Functional appliances: the growth peak is the window that cannot be recovered

Functional appliances work by positioning the mandible forward and holding it there, with the aim of stimulating condylar growth in the growing patient.

Efficacy depends decisively on when one intervenes. The useful period coincides with the pubertal growth peak, and assessing it requires indicators of skeletal maturation rather than age.

Assessment of the cervical vertebrae on the lateral cephalogram is the most practical method, because it uses an examination already taken for orthodontic diagnosis.

Treatment begun too early obliges the patient to wear the appliance for years with limited benefit; begun after the peak, it produces predominantly dental effects.

The extent of the skeletal effect is the point on which the literature has tempered early expectations. Systematic reviews indicate a genuine increase in mandibular length, but a modest one relative to what was hoped.

A substantial part of the observed correction derives from dentoalveolar movement: retroclination of the upper incisors and proclination of the lower ones. This is not a failure, but it should be communicated honestly to parents.

The Twin Block is the most widespread removable device, owing to its effectiveness and to the fact that the patient can speak and eat while wearing it, which improves compliance over traditional monoblocs.

Its limitation is compliance: it requires many hours of wear a day, and a patient who wears it only at night achieves little.

The Herbst is fixed and solves the compliance problem, because it works around the clock without the patient being able to remove it. It suits poorly compliant adolescents and cases where available time is short.

In exchange it demands more maintenance: telescopic arms can disconnect or break, and unscheduled repairs are frequent in the early months.

Parental expectation must be managed at the outset. The request is almost always to correct the profile, and the correct message is that the appliance improves the relationship between the arches and has an effect on the profile, but does not alter facial structure as surgery would.

In cases with severe skeletal discrepancy, functional treatment may improve the situation without resolving it, and orthognathic surgery once growth is complete remains an option to mention from the beginning.

In summary: timing relative to the growth peak determines the result more than the device chosen, the skeletal effect is real but modest, the Twin Block depends on compliance while the Herbst circumvents it at the cost of more maintenance.