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 Table of Contents  
Year : 2022  |  Volume : 14  |  Issue : 2  |  Page : 189-194

Comparative evaluation of stability of mandibular anterior crowding correction done with two different treatment protocols: A retrospective study

Department of Orthodontics and Dentofacial Orthopedics, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India

Date of Submission23-Sep-2021
Date of Decision16-Feb-2022
Date of Acceptance28-Feb-2022
Date of Web Publication26-Apr-2022

Correspondence Address:
Dr. Purva Verma
Department of Orthodontics and Dentofacial Orthopedics, Saveetha Dental College and Hospitals, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai 600077, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jioh.jioh_260_21

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Aim: To assess and compare 1-year treatment stability after correction of lower anterior crowding with nonextraction approach using passive self-ligation appliance and lower incisor extraction protocol with conventional ligation approach. Materials and Methods: This retrospective study included total 32 subjects. The inclusion criteria of the study were adult subjects with class I skeletal and dental malocclusion with mild-to-moderate mandibular anterior crowding of 4–6 mm. Subjects were divided into two groups: Group A treated with passive self-ligation nonextraction protocol (n = 15) and Group B treated with conventional ligation lower incisor extraction protocol (n = 17). The primary outcomes were the changes in arch dimension and dental crowding at three time points. Changes in intermolar width (IMW), intercanine width (ICW), little’s irregularity index, and mandibular incisor inclination at T0 (pretreatment), T1 (postdebonding), and T2 (1-year postdebonding) were evaluated. Descriptive statistics, normality tests, and intergroup comparison (independent t test) were performed. Results: Change in IMW was similar in both groups with no significant difference at T1 and T2. Change in ICW at T1 was significantly higher in Group A (2.01 mm) than Group B where ICW decreased by 0.94 mm. The relapse in ICW was significantly more in Group A. Difference in relapse of lower incisor crowding and inclination was significant between groups and it was more in Group A (P < .05). Conclusion: Orthodontic treatment with lower incisor extraction protocol with conventionally ligated approach has stable treatment outcomes than with nonextraction approach using passive self-ligation appliance Class I cases with moderate-to-severe mandibular anterior crowding.

Keywords: Lower Incisor Extraction, Non-Extraction, Passive Self-ligation, Stability

How to cite this article:
Verma P, Jain RK. Comparative evaluation of stability of mandibular anterior crowding correction done with two different treatment protocols: A retrospective study. J Int Oral Health 2022;14:189-94

How to cite this URL:
Verma P, Jain RK. Comparative evaluation of stability of mandibular anterior crowding correction done with two different treatment protocols: A retrospective study. J Int Oral Health [serial online] 2022 [cited 2022 Jun 27];14:189-94. Available from:

  Introduction Top

Crowding of the mandibular anterior teeth is a very common clinical finding and can be corrected by orthodontic treatment involving methods of gaining space such as arch expansion, interproximal reduction, or extraction of the lower anteriors. Little’s irregularity index is used to assess dentoalveolar discrepancy in the lower arch at different time points and can be used to assess the long-term stability of the treatment performed.[1]

A nonextraction treatment protocol for managing moderate dental arch crowding can be accomplished by using passive self-ligation brackets.[2] The passive self-ligation bracket system claims to produce low friction and low forces, which leads to ideal biologic tissue response and gives stable treatment results.[3] Combination of passive self-ligation brackets with hi-tech wires causes arch development and alleviates crowding. According to the Damon philosophy, passive self-ligation appliances generate lighter forces that do not supersede the muscular forces of facial muscles, and thereby the peri-oral musculature exerts a lip-bumper-like effect and prevents proclination of lower incisors.[4] Tooth movement occurs along the path of least resistance and the arch expands laterally, posteriorly, and the anterior crowding is alleviated by adaptation of bone and soft tissues.[5] However, these claims have been contradicted by numerous studies.[6]

Patients with borderline mandibular anterior crowding owing to a mandibular tooth material excess can be traditionally managed by a protocol involving lower incisor extraction with fixed appliances.[7] Previous literature has reported on lower incisor extraction as an alternative to alleviate crowding in certain cases.[8],[9] Lower incisor extraction is indicated in subjects with an Angle’s Class I molar relationship and a mandibular anterior crowding of 4–6 mm, Bolton’s discrepancy owing to either an increased anterior tooth material in the lower arch or decreased tooth material in the upper arch.[10] Lower incisor extraction can also be done as a camouflage option in Class III malocclusions, or rarely in Class II division I cases coupled with upper premolar extractions maintaining posterior occlusion but achieving normal canine occlusion.[11] Cases where bimaxillary extractions are indicated, subjects with deep overbite or subjects with a Bolton’s discrepancy owing to a deficient mandibular anterior tooth material/maxillary anterior excess are contraindicated for lower incisor extraction.[12] In indicated cases, lower incisor extraction can be advantageous as the treatment time is reduced, anchorage demands are less, root parallelism is achieved easily, and soft-tissue profile improves considerably.[13]

There are no published studies comparing and reporting on the long-term stability of mandibular arch dimensions and lower incisor inclinations between nonextraction protocol with passive self-ligation system and lower incisor extraction protocol with conventional ligation. The aim of this retrospective study was to quantitatively evaluate the treatment outcome stability after extraction of one lower. Incisor treated with conventionally ligated MBT appliance and to compare it with the results of nonextraction treatments using passive self-ligation appliance. The null hypothesis was that no significant difference exists in posttreatment stability with two modalities.

  Materials and Methods Top

Setting and design

This study was a retrospective study conducted in the Department of Orthodontics and Dentofacial Orthopaedics, Saveetha Dental College and Hospital, Chennai, India. The study was approved by the Scientific Review Board of the institute (SRB Ref No.: SRB/SDC/ORTHO-1811/21/112). A sample size of 42 was obtained, which was calculated at a significance level of 0.05 and power of 80%.[14] The data for the study were collected from the case records of patients who underwent treatment with a nonextraction protocol using passive self-ligation (Damon Q, Ormco) and subjects treated with conventionally ligated PEA bracket (0.22 slot MBT prescription) with a single incisor extraction protocol. The subjects were selected based on convenience sampling method.

Case records of patients from January 2014 to January 2020 were extracted for the study. The inclusion criteria of the study were (1) A class I skeletal and dental malocclusion, (2) mild-to-moderate mandibular anterior crowding with Little’s irregularity index of 4–6 mm), and (3) anterior Bolton’s ratio of more than 91.3%. Subjects were excluded if they had result-altering variables associated as (1) crossbites, (2) underwent functional appliance therapy/ orthopedic therapy, (3) H/o previous orthodontic treatment, and (4) previous history of extractions or congenitally missing teeth. Group A included subjects treated using the passive self-ligation system (Damon Q, Ormco) with recommended wire sequencing and adequate finishing. Group B included records of subjects treated with conventionally ligated edgewise appliances treated with a lower incisor extraction protocol. Of the total 42 patient records which satisfied the eligibility criteria for the study, only 32 full records at 1-year follow-up period were available which included 15 subjects in Group A and 17 subjects in Group B. In Group B, the extracted lower incisor was either lingually or labially blocked out or was rotated and had a poor prognosis owing to periodontal bone loss. All patients in both groups had been given a lingual bonded retainer in the lower arch and Essix/Begg’s retainer in the upper arch for retention after completion of orthodontic treatment. The study was finished over duration of 6 months starting from January 2021 to June 2021. Treatment records analyzed included digital models and lateral cephalograms [Table 1].
Table 1: Pretreatment demographic data and clinical characteristics of study sample

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Transverse measurements were made on all digital models scanned using the 3 Shape intraoral scanner (Trios, Orthodontic Scanner, Copenhagen, Denmark). All measurements were performed using Ortho Analyzer software. The measurements on lateral cephalograms were made using FACAD software (Version 3.12, Linkoping, Sweden). The primary outcome assessed were changes in transverse mandibular arch dimension, little’s irregularity index, and lower incisor inclination.

Transverse dimension

  1. Intermolar width (IMW): measured from the central fossa of the first mandibular molar of one side to the central fossa of the first mandibular molar on the contralateral side.

  2. Intercanine width: measured from the central fossa of the mandibular canine cusp tip of one side to the mandibular canine cusp tip of the contralateral side [Figure 1].
Figure 1: IMW and ICW measured digitally using Ortho Analyzer software

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Little’s irregularity index: the linear distance between contact points of mandibular anteriors (mesial of right canine to mesial of left canine) was assessed on digital models.

Radiographic measurements

  1. IMPA: angle between the intersection of the long axis of upper incisors and the mandibular plane. The radiographic measurements were made using FACAD software [Figure 2].
Figure 2: Lower incisor inclination (IMPA) recorded on digital lateral cephalograms

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All measurements were recorded by the first author and re-assessed by another author after 2 weeks. All parameters were evaluated at three-time intervals T0, T1, and T2:

  1. T0 = pretreatment

  2. T1 = at completion of treatment

  3. T2 = 1-year after completion of treatment

The change in each parameter was assessed by calculating differences from one time point to another. The following differences were calculated:

  1. T1–T0: The mean change at treatment completion.

  2. T2–T1: change after 1 year of treatment completion

  3. T2–T0: Overall change.

Statistical analysis

Statistical analysis was performed with the SPSS software program (IBM, version 23.0, Chicago, Illinois). The significance level was set at P < .05. The normality of data distribution was analyzed using the Shapiro–Wilk test. Intraobserver reliability was tested using kappa statistics. Comparability of groups based on gender was evaluated using chi-square test. Intergroup comparison was performed using an independent t test.

  Results Top

The data distribution was normal (P < .05) and a kappa value of 0.81 indicated strong agreement between the two authors. Groups were comparable based on age and gender (P > .05). Groups were also comparable for transverse mandibular dimensions, lower anterior crowding, and lower incisor inclination at T0 (P > .05) [Table 1].

  1. Intermolar width.

No significant intergroup difference in IMW change at T1 (P > .05) and at T2 (P > .05) was noted. Also, the overall change in IMW did not differ significantly between the two groups (P > 0.05) [Table 2].
Table 2: Intergroup comparison of change in intermolar width at different time points using the independent t test

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  • 2. Intercanine width.

A significant intergroup difference in ICW at both T1 and T2 (P < .05) was noted. ICW increased significantly in Group A at T1 and there was a significant relapse at T2 in Group A (P < .05). There was a significant intergroup difference in overall change and ICW reduced more in Group B (P < .05) [Table 3].
Table 3: Intergroup comparison of change in intercanine width at different time points assessed using independent t test

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  • 3. Lower incisor inclination.

LII increased in Group A and a significant intergroup difference was noted at T1 (P < .05). At T2, no significant intergroup difference in relapse was noted (P > .5). Overall, LII increased significantly in Group A (P < .05) [Table 4].
Table 4: Intergroup comparison of change in lower incisor inclination at different time points assessed using the independent t test

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  • 4. Little’s irregularity index.

No significant intergroup difference in LI index was noted at T1 (P > .05). A significant intergroup difference in relapse at T2 was noted and more relapse occurred in Group A. Overall change in LII was significantly higher in Group A (P < .05) [Table 5].
Table 5: Intergroup comparison of Little’s irregularity index at T0, T1, and T2

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  Discussion Top

This study attempted to investigate the stability of treatment outcomes in the mandibular arch following treatment with a nonextraction protocol with a passive self-ligation appliance and a lower incisor extraction protocol with MBT prescription. This retrospective study involved case records of patients treated in a university hospital setup from January 2014 to January 2020. Availability of all records at different time intervals was a prerequisite for including the samples in the investigation.

Parameters assessed for evaluation of treatment stability included intermolar width, intercanine widths, Little’s irregularity scores, and lower incisor inclination. No significant difference was found in the pretreatment values in both groups for all parameters (P > .05). Dental arch width and arch form should be maintained during and after completion of orthodontic treatment to ensure treatment stability.[15] Increase in transverse arch width during treatment tend to relapse during the retention phase.[16] In this study we compared the stability in transverse dimension following two different treatment protocols, a nonextraction protocol treated using passive self-ligation appliance and lower incisor extraction protocol treated using conventionally ligated MBT bracket system with similar retention protocols. These two protocols were chosen as they are commonly used in orthodontic practice to alleviate moderate to mild crowding of the lower anterior teeth. Previous studies have reported an increase in IMW with the passive self-ligation appliances.[2] In this study also IMW increased with passive self-ligation mechanotherapy employing a nonextraction protocol. Significant increase was noted in ICW and lower incisor inclination at the end of treatment in Group A. Labial tipping has been seen invariably when a nonextraction treatment protocol is used to resolve crowding without the use of simultaneous distalization.[17]

In Group B, the IMW increased, and ICW decreased marginally after treatment (T1) and was well maintained at 1-year follow-up (T2). Lower incisor angulation decreased which was expected as one incisor was extracted. Studies have reported that functionally stable and esthetic results are obtained with lower incisor extraction.[10],[11] As pointed out by Valinoti,[18] lower incisor extraction treatments have a low tendency of relapse as the incisor is closer to the area of problem and requires less effort and movements in space closure. Riedel et al.[19] also proposed that lower incisor extraction protocol provided a more stable anterior occlusion. In terms of treatment stability, various methods to assess long-term stability of orthodontic treatment have been used.

On intergroup comparison, significant differences were found in terms of ICW, LII, and LI Index. The mean increase in IMW (T1–T0) was similar in both groups and the relapse of IMW width at T2 was nearly twice as with Group A, but the difference was not statistically significant(P > .05). Previous studies reported an increase in IMW in subjects treated with nonextraction protocol using both conventionally ligated appliances and self-ligation but the increase was more in subjects treated with the passive self-ligation.[20],[21] Intergroup differences in ICW were significant between both groups at T1 and T2. One year after treatment, the ICW relapsed more in Group A whereas it was constant in Group B. Overall ICW increased in Group A, whereas it decreased marginally/remained unchanged in Group B. The transverse dimensions increased with Group A; it was expected as the expanded archwires are used with passive self-ligation brackets. Lower incisor angulation was significantly reduced after treatment with lower incisor extraction protocol, whereas a significant increase in LII was noted in Group A. One-year posttreatment, that is, at T2 the lower incisors further proclined in Group A. Overall, labial inclination of lower incisors increased significantly in Group A. This is also reflected in LI index values in Group A subjects, where LI index increased again at T2.

A decrease in incisor irregularity index was noted in both groups at T1. A significant relapse was noted in Group A, where a mean increase 1.09 mm in LII was noted at T2 (P < .05). In terms of overall change (T2–T0) a significant difference was observed in both groups wherein the overall reduction in LII in Group A was 2.86 mm and 4.62 mm in Group B (P < .05). Studies by Yu et al.[22] and Ab Rahman et al.,[14] who evaluated stability with self-ligation appliance and conventional appliance, concluded no difference in terms of incisor irregularity value between both the groups. Their studies compared subjects with two different appliances but all were treated with nonextraction protocols.

Not much literature is available reporting on the impact of two different bracket systems on stability of orthodontic treatment. And, no literature has reported on stability of treatment with two different bracket systems employing two different modalities. A direct comparison of the study results is thereby difficult. Also, the findings of this study do not support the “lip bumper” effects of the self-ligating brackets. An increase in intercanine width will be unstable, therefore a higher tendency for relapse can be expected.[23]

It is evident from the results of the current study that relapse tendencies are less in subjects treated with single incisor extraction with conventional appliances than with a nonextraction passive self-ligation protocol. The null hypothesis was rejected as a significant difference was noted in posttreatment stability in subjects treated with two different orthodontic modalities. In the limitations of this study, treatment effects on only the mandibular arch have been studied. Buccolingual inclination assessment using cone beam computed tomography (CBCT) of molars would have provided a clearer picture of whether the increased molar width is a result of true arch expansion or dentoalveolar tipping. Well-planned prospective studies are needed to report on treatment effects of the Damon system with a nonextraction protocol compared to extraction protocols.

  Conclusion Top

The following conclusions can be drawn from this study:

  • A significant relapse in intercanine width and lower anterior crowding was observed in subjects treated with passive self-ligating mechanotherapy.

  • Lower incisors tend to procline more in subjects treated with passive self-ligating appliances during retention.

  • Significant reduction in lower incisor inclination was noted in conventionally ligated edgewise appliances treated with a single-incisor extraction.

  • Acknowledgement

    The authors would like to acknowledge Department of Orthodontics, Saveetha Dental College for providing us with patient data.

    Financial support and sponsorship

    This study was self-funded.

    Conflicts of interest

    There are no conflicts of interest.

    Authors’ contributions

    Study conception was done by RKJ. Data collection, data acquisition and analysis, data interpretation was done by PV and verified by RKJ. Manuscript writing wad one by PV and final manuscript editing was done by RKJ. All the authors approved the final version of the manuscript for publication .The manuscript has been read and approved by all the authors, that the requirements for authorship as stated earlier in this document have been met, and that each author believes that the manuscript represents honest work if that information is not provided in another form.

    Ethical policy and institutional review board statement

    The study was approved by Scientific Review Board of institute (SRB Ref No.: SRB/SDC/ORTHO-1811/21/112).

    Declaration of patient consent

    The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

    Data availability statement

    The data set used in this study is available on request from corresponding author (Purva Verma, email: [email protected]).

      References Top

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    Mateu ME, Benítez-Rogé S, Calabrese D, Lumi M, Iglesias M, Méndez P, et al. Prospective clinical study of transverse development with orthodontics with self-ligating brackets. Acta Odontol Latinoam 2020;33:112-6.  Back to cited text no. 2
    Lima NCJ, de Mendonça Campos Freitas Falcão IC, de Freitas KMS, de Lima DV, Valarelli FP, Cançado RH, et al. Comparison of changes in dental arch dimensions in cases treated with conventional appliances and self-ligating Damon system. Open Dent J 2018;12:1137-46.  Back to cited text no. 3
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      [Figure 1], [Figure 2]

      [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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