Application And Study Of Three Dimension Computed Tomography For Orthodontics

Part IACCURACY ANALYSIS OF 3D-CT VOLUMERENDERING FOR CRANIOFACIL LINEARMEASUREMENTSObjective This study was designed to determine consistency of craniofacial measurements using Spiral computed tomography volume rendering by computer systems and sliding caliper, and evaluated the precision and accuracy of 3D rendered images craniofacial measurements by sixteen-slice helical CT, Methods The study population consisted of 12 cadaver heads that were examined with spiral CT. The archived CT data were transferred to a workstation, and 3D-CT volume rendered images were generated using computer graphics tools. Linear measurements (n=21), based upon conventional craniometric anatomical landmarks (n=18) were made, respectively by display tools and sliding caliper. The consistency between the two measurements was analyzed by paired t test. The precision and accuracy of 3D rendered images craniofacial measurements was calculated. Results The results demonstrated no statistically significant difference between imaging measurement and physical measurement; Precision and accuracy of 3D rendered images was 0.94% (range from 0.25-2.76%) and 0.24% (range from -0.76-1.73%) , respectively. Precision of direct measurements was 0.81% ( range from 0.20-2.02%). The difference of mean values between 3D rendered images and dry skull measurements was 0.20mm (range from-0.44-1.00 mm). Conclusions There is significant consistency between spiral CT measurement and physical measurement for craniofacial linear distance. 3D-CT volume rendering images using craniometric measurements can be used for clinic and studies instomatology.PART IICORTICAL BONE THICKNESS AND ANGULATIONSUSING LIMITED CONE BEAM COMPUTED TOMOGRAPHY FOR ADULT ORTHODONTICIMPLANTSObjective The buccal alveolar bone between the first molar and second premolar usually is the best microimplant area for retraction of the anterior teeth and for intrusion of the molars. The purpose of this study was to quantitatively evaluate the cortical bone thickness (CBT) and implant augulation in various locations in the maxilla and the mandible for adult orthodontics.Methods The sample consisted of 11 men and 11 women between 20 to 43 years of age. Limited cone beam computed tomographic images were reconstructed. Cortical bone thicknesses were measured at 3 angles (30°, 45°, and 90°) in the buccal regions from alveolar tip to the bottom of maxilla and mandible at the interval 1 mm. The minimum CBT and insertion angulations at the above areas were also assessed.Results At 90° insertion, upper cortical bone were thickest closest to and farthest from the cementoenamel junction (CEJ) and thinnest in the middle, lower CBT were increased from occlusion level to apical level except 1 mm site; At 30° and 45° insertion, CBT were increased gradually from alveolar tip except upper 1 mm site, and resulted in approximately 2, 1.4 times as much at30°, 45°compared with 90°. The minimum CBT and insertion angulations atvarious locations were different.Conclusions Surgical placement of microscrew for orthodontic anchorage inthe molar region requires consideration of the placement site and angle basedon anatomical characteristics. The safest location for placing miniscrew mightbe attached gingival. Oblique 30° insertion microimplant can increased CBTexcept upper 1mm site.Part IIITHE STUDY OF THE MANDIBULAR POSTERIORTEETH INCLINATIONS AND ALVEOLARMORPHOLOGY BETWEEN DIFFERENT GROWTHPATTERN OF NORMAL OCCLUSION BY CT SCANNINGObjective The purpose of the study is to evaluate relationship between the growth pattern of normal occlusion and posterior teeth inclinations, cortical bone thicknesses, mandibular heights and widths.Methods The subjects consist of 16 adults(8 male, 8 female)with individual normal occlusion, aged 23 to 41.For each subject, the three-dimensional digital radiograph of skull ,maxilla, mandible and dental arch will be available by 16-slice spiral computer tomography(CT, General Electric, GE, Light Speed plus, 2004)scanning. Then, the upper anterior face height (UAFH) and lower anterior face height (LAFH), FMA (inclination of the mandibular plane relative to Frankfort horizontal plane), and the inclinations of posterior teeth, cortical bone thicknesses and alveolar heights of the mandible are measured using Volume viewer software (Voxtool3.0.64q).The relationship among these structures could be available after the T-test of the results which obtained by the software.Results The average values of the inclination of the mandibular first molars and second molars for the vertical growth pattern subjects (the second group)are 77.86±3.48° and 80.23±2.10° respectively,the ones for the horizontal growth pattern subjects (the second group)are 82.85±4.30° and 82.69±1.92°.There is significant difference between the two groups(P<0.05). But no other significant difference is observed regarding buccal and lingual cortical bone thickness of the mandible between the two groups. The alveolar heights of the mandible for the vertical growth patterns are obviously greater than the horizontal ones.Conclusions The mandiblular molars in subjects with vertical growth patterns have a statistically significantly greater buccal inclination as compared with those with horizontal growth patterns. No statistically significant differences in the buccal and lingual cortical bone thickness of the mandible between the vertical growth patterns and the horizontal ones. The mandibular heights of the mandible for the vertical growth patterns are obviously greater than the horizontal ones.