Twelve-year follow-up of mandibular incisor stability: Comparison between two bonded lingual orthodontic retainers

Abstract

Objective: To compare the long-term outcome 9 years after removal of two different types of fixed retainers used for stabilization of the mandibular anterior segment. Materials and Methods: Sixty-four children who had undergone orthodontic treatment with fixed appliances in both arches were divided into two groups depending on which kind of retainer being used. Twenty-eight of the patients had a canine-to-canine retainer bonded to the canines and 36 had a bonded twistflex retainer 3-3, bonded to each tooth. Measurements were made on study models and lateral head radiographs, before and after treatment, 6 years after treatment, and 12 years after treatment, with a mean of 9.2 years after removal of the retainers. Results: No significant differences were found between the two groups at the long-term follow-up according to Little's Irregularity Index or available space for the mandibular incisors. The overjet and overbite were reduced after treatment in both groups and stayed stable throughout the observation period. Also, no differences in bonding failures between the two retainers were found. Conclusions: Both a canine-to-canine retainer bonded only to the canines and a twistflex retainer 3-3 bonded to each tooth can be recommended. However, neither of the retention types prevented long-term changes of mandibular incisor irregularity or available space for the mandibular incisors after removal of the retainers.

Relationship between oral function and mandibular anterior crowding in early mixed dentition

“…Plaster models were measured in 0.01 mm units using a digital caliper (Mitutoyo, Kanagawa, Japan) for all measurements. The 13 measured items included the maxillary and mandibular intercanine widths, mandibular intercanine perimeter distance, lateral arch lengths from the maxillary and mandibular central incisors to first molars, sum of the widths of the mandibular four incisors, available mandibular incisor space (intercanine perimeter distance minus the sum of the widths of the four incisors), maxillary inter‐first molar width (distance from central sulcus to central sulcus of the upper first molars), overjet, and overbite; these items were presumably related to mandibular anterior crowding based on the findings of previous studies (Figure 1; Louly, Nouer, Janson, & Pinzan, 2011; Schutz‐Fransson, Lindsten, Bjerklin, & Bondemark, 2017). Additionally, Little's irregularity index (LII) was measured; this was defined as the sum of displacement of the anatomic contact points of the mandibular anterior teeth (Figure 2).…”

“…Co., Ltd., Kyoto, Japan) in accordance with the manufacturer's instructions and were traced. Cephalometric reference points and measurements were assessed following the method of Schutz‐Fransson et al (2017). Reference lines and points are shown in Figure 3, and the following 11 measurement items were recorded: 1.…”

Periodontal parameters of two types of 3 x 3 orthodontic retainer: a longitudinal study

“…It has been suggested that the stability of the mandibular interincisor region may only be guaranteed if retainers are maintained throughout life. 13 , 14 The need for maintaining the intercanine distance is emphasized, as it undergoes changes with age, irrespective of orthodontic treatment. The question remains whether the retainers should be bonded to all the incisors, or whether it would be acceptable for them to be bonded only to the canines.…”

“…2 , 7 , 8 Nevertheless, apparently retainers bonded to mandibular anterior teeth have presented worst periodontal indexes than those observed for retainers bonded to the canines only. 9 - 14 However, when there is excessive misalignment of the incisors before orthodontic treatment, it appears to be rational to stabilize them individually, considering the probable dissatisfaction of patients in case of short term instability. 2 , 4 , 7 , 8 , 15 , 16 Another alternative is to inform the patient about the possibility of instability in the area, and adopt classical retainers bonded to the canines only, and if any alteration should occur, proceed with localized correction, followed by new stabilization.…”

Intention to treat (ITT) analysis as reported in orthodontic randomized controlled trials—evaluations of methodology and recommendations for the accurate use of ITT analysis and handling dropouts

“…If dropouts occur at the 5-year follow-up registration and the LOCF method is applied, the registrations for the 2-year follow-up have to be used for those subjects who dropped out at the 5-year registration. However, it is well known from previous studies regarding incisor stability that the Little Irregularity Index worsens in the long term (21,22). Consequently, when the LOCF procedure is applied, the risk is clear that the kept Little Irregularity Index at the 2-year follow-up registration (now also used as the 5-year registration) will be lower than it would have been if the subject had been maintained at the trial registration as planned at the 5-year follow-up.…”