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

Abstract

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 < 0.001). On average, the pre-occlusal phase had the highest velocity at 97.2 microns/day (se = 1.72), the pre-emergent was lower at 84.9 (se = 2.29), and the functional was the lowest at 21.7 (se = 0.45), ( p < 0.001). The eruption rate decreased from the first to third molar and was also different between phases: the pre-occlusal phase had the highest rate, closely followed by the pre-emergent phase while the functional eruption rate was significantly lower than the other phases.

Notch Coordinates Periodontal Ligament Maturation through Regulating Lamin A

“…We selected postnatal days 18 (P18, preocclusion eruption) and 28 (P28, 1 wk after occlusion establishment) of the Wistar rat's second root pair of the first lower molar as the study models. The eruption stage was confirmed by daily in vivo micro-CT imaging based on our previous study (Denes et al 2018). Histological analysis and micro-CT confirmed that the root development of the P18 tooth was at the initial elongation stage, while at P28, root development reached near completion (Fig.…”

“…The Wistar rat and tooth eruption stages were determined based on data of a previous study (Denes et al 2018) and verified by micro-computed tomography (CT) scans. The work was approved by the ethics committee of animal research of the Canton of Geneva (n° GE/72/15).…”

Core Matrisome Protein Signature During Periodontal Ligament Maturation From Pre-occlusal Eruption to Occlusal Function

“…Based on our previous study (Denes et al, 2018), we hypothesized that the rapid change in eruption velocity seen during the transition from pre-occlusal to functional eruption may be in response to the appearance of occlusal forces. Occlusal loading influences the PDL width (Denes et al, 2013), structure (Mcculloch et al, 2000), and recovery (Terespolsky et al, 2002;Mine et al, 2005), therefore we examined differential expression during this transition to functional eruption with its first masticatory forces.…”

“…The animals were killed by CO 2 at three time points, according to the rat molar eruption stages: daily in vivo micro-CT imaging was used to identify the pre-occlusal eruption (P18), initial occlusal contact (P21) and 1-week after occlusion (P28) with a technique previously described (Denes et al, 2018) (Supplementary Figure S1). The incisors were extracted, the mandibles were dissected and the immediately frozen with PrestoChill (Milestone R ) in cryo-embedding at −40 • C and subsequently stored at −80 • C.…”

“…Tooth movement has been shown to induce remodeling of the PDL through simultaneous synthesis and degradation of collagen by fibroblasts (Ten Cate et al, 1976), but little is known about the changes occurring during tooth eruption. During the transition from pre-occlusal to functional eruption the tooth reaches initial occlusal contact and eruption slows down (Denes et al, 2018).…”