# RETENTION*

STANLEY PAUL, M.D.Sc.

Angle defined retention in the following words:—

"After the malposed teeth have been moved into the desired position, they must be mechanically supported until all the tissues involved in their support and maintenance in their new positions, shall have become thoroughly modified, both in structure and function, to meet their new requirements."

In spite of modern advances in mechano-therapy, very few orthodontists to-day underestimate the need for retention.

## Review of Literature.

Our present concepts on retention seem to be a combination of several schools of thought. Many early writers held the view that occlusion was the major factor in retention. Thus we find Kingsley¹ writing:

"The occlusion of the teeth is the most potent factor in determining the stability in a new position."

In 1925 Lundstrom² suggested that the apical base was one of the most important factors in the correction of mal-occlusion and the maintenance of a correct occlusion. McCauley³ suggested that the intercanine width and intermolar width should be maintained as originally, to minimise retention problems.

Tweed⁴ maintained that for stability the mandibular incisors must be kept upright and over basal bone.

Alfred Rogers⁵ stressed the importance of muscle balance for proper function and stability of the occlusion.

Hahn⁶ stated that even though treatment techniques had changed radically, retention had made only one change, "the transition from the use of mechanical devices which were designed to hold the teeth immovable in their new positions to those which permit the teeth freedom of movement in every direction save that in which the teeth tend to return."

Hellman⁷, even went as far as to say that retention should not be a separate problem, but the continuation of treatment.

Retention will depend on what we accomplish during treatment and the care that we exercise to establish a proper occlusion with normal muscle balance and taking the availability of apical base into account.

As Graber⁸ states stability is a major factor in treatment, for without stability either ideal function or ideal aesthetics, or both may be lost.

## Factors in Retention.

The following factors are essential either prior to or during the retentive period.

### 1. The Attainment of Normal Occlusion.

This will require proper diagnosis and treatment planning and careful mechanics. These steps will have to be accomplished within a patient's potential for growth and normal function, if a stable occlusion is to result.

Growth and function are variables for each individual, which are beyond the control of the orthodontists, leaving mechanotherapy to be easily kept under control.

### 2. Removal of Aetiological Factors.

This refers to those factors over which we have some control namely habits.

3. Relapses are less likely to occur when retention is discontinued after active growth is completed.

4. Many advise over-treatment to shorten the retention period and minimise relapse, when it does occur.

### 5. Age.

The younger the patient the faster the repair process occurs.

<footnote>*Based on a Lecture given to The Queensland Branch of The Australian Society of Orthodontists, 4th June, 1970.</footnote>
Reidel¹⁹ mentions the following conditions as requiring no retention.

**1. Corrected Crossbites.**

(i) Anterior: When adequate overbite is present.

(ii) Posterior: When there is no abnormal tipping of the teeth in order to correct the crossbite and there is proper intercuspation.

**2. Serial Extraction Cases.**

The degree of perfection in these cases varies. High cuspid extraction cases are the best examples of this procedure.

3. Corrections that have been achieved by the retardation of maxillary growth once the patient has passed his or her growth period.

4. Cases where teeth have been separated to make room for previously blocked out teeth.

I would now like to consider retention in connection with:—

(i) The masticatory complex.

(ii) Muscle changes.

(iii) Different types of malocclusions.

(iv) Basal bone.

(v) Local post-treatment tissue changes.

(i) **The Masticatory Complex** consist of teeth, bones, muscles and the temporo-mandibular articulation.

Extensive changes in tooth position require compensatory changes in some, if not all, of the components of the complex, in order to restore equilibrium.

These compensatory changes may take longer than it takes to move teeth into their new position. Retention is therefore required until equilibrium is established, if it is ever re-established.

How long the teeth need to be retained can only be worked out at present by trial and error.

Many cases of relapse after apparently successful orthodontic therapy are the result of difficulty experienced by some patients in ac-

comodating to the new pattern of masticatory function. It may take some time before the new functional pattern reached the conditioned reflex stage¹⁰.

**(ii) Muscle Changes.**

The recognition that muscular adjustment may take a longer time has led to use of retainers for longer periods.

Length of retention will have no meaning if the new position is in conflict with functional forces exerted on the teeth.

**(iii) Different Classes of Malocclusion.**

The duration of retention in Class II cases will vary according to whether extractions have been carried out or not.

The amount of growth following orthodontic treatment will also effect retention.

Muscle adaptation to new relationships requires longer periods of retention in Class II, Division II and Class III cases.

**(iv) Basal Bone.**

Tweed was the first to attribute relapse in certain cases of treated malocclusions to disproportion between tooth size and what he termed basal bone.

**(v) Local Tissue Changes.**

I would like to touch briefly on these. Reitan¹¹ states that the periodontal fibres are highly individual in their reactions, and variation between the types of fibres in various persons of the same age group, become manifest during the retention period.

In some persons fibres may become arranged more readily than in others. Cases treated and stabilised according to similar principles may behave differently during the retention period as a result of the variation in fibrous tissue response. Reitan considers it important to retain teeth until fibrous tissue has become re-arranged.

The principal fibres of the periodontal ligament will rearrange themselves in 8 to 9 weeks. The supra-alveolar structures behave differently and may remain stretched during a longer period¹¹. This difference in reaction between the two groups of fibres is of great clinical significance. If a tooth of a group of teeth is released after fairly rapid movement, all the
fibres of the periodontal ligament tend to contract and rearrange themselves. If the tooth is retained for a period of 2 to 3 months, there is less tendency toward further rearrangement of the principal fibres, whereas a tendency to contaction still exists in the supra-alveolar group.

### Retainers.

I do not propose to go into details except to say that removable appliances have the advantage of permitting normal function of the teeth, while they are being retained. This allows the periodontal ligament to rearrange itself. A positioner type of retainer is thought to be useful in open bite cases.

### Retention Period.

Retention appliances should be discontinued on a trial basis. The patient should be observed frequently at first to note any deleterious changes. There is no arbitrary time for wearing retainers. Discontinuance of retention should be accomplished gradually by increasing the length of time when the appliance is not worn. According to Salzmann¹², traumatic occlusion should be corrected before retention is discontinued.

The length of time during which retention should be applied is not definitely known and varies from patient to patient. Usually retention is necessary for a period of one year, during the last six months of which time the teeth are afforded an increasing amount of freedom so that individual teeth may find their position in function.

Reitan feels that relapse can be avoided if the retainer is placed immediately after the removal of appliances and reaching a peak within 17 hours.

### Conclusion.

When one considers the tremendous changes that have taken place in our concepts of diagnosis and appliance design and when one realises how little has changed in our attitudes towards retention, it seems that it is time to take a more imaginative look at this side of orthodontic treatment.

May I conclude with this quotation:—

> "Neither the perfect patient nor the perfect appliance exists and to plan treatment as if either does, invites a high degree of failure."

Children's Dental Hospital,
St. Paul's Terrace,
BRISBANE 4000.

### REFERENCES:

1. KINGSLEY, as quoted by Reidel in Chapter 9, of Current Orthodontic Concepts and Techniques (T. M. Graber, Editor), Volume II Saunders, Philadelphia, 1969.

2. LUNDSTROM, Malocclusions of the teeth regarded as a problem in connection with the apical base. Int. J. Orthodont. 11: 591-1109, 1925.

3. McCAULEY, D. R.: The cuspid and its function in retention. Amer. J. Orthodont. 30:196-205, 1944.

4. TWEED, C. H.: Indications for the extraction of teeth in orthodontic procedures. Amer. J. Orthodont. 30: 405-428, 1944.

5. ROGERS, A. P.: As quoted by Reidel in Chapter 9 of Current Orthodontic Concepts and Techniques, (T. M. Graber, Editor), Volume II.

6. HAHN, G. W.: Retention — the step-child of orthodontia, Angle Orthodont. 14: 3-12, 1944.

7. HELLMAN, M.: Failures in orthodontic treatment, Int. J. Orthodont, & Oral Surg. 22: 343-360, 1936.

8. GRABER, T. M.: Postmortems in post-treatment, adjustment. Amer. J. Orthodont. 52: 331-352, 1966.

9. REIDEL, R. A.: Retention, Chapter 9 in Current Orthodontic Concepts and Techniques (T. M. Graber, Editor), Volume II, Saunders, Philadelphia, 1969.

10. SALZMANN, J. A.: Practice of Orthodontics, Lippincott, Philadelphia, 1966, Volume II, Page 1038.

11. REITAN, K.: Principles of retention and avoidance of post-treatment relapse. Amer. J. Orthodont. 55: 776-790, 1969.

12. SALZMANN, J. A.: Practice of Orthodontics, Lippincott, Philadelphia, 1966, Volume II, Page 1043.