Swords Orthodontics
17 Main St, Swords, Co Dublin, Ireland

8 Reasons Why Orthodontic Twin Blocks Might Not Work

When Twin Blocks Don’t Work

Twin Blocks are probably the most widely used functional orthodontic appliance in the world, if not the most popular (which they probably are). A functional appliance is one that modifies the way that the mouth works (functions), and uses the muscles around the mouth to achieve a particular orthodontic effect.

Orthodontists like twin blocks because they can correct big overjets (where the top teeth stick out beyond the lower ones more than normal) and they do it fast! They also can be used to widen out the top jaw at the same time, and they can hold the space for erupting teeth.

Twin blocks wouldn’t have got to this state of popularity if they weren’t regularly effective, but sometimes you don’t see the results you want. At Swords Orthodontics, and I think most orthodontists would agree, this is generally down to a small number of things:

  1. Lack of co-operation by the patient
  2. Patient started twin blocks too late
  3. Patient started twin blocks too early
  4. Poor twin block design
  5. Unfavourable facial skeleton to begin with
  6. Unfavourable facial growth during treatment
  7. Unknown reasons (idiopathic)
  8. Some combination of the above


Of these, number 1, poor patient co-operation is by far the most common. They are among the easiest of functional orthodontic appliances to wear, but they will take some getting used to and some commitment. They don’t work when they are out of the mouth, they don’t work if a patient flips them around in their mouth, they don’t work if the patient postures their jaw (holds it in a particular position) so that the lower block is below the top block – it should be in front of the top block.

I advise my patients to wear their twin blocks 23 hours a day, accepting that there will be some time out of the mouth for eating and cleaning. If a patient is playing contact sport or swimming then another few hours a week would be fine, but that’s about it. Night time wear isn’t going to be enough to get the results you want.

Too early or too late?

Ideally twin blocks work best when a patient hits the maximum speed of their growth spurt. If you start them too early, there won’t be much growth yet. The growth will probably happen sooner or later, but the patient might be bored with them and less likely to co-operate. If you start too late, the growth has largely happened or has slowed down, so the twin blocks are less effective. They really aren’t meant for adults, but your jaws may well have reached their adult size well before you can vote! Your orthodontist can assess your growth potential and advise you if twin blocks are likely to be a benefit.

Poor Twin Block Design

This is really a matter for the orthodontist and the person who makes their twin blocks. In a well-designed, well-made block, it should grip the teeth well and be almost automatic that the patient closes their mouth into the ideal position to correct the overjet. If it’s easy for a patient to bite the wrong way, or the blocks don’t push their teeth forward far enough, then the block may need adjusted.

An experienced orthodontist with a good relationship with their brace-making support team is unlikely to have these problems.

Unfavourable skeletal pattern

Twin blocks are a versatile appliance – you can use them in a variety of orthodontic problems, but certain facial skeletal shapes respond better than others to twin block treatment. Your orthodontist will probably assess this at the start of the treatment, but may still go ahead with twin blocks if they are the simplest option at that stage.

Unfavourable skeletal growth

Some days you get a hunch for it, and some days it surprises you, but it does happen that twin blocks don’t deliver the results because the face doesn’t really grow the way you expect. I have seen this in patients with facial growth disorders and previous fractures to the jaws. There are still things we can do to get a good result for them overall, but like the previous example of an unfavourable facial skeletal pattern, trying the twin blocks is still a simple approach to try for some improvement in the way the teeth meet.

Unknown reasons

Idiopathic is just a fancy word for situations where you don’t have an explanation for what you see. Usually poor twin block results are explained by one of the scenarios above, so it’s more likely that the patient wasn’t telling me the truth about their twin block co-operation (though I can usually tell the truth from signs in the mouth), or I just haven’t figured out the reason.

Sometimes these things happen in combination. A patient might get fed up if we start too early and lose co-operation, for instance.

There are alternative appliances to twin blocks and there are alternative approaches to solving the problems that twin blocks solve, but they all have their own advantages and disadvantages. If you don’t think your twin blocks are working, talk to your orthodontist.

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