Comparison of Retention Characteristics of Clear bow Hawley’s and Vacuum Formed Retainers—A Randomized Controlled Trial

Sowmithra Devi; Ravindra Kumar Jain

doi:10.4103/jofs.jofs_259_22

ORIGINAL ARTICLE

Year : 2022 | Volume : 14 | Issue : 2 | Page : 128-133

Comparison of Retention Characteristics of Clear bow Hawley’s and Vacuum Formed Retainers—A Randomized Controlled Trial

Sowmithra Devi, Ravindra Kumar Jain
Department of Orthodontics, Saveetha Dental College, Saveetha Institute of Medical And Technical Sciences (SIMATS), Saveetha University, Chennai, India

Date of Submission	31-Oct-2022
Date of Decision	10-Nov-2022
Date of Acceptance	15-Nov-2022
Date of Web Publication	10-Jan-2023

Correspondence Address:
Dr. Ravindra Kumar Jain
Department of Orthodontics, Saveetha Dental College, Saveetha Institute of Medical And Technical Sciences (SIMATS), Saveetha University, Chennai
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jofs.jofs_259_22

Abstract

Introduction: Retention is an important stage of orthodontic treatment which involves maintaining the teeth in the corrected position. The aim of this trial was to compare the retentive capacity of Clear bow Hawley (CBR) and Vacuum formed retainer (VFR) 1 year after completion of orthodontic treatment. Materials and Methods: This prospective randomized controlled trial included 46 subjects who were treated with fixed orthodontic appliances and were advised to use removable orthodontic retainers. The subjects were randomly allocated to two groups, group 1–23 subjects who received CBRs and group 2–23 subjects who received VFRs. Retainers were advised immediately after debonding and patients were recalled after 1 year. Lateral cephalograms and intraoral scans were taken and certain parameters (inter canine, intermolar width, little’s irregularity index, arch length) were evaluated. Descriptive statistics and paired t-test were done to determine and compare the retentive capacity of the retainers. Results: No statistically significant relapse was noted and no differences between retainers for inter canine, intermolar width, arch length, little’s irregularity index, and cephalometric changes were noted (P > 0.05). Conclusion: Both the CBRs and VFRs are equally effective in retaining the corrected malocclusion, CBRs can be considered as a very good alternative to VFRs.

Keywords: orthodontic appliance, retention, relapse

How to cite this article:
Devi S, Jain RK. Comparison of Retention Characteristics of Clear bow Hawley’s and Vacuum Formed Retainers—A Randomized Controlled Trial. J Orofac Sci 2022;14:128-33

How to cite this URL:
Devi S, Jain RK. Comparison of Retention Characteristics of Clear bow Hawley’s and Vacuum Formed Retainers—A Randomized Controlled Trial. J Orofac Sci [serial online] 2022 [cited 2023 Jun 8];14:128-33. Available from: https://www.jofs.in/text.asp?2022/14/2/128/367446

Introduction

Retention is an important stage of orthodontic treatment which involves maintaining the teeth in the corrected position. According to Moyers, “The holding of teeth following orthodontic treatment in the treated position for the period of time necessary for the maintenance of the result.”^[1] Age related changes in the dentition can also greatly affect the stability of treatment outcomes.^[2] Periodontal fibers take 3 to 4 months to reorganize while gingival fibers take 4 to 5 months to reorganize with supracrestal fibers requiring 232 days.^[3] But Reitan claims that principal fibers of periodontal ligament require 8 to 9 months for reorganization whereas the supracrestal fibers remain stretched for a longer time implying that long-term retention is required.^[4] Removable retainers can be Hawley’s, Begg wrap-around retainers which have a labial bow.^[5] Vacuum formed retainers are esthetic in appearance and also effective at retention.^[6] Fixed retainers have certain advantages which include esthetics, patient compliance, efficacy, and appropriateness for lifelong retention.^[7] A recently introduced retainer to overcome the limitations of existing retainers is the “Clear Bow Hawley’s Retainer (CBR).” A previous case report by Needham et al. in 2016 had reported the esthetic advantage of using CBR, a removable type of retainer which has a clear strap made up of food-grade polyethylene terephthalate (PET) replacing the metal labial bow of conventional HR and grade 316 stainless steel, joined together at a Coil tight Joint.^[8] An evaluation of patient acceptance comparison between CBRs and VFRs was studied and reported.^[9]

Various studies evaluated the retentive characteristics of different removable retainers, such as HR and VFR.^{[6],[10],[12]} In all of the previously mentioned studies, retentive capacity of the retainers was assessed at different time intervals using lateral cephalograms and study models. No previous studies have evaluated the long-term retentive capacity of CBR. The design of the CBR is similar to that of the HR but the material used for fabrication is different which might influence its retentive capacity on a long-term basis.

The present trial aims to evaluate and compare the retentive capacity of CBRs and VFRs after a 1-year retention period. The null hypothesis is no difference between the two retainers in terms of their effectiveness in maintaining the results of orthodontic treatment and the alternate hypothesis is that there is a significant difference in the retentive capacity of the retainer.

Materials and Methods

This study was designed and conducted as a prospective randomized controlled trial. Ethical approval for this study (protocol no. IHEC/SDC/ORTHO-2001/21/653) was provided by the Ethical Committee NAC of Saveetha University and Hospitals on 2nd april 2021.

This trial was approved by the institutional scientific review board of Saveetha University. The patient recruitment for the study was started in March to April 2021 and the study was completed by May to June 2022.

The inclusion criteria were: (1) Subjects more than 18 years of age for whom orthodontic treatment was completed with good finishing assessed with Peer Assessment Rating (PAR) index. (2) Skeletal class 1. Exclusion criteria for sample selection are: (1) Subjects not willing to use removable retainers or indicated for bonded retainers. Subjects in whom rapid arch expansion/orthognathic surgery was done. (2) Subjects with hypodontia, cleft lip palate/craniofacial anomalies. (3) Treatment with passive self-ligation mechanotherapy.

Based on selection criteria, 46 participants were included in the study. All participants underwent orthodontic treatment at the Department of Orthodontics Saveetha dental college and hospitals by post-graduates. All the participants were contacted through telephone and recalled for review at the end of 1 year. A total of 40 participants reported for review at the end of 1 year of retention period but four participants could not be contacted and two patients moved to another place so they were lost to follow up.

Consolidated Standards of Reporting Trials (CONSORT) flow diagram depicts the patient recruitment, follow up, and eligibility for data analysis [Figure 1]. Description of cephalometric and occlusal parameters assessed in this study ([Table 1]). The characteristics of the recruited participants are detailed in ([Table 2]).

Figure 1 Clear bow Hawley’s retainer and Vacuum formed retainer.

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Table 1 Description of cephalometric and occlusal parameters assessed in this study

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Table 2 Characteristics of participants included in the trial

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The sample size calculation was done using G*Power 3.1.9.4 software (Germany) with a significance of 5% (0.05) and a power of 90% from the previous study by Chagas et al. A sample size of 46 was obtained after calculating the total sample size. However, the final sample was 40 as six subjects were lost to follow up after 1 year (four participants from group 1 and two participants from group 2).

Randomization was done using a table of random numbers and each patient was asked to pick one concealed envelope from a black box. The primary investigator who collected the responses was blinded about the type of intervention received by the participants. Blinding of the study subjects and the primary investigator was not possible in this study. Written informed consent was obtained from all of the study participants after explaining the purpose of the study. Group 1 consisted of 19 subjects who received CBRs and group 2 consisted of 21 subjects who received VFRs.

Before debonding of fixed appliances, finishing of the case was assessed with PAR index by the primary investigator. Written and informed consent was obtained from all the participants in accordance to recent Helsinki declaration guidelines. Fixed orthodontic appliances were removed using a debonding plier (GDC, India) and the residual adhesive was cleaned using 12-fluted tungsten carbide bur.

Impressions of the upper and lower arches of the participants were made and sent to the lab for fabrication of CBRs and VFRs. The CBR has a 2.75-mm wide labial bow made of PET extended till the canine or 1st premolar according to the case (extended till premolar if required), as shown in [Figure 1]a. All retainers were fabricated by the same technician at the same laboratory. VFRs were made with PET material of thickness 1 mm and vacuum formed using a Biostar machine, extended till the last erupted tooth [Figure 1]b. Once fabricated, they were delivered to patients by a single clinician and were instructed to wear full time except during meals and brushing. Full time wear was instructed to the patients for the first 6 months and night time wear for the next 6 months according to Reiten’s retention protocol as periodontal fibers may take 8 to 9 months for reorganization.^[4] Patients were recalled after 1 year to evaluate the retentive capacity of the retainer. Lateral cephalograms and digital intraoral scans (TRIOS 3 Shape intraoral scanners) were taken to evaluate cephalometric and occlusal contact changes using Dolphin Imaging software version 8.0 and 3 Shape Dental System software version 5.0. Appropriate calibration of the lateral cephalogram was done in Dolphin software with accuracy of 0.1 mm. All measurements were done by a single investigator to avoid any bias and participant allocation was concealed too. Kappa statistics was done to assess Intra Class Correlation (ICC) for cephalometric and occlusal parameters assessed in the study. ICC values <0.5 are indicative of poor reliability, values between 0.5 and 0.75 indicate moderate reliability, values between 0.75 and 0.9 indicate good reliability, and values >0.90 indicate excellent reliability. The ICC values of cephalometric and occlusal parameters showed a reliability value of 0.92 (0.899–1.000) indicating high reliability. Descriptive statistics was done to find out the mean difference values of all the cephalometric and occlusal parameters assessed in the study for both the groups. Paired t-test was done to evaluate differences between T0 and T1 of group 1 and 2 for cephalometric and occlusal contact changes.

Results

The data collected were entered in excel spreadsheet and were imported to SPSS (Armonk, NY: IBM Corp.) software version 23.0. A single investigator was in charge of data collection and entry. An independent statistician who was not engaged in the study performed the statistical analysis. Cephalometric and dental arch dimensions of subjects at T0 are depicted in [Table 3]. Descriptive statistics and paired t-test showing mean cephalometric parameters which do not show any significant difference between pre (T1) and post (T2) retention of the CBR and VFRs appliance ([Table 4]) (P > 0.05). The retention of the appliances was evaluated by assessing the dental arch dimensional changes at T0 and T1 for both the groups ([Table 5]). Dental arch dimensional changes of both groups did not show any statistically significant difference between the two retainers indicating an equivalent efficacy of both the retainers in maintaining the orthodontic treatment results (P > 0.05) ([Table 5]).

Table 3 Cephalometric and dental arch dimensions of participants at T0

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Table 4 Intragroup and intergroup differences of cephalometric parameters assessed in both the groups (P < 0.05)

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Table 5 Intragroup and intergroup comparison of arch dimension changes (P < 0.05)

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Intergroup comparison using independent t-test did not show a statistically significant difference between the group 1 and 2 for both cephalometric and occlusal parameters (P > 0.05) ([Table 4] and [Table 5]).

Discussion

Following the cessation of active orthodontic tooth movement, the retention phase of treatment sustains the teeth in their corrected locations. Orthodontic retainers restrict teeth from reverting to their pretreatment positions when periodontal, occlusal, and soft tissue pressures are applied. Forty six subjects after completion of orthodontic treatment were involved in this study and at the end of 1 year (T1) an evaluation of the retentive capacity of the two different retainers was assessed using lateral cephalograms and digital models for 40 subjects. The results of the study showed no significant relapse in dental arch dimensions and cephalometric parameters at T1 with both retainers. On intergroup comparison no significant difference in terms of cephalometric and dental arch dimension changes was noted (P > 0.05).

Inter canine and intermolar width changes are one of the important parameters to assess relapse and in this study super imposition of digital models is done to assess the same. It was found that the maxillary inter canine width showed a slight increase at T1 for group 1 and mandibular arch for group 2 but no statistically significant difference between the groups was noted (P > 0.05). Similar results were noted in another study by Demir et al. in which it was reported that no significant difference between HRs and VFRs for IC changes was noted.^[11]

Factors like type and severity of malocclusion, amount of performed tooth movement, method of gaining space, type of biomechanics used can influence the retention of a corrected malocclusion. In the study no segregation of the study subjects based on the above factors was done as the aim was only to assess the retention capacity of the retainer used. The maxillary arch in group 2 showed slight decrease in intermolar width but no statistically significant difference in IM width between groups and also within groups (P > 0.05) was observed. In a study by Motamedi et al., decrease in intermolar width for extraction cases and increase in intermolar width for non-extraction cases were observed in patients on orthodontic retainers.^[13]

The LI index as proposed by Robert M. Little helps to measure the horizontal linear displacement of anatomic contact points of each mandibular incisor from the adjacent anatomic point and sums the five displacements together. The LI index of subjects treated with CBRs showed an increase in the irregularity of teeth at T1 but no statistically significant difference was observed in intra-group and intergroup comparisons of both the retainers (P > 0.05). AL increased in the lower arch in both group 1 and group 2 whereas it decreased in the upper arch of both the groups but these observed changes were minimal with no statistically significant difference (P > 0.05). Relapse of tooth inclination was assessed using the lateral cephalometric radiographs. Intergroup and intragroup comparison tests revealed a minimal mean difference for all the cephalometric parameters that was <0.5 in both the groups and a statistically non-significant difference between T0 and T1 for both the groups. The results of the present study are similar to another study by Demir et al. where they compared retention characteristics of Essix and Hawley retainer with a retention period of 1 year and obtained no significant differences for cephalometric parameters.^[11]

A previous study on comparison of stability of orthodontic treatment results between Hawley’s and VFR concluded that both the retainers are equally effective in maintaining the results of the treatment.^[14] Ashari et al. reported a 2-year comparative assessment of retentive capacity of VFRs and HRs and found a similar retentive capacity for both the retainers by assessing the inter canine, inter premolar, and intermolar width in dental casts.^[15] Similarly, a systematic review assessing the retention, patient satisfaction, and survival time of HRs and VFRs concluded that there is no difference in inter canine and inter molar widths suggesting non-significant difference in retentive capacity of both retainers.^[16] Occlusal contact changes had been previously reported between HRs and VFRs and it was observed that HRs had improved occlusal contacts.^[17] In a previous study by Devi et al., comparison of patient satisfaction between CBRs and VFRs showed that the CBRs were preferred in terms of esthetics and comfort and in this study, it is noted that retention characteristics of CBRs are comparable to that of VFRs.^[9] Hence, CBRs can be used a good alternative for VFRs.Limitations of the study include patient compliance which is subjective and has the possibility to influence the results of the study. Blinding of the personnel and participants was not possible due to the inherent potential of the trial. Future studies should be carried out to overcome these drawbacks.

Conclusion

Both the retainers were effective in retaining the corrected occlusion after orthodontic treatment and in comparison, no difference in retentive capacity was noted between them. Hence, CBRs can be considered as an alternative to VFRs as it is esthetic and will also allow occlusal settling.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors report no conflicts of interest.

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