
5 Prof. and HOD, Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India

Date of Submission05-May-2016
Date of Acceptance07-Oct-2017
Date of Web Publication18-Jan-2018

Correspondence Address:
Dr. Rehana Bashir
Department of Orthodontics and Dentofacial Orthopedics, Institute of Dental Studies and Technologies, Kadrabad, Modinagar - 201 201, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jios.jios_101_16

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  Abstract 

Introduction: An important objective of orthodontic treatment is to obtain the correct angulation and inclination for all the teeth. Very few studies have been conducted so far comparing the expression of angulation and inclination in conventional and self-ligating brackets (SLBs). The present study was designed to evaluate and compare the inclination and angulation in conventional brackets and active and passive SLBs. Materials and Methods: Totally 21 patients who required four 1st premolar extractions were selected and were randomly allotted to three groups: Group 1: Conventional Brackets (3M Unitek MBT) (mean age 19.14 ± 2.12 years), Group 2: Passive Brackets (Smart Clip Brackets-3M Unitek MBT) (mean age 19.71 ± 1.80 years), Group 3: Active Brackets (Empower Brackets-American Orthodontics MBT) (mean age 18.29 ± 2.29 years) computed tomographic records were collected before the start of treatment, after leveling and aligning and at 6 months into retraction. Results: The data were evaluated using SPSS version 16.0 using one-way ANOVA and post hoc Bonferroni tests. There was no statistically significant difference in the expression of angulation and inclination in conventional, active, and passive SLB systems. Conclusion: Self-ligating brackets seem to be no better than conventional brackets when it comes to the expression of angulation and inclination.

Keywords: Angulation, inclination, self-ligating brackets


How to cite this article:
Bashir R, Sonar S, Singla A, Srivastava A, Batra P. A comparative computed tomographic evaluation of expression of angulation and inclination in self ligating brackets. J Indian Orthod Soc 2018;52:3-11

How to cite this URL:
Bashir R, Sonar S, Singla A, Srivastava A, Batra P. A comparative computed tomographic evaluation of expression of angulation and inclination in self ligating brackets. J Indian Orthod Soc [serial online] 2018 [cited 2018 Feb 19];52:3-11. Available from: http://www.jios.in/text.asp?2018/52/1/3/223649


  Introduction Top


Fixed appliances are a common component of contemporary orthodontic treatment, and in which the engagement of the bracket with a full-size rectangular arch wire, confers adequate torque and tip to the tooth to allow it to assume the correct inclination and angulation necessary to achieve Andrews six keys to normal occlusion.[1]

Torque as described by Rauch [2] is a moment generated by the torsion of a rectangular wire in the bracket slot. The sources of variation in the expression of torque involve the stiffness of wire alloys, the play between wire and slot, the ligation modes, and the bracket design. Recently, the introduction of active and passive self-ligating brackets (SLBs) has presented a challenge to the specialty because of the novel ligation mode and the potential alterations in load and moment expression during mechanotherapy. Whereas some of these systems seem to have less friction in vitro, their torquing characteristics have not been studied in detail until now.[3],[4],[5]

There have been only small studies of torque expression until now because of the complexity of the experimental configuration. Numeric analyses have not been carried out for torque expression in various bracket-archwire combinations.[5],[6],[7],[8],[9],[10],[11]

A major objective of orthodontic treatment is to normalize the tooth positions in three planes of space, with the goal of approaching predefined cephalometric or occlusal standards. The mesiodistal axial inclination (tip) of permanent teeth should also be considered in an occlusion analysis. Andrews [1] determined the mean values of tooth crown angulation and chose this condition as one of the six keys to be evaluated in an ideal static occlusion. However, little literature is available in which the comparison between the expression of tip in different bracket combinations have been done.

The study of the developmental changes in the position of teeth and their mesiodistal axial inclination is a vital subject since proper axial inclination is considered as one of the keys to normally positioned teeth.[12] Moreover, this inclination is very important for proper distribution of occlusal forces and stability of teeth in their position in the dental arch.[13] Dewel [14] postulated that the analysis of the axial inclinations of certain key teeth could serve greatly in the clinical diagnosis of dental irregularities. Wheeler [15] said that the axial inclinations are essential for adapting the teeth to the curved occlusal planes of the dental arches since incisal and occlusal surfaces of the upper teeth confirm to convex plane and those of lower teeth to concave plane. He also stated that the long axes of teeth are not at right angle to horizontal plane.

However, limited evidence is available on the potential forces applied to the teeth by the various combinations of archwire and self-ligating mechanisms; most of the force derives from simple experimental configurations that do not register force variation as a function of the direction of displacement, i.e., first, second, or third-order movement.[4],[5] In addition, other factors, for example, archwire cross-section, bracket slot dimensions, variation in the extent and type of crowding (widespread or localized), and relaxation of the clip in active SLBs,[11] might modulate the forces transmitted to teeth.[16]

The purpose of this study was to evaluate and compare the angulation and inclination achieved with conventional, active, and passive SLBs.

Aim and objectives

The aim and objectives of this study are to evaluate and compare the change in angulation and inclination of all teeth after leveling and aligning and after 6 months of retraction in conventional, active, and passive SLBs.


  Materials and Methods Top


A total of thirty patients requiring orthodontic treatment were prospectively selected for the study. Nine patients failed to meet the selection criteria to participate in the study [Flow Chart 1]. All recruited patients signed a consent letter indicating their voluntary participation. Ethical committee approval was also taken (protocol number-IDST/ERBC/2013/09).



Twenty-one patients were analyzed. All the patients selected had permanent dentition with good periodontal and general health. The sample size was based on having an 80% power and α = 0.05[17] keeping in mind the low prevalence of the specific malocclusion criteria required for the study in the North Indian region.[18] They were randomly divided into three groups in which three different types of brackets were bonded:

  1. Group 1: Conventional Brackets (3M Unitek MBT-0.022'' slot)
  2. Group 2: Passive Brackets (Smart Clip Brackets-3M Unitek MBT-0.022'' slot)
  3. Group 3: Active Brackets (Empower Brackets-American Orthodontics MBT-0.022'' slot).


The treatment plan included fixed orthodontic therapy and extraction of the upper and lower first premolars.

The leveling and aligning were completed in all the three groups with a sequence of wires (0.014” NiTi, 0.016” NiTi, 0.018” NiTi, 0.017” × 0.025” NiTi, 0.019” × 0.025” NiTi and 0.019” × 0.025” SS). Before en-masse retraction, the 0.019” ×0.025” SS wire was left in situ for 4 weeks to express itself. Retraction was carried out on this wire with steel hooks placed mesial to canine with NiTi closed coil springs delivering a force of 100 g on each side.

Computed tomographic (CT) (GE Medical Systems, USA, Model: 2369660, Type: CT/eSingle Slice Spiral CT, Operating System: Linux, Work Station: Advantage window, Volume Viewer: Voxtool 3.0.64q) were taken at following stages:

  1. T0: Before placement of brackets
  2. T1: After initial leveling and aligning
  3. T2: After 6 months of retraction.


Assessment of angulation

Tracings of CT scan printouts (frontal, lateral right view, and lateral left view) of the patients were done on 0.003 inch thick acetate matte tracing paper.

Maxillary and mandibular central and lateral incisors

The long axis of maxillary and mandibular centrals and laterals were drawn on their respective CT image tracings (frontal view taken). The angle between the long axis of these teeth and the line perpendicular to occlusal plane (plane taken parallel to the display window) gives the angulation for these teeth. Angulation was measured for both the right and left sides. The angulation was measured for these teeth before the start of treatment, at leveling and aligning stage and at 6 months into retraction and compared with the angulation values of other two groups [Figure 1] and [Figure 2].
Figure 1: Computed tomography scan image used for measuring the angulation of maxillary and mandibular central and lateral incisors

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Figure 2: Computed tomography scan image used for measuring the angulation of maxillary and mandibular central and lateral incisors

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Maxillary and mandibular canines, second premolars, and molars

The long axis of maxillary and mandibular canines, second premolars, and molars were drawn on their respective CT image tracings (lateral right and left views taken). The angle between the long axis of these teeth and the line perpendicular to occlusal plane (plane taken parallel to the display window) gives the angulation for these teeth. Angulation was measured for both the right and left sides for these teeth. The angulation was measured for these teeth before the start of treatment, at leveling and aligning stage in each of the group and at 6 months into retraction and compared with the angulation values of other two groups [Figure 3] and [Figure 4].
Figure 3: Computed tomography scan image used for measuring the angulation of maxillary and mandibular canines

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Figure 4: Computed tomography scan image used for measuring the angulation of maxillary and mandibular canines, second premolars amd molar

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Assessment of inclination

Maxillary and mandibular central and lateral incisors

On their respective CT image tracings (lateral right and left views taken), the angle between line drawn tangent to the most labial surface of maxillary and mandibular centrals and laterals and line perpendicular to the occlusal plane (plane taken parallel to the display window) gives the inclination for these teeth. Inclination was measured for both right and left side. The inclination was measured for these teeth before the start of treatment, after leveling and aligning stage and at 6 months into retraction and compared with inclination values of other two groups [Figure 5] and [Figure 6].
Figure 5: Computed tomography scan Image used for measuring the inclination of maxillary and mandibular central and lateral incisors

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Figure 6: Computed tomography scan image used for measuring the inclination of maxillary and mandibular central and lateral incisors

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Maxillary and mandibular canines, second premolars, and first molars

On their respective CT image tracings (frontal view taken), the angle between line drawn tangent to the most labial surface of maxillary and mandibular canines, second premolars, first molars, and line perpendicular to the occlusal plane (plane taken parallel to the display window) gives the inclination for these teeth. Inclination was measured for both right and left side. The inclination was measured for these teeth before the start of treatment, after leveling and aligning stage in each of the group and at 6 months into retraction and compared with inclination values of other two groups [Figure 7] and [Figure 8].
Figure 7: Computed tomography scan image used for measuring the inclination of maxillary and mandibular canines, second premolars and molars

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Figure 8: Computed tomography scan image used for measuring the inclination of maxillary and mandibular canines, second premolars, and molars

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  Results Top


Statistical analysis

The data were analyzed using the SPSS (Statistical Package for Social Sciences) version 16.0 (IBM, Chicago, Illinois, US). The statistical analysis for the study was done for three stages and in three groups:

  • T0 - Pretreatment
  • T1 - After leveling and alignment
  • T2 - After 6 months into retraction
  • Group 1 - Conventional Brackets
  • Group 2 - Passive brackets
  • Group 3 - Active brackets


Mean and standard deviation (SD) for each of the 3 groups were calculated, and one-way ANOVA tests were conducted.

Post hoc tests - Bonferroni multiple comparison test were done for each group with other two groups and between T0 and T1, T1 and T2, and T0 and T2.

The values are represented in number (n), Mean (M), and SD. Significance between groups was calculated, i.e., P < 0.05 was counted as statistically significant.

The error of measurement (EM) of the readings was calculated using the Dahlberg's formula:



di = difference between the first and the second measure; N = sample size which was re-measured.

The EM was not statistically significant and the P = 0.243.

In the present study, no significant difference has been found in the expression of torque (inclination) and tip (angulation) between these three bracket types. In the intragroup comparison at pretreatment, at leveling and aligning and at 6 months into retraction significant differences were found between all the groups, in their respective stages [Table 1] and [Table 2].
Table 1: Angulation of teeth

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Table 2: Inclination of teeth

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  Discussion Top


Self-ligating brackets have received much attention as an active research subject, especially during the past few years. The introduction of a wide variety of these appliances by almost every manufacturer is indicative of the increased interest placed on this product by the industry and clinicians. Some of these systems, as claimed and seen experimentally seem to present reduced friction in vitro, their torquing characteristics remain unknown. The latter may be lower relative to their standard edgewise counterparts since torque requires the development of friction between the edges of the activated archwire and the bracket slot walls, to facilitate buccolingual inclination. It is also interesting to note that there is a high variability among various prescriptions with respect to anterior dentition torque values. Thus, the maxillary central incisor torque in preadjusted appliances ranges from 12° in the Roth discipline to 22° for the bioprogressive prescription.[19]

In the present study, CT have been used to measure the inclination and angulation of the teeth. Many studies [20],[21],[22],[23] have been carried out previously in which the angulation and inclination have been measured on lateral cephalograms and orthopantomograms. These imaging techniques have an inherent flaw of being a two-dimensional representation of three-dimensional setting, for example, on a cephalogram, there is inherent uncertainty caused by the superimposition of all four incisors on the radiograph while panoramic X-rays have distortions and do not reflect the true three-dimensional teeth angulations because the X-ray beam is not always orthogonal to the target teeth.[24],[25] On the other hand, while it may be ethically debated regarding the usage of multiple tomographic scans, thereby increasing the said exposure;[26] the writings of Machado [27] and Swenson [28] explain, as in the case of postorthognathic surgery follow-up, the benefits outweigh the risks involved. It is worthwhile to note that although cast or digital model-based study are based on the above-mentioned notion that multiple radiographic exposure is in detrimental to the study subjects, it must be also important to understand that CT are far superior in assessing the spatial positions of the roots when compared to the model-based techniques.[29]

Different investigators have used different reference lines for the evaluation of inclination and angulation. Ursi et al.[30] postulated that the inclination of the upper teeth might be registered in relation to the line passing through the most inferior points of the right and left orbits. Hamdany [31] have used the line joining the midpoint of the overlap of the mesiobuccal cusp of the upper and lower first molars bilaterally as the occlusal plane. Cattaneo et al.[25] have assessed the labiolingual inclinations by modifying the Bjork “occlusal line inferior.”[32]

In the present study, for the assessment of inclination and angulation, the occlusal plane has been taken as parallel to the display window. This is similar to the occlusal plane taken by Bouwens DG et al. in their study.[33] The occlusal plane was thus defined as the plane passing through two “molar points” placed at the tip of the distofacial cusp of the most distal molar in occlusion in each side and an “average incisor point” created as the interpolation of the right and left incisal edges of the lower central incisors. This has been done to minimize the effect of different labiolingual and mesiodistal inclination as well as vertical position between the left and the right incisors.

However, most of these studies were carried out on orthopantomograms and lateral cephalograms. While using the lateral cephalograms and panoramic radiographs for drawing the occlusal reference line, the inherent error in the demarcation of landmarks always persists. Hence, the main advantage of using lower border of display window, as an occlusal plane is its reproducibility.

Manufacturers of both active and passive SLBs have indicated the advantage of their solution for better torque control: while the passive brackets are claimed to produce a “lip-bumper effect” resulting in a better torque control of the lower incisors, the manufacturers of the active clip claimed that this renders a better torque control.[25],[30]

In the present study, however, no significant difference has been found in the expression of torque (inclination) between these three bracket types. In the intragroup comparison, at pre-treatment, at leveling and aligning stage, and at 6 months into retraction; significant differences were found between pretreatment and at leveling and aligning stage in all the groups. respectively.

In the study done by Pandis et al.[19] they tested the hypothesis regarding the engagement mode of wire in the self-ligating, and conventional brackets affects the buccolingual inclination of maxillary incisors. However, they could not find any statistically significant difference between the brackets on the torque of maxillary incisors. Their results are similar to the results of our study, that SLBs are equally efficient to conventional brackets in delivering torque.

Cattaneo et al.[25] found a significant proclination in the mandibular anterior teeth while using SLB systems, which claim to have a better torque control than the conventional bracket systems hypothesizing that the considerable play between the SLB slots and the wire could be the attributing factor. The results of our study differed from that of the study of Cattaneo et al., as there was no significant difference shown in the torque control within the three different bracket types (conventional, smart clip, and Empower) and there was no significant difference in the amount of unwanted proclination in all these three groups of brackets.

Badawi et al.[6] compared the third-order torque moment delivered by a 0.019 × 0.025-inch stainless steel arch-wire engaged into active and passive SLBs. Although their setup varies slightly from ours (only one bracket was studied at a time, in vitro), their results corroborate with the conclusion of our study.

As with any other product, the manufacturing process of brackets results in some variation in sizes, dimensional accuracy, and the torque prescription consistency.[34] According to Cash et al.[35] the slots are always oversized between 5% and 17%. However, in spite of this structural variability, in all the three groups of brackets that were included in our study, the expression of torque did not show statistically significant difference.

Archambault et al.[36] studied the torque expressions of conventional and various active and passive SLBs in 0.022 slot dimension. They found out that the engagement angle between the slot and the wire depends on the archwire dimension and bracket dimension. They found out that the effective torque in active SLBs can be achieved with archwire torsion of 15°–30° and at 23°-35° for passive SLBs with a wire dimension of 0.019 × 0.025 SS. In our study, no significant difference has been found in the expression of angulation between these three bracket types. The fact that the above-mentioned study was an in vitro one along with how there is noted difference in the clinical application and handling of materials may explain the difference in the results. In the intragroup comparison, at pretreatment, at leveling and aligning and at 6 months into retraction; significant difference was found between pretreatment and at leveling and aligning and at 6 months into retraction in all the groups indicating all the three brackets groups were successful in expressing the torque in-built into the system. Although it is to be conceded that the sample size although calculated to the necessary power, is on the smaller scale and a larger sample size with a longer follow-up time would further widen the horizon and enhance the knowledge of this interesting research subject. In the humble opinion of the authors, no study has been done so far in which the comparative changes in angulation of these three brackets have been evaluated and further studies are required to gain valuable data in this area of study.


  Conclusion Top


SLBs seem to be no better than conventional brackets when it comes to the expression of angulation and inclination. When the values of inclination and angulation of SLBs at mid-treatment and after 6 months into retraction were compared with those of conventional brackets, statistically no significant difference was found.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
 
 
    Tables

  [Table 1], [Table 2]



 

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