Long term Dento-skeletal changes

Long term Dento-skeletal changes with the Bionator, Herbst, Twin Block and Mara functional appliances.

Siara Olds et al 2010
Angle Orthodontist 2010; 80:18-29.

The effects of functional appliances has been surrounded with controversy and uncertainty. Some animal studies has shown when the mandible is brought forward there can be cellular changes in the condylar head and the glenoid fossa may remodel.  There are questions that still need to be answered.  Are these findings substantiated with clinical research in humans; (2) Is the growth of the mandible different with functional treatment than that of similar controls; and (3) Is this treatment stable over the long-term?  Stability of C-II treatment can be influenced by rotational growth patterns, treatment timing and retention amongst other factors.

The present study was designed to assess the treatment outcome of tooth-borne functional appliance- es (Bionator, acrylic splint Herbst, Twin Block, and mandibular anterior repositioning appliance [MARA]) and their stability over time and after fixed appliance therapy, when compared to each other and to untreated controls with similar Class II malocclusion 

Study Type: Retrospective Long term clinical trial

Population: 80 patients treated by 2 orthodontists

Sample: 80 patients divided equally among Bionator, removable acrylic Herbst, Twin Block, and MARA functional appliance groups . The distribution of sexes were closely matched, and similar treatment ages. 10-11yrs old, but were matched carefully via CVM. The untreated control group comprised 21 children from the Michigan and Denver Growth Study samples.

Inclusion:The inclusion criteria for the treated sample were: (1) Class II division 1 malocclusions characterised by a retrognathic mandible (SNA> or =80°, SNB  <76°, and SN-GoGn < or = 35°), (2) CVM between stage 2 and 3 at initial records, (3) landmarks were identifiable on all of the radiographs, and (4) treatment of functional appliance therapy was not combined with a headgear.  All patients wore the functional appliances until full eruption of the permanent dentition, at which time the second phase of fixed appliance treatment commenced.

Data: Lat ceps taken  at T1 (initial), T2 (completion of functional therapy) and T3 (completion of  fixed appliance therapy - 41-49months)

Analysis: Lat ceps traced by one investigator.  ANOVA - analysis of variance


  • No sig difference pretreatment for most of the sample.
  • Comparison of the different treatment groups with the controls depicted no statistically significant difference in most of the measurements associated with growth at all time points studied.
  • The overbite, overjet, and the Wits values were the only measurements that demonstrated significant differences at the end of the observation period, (T3– T1).  -dental changes only*
  • When comparing the treatment groups among themselves, the Herbst appliance, followed by the MARA, demonstrated a significant effect on restricted maxillary growth and produced a steeper occlusal plane. The Twin Block was most effective in controlling the mandibular plane angle and had the greatest long- term effect on the labial version of the mandibular incisors


  • No significant long-term dento-skeletal differences were observed between the various treatment groups and matched controls.
  •  When comparing the treatment groups among themselves, the Herbst and MARA appliances significantly restricted maxillary growth and produced a steeper occlusal plane.
  • The Twin Block was most effective in controlling the mandibular plane angle and had the greatest effect long term on labial version of the mandibular incisors.


The Bionator group showed significant opening of the gonial angle (Ar-Go-Me) after functional treatment. This 2.0° per year increase in the gonial angle was greater than any of the untreated and treated samples and is most likely attributed to the growth direction of the condyle and remodelling of the posterior border of the ramus.

All groups showed similar Long term growth compared with the controls. This finding is in agreement with that reported by Livieratos and Johnston who suggested that functional appliances place a mortgage on mandibular growth. Control clinical trials also found no significant alteration of mandibular length long term with the utilisation of functional appliances.

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