Can bone-borne Class II correctors grow the mandible?
Orthodontists have been trying to grow mandibles to correct class II malocclusion since the dawn of time. However, most high-quality research has concluded that this is not possible. As a result, current knowledge suggests that most class II correction is dentoalveolar. Recently, researchers have developed a Class II corrector that is bone-borne. Although these have been examined in case reports, there has been a shortage of high-quality research. This new study begins to address that gap.
A team from Alexandria, Egypt did this study. The Angle orthodontist published the paper.
Yasmine M. Mahmoud et al
Angle Orthodontist. Advanced access. DOI: 10.2319/111324-934.1
The same team published a second paper on this study in which they included data on dento-aveolar changes. You can access this paper at
I am going to report on both papers in a single post.
What did they ask?
They did this study to;
“Assess the effect of two different force systems using maxillary skeletal anchorage on the treatment of growing skeletal Class II subjects”.
What did they do?
They conducted a three-arm, parallel-group, randomised controlled clinical trial. They registered. The trial at clinicaltrials.gov.
The PICO was.
Participants
Orthodontic patients aged 11 to 13 years with Class II malocclusion due to mandibular deficiency, exhibiting overjet greater than 5 millimetres.
Intervention one.
2 Y-shaped mini plates fixed into the mandibular synthesis with two straight mini plates fixed into the zygomatic buttress. A forward pushing force was applied with the SARA appliance that applied 250g of force.
Intervention two.
2 L-shaped mini plates fixed to the external obliques bridge of the mandible and two straight mini plates fixed in the nasal buttress. A 250gm pulling force was applied using a Class 2 Spring corrector.
The appliances were removed after nine months.
One surgeon placed the surgical miniplates under local anaesthesia.
Comparison.
These participants were randomised to delayed treatment for nine months.
Outcomes.
They provided extensive data on 23 dentoalveolar and 23 skeletal measurements. However, the primary skeletal outcome was the effective mandibular length (Co-Gn). I decided that the most important dentoalveolar outcome was the overjet.
They performed a sample size calculation based on previous studies that indicated they needed to enrol 12 patients per group. They used a prepared table for randomisation with block allocation. The allocation was concealed using sealed envelopes.
They performed a univariate analysis of their data. This resulted in multiple tests across a total of 64 outcome measures, increasing the risk of false positives. A better approach would be to select a few clinically relevant outcomes and analyse these with a multivariate method. However, this may be problematic due to the small sample size.
What did they find?
They enrolled 13 participants per group. One dropped out of the bone-borne group.
The team provided a large amount of data derived from CBCT radiographs obtained at the start and at nine months into treatment. To keep things concise, I’ve focused on the two main outcomes I identified and included their means and 95% confidence intervals (calculated separately as the paper didn’t include them).
| Outcome (mm) | Bone anchor (Push) | Bone anchor (Pull) | Control |
| Co-Gn | 103.54 (101.6– 105.3] | 104 [101.2 – 106.7] | 98.7 [97.5 – 99.8] |
| Overjet | 2.62 [2.0 – 3.1] | 1.92 [1.3 – 2.4] | 10.08 [9.4 – 10.5 |
When they looked at the harms of the treatment. They reported that 14 (8.97%) of the 156 miniplates failed. The team also found that 23% of the springs in the “pull’ group failed.
The final conclusion was;
“Both the pushing and pulling force mechanics used in conjunction with bimaxillary miniplate anchorage promoted the correction of class two skeletal man exclusion mainly through a skeletal increase of the mandibular length”.
What did I think?
I found this publication very interesting as it describes a complex and ambitious randomised controlled trial. They aimed to answer a clinically relevant question about new types of functional appliances. The study was well-executed, resulting in two publications. My only criticism is that the work might have been more impactful if they had combined the two papers into one. Unfortunately, they chose to present two separate sets of data in a somewhat complicated manner.
Additionally, the paper would have been clearer if they had included fewer outcome measures. I have mentioned this several times before, but these two papers contained the highest number of cephalometric measurements I have seen in a long time. Therefore, I decided to report only two outcome measures to highlight the most significant findings.
I was also very impressed that they included an untreated control group in their study. This strengthened the study by allowing them to compare normal growth with the effects of the appliances.
These findings suggest that treatment with bone-borne functional appliances (using either push or pull mechanics) increases mandibular length. These differences ranged from 6 to 7 mm, which is clinically significant. The overjets were also reduced to normal values.
While we may be impressed by the amount of skeletal change achieved with these appliances, I wonder whether we should exercise caution, as this study was quite small. This means there is a risk of high uncertainty in their findings. Ideally, I would like to see studies with larger sample sizes. As a result, this is a rather good pilot study that can inform and power larger trials.
Risks
Furthermore, we must consider whether the risks and discomfort associated with the surgery was a contraindication for this treatment. The authors noted that this treatment was fairly invasive, requiring two operations—one to place the appliances and another to remove them. There was also a significant failure rate with the bone anchors. We should keep this in mind when evaluating the burden of care associated with this approach.
Final thoughts
In summary, I believe this study is an important preliminary step for further research into this potentially effective yet invasive technique, which warrants additional investigation.
Emeritus Professor of Orthodontics, University of Manchester, UK.
I don’t pretend to criticize the study because that would be presumptuous, but what I’d like to know is the extra length of the mandible is accompanied by a “forward” projection of the PG.
I wonder why they don’t use measurements involving soft tissue; I’m thinking of Arnett and the TVL.
In essence, before placing bone plates on an adolescent, I have to be truly convinced that this is clinically and not only cephalometrically significant.
Thanks and I agree. While the study uses tradtional cephalopods outcome measures, it would have been nice if they had included other measurements that are relevant to our patients for example profile changes and perceptions. However, this is similar to many orthodontic studies and is an illustration of why we need to change,
Sooner or later there will be a change in these assessments, and I am sure that much of the credit will be yours in directing the light of scientific research on the dark side of the moon.
I can’t help but wonder whether the mandibular growth observed is what Dr L Johnston described as “mortgaging of mandibular growth? Will the control group eventually catch up? We need a long term follow up.
Hi Dr Bennett Mui and Dr O’Brein,
The primary discussion about this study appears to be the “catch-up growth” phenomenon in the mandible. This investigation reports statistically significant mandibular growth following functional Class II treatment with skeletal anchorage. Importantly, the authors assessed true mandibular length by measuring the distance from condylion (Co) to gnathion (Gn). In contrast, many previous studies that concluded functional appliances do not enhance mandibular growth relied on the articulare (Ar) to pogonion (Pg) distance. The location of articulare is highly dependent on posterior cranial base projection and varies with the anteroposterior position of the mandible, rendering Ar–Pg an unreliable measure of actual mandibular corpus length.Although it remains uncertain whether untreated control subjects would exhibit comparable late mandibular growth through a natural catch-up phenomenon, the present study provides robust evidence of substantial mandibular growth acceleration during functional Class II correction when skeletal anchorage is utilized.
Based on decades of research on this issue it would be a giant leap of faith to believe that a device employing a different method of positioning the mandible in a forward position and distracting the condyle from the fossa, would somehow magically produce growth of the mandible or condyle.
Trying to ascertain mandibular growth from a cephalograph is like trying to measure a balloon with a ruler – it ain’t gonna work out well. Moreover, some orthodontists appear to have a rather nuanced perspective of ‘growth’. In this commentary, Kevin presumably is using the term ‘growth’ in layman terms. Biologically/scientifically, a more rigorous definition is needed. For example, physiologic growth is empirically the summation of molecular pathways, which include hyperplasia, hypertrophy, differentiation, cell death/apoptosis, atrophy, extracellular matrix changes and remodeling inter alia. Clinically, to assess these changes, mathematical techniques could be used to determine the degree of shape-change, size-change and directionality i.e. allometry, isotropy, anisotropy etc. – and then interrogate these changes in 3D statistical shape space to see what happened, where it happened and by how much. These techniques have been used in sleep apnea research [1] – not sure why orthodontists appear to be reluctant stepping outside the cephalometric comfort zone?
1. Martínez-Suarez et al (2025) Association between morphological variations of mandibular bone and pharyngeal airways: A morphometric cone-beam computed tomography (CBCT) study. Cureus 17(10): e95859.