Collagen fiber orientation affects osteoclastic resorption

The bone surrounding the teeth is constantly remodeled throughout life, particularly during tooth movement and following tooth loss. Alveolar bone proper contains many highly oriented extrinsic fibers, but whether their orientation affects resorption is unknown. To determine if it does, we selected sperm whale cementum to provide large anisotropic substrates resembling extrinsic fiber bone. Slices cut either perpendicular or parallel to the extrinsic fiber axis were cultured for 24 hours with pre-hatched chick osteoclasts. Resorption pit areas and volumes were measured by video-rate reflection confocal microscopic mapping. Pits in the perpendicular group were smaller in area and were deeper than those in the parallel group (median values, 402 micron2 and 572 micron2, n > 950, p < 0.0001; volume/area 5.37 microm and 4.58 microm); volume differences only just reached significance (2,137 micron3 and 2,554 micron3, p < 0.05). These results show that the fiber orientation within a substrate can profoundly influence the shape of resorption lacunae. This pattern of resorption may help in the maintenance of an optimally functioning attachment of periodontal ligament fibers to alveolar bone.