Rate and growth pattern of radicular apical third tissue apposition in tetracycline-labeled rats

The aim of this in vivo study was to find a way to conduct qualitative and quantitative evaluations of radicular apical third apposition in rats. Twenty rats were injected intraperitoneally with tetracycline at weight-adjusted doses. Mesio-distal sections of the first mandibular molar regions were prepared. The 60 to 80 microns sections were examined by fluoromicroscopy using reflected light. Visible lines of fluorescence could be seen in the radicular dentin and the cementum. Each line corresponded to one injection. It was possible to define two periods: the first, from day 22 to day 59, corresponded to the immature tooth; the second, from day 59 to day 101, to the mature tooth. During period 1, the mean speed of radicular lengthening by cemental and dentinal apposition was 23.95 microns/24 h. The increase in mesio-distal diameter by cemental apposition was 12.15 microns/24 h. During period 2, the mean speed of radicular lengthening by cemental apposition was 8.23 microns/24 h. It is therefore possible to use this method to conduct quantitative and qualitative evaluations of apical morphogenesis by cemental and dentinal apposition.