RETENTIONRELAPSE

After malposed teeth have been moved into the desired position they must be mechanically supported until all tissues involved in their support and maintenance of their new positions shall have become thoroughly modified, both in structure and in function, to meet the new requirementsAngle (1907)

CONTENTS

INTRODUCTIONSCHOOLS OF THOUGHT FOR RETENTIONSEMANTICS OF POST ORTHODONTIC TREATMENT CHANGESTHEOREMS OF RETENTIONFACTORS INFLUENCING RETENTION AND STABILITYFACTORS THAT MODIFY THE RETNTION PROTOCOLCAUSATIVE FACTORS FOR RELAPSERETENTION AFTER CLASS II CORRECTION CLASS III CORRECTION DEEP BITE CORRECTION ANTERIOR OPENBITE CORRECTIONLONG TERM RETENTION STUDIESRETENTION PLANNING TIMING OF RETENTIONRETENTION APPLIANCESRECOVERY AFTER RELAPSECONCLUSION

INTRODUCTION

Orthodontists have long since been aware of the fact that teeth that have been moved in or through bone by mechanical appliances have a tendency to return to their former positions. It is the purpose of Retention to counteract this tendency. Although it has been stated that correct diagnosis and planning of treatment, followed by a careful stabilizing of the final result, would minimize the importance of retention, Relapse tendencies still exist in a fairly high percentage of cases treated. Our ability to achieve long term Stability and our understanding of the factors underlying stability may be the least well founded in this triad, clear indication being our need for retention of achieved results at times long term retention.

DIFFERENT SCHOOLS OF THOUGHT FOR RETENTION

THE OCCLUSION SCHOOLKingsley (1880) stated, The occlusion of the teeth is the most potent factor in determining the stability in a new position.

THE APICAL BASE SCHOOLIn the middle 1920s a second school of thought formed around the writings of Axel Lundstrom (1925), who suggested that the apical base was one of the most important factors in the correction of malocclusion and maintenance of a correct occlusion. McCauley (1944) suggested that intercanine width and intermolar width should be maintained as originally presented to minimize retention problems. Strang (1958) further enforced and substantiated this theory. Nance (1947) noted, Arch length may be permanently increased only to a limited extent.

THE MANDIBULAR INCISAL SCHOOLGrieve (1944) and Tweed (1952) suggested that the mandibular incisors must be kept upright and over basal bone.

THE MUSCULATURE SCHOOLRogers (1922) introduced a consideration of the necessity of establishing proper functional muscle balance.

SEMANTICS OF POSTORTHODONTIC TREATMENT CHANGES [Semantics: the study of language meaning]

RETENTION Moyers (1973) 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.Joondeph and Riedel (1985) explain retention as the holding of teeth in ideal aesthetic and functional positions. Retention is accomplished by a variety of mechanical appliances.

RELAPSERobert Moyers states that relapse is the term applied to the loss of any correction achieved by orthodontic treatment.Horowitz and Hixon (1969) defined relapse in general as changes in tooth position after orthodontic treatment.Enlow (1980) defined relapse as a histogenetic and morphogenic response to some anatomical and functional violation of an existing state of anatomic and functional balance. It is usually thought of as a rebound movement in which teeth recoil back somewhere close to their original positions once retentive forces are moved.

STABILITYStability is the condition of maintaining equilibrium. This refers to the quality or condition of being stable; the fixity of position in space or the capacity for resistance to displacement.

PHYSIOLOGIC RECOVERYHorowitz and Hixon (1969) explain physiologic recovery as the change to the original physiologic state after completing treatment.

DEVELOPMENTAL CHANGESDevelopmental changes are those which occur irrespective of whether orthodontic treatment was implemented or not. These changes could easily be overlooked when assessing post treatment relapse.

POSTRETENTION SETTLINGSettling can be described as the establishment of a desired position, the act of ceasing to move or settling down and maintaining a correctly balanced position. This term thus indicates the post treatment changing process versus a term such as metaposition, which refers to the meticulously planned changes after the removal of the orthodontic appliances.

METAPOSITIONMetaposition denotes the desirable and expected post treatment changes that are anticipated (Ricketts, 1993). These changes are not relapse and must be part of the treatment itself.

RECIDIEFThe term recidief has been used to describe changes that occur from the end of treatment back to the original situation (Dermaut, 1974).

WHY IS RETENTION NECESSARY?

The proposed basis for holding the teeth in their treated position is to: 1) Allow for periodontal and gingival reorganization; 2) To minimize changes from growth; 3) To permit neuromuscular adaptation to the corrected tooth position; and 4) To maintain unstable tooth position, if such positioning is required for reasons of compromise or esthetics.

BASIC THEOREMS FOR RETENTION

Richard A Riedel (AO 1960) had discussed a number of possible explanations of Retention and Relapse.

THEOREM 1: Teeth that have been moved tend to return to their former positions.THEOREM 2: Elimination of the cause of malocclusion will prevent recurrence.THEOREM 3: Malocclusion should be overcorrected 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 to reorganize around newly positioned teeth.

THEOREM 6: If 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 teeth have been moved, the less likelihood of relapse.THEOREM 9: Arch form, particularly in the mandibular arch, cannot be permanently altered by appliance therapy. To Riedels theorems might be added the following:THEOREM 10: Many treated malocclusions require permanent retaining devices. This is less true for cases treated to meticulous occlusal goals and with respect for the dynamics of growth and occlusal functionRobert E Moyers (1970).

FACTORS INFLUENCING RETENTION AND STABILITY

Factors that affect post treatment stability include.. Alteration of arch form Periodontal and gingival tissues Mandibular incisor dimensions Influence of environmental factors and neuromusculature

Consideration of continuing growth Post treatment tooth positioning and establishment of functional occlusion Role of developing third molars Influence of the elements of the original malocclusion

ALTERATION OF ARCH FORM

It is generally agreed that arch form and width should be maintained during orthodontic treatment. In certain cases, where arch development has occurred under adverse environmental conditions, arch expansion as a treatment goal may be tolerated.

Mills (Br Dent J 1966) found stability after proclination in cases with skeletal deep bites and retroclined incisors in conjunction with a digit or lip entrapment habit.

rtun (AO 1990) stated that proclination may be successful provided that the lower incisors are initially retroclined, a reason for the retroclination determined, and the cause eliminated during treatment. Evidence shows that intercanine and intermolar widths decrease during the postretention period, especially if expanded during treatment. For this reason, the maintenance of arch form rather than arch development is generally recommended.

Little et al (AJO 1981) maintained that intercanine and intermolar width will relapse if expanded in Class II Division 2 cases as much as in other Angle classifications. In cases of mandibular expansion concurrent with Rapid Palatal Expansion Haas(AO 1980) and Sandstrom et al.(AJO 1988) found that maintenance of 3 to 4 mm intercanine width and up to 6 mm intermolar width was possible when expansion was carried out concurrently with maxillary apical base expansion

De La Cruz et al. (AJO 1995) carried out a 10 year postretention study on 87 patients to determine the long-term stability of orthodontically induced changes in maxillary and mandibular arch form. The results showed that although there was considerable individual variability, arch form tended to return toward the pretreatment shape. They concluded that the patient's pretreatment arch form appeared to be the best guide to future stability.

PERIODONTAL AND GINGIVAL TISSUES

Orthodontic movement to correct tooth rotations is proposed to result in stretching of the collagen fibers. The PDL reorganization is important for stability because of the periodontal contribution to the equilibrium that normally controls tooth position. Within 4 to 6 months, the collagenous fiber networks within the gingiva have normally completed their reorganization, but the elastic supracrestal fibers remodel extremely slowly and can still exert forces capable of displacing a tooth at one year after removal of an orthodontic appliance.

Brain(AJO 1969) and Edwards(AJO 1970) advocated gingival fiber surgery (Circumferential Supracrestal Fiberotomy) to allow for the release of soft tissue tension and reattachment of the fibers in a passive orientation after orthodontic tooth rotation. In 1971 a prospective study was initiated by Edwards with 160 patients up to 14 years post treatment. The results were published in 1988 (AJO 1988) and show a significant difference in the irregularity index between the control and treatment groups at both 6 and 14 years post treatment. No significant loss of attachment or other periodontal abnormalities were reported

MANDIBULAR INCISOR DIMENSIONS

The notion that mandibular incisor dimensions were correlated with lower incisor crowding was reintroduced by Peck and Peck (AO 1972) after a study of 45 untreated normal occlusions. They advocated reduction of mandibular incisors to a given faciolingual/mesiodistal ratio to increase stability. Peck and Peck's work, however, was criticized since their recommendations were based on a study involving untreated rather than treated cases. Young patients with ideal lower incisor alignment were used in the study. It is possible that these cases would show crowding if followed long term.

To evaluate whether the Peck and Peck ratio had long-term value, Gilmore and Little (AJO 1984) studied 134 treated and 30 control cases a minimum of 10 years postretention. They showed a weak association between long-term irregularity and either incisor width or the faciolingual/mesiodistal ratio.

INFLUENCE OF ENVIORNMENTAL FACTORS AND NEUROMUSCULATURE

Strang(AO 1959) theorized that the mandibular intercanine and intermolar arch widths are accurate indicators of the individual's muscle balance and dictate the limits of arch expansion during treatment. Weinstein et al. and Mills (Br Dent J 1966) stated that the lower incisors lie in a narrow zone of stability in equilibrium between opposing muscular pressure, and that the labiolingual position of the incisors should be accepted and not altered by orthodontic treatment. Reitan(AJO 1969) claimed that teeth tipped either labially or lingually during treatment are more likely to relapse.

The initial position of the lower incisors has been shown to provide the best guide to the position of stability in two separate studies (Little et al. AJO 1985 & Houston et al. EJO 1990). In over 50% of cases the lower incisors ultimately stabilized at a point between the pretreatment and post treatment positions. These results indicate that if lower incisor advancement is a treatment objective, permanent retention is essential for maintenance of the result.

CONSIDERATION OF CONTINUING GROWTH

Litowitz (AO 1948) stated that cases exhibiting greatest amount of growth during treatment showed less relapse. Riedel (AO 1960) reflected on the fact that growth may aid in the correction of orthodontic problems but may also cause relapse of treated cases. Nanda and Nanda (AJO 1992) agree with this and maintain that any skeletal changes that occur during retention may attenuate, exaggerate, or maintain the dentoskeletal relationship.

Facial development may result in secondary crowding especially in extreme growth patterns such as forward mandibular growth rotation where increased lingual movement of lower incisors may be seen. Others have stated that growth is not a major influence in development of mandibular anterior irregularity, (Sinclair & Little AJO 1985) and this is likely the case in an average grower.

Nanda and Nanda(AJO 1992) found that the pubertal growth spurt for patients with skeletal deep bite occurs on average 1.5 to 2 years later than is the case for open bite cases. For this reason, a longer retention period for the skeletal deep bite patients is advocated to counteract the continuing effect of dentofacial growth after the completion of orthodontic treatment.

POSTTREATMENT TOOTH POSITIONING AND ESTABLISHMENT OF FUNCTIONAL OCCLUSION

Adequate interincisal contact angle may prevent overbite relapse and good posterior intercuspation prevents relapse of both crossbite and AP correction. Less relapse of mesiodistal movement occurs in the absence of occlusal stress. A perfect molar relationship was found to be a significant factor in maxillary incisor alignment in a study of 226 postretention cases, (Schwarze CW BJO 1995) and a RCP - ICP slide was found to have a statistically significant, though clinically only moderate, influence on mandibular incisor irregularity postretention (Weiland FJ EJO 1994).

ROLE OF DEVELOPING THIRD MOLARS

The role of third molars in lower incisor crowding has been debated for more than a century. One theory commonly reported is that of the third molars creating space to erupt by causing anterior teeth to crowd.

Woodside (JCO 1970) postulated that in the absence of third molars, the dentition could settle distally in response to forces generated by growth changes or soft tissue pressures. This implies a passive role of the third molars in the development of late crowding by hindering that adjustment. Recent studies show a statistically significant but not a clinically significant role of third molars in postretention crowding.

..

Broadbent(AO 1941) was an early advocate of the insignificant role played by third molars in late lower incisor crowding. Several studies show a reduction in arch length and an increase in crowding with age. However, no difference in incisor crowding could be found in groups with impacted, erupted, missing, or extracted wisdom teeth.

Richardson(AO 1982) demonstrated a significant forward movement of first molars between the ages of 13 and 17 years. This was correlated with the increase in lower arch crowding that occurred during the same period.

Ades et al. (AJO 1990) compared four groups of patients who were a minimum of 10 years out of retention. They found no difference in mandibular incisor crowding, arch length, intercanine width, and eruption patterns of mandibular incisors and molars between the groups.

In summary, all of the conflicting data regarding third molars tends to indicate 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.

INFLUENCE OF THE ELEMENTS OF THE ORIGINAL MALOCCLUSION

Overbite increase postretention is related to the amount reduced during treatment, although generally 30% to 50% of the correction is retained. It is suggested that overbite relapse tends to occur in the first 2 years posttreatment and maintenance of intercanine width is thought to increase stability. Most studies do not support a greater relapse in Class II Division 1 cases when compared with other malocclusion groups, however, a slight change in overjet toward pretreatment values was demonstrated in all malocclusion groups.

When teeth are aligned by orthodontic treatment, there is a documented tendency for a return toward the original pattern of malocclusion (Kalplan AJO 1966). For this reason, rotational overcorrection has been advocated.

Little et al. (AJO 1981) however, noted that there are many exceptions to this rule with greater than 50% of the rotations or displacements relapsing in an opposite direction.

ROLE OF TRANSVERSE DISCREPENCIES

There is inevitably a tendency for relapse associated with Rapid Palatal Expansion techniques. Typically the clinician must significantly overcorrect in the transverse dimension, anticipating that a more normal relationship will occur during the relapse stages. Additionally the expansion appliance must be maintained passively or removable appliance placed to aid in transverse retention.

..

Storey (AJO 1973) has documented experimentally that rapid expansion results in a predominantly destructive process in which the sutural connective tissue becomes disruptive and edematous. This is followed by eventual filling of immature bone as a healing response. The growing of bone of sufficient maturity requires a slow steady rate of formation with lateral separation of bones on the order of 0.5 to 1mm per week. Results of Storeys experiments show that slow separation with continued growth of bony serrations within the suture provides the best retention with the least potential for relapse.

Castro, Cotton, and Hicks (University of Washington, AJO 1973, 1979) have further evaluated experimentally and clinically the stability of palatal expansion with light continuous forces and have concluded that this technique is more stable than rapid expansion.

..

Anatomically, the limitation of palatal expansion is not the fusion of the midpalatal suture but rather changes in morphology of suture caused by maturation. As the patient ages, further intercuspation and interdigitation of bony serrations take place until the suture becomes mechanically difficult to expand at older ages. These changes may occur as early as 13 to 14 years. Early expansion with light forces, achieved before these maturation changes will allow maximal skeletal separation, with normal physiological bone deposition enhancing the long term stability in this plane of space.

GENDER AND SEX DIFFERENCES

Growth is an aid in the correction of many types of orthodontic problems, but it also may cause relapse in treated orthodontic patients. Orthodontists take advantage of growth when treating patients in the transitional dentition period with headgear anchorage or functional appliances. With cervical traction the normal forward movement of the maxillary molars seems to be restrained while the mandible continues in its course of growth, and a normal tooth relationship may eventually be reached (Harris J AJO 1962, Lagerstrm AO 1967).

The forward translation of the mandibular denture on its base after the use of class II elastics or functional appliances is generally regarded as being undesirable, for apparently the mandibular posterior teeth do not migrate distally again. Mandibular anterior teeth in their attempt to upright to their former positions, frequently break contact and crowd to the lingual.

PRINCIPLES OF RETENTION AGAINST INTRA-ARCH INSTABILITY:Comparing the position of the teeth at the conclusion of treatment with their original positions can identify the direction of potential relapse. [Teeth will tend to move back in the direction from which they came, primarily because of elastic recoil of gingival fibers but also because of unbalanced tongue-lip forces.] Teeth require essentially full-time retention after comprehensive orthodontic treatment for the first 3 to 4 months after a fixed orthodontic appliance is removed. [To promote reorganization of the PDL, however, the teeth should be free to flex individually during mastication, as the alveolar bone bends in response to heavy occlusal loads during mastication. This requirement can be met by a removable appliance worn full-time except during meals or by a fixed retainer that is not too rigid.]

Because of the slow response of the gingival fibers, retention should be continued for at least 12 months if the teeth were quite irregular initially but can be reduced to part-time after 3 to 4 months. After approximately 12 months it should be possible to discontinue retention in non-growing patients. Some patients who are not growing will require permanent retention to maintain the teeth in what would otherwise be unstable positions because of lip, cheek, and tongue pressures that are too large for active stabilization to balance out. Patients who will continue to grow, however, usually need retention until growth has reduced to the low levels that characterize adult life.

OCCLUSAL AND OTHER FACTORS WHICH MAY MODIFY THE RETENTION PROTOCOL

Comprehensive orthodontic treatment is usually carried out in the early permanent dentition, and the duration is typically between 18 and 30 months. This means that active orthodontic treatment is likely to conclude at age 14 to 15, while anteroposterior and particularly vertical growth often do not subside even to the adult level until several years later. Long-term studies of adults have shown that very slow growth typically continues throughout adult life, and the same pattern that led to malocclusion in the first place can contribute to deterioration in occlusal relationships many years after orthodontic treatment is completed.

The various factors include.

-Lower Incisor alignment-Corrected Rotations of anterior teeth-Changes in the anteroposterior lower incisor position-Correction of Deep Overbite-Correction of Anterior Open Bites-Patients with a history of periodontal disease or root resorption-Growth Modification treatment-Correction of Posterior and anterior Crossbites-Adult Patients-Spaced Dentitions

Lower incisor alignment:

Increases in lower incisor irregularity occur throughout life in a large proportion of patients following orthodontic treatment and also in untreated subjects. Recent evidence suggests that most change will take place by the middle of the third decade (Richardson ME EJO 1998). It has been suggested that prolonged retention of the lower labial segment until the end of facial growth may reduce the severity of lower incisor crowding (Sadowsky C AJO 1994).

Patients expectations of the stability of their lower incisor alignment should be considered on completion of orthodontic treatment. If an individual is unwilling to accept any deterioration in lower incisor alignment following orthodontic treatment then permanent fixed or removable retention may have to be considered

Corrected rotations of anterior teeth:

As the supracrestal gingival fibres are known to take the longest amount of time to reorganise, prolonged retention of corrected rotations may be helpful in reducing relapse. While the use of adjunctive circumferential supracrestal fiberotomy has been shown to be effective in reducing relapse within the first 4-6 years after debonding, the additional long term clinical benefit from the procedure is relatively small (Edwards JG AJO 1988). Changes in the antero-posterior lower incisor position:

Any intentional or non-intentional change of more than 2mm indicates the need for long-term or indefinite retention (Proffit).

Correction of deep overbite:

Following the correction of a very deep overbite, the use of an anterior biteplane until the completion of facial growth has been recommended. This may be particularly useful when there is evidence of an anterior mandibular growth rotation. (Proffit, Burstone & Nanda)

Correction of anterior open bites: While the use of retainers incorporating posterior biteblocks has been recommended for prolonged retention of anterior open bite malocclusions with unfavourable growth patterns, there is currently a lack of scientific evidence to support this. (Proffit)

Patients with a history of periodontal disease or root resorption:

In patients with previously treated severe periodontal disease, permanent retention is advised. For those with minimum to moderate disease, a more routine retention protocol can be used (Zachrisson) . There is evidence of an increased risk of deterioration of lower incisor alignment post-retention in cases with root resorption or crestal bone loss (Sharpe W AJO 1987). These cases may therefore benefit from prolonged retention. Growth modification treatment: Following the use of headgear or functional appliances, retention using a modified activator appliance has been reported as effective in maintaining Class II correction (Weislander L AJO 1993).

Correction of posterior and anterior crossbites:

When the incisor overbite and posterior intercuspation are adequate for maintaining the correction, no retention is necessary (Kaplan AJO 1988).

Adult Patients:

When the periodontal supporting tissues are normal and no occlusal settling is required, there is no evidence to support any changes in retention protocol for adult patients compared with adolescent patients. Spaced dentitions

Permanent retention has been recommended following orthodontic treatment to close generalised spacing or a midline diastema in an otherwise normal occlusion (Graber & Vanarsdall).

CAUSATIVE FACTORS FOR RELAPSEMost of the causative factors may be related to,

-Craniofacial growth-Dental development &-Muscle function

CRANIOFACIAL GROWTH

-Bjork (1968) showed the high variability of normal facial growth in one of his first studies describing the use of metal implants in cephalometrics. Late growth changes may be responsible for posttreatment relapse, especially after correction of class III malocclusion.-Growth and changes in muscles and surrounding soft tissue structures are relatively well synchronized with the growth of the skeletal framework. The craniofacial complex is regarded as a structure with specific functions, classified as functional cranial components, and consisting of a functional matrix and a skeletal unit, which protects and supports this matrix. It has been shown that parts of the functional matrix have a direct influence on the bone during orthodontic treatment. .......................

-Relapse of the overjet and overbite has been observed and has been mainly due to changes in incisor inclination. The tendency to relapse is slightly greater in class II division 2 cases than in class II division 1 cases. As the maxillary growth is completed on average 2 to 3 years before mandibular growth, dentoalveolar structures may have difficulties in compensating for this discrepancy, which may result in an increased overbite.

-Bjork (1972) and Sakuda (1976) showed that the dentoalveolar structures may be influenced by the facial morphology. Permanent teeth in low angle cases should have a more anteriorly directed path of eruption than in normal individuals, which, together with a deep bite, might unfavourably influence the stability in the lower anterior region. Mandibular incisor crowding is also believed to be related to anterior (upward) rotation of the mandible.

DEVELOPMENT OF THE DENTITION

Continuous eruption of teeth The physiologic changes of the dentition from early childhood into adolescence, and from young adulthood into adulthood are gradual process. A slight continuous eruption of teeth has been observed even after the establishment of occlusion post adolescence.

Arch length changes The arches reduce sagittally until the age of 14 years and even later. Crowding of the lower incisors quite commonly develops in modern man and coincides with this decrease in arch length.

Tooth size The mesiodistal tooth size has been discussed as a causative factor of the late crowding. Begg (1954) analyzed interproximal attrition in old Australian aborigines and concluded that teeth in modern man are too large for the dental arches and hence become crowded. Corrucini (1990) showed that small jaws rather than large teeth underlie tooth-arch discrepancy.

..

Mandibular 3rd molars Richardson (1989) stressed that the third molar plays a passive role in the development of late lower arch crowding.

Arch width changes Richardson (1995) showed that increased lower arch crowding could be found in association with both increased and decreased arch width, depending on the direction of movement of the canines. Decrease of the mandibular intercanine width is generally considered to be associated with late lower crowding.

Because dental development continues at a slow persistent rate from adolescence into adulthood, there is no definitive method to distinguish between normal age-related events and relapse after orthodontic treatment.

SOFT TISSUE MATRIX

-The dentoalveolar changes are not only the result of the influence of growth on tooth movements but also a function of the soft tissue matrix surrounding the hard tissue structures.

-It has been stressed that in the absence of muscular imbalance, a well-established interdigitation may greatly assist in maintaining the end result of tooth movement. Establishing the most precise intercuspal relationship between dental arches will not prevent relapse from occurring if a strong adverse muscular pressure exists.

-It is therefore important to stress that if a malocclusion, caused or maintained by muscular or other soft tissue dysfunction, has been morphologically corrected without any alteration in muscular behaviour, a stable posttreatment result is unlikely.

TREATMENT TIME & PATIENTS AGE

-Corrections carried out during periods of growth and eruption of teeth is considered to be less likely to relapse.

-According to Reitan (1967), there will be little or no relapse following orthodontic movement of an erupting tooth, because its supporting tissues are in a stage proliferation as a result of the eruption process.

-New fibers will be formed as the root develops, and these new fibers will assist in maintaining the new tooth position.

PERIODONTAL FORCE AND RELAPSE

Southard and Tolley (AJO 1992) investigated the interproximal force (IPF) at the mandibular first molar-second premolar contact and determined that whether the periodontium maintains the contacts of approximating mandibular teeth in a continuous state of compression. Results indicated that,

-Contacts of approximating mandibular teeth are maintained in a continuous state of compression. This compressive force is generated by the supporting periodontium and acts through the dental contact points, even when the dental arches are apart. Further, this force is increased for a period after chewing.

-If inter proximal force (IPF) does exert an influence on dental alignment, it probably acts in conjunction with lip and cheek forces to collapse the arch and is opposed by tongue force, which tends to expand the arch. It follows that the influence of IPF should be more evident in the anterior region of the arch where the contact points are narrower, the crowns more tapered, and the expansive force from the tongue more intermittent than in the posterior region of the arch.

-The existence of a continuous, compressive force (IPF), originating in the periodontium and acting on approximating teeth at their contact points, which is increased after occlusal loading, may help to explain long-term post treatment crowding of the mandibular anterior teeth, physiologic drifting of teeth, and maintenance of posterior dental contacts after interproximal wear.

RETENTION AFTER CLASS II CORRECTION:

Relapse toward a Class II relationship must result from some combination of tooth movement (forward in the upper arch, backward in the lower arch, or both) and differential growth of the maxilla relative to the mandible. In Class II treatment, it is important not to move the lower incisors too far forward, but this can happen with Class II elastics. In this situation lip pressure will tend to upright the protruding incisors, leading relatively quickly to crowding and return of both overbite and overjet.

Overcorrection of the occlusal relationships as a finishing procedure is an important step in controlling tooth movement that would lead to Class II relapse. Even with good retention, 1 to 2 mm of anteroposterior change caused by adjustments in tooth positions is likely to occur after active treatment stops. As a general guideline, if more than 2 mm of forward repositioning of the lower incisors occurred during treatment, permanent retention would be required.

..

The slower long term relapse that occurs in some patients who did not have inappropriate tooth movement results primarily form differential jaw growth. This relapse tendency can be controlled in one of two ways:

- The first is to continue headgear to the upper molars on a reduced basis (at night, for instance) in conjunction with a retainer to hold the teeth in alignment. This is quite satisfactory in well motivated-patients who have been wearing headgear during treatment and is compatible with traditional retainers that are worn full-time initially.

.

- The second method is to use a functional appliance of the activator-bionator type to hold both tooth position and the occlusal relationship. If the patient does not have excessive overjet at the end of active treatment, the construction bite for the functional appliance is taken without any mandibular advancement- the reason being to prevent a Class II malocclusion from recurring. A potential difficulty is that the functional appliance will be worn only part-time, typically just at night, and day time retainers of conventional design also will be needed to control tooth position during the first few months. For patients with less severe problems, in whom continued growth may or may not cause relapse, it may be more rational to use only conventional maxillary and mandibular retainers initially, and replace them with a functional appliance to be worn at night if relapse is beginning to occur after a few months.

This type of retention is often needed for 12 to 24 months or more in patients with a severe skeletal problem initially. The guideline is: the more severe the initial Class II problem and the younger the patient at the end of active treatment, the more likely that either headgear or a functional appliance will be needed as a retainer.

RETENTION AFTER CLASS III CORRECTION:

Relapse from continuing mandibular growth is very likely to occur and such growth is extremely difficult to control. Applying a restraining force to the mandible, as from a chincap tends to rotate the mandible downward, causing growth to be expressed more vertically and less horizontally, and Class III functional appliances have the same effect. If face height is normal or excessive after orthodontic treatment and relapse occurs from mandibular growth, surgical correction after the growth has expressed itself may be the only answer. In mild Class III problems, a functional appliance or a positioner may be enough to maintain the occlusal relationships during post treatment growth.

RETENTION AFTER DEEP BITE CORRECTION:

In correcting excess overbite, the majority of patients require control of vertical overlap of incisors during retention. This is accomplished most readily by using a removable upper retainer combined with a bite plane so that the lower incisors will encounter the baseplate of the retainer if they begin to slip vertically behind the upper incisors. The retainer does not separate the posterior teeth. As vertical growth continues into the late teens, the retainer often is needed for several years after fixed appliance orthodontics is completed.

RETENTION AFTER ANTERIOR OPEN BITE CORRECTION:

Relapse into anterior open bite can occur by any combination of depression of the incisors and elongation of the molars. Active habits such as thumbsucking and tongue-thrust swallowing are often blamed for relapse into open bite, but the evidence to support this contention is not convincing. In patients who do not place some object between the front teeth, return of open bite is almost always the result of elongation of the posterior teeth, particularly the upper molars without any evidence of intrusion of incisors. Excessive vertical growth and eruption of posterior teeth often continue until late in the teens or early twenties. Controlling eruption of the upper molars is therefore the key to retention in open bite patients.

..

High pull head gear to the upper molars, in conjunction with a standard removable retainer to maintain tooth position, is one effective way to control open bite relapse. A better alternative is an appliance with bite blocks between the posterior teeth (an open bite activator or bionator), which stretches the patients soft tissues to provide a force opposing eruption. A patient with a severe open bite problem is particularly likely to benefit from having conventional maxillary and mandibular retainers for daytime wear, and an open bite bionator as a nighttime retainer from the beginning of the retention period.

RETENTION OF LOWER INCISOR ALIGNMENT:

Continued skeletal growth can not only affect the occlusal relationships, but also alter the position of the teeth. If the mandible grows forward or rotates downward, the effect is to carry the lower incisors into the lip, which creates a force tipping them distally. For this reason continued mandibular growth in normal or Class III patients is strongly associated with crowding of the lower incisors. Incisor crowding also accompanies the downward and backward rotation of the mandible seen in open bite problems. A retainer in the lower incisor region is needed to prevent crowding from developing, until growth has declined into adult levels. It also has been suggested that orthodontic retention should be continued, at least on a part-time basis, until the third molars have either erupted into normal occlusion or have been removed.

LONG-TERM RETENTION STUDIES

.

TREATMENT MODALITIES

Several long-term retention studies evaluating the stability of different treatment modalities have been reported. The main center for much of this research is the University of Washington. Most of the research is centered on the mandibular arch with the assumption that alignment of the lower arch serves as a template around which the upper arch develops and functions.

Most of the studies report on the Irregularity index (Little R AJO 1975), arch length, and intercanine width. It is important to note that the terms crowding and arch length deficiency are not synonymous with the irregularity index. The irregularity index measures displaced anatomic contact points of the teeth and gives an objective value to subjective crowding of the case. Arch length deficiency on the other hand represents the space needed for alignment of teeth.

The following treatment modalities have been studied:

Late extraction followed by full treatment Serial extraction without treatment Serial extraction followed by appliance therapy Non extraction therapy with expansion Early mixed dentition treatment without fixed appliance therapy Non extraction therapy with generalized spacing Lower incisor extractions

LATE EXTRACTION FOLLOWED BY FULL TREATMENT

Little et al.(AJO 1981) reports on 65 first premolar extraction patients at least 10 years postretention. Mandibular arch shortening was seen in 63 of the 65 patients. The crowding posttreatment was not associated with the degree of arch length reduction. Intercanine width change during the treatment and the duration of retention were not predictive of postretention crowding. The overall success rate, defined as an irregularity index of less than 3.5 mm, was less than 30% with 20% showing marked crowding.

Shields et al.(AJO 1985) reevaluated 54 of the patients from the 1981 study and failed to find any clinically significant predictors or associations of value between the dental-cast measurements and cephalometric data. Any change in cephalometric parameters postretention failed to explain postretention crowding.

SERIAL EXTRACTION WITHOUT TREATMENT

Kinne (University of Washington 1975) reported on 55 patients who had undergone serial extraction without any appliance therapy. The patients, examined at least 10 year after the extraction of premolars, showed an increase in post treatment irregularity.

Persson et al. (EJO 1989) reported on 42 patients an average of 20 years after serial extraction therapy. Most of the cases showed redevelopment of crowding, however, it was less pronounced than pretreatment and when compared with untreated normals there was no difference in the crowding evident between the two groups.

SERIAL EXTRACTION FOLLOWED BY APPLIANCE THERAPY

Anticipated future stability is one of the objectives of serial extraction therapy. Tweed(1966) postulated that early self-alignment should result in improved stability. Engst (University of Washington 1977) studied 30 patients at 5 years postretention, and Little et al. (AO 1990) reported on the same sample at least 10 years postretention. Clinically unsatisfactory mandibular anterior alignment occurred in 73% of the cases and decreases in intercanine width and arch length was found in 29 of the 30 cases.

McReynolds and Little (AO 1991) found no difference in postretention irregularity between first and second premolar extraction cases. Both the first and second premolar extraction cases showed a reduction in arch length and width and were unpredictable relative to long-term alignment. When compared to the late premolar extraction group, the success rate of less than 30% was no different.

NONEXTRACTION THERAPY WITH EXPANSION

Twenty-six patients who had at least 1 mm of arch development during the mixed dentition were studied at least 6 years postretention (Stein UoW 1974 & Little AJO 1990). All the patients showed a reduction in arch length after treatment and only five patients maintained an overall increase of 1 mm. Moussa et al. (AJO 1995) reported on a sample of 55 patients who had undergone rapid palatal expansion in conjunction with edgewise mechanotherapy a minimum of 8 years postretention. Their results showed good stability for upper intercanine, upper and lower intermolar widths, and lower incisor irregularity. Stability of the mandibular intercanine width, however, was poor with the posttreatment position closely approximating the pretreatment dimension.

..

The stability of nonextraction treatment with prolonged retention was studied by Sadowsky et al., (AJO 1994) who looked at 22 patients an average of 8.4 years postretention (minimum, 5 years). The mandibular incisor irregularity increased during the postretention period but at 2.4 mm was still in the acceptable range.

Elms et al. (AJO 1996) recently reported on a sample of 42 patients with Class II Division I malocclusion, who were treated without extraction and with headgear and fixed appliances. Final records were taken an average of 6.5 years postretention (minimum, 3 years). Some incisor reproximation was preformed on removal of the mandibular bonded retainer. Ninety percent of the sample had incisor irregularity of less than 3.5 mm postretention. They conclude that the factors responsible for the stability seen are the application of proper mechanics, a cooperative patient, and favorable downward and forward mandibular growth.

The above cases showed only minimal crowding pretreatment

EARLY MIXED DENTITION TREATMENT WITHOUT FIXED APPLIANCE THERAPY

Dugoni et al.(AO 1995) reported on the postretention stability of cases who had early mixed dentition treatment followed by the placement of a mandibular bonded retainer. No appliance therapy was carried out in the permanent dentition. Circumferential supracrestal fiberotomy or interproximal enamel reduction was carried on removal of the bonded retainers. The irregularity index in this sample at the postretention stage showed satisfactory mandibular incisor alignment in 76% of the cases. In contrast to other studies, maintenance of postretention intermolar width was also noted. It is suggested that the early establishment of an intermolar width and improved occlusion in the mixed dentition provides better long-term stability.

NONEXTRACTION THERAPY WITH GENERALIZED SPACING

Thirty patients with mandibular spacing pretreatment were studied 10 years postretention (Little AJO 1989). Of all the treatment modalities studied, this treatment displayed the most long-term stability with an irregularity index value of 3.38 mm. This was still slightly higher, however, than the value of 2.7 mm for untreated norms. Minimal relapse of overjet and overbite was evident. Some intercanine width reduction was evident in most cases. The overall success rate in this group was 50% postretention.

Mandibular spaces did not reopen in any case. However, the maxillary arch showed more variation; the midline diastema was the most common areas of space recurrence.

LOWER INCISOR EXTRACTIONS

Riedel (JCO 1976) observed an increase in post treatment stability after an informal review of patients who had two mandibular incisors removed. He then carried out a long-term study to specifically determine the stability and relapse of the mandibular incisor extraction therapy (AO 1992). Twenty-four patients who had a single mandibular extraction followed 6.5 years postretention and 18 patients with two mandibular incisor extractions followed for a period of 9.75 years were studied. Twenty-nine percent of the single incisor extraction group and 56% of the two incisor extraction group demonstrated unacceptable mandibular incisor alignment at the postretention stage. This compares favorably to the results of previously reported premolar extraction cases.

SUMMARY OF POSTTREATMENT CHANGES:

Intercanine width reduction is seen posttreatment whether the case was expanded during treatment or not. The intermolar width tends to return to the pretreatment value during the postretention period in most of the studies. These reported changes in intercanine and intermolar width are greater in the mandibular arch than the maxillary arch. Although most of the arch changes are seen before age 30, mandibular anterior crowding continues into the fifth decade. As summarized by Little et al. treated cases should be viewed as dynamic and constantly changing, at least through the third and fourth decade and perhaps throughout life. Of all the treatment modalities studied only three showed acceptable long-term mandibular incisor alignment postretention. These were the early mixed dentition treatment with no fixed appliance therapy, the nonextraction therapy with generalized spaces, and the lower incisor extraction cases.

ORTHOGNATHIC SURGERY MAXILLARY SURGERIES Schuchardt (1959) first reported superior movement of the maxilla, who used a two-stage approach and limited his surgical procedure to the posterior maxilla. He reported relapse problems that in retrospect probably were caused primarily by incomplete mobilization of the dentoalveolar segments at surgery.

Willmar (1974) undertook the first quantitative follow-up study on LeFort I osteotomy with the use of surgically placed metal markers. Although 106 patients were studied, only three had ''idiopathic long face.'' These cases demonstrated stability of markers and occlusion throughout the 1-year observation period, with an ''insignificant" 10% superior relapse occurring at the anterior marker.

Bell and McBride (1977) examined 41 patients with vertical maxillary excess who underwent maxillary superior repositioning by LeFort I osteotomy. They evaluated their results clinically and noticed stability without relapse in the cases examined.

Hartog (1982) evaluated skeletal stability and soft-tissue changes after superior repositioning of the maxilla, and reported that good stability was attained. The sample included multiple segments and combined procedures with only three one-piece osteotomies.

Washburn, Schendel, and Epker (1982) reported their experiences with superior maxillary repositioning in a group of 15 young patients and indicated that the postsurgical jaw relationship was maintained even in patients who experienced postsurgical growth.

MANDIBULAR SURGERIES

Lake, McNeill, Little (AJO 1981) evaluated surgical advancement of the mandible by retrospective cephalometric and computer analysis for longitudinal skeletal and dental changes an average of 3 years after surgery. 52 patients (19 males and 33 females) underwent surgical advancement of the mandible by means of bilateral sagittal osteotomy of the mandibular vertical rami. From the results, relationships between specific parameters and skeletal relapse have been demonstrated:-Positional change of the proximal segment was found to be the most important parameter in determining stability or relapse of the advanced mandible. -Anteroinferior condylar displacement and increase in posterior facial height at the time of surgery or immediately postoperatively were associated with subsequent skeletal relapse of the distal mandibular segment.-The magnitude of advancement was a primary factor in mandibular stability. As the magnitude of advancement increased, the net amount of relapse tended to increase. -The dynamic function and variability of the mandible's musculoskeletal system and its periosteal integument may play a dominant role in the nature of the postsurgical response.-Preoperative measurement of the mandibular plane angle did not prove to be a reliable predictor of subsequent mandibular relapse. However, patients with high mandibular plane angles did undergo more relapse than did patients with either normal or low angles.-No significant relationship was found between skeletal relapse and the age of the patient..

Huang and Ross (AJO 1982) evaluated the short-term and long-term effects of surgical lengthening of the retrognathic, growing mandible in children. Twenty-two patients 12 boys and 10 girls underwent mandible-lengthening procedures at the mean ages of 14.1 years (boys) and 13.4 years (girls).

The results indicated that,-The response to this mandible-lengthening surgery in the growing child varied with the amount of lengthening performed but did not appear to vary with age (after 11 years), sex, etiology of the mandibular discrepancy, mandibular plane angle, deep- or open-bite, or concomitant surgical procedures.

-Lengthening of more than 11 mm. was usually accompanied by extensive relapse, with major remodeling of the condyle or posterior symphysis or both.Lengthening of less than 9 mm. was followed by little or no relapse.

-No further clinically significant growth of the mandible occurred following mandible lengthening as performed after the age of 11 years.

-The mandible returned to its preoperative growth direction within 2 years after surgery.

FUNCTIONAL APPLIANCE TREATMENT

Pancherz (AJO 1991) performed a long term cephalometric investigation to analyze the nature of Class II relapse after Herbst appliance treatment, comparing stable and relapse cases at least 5 years after treatment. A total of 118 patients with Class II, Division 1 malocclusions were treated with the Herbst appliance. Lateral cephalograms taken before and immediately after Herbst treatment, as well as 6 months and 5 to 10 years after treatment, were analyzed.

The results revealed that,-Relapse in the overjet and sagittal molar relationship resulted mainly from posttreatment maxillary and mandibular dental changes.

-In particular, the maxillary incisors and molars moved significantly to a more anterior position in the relapse group than in the stable group.

-The interrelation between maxillary and mandibular posttreatment growth was favorable and did not contribute to the occlusal relapse.

-It is hypothesized that the main causes of the Class II relapse in patients treated with the Herbst appliance were a persisting lip-tongue dysfunction habit and an unstable cuspal interdigitation after treatment...

Wieslander (AJO 1993) investigated the long-term effect of treatment with headgear-Herbst appliance in early mixed dentition in children with severe Class II malocclusions. A group of children age 8 years 8 months was initially treated for 5 months with a headgear-Herbst appliance followed by a 3- to 5-year period of activator retention. The patients were studied out of retention at the mean age of 17 years 4 months and compared with an untreated control group.

Positive findings of the study includes the following:-A rapid improvement of the anteroposterior jaw discrepancy because of 24-hour wear of the appliance for 5 months.-A significant maxillary effect during active treatment and retention resulting in a 2.3 mm posterior gain after retention, which compensates for the mandibular relapse tendency. It resulted in an average statistically and clinically significant 2.9 reduction of the ANB angle and a 3.8 mm skeletal improvement of the sagittal jaw relationship out of retention.

Negative findings include the following:-A prolonged retention ranging over several years of activator wear was necessary to minimize relapse after Herbst treatment.-A modest long-term effect on the mandible 8 years after treatment. In many cases the long-term mandibular effect was considerably larger and of clinical importance. However, in other cases that cooperated poorly during retention, it was less.-A rather small increase in mandibular length. The significant average 2.0 mm increase in the condylion-gnathion distance observed after 5 months of Herbst treatment was reduced to 1.2 mm after retention and was not statistically significant.

RETENTION PLANNING

Retention Planning is divided into three categories, depending on the type of treatment instituted:

(1) limited retention(2) moderate retention ( in terms of both time and appliance wearing)(3) permanent or semi permanent retention

CONDITIONS WHERE LIMITED RETENTION IS REQUIRED:

(a) Corrected Crossbites -Anterior: when adequate overbite has been established-Posterior: when axial inclinations of posterior teeth remain reasonable after corrective procedures have been completed

(b) Dentitions that have been treated by serial extraction-High canine extraction cases -Cases calling for extraction of one or more teeth (c) Corrections that have been achieved by retardation of maxillary growth, whether dental or skeletal, after the patient has passed through the growth period (d) Dentitions in which the maxillary and mandibular teeth have been separated to allow for eruption of teeth previously blocked out.

CONDITIONS WHERE MODERATE RETENTION IS REQUIRED:

(a) Class I non extraction cases, characterized by protrusion and spacing of maxillary incisors. These require retention until normal lip and tongue function has been achieved.

(b) Class I or Class II extraction cases probably require that the teeth be held in contact, particularly in the maxillary arch, until lip and tongue function can achieve a satisfactory balance. It is generally desirable to use a maxillary Hawley type of retainer until normal functional adaptation has occurred. It is sometimes also desirable to use either a maxillary Kloehn-type headgear, whose force is directed to the permanent first molars, or a labiobuccal type of appliance, with cervical or occipital resistance applied at night.

.

(c) Corrected deep overbites in either Class I or Class II malocclusions usually require retention in a vertical plane.

-if anterior teeth were depressed to achieve overbite correction, a bite plane on a maxillary retainer is desirable. To be effective in retaining overbite correction, the bite plane should be worn continuously for perhaps the first 4 to 6 months, including while the patient is eating. In deep overbite cases overcorrection is usually desirable and equilibration and adjustment to functional occlusion is necessary. -If overbite correction was achieved as a result of bite opening and mandible was forced away from the maxilla, vertical dimensions should be held until growth (ie, mandibular ramal height) can catch up. -Severe occlusal plane tipping may also require extended retention protocols and possibly additional maxillary restraint as well.

.

(d) Early correction of rotated teeth to their normal positions. -Perhaps before root formation has been completed -In the mandibular incisor area a removable type of appliance with a labial bow is probably best. In this area, the occlusal splint type retainer or cast lower partial, as suggested by Lande, may be useful.

(e) Cases involving ectopic eruption of teeth or the presence of supernumerary teeth require varying retention times, usually prolonged, and occasionally a fixed or permanent retentive device.

(f) The corrected Class II div 2 malocclusion generally requires extended retention to allow for the adaptation of musculature.

CONDITIONS WHERE PERMANENT OR SEMI PERMANENT RETENTION IS REQUIRED:

(a) Cases in which expansion has been the choice of treatment, particularly in the mandibular arch, may require either permanent or semipermanent retention to maintain normal contact alignment.

(b) Cases of considerable or generalized spacing may require permanent retention after space closure has been completed.

(c) Instances of severe rotation or severe labiolingual malposition may require permanent retention, as provided by bonded retainers.

(d) Spacing between maxillary central incisors (diastema) in otherwise normal occlusions sometimes require permanent retention, particularly in adult dentitions.

TIMING OF RETENTION: SUMMARY

Retention is needed for all patients who had fixed orthodontic appliance to correct intra-arch irregularities. It should be:

Essentially full time for the first 3 to 4 months, except that the retainers not only can but should be removed while eating (unless circumstances like periodontal bone loss require permanent splinting).

Continued on a part time basis for at least 12 months, to allow time for remodeling of gingival tissues.

If significant growth remains, continued part time until completion of growth.

This would mean that nearly all patients treated in the early permanent dentition will require retention of incisor alignment until the late teens, and in those with skeletal disproportions initially, part time use of a functional appliance or extra oral force probably will be needed.

RETENTION APPLIANCESRequirements of Retaining Appliances: It should restrain each tooth that has been moved into the desired position in directions where there are tendencies towards recurring movements.It should permit the forces associated with functional activity to act freely on the retained teeth, permitting them to respond in as nearly a physiologic manner as possible.It should be as self-cleansing as possible and should be reasonably easy to maintain in optimal hygienic condition. It should be constructed in such a manner as to be as inconspicious as possible, yet should be strong enough to achieve its objective over the required period of use.

RETAINER DESIGN

Removable retainers with a labial bow (Hawley, Begg and Barrer type retainers): Removable Appliances can serve effectively for retention against intra-arch instability and are also useful as retainers (in the form of modified functional appliances or part-time headgear) in patients with growth problems. These retainers are robust and can be worn during eating. Hawley retainers have been recently shown to have the advantage of facilitating posterior occlusal settling in the initial three months of retention (Sauget E, AO 1997). The labial bow can be used to accomplish simple tooth movements if required, and an anterior biteplane can easily be incorporated for retention of a corrected deep overbite.

HAWLEYBARRERWRAP AROUND

Removable vacuum formed retainers (Transparent Plastic Invisible Retainers):

Vacuum formed retainers are relatively inexpensive and can be quickly fabricated on the same day as appliance removal. They are discreet and can be modified to produce tooth movements if required. Full posterior occlusal coverage (including second molars if present) is advisable in order to reduce the risk of overeruption of these teeth during retention. The Essix retainer is an example of the invisible retainer that only incorporates the six anterior teeth of each arch. These appliances allow for the settling of the posterior teeth into better occlusion. Due to their inherent flexibility, however, they cannot be used to retain cases in which arches have been expanded during orthodontic treatment.

Recent research has shown that vacuum formed retainers were significantly less effective in promoting posterior occlusal settling than Hawley retainers (Sauget E, AO 1997). However this is likely to be of little importance if good posterior intercuspation has been established by the time of debonding.

ESSIX THERMOPLASTIC COPOLYESTER RETAINERS

Fixed bonded retainers (Smooth wire, Flexible Spiral wire):

Fixed retainers are indicated for long-term retention of the labial segments, particularly when there is reduced periodontal support, and for retention of a midline diastema (Proffit). Fixed retainers are discreet and reduce the demands on patient compliance. However they are associated with failure rates of up to 47% (Bearn DR, AJO 1995), particularly on upper incisors when there is a deep overbite. In addition, calculus and plaque deposition is greater than with removable retainers. Fixed retainers therefore require long term maintenance.

There are four major indications:Maintenance of lower incisor position during late growthDiastema maintenanceMaintenance of pontic or implant spaceKeeping extraction space closed in adults

Flexible spiral wire retainers allow differential tooth movement and are particularly useful for patients with loss of periodontal support. Current orthodontic opinion recommends either the use of 0.0215 inch multistrand wire, (Heier EE, AJO 1997) or 0.030 - 0.032 inch sandblasted round stainless steel wire (Zachrisson JCO 1995).

Active Retainers:

Relapse or growth changes after orthodontic treatment will lead to a need for some tooth movement during retention. This usually is accomplished with a removable appliance that continues as a retainer after it has repositioned the teeth.

It usually used in two specific situations:Realignment of Irregular Incisors (Spring Retainers), and asFunctional appliances to manage Class II or Class III relapse tendencies. SPRING RETAINER

Positioners:

Positioners are elastomeric or rubber removable retainers that are either preformed or custom made. Preformed positioners are available for bicuspid extraction cases and non-extraction cases. Sizes are determined by measuring the mesiodistal dimensions of the six anterior teeth. These preformed positioners cannot compensate for individual variation in the size of the teeth, arch width, arch form or tooth size discrepancies. For these reasons, they should only be used temporarily.

Custom-made positioners are fabricated on articulated models in which teeth from both arches have been sectioned from the models, realigned and waxed in an ideal configuration. This incorporates minor corrections in tooth position and occlusal relationship. The elastomeric or rubber material is then formed around the teeth and the coronal portion of the gingiva.POSITIONERS

RECOVERY AFTER RELAPSE

Despite the utmost care in Treatment and Retention, if Relapse occurs the following can be considered:

Retreatment may take the form of rebanding or rebonding most if not all teeth. It is sometimes expedient to consider the removal of certain teeth, particularly if the relapse occurs in the form of crowding. In any case attempt should be made to discover and eliminate factors that appear contributory to relapse.

The mandibular lingual arch helps to realign the teeth in instances of mandibular collapse or crowding. Light pressure against mandibular anterior teeth may be used to realign them.

Springs and clasps can be added to maxillary Hawley retainer to assist in repositioning and control of labiolingual deviations.

Spring retainers using both facial and lingual acrylic for added leverage and labial bows for increased flexibility may be used for minor realignment. Teeth are sectioned and aligned on the retainer model and active retainer is fabricated to the realigned relationship. Interproximal stripping is sometimes beneficial.

5) The maxillary labiobuccal retainer, Kloehn-type headgear, or functional appliances may be used against the maxillary arch to provide recorrection in instances of relapse toward a Class II relationship.

6) Habit training in the form of tongue and lip therapy may be beneficial when abnormal habit patterns have caused orthodontic relapses. Removable appliances are also helpful as tongue restraints.

7) Equilibration and trimming may be all that is necessary to achieve esthetic and functional satisfaction for the patient and orthodontist.

8) In certain cases it may be desirable to suggest that the patient accept minimal relapses rather than continue with prolonged treatment or retention.

Maintaining the treatment result following orthodontic treatment is one of the most difficult aspects of the entire treatment process. Normal maturational changes, together with post-treatment tooth alterations, conspire against long-term stability. All treated malocclusions must eventually be returned from control by appliances to control by the patients own musculature. Permanent retention is increasingly being recommended as the only way to ensure long-term stability of an orthodontic treatment result. Proper goals of treatment, careful mechanotherapy, precise occlusal equilibration, and well-chosen retention procedures play a role in achieving occlusal homeostasis. CONCLUSION