Rhythmic incremental growth lines occur in dental hard tissues of vertebrates, and dentinogenesis in rodent incisors is suggested to be controlled by the 24-hr circadian clock. Rodent incisors continue to grow throughout the animal's life; however, similar to human teeth, rodent molars stop growing after crown formation. This similarity suggests that the mouse molar is an excellent model to understand the molecular mechanisms underlying growth of human teeth. However, not much is known about the rhythmic dentinogenesis in mouse molars. Here, we investigated the incremental growth lines in mouse molar dentin using tetracycline as the growth marker. The incremental growth lines were observed to be generated at approximately 8-hr intervals in wild-type mice housed under 12:12 hr light-dark conditions. Moreover, the 8-hr rhythmic increments persisted in the wild-type and Bmal1-/- mice housed in constant darkness, where Bmal1-/- mice become behaviorally arrhythmic. These results revealed that the dentinogenesis in mouse molars underlie the ultradian rhythms with around 8-hr periodicity. Further, the circadian clock does not seem to be involved in this process, providing new insight into the mechanisms involved in the tooth growth.

中文翻译：

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小鼠磨牙牙本质中的增量生长线代表8小时的Ultradian节律。

在脊椎动物的牙齿硬组织中出现节律性的生长线，啮齿动物切牙的牙本质发生被认为是由24小时生物钟控制的。啮齿动物的门齿在动物的整个生命中都在不断增长。然而，与人类牙齿类似，啮齿动物的磨牙在冠形成后停止生长。这种相似性表明，小鼠磨牙是了解人类牙齿生长的分子机制的绝佳模型。但是，关于小鼠磨牙的节律性牙本质发生的了解还很少。在这里，我们使用四环素作为生长标记物，研究了小鼠磨牙牙本质中的增量生长线。在饲养于12:12小时的明暗条件下的野生型小鼠中，观察到以大约8小时的间隔生成了增量生长线。此外，在持续处于黑暗中的野生型和Bmal1-/-小鼠中，8小时的节律性持续存在，而Bmal1-/-小鼠在行为上有心律失常。这些结果表明，在小鼠磨牙中的牙本质发生是大约8小时周期的超节奏的基础。此外，昼夜节律时钟似乎不参与该过程，从而提供了对牙齿生长所涉及的机制的新见解。