The base and crown of these are composed of dentine separated by an uncalcified layer and they are replaced at intervals.
ðə bˈeɪs ænd kɹˈaʊn ʌv ðiːz ɑːɹ kəmpˈoʊzd ʌv dˈɛntiːn sˈɛpɚɹˌeɪɾᵻd baɪ ɐn ʌŋkˈælsᵻfˌaɪd lˈeɪɚ ænd ðeɪ ɑːɹ ɹᵻplˈeɪst æɾ ˈɪntɚvəlz.