Retention in Orthodontics
Comprehensive orthodontic therapy requires that treatment goals be established during the time of treatment planning. Begin treatment with the end in mind. These goals should include patient esthetics, improved occlusal function, and long-term retention. Little et al.< ?xml:namespace prefix = "mbp" />1 states that the only way to ensure continued satisfactory alignment after treatment is by the use of fixed or removable retention for life. Therefore, instability or a tendency toward relapse should be anticipated. Patients should be advised of the potential for relapse prior to treatment and of the need to stay in long-term retention.
Orthodontists should work to produce an occlusion that is functionally efficient, esthetic, and healthy. Long-term retention helps to ensure stability of the dentition. Interdigitation of the posterior occlusion plays a significant role in the control of anteroposterior and vertical facial growth and is an important factor in jaw relationships.2 Numerous authors have stated that good intercuspation and occlusal contacts may be the key to a stable orthodontic result.3–8
Many of the current concepts in occlusion are derived from a benchmark study by Andrews9 to determine the keys to normal occlusion. Criteria for inclusion of these nonorthodontic patients in the study were a pleasing appearance, straight teeth, and a good bite that would not benefit from orthodontic treatment. In these individuals, Andrews found six keys in their normal occlusions:
It has long been the goal of orthodontists to treat their patients using these six keys as guides for establishing a normal occlusion that is esthetic and with good occlusal function. Many of these keys were included in the Objective Grading System developed by the American Board of Orthodontics (ABO) in the mid-’90s.
In an effort to enhance the reliability of the ABO examiners and provide the candidates with a tool to assess the adequacy of their finished orthodontic results, the Board has established an Objective Grading System to evaluate the final dental casts and panoramic radiographs.10 The Directors of the ABO developed this grading system for assessing occlusal and radiographic results of orthodontic treatment. Using this system, orthodontists can grade their treated cases to determine if they are producing excellent clinical results.
1 What is retention?
Retention is the last phase of orthodontic treatment and one of the most important, where teeth are held in an esthetic and functional position.11,12 Retention of the corrected malocclusion is just as important as the diagnosis, treatment plan, and actual orthodontic treatment to correct the patient’s malocclusion. Planning for retention should be done prior to any orthodontic treatment for each individual case. The type of retention should be determined at the beginning of treatment as well as any procedures to help retain the final functional and esthetic occlusion.
2 Why is retention necessary?
The need for retention is important to maintain the stability of the occlusion achieved by the orthodontist and patient.13 Without stability, the esthetic and functional result may relapse. The improvements achieved from long and painstaking treatment may be lost because of relapse after the orthodontic appliances are removed. Teeth that have been moved orthodontically have an inherent tendency to return to their original malocclusion positions.
3 What are the general factors affecting stability?
Throughout the orthodontic literature, many factors have been discussed concerning stability of the orthodontic treatment result.14,15 Three factors are consistently mentioned as to why retention is necessary to maintain the orthodontic correction:
The time needed for the gingival and periodontal ligament fibers to reorganize.
Growth, especially mandibular growth, may alter the orthodontic correction.
Soft-tissue pressure from the oral musculature may lead to a relapse tendency.
4 Why is growth a consideration in retention?
The nature and duration of retention depends on the patient’s maturational status and on anticipated future growth.16 Growth produces occlusal changes in all three skeletal dimensions. The transverse dimension is completed first and has a lesser effect on the occlusion than the vertical and anteroposterior dimensions. However, if a patient has had transverse expansion, there is a degree of rebound even in the transverse dimension. Ideally, an adolescent patient should wear orthodontic retainers indefinitely; however, at a minimum, the retainers must be worn until growth is completed in adulthood. Even adults show some craniofacial remodeling that can cause alteration of the occlusion. In orthodontics, we are dealing with a living, dynamic system of growth. Throughout our life, orthodontic retention will help to minimize the changes in our occlusion. Therefore, retention should be considered for life if the occlusal alignment is to be maintained.
5 What are retention considerations in extraction and nonextraction cases?
There is not a specific retention philosophy for extraction cases and another for nonextraction cases. The orthodontist decides on the individual’s retention plan at the beginning of treatment when the diagnostic records are used to establish the patient’s treatment plan. By following this plan, it will be possible to achieve an esthetic and functional occlusion.
Edwards16 has shown that in extraction cases, excess gingival tissue forms as the adjacent teeth are moved toward one another in closing the extraction site. This excess gingival tissue should be surgically removed to prevent relapse.
6 What are retention considerations in Class II cases?
Skeletal Class II malocclusions are corrected in two ways: restricting maxillary growth with headgear appliances, or using a functional appliance such as a Herbst or Twin Block. Class II elastics are also used, but this may cause proclining and flaring of the lower incisors. If proclined, the lower incisor will upright and crowd because of lip pressure once retention is removed. To overcome these relapse tendencies, discontinue Class II elastics at least 2 months prior to debonding. Overcorrection of the Class II treatment is recommended due to differential jaw growth resulting in long-term relapse.
This relapse tendency can be controlled by continuing to wear a headgear at night or using a functional appliance such as a Bionator to hold the occlusal relationship.15 Obviously, this type of retention is for the patient with a more severe skeletal problem initially.
7 What are retention considerations in Class III cases?
Early correction of skeletal Class III malocclusions in the mixed dentition using a palatal expander and protraction facemask is useful for altering the skeletal components.17,18 It is more successful in deep bite cases than in open bite cases, since the mandibular plane angle and anterior facial length will increase. Retaining the correction can be frustrating because of continued mandibular growth, which is difficult to control. Correction of true Class III malocclusions in adults caused by maxillary hypoplasia, mandibular prognathism, or a combination of the two most often requires orthognathic surgical correction. A gnathologic positioner is a useful retainer in mild Class III malocclusions. Use of chin caps to restrict mandibular growth is not very effective.
8 What are retention considerations in open bite cases?
An open bite malocclusion may be dental or skeletal in nature. A dental open bite may be caused by depression of the incisors because of a habit such as thumb- or finger-sucking or poor tongue posture. A good cephalometric value to differentiate between a dental and skeletal open bite is incision-stomion; dental open bites have intruded maxillary incisors whereas skeletal open bites have a normal incisor position. The open bite must be accurately diagnosed and treated if relapse is to be prevented.
In skeletal open bite, incisors are in a normal position, but the posterior teeth have elongated. Controlling the eruption of the maxillary molar with high-pull headgears and a transpalatal bar with a midline acrylic palatal button 4 mm off of the palate is useful to control extrusion. If correction of severe open bite is not started in the mixed dentition, it will most likely require orthognathic surgery in late adolescence or adulthood. The skeletal open bite phenotype is easily diagnosed in the early mixed dentition.
9 What are the considerations in deep bite cases?
Deep bites are common in certain malocclusions such as Class II division 2 and are caused by overeruption of the maxillary incisors, mandibular incisors, or both. Once the deep bite is corrected, it must be controlled in retention or it is likely to relapse.19,20 Retention is accomplished with a maxillary removable retainer with a bite plate, which the lower incisors and cuspids will contact if the bite begins to deepen. The appliance should not cause the posterior teeth to disocclude. This retainer should be worn at night until the late teens or early 20s to maintain occlusal stability.
10 What are the indications for bonded lingual retainers?
Fixed orthodontic retainers are usually wires bonded to the lingual surface of the mandible anterior teeth for esthetics and prolonged retention.21,22 These may be fabricated directly in the mouth or indirectly from an accurate stone model. The bonded retainer is placed in the patient’s mouth and secured with a light cured composite resin. The fixed retainer is useful to retain the mandibular canine-to-canine region, and a bonded retainer is more esthetic than a banded retainer. The fixed bonded retainer is also used to maintain corrected midline diastema and to maintain pontic or implant space. It is also useful for maintaining the vertical position of teeth extruded into the arch such as palatally impacted cuspids. In most instances the retainer wire is bonded to the terminal teeth (canines) of the retainers (Fig. 23-1, A) and not bonded to every tooth. Fixed retainers make interproximal hygiene procedures more difficult. However, with good flossing procedures, thes/>
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