Absolute and relative growth of the rat craniofacial skeleton

Growth of the craniofacial region involves a mosaic of intramembranous and endochondral growth sites that grow at varying rates and mature at different times.

The goal of this study was to compare absolute and relative growth of the craniofacial skeleton in wild-type Lewis rats to measures of somatic growth.

Lateral and dorsoventral X-rays of the head as well as the hindlimb were obtained weekly from 4 to 9 weeks of age. The X-rays were scanned, digitized, and selected linear distances were measured between points. Multilevel statistical models were used to generate absolute growth curves.

Although most growth curves were linear, several were quadratic (exhibiting a deceleration with age), and one displayed a third-order curve. Considerable variation in relative maturity was evident at the first time interval, ranging from 42% of mature (9 week) size (weight) to 97% of mature size (cranial width). Tibial length and body weight were less mature than most, but not all, craniofacial measures. With one exception (bizygomatic width), width measures were relatively more mature than vertical or depth measures. Vertical measures tended to be among the least mature of the craniofacial dimensions. Among the depth (length) measurements, there was a trend of higher maturity for cranial vault/cranial base measures and lower maturity for facial measures.

The wide spectrum of relative and absolute growth potentials demonstrated in this study indicate that the rodent craniofacial complex is amenable to testing the hypothesis that a component's response potential is related to its growth potential.