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CRITICAL REVIEW OF CRITICAL REVIEW OF LONG TERM RELAPSE LONG TERM RELAPSE

STUDIESSTUDIESINDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

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INTRODUCTION TERMINOLOGY OF POSTORTHODONTIC CHANGES RETENTION AND RELAPSE-DEFINITIONS DIFFERENT SCHOOLS OF THOUGHT FOR RELAPSE BASIC THEORMS FOR RELAPSE CAUSATIVE FACTORS FOR RELAPSE TREATMENT CHANGES IN DENTITION AND STUDIES FOR ITS RELAPSE EXTRACTION VS NON-EXTRACTION TREATMENT – RELAPSE STUDIES ANTERIOR OPEN BITE AND RELAPSE STUDIES ORTHOPEDIC TREATMENT AND RELAPSE FUNCTIONAL APPLIANCE TREATMENT AND RELAPSE ORTHOGNATHIC SURGERY AND RELAPSE STUDIES CONCLUSION

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INTRODUCTIONINTRODUCTION Relapse can be defined as a return toward the preexisting (pretreatment) condition, and relapse of teeth after orthodontic treatment has been a topic of persistent interest throughout most of this century.  Angle stated that “The problem involved in retention is so great as to test the utmost skill of the most competent orthodontist, often being greater than the difficulties being encountered in the treatment of the case up to this point.” Tweed stated that determining the anterior limits of the denture was the key to stability.

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Mershon stated that the final position of the teeth was like “an argument with Mother Nature,” who always won.

Hawley said that he would “give half of his fee to anyone who would be responsible for the retention of his results when the active appliance was removed.” Almost most of the conditions like mandibular anterior crowding, arch length and width, arch form, deep bite, anterior open bite, tooth rotations, and treatment approaches like intrusion, arch expansion, extractions, functional appliance therapy, orthopedic treatment and orthognathic surgeries showed the tendency for relapse after treatment over prolonged period of time.

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A major objective of orthodontic treatment is to achieve long-term stability of the occlusion. Most studies of relapse have examined patients within 5 years of orthodontic treatment; few studies of people treated a decade or more in the past have been published.

Recently various authors studied relapse on a long-term basis to assess the stability and outcome of orthodontic treatment.

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TERMINOLOGY OF POSTORTHODONTIC TERMINOLOGY OF POSTORTHODONTIC CHANGESCHANGES 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 posttreatment relapse.

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GROWTH RECOVERY

Skeletal alterations or orthopedic metamorphosis can be induced as part of phase 1 or early treatment in the young patient when growth processes are still active. Factors such as the genetic characteristics, the force of gravity, and the skeletal pattern become reoperative and express themselves again. Subsequently, growth patterns will “recover” from the original treatment changes and a second metamorphosis back to the originally determined genetic pattern is seen to occur, especially in the mandible. This type of change is not relapse, but rather unfortunate growth changes.

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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 posttreatment changing process versus a term such metaposition, which refers to the meticulously planned changes after the removal of the orthodontic appliances. METAPOSITIONMetaposition denotes the desirable and expected posttreatment changes that are anticipated (Ricketts, 1993). These changes are not relapse and must be part of thet treatment itself.

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RECIDIEFThe term “recidief” has been used to describe changes that occur from the end of treatment back to the original situation (Dermaut, 1974). IMBRICATIONImbrication is the term often used to describe incisor irregularity or crowding whether seen before or after treatment.

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RELAPSE AND RETENTION - DEFINITIONSRELAPSE AND RETENTION - DEFINITIONS

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’. Riedel (1976) believed that the word ‘relapse’ was too harsh a description of the changes that follow orthodontic treatment and he preferred the term “posttreatment adjustment” for these changes.

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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. The orthodontist must distinguish the rapid relapse occurring during the period of remodeling of periodontal structures, from the slow relapse which responds to late changes occurring during the post-retention period.

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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.

DIFFERENT SCHOOLS OF THOUGHT FOR RELAPSEDIFFERENT SCHOOLS OF THOUGHT FOR RELAPSE THE OCCLUSION SCHOOL Kingsley (1880) stated, “The occlusion of the teeth is the most potent factor in determining the stability in a new position”.

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 THE APICAL BASE SCHOOL In 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 to a limited extent.

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THE MANDIBULAR INCISAL SCHOOL Grieve (1944) and Tweed (1952) suggested that the mandibular incisors must be kept upright and over basal bone. THE MUSCULATURE SCHOOL Rogers (1922) introduced a consideration of the necessity of establishing proper functional muscle balance.

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BASIC THEORMS FOR RELAPSEBASIC THEORMS FOR RELAPSE Riedel (1975) has discussed a number of popular explanations of retention and relapse.THEORM 1: Teeth that have been moved tend to return to their former positions.THEORM 2: Elimination of the cause of malocclusion will prevent recurrence.THEORM 3: Malocclusion should be overcorrected as a safety factor.THEORM 4: Proper occlusion is a potent factor in holding teeth in their corrected positions.THEORM 5: Bone and adjacent tissues must be allowed to reorganize around newly positioned teeth.

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THEORM 6: If lower incisors are placed upright over basal bone, they are more likely to remain in good alignment.THEORM 7: Corrections carried out during periods of growth are less likely to relapse.THEORM 8: The farther teeth have been moved, the less likelihood of relapse.THEORM 9: Arch form, particularly in the mandibular arch, cannot be permanently altered by appliance therapy.

An additional theorem added to Riedel’s theorem is,

THEOREM 10: Many treated malocclusions require permanent retaining devices.

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CAUSATIVE FACTORS FOR RELAPSECAUSATIVE FACTORS FOR RELAPSE Many potential causative factors of relapse have been discussed, accompanied by cause-and-effect conclusions for clinical guidelines. These include,

1) Patient age2) Length of retention3) Mandibular rotation4) Arch dimensions5) Third molars6) Tooth size7) Apical base8) Position of mandibular incisors9) Oral habits, and the skill of the operator

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Most of these causative factors may be related to,a) Craniofacial growthb) Dental developmentc) 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.

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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.

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     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.

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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.

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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.

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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.

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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.

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TREATMENT TIME / PATIENT’S 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 of 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.

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PERIODONTAL FORCE AND RELAPSE Southard and Tolley in 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.

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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.

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    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 posttreatment crowding of the mandibular anterior teeth, physiologic drifting of teeth, and maintenance of posterior dental contacts after interproximal wear.

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TREATMENT CHANGES IN DENTITION AND TREATMENT CHANGES IN DENTITION AND STUDIES FOR ITS RELAPSESTUDIES FOR ITS RELAPSE LONG TERM STABILITY OF ORTHODONTIC TREATMENT

Bishara (AJO 1963) examined the tendency for overbite, overjet and intercanine width to return toward the original condition. In a sample of 31 patients with four bicuspid extractions and edgewise mechanics, he studied the stability of treatment a minimum of six months out of retention.

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He found that, The percentage of overbite relapse was clearly greater than that of overjet relapse. The maxillary intercanine width was more stable than the mandibular intercanine width. He pointed out that this may be explained by the fact that “whereas the mandible continues to grow downward and forward, the maxilla is more stable” and that “the lower dentition is confined within the maxillary arch thereby assuming a smaller arch length over time.”

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Sadowsky and Sakols in AJO 1982 evaluated the long-term stability of orthodontic treatment in a group of ninety-six former patients who were treated between 12 and 35 years previously with a full-banded edgewise appliance prior to adulthood, with an average posttreatment time of 20 years. Patients had Class I and Class II malocclusions only.

The Class I cases were almost equally divided between extraction and nonextraction treatment approaches, while almost twice as many of the Class II cases were treated with a nonextraction approach as were treated with an extraction approach.

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They concluded that, It was apparent that many years after orthodontic treatment a large number of cases (72 percent) exhibited dental relationships that were outside an ideal range. In most cases, however, patients showed an improvement in their occlusions over the long term. In contrast, the long-term result as compared to the original malocclusion exhibited increased overbite in fourteen cases (16 percent), increased mandibular anterior crowding in nine cases (9 percent), and increased overjet in five cases (5 percent). It is suggested that orthodontists should be well aware of long-term changes in dental relationships many years after treatment and take these into account when advising patients as to the potential benefits of orthodontic treatment.

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Uhde et al (Angle 1983) examined the posttreatment changes in 72 patients treated with edgewise mechanics, of which 27 had extractions and 45 were treated by non-extraction means. Retention of the teeth was done with an upper Hawley type appliance and a lower fixed lingual retainer. The patients were from 12 to 35 years out of retention when the study was performed.

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The findings were that, Overbite and overjet tended to increase irrespective of the initial malocclusion. The molar relationships shifted slightly toward Class II with time, and the intercuspid width was in general unstable in the lower arch and more stable in the upper arch. All groups showed some posttreatment crowding in the lower arch, but less than the pretreatment. No difference was found in the amount of postretention crowding between patients with extractions and those without extractions.

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Vaden and Harris in AJO 1997 quantified changes in tooth relationships in a series of 36 patients who were treated with premolar extractions and fixed conventional edgewise appliances and evaluated at 6 years and again at 15 years after treatment. They concluded that, The maxillary and mandibular arches became shorter and narrower with age. More than half (58%) of the mandibular incisor irregularity index correction was maintained. At the second recall examination, 15 years after treatment, the mandibular incisor irregularity index averaged 2.6-well within the range termed "minimal irregularity" by Little.

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Most of the posttreatment mandibular incisor irregularity in this sample was at the lateral incisor-canine contact area, with the canine slipping anterior to the lateral incisor, giving the arch a square appearance. This slippage at the lateral incisor-canine contact area may have resulted from the canine's return to the pretreatment intercanine width or from the anterior component of force. Most (96%) of the maxillary incisor irregularity correction was maintained. At the second recall, the maxillary irregularity index was only 1.8. More than 90% of the patients in this study were better off 15 years after treatment than they were before treatment.

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Burleigh in AJO 1998 used a case-control study design to test whether pretreatment malalignment in terms of irregularity and spacing of the maxillary anterior teeth and the quality of the orthodontic alignment are of significance for postretention relapse of alignment. Sets of study models made before and after orthodontic treatment, and long-term out of retention of 745 patients were screened.

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The results suggest that, Anatomic contact point displacement of the maxillary anterior teeth and maxillary incisor rotation relative to the dental arch, as well as interdental spacing before treatment, are significant risk factors for postretention relapse of alignment. The pattern of postretention contact point displacement and interdental spacing may be random relative to the pattern of initial tooth positions, whereas the pattern of rotational displacement relative to the dental arch has a strong tendency to repeat itself.

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Al Yami et al in AJO 1999 studied the stability of orthodontic treatment after 10 years postretention. Dental casts of 1016 patients were evaluated for the long-term treatment outcome using the Peer Assessment Rating (PAR) index. The PAR index was measured at the pretreatment stage, directly posttreatment, postretention, 2 years postretention, 5 years postretention, and 10 years postretention. 

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The results indicate that 67% of the achieved orthodontic treatment result was maintained 10 years postretention. About half of the total relapse (as measured with the PAR index) takes place in the first 2 years after retention. All occlusal traits relapsed gradually over time but remained stable from 5 years postretention with the exception of the lower anterior contact point displacement, which showed a fast and continuous increase even exceeding the initial score. The results of this type of studies enable clinicians to inform their patients about treatment limitations in order to better meet their expectations.

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

Studies by Welch (1956), Amott (1962), Arnold (1963), and Kahl-Nieke (BJO 1995) show the evidence 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.

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Shapiro (AJO 1974) studied the posttreatment stability of patients with Class I and Class II malocclusions, treated with and without extractions and found that Class II division 2 cases had a greater ability to maintain intercanine width increases in the lower arch than Class II division 1 and Class I cases. He further noted that the arch length reduction during treatment in the Class II division 2 cases was less than in the other types of malocclusions.

This statement, however, was based on a sample of six patients and was not accepted by Little et al (AJO 1981) who explained that intercanine and intermolar width will relapse if expanded in Class II Division 2 cases as much as in other Angle classifications.

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DEEP BITE CORRECTION AND ITS RELAPSE Correcting deep bite can be accomplished by true intrusion of anterior teeth, extrusion of posterior teeth, or a combination of intrusion and extrusion. The results of most studies concerning the stability of overbite correction indicate a decrease in overbite during treatment followed by as increase in overbite after appliance removal. 

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Simons (AJO 1973) found that patients with an initially deep overbite had the deepest overbite 10 years postretention and that protrusion of incisors was correlated with overbite relapse but was not related to whether or not extractions were performed. He believed that occlusal plane changes during treatment tended to relapse to their original angulation, and this correlated with deep bite relapse. He concluded that mandibular growth, with a vertical component, was correlated with overbite stability.

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Most studies evaluating overbite stability are those in which the overbite was corrected by molar extrusion. Schudy (Angle 1968) stated that the lower incisors have a very strong tendency to extrude in the posttreatment period and should never be intruded unless unavoidable. Creekmore (1967) and Zingeser (1964) also reported that incisors should not be intruded except in rare circumstances in which no vertical growth is occurring. This is because molar extrusion to correct deep overbite in patients with no vertical growth is difficult and unstable.

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Dake and Sinclair (AJO 1989) studied the stability of incisor intrusion as a method of correcting deep bite. They studied incisor intrusion with the utility arch in 30 Class II patients with an overbite of more than 50 percent. All of these patients were treated without extraction while they were still growing. They found that after treatment, Maxillary incisors uprighted and extruded about 2 mm after being intruded an average of only 1.2 mm. Since all measurements were made at the incisal edge, it is questionable if true intrusion was achieved or just flaring and molar extrusion.   

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However, deep overbite was successfully treated in these patients since molar extrusion and growth did occur during and following treatment.

Lower incisor intrusion during treatment was not associated with posttreatment overbite relapse.

They also noted overbite relapse of 20 percent using reverse curve of Spee wire mechanics and overbite relapse of 34 percent in then group treated with utility arch mechanics.

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MANDIBULAR ANTERIOR CROWDING - RELAPSE MANDIBULAR ANTERIOR CROWDING - RELAPSE STUDIESSTUDIES Fastlicht in AJO 1970 compared the degree of crowding of the anterior teeth in cases, which were treated orthodontically years before with those which were not treated, in order to determine whether treatment had had an influence through time on the crowding of the incisors, and clarified the causes of mandibular crowding. Sample consisted of two groups orthodontically treated and untreated of 28 patients in each group.

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The conclusions derived were, The crowding of the incisors was an anatomic-physiologic phenomenon of adaptation observed in orthodontically treated cases, as well as in untreated cases, which resulted from the combination of several factors, such as sex, anatomic predisposition dolichocephalic or long-faced persons, tooth-size discrepancies, exaggerated overbite, extrusion of the canines, reduction of the intercanine width, age, muscle function, and, in some cases, imperfect mechano-therapy. There was less crowding of the incisors in the treated group. Thus, it is assumed that treatment has a favorable influence over the stability of the dental arches.

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The larger the mesiodistal width of the incisors, the greater the crowding will be, if there is a lack of proportion. Maxillary and mandibular incisors were larger in males. Crowding of the mandibular incisors was more noticeable in males. The third molars were not related to crowding of the incisors. Age was a positive but secondary factor in crowding of the incisors. In general, the values and differences of the variables between sexes turned out to be more regular and significant in females. Positional changes of teeth were noted to be less in the maxilla than in the mandible.

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Little, Wallen in AJO 1981 evaluated the mandibular anterior alignment, using serial long-term dental cast records of cases treated by conventional edgewise orthodontic means following removal of all four first premolars. Sixty-five cases with complete records before treatment, at the end of treatment, and a minimum of 10 years out of retention (at least 10 years after complete removal of all retainer devices) were taken.

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They concluded that, Long-term alignment was variable and unpredictable. No descriptive characteristics, such as Angle class, length of retention, age at the initiation of treatment, or sex, and no measured variables, such as initial or end-of-active-treatment alignment, overbite, overjet, arch width, or arch length, were of value in predicting the long-term result. Arch dimensions of width and length typically decreased after retention whereas crowding increased. This occurred in spite of treatment maintenance of initial intercanine width, treatment expansion, or constriction.

Success at maintaining satisfactory mandibular anterior alignment is less than 30 percent, with nearly 20 percent of the cases likely to show marked crowding many years after removal of retainers.

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Pretreatment, end of treatment, 10-year postretention, and 20-year postretention records of 31 four premolar extraction cases were assessed by Little, Riedel, and Årtun in AJO 1988 to evaluate stability and relapse of mandibular anterior alignment. This study is a sequel to the previous study by Little and Wallen in AJO 1981.The results showed that,       Crowding continued to increase during the 10- to 20-year postretention phase but to a lesser degree than from the end of retention to 10 years postretention.       Only 10% of the cases were judged to have clinically acceptable mandibular alignment at the last stage of diagnostic records. Cases responded in a diverse unpredictable manner with no apparent predictors of future success when considering pretreatment records or the treated results.

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Jon Årtun, Garol and Little in Angle 1996 evaluated the long-term stability of mandibular anterior alignment in a large group of Class II, Division 1, patients who demonstrated successful occlusal results at the end of active treatment. Sets of study models and cephalograms of 33 males and 45 female patients made before, after orthodontic treatment and long-term postretention (14 years out of retention) were examined. The results demonstrated,      An increase of incisor irregularity and a reduction of intercanine width and arch length postretention.

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Long-term changes in incisor alignment are highly variable, and chances of maintaining incisor alignment are less than 50%, despite successful occlusal results at the time of appliance removal. Narrow pretreatment intercanine width and high pretreatment incisor irregularity were significant predictors of relapse. Treatment increase of intercanine width and postretention decrease of intercanine width and arch length were associated with relapse. These results may support a rationale for “semi-permanent” retention of the mandibular anterior segment following appliance removal.

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Anwar Ali Shah in AJO 2003 reviewed the mandibular incisor postretention stability outcomes in the setting of different treatment techniques and different ages of beginning orthodontic treatment. He reviewed posttreatment studies by various authors and concluded that, All the studies reviewed demonstrate all the inherent problems of a retrospective study. Randomized controlled trials would be the best solution; these are currently difficult due to problems with ethical approval, difficulty of a long term follow-up, and drop out of patients from the study.

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Unless a study can be designed in which both groups, extraction and non-extraction, are equally likely to make either decision, no valid conclusion can be derived. Mandibular incisor relapse seems to be minimal when palatal expansion is combined with a prolonged retention period. In the future, it would be interesting to study mandibular relapse in patients having palatal expansion and also comparable retention periods as patients having first premolar extractions.

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ROLE OF MANDIBULAR 3ROLE OF MANDIBULAR 3RDRD MOLARS IN MOLARS IN MANDIBULAR ANTERIOR CROWDINGMANDIBULAR ANTERIOR CROWDING Richardson in AJO 1989 reviewed the evidence in support of the theory that the presence of a third molar is one of the causes of such crowding and found that, Late lower arch crowding in the untreated individuals during the postadolescent period is caused by pressure from the back of the arch and presence of a third molar is the cause of late lower arch crowding. This does not preclude the involvement of other causative factors. The cause of late crowding may differ from one subject to another or there may be more than one factor contributing to the development of late crowding in any one individual.

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Studies Relating Third Molars to Crowding of the Dentition Bergstrom and Jensen’s study (1961) was designed to determine the extent to which third molars are responsible for secondary tooth crowding. They concluded that the presence of a third molar appeared to exert some influence on the development of the dental arch but not to the extent that would justify either the removal of the tooth germ, or the extraction of the third molars, other than in exceptional instances.

In another study, Vego (Angle 1962) longitudinally examined 40 individuals with lower third molars present and 25 patients with lower third molars congenitally absent. He concluded that the erupting lower third molars can exert a force on the neighboring teeth. He also indicated, that there are multiple factors involved in the crowding of the arch.

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Retrospective studies indicating a lack of correlation between mandibular third molars and postretention crowding Kaplan (AJO 1974) investigated whether mandibular third molars have a significant influence on posttreatment changes in the mandibular arch, specifically on anterior crowding relapse. He concluded that the presence of third molars does not produce a greater degree of lower anterior crowding or rotational relapse after cessation of retention. According to Kaplan, the theory that third molars exert pressure on the teeth mesial to them could not be substantiated. 

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Ades et al, Joondeph and Little (AJO 1990) in their cephalometric study, found no significant differences in mandibular growth patterns between the various third molar groups whether erupted, impacted or congenitally missing, also with and without premolar extractions. They concluded that there is no basis for recommending prophylactic third molar extractions to alleviate or prevent mandibular incisor crowding.

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Bishara in AJO 1999 reviewed the various pertinent studies that studied the role of third molars in lower anterior crowding. He concluded that,      The influence of the third molars on the alignment of the anterior dentition may be controversial, but there is no evidence to incriminate these teeth as being the only or even the major etiologic factor in the posttreatment changes in incisor alignment.       The evidence suggests that the only relationship between these two phenomena is that they occur at approximately the same stage of development, i.e., in adolescence and early adulthood. But this is not a cause and effect relationship.If extraction is indicated, third molars should be removed in young adulthood rather than at an older age.

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CURVE OF SPEE AND ITS RELAPSECURVE OF SPEE AND ITS RELAPSE Kyle R. Shannon in AJO 2004 evaluated the treatment of the curve of Spee and its stability after treatment. The mean posttreatment period was 2 years 8 months, with a range of 2 years to 5 years 8 months. There were 23 Class I, 21 Class II division 1, and 6 Class II division 2 patients out of whom 20 were treated as extraction and 30 as non-extraction cases. Results showed that, The mesiobuccal cusp of the first molar was most commonly the deepest part of the curve followed closely by the distobuccal cusps of the first molar and the second premolar.

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Smaller mandibular plane angle, smaller FOP-MP angle, mesially inclined first and second molars, deep overbite, and increased overjet all correlated with deeper pretreatment curve depth. The mesiobuccal cusp of the first molar relapsed 20% and continued to be the deepest part of the curve. Patients with fixed retainers after treatment exhibited significantly less relapse than those with removable mandibular retainers. This study found no relationship between skeletal measurements (FMA, ANB, PFH, LAFH) to curve of Spee relapse. This is in contrast to findings by Givins (1970), who found more relapse in patients with low mandibular plane angles.

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No significant differences in curve of Spee relapse were found between Class I, Class II division 1, or Class II division 2 malocclusions and also between extraction and non-extraction groups. Patients with more second molar uprighting during treatment exhibited more curve relapse than those with less molar uprighting. The more the curve of Spee was leveled with treatment, the more it relapsed after treatment.

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EXTRACTION VS NON-EXTRACTION EXTRACTION VS NON-EXTRACTION TREATMENT – RELAPSE STUDIESTREATMENT – RELAPSE STUDIES The controversy regarding the role of extractions in preventing relapse of orthodontic treatment still exists after nearly a century of debate.  Kuftinec and Strom (AJO1975) examined 50 cases, 25 extraction and 25 non-extraction, four months or more after discontinuing retention and found that lower incisor relapse was greater in non-extraction cases. 

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Sandusky (1983) reported on postretention stability of 85 extraction cases treated by Tweed and Tweed Foundation members. He reported less than 10 percent relapse of the lower incisors using Little’s irregularity index. He found the lower incisors tended to move forward postretention and the occlusal plane-Frankfort horizontal plane-angle decreased.

Glenn in AJO 1987 studied 28 cases of non-extraction treatment an average of eight years postretention. He found that incisor irregularity increased slightly postretention. Lower incisors were proclined during treatment and tended to remain stable postretention. Class II malocclusions with large ANB differences showed the most lower relapse postretention.

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Little and Riedel in Angle 1990 evaluated 30 patients who had undergone serial extraction of deciduous teeth plus first premolars followed by comprehensive orthodontic treatment and retention. Records were taken for the stages pre-extraction, start of active treatment, end of active treatment, and a minimum of 10 years postretention. All cases were treated with standard edgewise mechanics and were judged clinically satisfactory by the end of active treatment. Results showed that, Twenty-two of the 30 cases (73%) demonstrated clinically unsatisfactory mandibular anterior alignment postretention. Intercanine width and arch length decreased in 29 of the 30 cases by the postretention stage. There was no difference between the serial extraction sample and a matched sample extracted and treated after full eruption.

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McReynolds, Little in Angle 1991 evaluated the dental casts and cephalometric radiographs of 46 patients, treated with mandibular second premolar extraction and edgewise orthodontic mechanotherapy, for changes over a minimum 10-year postretention period. The sample was divided into two groups: early (mixed dentition) extraction of mandibular second premolars and late (permanent dentition) extraction of mandibular second premolars.

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Results showed, No difference in long-term stability between the two groups. Arch length and arch width decreased with time and incisor irregularity increased throughout the postretention period. No predictors or associations could be found to help the clinician in determining the long-term prognosis in terms of stability. The sample was regrouped according to the postretention degree of incisor irregularity. Statistically significant differences in cephalometric measurements were found between the minimally crowded group and the moderately to severely crowded group.

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Paquette, Beattie, and Johnston in AJO 1992 compared the long-term effects of extraction and nonextraction edgewise treatments in 63 patients with Class ll, Division 1 malocclusions. A lateral cephalogram, study models, and a self-evaluation of the esthetic impact of treatment were obtained from each of the 33 extraction and 30 nonextraction subjects. The average posttreatment interval was 14.5 years. They concluded that, For the borderline patient, nonextraction treatment produced a significantly more protrusive denture (about 2 mm), both at the end of treatment and at recall over a decade later.

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Despite the significant between-treatment differences, the majority of the subjects in both groups showed less than 3.5 mm of lower anterior irregularity. In general, the pattern of relapse was unrelated to the type of treatment or to the posttreatment position and orientation of the denture and, instead, appears to constitute a dentoalveolar compensation produced by the differential growth of the jaws following treatment. Ultimately, both the overjet and molar corrections were derived almost entirely from the differential growth of the jaws, rather than tooth movement relative to basal bone

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Luppanapornlarp and Johnston in Angle 1993 assessed the anatomical basis of the extraction/nonextraction decision and performed a long-term comparison of outcomes in “clear-cut” extraction and nonextraction Class II patients. They concluded that, Premolar extraction reduces soft- and hardtissue convexity by 2–3 mm, whereas nonextraction therapy has little effect In general, posttreatment changes (including an additional convexity reduction) are about the same in both groups

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When growth is finished, clear-cut nonextraction patients tend to have “flatter” profiles than do premolar-extraction patients who present with ponderable crowding and spacing Pre- and posttreatment tooth movements tend to be related to the pattern of jaw-growth; some forms of relapse, therefore, may be a dentoalveolar compensation for residual posttreatment growth. In nonextraction treatment, the upper buccal segments are commonly “distalized,” whereas they tend to come forward if premolars have been extracted.

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Elms, Buschang and Alexander in AJO 1996 evaluated the long-term stability of Class II, Division 1 in 42 patients (34 females and 8 males) treated with nonextraction cervical face bow therapy. Model analysis and cephalometric analysis were performed. The results showed that, Mandibular intercanine width decreased 0.3 mm during the postretention period; the remaining width measures increased or remained stable. Arch length, which did not change during treatment, decreased 1.0 mm after treatment. Both overjet (0.5 mm) and overbite (0.4 mm) showed small increases after retention. Mandibular incisor irregularity was decreased 2.7 mm during treatment and increased only 0.4 mm after treatment.

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ANTERIOR OPEN BITE AND RELAPSE STUDIES ANTERIOR OPEN BITE AND RELAPSE STUDIES  Anterior openbite malocclusion is considered one of the most difficult problems to treat by any means. Proper diagnosis, successful treatment, and long-term retention of openbite malocclusion have been a constant subject of discussion and research studies. Lopez-Gavito and Wallen in AJO 1985 evaluated the long-term response of the anterior open-bite malocclusion in forty-one white subjects who had undergone orthodontic treatment and were out of retention a minimum of 9 years 6 months. They concluded that, More than 35% of the treated open-bite patients demonstrated a postretention open bite of 3 mm or more.

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There was a significant trend toward decreasing mandibular arch dimensions with time, with the exception of the Irregularity Index which increased. These dental changes were not significantly different when the sample was divided into postretention relapse and stable open-bite categories. Neither the magnitude of pretreatment open bite, the mandibular plane angle, nor any other single parameter of dentofacial form proved to be a reliable predictor of posttreatment stability or relapse. With numerous exceptions, the subgroup demonstrating relapse of the treated open bite showed the following characteristics posttreatment across time:

Less mandibular anterior dental height. Less upper anterior facial height. Greater lower anterior facial height. Less posterior facial height.

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Huang and Justus in Angle 1990 studied the stability of anterior open bite in 33 patients treated with crib therapy. They concluded that, Patients who achieve a positive overbite with crib therapy have a good chance of maintaining a positive overbite after orthodontic treatment is completed and is applicable for both growing and non-growing patients. The reason for this increased stability may be due to a modification of tongue position or posture

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Kim et al in AJO 2000 evaluated the stability of anterior openbite correction in 55 white patients treated with multiloop edgewise archwire therapy. The lateral cephalograms were analyzed for skeletal, esthetic, and dentoalveolar changes. The results suggest that, The openbite was corrected by retraction and extrusion of the anterior teeth and the uprighting movement of the posterior teeth. The upper and lower occlusal planes moved toward each other.

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There were some significant changes in the skeletal variables in the growing group. The anterior LFH, anterior TFH, and posterior LFH increased. The palatal plane moved downward anteriorly, and the gonial angle decreased. There were not any significant changes in skeletal variables for the nongrowing group. There was retraction of the upper lip in both the growing and the nongrowing groups.The correction of openbite obtained by the MEAW therapy was proven to be very stable. The relapse in the overbite during the 2-year follow-up period was 0.23 mm for the growing group and 0.35 mm for the nongrowing group; these figures were not significant.

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Freitas et al in AJO 2004 evaluated the stability of extraction therapy for the anterior open bite in the permanent dentition an average of 8.35 years after retention. Records were obtained for pretreatment, posttreatment, postretention stages from 31 patients who had undergone orthodontic treatment with fixed appliances. The results suggested that, Eight patients (25.8%) showed a clinically significant relapse of the open bite. Consequently, 74.2% of the patients in the experimental group showed a clinically significant stability of the anterior open bite correction in the long term. During posttreatment period counterclockwise rotation of the mandible occurred and this might have contributed to the stability of the overbite after treatment This study suggests that the extraction approach seems to be more stable than non-extraction.

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ORTHOPEDIC TREATMENT AND RELAPSE STUDIESORTHOPEDIC TREATMENT AND RELAPSE STUDIES PALATAL EXPANSION AND ITS RELAPSE Expansion through maxillary suture widening by rapid maxillary expanders has been claimed to promote stability after retention. Stability has been attributed to the skeletal component of arch enlargement obtained by the expansion appliance as opposed to dental expansion as a result of edgewise appliance mechanotherapy. Studies on immediate treatment effects of rapid palatal expansion have reported increases in arch width as a result of combined skeletal and dental expansion. Short-term follow-up has indicated a rebound effect of the dental component, yet a relative stability of the skeletal aspect of the expansion.

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The implant studies by Krebs (1964) during a 7-year observation period found a substantial reduction in dental arch width after discontinuation of retention which continued for as long as 4 to 5 years. Skieller (1964) carried out scientific study where he inserted metal implants into thirteen girls and seven boys, using an expansion appliance. This was opened at the rate of 0.5 mm. per week for 7 months and then maintained for 12 months. He found that both the teeth and the vault widened and that the vault continued to widen both during retention and thereafter. The teeth, however, commenced to relapse at the end of the expansion and continued to do so out of retention, with the relapse amounting on average to about 25 percent of the total opening.

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Although he does not mention it, Skieller's, figures show that the dental relapse was less for the patients under 9 years old and noticeably higher for those over 12 years of age.

Stockfish (1969) found 50% of relapse within 3 to 5 years after retention after rapid palatal expansion. Linder-Aronson and Lindgren (1979) performed a 5-year posttreatment study and noted that only 45% of the initially achieved rapid palatal expansion was maintained. They also found a residual expansion of 38% and 59% for intercanine and intermolar widths, respectively, over a period of observation.

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Mew in AJO 1983 studied twenty-five patients (10 boys, 15 girls) who were consecutively treated with maxillary expansion. The cases were overexpanded 2 to 4 mm. The expansion was measured 2 or 3 months out of retention to allow the overexpansion to settle. Measurements were made again 2½ years out of retention. The net expansion had been 3.5 mm., and this had subsequently not relapsed. Herold (BJO 1989) reported that the increase in intercanine and intermolar widths observed during treatment with palatal expansion was followed by relapse, with a residual increase of 2.1 mm (62.5%) and 3.1 mm (56.4%), respectively.

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Moussa et al, O’Reilly in AJO 1995 evaluated the long-term changes of maxillary and mandibular dental arch measurements in patients who were treated with the soft tissue-borne palatal expander and edgewise appliances and its stability. The sample comprised of 165 dental casts randomly selected from patients who had been out of retention for 8 to 10 years at a mean age of 30 years.

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They concluded that, Maxillary intercanine width and maxillary and mandibular intermolar widths after retention closely approximated the posttreatment dimensions and were larger than their pretreatment dimensions. Mandibular intercanine width, arch length, and arch perimeter after retention closely approximated pretreatment dimensions. Incisor irregularity after retention was minimum for both maxillary and mandibular arch. Treatment with the rapid palatal expander presented good stability for upper intercanine width, upper and lower intermolar widths and incisor irregularity. Lower intercanine, arch length, and perimeter presented poor stability.

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Jeffrey L. Berger in AJO 1998 examined and compared the stability of orthopedic and surgically assisted rapid palatal expansion over time. Orthopedic expansion group consisted of 14 males and 10 females with ages ranged from 6 years to 12 years and Surgically assisted rapid palatal expansion group consisted of 12 males and 16 females with ages ranging from 13 years to 35 years. Dental models and PA cephalograms were obtained immediately before and after expansion, at removal of the expansion device, and 1 year after removal of the appliance.

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From the study he concluded that, Clinically, there is no difference in the stability of surgically assisted rapid palatal expansion and nonsurgical orthopedic expansion. The length of time after appliance removal was a year or slightly longer. These patients were kept in retention during the 1-year period thus demonstrating the importance of retainers to control perioral forces and maintain stability. Both the orthopedic and the surgical groups showed stable results.

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CHIN CUP THERAPY Adolfo Ferro in AJO 2003 evaluated the long term stability of skeletal Class III patients treated with splints, Class III elastics, and chincup (SEC III) and investigated the main determinants of relapse. Cephalometric data for 52 patients (22 men, 30 women) at pretreatment, posttreatment, and 3 years after retention were studied. The results showed that, The SEC III appliance achieved a long-term Class III occlusal correction in a high percentage (88.5%) of successfully treated patients. Thus, SEC III treatment is reliable at least at the end of the facial growth, as defined by age.

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At the end of the follow-up period (an average of 9 years), only 6 of the 52 patients had clinical relapse (overjet ≤0) At the end of treatment, the best predictors of relapse seem to be low Wits appraisal, ANB angle, and overbite, and large SNB. Significantly greater decreases of the Wits appraisal and increases of ramus length during the follow-up were further associated with relapse. Relapse appears to be affected by increased growth of the mandibular ramus and the ramus growth was remarkable only in patients with reduced overbite, low Wits appraisal and ANB angle, and high SNB angle.

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FUNCTIONAL APPLIANCE TREATMENT AND FUNCTIONAL APPLIANCE TREATMENT AND RELAPSE STUDIESRELAPSE STUDIES Pancherz in EJO 1981 did a short term follow-up study after Herbst appliance treatment of Class II malocclusions. He found that on a short-term follow-up basis, it is as if a Class I dental arch relationship is maintained by a stable cuspal interdigitation of the upper and lower teeth, while relapse tends to occur in cases with unstable occlusal conditions. 

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Pancherz and Hansen in EJO 1986 studied a group of patients with malocclusions who were treated with the Herbst appliance in the early permanent dentition 6 and 12 months after active treatment and found that dentoalveolar and skeletal relapse was about 30% of the accomplished treatment effect. The relapse occurred primarily during the first 6 months after treatment and resulted in the tendency toward increased overjet.

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Pancherz in 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.

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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.

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Wieslander in 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.

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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.

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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.

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Somchai Satravaha in AJO 1999 examined the skeletal changes produced by Class III activator during the treatment of patients with skeletal Class III malocclusions and characterized the stability of these changes in the years after treatment (6.6 ± 2.1 years after the end of activator treatment). The results indicated that, During the treatment, the Class III activator produced a statistically significant skeletal effect and this change remained through the postactivator period. The gonial angle exhibited a compensatory decline during the postactivator period. The skeletal profile was improved after the treatment and was not lost during the posttreatment period despite significant increase in maxillomandibular differential.

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ORTHOGNATHIC SURGERY AND RELAPSE ORTHOGNATHIC SURGERY AND RELAPSE STUDIESSTUDIES MAXILLARY SURGERIES AND ITS RELAPSE 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. 

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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.

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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.

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Proffit, Phillips, and Turvey in AJO 1987 analyzed the cephalometric data from 61 patients who had undergone superior repositioning of the maxilla via LeFort I osteotomy by means of the downfracture technique and evaluated the stability of skeletal and dental landmarks at various time intervals up to 1 year.None of these patients had concurrent mandibular ramus or body osteotomy except genioplasty and all had at least 2 mm intrusion at the maxillary incisor or molar. The results indicated that, During the first 6 weeks postoperatively, the maxilla showed a strong tendency to move farther upward in the patients in whom it was not stable. The posterior maxilla was vertically stable in 90% of the patients, the anterior maxilla in 80%.

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Horizontally, skeletal landmarks were stable in 80%, but when changes occurred, there was a tendency for the anterior maxilla to move back when it had been advanced. After the first 6 weeks, the posterior maxilla was stable vertically in all patients, but in 20% anterior maxillary landmarks moved downward, opposite to the direction of movement during fixation. In 11 of the 15 patients who demonstrated vertical changes postsurgery, the movement from fixation release to 1 year follow-up was opposite and approximately equal to the initial change, so that the net movement after 1 year was less than 2 mm.

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Only 6.5% (four patients) demonstrated 2 mm or greater net vertical movement for any of the variables studied 1 year after surgical treatment.

There was no indication that the amount of presurgical orthodontic movement of incisors, the presence of multiple segments at surgery, the age of the patient, the presence or absence of genioplasty, or the presence or absence of suspension wires was a risk factor for instability.

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MANDIBULAR SURGERIES AND ITS RELAPSE Lake, McNeill, Little in AJO 1981 evaluated surgical advancement of the mandible by retrospective cephalometric and computer analysis for longitudinal skeletal and dental changes an average of 3½ 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.

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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.

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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.

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Huang and Ross in 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.

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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.

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Ellis and Carlson (J Oral Maxillofac Surg 1983) performed an experimental investigation of mandibular advancement in Macaca mulatta monkeys. The skeletal stability two years after mandibular advancement surgery with and without suprahyoid myotomy was evaluated. The results demonstrated that, Mandibular advancement without suprahyoid myotomy was associated with a statistically significant 13% relapse. There was no relapse after mandibular advancement with suprahyoid myotomy. It was concluded that, the suprahyoid muscle complex does play a significant role in relapse after mandibular advancement.

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Because of the fact that skeletal relapse after mandibular advancement without myotomy occurred only during the period of maxillomandibular fixation, that is, the first 6 weeks, it was hypothesized that, (1) The surgical procedure caused a stretching of the suprahyoid complex resulting in a posteriorly oriented force on the distal bone segment, and (2) This force was transitory in nature and became diminished over time as the suprahyoid muscle complex adapted to the initial stretch by permanently increasing in length.

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David Carlson in AJO 1987 performed an experimental investigation as a sequal to the previous investigation by Ellis and Carlson (J Oral Maxillofac Surg 1983).

They studied the short-term change and long-term (2 years postsurgery) adaptation of the suprahyoid muscle complex after mandibular advancement surgery with and without suprahyoid myotomy in 10 adult rhesus monkeys (Macaca mulatta).

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The results for the nonmyotomy group showed that, (1) The suprahyoid complex was elongated approximately two thirds the amount of mandibular lengthening, (2) The major immediate adaptations within the suprahyoid complex after the surgical procedure occurred at the muscle-bone interface and the muscle-tendon interFace, (3) The change in length at the muscle-tendon junction was maintained throughout the 2-year follow-up period, indicating that significant long-term adaptations took place primarily at that location, and (4) No significant short-term changes or long-term adaptations were seen within the anterior digastric muscle or the intermediate digastric tendon.

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Within the myotomy group, it was found that (1) the suprahyoid complex recoiled immediately after myotomy such that the anterior belly of the digastric muscle became separated from the advanced distal mandibular segment by more than twice the amount of mandibular lengthening, (2) The anterior digastric muscle remained essentially at this posterior position throughout the 2-year follow-up period, and (3) Though not significant, there was a trend for a decrease in the length of the anterior digastric muscle belly.

On the basis of these results, it was concluded that both short-term changes and long-term adaptations to lengthening of the suprahyoid complex as a result of mandibular lengthening occur primarily within the connective tissues comprising the muscle-tendon and muscle-bone interfaces, not within the muscle fibers themselves.

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Komori in AJO 1987 evaluated the use of skeletal fixation for skeletal stability during the period of intermaxillary fixation following a modified sagittal split ramus osteotomy for mandibular prognathism. A combination of bilateral maxillary peralveolar wires and circummandibular wires in the canine region was used for the fixation. A total of 17 Japanese patients as two groups- 10 patients with fixation and a control group without the fixation were compared cephalometrically.

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The results showed that, Statistically significant differences existed in the amount and pattern of relapse; the fixation produced a significant effect on retention of the corrected chin position. As a consequence, downward and backward rotation of the distal fragment of the mandible and compensatory incisor extrusion were notably controlled. However, upward shift of the posterior end of the distal fragment occurred persistently even in the fixation group, causing considerable intrusion of the posterior teeth in comparison with the control group.

This seems to indicate that tension, probably exerted by the pterygomasseteric sling, is important in postoperative skeletal instability.

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DOUBLE JAW SURGERIES AND ITS RELAPSE Numerous theories have been advanced to explain the reasons for relapse in these kinds of surgery: (1) Stretching of the muscles of mastication and the suprahyoid musculature (Poulton 1973, McNamara 1978) (2) Condylar distraction during surgery (Epker 1978, Schendel 1980, Worms 1980)(3) Upward and forward rotation of the mandible (Poulton 1973, Epker 1978)(4) Changes in rotational position between the proximal and distal segments (Reitzik 1973, Lake 1981)

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Numerous fixation techniques have also been advocated to reduce postsurgical relapse. These have included,(1) Upper- and lower-border wiring (Booth1981) (2) Steinmann pins to stabilize the maxilla (Bennett 1985) (3) Skeletal-wire fixation (Schendel 1980) and (4) Rigid fixation (Champy 1978)

Early studies of mandibular advancement and maxillary LeFort I osteotomy by Poulton (AJO 1971), Wilmar (AJO 1974) revealed that mandibular relapse tended to be greater than maxillary relapse.

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Brammer (1980) studied the stability after bimaxillary surgery to correct vertical maxillary excess and mandibular deficiency.

He concluded that the stability of double jaw surgery reported less mandibular relapse but more maxillary relapse than for the same procedures performed independently in one jaw at a time.

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Satrom, Sinclair in AJO 1991 compared the stability of rigid fixation with that of skeletal-wire fixation in a sample of 35 patients who had undergone maxillary impaction and simultaneous mandibular advancement.

The authors concluded that, The maxilla was relatively stable for both fixation techniques, remaining within 1 mm of its postsurgical position, both horizontally and vertically. Rigid fixation tended to improve maxillary stability, primarily by limiting relapse to less than 2 mm.

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Mandibular length was significantly more stable in the rigid-fixation sample. Rigid fixation produced significantly better control of the angulation between the proximal and distal segments. This rotational control appeared to be a major factor in the increased overall stability of the rigid-fixation sample.

The amount of relapse was correlated to the amount of mandibular advancement in the wire-fixation sample but not in the rigid-fixation sample.

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CONCLUSIONCONCLUSION

Treatment goals are usually stated in cephalometric terms for individual tooth positions with insufficient attention to accommodating for skeletal variations. Nor are treatment goals often phrased in terms of occlusal dynamics. Most malocclusions are stable before therapy. If they are not at the end of the treatment, it may be the fault of the dentist. All treated malocclusions must eventually be returned from control by appliances to control by the patient’s own musculature.

Proper goals of treatment, careful mechanotherapy, precise occlusal equilibration, and well-chosen retention procedures play a role in achieving occlusal homeostasis.

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