The trajectory of human prenatal enamel growth slows through the trimesters

Typically, human fetal growth rates change

through the trimesters depending on the tissue

type. Linear growth in long bones peaks in the

second trimester and increases in fetal weight are

greatest in the third. Human deciduous tooth

enamel starts to develop at different times in

utero, commencing with the central incisor and

lastly with the second molar. But whether the

trajectory of prenatal enamel growth remains the

same for each tooth type is poorly understood.

Here, I use histological methods to determine

how long it takes a 250?m (in 25?m increments)

thick layer of prenatal enamel to form in

maxillary incisors, canines, and molars (n=88). I

also calculate prenatal extension rates to assess

how quickly these teeth grow in height. I relate

the trajectory of growth in thickness and height

to the trimesters. Findings are tested on

mandibular lateral incisors and second molars

(n=33).

Results show that the growth trajectory

changes through the trimesters. Incisor enamel

initiated early in the second trimester and 250?m

formed over 52-57 days. Canines and second

molars initiated closer to birth and required 60-

64 days to form the same depth of enamel.

Although initial extension rates were positively

correlated with crown height within each tooth

class (incisors, r=0.714; molars, r=0.676), they

were significantly greater (p<0.005) in incisors

when compared to the taller canines and second

molars. These findings provide evidence that

initial prenatal enamel growth is faster in incisors

than all other deciduous tooth types. I infer this

is related to their early postnatal eruption.