Most removable braces consist of a plastic body (PMMA) and some retaining clips and active components made out of steel wire. The plastic body is normally positioned on the inside of the teeth, so that a large part of the gum in the upper jaw is covered by plastic and in the lower jaw, the inside of the teeth and gum are also covered by plastic. For stability reasons, the plastic base needs to be of a certain thickness so it takes up the same amount of space that would normally be occupied by the tongue.
This is the reason why most removable braces have a huge effect on speech. In particular, the so-called double braces such as the Ativator or the Bionator can often lead to slurred speech. The effect is sometimes so severe that removable braces simply cannot be worn at school. But children also want their freedom in the afternoons so that they can play games and sports in an unimpaired way – so removable braces also pose a problem here and so are not generally worn.
Scientific studies have established that these are the reasons why removable braces can only be worn at night because this is the only time when any kind of speech impediment just does not matter. But just wearing a brace at night will have little or no effect so much of the treatment with removable braces actually fails.
On the other hand, fixed braces do not normally affect speech in any way at all, because they are usually attached to the outside of the teeth and therefore cannot hinder the function of the tongue. Some fixed dental aids such as the palatal bar or gum extension appliances are actually fixed to the palate area but leave the front of the gums free which is the most important thing as far as speech is concerned. Even these devices do not normally impair the speech.
In some sensitive people the fixed brace and bracket that is attached to the inside of the teeth (Lingual technique) can hinder the formation of certain sounds. But in most patients this normally disappears after a few weeks once they have got used to it.