Bone-anchored protraction reduces the need for orthognathic surgery.

Occasionally, a journal publishes a paper that will likely be recognised as a “Classic.” This UK-based team has done an excellent trial examining the effectiveness of bone-anchored protraction treatment. Importantly they report outcomes relevant to both clinicians and our patients. This research also shows that it is possible to carry out a low-cost, long-term study.  I cannot praise this team enough.

Padhraig Fleming has provided us with this summary post about this study.

Class III Correction: A Bump from BAMP?

We have had a wealth of research examining our ability to modify growth in Class II malocclusion. High-quality prospective studies seem to suggest that our lasting effect on anterior-posterior skeletal growth is modest—if it does indeed exist. More recent research by Nicky Mandall’s group in the U.K. also suggests that the long-term skeletal impact of protraction facemasks in young children is very limited. However, our quest to modify skeletal growth continues. Increasingly, the adjunctive use of mini-screws and mini-plates is being explored to stretch the limits of orthodontic change. 

The use of bone-anchored maxillary protraction (BAMP) has shown promise in previous retrospective studies with evidence of positive skeletal effects, at least in the short term. Moreover, while some suggest that protraction facemasks may be more potent in pre-adolescents, BAMP is advocated in a slightly more mature cohort.

It was exciting to see the recent publication of this excellent multi-centred study in the Journal of Orthodontics.

What did they do? 

They conducted a randomised controlled trial involving two groups and 57 participants.

Participants: 

57 White Caucasian children aged 11–14 years with Class III skeletal pattern associated with maxillary retrusion, three or more incisors in crossbite in retruded contact position, and erupted lower canines and first premolars.

Interventions:

They randomly allocated patients to either BAMP (28) or untreated control (29). They did this electronically with stratification for gender and variable block size to ensure the groups were relatively equal. Deep overbites were managed with adjunctive use of a lower removable appliance with occlusal acrylic coverage.

The clinical endpoint was a positive overjet of 1 mm or more. If correction did not occur, the patients continued with their elastic wear until 18 months after registration. At this point they removed the plates. Between 18 months (DC2) and 3 years (DC3), an upper fixed appliance was placed where indicated.

Outcome measures: 

The primary outcome measure was the perceived need for orthognathic surgery, based on the evaluation of blinded records (clinical images, models, and radiographs) by three expert raters. They coupled this subjective assessment with an objective evaluation of dental and skeletal change and a measure of psychological impact. 

What did they find?

The authors undertook an intention-to-treat analysis accounting for drop-outs. They assessed the need for orthognathic surgery at 15.6 to 15.9 years. The panel felt that Fewer patients (P= 0.04) in the BAMP group (48%) required surgery than in the control group (75%), representing a 27% reduction in subjective need for surgery. 

Regarding the objective outcomes, most between-group differences did not exceed 1mm or 1 degree. These were, therefore, considered to be clinically insignificant. In terms of skeletal effect, ANB increased by 1.2 degrees in the BAMP group during treatment (P= 0.004). However, this effect was diluted 18 months later (to 0.7 degrees), with statistical significance lost (P= 0.16).

What about the dental effects? Again, the overjet improved during the treatment phase with BAMP (by 1.5 mm relative to the control). This difference was also reduced by T3, albeit to a lesser extent than the skeletal effect (to 1mm; P= 0.06). Oral health-related quality of life was statistically better in the treated group, although this was attributed to the confounding effects of alignment with fixed appliances. 

Of interest, the mean operating time was 88 minutes for placement, with a plate infection rate of 11% (all related to maxillary plates). Eight patients returned to the theatre for the replacement of infected plates.

What did I think?  

This study was excellent. However, I knew this research was happening and have patiently waited for the results for some time. The findings are hugely interesting. Notably, the effects observed in this study were lower than those reported in previous retrospective studies. We have seen this before in studies relating to growth modification and papers considering fixed appliance mechanics. Moreover, the pattern observed in the long-term functional studies is also mirrored, whereby early growth acceleration is eroded over time, while occlusal changes seem to be preserved to a greater extent. 

The design and methodology of this study are exceptional. Clinical trials are difficult to conduct, and samples are often hard to come by. The multi-centred approach helped to overcome this. However, a great deal of effort and coordination are needed to see this through. It was, therefore, great to see a really useful end product. 

Notably, the findings mirror this group’s previous research involving protraction facemask therapy. The present study included an older age group. I am aware that some recommend an arbitrary upper age threshold for successful protraction facemask therapy (of 10-11 years). I am not sure that the evidence for this is compelling. Comparing the two studies makes me wonder how much additional benefit is derived from the skeletal anchorage. Of course, a third group or, indeed, a further study would be required to answer this. This excellent study has left me wanting more!

Objective measurements

A further interesting finding was the lack of effect of treatment on occlusal plane rotation. Previous work has suggested that a protraction facemask profoundly affects the occlusal plane. Less occlusal plane change with BAMP is, of course, intuitive as the elastics are run between the plates rather than involving the dentition directly. While occlusal plane effects do not represent skeletal change, they significantly contribute to the anterior correction we obtain with various appliances. It is, of course, difficult to quantify this effect. 

Finally, the subjective evaluation method could be criticised as it was confined to three professionals. It is again interesting that the relatively small objective differences translated into the 27% reduction in the perceived need for surgery, particularly given the minor skeletal differences. This finding may reflect our professional bias as orthodontists – we often focus on the occlusion – perhaps myopically! It would be nice to see whether a group of lay raters reach similar conclusions after reviewing the clinical records.

What can we conclude?

In 11- to 14-year-olds with skeletal III discrepancy and multiple teeth in crossbite, BAMP may offer a reduced subjective need for orthognathic surgery. However, while BAMP may lead to a significant short-term skeletal effect, this impact is diluted over 3 years with the primary lasting effect being an improvement in overjet.