SCIENTIFIC ARTICLE

Maxillary protraction for early orthopediccorrection of skeletal ClassIII Paul W. Major DDS, MSc, MRCD(C)H.E. EIBadrawy, MS, HDD, DDS

Abstract The clinical use of combinedmaxillary expansion and protraction headgearis reviewed. The diagnostic considerations necessaryfor appropriatecase selection are discussed. A description of appliancetechnique is providedin sufficient detail to familiarize the pediatric dentist with the associatedclinical procedures.(Pediatr Dent 15: 203--07, 1993) Introduction Differential diagnosis Treating the developing Class III skeletal malocclusion In treatment planning, correction of a Class III maloc- is one of the more challenging problems facing clinical clusion several diagnostic features should be considered. orthodontists. The incidence of this type of malocclusion Functionalassessment in a major Canadian city was found to be approximately 1 Anaccurate diagnosis of the relationship of maxilla to 1%of the population with no apparent gender difference. mandible in centric relation is very important. Anterior Some racial groups, in particular Asians, have a much positioning of the mandiblegenerally results from abnor- higher frequency. It has been estimated that in Japan 3- mal tooth contacts that force the mandible forward. Pa- 13%of the population have a Class III skeletal malocclu- sion.2 tients presenting with a Class I skeletal pattern, normal facial profile, and Class I molarrelation in centric relation, Manypractitioners avoid early treatment of the Class but a Class IlI skeletal and dental pattern in centric occlu- ~ skeletal malocclusion because they believe the condi- sion very often have abnormal incisor positioning. Treat- tion is caused by mandibular overgrowth and therefore mandibular surgery is inevitable. Attempts to restrict ment of this pseudo Class III problem should be under- taken as early as possible by advancing the maxillary mandibular growth using chin cup retraction devices largely have been abandoned. Recent studies suggest that incisors and/or retracting the mandibular incisors. Even a true Class III malocclusion can appear muchmore seri- malocclusions3 corrected in this wayhave limited stability and latent mandibulargrowth and a return to the pretreat- ous if there is an anterior path of mandibularclosure. ment condition are common.4, 5 Cephalometricassessment There is also concern about the long term-effects of chin is commonlyused to differen- cup therapy on temporomandibular joint health. Poste- tiate between maxillary retrusion and mandibular protru- rior condylar displacement has been implicated in devel- sion. The ANBangle in Class III samples is generally oping TMJinternal derangement,6 and it is reasonable to negative with a smaller than normal SNAangle (Fig I a,b). postulate that forces of sufficient magnitude to inhibit Unfortunately cephalometric analysis maybe potentially condylar growth may cause the capsular ligaments to misleading. Sue et alo9 reported that when SNAand SNB stretch, increasing the risk of TMJdysfunction. were used, the mandible was implicated as the major Several recent studies have shownthat the majority of contributor, but whenA point to Facial Plane and Nasion Class ~I exhibit maxillary retrusion. Ellis perpendicular to A point were used, the majority of cases and McNamara7 found that 65%of their sample exhibited were dassified as maxillary retrusion. Individual variations a retrusive maxilla. Although this was associated with in cranial base flexure and anterior/posterior displacement mandibular protrusion in 30%of the cases, it was also of Nasion(N) alter the ANBangle2 ° Alternative cephalomet- associated with normal mandibular skeletal position in ric values to assess maxillary anterior/posterior relationship 25%of the cases. Similarly Guyer et al.s reported that of to1 the mandible and cranial base include Wits appraisaU their total Class ~I sample, 9.5% had simple maxillary effective midfacelength, 12 Frankfort horizontal to NA,~° A retrusion and 34%had combined maxillary retrusion and point to Nasion perpendicular, 12 and A point to Facial mandibular protrusion. In view of the high frequency of Plane.13 All cephalometric measurementsmust take into maxillary retrusion, managing manyClass III malocclu- account the amountof anterior functional shift from cen- sions should include maxillary advancement as a major tric relation to centric occlusion. If the lateral cephalogram objective. Early intervention with orthopedic maxillary is taken with the patient in centric relation, any increased protraction provides a nonsurgical alternative. vertical dimension must be taken into account.

Pediatric Dentistry: May/June,1993 - Volume15, Number3 203 %

Cauc~ Caucasian Patient Normal Patient Normal SNA 75° 81° SNA 81° 81° SNB 79° 79° SNB 85° 79° ANB -4° +2° ANB -4° +2° Fig 1. A. (left) ClassIII skeletalpattern due to maxillaryretrusion. (Note the smallerthan normal SNA angle and associated negativeANB angle.) B. (right) ClassIII skeletalpattern due to mandibularprotrusion. (Note the larger thannormal angleand associated negative ANB angle.

Clinical assessment concave tissue contour indicates a midface deficiency. Because the treatment objective is to optimize fadal Similarly, chin position can be evaluated by using two esthetics, treatment decisions should be based more on the fingers to block out the upper and lower lips. The chin patient’s facial features than cephalometric values. A fa- should not be positioned anterior to a vertical line extend- cial evaluation involves an analysis of facial proportions, ing down from soft tissue Nasion. The lip posture is chin position, and midfaceposition. 14 Maxillary deficiency assessed for evidence of overclosure, amount of incisor is evidenced by flattening of the infraorbital rim and the display at rest and whether the lip looks adequately sup- area adjacent to the nose. Very often patients will appear ported by the maxilla. It is important to realize that facial to have droopy lower eyelids and show excessive sclera. convexity normally decreases as the patient matures. A Lookingat the patient in profile, block out the lower lip degree of chin prominence that would be normal in an and chin with your hand to accentuate the midface. In a adult maysuggest a Class lII skeletal pattern in a young well-balanced face there is a convexity extending from the child. inferior border of the orbit through the alar base of the Vertical facial proportions and skeletal relationships nose down to the comer of the mouth. A straight or also should be assessed. Clinically, vertical proportions

A - Frontomaxilla~y B - Zygomaticotemporal C- ZygornatJcomaxi]la.,y Fig 2. Normalfacial proportions. Fig 3. TheFrankfort mandibular plane D o Pte~ygopalatine angle. Fig4. Orientationof the circum-maxillary sutures.

204Pediatric Dentistry: May/June, 1993- Volume 15, Number3 can be assessed rotation is the result of downwardmovement of the pos- by comparing the terior nasal spine. The center of resistance of the maxillary midface height to complex has been estimated to be positioned between the the lower face maxillary first and second premolar sagitally, and be- height. The dis- tween the lower margin of the orbit and the distal apex of tance from soft the~ maxillary permanentfirst molar vertically. Center o! ~ tissue Nasion to Conventional protraction headgear devices use Resista~nce ~ ~) Subnasal (where stretched between some point of attachment on the max- the nose joins the illary teeth and the headgear. For patient comfort the upper lip) should elastics must comeout of the mouthwithout distorting the equal the dis- lips, whichlimits the clinicians’ control of the direction of tance from force application. Becausethe elastics’ protraction force is (~one ~/nts Force Co’oP Subnasal to soft applied at a distance below the center of resistance, the tissue1~ Menton maxillary complex is subjected to a forward and down- (Figis 2). Nanda ward force as well as a counterclockwise rotational force. Fig 5. Forcecomponents associated with reported that the (Fig 5) Other changes that have been observed with con- protractionheadgear. patterns of ante- ventional protraction headgear include a posterior (dock- rior facial propor- wise) rotation of the mandible, increased anterior face tions are estab- height and increased facial convexity.27 Most of the man- lished at an early age and are maintained during growth. dibular changes can be attributed to increased downward Growthdirection is difficult to accurately predict, but growth of the maxilla. The protraction headgear does, growth trends maybe clinically or cephalometrically as- however, transfer part of the reciprocal force to the man- sessed by measuring the Frankfort plane angle. 16 Patients dible, and it has been shownthat stress trajectories do exhibiting excess vertical growth generally will have a concentrate along the ramus and condylar neck of the larger than normal mandibular plane angle (Fig 3). Other mandible,as Other less widely used protraction headgear cephalometric assessments of growth direction indude have been designed to overcomethis problem by using a FHto Y axis, facial axis,~3 and posterior / anterior face height complex facebow attachment mechanism,as, as ratio. 17 Clinical proceduresthat openthe bite and result in Clinical studies indicate that the maxilla can be ad- increased vertical dimension should be avoided in cases vanced 2-4 mmover a 12- to 15-monthperiod of treatment already displaying excessive lower face height. with a protraction headgear worn 14 hr per day.~24,27 The amount of anterior maxillary movement is larger in Skeletal effects of protraction headgear younger patients (under 9 years of age).24 Although long- The most important growth sites in the development of term follow-upstudies are not available, it is reasonable to the nasomaxillary complex are the circummaxillary su- assume the maxillary changes are relatively stable. The tures.iS, 19 These include the frontomaxillary, long-term stability of midpalatal suture expansion is well zygomaticotemporal, zygomaticomaxillary, and the documentedand the histologic effect on the circum-max- pterygopalatine sutures. These sutures are situated paral- illary sutures with protraction headgear is very similar. lel to each other and are oriented so they project down- Whenrelapse is observed it is likely due to an increase in ward. Growthat these sutures has the effect of shifting the mandibulara7 protrusion, maxillary complex downwardand forward (Fig 4). a°, Clinical apj}lications and treatment Animaland skull studies al using maxillary protrac- considerations tion devices showsignificant anterior displacement of the caseselection maxillary complexand significant changes in the circum- maxillary sutures and maxillary tuberosity. Tension pro- Patients selected for protraction headgear treatment duced within the sutures causes an increase in vascularity should have a retrusive maxilla with a normal or mildly and a concomitant differentiation of the cellular tissue protrusive mandible and inadequate or normal maxillary resulting in increased osteoblastic activity. While recog- vertical development. Cases presenting with excessive nizing the limitations of skull studies, it is reasonable to incisor display, anterior openbite, or excessive lower face conclude that maxillary protraction appliances have their height should not be treated with protraction headgear. primary skeletal effect at the midfacial sutural growth sites. Very often patients presenting with Class ~I skeletal During the use of conventional maxillary protraction malocclusions have bilateral posterior crossbites due to appliances, clinicians have observed extrusion and ante- deficient transverse maxillary growth combined with the rior rotation of anchor teeth, downwardmovement of the abnormal sagittal relationship of the maxilla and man- maxilla, anterior movementof the maxilla, anterior (coun- dible. Maxillary expansionprior to protraction, as well as terclockwise) rotation of the maxilla, and a constriction of addressing the transverse discrepancy, has the added ben- the anterior region of the maxilla.2~24 Anterior maxillary efit of initiating downward29 and perhaps forward move-

Pediatric Dentistry: May/June, 1993 - Volume 15, Number 3 205 ment of the maxilla.B° Palatal expansion af- fects not only the intermaxillary suture sys- tem, but the entire circum-maxillary suture system.31 Palatal expansioninitiates cellular response in the sutures, allowing a more positive reaction to protraction force. Palatal expansion should be started with a fixed rapid palatal expansion appliance (hyrax) at least 7-10 days prior to initiating protraction force. The hyrax expansion ap- pliance should be activated by turning the (a) jack screw1 / 4 turn daily, resulting in 1 -ram palatal width increase every four days .3o The Fig 7. Protractionheadgear. length of preprotraction expansion will de- pend on the severity of the posterior trans- to monitor pro-gress. The over- verse discrepancy. jet should be overcorrected and A .045" wire is soldered to the buccal as- the protraction headgear contin- pect of the hyrax expansion appliance. The ued at nights for 4 to 6 months wires should extend forward into the cus- depending on the patient’s ten- pid region and be bent into a hook to attach dency to relapse. Full banded the extraoral elastics to the protraction head- orthodontic therapy will be re- gear (Fig 6). quired following Phase I ortho- pedic correction. The protraction Headgearadjustment (b) The headgear pads should be adjusted to headgear may be necessary dur- comfortably contact the forehead and chin, Fig 6. Modifiedhyrax expansion ing Phase II to help control dis- appliance. and the elastics should be directed with a proportionate growth between slightly downwardforce (Fig 7). The direc- the maxilla and mandible dur- tion of the elastic force can be modifiedslightly depending ing the prepubertal growth spurt. on the degree of anterior maxillary rotation versus bite Patient motivation opening that is desired. Morehorizontally directed force Patient complianceis critical to successful treatment. will reduce the amount of bite opening but increase the Positive reinforcement using a series of short- and long- rotational effect (Fig 5). Excessivepressure from the super- term goals is vital. Praise and rewards are most effective ior edge of the chin cup maycause labial gingival reces- when developed together with the patient, and awarded sion. upon the attainment of each goal. Contacting the child’s Application of force should begin with light elastics teacher to explain the nature of the problemand the objec- (100-150grn per side) until the patient has adapted to the tives32 of the protraction headgear appliance is helpful. appliance, then the force should be increased to 300-500 The teacher can then explain the situation to the child’s grn per side. The elastics should be replaced daily. class, helping to eliminate negative peer pressure at school. Treatmenttiming Protraction headgear has been shownto be most effec- Conclusion tive in the full primaryor early transitional dentition, with Protraction headgearis a very useful and effective means considerablyless skeletal changeafter 9 years of age.2~ It is of treating young patients presenting with a Class HI skel- also important to initiate treatment early enoughso that etal pattern. Patients should exhibit a retrusive maxilla adequate root structure is still present on the primaryfirst and should not exhibit excessive vertical development or molars to anchor the expansion appliance. anterior open bite. Assumingthese diagnostic criteria are Depending on the severity of the problem and the age carefully observed, this treatment technique will produce of the patient, wearing the appliance 24 hr/day will usu- consistent results. The appliance mechanicsare relatively ally correct the problem within 4 to 8 months. The same simple and can be managedeffectively by pediatric den- result can be achieved with 14-hr/day wear over a period fists experienced in orthodontic diagnostic procedures. of 12 to 16 months. This treatment approach should be considered and, when Patientrecall appropriate, offered to the patient and parents. The patient should be seen approximately one week Dr. Major is an associate professor and chairman of the Division of after appliance insertion to evaluate patient compliance , Faculty of Dentistry, University of Alberta. Dr. and to ensure that the appliance is properly adjusted. The E1Badrawyis a professor and chairman of the Division of Pediatric patient can be evaluated at regular 4- to 6-weekintervals Dentistry, Faculty of Dentistry, University of Alberta.

206 Pediatric Dentistry: May/June,1993 - Volume15, Number3 1. Harle GD: The prevalence of malocclusion in grade eight children there a relationship? An epidemiologic study. Angle Orthod in Edmonton. MScThesis, 1976. 55:127-38, 1985. 2. Ishii H, Morita S, Takeuchi Y, NakamuraS: Treatment effect of 18. Ranly DM:A synopsis of Craniofacial Growth: 2nd ED, Norwalk, combined maxillary protraction and chincap appliance in severe CT: Appleton & Lange, 1988. skeletal Class III cases. AmJ Orthod Dentofacial Orthop 92:304- 19. Enlow DH: Handbook of Facial Growth. 2nd ED. Philadelphia: 12, 1987. WBSaunders Co, 1982. 3. Mitani H, FukazawaH: Effects of chincap force on the timing and 20. Hata S, Itoh T, Nakagawa M, Kamogashira K, Ichikawa K, amount of mandibular growth associated with anterior reversed Matsumoto M, Chaconas S: Biomechanical effects of maxillary occlusion (Class III malocclusion) during puberty. AmJ Orthod protraction on the craniofacial complex. AmJ Orthod Dentofacial Dentofacial Orthop 90:454-63, 1986. Orthop 91:305-11, 1987. 4. Ritucci R, Nanda R: The effect of chin cup therapy on the growth 21. Tanne K, Sakuda M: Biomechanical and clinical changes of the and development of the cranial base and midface. AmJ Orthod craniofacial complex from orthopedic maxillary protraction. Angle Dentofacial Orthop 90:475-83, 1986. Orthod 61:145-52, 1991. 5. Sugawara J, Asano T, Endo N, Mitina H: Long-term effects of 22. MermigosJ, Full CA, Andreasen G: Protraction of the maxillofa- chincap therapy on skeletal profile in mandibular . cial complex. AmJ Orthod Dentofacial Orthop 98:47-55, 1990. AmJ Orthod Dentofacial Orthop 98:127-33, 1990. 23. Cozzani G: Extraoral traction and Class III treatment. AmJ Orthod 6. Wyatt WE: Preventing adverse effects on the temporomandibu- 80:638-50, 1981. lar joint through orthodontic treatment. AmJ Orthod Dentofacial 24. Sakamoto T: Effective timing for the application of orthopedic Orthop 91:493-99, 1987. force in the skeletal Class III malocclusion. AmJ Orthod 80:411- 7. Ellis E III, McNamaraJA Jr: Componentsof adult Class III maloc- 16, 1981. clusion. J Oral Maxillofac Surg 42:295-305, 1984. 25. Nanda R: Biomechanical and clinical considerations of a modi- 8. Guyer EC, Ellis E IIL McNamaraJA Jr, Behrents RG: Components fied protraction headgear. AmJ Orthod 78: 125-39, 1980. of Class III malocclusion in juveniles and adolescents. Angle 26. Staggers JA, GermaneN, Legan HL: Clinical considerations in the Orthod 56:7-30, 1986. use of protraction headgear. J Clin Orthod 26:87-91, 1992. 9. Sue GI, Chaconas SJ, Turley PK, Itoh JK: Indicators of skeletal 27. Wisth PJ, Tritrapunt A, Rygh P, B~e OE, Norderval K: The effect Class III growth. J Dent Res 66:348, (Abstr 1932) 1987. of maxillary protraction on front occlusion and facial morphol- 10. BinderRE:Thegeometryofcephalometrics. JClinOrthod13:258- ogy. Acta Odontol Scand 45:227-37. 63, 1979. 28. de Alba y Levy JA, Caputo AA, Chaconas SJ: Effects of orthodon- 11. Jacobson A: The "Wits" appraisal of jaw disharmony. Am J tic intermaxillary Class III mechanics on craniofacial structures Orthod 67:125-38, 1975. Part I -- Photoelastic analysis. Angle Orthod 49:21-8, 1979. 12. McNamaraJA Jr: A method of cephalometric evaluation. AmJ 29. Haas AJ: Palatal expansion: Just the beginning of dentofacial Orthod 86:449-69, 1984. orthopedics. AmJ Orthod 57:219-55, 1970. 13. Ricketts RM: Perspectives in the clinical application of 30. Bell RA: A review of maxillary expansion in relation to rate of cephalometrics: the first fifty years. AngleOrthod 51:11 5-50,1981. expansion and patient’s age. AmJ Orthod 81:32-7, 1982. 14. Powell N, HumphreysB: Proportions of the Aesthetic Face. New 31. Silva OG, Boas MCV,Capelozza L: Rapid maxillary expansion in York: Thieme-Stratton Inc, 1984. the primary and mixed dentitions: A cephalometric evaluation. J 15. Nanda SK: Patterns of vertical growth in the face. AmJ Orthod AmOrthod Dentofacial Orthop 100:171-81, 1991. Dentofacial Orthop 93:103-16, 1988. 32. Turley PK: Orthopedic correction of Class III malocclusion with 16. Solow B, Houston WJB:Mandibular rotations: concepts and ter- palatal expansion and custom protraction headgear. J Clin Orthod minology. Eur J Orthod 10:177-79, 1988. 22:314-25, 1988. 17. Siriwat PP, Jarabak JR: Malocclusion and facial morphology. Is

Pediatric Dentistry: May/June,1993 -Volume15, Number3 207