Although it is believed that odontoclasts, which mediated root resorption of deciduous teeth, possess common properties to osteoclasts, these regulatory mechanisms differ from osteoclastic bone resorption. It is well established that calcitonin receptor is an important osteoclast marker and that calcitonin is a potent inhibitory hormone of osteoclastic bone resorption. However, the presence and function of calcitonin receptors in human odontoclasts are still controversial. We summarize the physiological properties and differentiation mechanisms of odontoclasts, and the effects of calcitonin on root resorption, including our recent results using human odontoclasts and periodontal ligament cells freshly isolated from deciduous tooth roots.