To assess the possible three-dimensional changes in condylar volume in Class II Division 2 growing patients following the use of Invisalign clear aligners to “unlock” the mandible. Unlocking the mandible was done through proclining the maxillary incisors, correcting the overbite, and expanding the maxillary arch

Morsi, Hanie

English

eCommons at Roseman University

The concept of ”unlocking” the mandibleAbstractMorsi H,  Willshire B, El Bialy T Faculty of Medicine & Dentistry, University of AlbertaAssessment of Condylar volume changes in Class II Division 2 patients treated with proclination of maxillary incisors, overbite reduction and dentoalveolar expansion using Clear AlignersClass II Division 2 MalocclusionMethodsSignificance & SummaryPurpose: To assess the possible three-dimensional changes in condylar volume in Class II Division 2 growing patients following using Invisalign clear aligners to “unlock” the mandible. Unlocking the mandible was done through proclining the maxillary incisors, correcting the overbite, and expanding the maxillary arch.Methods: The study sample was provided by (T.E), an Invisalign-experienced orthodontist in Edmonton, AB, Canada. The inclusion criteria in this study are as follows: (1) Adolescent patients (age range: 12-16 years), (2) Skeletal Class II (ANB > 4°), (3) Dental Class II Division 2 Malocclusion (molar and canine Class II, retroclined maxillary incisors, increased overbite), (4) Normal or forward grower (FMA < 29 degrees) (5) Planned dual arch Invisalign orthodontic treatment (to procline the maxillary incisors, correct the overbite and expand the maxillary arch)- except for the control group (6) Available T1 (before the start of treatment) and T2 (one year after T1) cone-beam computed tomography (CBCT) generated lateral and posteroanterior cephalograms, (7) Aligners made of SmartTrack material (year 2012 to present), (8) Good patient compliance throughout treatment as assessed by the treating orthodontist, and (9) No planned Class II mechanics. A total of 15 patients served as a treatment group, and 8 patients served as a control group. Individuals in both groups were matched according to age, gender, growth pattern, Class II and malocclusion severity. For each participating subject, a CBCT was obtained at T1 and T2 time points. Invisalign clear aligners were used for the treatment group to procline maxillary incisors, correct the overbite, and expand the maxillary arch. No intervention was introduced for the control group between T1 & T2. The mean condylar volume at T1 and T2 was analyzed with 3D Slicer Software, and was compared between the two, treatment and control, groups. The semi-automatic segmentation via 3D Slicer software and the identification of cephalometric landmarks was done by the principal investigator (H.M). Twenty-five percent of the samples will be randomly selected to be re-analyzed after two weeks of the first assessment.Results: our preliminary data indicates a more condylar volume increase for the treatment group versus the controls (p < 0.05).Figure 1. Dental Features of Class II Div 2 MalocclusionFigure 4. Unlocking the mandible by proclining maxillary incisors, correcting the overbite, and expanding the maxilla• The mandible is thought to rotate counter-clockwise to compensate for the length discrepancy, giving it a more prominent chin and prognathic appearance than Class II Division 1 (4)• The body of the mandible is underdeveloped with a retroclined symphysis, while the chin tends to be prominent (5). This has been explained by inhibiting the development of the alveolar process by the retroclined upper incisors, while the absence of the same inhibition to the normal growth of the mandible and symphyseal area (6)• Consequently, mandibular forward repositioning could theoretically be encouraged if those restrictions are eliminatedMandibular CondylesClear AlignersFigure 5. To encourage the “unlocking” of the mandible, utilizing clear aligners, the orthodontist can expand the upper arch, procline the upper incisors, and correct deep overbite, through modifying the teeth positions• Mandibular condyles are established in the literature as growth sites for the mandible, and the condyles play a critical role in formulating the final skeletal dimensions of the mandible• Growing demand for clear aligners. Determining whether actual condylar growth is happening could affect the treatment options offered by the orthodontists to treat Class II D2 patients• Our preliminary results indicate a statistically significant increase in condylar volume for the treatment group from T1 to T2• Further studies with larger sample sizes are recommended to corroborate our findingsmorsi@ualberta.ca References1. Massler M, Frankel JM. Prevalence of malocclusion in children aged 14 to 18 years. Am J Orthod. 1951 Oct 1;37(10):751–68. 2. Elsevier: Contemporary Orthodontics, 6th Edition: Proffit, Fields, Larson & Sarver3. Haas AJ. Headgear therapy: the most efficient way to distalize molars. Semin Orthod 2000;6:79-904. Kirschneck C, Römer P, Proff P, Lippold C. Association of dentoskeletal morphology with incisor inclination in angle class II patients: a retrospective cephalometric study. Head Face Med. 2013 Sep 3;9:24. 5. Pancherz H, Zieber K, Hoyer B. Cephalometric characteristics of Class II division 1 and Class II division 2 malocclusions: a comparative study in children. Angle Orthod. 1997;67(2):111–20. 6.  Arvystas MG. Nonextraction treatment of severe Class II, Division 2 malocclusions. Part 1. Am J Orthod Dentofac Orthop Off Publ Am Assoc Orthod Its Const Soc Am Board Orthod. 1990 Jun;97(6):510–21. 7. Minina E, Wenzel HM, Kreschel C, Karp S, Gaffield W, McMahon AP, et al. BMP and Ihh/PTHrP signaling interact to coordinate chondrocyte proliferation and differentiation. Dev  Engl. 2001 Nov;128(22):4523–34. 8. Mao JJ, Nah HD. Growth and development: hereditary and mechanical modulations. Am J Orthod Dentofac Orthop Off Publ Am Assoc Orthod Its Const Soc Am Board Orthod. 2004 Jun;125(6):676–899. Moss ML. The functional matrix hypothesis revisited. 1. The role of mechanotransduction. Am J Orthod Dentofac Orthop Off Publ Am Assoc Orthod Its Const Soc Am Board Orthod. 1997 Jul;112(1):8–11. 10. Feu D, Catharino F, Duplat CB, Capelli Junior J. Esthetic perception and economic value of orthodontic appliances by lay Brazilian adults. Dent Press J Orthod. 2012 Oct;17(5):102–14. 11. Walton DK, Fields HW, Johnston WM, Rosenstiel SF, Firestone AR, Christensen JC. Orthodontic appliance preferences of children and adolescents. Am J Orthod Dentofac Orthop Off Publ Am Assoc Orthod Its Const Soc Am Board Orthod. 2010 Dec;138(6):698.e1-12; discussion 698-699. 12. Mirzasoleiman P. Mandibular Projection in Class II Division 2 Subjects Following Maxillary Incisor Proclination, Overbite Correction and Dentoalveolar Expansion Using Clear Aligners [A Thesis submitted to The Faculty of Graduate Studies]. The University of Manitoba; 2021. Courtesy of dentodontics.files.wordpress.comFigure 2. C II D 2 problems (1)Source: Getty ImagesCourtesy: sylvainchamberland.comCourtesy: pocketdentistry.comCourtesy: aegisdentalnetwork.como 2-5% in different populations o About one fifth of all class II cases in some populations (2)Figure 3. C II D 2 Prevalence❖Appearance❖ Palatal soft tissue trauma❖Mandibular anterior teeth attrition- Convex profile- Brachyfacial pattern- Prominent chin• “Many orthodontists who have treated a patient with a Class II Division 2 Malocclusion by changing it to a Class II Division 1 contend that they have observed the mandible move forward as much as one-half premolar width virtually every time and the author concurs”  Dr. HAAS, 2000 (3)(Am J Orthod Dentofacial Orthop 2017;152:389-401BodyParts3D• Condyles cartilage does have the ability to grow to adapt to different stimuli (7)• Whether the mandibular growth is primarily influenced by the environment, or genetically determined is till debatable (8)• There is an increased demand for clear aligner therapy due to a growing need for aesthetic orthodontic treatments among adolescents and adults(10,11)• A recent study has shown significant forward positioning and increased skeletal growth of the mandible in the treatment group, Class II Division 2 subjects treated with unlocking the mandible using clear aligners, versus the control group (12)•  Whether the treatment stimulated the skeletal growth, or whether the condyles repositioned anteriorly or underwent actual growth remains unknownPatients selectionTreatment Group Control Group15 patients10 patientsMatching Criteria• Age• Gender• Growth pattern• Class II & malocclusion severityA retrospective cohort studyCBCT scansT-1 T-2Before One year into tx/ One year after T1 for controlsDICOM Files3D Slicer SoftwareSemi-automatic segmentation & identification of cephalometric landmarks• Adolescent patients (age range: 12-16 years)• Skeletal Class II (ANB > 4°, Wits analysis ≥ 0.5 mm)• Dental Class II Division 2 Malocclusion (molar and canine Class II, retroclined maxillary incisors, ≥ 50% overbite)• Normal or forward grower (FMA < 29 degrees)• Planned dual arch Invisalign orthodontic treatment (to procline the maxillary incisors, correct the overbite and expand the maxillary arch)• Available T1 (before the start of treatment) and T2 (one year into treatment) cone-beam computed tomography (CBCT)• Aligners made of SmartTrack material (year 2012 to present)• Good patient compliance throughout treatment as assessed by the treating orthodontist• No planned Class II mechanicsSelection CriteriaGenetic control Epigenetic controlTheories of Condylar growthCondyles grow under genetic control to push the mandible downward and forward (7,8)• (indirect genetic control) along with soft tissue stimuli (like skeletal muscles) determine the condylar growth• Under soft tissue stimulation, the mandible will move downward and forward, and the condyles will respond by growth on the posterior and superior aspects (9)Edwardolive/Getty ImagesPreliminary Data• Change in condylar volume was calculated by taking T2 Avg -T1 Avg to determine how much this variable changed • Repeated measures (within-subjects) ANOVA was used to assess the preliminary data for condylar volume • A total of 20 subjects (10 tx and 10 controls) condylar volume were included. The average of right & left condylar volumes were taken at each time point• Overall, our preliminary data highlight that the mean condylar volume statistically significantly increased for both groups from T1 to T2 (p < 0.05).• As depicted in Table 1, at T2, the differential growth between the two groups was significant (p = 0.10), with the treatment group undergoing more condylar volume increase.• Results should be interpreted with caution owing to the limited sample sizeFigure 6 & Table 1. Change in condylar volume over time for tx and control groupsFigure 6 Table 1

Assessment of Condylar volume changes in Class II Division 2 patients treated with proclination of maxillary incisors, overbite reduction and dentoalveolar expansion using Invisalign Clear Aligners

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Assessment of Condylar volume changes in Class II Division 2 patients treated with proclination of maxillary incisors, overbite reduction and dentoalveolar expansion using Invisalign Clear Aligners

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