Dentoskeletal Changes Associated With Herbst Appliance Therapy
Condition: Malocclusion, Angle Class II
MeSH terms: Malocclusion; Malocclusion, Angle Class II; Overbite
Study type: Interventional

Summary: 
      The aim of the study is to perform a three-dimensional (3D) evaluation of the dentoskeletal
      changes in pubertal Class II malocclusion subjects treated with the Herbst appliance (HAG),
      in comparison with a Class II comparison group (CG). 3D virtual models generated from three
      time-point CBCTs (T0, baseline; T1, immediately after Herbst insertion; and T2, 8 months
      after) of 25 HAG patients will be evaluated. Virtual models obtained from 25 Class II
      malocclusion patients, in the same stage of biologic maturation and skeletal abnormality, but
      with no orthopedic treatment will be constructed for the CG subjects. These CG patients are
      under orthodontic treatment, but only with teeth alignment. Voxel based registration on the
      anterior cranial fossa will be used to assess maxillary and mandibular displacement/articular
      fossa remodeling; regional registration on the mandibular corpus will be performed to
      evaluate mandibular growth and mandibular dental changes; and regional registration on the
      anterior region of the maxilla will be performed to evaluate maxillary growth and maxillary
      dental changes.
    

Detailed description: 
      1. BACKGROUND Class II malocclusion is highly prevalent worldwide, and it is a major reason
           for orthodontic treatment to be initiated. This type of malocclusion can be restricted
           to the dentoalveolar region, but the majority of Class II patients exhibit a strong
           skeletal component to the malocclusion, including most frequently mandibular skeletal
           retrusion and an increased lower anterior facial height. With increased severity of the
           mandibular deficiency, the orthodontist is challenged to treat the underlying skeletal
           problem appropriately.

           For growing patients, the use of fixed and removable mandibular advancement appliances
           has been advocated for many decades. A variety of fixed Herbst appliance designs have
           achieved worldwide acceptance in that they eliminate most major patient compliance
           factors. Today the Herbst appliance (HA) is by far the most frequently used mandibular
           jumping device in the United States, with more Herbst appliance being fabricated than
           all other functions appliances combined.

           The Herbst appliance originally was introduced by Emil Herbst in the early years of the
           twentieth century, but it did not achieved worldwide clinical acceptance until its
           re-introduction by Hans Pancherz 70 years later. Since then, a significant number of
           clinical and scientific studies has been conducted about HA, particularly by Pancherz
           and colleagues.

           Two-dimensional cephalometric studies have reported increases in the length of the
           mandible and in forward displacement of the mandible following HA in comparison to
           matched untreated controls. On average, 2 mm of mandibular length gain (measured from
           Gonion to Pogonion) and 1.5 degree of improvement in the SNB angle can be observed
           following Herbst appliance therapy.

           Investigations in experimental animals have provided the histological evidence of the
           changes in the condyles, rami, and articular fossae when the mandible is advanced in a
           laboratory setting. Previous reports have showed an increased proliferation of the
           condylar cartilage in monkeys that had their mandible advanced with the Herbst
           appliance. These adaptations occurred primarily in the posterior and posterosuperior
           regions of the condyle. They also reported significant bone deposition along the
           posterior border of the mandibular ramus during the early part of the experimental
           period as well as significant deposition of new bone on the anterior surface of the
           postglenoid spine at the articular fossae. It should be noted, however, that the
           post-glenoid spine is not well-defined in humans.

           Clinical investigations using Magnetic Ressonance Imaging (MRI) and lateral radiographs
           have showed that changes in the mandibular condyles and articular fossae may occur with
           Herbst therapy. It has been demonstrated that following Herbst therapy some articular
           fossa remodeling can be seen at the anterior surface of the postglenoid spine, which
           causes a relocation of the articular fossae in a downward and forward direction. But
           such fossa adaptation in Herbst patients is less extensive than in experimental animals,
           with much individual variation in response evident.

           Although most Herbst studies are convergent as to the extent of skeletal and
           dentoalveolar adaptations, some questions still remain:

             -  How much mandibular growth can be achieved with therapeutic mandibular advancement?

             -  How much mandibular rotation and skeletal bite opening occurs?

             -  How much of the original mandibular advancement is maintained long-term?

             -  Is there is an adaptive behavior of the articular fossa after mandibular
                advancement, with bone remodeling occurring in the fossa.

           In the last decade, a new methodology using 3D virtual modeling has been developed
           allowing a change in the paradigm of assessing the skeletal changes associated with
           growth and treatment; this technology that has opened new horizons in scientific
           investigations of dentofacial orthopedics. Recently, the American Journal of
           Orthodontists and Dentofacial Orthopedics published the first 3D report on Herbst
           treatment, a pilot study in which 7 Class II subjects treated with the Herbst appliance
           were compared with 7 Class II subjects treated with fixed appliances and intermaxillary
           elastics. It was reported that Class II patients undergoing Herbst treatment
           demonstrated anterior displacement of the condyles and articular fossae along with
           maxillary restraint when compared with the Class II patients used for comparison.

           The aim of the present prospective controlled clinical trial is to investigate the
           skeletal changes in the mandible and articular fossae in Class II patients undergoing
           Herbst appliance therapy, using 3D virtual models in comparison to a control group
           comprising Class II subjects.

        2. PATIENTS AND METHODS b.1) Study design

      This is a non-randomised controlled clinical trial, with intervention. Two groups are been
      planned: 1) Class II malocclusion subjects treated with Herbst appliance (HAG); and 2) Class
      II malocclusion subjects treated only with teeth alignment. The two groups are matched by
      stage of skeletal maturation, type of malocclusion, chronological age, and gender. There is
      no blinding for the outcome evaluators. Due to ethical concerns, the comparison group will be
      composed of Class II subjects that need previous alignment and leveling of the teeth before
      orthopedic phase of their treatment.

      b.2) Participants - settings and location where the data are collected The treatment are been
      performed in the Orthodontic Clinic of Pontifical Catholic University of Minas Gerais (Belo
      Horizonte, Brazil). This is a private university, but the patients are mostly low-income
      subjects. Data has been collected from August 2013 and finished on September 2015.

      b3) Sample size Based on the standard deviation of 1.85 mm reported by Pancherz et al.28, an
      alpha significance level of 0.05 and a power of 0.80 to detect changes of 1.5 mm, a
      preliminary sample size of 25 patients per group was calculated.

      Therefore, 25 individuals have received a Herbst appliance at the beginning of their
      treatment with a one-step full activation - Herbst Appliance Group (HAG); while 25 skeletal
      Class II malocclusion individuals, with indication for HA therapy, but with other clinical
      conditions that required prior treatment before HA insertion, have been allocated to the CG.
      The two groups have been matched by chronological age (between 12 years and 16 years-old), by
      stage of skeletal maturation and by the stage of dental development (permanent dentition).

      b4) Appliance design

      The Herbst appliance design included bilateral telescoping arms (3M Abzil, São José do Rio
      Preto, Brazil) articulated with pivots that were positioned in both the maxillary and
      mandibular arches. The pivots were welded to a rigid cantilever wire (.040-in stainless
      steel) extending from the lower first permanent molar bands (TP Orthodontics, La Porte, IN)
      to the canine regions of the mandible. In the maxillary arch, the pivots were welded to bands
      on the permanent first molars. A Hyrax expander (Morelli Ortodontia, Sorocaba, Brazil) and a
      .040-in stainless steel (SS) lower lingual arch were added to the HA structure to improve
      appliance stability and transverse dimensional control. Two .028-in SS wires were used as
      occlusal rests in the permanent second molars to avoid their extrusion after activation. The
      occlusal rests were removed when they interfered with the occlusion to avoid bite opening.

      b5) Method of registration

      Cone beam computed tomography (CBCT), intra-oral pictures, and extra-oral pictures have been
      collected in three time-points for HAG (T0, T1, and T2), and in two time-point for CG (T0,
      and T2), as a regular protocol of orthodontic record for these clinical treatments.

      b6) Method of measurement

      Analysis of serial CBCT images to evaluate changes between T0, T1, and T2 include 3D analysis
      methodology using ITK-SNAP (open-source software, www.itksnap.org); SLICER (open-source
      software, www.slicer.org; and VAM - Vectra Analysis Model software version 3.7.6 (Canfield
      Scientific Inc., Fairfield, NJ). The tridimensional image analysis procedures included: (1)
      approximation of scans; (2) construction of 3D label models; (3) voxel based image
      registration; and (4) quantitative and qualitative assessments using 3D mesh surface models.

      Quantitative assessment of the positional changes between the 3D surface models of the
      cranial base, maxilla, and mandible will be performed using point-to-point landmarks
      measurements (VAM software), and virtual analytics (SLICER software).

      Interactive visual analytics include graphic displays with qualitative assessments using
      semitransparent overlays of the 3D surface models at the different time-points and
      quantitative assessments of the surface displacements using color-coded surface distance
      maps. All visual analytics assessments will be performed using two modules (Model-to-Model
      Distance and Shape Population Viewer) in the SLICER software.

      Voxel based registration on the anterior cranial fossae will be used to assess maxillary and
      mandibular displacement/articular fossae remodeling; regional registration on the mandibular
      symphysis will be performed to evaluate mandibular growth and mandibular dental changes; and
      regional registration on the anterior region of the maxilla will be performed to evaluate
      maxillary growth and maxillary dental changes.

      b7) Method of analysis

      For the primary and secondary outcome measures it will be used Statistical Package for the
      Social Science (SPSS) software (version 16.0 Chicago, IL). Descriptive statistics will be
      presented for both groups. Statistical differences between the two groups will be calculated
      with Mann-Whitney test (comparison between the difference of the means of the HAG and CG).
      The comparison between the changes within each group will be performed using the Wilcoxon's
      test.
    

Intervention name(s): Herbst appliance
Intervention type(s): Device
Intervention description(s): Group treated with conventional Herbst appliance for mandibular advancement during orthopedic treatment.
Allocation: Non-Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Herbst appliance; Computed tomography; 3D imaging; Growth and development; Orthodontic Appliances, Functional