Back to Basics 3: Functional appliance treatment during the growth spurt

This is the third blog on craniofacial growth by Martyn Cobourne.  He discusses the evidence relating to mandibular growth during functional appliance treatment. In particular, if this treatment coincides with the growth spurt, do we get more growth?

Functinoal appliances and growth

It is generally accepted that functional appliances are most effective when used in the growing child. Furthermore, longitudinal growth studies have suggested that a peak in mandibular growth does occur. In addition, it takes place simultaneously or just after the adolescent growth spurt (or, more specifically, peak height velocity, PHV). Therefore, timing functional appliance therapy to coincide with PHV might be expected to accelerate and achieve greater overall mandibular growth compared to treatment undertaken outside this window of time. This is desirable because class II malocclusion is often characterized by mandibular deficiency.

• However, the onset, duration, and intensity of the mandibular growth spurt is associated with significant individual variation, and precise correlations with PHV are far from established.

These points notwithstanding, some orthodontists have embraced the prediction of the adolescent growth spurt as part of their routine clinical practice for managing class II cases with functional appliances. We discussed the relative merits and reliability of predicting the growth spurt previously. Here we discuss current evidence relating to treatment effects with functional appliances concerning growth status in class II patients.

What does research tell us?

A high-quality systematic review of this subject area has been carried out (Perinetti et al., 2015ab), but the findings need to be interpreted with caution – primarily because the source data is heterogenous and at high risk of bias.

• The heterogeneity arises from the different methods the original studies have used. These include different maturational indices of skeletal maturity; other functional appliance systems; outcomes evaluated for the functional appliance phase only or for comprehensive treatment; and using different cephalometric variables to establish changes in mandibular dimensions.
• There is a high risk of bias because the available studies are generally retrospective or non-randomized prospective. In addition, they often lack a control group or use control data from historical growth studies (children born several generations earlier, with less overall growth and different rates of maturation through secular differences).
• Notably, the use of retrospective data in this area of research is a particular issue. This is because sample gathering will inevitably be associated with positive case selection – those with successful outcomes, invariably meaning that those exhibiting favourable growth predominate within the experimental groups. However, in mitigation, it is ethically difficult to delay functional appliance treatment to patients identified as being in the pubertal growth spurt as part of the randomization for any RCT.

What can we conclude?

All these points notwithstanding, the data for removable functional appliances suggest that patients treated in the pubertal period attain around 2 mm more annualized growth in total mandibular unit length and ramus height compared to pre-pubertal patients (Perinetti et al., 2015a).

In addition, studies of fixed functional appliances suggest an increase of around 1.8 mm mandibular unit length in pubertal patients compared to post-pubertal during comprehensive treatment (Perinetti et al., 2015b).

Given the relatively small differences that have been found (around 2 mm of linear mandibular unit length increase that does not consider growth direction). In addition to the potential bias of these data (and therefore over-estimating this effect size), an obvious clinical benefit of undertaking functional appliance treatment timed specifically to coincide with PHV would seem unproven. Indeed, delaying treatment for a pre-pubertal child in the late mixed dentition on this basis would not seem to be in their best interest.

Starting functional appliance treatment during the transition from late mixed to early permanent dentitions (and the younger the child is, the better) – utilizing growth and allowing easy passage from the functional to fixed appliance phase in the early permanent dentition would seem to be the most pragmatic approach.