--- title: "Functional Appliances for Children UK | Twin Block & Herbst" url: https://virtualconsultant.online/functional-appliances description: "Functional appliances such as twin blocks and Herbst appliances use a growing child's own jaw growth to correct bite problems before fixed braces." updated: 2026-09-04T00:00:00Z publisher: Virtual Consultant Online --- Children Jaw Correction Twin Block Growth Class II # Functional Appliances for Children UK Functional appliances use the forces of jaw growth to correct bite problems in children before all adult teeth come through. This page explains what functional appliances do, which types are most commonly used in the UK, what the treatment involves, and how it differs from standard braces. [Start Photo Assessment](https://virtualconsultant.online/evaluations/quote) [Children's Orthodontics](https://virtualconsultant.online/childrens-orthodontics) ## What a functional appliance does Functional appliances are orthodontic devices that harness the natural growth of the jaws to correct the bite. Rather than moving individual teeth (as fixed braces do), functional appliances reposition the lower jaw — holding it in a more forward position to encourage the jaw bones to adapt and grow towards the new position. They are most effective during the pubertal growth spurt, typically ages 10 to 14, when jaw growth is at its most active. Once growth slows, the same level of correction becomes much harder to achieve without surgery. ## What conditions are treated with functional appliances Functional appliances are primarily used for class II malocclusion — a bite where the upper teeth and jaw protrude significantly in front of the lower jaw, often associated with a large overjet (the upper front teeth sticking out). This is sometimes colloquially called an overbite or 'buck teeth'. They may also be used in some class III presentations where the lower jaw is behind the upper but growth modification is possible. Not all class II bites require functional appliance treatment — the severity, growth stage, and patient cooperation are all factors in the recommendation. ## The Twin Block appliance The Twin Block is the most widely used functional appliance in the UK. It consists of two separate removable parts — one fitting over the upper teeth and one over the lower — with angled acrylic blocks that connect when the jaws close, holding the lower jaw in a forward position. The Twin Block is worn full time (including eating) and is generally required for 9 to 18 months. It is bulky initially and affects speech, particularly in the first few weeks. Patient compliance is critical — the appliance only works when worn. ## The Herbst appliance The Herbst appliance is a fixed functional device — it is attached to the teeth rather than being removable. Metal tubes and rods connect the upper and lower arches and hold the lower jaw in a forward position continuously. Because it is not removable, it does not rely on patient compliance for wear time, which can make it more predictable in motivated-but-forgetful patients. The Herbst appliance is less commonly used in the UK than the Twin Block but is well-established. It is more expensive to fit and adjust and cannot be removed by the patient. ## What happens after functional appliance treatment After the active phase of functional appliance treatment, patients typically move into a second phase of treatment with fixed braces to align individual teeth and fine-tune the bite. The jaw position achieved by the functional appliance is maintained by the subsequent braces and final retainers. Most patients require fixed braces for 12 to 18 months after completing functional appliance treatment. The total treatment time including both phases is typically two to three years. ## Compliance requirements and realistic expectations Removable functional appliances (particularly the Twin Block) require consistent full-time wear to be effective — the evidence base for functional appliances assumes compliant wear of 20 or more hours per day. Results from non-compliant wear are significantly reduced. Parents and patients should discuss compliance expectations honestly before starting. Speech is affected initially for most patients. The adjustment period is typically two to four weeks. Functional appliances are not painful in the way that tightened fixed braces can be, but initial jaw soreness from the repositioned bite is common. ## NHS and private options for functional appliances Functional appliance treatment for eligible children is available on the NHS where a class II malocclusion meets the IOTN threshold for treatment need. NHS provision for functional appliances varies by region, and waiting lists for NHS orthodontic treatment can be lengthy. Private treatment is available without the NHS threshold requirement, allowing earlier treatment or access in areas with limited NHS provision. Private functional appliance courses typically cost £1,500 to £3,000, with subsequent fixed braces as a separate cost. ## Useful related pages [Children's orthodontics](https://virtualconsultant.online/childrens-orthodontics) [Phased orthodontics](https://virtualconsultant.online/phased-orthodontics) [Early orthodontic treatment](https://virtualconsultant.online/early-orthodontic-treatment) [Parents orthodontics guide](https://virtualconsultant.online/parents-orthodontics) [NHS treatment qualification](https://virtualconsultant.online/about/do-i-qualify-for-nhs-treatment) This guide is for general information only. It is not a diagnosis, treatment plan, or substitute for advice from a registered dentist or orthodontist. ### Compare next steps [Orthodontist Near Me](https://virtualconsultant.online/locations/orthodontic-treatment-near-me) [Clear Aligners Near Me](https://virtualconsultant.online/treatments/clear-aligners-near-me) [Invisalign Near Me](https://virtualconsultant.online/locations/invisalign-provider-near-me) [Browse Locations](https://virtualconsultant.online/locations) ### Ready for a clearer starting point? Upload guided photos and receive an indication of likely treatment options and pricing before booking appointments. [Get an Online Quote](https://virtualconsultant.online/evaluations/quote) ### Frequently Asked Questions How old does my child need to be for a functional appliance? Functional appliances are most effective during the pubertal growth spurt, typically between ages 10 and 14, though the ideal timing depends on when your child's peak growth phase occurs. Treatment started too early (before significant jaw growth has begun) or too late (when growth is largely complete) achieves less correction. Your orthodontist will assess growth stage through jaw development, hand and wrist x-rays in some cases, and pubertal development indicators. How long does a child need to wear a Twin Block? Most children wear a Twin Block for 9 to 18 months before moving into the fixed brace phase of treatment. The exact duration depends on how much jaw correction is needed and how compliant the patient is with wear. Full-time wear (including meals) is required for the treatment to be effective within the expected timeframe. Incomplete wear extends the functional phase or reduces the result. Does a functional appliance hurt? Functional appliances are generally not painful in the same way as tightened fixed braces, but there is usually jaw soreness and muscle fatigue in the first one to two weeks as the jaw adjusts to the new position. Speech is also affected initially — most patients adapt within two to four weeks. The appliance itself does not cause pain to individual teeth the way bracket adjustments do. Can a functional appliance avoid the need for jaw surgery? In growing patients, functional appliances can reduce the severity of a jaw discrepancy to a level that can be managed with braces alone. In patients who begin treatment after growth has largely completed, jaw surgery (orthognathic surgery) combined with braces may be the only way to achieve a significant change in jaw position. Early treatment — when growth is still active — provides the best chance of avoiding surgical correction in moderate-to-severe class II cases. What is the difference between a functional appliance and a palate expander? A palate expander widens the upper arch (the palate), addressing a narrow upper jaw and crossbite. A functional appliance repositions the lower jaw to correct the relationship between the upper and lower jaws. They address different problems and are sometimes used together — an expander to widen the upper arch first, followed by a functional appliance to address the lower jaw position. Will my child need braces after a functional appliance? In the majority of cases, yes. Functional appliances correct the jaw relationship but do not fully align individual teeth. A subsequent course of fixed braces, typically 12 to 18 months, is usually needed to align the teeth and refine the bite following functional appliance treatment. Your orthodontist should outline the expected full two-phase treatment plan, including both phases' approximate duration and cost, before you commit to starting. Explore your options Quick links Not sure where to start? Use these quick links to explore orthodontic treatments, typical costs, and helpful guides that explain what different options involve. 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Upload guided photos and get a tailored recommendation for your teeth and bite. [Start Photo Assessment](https://virtualconsultant.online/evaluations/quote) [Find an Orthodontist](https://virtualconsultant.online/locations) Citation details Title Functional Appliances for Children UK | Twin Block & Herbst Publisher Virtual Consultant Online Published 2026-06-26 Updated 2026-09-04 URL [https://staging.virtualconsultant.online/functional-appliances](https://staging.virtualconsultant.online/functional-appliances)