Modified Herbst Approach to Improve Chin Projection

Purpose The present study will compare facial, skeletal, and dental changes among adolescents with mild to moderate Class II malocclusion using two Class II orthopedic orthodontic approaches. Patient-reported outcomes will also be assessed through validated questionnaires and qualitative interviews. Hypothesis Participants that use the modified Herbst approach do not showcase facial, dental, and skeletal changes that are different than those using the conventional Herbst approach. Justification One of the most common causes of a Class II malocclusion is a deficient mandibular projection (either due to reduced size or retruded position). Although in adults the only reasonable way to improve the mandibular projection is through surgical repositioning, in growing individuals an orthopedic alternative may significantly reduce the perceived need for this type of surgery later in life. Several craniofacial orthopedic appliances have been used to attempt an orthopedic correction of Class II malocclusion of a mandibular origin, aiming to possibly improve functional, muscular, skeletal, and dental disharmonies.1,2,3 A wide array of related publications exist that have been summarized through several systematic reviews with or without meta-analysis. The Herbst appliance is widely known for its relative effectiveness in correcting Class II malocclusions. It is most commonly used as a fixed appliance that repositions the jaw to a more anterior and downward position displacing the condyles away from the articular eminence.4,-8 This is thought to facilitate condylar bone apposition; hence, increasing mandibular size dimensions. Several papers have considered the efficiency of the Herbst appliance in Class II correction during early permanent dentition. But only one study evaluated changes produced by the Herbst appliance in mixed dentition patients and it concluded that the effects of the Herbst appliance were mainly dentoalveolar.5 Several different designs of the Herbst appliance have been reported in the literature.6-11 A modified Herbst approach by Manni has shown promising results. An increment in the mandibular chin projection of 5 mm has been reported. Due to the fact that the reported positive changes are so far only based on case reports and retrospective data12-24, a randomized controlled trial seems to be the next prudent step. Objectives Assess if the modified Herbst approach produces facial, dental, and skeletal changes that are different than those using the conventional Herbst approach. Assess if the use of the modified Herbst approach facilitates a treatment experience (overall quality of life, oral health-related quality of life, and described experience) that is different than the one with the conventional Herbst approach. Methods Each potential participant will undergo an orthodontic clinical screening to determine if they fill the inclusion criteria (mild to moderate Class II malocclusion in a growing individual - two distinct Class II malocclusion phenotypes - see eligibility criteria below). Eligible individuals will be approached with an opportunity to participate in the research study. After understanding the research purpose and possible side effects, and if they choose to participate, they will voluntarily sign the informed consent form. They will be randomly assigned to one of two groups. The allocation sequence will be done through randomization tables by a statistician and sealed envelopes generated. Once a willing participant is deemed to have fulfilled the inclusion criteria and provided informed consent the randomization will occur. For each Class II malocclusion type, two groups will be randomly generated. Group 1 - Class II type A malocclusion - proclination of upper incisors indicated. A hybrid Herbst appliance approach will be used (current available conventional treatment). The upper jaw component will be a maxillary expander secured on the first molar bands. The lower arch would have an uncemented lower acrylic full coverage splint-type. In between Herbst-type pistons will be used. For Type, A upper brackets will be initially bonded and upper incisors proclined until normal inclination values are attained. Group 2 - Class II type B malocclusion - proclination of upper incisors not indicated. A modified hybrid Herbst appliance approach (same hybrid Herbst appliance approach but with the addition of temporary anchorage devices (TADs) in both arches) will be used (alternative treatment). In the upper arch, the TADs would be inserted in the paramedical palatal area. In the lower arch, they would be inserted buccally between the roots of the lower second premolar and the first permanent molar. Elastomeric chains will be used to link these TADs to the first molars in the upper arch and to a buccal bottom on the lower canines. For Type, A initially upper brackets will be initially bonded and upper incisors proclined until normal inclination values are attained. Both treatment arms will start as soon as the randomization has been done. Full orthodontic records (2D x-rays, photos, and dental casts) will be obtained for both groups at baseline and after this treatment phase is completed. Further comprehensive treatment will be offered to these patients as this initial management approach is not expected to fully align and level the teeth. This would be an additional elective option at an additional cost. Two validated quality-of-life tools will be used. The CPQ11-14 assesses oral health-related quality of life and the EuroQoL assesses the overall quality of life. These two tools will be collected before and after this management approach. Additionally, a qualitative approach will be used at the end of the trial participants to better understand the participant's journey through the process. Sample size A sample of 40 patients (8 patients per treatment group are needed but the total sample is set to 10 considering a 20% loss during follow-up) will be sought. This sample was based on alfa of 5% and a beta of 20%. A clinically significant difference of 4.9 mm in Pg to OLp and a variance of 12.25 was set as clinically meaningful based on the pilot retrospective study by Manni et al.16. n=f(a,b)\*2SD2/Dif2 25 f(a,b)=7.85 (Table XIII page 22) 25 sd=12.25 Manni et al.16 Expected difference= 4.9 mm Pg to OLp Manni et al.16