All PhD Theses

A.M. Renkema-Padmos

Permanent retention from a long-term perspective

13-12-2013

A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 13th of December 2013

SUMMARY

Chapter 1 gives a brief introduction about orthodontic relapse, post-treatment changes,  0rthodontic retention in general, and more specific, retention with bonded retainers. Bonded retainers have been widely used as an orthodontic retention appliance for the past four decades. It addresses the need for prolonged retention with minimum patient compliance. Definite disadvantages of bonded retainers include the risk of retainer failures and the accumulation of plaque. Studies reporting on the effectiveness, failure rates and detrimental effects of bonded retainers are based on small patient groups and/or short observation periods. The overall objective of this thesis and specific aims are presented.

The aim of the survey described in chapter 2 was to get more insight into retention strategies applied in Dutch orthodontic practices. The overall response rate was 91 per cent. Most orthodontists placed a bonded retainer in the upper and lower arch, except when the upper arch was expanded during treatment or when extractions were performed in the upper arch, in which case they placed a removable retainer. Opinions regarding the use of removable retainers varied in terms of daily wear and the duration of the retention phase. Contra-indications for bonded retainers were given by 96% of the orthodontists, with poor oral hygiene being the most commonly mentioned. Orthodontists who only used bonded retainers (5%) did not want to depend on patient compliance. The few who only used removable retainers (3%) quoted bond failures and breakages as main reason for not using bonded retainers. As far as bonded retainers are concerned, 84% of the orthodontists preferred permanent retention. Almost 60% of the orthodontists believed that a practice guideline for retention after orthodontic treatment is needed, which was indicated  by the varied responses in this survey.

Chapter 3 describes a study to assess the long-term effectiveness of the   33-43 lingual (0.0215 x 0.027-inch stainless steel) retainer in preventing orthodontic relapse. In a group of 235 patients a 33-43 lingual retainer was placed after active treatment. During orthodontic treatment the mean irregularity index decreased significantly from 7.2 mm (SD, 4.0) to 0.3 mm (SD, 0.5); it increased significantly to 0.7 mm (SD, 0.8) at 2 years post-treatment and 0.9 mm (SD, 0.9) at 5 years post-treatment. During the 5-year post-treatment period the irregularity index was stable in 141 patients (60%) and increased by 1.0 mm (SD, 0.8) in 94 patients (40%). The 33-43 lingual stainless-steel retainer was effective in preventing relapse in the mandibular anterior region in 60% of the patients. A relatively high percentage experienced a small to moderate increase in mandibular incisor irregularity. Twenty per cent of the patients encountered retainer failures in this study. The number of failures negatively influenced the alignment of the mandibular anterior region.

In chapter 4 the results of a study to assess the long-term effectiveness of the FSW (0.0195-inch, 3-strand) retainer in maintaining orthodontic alignment are presented. In a group of 221 patients an FSW lingual retainer was bonded to the 33-32-31-41-42-43 following active treatment. During orthodontic treatment the mean irregularity index decreased significantly from 5.35 mm (SD, 3.47) to 0.08 mm (SD, 0.23). Alignment of the mandibular anterior teeth was stable in 200 patients (90.5%) up to 5 years post-treatment; in 21 patients (9.5%), a mean increase of 0.81 mm SD, 0.47) was observed. The increase of the irregularity was strongly related to bond failures. Undesirable post-treatment complications—torque differences of the incisors or an increased buccal canine inclination—were observed in 6 patients (2.7%). The 33-32-31-41-42-43 lingual FSW retainer was very effective in maintaining the alignment of the mandibular anterior region after active orthodontic treatment. It was concluded that, in patients with a FSW lingual retainer, regular check-ups are necessary to determine bond failures, post-treatment changes, and complications as early as possible.

The aim of the study described in chapter 5 was threefold: (1) to assess  the prevalence of gingival recessions in orthodontic patients before, immediately after, 2 years, and 5 years after orthodontic treatment, (2) to evaluate the development of recessions in various regions of the dental arches, and (3) to identify variables associated with the development of gingival recessions. Vestibular gingival recessions were scored for all teeth using initial, end-of-treatment, 2- and 5-years post-treatment plaster models of 302 orthodontic patients. All patients had a fixed retainer bonded lingual to either the mandibular canines only, or to all six mandibular front teeth. A continuous increase in gingival recessions after treatment was found from 7% at the end of treatment to 20% at 2 years post-treatment, and to 38% at 5 years post-treatment. Patients younger than 16 years of age at the end of treatment were less likely to develop recessions than patients older than 16 years at the end of treatment. The prevalence of recessions was not associated with gender or extraction treatment. The type of fixed retainer did not influence the development of recessions in the mandibular front region. The prevalence of gingival recessions steadily increased after orthodontic treatment and was higher in older than in younger patients. No variable, except for age at the end of treatment, seemed to be associated with the development of gingival recessions.

The aim of the study described in chapter 6 was to test the hypothesis that a change of the inclination of the lower incisors promotes development of labial gingival recessions. The study group consisted of 197 subjects—11 to 14 years at the start of orthodontic treatment—with a mandibular retainer bonded immediately after treatment. Clinical crown heights of mandibular incisors and the presence of gingival recessions in this region were assessed on pre-treatment, post-treatment, 2-years and 5-years post-treatment plaster models, and on lateral cephalometric radiographs mandibular incisor inclination at the 4 stages was determined. The sample was divided—depending on the change of lower incisor inclination by orthodontic treatment—into three groups: Retro, Stable, and Pro. The mean increase of clinical crown heights of mandibular incisors from the end-of-treatment to the 5-years post-treatment stage was 0.60 mm, 0.88 mm and 0.91 mm in the Retro-, Stable-, and Pro-group, respectively; the difference was not significant. At 5-years post-treatment, gingival recessions were present in 8.8%, 4.5%, and 16.3% of the patients from the Retro-, Stable-, and Pro-group, respectively. The difference was not significant. The changes in lower incisor inclination during treatment did not affect the development of labial gingival recessions in this group of patients. 

In chapter 7 the results of a study evaluating the long-term development of labial gingival recessions in orthodontically treated and untreated individuals are presented. In this retrospective case-control study the presence of gingival recession was scored on plaster models of 100 orthodontic patients (cases) and 120 controls at the age of approximately 12 (T12), 15 (T15), 18 (T18), and 21 (T21) years. In the treated group, T12 reflected the start of orthodontic treatment, and T15 the end of active treatment and the start of the retention phase with bonded retainers. The proportion of subjects with recessions was consistently higher in cases than in controls. Orthodontic treatment and/or the retention phase are risk factors for the development of labial gingival recessions. In orthodontically treated subjects mandibular incisors seem to be the most vulnerable to the development of gingival recessions. Risk factors for the development of gingival recessions should be investigated in a prospective study.

Finally, in chapter 8 a general discussion of the methodological issues is presented. It describes the limitations and strengths, the results and clinical implications of the thesis. This chapter ends with suggestions for further research, particularly to reduce bond failures of fixed retainers, and to elucidate risk factors for the development of undesired post-treatment changes and gingival recessions. Lastly, general conclusions are enumerated.