Differences in odontoblastic function between first and second permanent molars

Objectives: Research has shown that in small-toothed humans the first molar (M1) is larger than the second (M2) with thinner enamel, but few detailed studies have been carried out to investigate the extent of other differences between these teeth. The aim of this study was to determine if any difference occur in odontoblast function between the M1 and M2. Methods: Dentine height of paired M1 and M2 permanent mandibular molars was examined in 31 individuals from a Chalcolithic population in Northern Israel using radiographs taken parallel to the long axis of the teeth. In order to differentiate between primary and secondary dentine apposition in the M2, the data were divided into 2 sub-samples: 1) pairs where M1 roots were complete while the M2 roots were incomplete and 2) pairs where M1 and M2 had completed roots. Results: Results showed that dentin height in M2 was significantly lower than that of M1 both for pairs with M2 root completed (P=0.0001) and for pairs with M2 roots incomplete (P=0.0104). A significant positive correlation was found between dentin height of M1 compared to M2 in both sub-samples (P<0.05). Based on regression equations the amount of dentin apposition in M2 was approximately half than that of the M1 in both sub-samples. No significant differences were found between the M1 and M2 in crown height suggesting that this factor did not affect dentine height. Conclusion: The results indicate that the rate of dentin formation differs between the mandibular M1 and M2 with the M2 having a slower apposition rate.