A longitudinal study on timing and velocity of rat molar eruption: Timing of rat molar eruption

Rat molar eruption and occlusion data were compiled from several studies but several inconsistencies were found, rendering the planning of eruptional studies difficult and imprecise. Our aim was to measure eruption and occlusion days, as well as eruption velocity, in the upper and lower three molars from infancy to end of adolescence in the rat. A total of 19 male and female Wistar rats were scanned daily by micro-computed tomography (CT) from day 15 to 70. We measured the eruption of all maxillary and mandibular molars with reference points at the hard palate and mandibular canal at three stages: pre-emergent, pre-occlusal, and functional. Statistical analysis was performed with a mixed-model analysis of variance (ANOVA) and a Sidak post hoc test. The first molar erupts on average on day 17, the second molar on day 20, and the third molar on day 33. The eruption velocity of the first molar was the highest at 90.9 microns/day (standard error (se) = 12.80), followed by the second molar at 65.9 microns/day (se = 5.80), and the lowest was the third at 47.0 microns/day (se = 3.28), (p