Effects of broad arch form wires on arch development with passive self-ligating and conventional brackets: A cone beam tomographic study

Inclusion criteria

Subjects with skeletal Class I malocclusion with crowding of a minimum of 4 mm in the maxillary arch were treated on a non-extraction basis. A panel of five orthodontists would evaluate the criteria for deciding the non-extraction protocol. Patients above the adolescence age (18–40 years) with all permanent teeth erupted mesial to the second molars were selected to deter any misinterpretation of natural bone formation with growth [Table 1].

The sample size was calculated using G-power software version 3.1, keeping the alpha error at 0.05 and the power at 0.8. The sample size obtained per group was 17. To account for dropouts, the final sample size was kept at 20 per group, with a total of 60 patients, who were divided into three groups.

• Group 1 – Standard arch form with conventional elastomeric ligation brackets (022 MBT System Ormco Mini Diamond). Archwire sequence: (a) 0.014 Nickel-Titanium (NiTi), (b) 16x22 NiTi, (c) 17 × 25 titanium molybdenum alloy, (d) 19 × 25 stainless steel (SS) till completion of alignment

• Group 2 – Broad arch form wires (Ormco Corporation, CA, USA) with conventional elastomeric ligation brackets. Archwire sequence: (a) 0.013 CuNiTi, (b) 14 × 25 CuNiTi, (c) 18 × 25 CuNiTi, (d) 19 × 25 SS till completion of alignment

• Group 3 - Broad arch form wires with passive self-ligating brackets (Damon Q - Ormco Corporation, CA, USA) Archwire sequence: (a) 0.013 Cu NiTi f, (b) 14x25 CuNiTi, (c) 18 × 25 CuNiTi, (d) 19 × 25 SS till completion of alignment.

CBCT scans were taken using CS 9600 three-dimensional imaging software (Carestream Dental). All the scans were taken with standardized technical protocols: Carestream CBCT scanner, 120 kVP, 4 mA, 80 mm field of view, 0.15 mm thick slices, ultrahigh-resolution, and 0° gantry angulation. Scanner calibration was done at periodic intervals to obtain standardized values.

The obtained CBCT scans were converted into digital imaging and communications in medicine formats to measure ABT and ABH using the RadiAnt Software 2021.2. Multiplanar reconstruction was performed at three reference planes in the sagittal, axial, and coronal views. Measurements relevant to the study were obtained from 0.3 mm slices corresponding to (a) maxillary incisor, (b) maxillary second premolar, and (c) mesio-buccal root of maxillary first molar. Unilateral measurements at all three planes were taken, and potential biases in tooth inclination variations between quadrants were eliminated with judicious sample selection. Maximum intensity projection (MIP) was utilized for all slices to prevent overlap from adjacent slices. The cemento-enamel junction (CEJ) was identified on the radiograph by a horizontal reference plane connecting the intersection of the labial and lingual surfaces in the sagittal plane [Figure 1]. Following the segmentation of individual teeth, horizontal and vertical landmarks were delineated for measurement of alveolar ABT and ABH. All landmarks were cross-verified by two operators, and if there was a discrepancy seen, it was rechecked by a third operator before the measurements were finalized. The ABT and ABH values were compared at two different time intervals: (a) at the start of treatment (T0) and (b) after levelling and aligning up to a 19 × 25 SS wire (T1) for each of the three groups.

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Figure 1:

Reference plane for identifying the cemento-enamel junction passing through the pulp axis for measuring alveolar bone height and alveolar bone thickness measurements. Horizontal green line: Cemento-enamel junction of the tooth, Vertical green line: Long axis of the tooth.

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ABT

ABT was measured at 3 mm and 6 mm from the CEJ for the maxillary incisor, second premolar, and the mesiobuccal root of the 1^st molar. In the sagittal slice, the cross-section was obtained by passing through the pulp axis and center of the root perpendicular to the CEJ, representing a vertical reference plane. This plane served as a reliable indicator when projected onto the buccal alveolar bone at the identical cross-section. Horizontal measurements of ABT were done at 3 mm and 6 mm from the CEJ when projected onto this vertical reference plane [Figure 1]. Through this approach, the authors aimed to maintain optimum levels of accuracy and reproducibility.

ABH

ABH was measured from a slice corresponding to the maximum labiolingual thickness in the central incisor and bucco-palatal in the case of premolar and molar was identified and standardized across pre and post-scans. MIP was utilized for all slices to prevent overlap from adjacent slices. In the sagittal section, the ABH was measured as a line drawn perpendicular from the CEJ to the maximum concavity of the alveolar crest, keeping the vertical reference plane as a guide [Figure 1].

The ABT measurements at 3 mm and 6 mm, and ABH measurements were done at the maxillary central incisor, maxillary second premolar, and maxillary first molar [Figures 2-4].

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Figure 2:

Cross-sectional imaging to measure alveolar bone height at the maxillary central incisor region from the level of the cemento-enamel junction. The vertical reference line stands for the long axis of the tooth and the horizontal reference line stands for the CEJ of the tooth.

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Figure 3:

Cross-sectional imaging to measure alveolar bone height at the maxillary second premolar region from the level of the cemento-enamel junction. The vertical reference line stands for the long axis of the tooth and the horizontal reference line stands for the CEJ of the tooth.

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Figure 4:

Cross-sectional imaging to measure alveolar bone height at the maxillary first molar region from the level of the cemento-enamel junction. The vertical reference line stands for the long axis of the tooth and the horizontal reference line stands for the CEJ of the tooth.

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Arch width and length values

Evaluation of changes in arch width and arch perimeter between T0 and T1 was generated using the Trios intraoral scanner. With subsequent processing using 3shape software to create stereolithographic files of the digital models. The intercanine, interpremolar, and intermolar widths were measured horizontally from the cusp tips of the right and left sides [Figure 5]. Arch perimeter was measured from three reference points selected at the incisor, right, and left first molar regions [Figure 6].

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Figure 5:

Measurements of intercanine, interpremolar, and intermolar arch width from digital scans. The horizontal lines stand for the intercanine, interpremolar and intermolar widths.

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Figure 6:

Measurements of arch length from digital scans. The horizontal reference plane stands for the intermolar width.

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Reliability was calculated by intra-class correlation coefficients and 95% confidence intervals for each clinical parameter [Table 2].

All the data collected was assessed for the normality of distribution using the Kolmogorov–Smirnov test. Interphase changes (T1-T0) were calculated, and if normally distributed, the data were compared using paired t-tests and if it was not normally distributed, the Wilcoxon test was used.

Statistics

Statistical significance was considered P < 0.05 and was performed using the Statistical Package for the Social

Sciences software version 23.0. The comparison between the three groups was performed using the analysis of variance test of variance. The post hoc analysis was done using Tukey’s honest significant difference test. Reliability for each clinical parameter was calculated by the intra-class correlation coefficients at 95% confidence intervals.

Changes in ABT between T0 and T1 at 3 mm from CEJ

Group I decreased from 1.02 mm to 0.86 mm in incisors, 1.48 mm–1.29 mm in premolars, and 1.89–1.59 mm in molars, with a P = 0.464.

Group II decreased from 1.1 mm to 0.87 mm in incisors, 1.37 mm–1.25 mm in premolars, and 1.2 mm–1.06 mm in molars, with a P = 0.398.

However, in Group III, ABT measurements were variable and showed a marginal increase in the measured sites – 0.84 mm–0.98 mm in incisors, 1.75 mm–1.84 mm in premolars, and 2.1 mm–2.3 mm in molars, with a P = 0.187.

Results showed that the correction of crowding resulted in a reduction in ABT in Groups I and II, with a marginal increase in thickness in Group III. However, no significant differences were appreciated between the groups (P > 0.05) [Table 3].

Changes in ABT between T0 and T1 at 6 mm from CEJ

Group I decreased from 0.9 mm to 0.7 mm in incisors, 0.95 mm–0.78 mm in premolars, and 2.03 mm–1.71 mm in the molars. with a P = 0.693.

Group II decreased from 0.92 mm to 0.77 mm in incisors, 1.32 mm–1.09 mm in premolars, and 2.01 mm–1.7 mm in the molars, with a P = 0.497.

However, in Group III, ABT measurements increased from 0.78 mm to 0.85 mm in incisors, 3.2 mm–3.37 mm in premolars, and 2.63 mm–2.67 mm in the molars, with a P = 0.598.

Results showed that the correction of crowding resulted in a reduction in ABT in Groups I and II, with a marginal increase in thickness in Group III. However, no significant differences were appreciated between the groups (P > 0.05) [Table 3].

Changes in ABH between T0 and T1

There was an increase in the ABH values in all three sites measured (incisor, premolar, and the mesiobuccal root of the first molar).

Group I increased from 0.7 mm to 1.2 mm in the incisor region, 0.6 mm–1.2 mm in premolar, and 0.6 mm–1.1 mm in molar, with a P = 0.798.

Group II increased from 0.7 mm to 1.1 mm in the incisor region, 0.7 mm–1.2 mm in premolar, and 0.7 mm–1.1 mm in molar, with a P = 0.330.

Group III increased from 0.7 mm to 1.0 mm in the incisor region, 0.7 mm–0.8 mm in premolar, and 0.7 mm–0.8 mm in molar, with a P = 0.165.

Results showed that apical migration of the bone was least in Group III compared to Groups I and II. However, the results were not statistically significant (P > 0.05) [Table 4].

Changes in the arch width were compared between T0 and T1 for each of the three groups. The results showed that intercanine, inter first premolar, inter second premolar, and intermolar widths were significantly greater after treatment in all three groups at T1 (P < 0.05) [Table 5]. Results also showed maximum expansion in the premolar region in all three groups. This increase in arch width could be attributed to a combination of both bodily lateral expansion and tipping movements. However, Group III showed the least amount of undesirable tipping, but these results were not statistically significant (P > 0.05). Similarly, the arch length also showed a significant increase between T0 and T1 in all three groups (P > 0.05).