CranioCalc

Calculators

Jaw Index

Quantifies micrognathia in newborns from the alveolar overjet and the maxillary and mandibular arch lengths.

mm

Distance between the most anterior points of the upper and lower alveolar ridges.

mm

Tragion to subnasale to tragion, measured over the skin with a tape.

mm

Tragion to pogonion to tragion, measured over the skin with a tape.

Method

Jaw index = alveolar overjet × (maxillary arch ÷ mandibular arch)

A larger index means a more retruded, smaller mandible relative to the maxilla. There is no validated diagnostic cutoff. In the original report, healthy newborns had a mean of 4.2 (range 2.4 to 6) and infants with Robin sequence a mean of 15.3. A later study of 52 healthy newborns found a mean of 2.1 (SD 0.64) with a different overjet instrument, so values depend on measurement technique.

The index is most useful for documenting severity and tracking mandibular growth over time in the same infant, measured the same way each time.

Sources: van der Haven I, Mulder JW, van der Wal KG, et al. The jaw index: new guide defining micrognathia in newborns. Cleft Palate Craniofac J. 1997;34(3):240–241. Mermans JF, Ghasemi SM, Lissenberg-Witte BI, Don Griot JPW. The reproducibility of the jaw index in the measurement of healthy newborns. Cleft Palate Craniofac J. 2020;57(5):574–580. doi:10.1177/1055665619885726.

–
Enter all three measurements