[Relationship between tissular structure and strength of fresh bull periodontal ligament].

OBJECTIVE: To study the relationship between the width and the content of fiber in peridontal ligament (PDL) and the strength of peridontal membrane. METHODS: Fresh mandible of bull was obtained to prepare for a 5 mm x 2 mm x 10 mm cuboid including teeth, peridontal membrane, and alveolar bone. The width of the PDL was measured under a stereomicroseope. Pull stress was loaded on the test piece until it broke. The stress-strain curve was recorded. The broken ends of the PDL was dyed with siriue to adalyze the content of fiber. RESULTS: The relationship between the width of the PDL and the maximum stress was expressed as Y = 9.786e(-3.6693x). The relationship between the width of the PDL and the physiological ultimate stress was expressed as Y = e((2.188(-3.953)x). The relationship between the percentage of fiber and maximum stress was expressed as Y = 20.788-0.755x + 0.007x(2). The relationship between the percentage of fiber and the physiological ultimate stress was expressed as Y = 1.39e(-14) x x(7.666). The initial physiological stress was 0.28 N/mm2. CONCLUSION: The strength of PDL increases with the decrease of PDL width and increase of fiber content.

[A structural mechanics study with human maxillary premolar].

OBJECTIVE: To evaluate the stress distribution and offset of dental and periodontal tissues imposed by changes in inner diameter of pulp cavity. METHODS: Six models of maxillary second bicuspid tooth with different inner diameter of pulp cavity were established, including: (1) calcificated pulp without pulp chamberi (2) mostly calcificated pulp chamber with inward reduction of 0. 5 mm in normal pulp cavity; (3) initially calcificated pulp chamber with inward reduction of 0.25 mm in normal pulp cavity; (4) normal pulp cavity; (5) initially absorbed pulp chamber with outward expansion of 0.25 mm in normal pulp cavity; (6) mostly absorbed pulp chamber with outward expansion of 0.5 mm in normal pulp cavity. Vertical and oblique forces with 160 N were loaded on the central fossa, respectively, in order to calculate the stress distribution of dental and periodontal tissues and the maximum incipient offset of the teeth. RESULTS: With loaded vertical and oblique forces on central fossa, increased stress distribution of periodontal tissues and maximum incipient offset of teeth were found in all of the models, which increased with the increase of pulp cavity. CONCLUSION: The change in inner diameter of pulp cavity has an impact on the stress distribution of periodontal tissues and maximum incipient offset of the second upper bicuspid teeth.