3 Dimensional effects of protraction for Class III early treatment.

A few weeks ago, I shared an interesting study that examined the two-dimensional protraction headgear treatment for Class III malocclusion. The authors have now released another paper that evaluates the 3 dimensional changes associated with this treatment. It’s worth having a look at it.

In the earlier paper, the authors reported their RCT, in which they randomised patients having hybrid hyrax treatment to facemask protraction or mandibular bone-anchored support. They concluded that there were no differences between the two treatments. They have produced this additional paper.

Progress in Orthodontic published the paper.

What did they ask?

They did this study to 

“Compare the 5 year 3D skeletal effects of hybrid herbst and facemask (FM group) with hybrid hyrax and mandibular bone anchorage (MP group)”.

What did they do?

I have outlined the methods of this study before. But if you reading this as a stand alone post, here are the methods.

What did they do?

They did a single centre 2 arm parallel randomised trial with a 1:1 allocation.

The PICO was

Participants

Mixed dentition children with Class III malocclusion. This was defined anterior crossbites or end to end incisor relationships at the start of treatment.

Intervention

Hybrid Hyrax anchored by two miniscrews in the anterior palate and bands to the first molars.  They used the Alternate RME and constriction protocol (Alt-RAMEC).  In this group facemask treatment was used until the patients achieved a positive overjet of at least 2mm or had been treated for six monghs. This group was called the FM group.

Comparision

The operator treated these patients the HH and Alt-RAMEC treatment. In addition, the clinician fitted a mentoplate. This was fixed with two to four screws to the mandible via a small gingival incisision. This procedure was done using a general anaesthetic.  The patient then wore intermaxillary elastics. The endpoint of treatment was after 6 months or an overjet greater than 2mm. This group was called the MP group.

Outcome

The primary outcomes were 3D volumetric changes of the upper and lower jaws at the T1 and T2 post-treatment time points. They obtained this from serial CBCTs.

After the phase I treatment was completed, they treated all the patients with fixed appliances.

The team gathered data at the beginning of treatment (T0), one year after treatment (T1), and five years after treatment (T2).

They did a sample size calculation that showed they needed 12 patients per group.

They used a pre-prepared randomisation with allocation concealment in sealed envelopes. An intermediary allocated the patients. The clinician played no part in this process.

As with all orthodontic trials, it was not possible to blind either the clinician or the patient. However, they analysed the data blind.

What did they find?

28 patients took part in the study. There were no marked differences between the groups at the start of treatment. At the end of the five years, 24 patients remained in the trial.

They produced a fair amount of 3D data. These were the most important findings.

• Facemask and mandibular anchorage treatments were similar for maxillary advancement. Total maxillary changes for both groups totalled 1.4mm.
• Both treatments effectively controlled mandibular growth. However, they cannot conclude this with certainty because they did not compare the treatment effects to an untreated control.

They concluded 

“Both treatment protocols demonstrated comparable long term skeletal effects in Class III correction”.

What did I think?

My comments on the methodology are the same as those in my last blog post. This was a good small trial.  

Importantly, the results from this analysis of 3D data aligned with those from the 2D data. This reinforces the finding that there was no advantage to using bone anchorage with plates compared to utilising a facemark.

Nevertheless, this is a thin slice of a small study. This paper is very similar to the 2D publication. 

The authors provided a justification for the 3D outcome, noting that it addresses the limitations of lateral and frontal cephalograms, particularly regarding magnification errors. However, in an earlier paper, they also defended the 2D approach by highlighting that vertical and intermaxillary changes are challenging to quantify using 3D analysis.  

I cannot help thinking that if they had reported the 2D and 3D findings in one paper, the single publication would have been stronger and easier to interpret.

If I set this concern aside, this paper helps us understand the effects of different treatments for Class III malocclusion. Importantly, it shows that we can get the same results from the same patient sample using 2D and 3D analysis.

It is just a shame about the team’s publication strategy.

Now you have read this blog

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