Plain English Summary
Background and study aims
The position of the lower jaw can influence the position of the hyoid bone and the tongue, which can then affect the dimensions of the airway. Lower jaw advancement is a type of surgery that moves the jaw, and can change the dimensions of the airway. A Herbst appliance is a device that is attached inside the mouth to move the jaw. The jaw can be moved in a single step (maximum advancement) or in smaller, multiple steps (incremental advancement) using a Herbst appliance.
This study aims to look at the effects of maximum and incremental advancement using a Herbst appliance on airway dimensions and position of the hyoid bone in young adults with a retruded lower jaw.
Who can participate?
Patients aged 14-18 with mandibular retrognathia
What does the study involve?
Participants will be randomly allocated to one of two groups. One group will receive maximum advancement (MA), whereas the other will receive incremental advancement (IA). Both groups will receive mandibular advancement treatment using the Herbst-RPE appliance. The MA group will receive treatment for approximately 9-10 months. The IA group will receive treatment every 2 months until the treatment is complete.
What are the possible benefits and risks of participating?
The possible benefit of participating in this study is that patients will receive treatment more quickly, as they will not have to wait to be treated. There are no known risks to participants taking part in this study.
Where is the study run from?
Erciyes University, Faculty of Dentistry, Department of Orthodontics, Kayseri (Turkey)
When is the study starting and how long is it expected to run for?
November 2011 to September 2017
Who is funding the study?
This study does not require funding as all treatments are standard orthodontic treatments performed by Erciyes University
Who is the main contact?
Nisa Gul Amuk
Changes in pharyngeal airway dimensions following incremental and maximum bite advancement during Herbst appliance therapy in young adult patients: a randomized prospective clinical study
There is no difference between maximum bite advancement and ıncremental advancement with Herbst appliance therapy on pharyngeal airway dimensions and hyoid bone position.
Erciyes University Clinical Trials Ethical Committee, 06/12/2011, 2011/107
Interventional prospective single-center double-blinded randomised controlled parallel trial
Primary study design
Secondary study design
Randomised parallel trial
Patient information sheet
Not available in web format, please use contact details to request a participant information sheet
Skeletal class II malocclusion with mandibular retrognathy
Participants will be randomly allocated to receive either maximum advancement or incremental advancement in a 1:1 ratio using a random number table.
Both groups will receive mandibular advancement using the Herbst-RPE appliance with a stainless steel casted splint design.For the group receiving maximum advancement, advancement will be adjusted until a tet-a-tet incisor relation or super class I molar relationship is obtained. This will be completed for approximately 9-10 months. For the group receiving incremental advancement, a 2 mm shim will be inserted to the pivot ends of the plungers after a 4-5 mm initial forward movement of the mandible. For this group, advancement steps will continue every 2 months until a tet-a-tet incisor relation or super class I molar relationship is obtained.
Primary outcome measure
Changes in pharyngeal airway and hyoid position, assessed using lateral cephalometric radiography before using the Herbst-RPE appliance and immediately after appliance removal
Secondary outcome measures
Skeletal changes, assessed using lateral cephalometric radiography before using the Herbst-RPE appliance and immediately after appliance removal
Overall trial start date
Overall trial end date
Reason abandoned (if study stopped)
Participant inclusion criteria
1. Skeletal Class II malocclusion (ANB angle >4°) and mandibular retrognathy (SNB <78°)
2. Bilateral Class II molar and canine relationship (at least 3.5 mm)
3. Increased overjet (more than 7 mm)
4. Normal or decreased vertical dimensions (SN-GoGn ≤32)
5. Minimal crowding (≤4) and no missing teeth on upper and lower arches
6. Aged 14-18 years
Target number of participants
Total final enrolment
Participant exclusion criteria
1. Craniofacial anomalies
2. Musculoskeletal diseases
3. Severe facial asymmetry
4. Severe maxillary transverse deficiency
5. Poor oral hygiene
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Erciyes University, Faculty of Dentistry, Department of Orthodontics
Erciyes University Clinical Trials Ethical Committee
Erciyes Üniversitesi Merkez Kampüs Tıp Fakültesi Dekanlığı 38039 Talas Yolu Melikgazi/KAYSERİ
+90 0 352 437 49 10 - 11
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
We are intending publish this manuscript as original article in an peer-reviewed journal in June 2019
IPD sharing statement:
The data sharing plans for the current study are unknown and will be made available at a later date
Intention to publish date
Participant level data
To be made available at a later date
Basic results (scientific)
2019 results in https://pubmed.ncbi.nlm.nih.gov/30892615/ (added 26/10/2020)