[Comparative study of alveolar bone remodeling around the upper incisor area after Twin-block and high-pull headgear-activator functional orthopedic therapy].

PURPOSE: The aim of this clinical study was to evaluate the changes of alveolar bone morphology around the upper incisors before and after functional treatment in adolescents using cone-beam CT(CBCT). METHODS: Thirty patients with skeletal Class II mandibular retrusion who were successfully treated with high-pull headgear-activator(HGAC) and Twin-block were selected and divided into 2 groups (HGAC and Twin-block groups), 15 in each group. CBCT was performed before and after treatment, to observe upper incisor movement in the alveolar bone and alveolar bone remodeling. Statistical analysis was performed using SPSS 20.0 software package to analyze the changes of alveolar bone thickness, angle of central incisor and alveolar bone before and after treatment. RESULTS: Horizontally, the edge of the maxillary incisor appeared lingual movement in both groups, while the root apex appeared lingual movement in HGAC group and labial movement in Twin-block group. Vertically, the edge of the maxillary incisor was moved down and the root apex was moved up in all patients, whereas the moving distance was less in the edge and larger in the root apex in HGAC group. The thicknesses of major areas in the alveolar bone significantly increased in HGAC group, while in Twin-block group the labial thickness of the alveolar bone showed significant decrease and the palatal thickness showed significant increase. Moreover, the total thickness of the alveolar bone showed significant increase in both groups, yet Twin-block group showed more increase, and the angle of the alveolar bone showed more decrease in HGAC group. CONCLUSIONS: Both functional appliances can cause positive alveolar bone remodeling in maxillary incisor area. HGAC can achieve a controlled tilt inward movement of the maxillary incisors, intrude the incisors to a certain extent, and allow certain change in the bending angle of the incisor alveolar bone at the same time, which is conducive to improving ClassⅡcraniofacial pattern. Twin-block can tilt the maxillary incisor inward, suggesting that more attention needs to be paid to the control of the torque of the incisor when retracting anterior teeth in fixed orthodontic treatment after Twin-block functional treatment.

[Effect of alveolar surgery-aided rapid orthodontic tooth movement on bone formation].

OBJECTIVE: To test the effect of alveolar surgery on orthodontic tooth movement and born remodeling. METHODS: Alveolar surgery was performed on one side (experimental side) whereas the traditional tooth movement was performed on the other side (control side) of the teeth in ten dogs. The treatments lasted for four weeks. The bone formation was evaluated using the vital bone marker tetracycline and immunohistochemistry 1, 2, 3, 4 and 8 weeks after the treatments respectively. RESULTS: In the total of the four weeks, the distal movement of experimental tooth was much faster (4.31 +/- 0.46 mm) than control tooth (2.16 +/- 0.42 mm), whereas the anchorage lost (0.44 +/- 0.07 mm) was the same with the control (0.46 +/- 0.09 mm). Compared to the control side, the tetracycline labeling lines were wider; the increase of the expression level of BMP-2 appeared earlier, greater and lasted longer in the tension area of the experimental side. CONCLUSION: Alveolar surgery could promote bone remodeling and accelerate the movement of orthodontic teeth.

[The three-dimension finite element analysis of stress in posterior residual root restored with different designed post-core crown].

OBJECTIVE: To analyze the stress magnitude and distribution of remaining dentin in posterior residual root restored with post-core crown by three-dimension finite element methods. The variables were number, length and material of post. METHODS: The models of residual root of maxillary first molar restored with post-core crown were created by CT scanning, Mimics software and Abaqus software. Different number, length and material of posts were used in the modeling. The post was cemented with zinc-phosphate cement. A load of 240 N was applied to the occlusal surface in vertical direction and tensile, shear, and Von mises stresses were calculated. RESULTS: The maximum stresses on remaining dentin changed irregularly as the number and length of post. The maximum stresses on remaining dentin decreased slightly as elastic modulus of the material of post increase. CONCLUSION: The number, length, material of post have influence on magnitude and distribution of stress.