Retention and post-retention outcome
Birgit Thilander, Krister Bjerklin and Lars Bondemark
- The concept relapse
- Post-retention outcome
- To understand the definition ‘relapse’
- To describe the biological process during the relapse period
- To discuss the length of the retention period
- To understand and describe possible changes during the post-retention period
The orthodontic correction in growing children is just an event during a period of growth and development in the patient’s life. Although the interrelation between the teeth becomes established in childhood, continuous small changes occur throughout life, and the same is true for the craniofacial morphology, as described in Chapter 3. In this dynamic environment of continuing skeletal changes, functional demands and compensatory adaptations of the dentition, the orthodontic treatment is performed.
After withdrawal of the orthodontic forces, the retention period will take over. Orthodontic correction will remain stable if the teeth are aligned into a normal occlusion and provided with adequate retention. Moreover, the patient expects that the orthodontist shall finish the treatment period with an optimal result and stability that will last for years. However, every orthodontist knows that some patients will experience a tendency for the teeth to return to their original position, even after years of retention, a phenomenon described as relapse.
After the active orthodontic correction, the real problem will arise, i.e. how to retain and for how long, to obtain a stable result. Many different removable or fixed retainers have been used and each of them has both advantages and disadvantages. Bonded retainers in the incisor region of the mandible or maxilla are an often-used choice as they are independent of cooperation. The retainers can be bonded to the canines only, to the incisors and canines, or to incisors only (Figure 12.1). Also, removable retainers in the maxilla like a Jensen retainer (Figure 12.2), a vacuum formed splint (Essix stent) (Figure 12.3), a Hawley plate or some of its many modifications can be used (Shawesh et al., 2010; Thickett and Power, 2010).
A systematic review of the stability and side effects of orthodontic retainers (Bondemark et al., 2007) has shown low quality of evidence between fixed and removable retainers as regards stability, as well as presence of calculus or dental caries prevalence between the different types of retainers. Most often the choice of retention device depends on individual factors such as type of the initial malocclusion and expected patient cooperation.
The length of the retention period is controversial. Some recommend 2 to 5 years, whereas others have suggested a minimum of 10 years or longer. Of importance to remember is that if an undesirable growth pattern is treated only by compensations in the dentoalveolar system, subsequent post-treatment growth may upset a result that looks good when the patient is young.
Type of retainer and length of retention period are connected to relapse, a concept that has been discussed for years and still leaves many questions unanswered. Many theories have been proposed as to the aetiology of relapse, and many treatment and retention strategies have been recommended to minimise undesirable post-treatment changes. In general, an orthodontic tooth movement which is opposed to the direction of functional tooth migration is more liable to relapse than one in which the direction corresponds. Teeth that have been rotated tend to return to their former position. Supra-alveolar fibres are under tension by tooth rotation. Cutting through these fibres (fibretomy) can reduce the relapse of rotated maxillary incisors (Edwards, 1970).
A relapse from an orthodontic point of view is defined as ‘a return towards pre-treatment conditions’, and hence is an event of periodontal tissue reaction or dentofacial developmental changes. A general widening of the dental arches, particularly in the mandibular incisor area, will be prone to relapse, even after years of retention. In addition, orthodontic relapse of incisors is the real complaint for the patients due to the aesthetic aspects (Figure 12.4), while possible relapse of skeletal malocclusion (‘orthopaedic relapse’) seems to be of less importance.
As stated in Chapter 10, condyles and sutures respond to orthopaedic forces by changing the growth direction, and when the force is discontinued, the individual growth pattern takes over. If this is a ‘relapse’, it should be questioned about its definition ‘return to the original position’. This assertion is verified by a longitudinal follow-up study with the Herbst appliance (Pancherz et al., 2015), in which the importance of late adult facial growth changes must be considered in dentofacial orthopaedics with respect to treatment timing, post-treatment retention and relapse. Thus, the orthopaedic relapse is an indication that the individual growth pattern takes over again during the post-treatment period.