The periodontium exists for the purpose of supporting teeth during their function and it depends on the stimulation it receives from the function for preservation of its structure. Therefore, a constant state of balance always exists between the periodontal structures and the external forces. Alveolar bone undergoes constant physiologic
remodeling in response to external forces, particularly occlusal forces. Bone is removed from areas where it is no longer needed and added to areas where it is needed. The socket wall reflects the responsiveness to the external forces.
Osteoblasts and newly formed osteoid line the areas of tension, whereas lines of compression are lined by
osteoclasts. The forces also influence the number, density, and alignment of
trabeculae inside the bone. The bony trabeculae are aligned in the path of tensile and compressive stresses to provide maximum resistance to occlusal forces with a minimum of bone substance. When forces are increased, the bony trabeculae also increase in number and thickness and bone is added to the external surfaces. The periodontal ligament depends on stimulation provided by function to preserve its structure. Within physiologic limits the PDL can accommodate increased function by increasing its width. Forces that exceed the adaptive capacity of the periodontium produce injury called
trauma from occlusion. When occlusal forces are reduced the PDL atrophies, appearing thinned. This phenomenon is called
disuse atrophy. ==References==