ORTHODONTIC RETENTION- A REVIEW.

Types of retention:

According to Duration

Group I -No retention

Group II- Limited retention

Group III- Prolonged retention

Group IV- Permanent retention

Group I -No retention

Period of retention: Not applicable

Indications:

1. Anterior and posterior cross bite

2. Highly placed canine

3. Impacted mandibular 2nd premolar

Group II- Limited retention

Period of retention:

First 3to 4 months full time retention to be followed by part-time wear next 12 months.

Indications:

1. Class I proclination and spacing of maxillary incisor

2. Class I and Class II extraction cases

3. Corrected deep bite cases

4. Class II division 2 cases

Group III - Prolonged retention

Period of retention: cases require 232 days or more of retention

Indications:

1. Patients exhibiting abnormal musculature or tongue habits

2. Non-compliant patient who do not cooperate by not wearing the appliance regularly.

3. Completion of the treatment before completion of growth; especially in skeletal Class III and open bite, deep bite etc.

Group IV- Permanent retention

Period of retention: Lifelong

Indications:

1. Severe rotation

2. Midline diastema

3. Cleft palate cases

4. Generalized spacing

5. Expansion of lower arch

Types of retainers:

Depending on whether the patient can remove the retainer or not, the retainers can be classified as removable one and fixed one.

Removable retainers:

These retainers allow individual movement of teeth and initially need to be worn full time (except during eating and brushing), followed by part time wear, depending on the type of malocclusion. However, since the onus of wearing rests on the patient good patient compliance is essential with removable retainers, and if consistent wear is overlooked, relapse occurs. This method of retention places full responsibility directly on the patient in maintaining tooth alignment following orthodontic treatment. Removable retainers have the advantages of being easier to maintain oral hygiene as they can be removed at the time of eating and brushing and can be put back after proper cleaning. It has been shown that in many cases, removable retainers need only be worn at night to maintain dental stability.^13-15

The most common types of removable retainers used worldwide are the Hawley-type retainer and Thermoplastic retainer. Hawley's retainer has an acrylic baseplate and a wire labial bow with adams clasps on molars as retentive unit (Figure 1a and 1b). The thermoplastic retainers are made from clear plastic (Figure 2). There is some evidence to suggest that, at least in the short-term, patients prefer the appearance and comfort of thermoplastic retainers which are more cost-effective and slightly more effective in maintaining stability, particularly in the lower arch.^16,17

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Fixed retainers:

These are bonded onto the lingual/palatal surfaces of the teeth and cannot be removed by the patients at their will. Fixed retainers offer the advantage of being in place permanently hence removing the need for patient compliance with retainer wear (Figure 3). However, as they cannot be removed for cleaning, they are more prone to plaque and calculus accumulation.¹⁸ Oral hygiene maintenance becomes critical. It is therefore vital that patients are provided with clear instructions on oral hygiene measures associated with their bonded retainers. Since bonds of the retainers to tooth is critical factor so these need to be checked regularly to ensure that they are still bonded in place. In addition, there are reports of occasional, severe, unwanted tooth movements caused by different types of failed/faulty fixed retainers as a result of the bonding of some or all teeth within the span of the fixed retainer.^19-21

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Adjunctive retention procedures:

Adjunctive procedures are techniques that alter the hard or soft tissues in an attempt to reduce relapse, thereby aid in retention of the corrections made by the orthodontist at the end of the active phase of treatment. Examples include pericision and interproximal reduction.

Pericision:

Pericision is a simple soft tissue surgical technique aimed at severing the periodontal fibres around the neck of the teeth (dento-gingival and interdental fibres) and is sometimes referred to as supracrestal circumferential fiberotomy. The procedure is performed under local anaesthetic and there is weak evidence to suggest that it reduces relapse of rotated teeth, particularly in the maxilla.^22,23 The procedure should only be undertaken in cases in which there is a good gingival biotype and cortical bone support, minimal or no recession and the patient has excellent oral hygiene. Since it is a surgical procedure, it is usually reserved for severely rotated teeth.

Interproximal reduction:

It is suggested that interproximal reduction may compensate for the normally occurring reduction in inter-canine width which occurs during adolescence.²⁴

Requirements of a good retainer:

• It should restrain each tooth that has been moved into the desired position in directions where there are tendencies toward recurring movement.

• It should permit the forces associated with functional activity to act freely on the retained tooth, permitting them to respond in as nearly a physiologic manner as possible.

• It should be as self cleaning as possible and should be easy to maintain optimal hygiene.

Theories of retention:

Riedels gave nine theories of retention²⁵ and Moyers²⁶ added another theory as the tenth theorem.

Theorem 1: Teeth that have been moved tend to return to their former position.

Theorem 2: Eliminating of the cause of malocclusion will prevent relapse.

Theorem 3: Malocclusion should be over corrected as a safety factor.

Theorem 4: Malocclusion should be over corrected as a safety factor.

Theorem 4: Proper occlusion is a potent factor in holding teeth in their corrected positions.

Theorem 5: Bone and adjacent tissues must be allowed time to reorganize around newly positioned teeth.

Theorem 6: If the lower incisors are placed upright over basal bone they are more likely to remain in good alignment.

Theorem 7: Corrections carried out during periods of growth are less likely to relapse.

Theorem 8: The farther the teeth have been moved the lesser is the risk of relapse.

Theorem 9:

Arch form, particularly in the mandibular arch cannot be permanently altered by appliance therapy.

Theorem 10: Many treated malocclusions require permanent retaining devices.

Retention monitoring:

Retention protocols involve frequent monitoring for which the patient needs to visit a clinician who will review the same. In case of removable retainers, it is imperative to check the fit of the retainer, review the stability of the dentition and ensure that the patient is sticking to the prescribed retention regimen. Fixed retainers need to be inspected for any bond failure as that will ensure and preserve stability of results. Proper hygiene maintenance also needs to be evaluated so that they don't become a source of accumulation of plaque.

COVID-19 lockdown measures disrupted regular retention check-ups. Digital technology however allowed communication and virtual reviews. Patients with broken or lost retainers could be provided with new retainers manufactured using patients' existing digital scans. Technological advancements have allowed use of thermal monitors inserted into removable retainers which can detect normal intraoral temperature when the appliances are in the mouth. This can help determine how well patients are wearing their retainers.^27,28 The technology needs to be further developed to improve their reliability and reduce the size of the devices.²⁹ However to retrieve and analyse the data the patient needs to come for a review appointment. A mobile retainer reminder app was developed to improve adherence to retainers; however, it did not seem to significantly improve objectively assessed adherence levels, stability or patient experiences at three-month follow-up.³⁰ With conventional mobile reminder apps, tracking is dependent on patients entering the usage data themselves and some users perceived this as a ‘commitment’ and ‘time-consuming’.³¹ To overcome this issue, another pilot study coupling Bluetooth tracking with reminders has shown that this type of compliance tracking has a clinically acceptable level of accuracy and usability, validating its use within future clinical studies.³² AI is the use of computers and software that have the ability to perceive information and reason, and ultimately convert that information into intelligent actions.³³ A product called Dental Monitoring (Paris, France) makes use of this technology. This software uses intraoral photos taken by patients on smartphones to remotely monitor dentitions. It has most frequently been used to monitor aligner treatment, tracking individual tooth movement, detecting lost attachments and identifying poor oral hygiene. Pre-recorded, customisable instructions are then issued directly to the patients, notifying the supervising orthodontist, but not necessarily needing the clinician's direct input unless desired.³⁴

Patient awareness:

Even before the start of the treatment it is the responsibility of the orthodontist to make the patient aware of the need for retention at the end of the treatment and explain the unpredictable nature of relapse. Hence the patient is in the know how of the care that is expected from him with his retention protocol. It is at the diagnosis level only that the clinician decides on what kind of retainers are required for the patient depending on the type of initial malocclusion. It has to be explained in detail that repairing or replacing retainers will be at extra charges. Hence the financial burden will increase in case removable retainers are not worn as advised or broken fixed retainers are not fixed as these will lead to inadvertent tooth movements which may not be desirable. Hence to reduce the risk of relapse appropriate use of retainers has to be overemphasised. Advice should include a retainer review program to assess the need for repair or replacement.