The burden of proof: A critical review of orthodonticclaims made by some general practitioners

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The burden of proof." A critical review of orthodontic claims made by some general practitioners R. A. C. Chate, BDS, DDOrth. RCPS, MOrth. RCS, FDSRCS

Colchester, England The increased demand for orthodontic treatment in the developed countries has led to a recent proliferation of "motel courses" that are specifically designed for general practitioners. Most of the techniques presented are only those that have long been available for selection by discerning orthodontists. However, when they are applied exclusively and indiscriminately by inexperienced clinicians, this may result in either prolonged, unnecessary treatment or failure through instability. Therefore some of the claims that are made will be examined and discussed with a review of the literature. (AM J ORTHODDENTOFACORTHOP1994;106:96-105.)

T h e proliferation of postgraduate orthodontic education, which encompasses principles contrary to established practice in the United States, has previously been reported? Similar controversies concerning such presentations within the United Kingdom, 2 South Africa, 3 and the Antipodes 4 have now recently emerged, and their popularity exemplifies the inadequacy of undergraduate training in the development of critical skills required to appraise clinical and scientific data: "6 In the absence of any meaningful skepticism, persons can then become the legitimate prey of those who might exploit them) The consequences may be far reaching and have begun to manifest in southern England, with the publication of a practice brochure that has been issued to patients, and circulated to practitioners, to advertise short orthodontic courses. Many of the statements contained within it are either contentious or unsubstantiated, and for the most part are reproduced elsewhere. 7'8 As a consequence, their replication will form the basis of this critical review. THE VALUE OF EARLY TREATMENT CANNOT BE OVER STRESSED AS THE MAJORITY OF JAW DEVELOPMENT PROBLEMS BEGIN BEFORE THE AGE OF FIVE

The obvious misconception in this statement is that "jaw development problems" not demonstrable by this age rarely manifest later. Although this is clearly the case for congenital defects, it

Cop)Tight 9 1994 by the American Association of Orthodontists. 0889-5406/94/$3.00 + 0 8/1150012

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need not be for either acquired or developmental pathologic conditions, which may postdate this ag e . Similarly, normal cranio-facial development is such that marked individual transitions between skeletal patterns in either direction can occur between the ages of 7 and 15 years, 9 and 12 and 25 years. 1~ With the possibility of such adolescent deviation, any early assumptions made about facial structure are futile: 3 Indeed skeletal assessment at such a young age, presupposes that an accurate determination of the anteroposterior jaw relationship can be reliably made, when it cannot, even at the later age of 7 years. 9

EARLY TREATMENT INCREASES THE CHANCE OF COMPLETE CORRECTION, REDUCES TREATMENT TIME, AND GIVES THE SECOND TEETH A CHANCE TO GROW STRAIGHT NATURALLY \

This is almost a replication of a point of view expressed in 1912) 4 Both rely on the supposition that early occlusal anomalies may neither spontaneously improve with time nor arise as the permanent dentition is established. Ample evidence now exists to the contrary, and in particular longitudinal studies have shown that incisor overjets may spontaneously increase or decrease by up to 5 mm. 9"~2'~5"~sThis can continue throughout adulth o o d , 11'16'18"19 and may be due to alterations in the sagittal jaw relationship, which can, however, . be compensated for by a change in the incisor inclinations, n'~3":~ However, unlike Class I or Class II overjets which may change in either direction, Class III cases that change only deteriorate) 9 Similarly, unpredictable variation in the overbite can also

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occur up to the ages of 12t5 and 20 years, 19 by as much as 5 m m . t2a6,tS"lg"2t Anteroposterior movement of the lower posterior teeth is also possible in the deciduous dentition, with either mesia122-24 or distal movements,= which can continue into the mixed dentition, t7.~8.24 Before the exfoliation of the deciduous molars, mesial migration of the lower posteriors can occur in 30% of cases,z3 with a similar number moving towards a Class II pattern) 5 Excluding Class I cases, during adulthood this process of change continues as Class II and Class III molar relationships become more pronounced, z~ Dental crowding is also incessant, with deterioration predominating in samples studied from the mixed dentition to the early permanent dentition,9'~7":6 and beyond, into early, 12"27 and late adulthood) 6.:s Posterior crossbites may also appear, or disappear, between the deciduous and permanent dentitions,9'17"1s'29'3~where between 21% and 45% spontaneously improve,31"32and up to 16% arise during the transition.31'32 Buccal scissor bites also vary3~ and become more frequent with occlusal developmerit.9 However, the most spectacular examples of spontaneous corrections are seen in either young patients who simply desist from a digit sucking h a b i t , 9"17"29"33'34 o r in those whose overjets are initially categorized as severe) t Many others have previously commented that the occlusal state of the deciduous and mixed dentitions cannot portend the final outcome.* Nevertheless, few orthodontists would dispute the value of early treatment in certain circumstances. However, in view of the natural variations seen during dental development, any decisions made regar.ding early treatment must have a therapeutic bias. Otherwise early correction as a routine may be unnecessary, require prolonged retention, and increase the time spent in orthodontic treatment, the effect of which on the child has been previously condemned: 7

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tive regarding their application. Enthusiastic reintroductions of "growth enhancement" from the New World therefore continue to encounter skepticism, since despite considerable research, their precise mode of action remains o b s c u r e . 37.3s Animal experimental research is frequently cited as evidence that condylar growth is stimulated in response to either continuous39 or intermittent mandibular protrusion: ~ However, more recent studies have failed to replicate these findings, and have instead identified the earlier methodologic deficiencies that led to the conclusions that may now be untenable. 4~:z Cautious interpretation of clinical results is also required, if these are not drawn from stringently designed studies.38 Nevertheless, the following changes have been documented, as a consequence of functional therapy. Dentoalveolar

In Class II corrections, labiolingual tipping of the incisors is common,36"4353 together with mesial and distal movement of the mandibular and maxillary molars.36"43'47"s~ Vertical manipulation of the functional occlusal plane, with downward restraint of the maxillary buccal segments**'~ and unopposed vertical development of the lowers, also assists in the correction.44-n6.Ss Midface restriction

An important component of functional appliances would seem to involve the limitation of forward maxillary development. However, the amount of retraction of subspinale, whether in comparison to pretreatment values,47 or with untreated matched c o n t r o l s , 43"45"46'4s'54"56-59 remains small. Although "A point" has been criticized as an inadequate landmark to reflect orthopedic change,58-6~even when an alternative such as ihe anterior nasal spine is examined, similar small degrees of restraint are still recorded. 43"59"6~'62 Induction of mandibular growth

Although thesurge in popularity for functional appliances within the United States began 15 years ago,a6 because of an historical advantage, European orthodontists may have a more tempered perspec-

The potential to influence mandibular growth remains the area of greatest controversy:3 Many controlled studies have failed to demonstrate any s!gnificant enhancement.43,4s's2,s7.61 However, others have, yet the clinical relevance of an increase in the angle SNB of 1.5~46"4s'~'56 or of up to 2 mm per annum of increased mandibular length,* remains questionable: 9.63 Indeed, many functional appliances produce

"References 9, 15-17, 21, 23, 26, 30, 35.

"References 36, 46-48, 51, 54-56, 58, 60, 61, 64.

SIMPLE APPLIANCES HAVE BEEN DEVISED THAT CAN ENHANCE THE NATURAL GROWTH OF THE JAWS. THIS IS KNOWN AS DENTAL ORTHOPEDICS

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anteroinferior rotation of the maxilla, 36"6~ and an increase in lower facial height,* which through concomitant downward and backward rotation Of the mandible, negates any anterior expression of increased mandibular length. 36,4s4s'sl"s6'64 As a c~ sequence, incorporation of high-pull headgear to functional appliances has b e e n recommended, in an attempt to minimize such counter productive changes, s4"61"65'67"68and this may result in additional maxillary restraint.l Growth redirection of the condyle, and glenoid fossa

In comparison to matched controls, Class II cases demonstrate an equal amount of condylar growth after functional appliance treatment: ~ However, since this is significantly redirected in a more posterosuperior direction, this contributes to the total increase in mandibular length. 45"58"~~Similarly, clinical and experimental evidence seems to demonstrate that in response to continuous condylar distraction, the glenoid fossae remodel anteriorly.37.s4,60.6~ TREATMENT IS NOW AVAILABLE TO HELP RESTORE NORMAL G R O W T H

To state that treatment is available to "normalize" growth, is scientifically meaningless, and implies an understanding of craniofacial development that in reality remains incomplete. 7~ In addition, assertions that correction of skeletal and soft tissue structure at an early age, provides a basis for continued irreversible normal development, remain unproven. 64'7' On the contrary, the affects of functional appliances may be transient, with reversion to p r e t r e a t m e n t developmental patterns, either over the short-term, 5~ or long-term, 7' and that are related t o posterior growth rotations, 69"72the severity of the initial overjet, ~ persistent adverse soft tissue patterns, 73'7" and unstable cuspal interdigitation after treatment. TM THE COMMONLY HELD BELIEF THAT JAW SIZE AND SHAPE ARE INHERITED AND CANNOT BE CHANGED IS NOT TRUE

Undoubtedly, normal dentofacial growth is genetically determined, 75 but may be modified b y e n v i l : o n m e n t a l factors. 75"76 There is no doubt that functional appliances are able to correct Class II dental relationships, 45"52"77b u t t h i s does not prove "References 45, 46, 48, 51, 56, 59-61, 66. "i'References 47, 53, 54, 62, 65, 68, 69.

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an orthopedic mechanism exists. T~Indeed such corrections are generally accepted to be the result of a 70% to 30% dentoalveolar:skeletal effect. 45,63 Fixed appliances can also influence skeletal development to a similar extent, 45"59"77"78 and so the supposition that appliance selection is critical to achieve this remains in dispute: ~ TREATMENT WITH DENTAL ORTHOPEDICS LEADS TO A PLEASING HARMONY OF THE FACIAL FEATURES, AND MAKES MOST EXTRACTIONS UNNECESSARY

Orthodontic treatment, which produces an obtuse nasolabial angle, is generally accepted to be esthetically undesirable, 79 and one contributory factor, which is commonly implicated, involves the retraction of upper incisors. 79"8~ However, many studies have shown that there is neither a simple 8~~3 nor a predictable relationship between these two features, s~ Overall, the reduction in lip support is less than the amount of incisor retraction, 79'8~ but the upper lip can thicken, 82 and the nasolabial angle can also become more acute during this process: t The use of nonextraction fixed appliances to minimize any undesirable soft tissue reactions is also futile,7~'84 as the associated increase in lower face height adversely affects the nasolabial angle. 79'8~ In addition, the fallacy that functional appliances can correct mandibular deficiency without producing either maxillary restraint, upper incisor retroclination, or an increase in lower facial height, has already been discussed. In fact, several studies have compared the soft tissue profiles between cases treated with functional and fixed appliances, either with or without extractions, 49"82'8sas well as against controls. 82 When measurements a r e made to reference planes that exclude the nasal tip, both fixed and functional appliance treatments result in similar chin projections, 49"82"85 upper lip retrusion, and an increase in the nasolabial angle.82'85 Although the amounts are slightly greater for the latter two features with fixed appliances, the final differences between them are, however, insignificant.8z'Ss it was Edward Angle who coined the phrase "arch development" to describe the process of achieving a normal occlusion through buccal expansion and incisor proclination: 6 However, after initially following this philosophy, Tweed subsequently abandoned such an approach, on the basis that 80% of his recalls had poor facial esthetics, occlusal instability, and irreparable damage of the investing tissues in the incisor, and premolar regions. 87 In-

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stead he recommended the use of a Frankfort mandibular incisor angle, ~8 and since then, a plethora of choice has arisen on how to determine a stable lower incisor position. ~9 Generally, the "A-Po" line has become the most popular, although this does not render credence to the assumption of subsequent incisor immutability, as several studies have shown. 9~ That malocclusions can be corrected without extractions is not the issue, however, maintaining them continues to be the challenge. Although only 30% of cases treated with extractions and fixed appliances remain stable in the long term, 92 enlargement of the mandibular arch in the mixed dentition offers no better solution. Only 11% of such cases sustain their correction, so this approach produces the most relapse compared to any other method of treatment. 93 Fr~inkel, however, contends that under the influence of the vestibular shields, the mechanism of arch expansion with the function regulator is both different,94 and more stable, compared with that achieved with conventional dental plates. 95 However, a recent study has demonstrated that some relapse in arch width still occurs after Fr~inkel therapy. 96 Generally even though the maintenance of pretreatment arch dimensions does not always confer long-term stability,92 the preservation of arch form 35 and lower incisor position are still recommended. 97 However, until orthodontic treatment is less frequently based on clinical intuition, the cyclical reemergence of vogue philosophies is likely to perpetuate. 6 In the interim, any clinical polarization toward either an extraction or nonextraction approach must be regarded as dogmatic intransigence.

A CROSSBITE INCREASES THE LIKELIHOOD OF JAW JOINT PROBLEMS LATER IN LIFE

Crossbites can produce mandibular displacements from centric relation, 98 and although functional interferences are considered to be more important in their association with temporomandibular disorder (TMD) than the presence of an Angle defined malocclusion, the correlations nevertheless remain weak, 18"9~~~ if not disproven) ~176 Longitudinal adolescent studies have also shown that occlusal interferences and signs of TMD are common, ~8"~~176176 but inconsistent over time. 1~176 In view of this, some regard the high frequency of interferences to be the norm, and attribute this to hypofunction, and a reduction in functional w e a r ) ~

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In fact, hominid intercuspation that persists is anthropologically abnormal, and yet incorrect deductions about function, such as "incisal guidance" continue to be made, on the assumption that overbites are normal, or that there is a relationship between them, and the slope of the glenoid fossa, l~ Similarly, while "ideal functional occlusions" continue to be promoted to maintain the temporomandibular joint, 1~ evidence exists that "canine guidance" offers no selective protection. "~ It may be that any contacts made during function are unphysiological, whether they are described as gnathologically ideal or as an interference, and both could have an equal propensity to influence the joint. THE BENEFITS OF DENTAL ORTHOPAEDIC THERAPY ARE RELAXED JAW MUSCLES AND FREEDOM FROM JOINT DISORDERS

Recent electromyographic (EMG) studies have shown either no change, ~'1 or indeed a reduction in masticatory muscle activity, subsequent to the initiation of functional appliance therapy for Class II correction. "2"n3 This also includes the lateral pterygoid muscles, 42'"4 and therefore challenges the hypothesis that enhanced condylar growth occurs as a result of their increased neuromuscular activity. '15 Such E M G reductions are also transient, returning to, or exceeding pretreatment values within 3 to 6 months, "2''1z bearing in mind these values are comparatively reduced at the outset, to those for normal occlusions. H6 In addition, the implication is that dental orthopedic therapy precludes the development of temporomandibular disorder. This is based on the premise that premolar extractions, and retraction of upper anterior teeth, results in enforced mandibular distalization, and posterior condylar dfsplacement. The deducution however, is based on anecdotal reports, "7"1'8 and more recent studies have shown no such association in either untreated Class II deep bite malocclusions, "9 or in those whose correction involved an approach as previously described: 3"~2~ Similarly, in the long term, there is no relationship between the prevalence of signs and symptoms of TMD, and previous orthodontic treatment, ~8"1~ whether effected by either a fixed, ~241:7functional, ~z~'~,'2s or removable appliance, ~:9 or whether treated extraction or nonextraction. 126.127.13o WIDENING THE UPPER JAW ENLARGES THE NASAL AIRWAY AT THE SAME TIME. CORRECTING LOWER JAW DEVELOPMENT GIVES

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THE TONGUE MORE SPACE AND ENHANCES THE FLOW OF AIR IN THE THROAT. THE RESULTANT IMPROVED BREATHING CAN HELP A NUMBER OF CHILDHOOD AILMENTS OF THE EARS, NOSE, AND THROAT, PREVENTING IN SOME CASES, THE NEED FOR SURGERY.

Adolescent rapid maxillary expansion produces a 1:3 ratio of skeletal to dental arch expansion, as deduced from previously published data) 3~ These ratios reduce to 1:6 for quad helices) 32 and 1 "5 for removable appliances) 33 yet all three produce an average of 6 to 7 mm of molar expansion) 3~135 The clinical relevance of only 1 mm of maxillary separation with the latter two is therefore questionable, especially if the size of the method error ~33 is also considered. In addition, further analysis of previously published data reveals that, subsequently, there is a mean skeletal relapse of 24% 3 months out of retention) 3~ The debate therefore, as to whether nasal passage enlargement accompanies maxillary expansion is not n e w . ~4 Mean cross-sectional nasal cavity enlargements of between 1.4 mm and 4 mm for rapid e x p a n s i o n , 131'134"1360.8 mm for a quad helix, ~32 and 0.5 mm for a removable appliance have been reported) 33 However, corroborations from frontal cephalograms have been criticized as inadequate substitution for direct evaluation of nasal r e s i s t a n c e ) 37"13s This latter approach has therefore recently prevailed, and although comparability without standardization is precluded) 39 mean reductions in nasal resistance after rapid expansion have still b e e n f o u n d , x3614~T o ascertain the component contribution of maxillary separation, the use of a nasal decongestant has also been recommended) "t Compared with the change in normal functional resistance, the reduction in anatomic resistance, is either less significant)3~:39 or insignificant)38 This suggests rapid expansion exerts its effect by dilating the anterior nares, through the preferential expansion of the anteroinferior aspect of the nasal cavity. 138"14~ This may also explain the variable airway response, x39 where up to 35% of patients do not experience a reduction in nasal resistance) 38"~4~If, for example, the obstruction is posterior, rapi d expansion will have little effect) 36'~38 Therefore since neither enlargements of the nasal cavity, nor of the intermolar width, correlate with any change in nasal r e s i s t a n c e , 135-~37 expansion remains an unpredictable way of improving the nasal airway) 38"~39 As such, its selection primarily on this basis is not recommended for any orthodontic reasons, 142'143

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even though it is commonly chosen after a subjective diagnosis of "mouth breathing. '''38''** However, whatever such a diagnosis is based on, no consistent correlations have been found between any of the supposed indicative features, and increased nasal resistance. 135"142'1~'148Even the presumption that nasal resistance is synonymous with obstruction is misfounded) 38 since it only provides a representative measure of the minimum crosssectional area, and not the percentage components of oronasal respiration) 43 Instead, if either a valid designation of "mouth breathing" or of a change in respiratory mode is required, the use of a simultaneous nasal and oral respirometric technique (SNORT) is obligatory) 38:'3 since a person's percentage nasality cannot be extrapolated from nasal resistance.las.~3. ~s The supposition that "improved breathing" reduces the incidence of ENT pathology, is based on anecdotal c a s e reports, 149"~5~as well as anamnestic self-evaluations, after e x p a n s i o n ) 49.~Sz't52 The hypothesis is that as the maxilla is expanded both tensor palatine muscles are stretched. Since these originate around the ostia of the Eustachian tubes, this supposedly improves the functional clearance of the canals, reducing the incidence of serous otitis media, and conductive hearing loss) 5~ Timms contends this is supported by a study, which directly measured the interhamular separation with palpation, and subsequent measurement of the landmarks beneath the mobile soft tissues. The potential magnitude of this method error was acknowledged, but no attempt to evaluate it was reported. Similarly, the fact that the pterygoid plates are part of the sphenoid, which is a single bone with no midline sutural articulation to separate as a corollary to maxillary expansion, was also highlighted) 53 As a consequence, until controlled studies are published, such case reports do no more than illustrate coincidences. The reduction in upper respiratory tract infections is also hypothesized to be the result of the elimination of mouth breathing, with the cessation of pharyngeal drying) 5~ and the restoration of nasal filtration, and humidification of the inspired air) 52 However, "mouth breathers" are not typified by insufficient nasal respiration, 135 and anamnestic self-evaluations of improvement in either riasal obstruction or respiratory tract infections are also severely biased and unobjective. This is illustrated by the fact that perceived subjective improvement in nasal respiration is not correlated with any objective reduction in nasal resistance) 36

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The assumption that "development of the mandible" enhances pharyngeal air flow has also probably arisen from an inappropriate extrapolation. While mandibular retrusion is one feature commonly associated with obstructive sleep apnoea, 154 this does not prove compromised airways exist for persons who present with a range of mandibular retrognathia. Of greater significance in the pathogenesis of this condition, is the concomitant maxillary retrognathism, soft palate elongation, "4 and multiple levels of pharyngeal constriction. '55 What little evidence exists, suggests that there is no relationship between nasal airway resistance, and the skeletal pattern in normal persons, "6 whether classified as retrognathic, orthognathic, or prognathic. ~39 Even indirect evidence of forward movement of the base of the tongue, as a consequence of mandibular advancement with either protrusive appliances a57 or orthognathic surgery, 155ass can still be inconclusive. This is because, although the hyoid bone is generally accepted to represent the skeleton of the t o n g u e , 159a6~ m e a s u r e m e n t s taken from it to indicate the above are meaningless, unless all the other variables which can significantly influence its position have been controlled. As such, the hyoid bone seems to move anteriorly with surgical advancement, 16~ and superiorly with postured advancement? 57 However, many studies have shown the hyoid bone subsequently moves back toward its preoperative position, 15s'~6~ yet remarkably its relationship with the cervical spine remains constant. ~6~ The reason for this seems to involve an alteration of head posture, and cervical column angulation, which probably occurs as a physiologic adaptation to maintain the airway. '59"~6~ Similarly, even though the tongue elongates anteriorly, and thickens posteriorly subsequent to surgical mandibular advancement, in the long term it also returns towards its preoperative s h a p e . ~6~ Therefore, in summary, the evidence of nasal airway improvement, after either maxillary expansion or mandibular advancement as just reviewed, still remains too incomplete to offer substantiation. CONCLUSION

" I f a man will begin with certainties, he shall end in doubts, but if he will be content to begin with doubts, he shall end in certainties. ''~62 Indisputably, the common international reaction regarding short courses for general practitioners pivots around an earlier, and as yet unanswered question, "Who is qualified to teach orth-

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odontics? ''163 I would suggest that those whose preconceptions remain immutably based on teleologic common sense, are inadequately qualified. To this day, Darwin's view of the fallibility of such human presumption still pertains, and is epitomized as follows: "When it was first said that the sun stood still and the world turned round, the common sense of mankind declared the doctrine false. ''64 Therefore the specialty must continue to challenge these protagonists for validation, as well as perform experimental research on the foundations supporting the doctrine of such institutions. However, if the direction of future research is not to be determined by such vagaries, a radical improvement in undergraduate training will be required, to the extent that both the principles of scientific method and of data evaluation must be taught. It is only through the refinement of such critical faculties, that the itinerant "medicine men" with their "cure alls" will be denied an audience in the future. My thanks to Mr. N.S. Vasir and Professor J.P. Moss for their support, and constructive criticisms, to Mrs. J.M. Browne and Mrs. J.A. Turvil without whose unfailing diligence, this review would not have been possible, and to Christine Chate, who has endured the familial intrusion that has occurred as a consequence of this manuscript's preparation, over the last 3 years. REFERENCES 1. Johnston LE. Viewpoint. AM J ORTnOD DENTOFAC ORTnOP 1989;96:266-7. 2. Seel D. An Orthodontist's view on a Truitt course. Dent Prac 1989;April 6:6-9. 3. Letters to the editor: Orthodontics for the general practitioner. Mew JRC, Preston CB. AM J ORTnOD 1990;97:17a19a. 4. Mew J, West VC. Postgraduate Orthodontic Training. Letters to the editor. Aust Dental J 1989;34:186-88. 5. Ballard CF. The C.F. Ballard Award. B Dent J 1990;168: 427. 6. Johnson LE. Fear and loathing in Orthodontics: Notes on the death of theory. Br J Orthod 1990;17:333-41. 7. Fennel M, Frost S. Dentofacial orthopaedics and the general dental practitioner. Dent Pract 1992;30(22):1-3, (23):6-7. 8. Fennell M, Frost S. Dentofacial orthopaedics and the general dental practitioner. Dent Pract 1993;31(1):8-9. 9. Heikinheimo K, Salmi K, Myllarniemi S. Long term evaluation of orthodontic diagnoses made at the ages of 7 and 10 years. Eur J Orthod 1987;9:151-9. I0. Bjork A. Cranial base development. A follow up x-ray study of the individual variation in growth occurring between the ages of 12 and 20 years and its relation to brain case and face development. Am J Orthod 1955;41:198-225. 11. Bjork A. Estimation of age changes in overjet and sagittal jaw relation. Trans Eur Orthod Soc 1953:240-56.

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R.A.C. Chate Consultant Orthodontist Essex County ttospital Lexden Rd. Colchester Essex CO3 3NB