In vitro measurement of regional differences in the mechanical properties of the periodontal ligament in the rat mandibular incisor.

Mechanical testing was performed in various regions of the ligament at a velocity of intrusive loading of 5 mm/min. The perimeters of the lingual cementum and socket wall and the sectional area of the ligament were measured radiographically. Load-deformation curves were transformed into stress-strain curves using the area and width of the lingual part of the ligament. The mechanical properties of the ligament differed markedly along the long axis of the incisor; mechanical measures from the load-deformation and stress-strain curves decreased gradually from the incisal towards the basal regions. It is suggested that these regional differences in mechanical properties were much more marked than those in teeth of limited growth or in other connective tissues, and that the nature of the collagen fibres, together with surrounding cells, ground substance and blood vessels, may be important in determining such differences.