Objective: To evaluate the risk of root resorption, individual finite element models (FEMs) of extracted human maxillary first premolars were created, and the distribution of the hydrostatic pressure in the periodontal ligament (PDL) of these models was simulated. Materials and Methods: A continuous lingual torque of 3 Nmm and 6 Nmm respectively was applied in vivo to the aforementioned teeth. After extraction, FEMs of these double-rooted teeth were created based on high-resolution microcomputed tomographics (micro CT, voxel size: 35 microns). This high volumetric resolution made the recognition of very small resorption lacunae possible. Scanning electron micrographs of the root surfaces were created as well. This enabled the investigation of advantages and disadvantages of the different imaging techniques from the viewpoint of the examination of root resorption. Using the FEMs, the same loading conditions as applied in vivo were simulated. Results:The results of clinical examination and simulations were compared using the identical roots of the teeth. The regions that showed increased hydrostatic pressure (Ͼ0.0047 MPa) correlated well with the locations of root resorption for each tooth. Increased torque resulted in increased high-pressure areas and increased magnitudes of hydrostatic pressure, correlating with the experiments. Conclusion: If hydrostatic pressure exceeds typical human capillary blood pressure in the PDL, the risk of root resorption increases.
An ultrastructural study of the cementum and periodontal ligament (PDL) changes after continuous intrusion with two different and controlled forces in humans was carried out. Twelve first upper premolars, at stage 10 of Nolla, orthodontically indicated for extraction from six patients (mean age 15.3) were used. They were divided into three experimental groups, distributed intra-individually as follows: control (not moved), continuously intruded for 4 weeks with 50 or 100 cN force, utilizing a precise biomechanical model with nickel titanium super-elastic wires (NiTi-SE), which were developed and calibrated individually. The teeth were extracted, fixed, decalcified, and conventionally processed for examination in a Jeol 100 CX II transmission electron microscope. Evident signs of degeneration of cell structures, vascular components, and extracellular matrix (EM) of cementum and PDL were observed in all the intruded teeth, with more severe changes towards an apical direction and in proportion to the magnitude of force applied. Resorptive areas and an irregular root surface of the intruded teeth were noticed, according to the same pattern described above. Concomitant, areas of repair were also revealed in the cementum and PDL although the magnitude of forces remained the same throughout the experimental period. Thus, a reduction of continuous force magnitude should be considered to preserve the integrity of tissues.
The analysis in a scanning electron microscope (Jeol 6100, at 10-15 kV) revealed many resorption lacunae in the root surface, mainly on the lingual side in the apical third of the roots. Resorption processes were also observed on the buccal root surface in the cervical third. All experimental teeth showed resorption areas. Teeth which had been moved for a longer time period and with a higher magnitude of applied moments showed a higher degree of root resorption in width as well as in depth. Higher magnitude of moments produced exposure of root dentine, evidencing pronounced root resorption.
A scanning electron microscopy study of possible root resorptions and their localization after application of continuous forces of different magnitudes was conducted. Twelve upper first premolars, indicated for extraction, were previously intruded with constant forces. The teeth were divided into 3 groups: 1. non-moved control teeth, 2. continuous force application of 50 cN for 4 weeks, 3. continuous force application of 100 cN for 4 weeks. Specially designed NiTi-SE-stainless steel springs were utilized to exert the actual forces. After experimental tooth movement, the extracted teeth were dehydrated, metal-coated and examined by scanning electron microscopy. The intruded teeth showed resorptive areas consisting of lacunae (concavities) in the mineralized root surface. The teeth moved with 50 cN showed in the apical third several, in the medial third few, and in the cervical third no resorptive areas. In the case of the teeth moved with 100 cN, we observed resorptive areas in most of the apical third--including the apex contour-, several in the medial third, and none in the cervical third. In the control group no resorptions were observed. Thus, our results suggest that intrusion of human teeth with continuous forces induces root resorption, depending on the magnitude of force applied.
Objective: To evaluate the long-term skeletal and soft tissue changes induced by the bionator in Class II subjects. Materials and Methods: The treatment sample consisted of 20 Class II patients (6 males and 14 females) treated consecutively with the bionator. The sample was evaluated at T1, start of treatment; T2, end of bionator therapy; and T3, long-term observation (including fixed appliances). Mean age at the start of treatment was 10 years 2 months (T1); at posttreatment, 12 years 4 months (T2); and at long-term follow-up, 18 years 11 months (CS 6). The control group consisted of 20 subjects (8 males and 12 females) with untreated Class II malocclusions. Lateral cephalograms were analyzed at the three time points for all groups. Student's t-tests were used for comparisons of starting forms, and of the T1-T2 and T1-T3 changes between groups. Results: The bionator group showed significant, favorable T1-T2 changes both at the skeletal and dentoalveolar levels. The vertical dimension was increased. Significant modifications were assessed for the soft tissues as well. The treated group showed a final improvement in soft tissue pogonion of about 2.5 mm. Significant mandibular changes were noted in the treated group, with a net average 3.3 mm long-term increase in mandibular length compared with untreated Class II controls. Conclusions: This study suggests that bionator treatment of Class II malocclusion maintains favorable results over the long-term with a combination of skeletal, dentoalveolar, and soft tissue changes. (Angle Orthod 2010;80:10-17.)
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