Periodontal ligament/Bone 1

PDL and bone  (H&E stain)

This slide is of a tooth in situ with the periodontal ligament showing an area of bone surface where there is bone deposition (area 1), a region of bone resorption (area 2) and a region showing a reversal line (area 3).

The periodontal ligament is the soft connective tissue that attaches the tooth to the bone. It is highly cellular with numerous fibroblasts (occupying up to 50% of the connective tissue volume). The direction of the collagen fibres can be deduced from the orientation of these cells. The ligament also has numerous capillaries which occupy a significant proportion of the periodontal space and which may link to blood spaces in the surrounding alveolar bone via Volkmann's canals

The bone surface in area 1 where there is bone deposition shows a layer of osteoblasts. A lighter-stained layer of osteoid is evident between the osteoblasts and the mineralised bone (red arrow).  Also evident in area 1 is the layer of epithelial rests of Malassez running adjacent to the cementum surface of  the root (blue arrow). The bone surface in area 2 (diametrically opposite area 1) is undergoing resorption in a number of sites. The cells responsible for this are osteoclasts which are large multinucleated cells which often stain with a more orange/pink hue than surrounding cells. They sit in (Howship's) resorption lacunae.

Area 3 has a prominent reversal line. This is a 'fossilised' line in the bone that marks a previous resorbing bone surface that has subsequently had new bone deposited on it.