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Objective: To compare the extent and time course of alveolar bone loss and osteoclast activation in two murine models of periodontal disease: molar ligation and Porphyromonas gingivalis (P. gingivalis) oral inoculation., Methods: A split-mouth design was applied to two groups of mice (C57BL6, 6-8 weeks old, n=24 in both groups), resulting in four treatment groups: (1) Control group: unligated upper right 2nd molars receiving CMC only, (2)Ligature group: ligation of a 9-0 suture around the upper left 2nd molar, (3) P. gingivalis group: unligated upper right 2nd molar receiving P. gingivalis challenge only, (4)Ligature+P.gingivalis group: ligation of the upper left 2nd molar in combination with oral inoculation with 109 colony-forming units(CFU) P. gingivalis. Alveolar bone loss was measured as the cementoenamel junction and alveolar bone crest (CEJ-ABC) distance. In the study, 48 C57BL6 mice were designed and treated as described above, and osteoclasts were counted on histological sections following tartrate-resistant acid phosphatase (TRAP) staining and counts were normalized to alveolar bone surface distance. Then 36 C57BL6 mice were investigated, of which 30 were ligated a 9-0 silk ligature around the 2nd molar in the left maxillary quadrant and 6 were not ligated. After ligation for 1 week, the ligatures in 12 mice were taken off for either 1 week or 2 weeks. The CEJ-ABC distance of the 6 mice without ligation was baseline. The CEJ-ABC distances were measured and analyzed. The data were analyzed with one-way ANOVA., Results: Molar ligation induced marked alveolar bone loss after 3, 6, 9 and 12 weeks [(0.16±0.04) mm, (0.16±0.02) mm, (0.18±0.03) mm, (0.17±0.02) mm], vs. corresponding controls [(0.09±0.03)mm,(0.10±0.01)mm,(0.12±0.04)mm,(0.12±0.01)mm] and P. gingivalis group [(0.09±0.03)mm, (0.12±0.01)mm,(0.12±0.02)mm,(0.10±0.01)mm], P<0.05. Combined treatment with molar ligation and P. gingivalis did not further increase the CEJ-ABC distance. Evidence for osteoclast activation was found one day after molar ligation, and TRAP-positive cell numbers peaked on day 3 (12±4 vs. control 2±2, P<0.01). After taking off ligature following ligation for 2 weeks, it showed significantly regrowth of alveolar bone compared with that before removal of the ligature on day 7 [(0.07±0.02)mm vs. (0.13±0.01)mm, P<0.01]., Conclusion: Molar ligation is a rapid and effective way to induce periodontal bone loss in mice. Osteoclast activation occurs within 24 hours of ligature placement, and the extent of bone loss well exceeds that of the P.gingivalis-induced bone loss. Removing ligature after periodontal disease might help bone regeneration by regrowth of the alveolar bone.

Objective: To investigate the stress distribution of post and core restored maxillary premolar with reduced alveolar bone support., Methods: Cone-beam CT based 3D finite element models of post and core restored maxillary premolar were established, with 3 different alveolar bone support. Group I (control) simulated a clinical situation without horizontal bone loss. In group II, a horizontal bone loss of 25% and in group III of 50% were simulated. Both cast-metal post and prefabricated-fiber post were used. The influence of the alveolar bone height was investigated through three-dimensional elastic finite element static analyses by comparison of the resulting stress field, under vertical and oblique load. Local stress measures were introduced to allow for the assessment of tooth fracture., Results: The von Mises stress value (vertical/oblique) on dentin were measured as follows: group I-gold=22.570/66.354, group I-fiber=16.480/58.103; group II-gold=27.690/95.192, group II-fiber=18.260/68.452; group III-gold=37.363/135.010, group III-fiber=24.291/110.170., Conclusion: For post and core restored teeth with horizontal bone loss, the alveolar bone support may affect the stress distribution under vertical and oblique load. Reduction of the alveolar bone support may lead to severely increased stress concentration in the root dentin.

Objective: 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., Methods: 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., Results: 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., Conclusion: 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.

By three-dimensional finite element analysis,the present research inquired about the stress on the surface of alveolar bone of mandibular incisor with different level of bone loss under different loadings. For the mandibular incisor without bone loss, the maximums of the von Mises stress under vertical and 15 degree oblique loading were 13.171 and 14.315 MPa respectively, both located in the apical region, and the lingual displacement of the tooth were 0.056 and 0.197mm respectively; under 30 degree oblique loading, the maximum of the von Mises stress was 15.262 MPa, located not only in the apical region but also on the crest, and the lingual displacement of the tooth was 0.324 mm. However, when vertical loading was applied on the mandibular incisor with half of the alveolar bone loss, the maximum of the stress increased significantly, located in the apical regions. And under oblique loadings, the value of the stress of this model increased dramatically,being three to five times over that of mandibular incisor without bone loss. Both of them concentrated on the crest. The scope of its distribution decreased from area to point. The significant lingual displacement happened, amounting to 2.850 mm. So when the loss of alveolar bone is not less than half,occlusal adjustment and splinting should be considered during the initial treatment of periodontal disease in order to avoid the significant change of the stress and alleviate the damage to the periodontal tissues.

Objective: To investigate the influence of surface potentials of tooth hard tissue on bone remodeling., Methods: After insured the surface potentials of human extracted teeth with electrochemical methods, teeth sections and artificial hydroxyapatite were implanted into 25 rabbits' tibiae. The rabbits were sacrificed at 1, 2, 4, 6 and 8 weeks after implantation, respectively. The bone regeneration was compared between opposite two sides (cathode side and anode side) of tooth sections using hematoxylin-eosin (HE) staining, tartrate-resistant acid phosphatase (TRAP) activity detecting and tetracycline tracing method., Results: Resorption lacunae was seen in the tibiae facing to the enamel anode and new bone density in the implant bed near the cathode of tooth samples was much higher than that near the anode, while the number of TRAP positive cells near the cathode was smaller than that near the anode (P < 0.01). The fluorescent area of tetracycline tracing near the cathode was larger than that near the anode (P < 0.05)., Conclusions: The cathode of tooth hard tissue (cementum) could improve or trigger new bone formation, while the other side, anode (enamel), could improve the bone resorption. This study suggests that tooth hard tissue's electrochemical characteristic might affect the remodeling of alveolar bone, and tooth supraeruption and the alveolar bone loss after tooth extraction might result from the redundant or lack of root electrochemical stimulation to bone.