Orthodontic Retention and Relapse: A Puzzle in Orthodontics

Headnote

Abstract

Orthodontic retention and relapse is still a dilemma for orthodontists all over. It has been proved that teeth moved in the bone with the aid of any appliance tend to return to their original position. Maintaining the orthodontically moved teeth in the ideal and esthetic position poses a great challenge for the orthodontist. Frequently it has been seen that retention requires more skills than in regulating the various tooth movements. Various factors have been shown to influence the retention following the orthodontic treatment causing relapse. Therefore, the treatment plan should have a provision for retention in accordance with the various destabilizing factors.

Keywords: Retention; relapse; stability; etiological factors.

Introduction

Retention and relapse concern is one of the most important in Orthodontics. It came with the emergence of orthodontics and is still troubling the orthodontist all over. Even after numerous advances in the diagnostic methods, biomechanics and active treatment procedures, we are yet puzzledhowtosolvetheproblemofretentionandrelapse. The goals of orthodontic treatment are creation of best balance among occlusal relations, muscular stability, dental and facial esthetics, stability of the results and its long term maintenance. It is a well known fact that orthodontic treatment results will remain stable when teeth are aligned into good positions and a sufficient duration of retention is provided. The reason for holding the teeth in their treated position are many, like retention allow periodontal and gingival fibers reorganization, minimize changes due to growth, and permit neuromuscular adaptation to the new tooth position Moyers defined retention as "the holding of teeth following orthodontic treatment in the treated position for the period of time necessary for the maintenance of the result".1

Retention is that part of orthodontic treatment during which a passive appliance is used to maintain orthodontic correction of dental and skeletal structures and thereby counteract relapse or the tendency for return of characteristics to the original malocclusion.2 Retention is so important that the retention period has even been called "Secondary orthodontic treatment". Although it has been stated that correct diagnosis and planning of treatment, followed by a careful stabilization of the final result, would minimize the problem of retention, but relapse tendencies still exist in a high percentage of cases treated. Even after precautions in all steps of treatment, relapse after tooth movement still remains a complex problem, with a varying number of factors involved. To achieve long term stability of treatment results, a proper understanding of the changes occurring, various factors affecting relapse and retention procedures is important. Orthodontists have come to reahze that retention is not separate from orthodontic treatment but that it is part of treatment itself and must be included in treatment planning.

Factors influencing the retention after orthodontic treatment

There are many factors which affects the stability of teeth after orthodontic treatment. In this article we will discuss some important factors.

1. Alteration of arch form

It is a rule that we must make every effort to maintain the arch form and arch width during the treatment, specially inter-canine and inter-molar width.34 So treatment should be aimed at keeping the "pre-treatment" arch form maintained throughout the treatment. There are a few exceptions to this rule. In certain cases, where arch development has not taken place and arch is very narrow, arch expansion can be carried out. It is documented that inter-canine and inter-molar width specially mandibular revert back to their original dimension when expanded, because they are related to muscular balance inherent for an individual.25 8 Any change in the arch limits will disturb the muscular adaptation and balance, ultimately lending into relapse. Cruz concluded that patient's initial arch form is the best guide during treatment and for final stability. After the retention phase, arch form tends to return towards the pre-treatment shape.9

2. Consideration of continuing growth

The role of growth in long term stability of treatment changes is very controversial. It is a general belief that corrections which are carried out when patient is growing have less chances of relapse. So we must start the treatment as early as possible. Early diagnosis and treatment planning has many advantages in long term stability. Early orthodontic treatment prevents the malocclusion from becoming complex, prevents unfavorable hard and softtissue changes, prevent excessive dental and softtissue compensation of malocclusion, and allow treatment of skeletal malrelationship while sutures are immature and more prone to change.2

Other side of investigator's said that growth may help in the correction of orthodontic problems but it can also be a reason for relapse of a treated case. Any bony changes after treatment may results into relapse. In post-treatment duration nothing much can be carried out to modify the patient's growth pattern. Normally, when we complete our orthodontic freatment, many patients have undergone their pubertal growth spurt and others may have not even started with growth spurt. This is of greater significance in boys than in girls, as boys generally mature late. Hence failure to recognize the continuing effect of dento-facial growth after the completion of orthodontic treatment and its resulting favorable or unfavorable effects may jeopardize long-term stability of the orthodontic result. The retention devices should be selected on the basis of dentofacial morphology and the anticipated magnitude and directions of growth.310

3. Environmental factors and neuromusculature

During orthodontic treatment, there is a change in the position of the teeth, resulting in change or imbalance in themuscularpressure. Thisimbalance can result into relapse. It is said that the indicators of the muscular balance for any individual are inter-canine and inter-molar width particularly mandibular, and indivudual's muscular balance dictate the limits of arch expansion during treatment. So they must be maintained during treatment to prevent relapse." The position of the mandibular incisor is also a critical factor in the stability of orthodontic treatment. The lower incisors lie in the equilibrium between the opposing force of tongue and lips. Too much lingual or labial displacement may not remain stable due to disturbed equilibrium resulting in relapse, so pre-treatment position of lower incisors should be accepted. If during treatment, lower incisor prochnation is planned, then long term retention must be given to maintain the result.412

4. Etiology of malocclusion

Post-treatment stability increases when the cause of etiological factors of malocclusion are eliminated. So during diagnosis only it is important to find out the causes of malocclusion and every precaution during treatment should be carried out. Factors like thumb sucking, tongue thrusting, lip biting habits should be eliminated.13

5. Bone, periodontal and gingival tissues

Histologically, bone and tissue around newly moved teeth are altered and it takes time to complete reorganization. In orthodontic treatment there is stretching of periodontal and gingival fibers. These stretched fibers tend to recoil back to their original position resulting in relapse. These fibers reorganize in anew position after some time and it will aid in stability. So till the fibers get reorganized we need to keep the teeth in place. PDL fibers reorganize to the new position within 4-6 weeks (1-11/2 months), while gingival fibers take around 32-40 weeks (8-9 months) to reorganize.13

6. Post-treatment tooth positioning and establishment of functional occlusion

It is well believed that creating a normal occlusion and good intercuspation after orthodontic treatment aid in stability of treatment results. A correct inter-incisal angle may prevent overbite relapse and in horizontal direction good posterior intercuspation prevents relapse of both crossbite and AP correction. When occlusion has no trauma or stress there is less mesiodistal movement of teeth. Little movement of the teeth always occur just after completion of orthodontic treatment in an effort made by teeth in response to occlusal forces. During settling at the end of the treatment we must make every effort to get maximum intercuspation between the buccal cusps of the mandibular posterior teeth and the lingual cusps of the maxillary posterior teeth.1415

7. Role of developing third molars

The role of third molars in lower incisor crowding and post-treatment stability has always been questioned and debated in orthodontics. There are 2 sides to these theories, one in support and one in against this view. In modern population, there is a strong tendency to develop crowding of mandibular incisor teeth in the late teens and early twenties. Prevalence of missing third molar in today's generation is to the level of 60%-70% of the population. Mild crowding of the incisors tends to develop in well-aligned arches, or it increases if mild crowding is already present. Increased crowding of mandibular incisors takes place at about the time of third molar eruption. Although the mean age for third molar eruption is 20 years, mandibular anterior crowding continues well beyond the eruption of third molars in both untreated and treated individuals. It is considered as a normal physiological process of maturation. Those in support says that third molar while erupting exerts a mesial force on dentition causing anterior teeth to crowd. When third molar is not present, dentition would settle down distally due to change in forces of growth and softtissue pressure, which is not possible when third molars are present.

The group against says that the role of third molar is insignificant on the post-treatment crowding or late lower incisor crowding. It does not make any difference if third molar is present, absent or impacted or extracted. They suggest that there is reduction in arch length and an increase in crowding with age. It is a normal phenomenon that third molar does not make a difference. It seems that if third molars were a contributing factor in the development of late lower incisor crowding, their role is likely to be one of minor importance.16 21

8. Establishing marginal ridge relationships and contact points

Marginal ridges of adjacent teeth should be at the same level or within 0.5mm of the same level. Radiograph-ically, the cemento-enamel junctions should be at the same relative height, resulting in a flat bone level between adjacent teeth. Proper marginal ridge relationships in the finishing stage are primarily a function of bracket height. So proper bracket positioning during initial stages of treatment can make a lot of difference whenitcomestoretentionphase.15

9. Checking the parallelism of the roots

Generally, the roots of the maxillary and mandibular teethshouldbeparalleltoeachotherandperpendicular to the occlusal plane, as viewed in the panaromic radiograph. Hence, a panaromic x-ray should be taken before debanding to evaluate root parallelism. If roots are properly angulated, sufficient bone will be present between adjacent roots, an important consideration in periodontal health.15 There should be proper angulation of the teeth in relation to the occlusal plane so that the forces of occlusion are dissipated in the bony structure.

10. Concept of over-correction

As it is said that little movement of teeth/relapse always takes place after treatment, so it is better to over-correct the malocclusion. It is a common practice to over-correct Class II malocclusion into an edge-to-edge incisor relationship and Class III into a more positive overjet. In Class I malocclusion, individual tooth correction like rotation and correction of proclination should also be over-corrected for compensation of reversal. The over-correction is recommended for the compensation of the anticipated post-treatment adjustments: 1) To overcome muscle forces against the tooth surfaces, 2) root movements needed for stability, 3) to overcome orthopaedic rebound and 4) to allow setting Pretention.22

11. Circumferential SupracrestalFiberotomy

It is generally agreed that after orthodontic treatment, relapse is due to the displaced supra-alveolar connective tissue fiber. So, it was suggested by Edwards in 1970, that if these fibres are ressected by a surgical procedure, relapse tendency (particular rotational) can be eliminated. This surgical procedure, referred to as Circumferential Supracrestal Fiberotomy (CSF), has become well documented and popular. CSF cannot be done in every case and is mainly indicated in cases where the supragingival fibers have been markedly displaced, like severely rotated teeth, markedly crowded or bunched teeth, severely tipped teeth, diastema and spacing in the anterior teeth In addition to CSF we must need to get proper contact relationship between teeth, no occlusal prematurities and proper torquing of roots.23'24

12. Reproximation

It is said that mandibular incisor dimensions were correlated with lower incisor crowding. Reduction of mandibular incisors should be done to a given facio-lingual/mesiodistal ratio to increase stability. Lower incisor crowding after orthodontic treatment has always been a puzzle in orthodontics. A subj ect of renewed interest is the "reproximation" or "stripping" of lower anterior teeth and its purposed ability to reduce lower incisor re-crowding. This reduction of lower incisor width is often the last resort at holding tooth alignment and is usually employed after all conventional measures have failed. Its application has been empirical and its long-term effectiveness is questionable. Advantages of lower incisor reproximation are that it provides broader contact points and increase the available arch space in the mandibular anterior region resulting in increased stability after orthodontic treatment. The disadvantages of this procedure are the possibility of associated periodontal destruction and increased caries susceptibility in the mandibular anterior area. Well-aligned mandibular incisors are significantly smaller mesiodistally and significantly larger facio-lingually When viewed incisally a mesiodistal/facio-lingual (MD/FL) index describes the mandibular incisor crown shape. Ideally shaped lower centrals have a MD/FL index of 88%-92%, while the recommended range for the lower laterals is 90%-95%. Well-aligned mandibular incisors usually have MD/FL indices significantly lower than those of crowded incisors. When the ratio is more, reproximation is recommended as a mechanical method of reducing unfavorable incisor shapes.25

Conclusion

The problem of "retention and relapse" is likely to continue to test the orthodontist because of the complexities of the etiological factors and one has to be thorough with all the implicating concepts. The choice of the type of retention, durationofretention,hasagreatbearingonsuccessfulpost retention cases. Any violation of the biologic limit, which trespassesthelawofoptimality,willendinmiserablefailu-re.

A food for thought: Dietary habits of present generation causes less proximal and occlusal wearing. So compensatory mechanism of anterior and occlusal migration of the teeth is prevented, causing pressure on the anterior segment, which tends to cause crowding and fanning out of anter-iorteeth.

Nature has created an individual in certain format, which we as Orthodontist try to change and go against the nature. It is a law of nature to try and bring the distorted format to its original form, so it is always difficult to cheat the nature to a certain extent. Hence, the question arises, why we do orthodontic treatment. It's an attempt to make the person look more pleasing, attractive during a prime of the life (from age 12 to 30). After the prime the person who has undergone orthodontic treatment is not so conscious of the minor relapses that happen with time

References

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