Wild boar versus domestic pig-Deciphering of crown growth in porcine second molars

Based on the previously established periodicity of enamel growth marks, we reconstructed crown growth parameters of mandibular second molars from two wild boar and two domestic pigs of the Linderöd breed. Body weight gain and progression of dental development were markedly faster in the domestic pigs than the wild boar. While the final crown dimensions of the M₂ did not differ between domestic pigs and wild boar, mean crown formation time (CFT) of this tooth was considerably shorter in the domestic pigs (162 days) than in the wild boar (205 days). The difference in CFT was mainly attributable to a higher enamel extension rate (EER) in the domestic pig. Generally, EER was highest in the cuspalmost deciles of the length of the enamel-dentine-junction and markedly dropped in cervical direction, with lowest values occurring in the cervicalmost decile. In consequence, the cuspal half of the M₂ crown was formed about three times faster than the cervical half. In contrast to the EER, no marked difference in daily enamel secretion rate (DSR) was recorded between domestic pigs and wild boar. The duration of enamel matrix apposition as well as linear enamel thickness in corresponding crown portions was only slightly lower in the domestic pigs than the wild boar. Thus, the earlier completion of M₂ crown growth in the domestic pig was mainly achieved by a higher EER and not by an increased DSR. The more rapid recruitment of secretory ameloblasts in the course of molar crown formation of domestic pigs compared to wild boar is considered a side-effect of the selection for rapid body growth during pig domestication.