BACKGROUND:Large bone defect caused by various reasons has been a difficult problem in clinical practice. To establish a standard experimental animal model of critical bone defects has vital significance for evaluating the efficacy of bone osteogenesis using various materials and techniques.
OBJECTIVE:To establish the rabbit model of parietal critical bone defects and to determine the diameter of the critical defects of parietal bone in limited time.
METHODS:10 New Zealand white rabbits were selected. The skul seam was treated as the boundary. Four ful-thickness round defects of bone in the parietal bone were made, with diameters of 4, 5, 6 and 7 mm, so as to establish rabbit models of parietal critical bone defects. Gross anatomical observation, X-ray and cone beam CT were used to determine the bone density in the new bone defect area. The healing of bone defects was evaluated by histological examination.
RESULTS AND CONCLUSION:After 12 weeks, the 4 mm group showed high bone healing capacity significantly, and part of the bone bridge had been connected completely. Quantitative analysis of bone mineral density revealed that gray value at defect site and trabecular bone area at the same magnification and the same vision in the 4 mm group were significantly higher than the other three groups (P<0.001). Only a smal amount of new bone in the periphery of bone defects appeared in the 5, 6 and 7 mm groups. The center of defect site was mainly fil ed by fibrous connective tissue. The results confirmed that this study successful y established rabbit models of parietal critical bone defects. During the 12 weeks of observation, bone defects with a diameter of ≥ 5 mm could not be self-healed, which was conformed to the criteria of critical defects of bone, and could be used as a reference value for critical parietal bone defects of a rabbit.

Objective To compare the osteogenesis effect of platelet-rich fibrin (PRF) and platelet-rich plasma (PRP) and investigate the methods of repairing bone defect with PRF.Methods Four defects measuring 7 mm in diameter were made in the parietal bone of 16 New Zealand white rabbits.The defects named A,B,C,and D and were filled with PRF,PRF-mixed Bio-Oss (BO),PRP-mixed BO,and PRP separately.Every four rabbits were sacrificed at postoperative 2,4,8,and 12 weeks and defects were examined grossly,radiographically,and histologically.Besides,bone mineral density and bone trabecular area were determined and expressed as gray-scale values.Results Newly regenerated bone appeared at all defect areas at postoperative 2 weeks.Thereafter,more bone formations were observed over time and area B demonstrated the best bone healing followed by area C,A,and D in succession.Bone trabecular area in areas A,B,C,and D was 10.95 ± 0.58,15.45 ± 0.79,10.22 ± 0.43,and 6.58 ± 0.64 at postoperative 2 weeks with significant differences in pair comparison (F =22.869,P ＜0.01),followed by some increase at postoperative 4 and 8 weeks.Whereas,bone trabecular area in areas A,B,C,and D increased largely at postoperative 12 weeks (35.09 ± 0.58,59.44 ± 0.60,50.75 ± 1.56,and 30.94 ± 1.19) and showed significant difference when compared in a pair (F =1 002.904,P ＜ O.01).Conclusion PRF is superior to PRP in promoting bone formation,but a much better effect of PRF/BO composite is observed in bone repair.

UNLABELLEDTo construct a three-dimensional finite element model comparing between one-step and two-step methods in torque control of anterior teeth during space closure.

METHODSDicom image data including maxilla and upper teeth were obtained though cone-beam CT. A three-dimensional model was set up and the maxilla, upper teeth and periodontium were separated using Mimics software. The models were instantiated using Pro/Engineer software, and Abaqus finite element analysis software was used to simulate the sliding mechanics by loading 1.47 Nforce on traction hooks with different heights (2, 4, 6, 8, 10, 12 and 14 mm, respectively) in order to compare the initial displacement between six maxillary anterior teeth (one-step method) and four maxillary anterior teeth (two-step method).

RESULTSWhen moving anterior teeth bodily, initial displacements of central incisors in two-step method and in one-step method were 29.26 × 10⁻⁶ mm and 15.75 × 10⁻⁶ mm, respectively. The initial displacements of lateral incisors in two-step method and in one-step method were 46.76 × 10(-6) mm and 23.18 × 10(-6) mm, respectively. Under the same amount of light force, the initial displacement of anterior teeth in two-step method was doubled compared with that in one-step method. The root and crown of the canine couldn't obtain the same amount of displacement in one-step method.

CONCLUSIONSTwo-step method could produce more initial displacement than one-step method. Therefore, two-step method was easier to achieve torque control of the anterior teeth during space closure.

Cone-Beam Computed Tomography ; Finite Element Analysis ; Humans ; Incisor ; Maxilla ; diagnostic imaging ; Periodontium ; diagnostic imaging ; Software ; Tooth Crown ; diagnostic imaging ; Tooth Movement Techniques ; methods ; Tooth Root ; diagnostic imaging ; Torque

OBJECTIVETo evaluate the outcome of patients with skeletal Class III malocclusion treated with extraction of mandibular third molars and distalization of molars using implant anchorage combined with MBT appliance.

METHODSFifteen patients (mean age 24.0 ± 5.8) with skeletal Class III malocclusion were selected. The mandibular third molars were extracted and the mandibular molars were moved distally using implant combined with MBT appliance. Cephalometric analysis was carried out before and after treatment.

RESULTSAfter active treatment, ANB, Wits distance, AB-NP and the distance between upper and lower lip position to SnPg' increased by 1.65° ± 1.04°, (4.39 ± 1.93) mm, 3.20° ± 1.61° and (1.13 ± 0.99) mm, respectively. The differences were statistically significant (P < 0.05).

CONCLUSIONSThe skeletal Class III patients in the permanent dentition could be treated successfully with extraction of mandibular third molars and distalization of mandibular molars using implant anchorage combined with MBT appliance. The soft-tissue profile was improved.

Adult ; Cephalometry ; Dentition, Permanent ; Humans ; Incisor ; Malocclusion, Angle Class III ; therapy ; Molar ; Molar, Third ; surgery ; Tooth Extraction ; Tooth Movement Techniques ; methods ; Young Adult