[Study of the timing of tooth movement after repair of alveolar bone defects by rabbit BMSCs combined with beta-TCP].

PURPOSE: To investigate the effect of tooth movement at different time after repair of alveolar bone defects with tissue engineering bone constructed by rabbit bone marrow mesenchymal stem cells (BMSCs) and beta-tricalcium phosphate (ß-TCP). METHODS: Alveolar bone defect (6 mm×4 mm×8 mm) was made on the right side of 40 New Zealand rabbits, which was filled with tissue engineering bone constructed by BMSCs and ß-TCP as experimental sides. Tooth extraction on the other side was performed as control. The mandibular second molars in both sides were moved mesially 2, 4, 8 and 12 weeks after surgery. The specimens were taken 4 weeks after exertion. The distance of mandibular second molar moved was measured. The periodontal tissues were observed after H-E staining. TRAP staining was performed and osteoclasts were counted in the periodontal tissues on the pressure side. BMP-2 immunohistochemical staining was used to observe the average optical density of periodontal tissue on tension side. The results were analyzed with SAS 8.0 software package. RESULTS: The distance of tooth movement, the amount of TRAP positive cells and the optical density of BMP-2 in the experimental side of the 2-week and 4-week groups were all significantly lower than those in the control side, while there was no significant difference between the 8-week and 12-week groups. CONCLUSIONS: Eight weeks after repair of alveolar bone defect with rabbit BMSCs and ß-TCP is an appropriate time for orthodontic tooth movement.

[Study on periodontal responses on the compression side during early tooth movement into alveolar defect regenerated by a tissue engineering bone].

PURPOSE: To explore periodontal responses on the compression side during early tooth movement into alveolar defect regenerated by bone marrow mesenchymal stem cells (BMSCs) and porous granulated beta-tricalcium phosphate（ß-TCP） scaffolds. METHODS: Thirty New Zealand rabbits were used to establish bilateral mandibular defective alveolar bone model by extracting the mandibular first molars and expanding the sockets. The right mandibular alveolar defects were filled with a construct of ß-TCP scaffolds combined with BMSCs as experimental group. The left alveolar defects were repaired by ß-TCP scaffolds alone as control group. Eight weeks later, 6 rabbits were sacrificed to evaluate osteogenesis effect. The other rabbits were loaded orthodontic force to move the bilateral second molars forward for 4 weeks. Six rabbits in each group were sacrificed at 1, 2, 3, and 4 week after orthodontic tooth movement (OTM). The distance of OTM was measured, and the status of periodontal tissues was observed by H-E staining. The number of osteoclasts on the compression side of tooth was counted by tartrate-resistant acid phosphatase histochemistry. The results were compared between groups using SPSS 19.0 software package. RESULTS: After 8 weeks of bone grafting, the osteogenesis effect of the experimental group was better than the control group. The OTM distance in the experimental area was higher than that in the control area. At 2, 3 and 4 week of OTM, the number of osteoclasts in the experimental group was significantly higher than that in the control group. CONCLUSIONS: A tissue-engineered complex with ß-TCP scaffolds and BMSCs could well repair the alveolar bone defect. When the adjacent tooth moved into regenerated area, the new periodontal tissue had an active response, promoting to accelerate tooth movement.

Characteristics of intrabony nerve canals in mandibular interforaminal region by using cone-beam computed tomography and a recommendation of safe zone for implant and bone harvesting.

BACKGROUND: Cone-beam computed tomography can accurately show anatomic structure of intrabony nerve canals in mandibular interforaminal region. PURPOSE: The aim was to evaluate the characteristics of intrabony nerve canals in mandibular interforaminal region by using cone-beam computed tomography (CBCT) and determine a safe zone for implant and bone harvesting. MATERIALS AND METHODS: Hemimandibles (824) CBCT images were obtained. The length of the anterior loop (AL), the length and diameter of the mandibular incisive canal (MIC) and its spatial distance in various landmarks were measured. RESULTS: The prevalence of the AL was 93.57%, and the MIC was 97.33%. The mean lengths of the anterior extension of the anterior loop (aAL), caudal extension of the anterior loop (cAL) and the MIC were 2.53 ± 1.27 mm, 6.04 ± 1.66 mm, 9.97 ± 5.15 mm, respectively. The MIC was closer to buccal border and inferior margin of mandible. The length of the AL and diameter of the MIC varied with gender. CONCLUSIONS: The safe zone recommended for implant surgery is 4 mm anterior and 8 mm inferior to the mental foramen, and 10 mm above the inferior margin of mandible. The chin bone should be harvested at least 10 mm below the tooth apices along with a limited depth of 4 mm.