Toward a perspective on orthodontic retention?

ORIGINAL ARTICLE

Toward a perspective on orthodontic retention? Colin Melrose, BDS, FDS, MSc, MOrth,a and Declan T. Millett, BDSc, FDS, DDS, MOrthb Newcastle-upon-Tyne and Glasgow, UK Retention is one of the most difficult challenges facing the clinician in orthodontics. In this article we collate current knowledge regarding the origin of orthodontic relapse and attempt to rationalize the necessary factors in planning orthodontic retention. Despite extensive research, the various elements leading to relapse of treated malocclusions are incompletely understood, giving rise to wide variation in retention protocols among clinicians. Informed consent—with emphasis on the features of the original malocclusion and the patient’s growth pattern, the type of treatment performed, the need for adjunctive surgical procedures, the type of retainer, and the duration of retention—should be obtained during the planning of the retention phase. True perspective on orthodontic retention is lacking and there is a great need for further research to ensure that evidencebased clinical practice is adopted in retention strategies. (Am J Orthod Dentofacial Orthop 1998; 113:507-14.)

A phase of retention is normally required after active orthodontic tooth movement to

hold teeth in ideal aesthetic and functional relation1 and combat the inherent tendency of the teeth to return to their former positions.2 In this article we highlight current knowledge regarding the origin of posttreatment orthodontic relapse, the factors that may be considered in the planning of retention, and the lack of perspective in relation to retention practices. ORIGIN OF POSTTREATMENT RELAPSE

Stability can only be achieved if the forces derived from the periodontal and gingival tissues, the orofacial soft tissues, the occlusion and posttreatment facial growth and development are in equilibrium.3,4 FORCES FROM THE PERIODONTAL AND GINGIVAL TISSUES

Considerable residual forces remain in the tissues of the periodontium after tooth movement.2,4-6 Reorganization of the periodontal ligament occurs over a 3- to 4-month period after treatment2,7,8; whereas the gingival collagen-fiber network typically takes 4 to 6 months to be remodeled, the elastic supracrestal fibers remain deviated for more than a

Senior Registrar in Orthodontics, Department of Child Dental Health, Newcastle-upon-Tyne Dental School. b Senior Lecturer/Honorary Consultant in Orthodontics, Unit of Orthodontics, Glasgow Dental Hospital and School. Reprint requests to: Dr D.T. Millett, Unit of Orthodontics, Glasgow Dental Hospital and School, 378 Sauchiehall Street, Glasgow G2 3JZ, UK. Copyright © 1998 by the American Association of Orthodontists. 0889-5406/98/$5.00 1 0 8/1/82892

232 days.7 This deviation is most marked after correction of rotated teeth and space closure, with the lower lateral incisors, canines, and second premolars tending to migrate toward their original positions more frequently than other teeth.8 Transseptal fibers continue to exert compressive forces between mandibular contact points, possibly contributing to posttreatment crowding.9 FORCES FROM THE OROFACIAL SOFT TISSUES

Despite evidence that patterns of muscle activity are altered by some orthodontic treatment4 and claims emphasizing change in muscle function to promote stability,10 it is wise to carry out treatment within the limits imposed by the soft tissue environment.11 In particular, the resting pressures of the soft tissues determine final tooth position12 and the ultimate stability of any treatment.11,13 Although cheek14,15 lip,15-17 or tongue18-21 pressure during swallowing, speaking, or chewing may be within or above the average associated with effective orthodontic tooth movement,12,22,23 the duration of the forces is not sufficient to alter arch form.24 Lower labial segment

Movement of the lower labial segment beyond its narrow zone of labiolingual balance3,4 is unlikely to be stable25,26 unless other factors are altered simultaneously.11 Proclination of lower incisors may be stable in a few Class II cases in which the lower incisors have been retroclined by a digit-sucking habit or by contact with the palate or upper-incisor 507

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teeth11; in addition, lower-incisor stability may be achieved with concomitant mandibular surgery in Class III cases.13 The existing lower archform is the best guide to soft tissue balance, and treatment planning should be directed to building the upper arch around the lower.27 Arch width

Although Riedel28 emphasized that mandibular arch form should not be expanded as it compromises stability, maintenance of the original intercanine width does not guarantee stability.29,30 Indeed, a modest amount of intercanine expansion may be maintained more successfully in Class II Division 2 cases than in Class I and Class II Division 1 cases.31 Expansion of the mandibular intermolar distance also tends to reduce after treatment31,32 but may be maintained in some instances.31 Arch-width reduction has been observed 10 years after retention in patients who have undergone serial extractions,33 presurgical decompensation for Class III malocclusion,13 second premolar extractions with edgewise therapy,34 or mandibular arch-length increase during the mixed dentition.35 Similar trends have been found in normal untreated occlusions36 and in treated cases with initial generalized spacing.37 In no case were predictors or associations found with regard to the determination of long-term stability. Arch length

Mandibular arch length has been shown to be decreased substantially in both extraction31,32 and nonextraction cases35 after retention, as well as in normal untreated occlusions,36 in cases with original generalized spacing,37 and after serial extraction33 or presurgical proclination.13 Overjet

For the best prospect of overjet stability, a lip seal should be possible.38 Differential vertical39 and horizontal40 growth of the lips occurs in early adolescence, with more growth observed in boys than in girls,40,41 possibly promoting stability.39 Lower-lip cover only seems to have a definite association with the size of the final overjet when lip cover reaches 6 mm,42 and a variety of lip positions may be found in the presence of overjet measurements in the normal range.43 Overjet relapse is more likely with a large pretreatment overjet,25,42,44 although associated factors include relapse of molar, premolar, and canine relationships45; overbite relapse; an increase in interincisal angle; and retroclination of previously proclined lower incisors.25,26

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Soft tissue factors—persistent tongue thrust in particular— have also been implicated,46 but in a study of 50 orthodontically treated cases with an initial overjet of 10 to 15 mm, no firm predictors of overjet stability were identified.26 Where mandibular incremental growth is favorable,47 both during and after treatment, however, successful overjet correction appears quite stable.45 OCCLUSAL FACTORS AND OCCLUSAL FORCES

Angle recognized the relevance of occlusal factors to posttreatment stability.48 Teeth retained by the occlusion are stable, and no retaining appliances are required—for example, after labial or buccalsegment crossbite correction. For stable overbite reduction, a favorable interincisal angle is required,49 and the lower incisor must be 0 to 2 mm ahead of the upper-incisor centroid.50 A well-interdigitating occlusion prevents tooth migration,51,52 and a Class I molar relationship may aid stability,53 although it is no guarantee because posttreatment growth may alter significantly the sagittal molar relationship.54 Conversely, correcting a Class II to a Class I molar relationship can have a beneficial effect on growth, promoting maintenance of the molar correction.55 Dental malalignment has been positively correlated with the anterior component of force,56,57 which may cross the midline and progress through interproximal contacts but does not proceed beyond open contacts.56 Finishing to the gnathologic principles of functional occlusion58 to encourage stability has been emphasized, and a multidirectional chewing pattern may minimize tooth migration.59 POSTTREATMENT FACIAL GROWTH AND DEVELOPMENT

Facial growth continues throughout adult life; it varies among individuals and is considerable in some cases.60,61 Resembling adolescent growth, it is of lesser magnitude and rate than that observed during childhood, with the female mandible demonstrating a clockwise rotation and lesser growth; the opposite is true in male subjects.61 Total stability therefore does not exist in the craniofacial skeleton or dentition after treatment,62 and relapse in sagittal,63 vertical,64 or lateral65 skeletal dimensions may occur, depending on the posttreatment growth patterns of the patient rather than on the treatment itself. The post-treatment occlusion responds to these growth changes,36,62,66,67 with dentoalveolar adaptation from the investing soft tissue integument68,69

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tending to maintain the occlusal relationships where intercuspation is good.38 Such adaptation often manifests itself as lower-labial-segment crowding, but this phenomenon does not occur where there is significant forward maxillary growth.62 Lower-incisor crowding after retention has followed extraction of first31,32 or second premolars34 and serial-extraction33 and nonextraction therapy,70 with similar changes observed where the lower incisors were proclined before surgery.13 In untreated normal occlusions, female subjects showed more severe changes than male subjects but these changes were less extensive than those found after retention in a sample of treated cases.36 Attempts to identify all the factors contributing to posttreatment change in lower-labial-segment alignment have failed,62 although mesiodistal incisor dimension,71 arch-length deficiency,72 arch development,35 soft tissue factors,73 mesial drift,74 and residual Class II or III molar relationships71 are associated factors in this process. The evidence implicating third molars is equivocal.75 Inclusion of cases with different Angle classifications has, however, yielded samples with wide variations in growth pattern, skeletal relationship, and extraction pattern.76 In treated Class II Division 1 malocclusions only, narrow pretreatment intercanine width and high pretreatment incisor irregularity were significant predictors of relapse in lower-incisor alignment.76 PLANNING THE RETENTION PHASE

It is apparent that our knowledge of the variables contributing to posttreatment relapse remains incomplete, but any attempt at planning the retention phase requires some semblance of rationality in so far as possible. We consider the following six factors important in the planning of this phase of “treatment”: (1) obtaining informed consent, (2) the original malocclusion and the patient’s growth pattern, (3) the type of treatment performed, (4) the need for adjunctive procedures to enhance stability, (5) the type of retainer, and (6) the duration of retention. Patients must be advised before treatment that the retention phase is an integral part of orthodontic care. It should be emphasized that strenuous efforts will be made to obtain a stable result if such can be achieved and that, when stability is obviously unlikely, treatment is best withheld.77 With realistic treatment goals, patient expectations and ultimate satisfaction are likely to be improved.78 Our role as “physicians of malocclusion,” with the limitations this title implies, should be explained. We can

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diagnose the problem with a reasonable but not absolute degree of consistency79 and bring about a considerable improvement in most but not all cases. Most important, permanent “cure” is rare. The misconception that teeth, once aligned, will remain so for a lifetime must be dispelled.78 Treating malocclusion may be likened to treating a visual impairment. Prescription glasses improve eyesight in the short term, but further visual deterioration is inevitable. The problem is never cured but is ameliorated. Just as opticians never promise a cure, we should never promise permanent stability.78 Potential causes of relapse must be explained coherently so that the need for retention is evident and the patient’s role in maintaining the final result made paramount.80 Patients find the analogy of straightening crooked teeth to straightening curly hair81 particularly useful; both tend to revert to their original state unless correction is maintained. The fact that nature always has the final say should be emphasized. The other five factors listed above should be evaluated and the duration of retention chosen for each case in a decision-making process involving the patient or parent and the orthodontist.82 Once informed consent83 has been obtained, a suitable recall interval can be arranged. Original malocclusion and patient’s growth pattern

Because continued growth in the pattern that caused an anteroposterior or vertical skeletal displasia in the first place is a major cause of relapse after orthodontic treatment,84 a retention device should be prescribed from knowledge of the individual patient’s dentofacial structure and the anticipated magnitude and direction of growth.85 In many instances the retention program is designed to continue the goals of treatment.62 Overcorrection of the occlusal relationship as a finishing procedure has been recommended in controlling Class II relapse.58,86-89 If Class II traction has proclined the lower incisors by more than 2 mm, permanent retention is required.90 The tendency for differential jaw growth to produce sagittal relapse may be overcome by incorporating headgear in a maxillary retainer or providing a functional appliance as a retainer. Night-only wear of such an appliance is usually required for at least 12 to 24 months when the initial skeletal problem is severe, but wear should be continued until growth is reduced to adult levels.63 Long-term stability following functional-appliance therapy seems to depend on a favorable posttreatment growth pattern and a stable cuspal interdigitation.52,54

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After correction of mild Class III problems early in the permanent dentition, a functional appliance or a positioner may be sufficient to maintain occlusal relationships, but wear must be continued until growth is no longer significant.87 Control of more severe cases corrected at a similar age is difficult, with prediction of relapse unreliable.91 Maintenance of overbite correction, particularly in Class II Division 2 malocclusions, depends on favorable incisor axial inclinations,28,49 and wear of a maxillary removable retainer incorporating an anterior bite platform is likely for several years.92 The appliance may be worn at night once stability in other regards has been achieved. Controlling eruption of the upper molars is the key to retention in patients with anterior open-bite correction,90 but no reliable predictor of posttreatment stability has been found.64 Retention by means of high-pull headgear to a maxillary removable retainer or by an open-bite activator or bionator90 should ideally be continued into the late teens. Surgical reduction of the tongue in certain anterior open-bite cases may aid stability.93 Because development of lower-incisor crowding after retention is the norm, maintenance of perfect incisor alignment can only be guaranteed by indefinite retention in the retention of lower-labial-segment alignment.94 Retention of periodontally aligned teeth, space closure in an originally spaced dentition, and arch expansion/alignment in patients with cleft palate require permanent retention.90,94 Retention of rotated teeth should continue for at least 1 year8; however, if relapse is to be prevented entirely, prolonged retention is required.81,94 Type of treatment performed

After treatment with a removable appliance, often with the exception of crossbite correction and space maintenance, retention for at least 6 months (3 months full-time, 3 months nighttime) is recommended.8,27 Where treatment has been undertaken with fixed appliances, in particular to align rotated teeth, retention should span at least 12 months: 3 to 4 months full-time (with the retainer being removed for meals) and 8 to 9 months part-time.8,90 Retention may then be ceased, but in the growing patient it should continue until growth declines to adult levels.60,61 After functional-appliance or headgear therapy, continuous wear of the appliance, usually at night only, is recommended until growth declines to the low levels of adulthood.85,90

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Soft and hard tissue adjunctive procedures to enhance stability

Pericision,95 or circumferential supracrestal fiberotomy (CSF),96 reduces rotational relapse by about 30%.97,98 It is more successful in the maxillary than in the mandibular labial segment.98 Labiolingual relapse also is alleviated indirectly,98 and the effect on sulcus depth is minimal.99 Animal studies indicate that electrosurgery is as effective as CSF in minimizing rotational relapse.100 However, CSF is not successful in all patients, and other factors— including abnormal muscle pattern—may bring about relapse in incisor rotation.101,102 Where attached gingiva is scant, the papilla-dividing procedure is the recommended alternative to CSF.103 Surgical gingivoplasty, designed to reduce the chance of space reopening in extraction sites after active space closure, must be used in conjunction with proper positioning of the roots of adjacent teeth to achieve maximum benefit.104 Frenectomy, as described by Edwards,105 involves apical repositioning of the frenum with denudation of alveolar bone, destruction of the transseptal fibers, and gingivoplasty/recontouring of the labial or palatal gingival papilla in cases of excessive tissue accumulation. It has been shown to dramatically reduce the tendency for space to open in the upper midline. An abnormal labial fraenum or an intermaxillary osseous cleft, however, appears to be of minor significance in long-term stability in cases involving a small diastema (0.9 to 3.0 mm).106 Interproximal stripping to create a mesiodistal/ faciolingual ratio no greater than 0.72 for lowercentral incisors and 0.95 for lower-lateral incisors, has been suggested to enhance stability,107 but this ratio has not been found to be an important determinant of lower-incisor crowding.30,85 On the basis of data up to 10 years after treatment, CSF and reproximation in combination with overcorrection and selective root torque have improved posttreatment stability of the lower labial segment while eliminating the need for lower retention.108,109 Type of retainer

Removable, fixed, passive, and “active” retainers have been described.90 After being used initially for finishing, a positioner also may be used as a retainer, but it is less efficient in retaining incisor rotations and irregularities than a Hawley retainer.90 For the management of Class II or Class III relapse tendencies, a functional appliance may be used,90 whereas incisors that are becoming irregular may be re-

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aligned with a Barrer110 appliance (often in conjunction with interproximal stripping) or a modification thereof.111 Minor tooth movement may be carried out also through modification of full-coverage polycarbonate112 or clear sectional polyester (Essix) retainers,113 and thereafter the retaining appliance may be worn passively.90 To maintain closure of a median diastema or of an extraction space in adults and to maintain a pontic space or after correction of severe rotations,90,94 a fixed retainer is required.90,94 This retainer should be flexible114-116 to allow physiologic movement of retained teeth. Duration of retention

Where the occlusion will maintain correction of the treatment result, no retention is required. Shortterm retention spanning 3 to 6 months typically follows removable-appliance treatment and involves 3 months’ full-time wear (with the exception of mealtimes) followed by 3 months’ nighttime retainer wear.27 In the medium term, retention usually extends over 1 to 5 years, and a fixed retainer is often employed, although a modified functional appliance or headgear added to a removable maxillary appliance may be indicated, depending on the original malocclusion.38,90 Permanent retention is justified in patients with cleft lip or palate, in whom a prosthesis may be used as a retainer or in association with periodontal problems.38,90,94 No clear indications exist as to what period of retention is optimal in each case; few investigators have evaluated posttreatment changes in patients with similar malocclusions but different retention times. Wood44 found greater occlusal relapse in 30 treated Class II Division 1 malocclusion cases with retention for a mean 0.8 years compared with a similar treated sample who underwent no retention. A similar conclusion was reached by Cabassa et al.117 with Class II patients, treated with either a functional appliance or headgear, who were randomly assigned to a “retention” or “no-retention” group and then compared with an untreated control group. Because the period of retention was not specified and the sample size was modest, generalizations must not be drawn. The duration of retention should be decided for each case specifically in conjunction with the informed patient83 taking into consideration anticipated future growth.85 To combat the effect of further growth on lower-labial-segment alignment, indefinite retention is likely to be necessary in most cases,118 with the orthodontist or the general dentist monitoring the retainer according to an agreed-on

schedule.38 A fixed retainer may be replaced with a removable retainer after the patient reaches 21 years of age, then worn for as long as the patient desires to maintain optimal dental alignment.81 Issuing two removable retainers and delegating responsibility to the patient is likely the most costeffective means of managing retention.80 However, in cases where a health-service remuneration system covers only a finite period of supervision of the retention phase—for example, 6 months, “relapse”/ posttreatment occlusal and skeletal change may be more likely to manifest itself earlier than in situations in which retention is continued for several years. Because the optimal duration of retention for most orthodontically treated cases remains undetermined, wide variations in retention protocols exist among clinicians.119 Monitoring the glycosaminoglycan composition of gingival crevicular fluid120—in particular its chondroitin sulfate content— collected noninvasively during the retention phase may provide useful information about fundamental tissue turnover and help the clinician prescribe an individual retention regimen.121,122 In addition, control over the proliferative response of fibroblasts in transseptal-fiber remodeling may shorten retention time.123 Further work is required to obtain more firm data in these areas. DISCUSSION

In this article we have collated the current evidence relating to orthodontic retention and relapse and, from this evidence, considered the factors necessary in planning retention. Despite intensive research we remain largely ignorant of the many factors that contribute to posttreatment change. In the short term, gingival and periodontal forces2,5,7 are likely to have the most significance, but in the longer term the impact of continued growth into adulthood is probably paramount.124-126 Simplistic generalizations that posttreatment changes are due to one or two causes, or attempts made to place causative factors in some hierarchical scale, should be avoided.77 The authors of current publications have made a major issue of changes affecting the lower labial segment after treatment. These changes have generally been due not to orthodontic mechanics inducing instability but rather to normal maturational changes in the dentofacial complex.127 These changes should be seen in perspective. The multiplicity of factors affecting posttreatment tooth position—including periodontal forces, soft tissue forces, occlusal forces,

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and growth-rotational elements—interface with each other in such a complex manner that it is impossible to tease the effect of one from another. With gross uncertainty existing in regard to the origin of malocclusion23 and the unpredictability of relapse following correction,62,118 advice that retention should be continued indefinitely in the expectation of preventing deterioration in dental alignment and possibly skeletal pattern is now widely proclaimed.80,81,85 Implicit in this is the acknowledgment that not all cases demonstrate relapse, but, regrettably, we lack the means of identifying those that do and those that do not, so we are prescribing retention in some cases in which we do not need to. At a time when quality and effectiveness of many clinical practices are questioned128 and guidelines for clinical practice129 are being sought to assist in decisionmaking about appropriate health care for specific conditions, the question to be asked is, Are we practicing evidence-based orthodontics with respect to retention? The answer is, at present, no. Currently it is impossible to have true perspective or to be prescriptive about retention practices, as a result of the lack of objective evidence from well-conducted clinical trials with adequate sample sizes. The ethical considerations, however, involved in randomly assigning a patient to a retention or no-retention group are important and can only be considered realistically when there is an intention to retreat if necessary. Several large randomized clinical trials are in progress in the United States and the United Kingdom, designed to evaluate the effectiveness of early Class II correction. In time the findings of these studies may direct us in planning retention for this malocclusion group. Should tooth movement/relapse occur during retention or sometime after the patient elects to cease retention, it is important that some degree of objectivity be incorporated in any assessment of ultimate treatment outcome and in what constitutes “minor” or “major” relapse. Treatment outcome may be assessed with the use of an occlusal index130,131—for example, the PAR index131—and the occlusal changes rated as “greatly improved,” “improved,” or “worse/no different.” Alternatively, a success ratio, as proposed by Burstone,77 could be used. “Minor” relapse could constitute dental change that results in a decrease in PAR score but maintains the occlusal result in its end-of-treatment category, whereas “major” relapse might encompass a shift of category—for example, from “greatly improved” to “improved.” Objective residual treatment need should be clarified according to the

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dental-health component of the Index of Orthodontic Treatment Need.130,132 Subjective need should be assessed as well, but this is more difficult to evaluate. With the use of a coded scale, patients can be categorized as having “little or no need for treatment,” “borderline need,” or “great need for treatment.” Emphasizing the percentage success of treatment and limited need for further treatment rather than dwelling on “minor cracks in the paint” is likely to suffice in most instances, precluding unnecessary squandering of resources on further intervention. Thereby in many cases a true perspective will emerge for the individual patient with respect to treatment outcome, how the occlusion altered with time, and a commonsense approach adopted in dealing with postretention change. CONCLUSIONS Planning for and executing retention are two of the most difficult elements of clinical orthodontic practice. No means are yet available to help predict relapse or to give objective advice about duration of retention. Extensive further investigation is required to ensure that both effective and appropriate evidence-based practice is adopted in retention strategies. REFERENCES 1. Joondeph DR, Riedel RA. Retention and relapse. In: Graber TM, Vanarsdall RL, eds. Orthodontics: current principles and techniques. St. Louis: Mosby–Year Book, 1994. 2. Reitan K. Tissue rearrangement during retention of orthodontically rotated teeth. Angle Orthod 1959;29:105-13. 3. Moss JP. The soft tissue environment of teeth and jaws: an experimental and clinical study: Part 1. Br J Orthod 1980;7:127-37. 4. Moss JP. The soft tissue environment of teeth and jaws: experimental malocclusion: parts 2 and 3. Br J Orthod 1980;7:205-16. 5. Tanne K, Inone Y, Sakuda M. Biomechanical behaviour of the periodontium before and after orthodontic tooth movement. Angle Orthod 1995;65:123-8. 6. King GJ, Keeling SD. Orthodontic bone remodelling in relation to appliance decay. Angle Orthod 1995;65:129-40. 7. Reitan K. Clinical and histologic observations on tooth movement during and after orthodontic treatment. Am J Orthod 1967;53:721-45. 8. Reitan K. Principles of retention and avoidance of posttreatment relapse. Am J Orthod 1969;55:776-90. 9. Southard TE, Southard KA, Tolley EA. Periodontal force: a potential cause of relapse. Am J Orthod Dendtofac Orthop 1992;101:221-7. 10. Frankel R, Frankel C. Orofacial orthopedics with the function regulator. Basel: Karger, 1989. 11. Mills JRE. The stability of the lower labial segment: a cephalometric survey. Dent Rec 1968;18:293-306. 12. Proffit WR. Equilibrium theory revisited: factors influencing position of the teeth. Angle Orthod 1978;48:175-86. 13. Årtun J, Krogstad O, Little RM. Stability of mandibular incisors following excessive proclination: a study in adults with surgically treated mandibular prognathism. Angle Orthod 1990;60:99-106. 14. Ingervall B, Thu ¨er U. Cheek pressure and head posture. Angle Orthod 1988;58: 47-57. 15. Luffingham JK. Lip and cheek pressure exerted upon teeth in three adult groups with different occlusions. Arch Oral Biol 1969;14:337-50. 16. Thu ¨er U, Ingervall B. Pressure from the lips on the teeth and malocclusion. Am J Orthod Dentofac Orthop 1986;90:234-42. 17. Gould MSE, Picton DCA. Sub-atmospheric pressures and forces recorded from the labio-buccal surfaces of teeth during swallowing in adult males. Br J Orthod 1975;2:121-5. 18. Proffit WR. Lingual pressure patterns in the transition from tongue thrust to adult swallowing. Arch Oral Biol 1972;17:555-63.

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