Tooth extrusion effects on microvessel volumes, endothelial areas, and fenestrae in molar apical periodontal ligament.

Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used for transmission electron microscopic quantification of their effects on the periodontal ligament vessels. In this study, a continuous extrusive load of 1.0 N, applied to the rat maxillary first molar for 30 minutes, produced statistically significant changes in the microvascular bed of the tensioned apical periodontal ligament. The mean vascular volume, as a percentage of apical periodontal ligament volume, increased (p less than 0.01) in postcapillary-sized venules, venous capillaries, arterial capillaries, and terminal arterioles from 16.6% to 22.3%, 2.0% to 2.7%, 0.4% to 1.0%, and 1.0% to 2.5%, respectively. Mean endothelial surface area per cubic millimeter of apical periodontal ligament tissue increased (p less than 0.01) in postcapillary-sized venules from 16.8 to 25.7 x 10(6) microns 2/mm3, in venous capillaries from 3.0 to 4.8 x 10(6) microns 2/mm3, and in arterial capillaries from 0.7 to 1.5 x 10(6) microns 2/mm3. The number of fenestrae per square micron of endothelium in postcapillary-sized venules, venous capillaries, and arterial capillaries showed a mean increase from 0.02 to 0.07, 0.11 to 0.31, and 0.02 to 0.21 fenestrae/microns 2, respectively (p less than 0.01). Fenestrae per cubic millimeter of periodontal ligament tissue also demonstrated a statistically significant increase with extrusion (p less than 0.01) in postcapillary-sized venules from 0.37 to 1.55 x 10(6) fenestrae/mm3, in venous capillaries from 0.27 to 1.34 x 10(6) fenestrae/mm3, and in arterial capillaries from 0.02 to 0.22 x 10(6) fenestrae/mm3. Fenestrae in control vessels had a mean diameter of 54.2 +/- 0.56 nm (SE) compared with 61.1 +/- 0.7 nm in tensioned vessels (p less than 0.01). This investigation demonstrates multiple ultrastructural changes in the periodontal ligament microvascular bed after tooth extrusion.