Functional appliances at North Sydney orthodontics

At North Sydney Orthodontics we prefer to treat severe Class II malocclusion (increased overjet / buck teeth) using growth modification techniques (dento-facial orthopedics). Because the treatment advances the position of the lower jaw which is usually wide across the molars at the back and gets narrower towards the front. To make the dental arch widths match once the overjet is corrected the upper dental arch usually requires expansion especially across the premolar widths.

Twin Block Therapy

The Twin Block appliance was invented by British Orthodontist William Clark and is now regarded as one of the most successful functional appliance designs in the world. The success is attributable to their ease of use, being removable and made in two parts to permit normal mouth movement and eating. The appliance can be designed to improve the upper arch width and project the lower jaw forward simultaneously. Twin block therapy normally lasts approximately 9-24 months and is usually followed by fixed braces to get a perfect result. Functional appliances rely on favorable jaw growth for their success, and this treatment method is successful in over 75% of cases. Treatment is typically started between the ages of 9 to 12 years to obtain the best results. This appliance must be worn 20 hours per day for success. If there is poor cooperation or progress is not favorable due to adverse growth other treatment options may need to be considered in addition to fixed braces such as tooth extractions, jaw surgery or the use of a Herbst type appliance. Otherwise an incomplete correction of the dental relationships may need to be accepted.

'Herbst' Appliance

This appliance is a pair of pistons attached to a fixed appliance that force the lower jaw into the corrected position. The correction arises through a combination of dental tipping and orthopaedic change. We use this appliance in a slightly older age group (13-16 years). Rapid palatal expansion is often required to obtain the necessary increase in palatal width if this appliance is used. This appliance does not require activation by the patient and is not removable (a so-called non compliance appliance) so is useful where the cooperation of the patient is doubtful e.g. where previous twin block therapy was unsuccessful. Note the appliance shown is the Sabbah appliance which is the version of the Herbst appliance used in North Sydney Orthodontics.