Twin Block Braces: How Long, What It Feels Like, Cost

A twin block is a removable appliance used for children and teenagers whose upper front teeth stick out a long way in front of the lower teeth. The usual reason for that overjet is a lower jaw that sits further back than the upper jaw. During the growth spurt, the twin block holds the lower jaw in a forward position, and the muscles, joints and teeth adapt to the new bite. It is one of the most widely used functional appliances in UK orthodontics.

Who is a twin block for?

A twin block is usually recommended when:

• The overjet is large, often more than 6 mm
• The lower jaw is set back (a Class II pattern)
• The child is growing, typically around 10 to 14 years old
• The child and parents are ready to commit to full-time wear

Reducing a large overjet early also lowers the risk of the upper front teeth being chipped or knocked out in a fall, which is one of the main reasons it is often treated before the teeth are straightened.

Compare typical fees for every treatment, in central and outer London, in our London Invisalign and braces price index.

How does a twin block work?

The appliance is made up of two plates, one upper and one lower, each with a bite block on the back teeth. The blocks meet at an angle so that the only comfortable way to close is with the lower jaw posture forward. Worn constantly, this encourages:

• Changes in how the lower jaw grows during the growth spurt
• The lower front teeth tipping forward slightly
• The upper front teeth moving back
• The muscles adapting to the new jaw position

Upper plates often include a small screw to widen the upper arch as the bite corrects.

What does a twin block feel like?

The first week is the hardest. Expect:

• A full, bulky feeling and a lisp for the first few days
• Extra saliva
• Aching teeth and jaw muscles as you adapt to the forward position
• Difficulty eating at first; most children start eating with it in after one to two weeks

Speech usually returns to normal within one to two weeks. Reading aloud and talking with the appliance in speeds up adaptation. Our guide does Invisalign hurt? covers general tips for orthodontic discomfort that apply here too.

How long does a twin block take to work?

Many children see the overjet reduce within a few months. By 9 to 12 months, most have a corrected bite. Results depend on growth and, above all, wear: an appliance left in a drawer does not work. Children who wear it as directed usually finish this phase on time.

What happens after the twin block?

Once the jaw correction is achieved, the appliance is often worn at night for a few months to hold the result. Fixed braces are then used to straighten the teeth, close spaces and fine-tune the bite, typically for 12 to 18 months. Our guides to types of braces and braces colours are useful at this stage. After braces, retainers keep the result in place; see retainer costs.

Twin block vs other options

Adults cannot benefit from growth modification, so a large overjet in an adult is treated with braces or aligners and sometimes surgery. See our guide to overbite treatment for adults.

Is a twin block the right appliance for my child?

The best results come when three things line up: a large overjet caused mainly by a set-back lower jaw, active growth, and a child who is motivated to wear the appliance. If any of these is missing, another approach may be better. For example, a teenager who has finished growing will get less jaw change, and a child who is unlikely to wear a removable appliance may do better with a fixed functional appliance. We discuss these trade-offs openly with parents and children at the assessment.

How much do twin block braces cost in London?

Twin blocks are usually priced as part of the whole treatment rather than on their own. Typical private fees in London start from around £1,200 (outer) to £2,180 (central) for an interceptive phase and around £2,500 to £3,420 for children's fixed braces. Our braces cost in London and the UK page lists all fees. Children with a large overjet are often eligible for NHS orthodontic treatment, but waiting lists can be long, which is why some families choose private care.

Eating, cleaning and sport with a twin block

• Brush the appliance twice a day with a soft brush and cold water
• Brush your teeth before putting it back in
• Avoid sticky and very hard foods, and sugary drinks
• Take it out for contact sports and wear a mouthguard if advised
• Always store it in its case; most lost appliances are wrapped in a napkin at lunchtime

Common problems and fixes

Tips for the first two weeks

• Wear the appliance as much as possible from day one, including while sleeping; the more it is in, the faster you adapt
• Practise speaking by reading aloud for ten minutes a day
• Start with soft foods such as pasta, rice, eggs and yoghurt, then build up
• Use a mild pain reliever if the teeth or jaw ache, following the instructions on the pack
• Keep a chart of hours worn; many children find it motivating
• Tell school if they need to know, for example for sports or lunchtimes

Will the result last?

Correcting an overjet during growth tends to be stable when the bite is finished well with braces and retainers are worn as instructed. Some relapse of the overjet is possible, which is why the night-time support phase matters. Teeth also continue to shift slightly throughout life, so retainers are recommended long term.

Start with an assessment

The decision to use a twin block depends on the size of the overjet, the jaw pattern and the stage of growth, which an orthodontist will check with photos, a scan and an X-ray. Request a consultation and tell us your child's age.

Frequently asked questions

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