Growing the Mandible? Impossible, Right?

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Figure 1. Mandibular growth has been the subject of much conjecture in the orthodontic community, but is the real answer just too hard to swallow? Growing the mandible? Impossible, right?

By Rohan Wijey, BOralH (DentSci), Grad.Dip.Dent (Griffith), OM

ince the 2007 Cochrane treatment with braces tends to be more Review on Class II cor- retractive of the maxilla. Nonetheless, Don’t we need rection,1 the prevailing both approaches will result in reduction of to retract in some cases? catch-cry has been that “you overjet and ANB angle. A slightly better can’t grow mandibles”. The cephalometric measurement would be lass II cases can comprise either a fallacy of this blithe extrap- the facial angle (angle between Frankfort Cretrognathic mandible, prognathic olation lies in the fact that horizontal plane and Nasion to Pogonion), maxilla, or both. However, Mcnamara Sthe main criteria used in the comparison to determine the final position of the man- found as early as 1981 in his publication of early and late Class II correction was dible relative to the cranial base. Components of Class II malocclusion in measurement of overjet (mm) and ANB As the dental community continues to children 8-10 years of age, that less than angle (the cephalometric relationship of realise that their precious teeth are actually 4% of his Class II patients displayed a the maxilla to the mandible). In no way do attached to a head and a body, everyone prognathic maxilla and this figure would these measurements accurately compare has suddenly become more airway-con- be even less if we apply modern standards the differences in mandibular “growth” scious. Most dentists and orthodontists of an acceptable SNA angle.2 Therefore, between the two approaches. now realise that extraction and retraction the overwhelming majority of Class II We do know that early treatment with orthodontics may leave the maxilla and cases demand not only development functional appliances tends to be more mandible in a posterior position and may of the mandible, but also development protrusive of the mandible, while later decrease oropharyngeal airway volume. of the maxilla.

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Figure 2. Orthognathic surgery. Figure 3. The Frankel Appliance.

Figure 4. The Myobrace® for Teens appliance series.

Can we influence Therefore, there is no good evidence ered “highly stable”.4 However, after mandibular length? that demonstrates these can translate this first year, as much as 20% of man- the mandible. dibular advancement patients experience Maybe. The available studies fall on both decrease in mandibular length. In their sides of the fence. 2. Functional appliances systematic review, Joss et al. (2010) found that 60% may experience relapse Do we care? he largest systematic review (2015) in the long-term and other studies put the Tever conducted into functional appli- figure at 100%.5,6 o. Influencing mandibular length ances for Class II correction screened a The most compelling reason for relapse, Nis not important, but rather massive 2835 studies and found func- whether surgical or otherwise, is the non- allowing mandibular translation for a tional treatment by removable appliances adaption of the soft tissue environment. better facial profile and more patent may produce effective skeletal outcomes, “Whenever there is a struggle between airway are key therapeutic goals of the especially if performed during the pubertal muscle and bone, bone yields,” writes modern orthopaedist. growth phase.3 Graber in his lauded 1963 manifesto on the influence of muscles on malforma- How can we get 3. Orthognathic Surgery tion and malocclusion. More recently, a the mandible forwards? systematic review into BSSO advance- andibular advancement surgery ment surgery found “as muscles attempt 1. Elastics Mhas been used for a long period of to return to their original positions, they time to good short-term effect. According rotate the mandible in a clockwise posi- comprehensive systematic review to Proffit’s seminal 2007 review into tion, open the bite, and cause relapse”.7 A by Janson et al. (2013) found Class orthognathic surgery (incorporating over Pepicelli et al. (2005) corroborates it is II correction with elastics is mainly den- 100 papers, 50 invited contributions and “well accepted” that the position and toalveolar and causes lingual tipping, book chapters and 2264 patients), man- function of the facial and mandibular retrusion and extrusion of upper inci- dibular advancement of less than 10mm muscles are “critical influences” on sors, with intrusion of lower incisors. overjet during the first year is consid- alignment and stability.8

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Mentioning “muscle function”, however, does not immediately champion functional appliances and preclude fixed or surgical interventions. Despite the fact that some of the more curmudgeonly advocates of the old, traditional approach may completely ignore the influence of muscles, the functional appliances school has been guilty of the same while still paying it lip service.

4. Myofunctional appliances

surprisingly common misconception A amongst orthodontic practitioners is that functional appliances are the same as myofunctional appliances. In fact, they are polar opposites, both in terms of underpinning philosophy as well as mechanism of action. Functional appliances simply expand maxillas and posture mandibles forward without correcting soft tissue dysfunction at all. Myofunctional appliances, conversely, directly target these underlying muscular causes. Myofunctional appliances have been used for many years, beginning in the 1950s with the Frankel appliance (Figure 3). Not many children in the 21st century will be amenable to using Frankel appliances, however, modern iterations, such as the Trainer and Myobrace® Pre-Ortho- dontic Systems, have been used to much success over the last 25 years. The mechanism of action is to deactivate the causative labio-mentalis activity, which allows the mandible to assume its natural position. Tripathi and Patil (2011) found the pre-orthodontic Trainer “significantly stimulates growth of the mandible”,9 while Usumez et al. (2004) found the myofunctional Trainer group of subjects showed “sagittal growth of the mandible, increased SNB and facial height, reduced ANB... and overjet reduction.”10 Here are two cases that demonstrate the potential of myofunctional treatments in Class II correction.

Case 1

ase 1: 13y 6m. This girl was a mouth Cbreather with subsequent lowered tongue posture and labio-mentalis activity on swallowing. She was treated with the Myobrace for Teens system and showed a significant reduction in overjet and over- bite, together with clear translation of the mandible on viewing the facial profile. Case 1. Prior to treatment; and after 12 months using Myobrace T1 and T2 appliances.

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Case 2

ase 2: 11y 3m. This boy presented Csimply for correction of jaw development, having been recommended surgery by multiple previous practitioners. His lower lip trap had flared his upper anterior dentition and severe mentalis activity had resulted in a retrognathic mandible. He also used the Myobrace for Teens system to retrain his tongue resting posture and to swallow without peri-oral muscular ten- sion. It is anticipated he will no longer require surgery.

The Australian Society of Orthodontists (ASO) has long advocated the benefits of early treatment: “Early orthodontic treatment begins while a child’s jaw bones are still soft. They do not harden until children reach their late teens. As the bones are still pliable, corrective procedures such as braces work faster and more effectively than they do for adults. Early treatment is an effective preventive measure that lays the foundation for a healthy, stable mouth in adulthood.” Just like the ASO, we should be pre- pared to dissolve old dogmas and move our clinical practice towards the evidence; there is still a place for the lapidary move- ments of fixed appliances, the skeletal impacts of functional appliances and (after a certain age) even orthognathic Case 2. Prior to treatment; and after 12 months using Myobrace T1 and T2 appliances. surgery. However, regardless of the modality, incorporating a myofunctional References component to our treatment plans can help 6. Iseri H, Kisnisci R, Altug-Atac AT (2008) Ten-year follow-up of a patient with hemifacial microsomia us achieve therapeutic goals that we once 1. Harrison JE, O’Brien KD, Worthington HV (2007) treated with distraction osteogenesis and orthodontics: thought were impossible. Orthodontic treatment for prominent upper front an implant analysis. Am J Orthod Dentofacial Orthop teeth in children. Cochrane Database Syst Rev. Jul 134:296-304. About the authors 18;(3):CD003452. 7. Joss CU and Vassalli IM (2009) Stability after bilat- 2. McNamara JA (1981) Components of Class II malo- eral sagittal split osteotomy advancement surgery with cclusion in children 8-10 years. Ang Orthod 51:177-202. rigid internal fixation: as systematic review. J Oral Dr Rohan Wijey lives and works on the 3. Perinetti G, Primozic J, Franchi L, Contardo L Maxillofac Surg 67(2):301-13. Gold Coast. He is the Clinical Director of (2015) Treatment Effects of Removable Functional 8. Pepicelli A, Woods M, Briggs C (2005) The man- Myofunctional Research Co. and teaches Appliances in Pre-Pubertal and Pubertal Class II dibular muscles and their importance in orthodontics: dentists and orthodontists from around Patients: A Systematic Review and Meta-Analysis of A contemporary review. American Journal of Ortho- Controlled Studies. PLOS ONE. dontics and Dentofacial Orthopedics Vol. 128, No. 6. the world about early intervention and 4. Proffit WR, Turvey A, Phillips C (2007) The hier- 9. Tripathi NB, Patil SN (2011) Treatment of Class II myofunctional orthodontic appliances. archy of stability and predictability in orthognathic Division I Malocclusion with Myofunctional Trainer surgery with rigid fixation: an update and extension. System in Early Mixed Dentition. J Contemp Dent To find out more information about how to Head Face Med Vol. 3, p. 21. Pract 12(6):497-500. begin implementing The Myobrace System 5. Joss CU, Thuer UW.(2008) Stability of the hard 10. Usumez S, Uysal T, Sari Z, Basciftci FA, Karaman and soft tissue profile after mandibular advancement AI, Guray E (2004) The Effects of Early Preortho- and begin experiencing increased patient in sagittal split osteotomies: a longitudinal and long- dontic Trainer Treatment on Class II, Division 1 volume visit myoresearch.com. term follow-up study. Eur J Orthod 30:16-23. Patients. Angle Orthod 74(5).

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