The Effects of the Chin Cup on Temporomandibular Joint and Mandibular Dimensions
Condition: Class III Malocclusion
MeSH terms: Prognathism; Malocclusion; Malocclusion, Angle Class III
Study type: Interventional

Summary: 
      This in vivo comparative study will evaluate the changes in the mandibular dimensions and the
      glenoid fossa after skeletal class III subjects' therapy by chincup appliance and compare it
      with an untreated class III control group. Pre and post-treatment low-dose computed
      tomography images will be taken before and after achieving positive overjet and undergoing 16
      months of active treatment/ observation. Dimensional and volumetric changes in the mandible,
      condyles, and glenoid fossa will be calculated and compared to those observed in the control
      group.
    

Detailed description: 
      Chincup is a usual treatment strategy for growing subjects with skeletal Class III
      malocclusions due to the mandibular overgrowth. However, the review of the literature reveals
      controversies and contradictions regarding the efficacy of chincup therapy in the retardation
      of mandibular growth. Moreover, the adaption of the temporomandibular joint (TMJ) following
      this treatment isn't clear yet. Two recent systematic reviews recommended the need for
      high-quality studies.

      Computed tomography has been considered an ideal tool for evaluating the TMJ with the
      possibility of determining the real dimensions of the structures under study. Low-dose
      computed tomography was introduced as an alternative procedure with an effective dose
      proximately equal to traditional radiographs. Moreover, the volumetric analysis afforded by
      3D imaging has proven reliable and accurate in the evaluation of mandibular and condylar
      sizes. Therefore, the objective of this randomized control trial is to evaluate the
      dimensional changes in the mandible, condyles, and glenoid fossa after chin cup therapy for
      children with mandibular prognathism in comparison with untreated Class III patients

      Methods: patients ages between 6 and 8 with anterior crossbite, Class III relationships of
      the permanent first molars or mesial step relationships of the primary second molars, and
      short-faced pattern, will be selected from the orthodontic department in the faculty of
      dentistry at Damascus university. Thirty-eight subjects will be enrolled on the study, who
      will meet the following radiological inclusion criteria based on cephalometric images: Mild
      to moderate skeletal class III (4- <the sagittal skeletal angle< 0 degree), due to mandibular
      protrusion (SNB > 80°), and normal or horizontal growth pattern (Bjork's sum ≤396° ±5°).

      Patients in the experimental group will receive an individual fabricated bonded bite block
      and occipital chincup. A 400-500g/side retroactive force will be applied in the direction of
      the condyles. Patients or panthers will be instructed to wear the appliance /14-16/ hours a
      day. Pre-(T1) and post-treatment (T2) low-dose computed tomography images will be taken after
      a positive overjet of 2-4 mm is obtained and undergoing 16 months of active treatment/
      observation. The changes in condyle-mandibular volumes and superficial areas and relative
      positions of the condyles and glenoid fossa will be calculated and compared with those of
      untreated. Statistical analysis will be done by using the Statistical Package for Social
      Sciences, Windows version 26.0 (SPSS Inc., Chicago, Illinois, USA) Paired t-test and Wilcoxon
      signed-rank tests will be used for intragroup comparisons. For the intergroup comparisons,
      independent t-tests and Mann-Whitney U tests will be carried out.The confidence level is 95%
      (P< 0.05).
    

Intervention name(s): Chincup; Control group
Intervention type(s): Device; Other
Intervention description(s): Patients will receive an individual fabricated bonded bite block and occipital chincup. A 400-500g/side retroactive force will be applied in the direction of the condyles. Patients or panthers will be instructed to wear the appliance /14-16/ hours a day.; The changes in condyle-mandibular volumes and superficial areas and relative positions of the condyles and glenoid fossa will be calculated after 16 months of observation.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: chin cup; low-dose computed tomography; condyle-mandibular dimensions