The tongue is a strong and flexible muscle, and it must be able to move in various directions to manipulate food and allow for the enunciation of certain sounds. It's the length of the tongue web, also known as the lingual frenulum, that controls this flexibility.
Some babies are born with a lingual frenulum that is shorter than normal. This limits the extent to which the tongue can be flexible, sometimes preventing it from extending past the lower line of teeth.
The free tongue refers to the length of the tongue from the tip to the base where the lingual frenulum connects with it. Normally, the free tongue is longer than 16 millimeters (mm). The degree to which the free tongue is shorter than this helps identify the extent of a baby's ankyloglossia.
- Class I is when the free tongue is between 12 and 16 mm long
- Class II is between 8 and 11 mm
- Classes III and IV are more severe, referring to cases where the free tongue is between 3 and 7 mm or less than 3 mm long, respectively