Digital caliper

The digital calliper is used to determine a possible ankyloglossia (1), to measure the maxilla (2), or to measure the upper and lower indicator lines (3). Further explanation and proper execution of these measurements are taught during the advanced courses of OMFT.info.

The caliper is already equipped with a battery, so it is ready for use. First remove the plastic to allow the battery to make contact. In addition to the battery that is already in the instrument, an extra battery is included.

1. Determine a possible ankyloglossia
To determine whether there is limited tongue mobility due to a tongue tie that is too high and/or too short, the function of the free tongue part and the function of the dorsum can be examined. In that case, you measure with the digital caliper:

• Maximum Mouth Opening (MMO)
• Maximum Mouth Opening with the tip of the tongue placed against the Incisive Papilla (MMO PI)
• ​Interincisal Distance with the entire tongue suctioned flat against the palate (ID)

Then the following calculations can be made:

TRMR-TIP = Tongue Range of Motion Ratio from the Tip of the tongue on the Incisal Papilla.
Function of the free part of the tongue: (MMO PI : MMO × 100)

• 80% = above average
• 50% – 80% = average
• < 50% = below average
• ​< 25% = significantly below average

TRMR-LPS = Tongue Range of Motion Ratio Lingual Palatal Suction.
Function of the tongue dorsum: (ID : MMO × 100)

• 60% = above average
• 30% – 60% = average
• < 30% = below average
• ​< 5% = significantly below average

The three above measurements (a, b, and c) are demonstrated consecutively in this video.

2. Measuring the maxilla
The digital calliper can also be used to measure the Trans Palatal Width (TPW), also known as the McNamara width. This is the distance between the palatal cusp of tooth 16 and tooth 26. This measurement indicates whether there is sufficient space in the maxilla for the permanent teeth. The values below indicate the desired TPW in different (age) phases. If the TPW is below these values, there is insufficient space in the upper jaw (typically caused by a low resting tongue posture).

• Mixed dentition: TPW > 30 mm
• Second mixed dentition phase (12–16 years): TPW ≥ 37 mm
• ​Adult: TPW (J. Mew) 44 mm

Another method to determine whether the maxilla is too narrow after measuring with the digital calliper is to add the number 24 to the child’s age (up to around 14 years). The resulting number (24 + a 10-year-old child = 34) is the TPW the child should ideally have.

3. Measuring the upper and lower indicator lines
The digital calliper can also be used to measure the upper and lower indicator lines of the jaws, which provide an indication of the growth direction of the jaws.