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Impact of customized lingual appliances compared to labial appliances

Question about lingual appliances

Could you tell exactly if lisping experienced at first disappears or not?
If yes, how long does it take?


It’s an excellent question and I had already considered a blog page on this subject. You give me this opportunity.

Few studies exist on “lisping” (sigmatism) caused by lingual fixed appliances (Incognito™, Harmony®…), but I saw a few studies conducted on the subject and a colleague of mine and friend from Boston, Dr David Driss, presented an excellent research during the 2011 annual scientific meeting (Annual meeting) of the Angle East Society of Orthodontist. A few months later, in the same year, the AJODO published a similar study from the University of Toronto.

Rapid palatal expander

This recent study conducted at the University of Toronto, “Impact of a rapid palatal expander on speech articulation” by Stevens K., Bressmann T., Gong S-G and Tompson B., analyzes the disruptive effect on speech and the subsequent adaptation following the installation of a rapid palatal expander in the mouth.

Their study was conducted on 22 individuals. Speech recordings were performed during 6 observation times: before the installation of the expander, after the installation in the mouth, during expansion, during retention, after the expander was removed and 4 weeks after removal. Recordings included the reading of 35 sentences of text among which 3 sentences were retained for analysis.

Results show that when the expander is inserted, speech articulation is altered. With time, speech articulation improves and goes back to normal when the expander is removed.

The forming vowel /i/ goes back to normal during the treatment with the expander. The articulation of sibilant consonants /s/ and /∫/ is deformed during the installation of the expander, but the frequency of these sounds in Hertz (Hz) goes back to normal during the treatment.

Some patients adapt better than others to their expander.

In conclusion, the installation of an expander affects negatively speech articulation, but patients adapt with time. The adaptation time varies from 2 to 4 weeks.

Incognito™ lingual appliances and conventional labial appliances

A study compares the impact of conventional labial fixed appliances to customized lingual appliances (Incognito™). 30 individuals received labial fixed appliances and 30 other individuals had Incognito™ fixed appliances. The duration of the experimental observation period was 3 months and 3 observation times were done during the treatment: at 1 week, at 1 month and at 3 months. The individuals used an analog visual scale of 100 mm to evaluate oral discomfort, chewing, speech disorder and social functioning (effect on social life).

Comparison of impact of labial versus lingual fixed appliances-Dr Chamberland orthodontist in Quebec CityThere is a significant difference between the changes observed with lingual appliances versus labial appliances on:

1- Dietary change;

2- Difficulty in swallowing;

3- Leisure activities;

4- Avoidance of conversation;

5- Avoidance eat-out;

6- Social speech disturbance;

7- Self speech disturbance;

8- Reduction of tongue space;

9- Change in tongue position.

In other words, it’s worse with lingual appliances than with labial appliances.


Oral discomfort Incognito appliance versus conventional labial appliance-Dr Chamberland orthodontist in Quebec City

Comparison between oral discomfort caused by Incognito™ lingual appliances and conventional labial appliances.

The perception of greater pain with lingual appliances is explained by the reduction of tongue space and the change in tongue position (items 8 and 9). However, after 3 months, there is no difference of perception between both groups.

Speech disturbance-Dr Chamberland orthodontist in Quebec City

Comparison between speech disturbance caused by Incognito™ lingual appliances and conventional labial appliances.

More specifically, the evolution of speech disturbance is clearly shown on the above figure. Speech disturbance with lingual appliances is more important, as much socially as from autoperception, at 1 week, 4 weeks and 3 months. The reduction of speech disturbance during the observation period is explained by adaptation.

In conclusion, there are impacts caused by wearing either labial or lingual fixed appliances. These impacts decrease with time. In other words, the patient gets used to them.

Patients treated with lingual appliances experience a more important impact initially than those treated with labial appliances. Both groups of patients have similar levels of satisfaction of their appliances.

It is thus important to inform patients well about the different treatment methods to minimize the unpleasant consequences caused by wearing the appliance. Consequence like: “if I had known…”.


Stevens K., Bressmann T., Gong S-G et Tompson B, Impact of a rapid palatal expander on speech articulation, AJODO 2011;140:e67-e75.

Wu A, McGrath C, Wong RW, WiechmannD and Rabiee AB, Comparison of oral impacts experienced by patients treated with labial or customized lingual fixed orthodontic appliances, AJODO 2011;139:784-90

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