The relationship between eruption and length of mandibular incisors in young rats.
BACKGROUND
Rat incisor teeth exhibit continuous growth, hence they have frequently been used to study the eruption process. The aim of our study was to investigate changes in the eruption rate of impeded and unimpeded rat incisors and to determine if any relationship existed between eruption rate and length of the clinical crown.


METHODS
An image analysis technique was used to measure the length of the mandibular incisors of 23 young female Sprague-Dawley rats, aged 7 to 8 weeks. Over a four-week period, the mandibular right incisors of the 11 rats in the experimental group were shortened every two or three days. Another group of 12 rats served as the control.


RESULTS
The mean unimpeded eruption rate was 1.0+/-0.1 mm/day, while the impeded eruption rate was 0.6+/-0.1 mm/day. On day 2, the eruption rate of the unimpeded mandibular incisors accelerated to 163.9% when compared to the controls. The impeded mandibular incisors increased in length by 8.8% and 12.1% for the experimental and control groups respectively. An inverse relationship was identified between the eruption rate and the length of clinical crown of the impeded mandibular incisors, while the unimpeded eruption rate was unrelated to the length difference between the left and right incisors if the length difference exceeded 0.5 mm after accelerated eruption.


CONCLUSIONS
It was found that the mandibular incisors of young rats need to be shortened every two days in order to study unimpeded tooth eruption, and the shorter the tooth is cut the higher the rate of eruption.
Law
Kwok-Tung
KT
Paediatric Dentistry, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR.
Lee
Chun-Kei
CK
King
Nigel M
NM
Rabie
Abou-Bakr M
AB
D000818:Animals; D001835:Body Weight; D005260:Female; D007180:Incisor / Q000502:physiology*; D008334:Mandible / Q000502:physiology*; D008953:Models, Anatomic; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014078:Tooth Eruption