A TEM analysis of tissue channels in normal and orthodontically tensioned rat molar periodontal ligament.

This investigation tested the hypotheses that (1) tissue channels (TC) exist in normal periodontal ligament (PDL) between the cervical and apical zones, and (2) orthodontic tooth tension alters their number and distribution within this region. A continuous 1.0 N tension was applied to the maxillary first molar for 30 minutes and ionic tracer precipitate used to analyse TC in unstained TEM sections. In normal PDL, the mean number of tissue channels (MNTC) was 0.10 +/- 0.01/micron 2 in the 0-2-microns PDL zone extending from the vessel wall, 0.09 +/- 0.02/micron 2 in the 2-4-microns zone, and 0.06 +/- 0.02/micron 2 in the 4-6 microns zone. Differences were not statistically significant. Extrusion increased the MNTC to 0.28 +/- 0.01/micron 2, 0.20 +/- 0.02/micron 2, and 0.16 +/- 0.02/micron 2, in the 0-2-, 2-4- and 4-6-microns zones, respectively (P < 0.001). For normal PDL in the tooth, middle and bone circumferential thirds the TC distribution were even. In the tensioned PDL, TC in the circumferential tooth third (0.20 +/- 0.02/micron 2), middle third (0.19 +/- 0.01/micron 2), and bone third (0.23 +/- 0.02/micron 2) increased significantly (P < 0.001) from normal ligament. The total increase in experimental MNTC was associated mainly with the post-capillary-sized venules, venous capillaries, and arterial capillaries. With progression from the cervical to apical regions the MNTC in control PDL failed to significantly fit a quadratic regression pattern. By contrast, tensioned PDL showed a marked regression pattern (P < 0.001) indicating a reduction in MNTC with vertical depth.(ABSTRACT TRUNCATED AT 250 WORDS)