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. Twen ty rats were injected intraperitoneally with tetracycline at weight-adjuste d doses. Mesio-distal sections of the first mandibular molar regions were p repared. The 60 to 80 mu m sections were examined by fluoromicroscopy using reflected light. Visible lines of fluorescence could be seen in the radicu lar dentin and the cementum, Each line corresponded to one injection. It wa s possible to define two periods: the first, from day 22 to day 59, corresp onded to the immature tooth; the second, from day 59 to day 101, to the mat ure tooth. During period 1, the mean speed of radicular lengthening by ceme ntal and dentinal apposition was 23.95 mu m/24 h, The increase in mesio-dis tal diameter by cemental apposition was 12.15 mu m/24 h. During period 2, t he mean speed of radicular lengthening by cemental apposition was 8.23 mu m /24 h, It is therefore possible to use this method to conduct quantitative and qualitative evaluations of apical morphogenesis by cemental and dentina l apposition.