Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction

ABSTRACT Introduction: Extraction vs. non-extraction is a crucial decision in orthodontic therapy. Objective: The aim of the present study was to investigate the changes in the dental arch width and buccal corridor after orthodontic treatment using extraction and non-extraction therapy with Damon self-ligating system. Material and Methods: This retrospective study consisted of 35 patients (20 female and 15 male patients with median age of 12.5 years), treated by extracting 4 or 2 premolars, and 37 patients (16 female and 21 male patients with the median age of 12.8 years), treated without premolar extraction. Both groups were treated with Damon self-ligating system. Plaster models before (T0) and after (T1) treatment were measured, and the arch width values were determined at the level of the first molars, second premolars, canines and palatal rugae. Buccal corridor width was measured using the extraoral images at T0 and T1. Paired t-test was used for the analysis of the normally distributed data, and Wilcoxon Mann-Whitney U test was used for the data with non-normal distribution. Values of p<0.05 were set as statistically significant. Results: The upper intercanine width increased significantly in both groups (p<0.01). In the non-extraction group, the arch width increased significantly in the maxillary second premolar and first molar region (p<0.01) as well as in the region of the canines (p=0.04), second premolars (p=0.01) and first molars (p<0.01) of the mandible. The buccal corridor decreased significantly in the non-extraction group (p<0.01). Conclusion: Premolar extraction in combination with Damon self-ligating system did not lead to reduction of the dental arch width in the maxilla, nor did it increase the size of the buccal corridors.


INTRODUCTION
2][3][4][5][6][7] Premolar extraction is frequently deemed necessary in cases in which severe space deficiency compromises the harmonious alignment of teeth within the dental arch.,[24][25][26] A general correlation between the arch width and the buccal corridor has already been described, which means a decrease of the arch width can result in an increased size of the buccal corridor. 27,283][4] Even though a recent study showed the efficacy of Damon system in avoiding arch constriction following extraction therapy, 2 the effects of extraction therapy on the buccal corridor size and smile aesthetics using Damon system was not evaluated in this research and the evidence remains scarce.
7][38] The question arises whether orthodontic extraction therapy using self-ligating Damon system can meet the aesthetic requirements in regards to buccal corridor size.
The aim of the present study was to compare extraction vs. non-extraction therapy using self-ligating Damon system, regarding the changes in maxillary and mandibular dental arch widths, as well as of the buccal corridor size.

STUDY DESIGN AND ETHICS
The present single-centre retrospective study was approved by the ethics committee of the medical university of the Johann-Wolfgang Goethe University (Frankfurt, Germany).(no.: 20-686).

SAMPLE SIZE CALCULATION
The power calculation was based on a study by Bishara et al. 39 In order to achieve a test power of 80% at an alpha significance level of 0.05, at least 29 patients per each group were required to detect a mean difference greater than 1.5 mm.

INCLUSION AND EXCLUSION CRITERIA
Only patients treated using Damon self-ligating 0.022-in slot system in both dental arches (Ormco, USA), and presenting fully erupted group, the space deficiency was -4.46±1.31mm in the maxilla and -2.4±1.98 mm in the mandible.At the end of treatment, the subjects in the non-extraction group were between 12.2 and 21.9 years old (median age of 16.3 years).
The following variables were measured (all distances were measured in millimeters): 1. Intercanine width: Distance between the cusp tips of right and left canines in upper and lower jaws.Patient frontal extraoral smile images T0 and T1 buccal corridor measurements were done with the OnyxCeph analysis software (Image-Instruments, Chemnitz, Germany) (Fig. 3).
The following parameters were measured: 1.The distance between the last visible teeth (the distance PMR to PML, being PMR = last visible tooth on the right side, PML = last visible tooth on the left side) in millimeters.
2. The smile width, measured from inside corners of the mouth (the distance MR to ML, being MR = inside corner of the mouth on the right side, ML = inside corner of the mouth on the left side) in millimeters.
3. The buccal corridor ratio, calculated according to the following formula 22 : Ratio = (distance MR to ML -distance PMR to PML): distance MR to ML*100.

STATISTICAL ANALYSIS
The statistical evaluation was carried out by the Institute for Biostatistics and Mathematical Modeling of the Faculty of Medicine at the J. W. Goethe University in Frankfurt using the statistics software BiAS 11.12 (Hans Ackermann BiAS for Windows). 40The test for normal distribution was carried out using the Kolmogoroff-Smirnoff-Lilliefors test.In order to show the differences between the groups in the development of the parameters before treatment (T0) and after treatment (T1), the two-sample t-test was used for normally distributed parameters.The Wilcoxon-Mann-Whitney U test was used for the parameters that were not normally distributed.To determine the effect size, Cohen's d 41 was evaluated in the case of the two-sample t-test, and Rosenthal's R 42  size, the correlation coefficient r was evaluated according to Evans 43 .In this context, r was considered as follows: <0.2 = poor, 0.2 -0.4 = weak, 0.4 -0.6 = moderate, 0.6 -0.8 = strong and > 0.8 = optimally rated.
All measurements were performed by a single investigator and repeated after four weeks.The mean values were calculated for reliability analysis.

RESULTS
The results show the changes between time point T0 (before therapy) and T1 (after therapy).

EXTRACTION GROUP
The arch width at the level of the canines in the maxilla increased after orthodontic therapy (T0-T1) significantly (p < 0.01) (Table 1).
No significant change was shown in the arch widths at the level of the second premolars and at the level of the first molars in the maxilla after orthodontic treatment.The arch width at the level of the rugae in the maxilla showed no significant changes between T0 and T1.
The arch widths at the level of the canines, the second premolars and the first molars in the mandible did not show any significant changes in the extraction group between T0 and T1.The buccal corridor ratio was not subject to any significant changes during orthodontic extraction therapy (T0-T1).
Table 1 shows the results of the changes in the parameters assessed before and after the treatment in the extraction group.
Positive values indicate a decrease in the respective value, while negative values indicate an increase in the respective value.

NON-EXTRACTION GROUP
The arch width at the level of the canines in the maxilla increased after orthodontic therapy (T0-T1) significantly (p < 0.01) (Table 2).The arch widths at the level of the second premolars and at the level of the first molars in the maxilla likewise increased significantly (p < 0.01) between T0 and T1.The arch width at the level of the rugae in the maxilla showed no significant changes after orthodontic treatment.
In the non-extraction group, the arch widths increased significantly from T0 to T1 at the level of the canines, second premolars and first molars in the mandible (p = 0.04, p = 0.01, p < 0.01, respectively).

COMPARISON OF CHANGES BEFORE (T0) AND AFTER (T1) THERAPY BETWEEN EXTRACTION AND NON-EXTRACTION GROUP
The difference between the extraction and the non-extraction groups was not significant at the level of the maxillary and mandibular canines, but significant at the level of the maxillary second premolars (p < 0.01), maxillary first molars (p < 0.01), mandibular second premolars (p = 0.04) and mandibular molars (p < 0.01) (Table 3, Fig 4).At the level of the rugae in the maxilla, the comparison between the two groups showed no significant changes.The difference between both groups for the changes in the buccal corridor was found to be significant (p < 0.01) (Fig 5).

COMPARISON OF THE EXTRACTION OF FOUR PREMOLARS OR TWO UPPER PREMOLARS IN THE EXTRACTION GROUP (TEST GROUP)
The arch widths at the level of the canines in the mandible did not

CORRELATION BETWEEN DENTAL ARCH WIDTH AND BUCCAL CORRIDOR
A correlation between the change in the buccal corridor and the arch width at the level of the first molars in the maxilla was found in both groups.The results show that there was an optimal correlation between these two quantities in both groups.After premolar extraction, only the arch width at the level of the canines in the maxilla increased significantly (2mm).The arch widths at the level of the second premolars and the first molars in the maxilla and mandible, as well as the arch width at the level of the canines in the mandible, did not show any significant changes.These data show that there was no compression of the dental arch in the transversal dimension.The increased arch width at the level of the canines in the maxilla can be explained by the fact that with the distal movement of the canines after extraction, they were shifted to a wider part of the dental arch. 11,14,24,35,44Thus, the theory that the posterior dental arch becomes narrower as a result of mesial molar movement into a narrower part of the arch during space closure can be rejected. 11,15,16,18,24,35,44,45Furthermore, the arch width measurements at the level of rugae was incorporated as an additional variable in the present study, in order to mitigate potential » The authors report no commercial, proprietary or financial interest in the products or companies described in this article.

Bühling S , 5 Dental
Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction

Bühling S , 6 DentalSETTING
Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction The archive of the Department of Orthodontics and Orofacial Orthopedics of the Centre for Dentistry and Oral Medicine of the Johann-Wolfgang Goethe University Frankfurt was searched to find the eligible patients for this study.STUDY GROUPS Two groups of Extraction and Non-extraction cases were included in the present study.

7 Dental 8 Dental
lower canines at T0 were included in this study.All patients presented with skeletal Class I malocclusion, neutral growth pattern, Class I or Class II molar relationship, anterior overjet of 3 to 9 mm and space deficiency of 4 to 9 mm, and were considered borderline extraction cases at T0. Patients with extraction therapy of two premolars in the maxilla or four premolars (2 in the maxilla, and 2 in the mandible) or aplasia of the relevant premolars, without partial or complete space closure, were allocated in the extraction group.Bühling S, Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction Press J Orthod.2024;29(3):e2423159 Patients with transversal deficiency or history of treatment with expansion devices, as well as patients with dental aplasia (other than premolars and third molars), were excluded from the study.PATIENTS All patients were treated with Damon self-ligating 0.022-in slot system in both dental arches (Ormco, USA), using the following archwire sequence: 0.014-in CuNiTi Damon (Ormco, USA); 0.016-in CuNiTi Damon (Ormco, USA); 0.016x0.025-inCuNiTi Damon (Ormco, USA); 0.018x0.025-inCuNiTi Damon (Ormco, USA); 0.019x0.025-inSS (Ormco, USA).The 35 patients in the extraction group were at the beginning of the orthodontic therapy, ranging from 7.2 to 23.2 years old (median age of 12.5 years), and were treated by extracting 4 premolars (2 in the maxilla and 2 in the mandible), or two premolars in the maxilla.The space deficiency was -6.15±3.28mm in the maxilla and -3.37±2,88 mm in the mandible.At the end of treatment, the patients in the extraction group were between 11.7 and 27.5 years old (median age of 15.9 years).The 37 patients in the non-extraction group (control group) were at the beginning of the orthodontic therapy, ranging from 9.1 to 17.9 years old (median age of 12.8 years), and were treated without premolar extraction.In the non-extraction Bühling S, Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction

2 .
Interpremolar width: Distance between the buccal cusp tips of right and left second premolars in upper and lower jaws.

3 .
Intermolar width: Distance between the buccal cusp tips of right and left second premolars in upper and lower jaws.

4 .
Arch width at the height of rugae: Distance between the outermost contours of the right and left upper teeth measured just behind the incisive papilla at right angles to the suture palatina mediana, as described by Meyer et al. 26,27 Bühling S, Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction Dental Press J Orthod.2024;29(3):e2423159

Figure 1 :
Figure 1: Measuring points on the maxillary plaster model.

Figure 2 :
Figure 2: Measuring points on the mandibular plaster model.

Figure 3 :
Figure 3: Measuring points in the smile photos.MR = inside corner of the mouth on the right side, ML = inside corner of the mouth on the left side, PMR = last visible tooth on the right side, PML = last visible tooth on the left side (OnyxCeph3™, Image Instruments GmbH, Chemnitz, Germany).

Bühling S ,
Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction 11 Dental Press J Orthod.2024;29(3):e2423159 in the case of the Wilcoxon-Mann-Whitney U-test.In this connection, Cohen's d41 was divided according to the following values: 0.2 = low, 0.5 = medium and 0.8 = large.Rosenthal's R42 was classified according to the following values: 0.1 = low, 0.3 = medium, 0.5 = large, > 0.7 = very large.For the difference between the parameters before and after treatment within the two groups, one-sample t-test was used for the normally distributed, and Wilcoxon matched pairs test for the non-normally distributed data.To determine the effect size, Cohen's d 41 and Rosenthal's R 42 were evaluated.In order to test parameters for correlation, the simple linear correlation according to Pearson was used for normally distributed parameters.To determine the effect Bühling S, Schmied S, Eslami S, Brandt S, Plein N, Kopp S, Sayahpour B -Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction 12 Dental Press J Orthod.2024;29(3):e2423159

Table 1 :
Changes in the parameters assessed "before" and "after" treatment (T0-T1) within the extraction group (n = 35).Positive values indicate a decrease in the respective value, while negative values indicate an increase in the respective value.Statistical significance was set at p < 0.5.SD = standard deviation.Min = minimum.Max = Maximum.* Use of Median and Min/Max instead of average (SD).** Rosenthal effect size (1 = small effect size, 2 = medium effect size, 3 = large effect size).

Figure 4 :
Figure 4: Box plots: Median and quartiles of the change in arch width at the level of the first molars in the maxilla "before" and "after" therapy in the extraction group and in the non-extraction group.
show any significant changes.The dental arch widths at the level of the second premolars and first molars in the mandible showed significant differences between both extraction types (p < 0.01) (Fig 6).The values decreased significantly after the extraction of four premolars (p < 0.01).After the extraction of two premolars, the values increased significantly in the area of the second premolars and first molars in the mandible (p < 0.01, p = 0.05, respectively).No significant difference was found between the extraction methods for any of the other parameters assessed.

Figure 5 :
Figure 5: Box plots: Median and quartiles of the change in the buccal corridor ratio "before" and "after" therapy in the extraction group and in the non-extraction group.

Figure 6 : 18 DentalDISCUSSION
Figure 6: Box plots: Median and quartiles of the change in the arch width at the level of the first molars in the mandible "before" and "after" treatment in the group with extraction of 4 premolars and in the group with the extraction of 2 premolars.

Table 2 :
Change in the parameters assessed "before" and "after" the treatment (T0-T1) within the non-extraction group (n = 37).Positive values indicate a decrease in the respective value, while negative values indicate an increase in the respective value.

Changes in the arch width and buccal corridor after fixed orthodontic treatment with Damon self-ligating system: premolar extraction vs. non-extraction Dental
Press J Orthod.2024;29(3):e2423159