Introduction
The stability of treatment results is a major concern in orthodontics. Numerous retention regimens to maintain stability have been introduced. The objectives of this study were to evaluate the effects of vacuum-formed retainers (VFRs) on periodontal tissues and the retention efficiency of VFRs.
Methods
Forty patients were included in this study. Clinical effectiveness of VFRs for nighttime use only over a 12-month period was assessed by using the American Board of Orthodontics’ Objective Grading System. Periodontal measurements and indexes were recorded and evaluated immediately after removal of the braces and after 1, 6, and 12 months of VFR use.
Results
There was no significant change in the total Objective Grading System score between the end of the active treatment period and the end of the 12-month retention period. However, regarding periodontal measurements, the plaque and gingival indexes decreased, whereas the bleeding on probing, probing depth, calculus index, and clinical attachment loss increased between the evaluated periods.
Conclusions
In terms of periodontal health, the use of VFRs resulted in a slight periodontal attachment loss that seemed to be clinically insignificant, without gingival inflammation or recession. In terms of stability, VFRs were found to be effective in orthodontic retention.
Highlights
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Vacuum-formed retainers were found to be effective in orthodontic retention.
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Their long-term use resulted in a slight periodontal attachment loss.
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Their long-term use did not lead to gingival inflammation or gingival recession.
The success of an orthodontic treatment should not be defined only as the achievement of perfectly aligned teeth and occlusion; the definition must also consider the stability of the results. Long-term studies have shown that relapse occurs in approximately 70% of orthodontic patients, and that it is impossible to predict the degree of relapse. In the long term, relapse can be associated with changes related to growth and orthodontic treatment. Up to a year may be needed for the periodontal tissues, alveolar bone, and surrounding soft tissues to reorganize and adapt to the new positions of replaced teeth. Therefore, it is important to help prevent relapse with appropriate retention procedures.
Studies have introduced numerous retention regimens aimed at preventing relapse after orthodontic treatment. The most commonly prescribed types have been Hawley retainers, bonded canine-to-canine retainers, and vacuum-formed retainers (VFRs). Despite their disadvantages, such as reduced vertical settling and occlusal wear, VFRs are becoming increasingly popular due to their improved esthetics, ease of application, reduced cost, and ease of fabrication. The influence of retention regimens on periodontal health is as important as their effectiveness in preventing relapse. To date, only a few studies have focused on the periodontal health implications of orthodontic retainers. The aims of this study were to evaluate the effects of VFRs on periodontal health and their retention effectiveness.
Material and methods
The study protocol was approved by the Ethics Comittee of Istanbul University Faculty of Medicine for Human Subjects. The study was carried out at the Departments of Orthodontics and Periodontology clinics, Faculty of Dentistry, at Istanbul University. Written informed consent was obtained from all subjects or their legal guardians before their inclusion.
Forty patients were included in this study. The test group comprised 21 patients (14 female, 7 male) with a mean age (± standard deviation) of 15.9 ± 2.0 years (range, 12-19 years). The control group comprised 19 patients (16 female, 3 male) with a mean age of 16.0 ± 2.7 years (range, 10-19 years). Subjects in the test group received fixed orthodontic therapy using a straight-wire appliance. The control subjects were periodontally healthy persons who received no orthodontic treatment and were age-matched with the test group. This group was used to confirm the periodontal health status of the patients who had orthodontic treatment before the application of retainers. Values of the control group were also used as healthy references for comparisons with the test group.
Subjects were excluded from the study if they met any of the following criteria: (1) severe malocclusion according to the American Board of Orthodontics (ABO) discrepancy index; (2) need for fixed retention; (3) disability preventing removable appliance use; (4) periodontal disease; (5) any systemic disease, at any time, that could influence the periodontium; (6) antibiotic, anti-inflammatory, or steroid drug use; (7) rapid maxillary expansion; (8) interdental stripping or gingival fiberotomy; (9) cleft lip or palate or orthognathic surgery, or (10) smoking.
Among the participants who met the criteria for inclusion, those with similar degrees of malocclusion were included in the study. Degree of malocclusion was assessed by determining the ABO discrepancy index, based on candidates’ initial records. Initial periodontal records were taken at the debonding appointment after removal of the braces but before adhesive removal or polishing. Immediately after the records were taken, residual adhesives were removed, polishing was performed, oral hygiene instructions were given, and alginate impressions were taken for preparation of VFRs.
VFRs were constructed by the same laboratory technician with 0.04-in plastic material (Essix ACE; Dentsply International, York, Pa), which was trimmed to extend 2 mm in the buccal direction and 2 to 4 mm in the lingual direction ( Fig ). VFRs covered all of visible surfaces of all teeth. VFRs were produced and fitted on the same day as debonding. Upon receiving their VFRs, participants were instructed to wear them full-time for the first week and only at night thereafter, and to clean them once a day.
To assess the clinical effectiveness of the VFRs, retainers were scored by using the ABO’s Objective Grading System (OGS). Scoring was performed on the basis of casts and panoramic radiographs taken at the debonding appointment and 12 months after debonding. All measurements were performed by the same researcher (M.Ç.) using an ABO measuring gauge.
Initial periodontal measurements were performed at the beginning of the study at the same appointment when the fixed appliances were removed, before tooth surface cleaning. After these measurements were recorded, all test group patients received scaling, polishing, and oral hygiene instructions before application of the VFR. Test group patients were recalled for periodontal examinations at 1, 6, and 12 months after receipt of the VFR. Comparisons between time points in the test group were referenced to the 1-month measurement values. Control group patients were not recalled for further clinical evaluation because they were periodontally healthy and did not require orthodontic treatment.
Periodontal evaluation was carried out by recording the following indexes: plaque index, bleeding on probing, gingival index, probing depth, amount of gingival recession, clinical attachment level, and calculus index. All indexes except the calculus index were measured at 6 sites on each tooth, and the mean values of these measurements were calculated for each subject. Bleeding on probing values were recorded as the percentage of sites that bled within 30 seconds after probing; mean values were calculated for each subject. Gingival recession was measured from the cementoenamel junction to the free gingival margin. Clinical attachment loos was calculated by adding the gingival recession value to the probing depth value. The calculus index was measured from the lingual side of the mandibular incisors and canines, with the mean value calculated for each subject.
Statistical analysis
Mean values were considered as the unit of observation for statistical analysis. Descriptive statistical measures were determined for demographic, periodontal, and orthodontic data. Orthodontic and periodontal measurements at different time points in the test group were compared with the Wilcoxon signed rank test. Differences between the test and control groups were compared with the Mann-Whitney U test. For this evaluation, we used measurement values for the test group after 1 month of retainer use, the first measurement point. All analyses were carried out with the SPSS package for statistical analyses (version 22.0; IBM, Armonk, NY).
Results
The clinical effectiveness of VFRs in the test group was measured by determining the OGS score, based on results from plaster models and panoramic radiographs taken at debonding and after 12 months of VFR use. Differences in OGS scores between these times were statistically evaluated ( Table I ).
| Index | Baseline | 12-month follow-up |
|---|---|---|
| Alignment/rotations | 2.09 ± 1.18 | 3.43 ± 1.89 ∗ |
| Buccolingual inclination | 2.33 ± 1.56 | 1.86 ± 1.35 ∗ |
| Occlusal contacts | 2.95 ± 1.72 | 2.29 ± 1.23 ∗ |
| Interproximal contacts | 1.33 ± 0.66 | 1.67 ± 0.98 ∗ |
| Marginal ridges | 2.95 ± 1.28 | 2.52 ± 0.98 ∗ |
| Overjet | 2.67 ± 1.85 | 3.29 ± 1.62 |
| Occlusal relationships | 2.43 ± 1.29 | 2.48 ± 1.29 |
| Root angulation | 1.62 ± 1.20 | 1.62 ± 1.20 |
| Total score | 10.38 ± 4.74 | 11.10 ± 4.94 |
∗ Statistically significant difference of 12-month measurement compared with baseline measurement ( P <0.05).
The mean score of the OGS item “alignment/rotations” significantly increased by 1.34 between time points, with 76.2% of the patients showing an increase, and 23.8% showing no change in this score. The mean score of “occlusal contacts” significantly decreased by 0.66, with 47.6% of patients showing a decrease, 9.5% showing an increase, and 42.9% showing no change. The mean score of “marginal ridges” significantly decreased by 0.43, with 42.9% of patients showing a decrease, 9.5% showing an increase, and 47.6% showing no change. The mean score of “occlusal relationship” showed a nonsignificant increase of 0.05, with 23.8% of patients showing an increase, 23.8% showing a decrease, and 52.4% showing no change. The mean score of “buccolingual inclination” significantly decreased by 0.47, with 33% of patients showing a decrease and 67% showing no change. The mean score of “interproximal contacts” significantly increased by 0.34. The mean score of “overjet” showed a nonsignificant increase of 0.62, with 19% of subjects showing a decrease, 42.9% showing an increase, and 38.1% showing no change. The OGS item “root angulation” showed no difference between time points. The mean total score before retainer use was 10.38, which increased to 11.10 after 12 months of use (difference of 0.72, not significant). The total score decreased for 38.1%, increased for 52.4%, and remained the same for 9.5% of the subjects.
Table II presents the mean values for periodontal status at baseline (both groups) and at the 1, 6, and 12-month follow-ups (test group only). Compared with the control group, all test subjects were periodontally healthy at the first measurement after removal of the braces. In the test group, mean values of the plaque index and the gingival index decreased steadily throughout the study period, with no statistically significant differences between measurements recorded at 6 and 12 months compared with measurements at 1 month. Mean bleeding on probing percentages showed a slight increase without significant changes during the study period. Calculus index scores increased slightly but significantly between measurements at 1 month and at 6 and 12 months. Mean probing depth and clinical attachment level values increased slightly between 1 month and the end of the study period, but this increase did not reach statistical significance. Mean gingival recession values changed slightly at the 6- and 12-month measurements, but these differences were not significant.
| Index | Baseline | 1 month | 6 months | 12 months | |
|---|---|---|---|---|---|
| Test group | Control group | Test group | Test group | Test group | |
| PI | 1.09 ± 0.60 | 0.82 ± 0.24 | 0.83 ± 0.39 | 0.75 ± 0.48 † | 0.69 ± 0.35 † |
| GI | 1.07 ± 0.49 | 0.93 ± 0.38 | 0.83 ± 0.40 | 0.78 ± 0.33 † | 0.63 ± 0.25 † |
| BOP | 32.43 ± 14.62 | 26.84 ± 16.67 | 29.57 ± 14.50 | 31.00 ± 14.47 | 37.14 ± 12.91 † |
| PD | 1.70 ± 0.19 | 1.70 ± 0.13 | 1.73 ± 0.39 | 1.93 ± 0.47 † | 1.91 ± 0.53 † |
| GR | 0 | 0 | 0 | 0.01 ± 0.03 | 0.01 ± 0.02 |
| CAL | 1.70 ± 0.19 | 1.70 ± 0.13 | 1.73 ± 0.39 | 1.94 ± 0.69 † | 1.91 ± 0.53 † |
| CI | 0.79 ± 0.40 | 0.65 ± 0.50 | 0.79 ± 0.40 | 1.07 ± 0.44 ∗ † | 1.17 ± 0.37 ∗ † |
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