[Effects of the loss of alveolar bone on the areas of periodontal ligament, mechanical fulcrum and fracture resistance of root and post-core system].
To assess the effects of loss of alveolar bone on the areas of periodontal ligament (PL), mechanical fulcrum and fracture resistance of root and post-core system. One hundred and eight simulated roots in the same length, taper and diameter were made of polymethylmethacrylate and were divided into 13 groups. Then the wax patterns of post-cores were casted and cemented. Each specimen was embedded in acrylic resin in accordance with different loss of alveolar bone and different mechanical fulcrum. Base on the anatomic and physiological special features of the periodontal tissues, three mechanical methods were designed. The compress test was run by the speed of 1 mm/min and the fracture resistance was recorded. The areas of periodontal ligament were measured and calculated. When the loss of alveolar bone and the mechanical fulcrum were 0 mm and 12/12 group, 1 mm and 11/12 group, 2 mm and 10/12 group, 3 mm and 9/12 group, 3.5 mm and 8.5/12 group, 4 mm and 8/12 group, 4.5 mm and 7.5/12 group, 5 mm and 7/12 group,5. 5 mm and 6.5/12 group, 6 mm and 6/ 12 group, 7 mm and 5/12 group, 8 mm and 4/12 group, 9 mm and 3/12 group, the means of the areas of PL (mm2) and fracture resistance (N) were 178.95 and 232. 90 +/- 25. 93, 159. 64 and 195.58 +/- 12.46, 141.18 and 173.92 +/- 13.51, 123.27 and 154.00 +/- 11.74, 106.14 and 123.25 +/- 14.29, 89.67 and 96.86 +/- 6. 20, 73.90 and 59.14 +/- 7.28, 58.82 and 52.52 +/- 5. 82, 44.44 and 45.90 +/- 7.40, 30.76 and 58.60 +/- 6.63 (mm, N). The linear correlations were found between the percentage of the loss of alveolar bone and surplus areas of PL, the loss of alveolar bone and the fracture resistance of root and post-core system, the percentage of the areas of PL and the fracture resistance of root and post-core system, the distance of the fulcrum and the percentage of the loss of alveolar bone. The loss of alveolar bone caused the decrease in areas of PL, the dessent of mechanical fulcrum, and the diminution of the fracture resistance of root and post-core system.