Measurement of mandibles with microfocus x-ray computerized tomography and compact computerized tomography for dental use

PURPOSE: The trabecular bone patterns in jaws and tooth structure were analyzed using microfocus x-ray computerized tomography (micro-CT), and the usefulness of this method was reported. This study was performed to clarify the accuracy of micro-CT and to determine whether micro-CT could replace bone slice segments as a means for assessment of the accuracy of medical radiography units. In addition, the accuracy of compact CT for dental use (compact CT) was evaluated using the same method. MATERIALS AND METHODS: Three dried hemimandibles were used in this study. Images of mandibular interdental alveolar bone in the premolar and molar regions were obtained using micro-CT and compact CT. Measurement of the mandibular shape at 6 sites using micro-CT images and at 4 sites using compact CT images was performed, and then the values of the micro-CT and compact CT were compared with those of bone slice segments. RESULTS: The accuracy of mandibular measurement and the ratios of agreement for micro-CT were significantly higher than those for compact CT. Moreover, the coefficient of correlation of the rate of trabecular bone between compact CT images and bone slice segment images was 0.916. DISCUSSION: The significant difference in mandibular measurement between micro-CT and compact CT was considered to be related to pixel size. CONCLUSION: Micro-CT can replace bone slice segments for assessment of the accuracy of medical radiography units. In addition, compact CT can be used for imaging diagnosis in dental implant treatment. It is suggested that the ratio of trabecular bone could be used to evaluate the bone density.     

Cross-sectional imaging of the jaws for dental implant treatment: accuracy of linear tomography using a panoramic machine in comparison with reformatted computed tomography

PURPOSE: Although various panoramic X-ray machines with linear tomographic functions are now frequently applied to diagnosis related to dental implant treatment, the angles of the tomographic objective planes are automatically determined and cannot be adjusted for individual patients. To resolve this problem, a direct laser positioning (DLP) system was developed. In this investigation, the measurement accuracy of images obtained by the DLP system in comparison with those from reformatted computed tomography (CT) was assessed. MATERIALS AND METHODS: A rectangular parallel piped phantom was scanned with the system and the height and width were measured on linear tomograms. Ten sites in 3 dried mandibles and 21 mandibular molar sites in 15 patients were examined both with the DLP system and the reformatted CT to compare the measured values on both images. RESULTS: The phantom experiment showed that the difference between the actual and measured heights and widths of the phantom were within 1 mm. DISCUSSION: The difference between the values obtained by the DLP system and CT was slightly larger in the patients than those in the dried mandibles. CONCLUSION: The DLP measurement accuracy was deemed sufficient for clinical use.     

Assessment of three-dimensional X-ray images: reconstruction from conventional tomograms, compact computerized tomography images, and multislice helical computerized tomography images

Three-dimensional X-ray images (3D images) were used for imaging diagnosis in the oral and maxillofacial region. These images could be fundamentally reconstructed from various tomograms, though clinical 3D images were mainly reconstructed from computerized tomography (CT) images. In this investigation, 3D images were reconstructed from conventional tomograms with a panoramic unit, compact CT images, and multislice helical CT images, and the usefulness of each system was subjectively assessed for dental implant treatment. Three hemilateral dried human mandibles were used and were examined by linear tomography with a panoramic unit, compact CT, and multislice helical CT, and 3D images were reconstructed by using the rendering software for each system. The 3D images were visually evaluated on a 5-point scale covering the alveolar ridge, buccal and lingual bone surface, mental foramen, and tooth sockets. As a result, 3D images reconstructed from conventional tomograms with the panoramic unit were assessed as fair to unsure, compact CT 3D images were assessed as unsure to good, and multislice helical CT 3D images were assessed as good to excellent. It was concluded that compact CT 3D images and multislice helical CT 3D images were useful in dental implant treatment.     

颌面专用CT下颌骨检查技术

目的：研究颌面专用CT（QR-DVT 9000 NEWTOM）下颌骨检查技术的建立方法及技术要点,观察颌面专用CT下颌骨检查技术,在下颌骨X线检查中的优势.方法：对下颌骨疾病患者进行颌面专用CT扫描和重建成像,对其重建轴位影像进行曲面、矢状位、冠状位以及3D影像的后处理,并与常规X线片对比分析.结果：颌面专用CT下颌骨检查技术优于下颌骨常规X线检查,分别以水平位、曲面、矢状位、冠状位以及3D等多方位影像显示下颌骨的信息.结论：颌面专用CT下颌骨检查技术,在下颌骨的X线检查中有着明显的优势,并能够有效地指导临床手术.     

基于CT三维重建技术的颌骨侧断层交互分析法在牙种植外科设计中的应用

目的 通过基于颌骨三维CT影像技术,开发一种计算机辅助交互方式计算牙轴方向的临床应用软件,为牙种植合理设计提供便捷手段.方法 对种植患者进行64排螺旋CT扫描,获得DICOM数据,在计算机辅助种植规划软件上将CT影像数据生成颌骨三维模型,使牙根可视化,交互式放置和调整虚拟切割平面.结果 基于此种交互式设计分析,可以获取牙根轴位方向的信息,并由此评估缺失牙牙轴方向.结论 基于虚拟切割平面方向获得的牙根轴位方向,可最终为临床种植牙的植入方向、角度的把握及导板的制作提供科学依据.     

The role of objective plane angulation on the mandibular image using cross-sectional tomography

Cross-sectional jaw images in the buccolingual direction obtained by conventional or computerized tomography are used in the image diagnosis of dental implant treatment. This study was performed to clarify the subjective image quality of the mandibular depiction by shifting the angles of the tomographic objective plane. A panoramic machine with a linear tomographic function was used to obtain cross-sectional tomographic images on bilateral first molar regions of 10 dried human mandibles. The angles of tomographic objective planes were shifted horizontally within a range of +/- 20 degrees at intervals of 5 degrees from the tomographic objective plane, which was automatically determined. The image qualities of 4 anatomical structures-alveolar crest, buccal and lingual cortical bone, and mandibular canal-were subjectively scored on a 5-point scale method. As a result, the permitted tomographic objective angles were from -1.7 degrees to 2.5 degrees, a range of 4.2 degrees for all 4 anatomical structures. When this result was compared with a previous geometric result, the permitted range of the angles was quite narrow. The tomographic objective angles should be manually set in accordance with an optimal tomographic plane for individual patients by using the positioning technique in linear tomography.     

Effect of mandibular positioning on preimplant site measurement of the mandible in reformatted CT

The purpose of this study was to evaluate the effect of mandibular positioning on measurement of the reformatted cross-sectional image of the mandible in computed tomography (CT) according to the area on the mandible. Five dried mandibles, partially edentulous in the premolar and molar areas, were selected. The inferior border of the mandible was placed at 0-, 5-, 10-, 15-, and 20-degree angles to the CT scanning plane, and CTs were taken. The marked area of the reformatted cross-sectional image taken at each angle was found, and the distance from the most superior border of the mandibular canal to the alveolar crest was measured. As the angle between the CT scanning plane and mandibular plane increased, the distance from the most superior border of the mandibular canal to the alveolar crest also increased. The degree of increase was more pronounced in the posterior portion of the mandible than in the anterior portion of the mandible. As mandibular positional change in the CT gantry can affect the vertical measurement of the reformatted cross-sectional image, a correct guiding plane is necessary to accurately position the jaw to the CT scanning plane.     

Accuracy in measurement of distance using limited cone-beam computerized tomography

PURPOSE: The purpose of this study was to evaluate the accuracy of measurement of distance on the images produced by limited cone-beam computerized tomography (CT). MATERIALS AND METHODS: Five cadaver mandibles were examined by spiral computerized tomography (SCT) and limited cone-beam computerized tomography (LCBCT). The vertical distance from a reference point to the alveolar ridge was measured by caliper on the sliced mandible, and measurement error on the CT images was calculated in percentages based on the actual values and the measurement values obtained from the CT images. RESULTS: Measurement error was determined to range from 0 to 1.11 mm (0% to 6.9%) on SCT and from 0.01 to 0.65 mm (0.1% to 5.2%) on LCBCT, with measurement errors of 2.2% and 1.4%, respectively (P < .0001). DISCUSSION: This study suggests that distance can be measured accurately using LCBCT. The size of the rectangular solid images obtained using LCBCT (30 mm wide and 42.7 mm long) is thought to be adequate for observation of mandibular bony structure and for preoperative assessment before dental implant placement. CONCLUSION: In this experiment on cadaver mandibles, LCBCT was shown to be a useful tool for preoperative evaluation in dental surgery because the relatively small field size of its images limits the patient's exposure to radiation.     

下颌平面角影响种植体应力分布的有限元分析

目的通过在不同下颌平面角角度下对下颌第一磨牙种植体的力学特性进行有限元分析,得出下颌平面角角度对种植体受力的影响规律,为临床种植提供理论参考。方法采集3种不同下颌平面角（低角、均角、高角）CT数据,建立种植复合体有限元模型,设计正交实验方案,记录数据,分析处理,得出有限元分析结果。结果最优参数组合为：低角,4.8 mm,Ⅱ型骨。各个因素的主次关系依次为种植体直径、下颌平面角角度、骨密度。结论下颌平面角角度对种植体的稳固有一定的影响,在同样咬合力的情况下,高角种植体所受应力最大,其次是均角,低角最小。     

Bifid mandibular canal in Japanese

The location and configuration of mandibular canal variations are important in surgical procedures involving the mandible, such as extraction of an impacted third molar, dental implant treatment, and sagittal split ramus osteotomy. We report 3 Japanese patients with bifid mandibular canals using panoramic radiograph and multi-slice helical computed tomography (CT) images. In 2 of the 5 sides, the bifid mandibular canal was suggested on panoramic radiograph. The bifid mandibular canal had a short and narrow upper canal toward the distal area of the second molar in 4 sides, and a short and narrow lower canal toward the distal area of second molar in 1 side, as revealed on reconstructed CT images. Since the location and configuration of mandibular canal variations are important in surgical procedures involving the mandible, they should be carefully observed using reconstructed CT images.     

A positioning device for computed tomography: a clinical report

This clinical report describes a device (Centrascan) used to assist in the correct alignment of the patient's head during computed tomography (CT) assessment of a proposed implant site. To obtain the desired anatomic detail, CT requires precise alignment of the axial images at right angles to the long axis of the proposed implant. This clinical report compared the anatomic morphology of a projected implant site derived from axial images provided by DentaScan software analysis of the CT scan acquisition. Images from a conventional scan, with the patient's head aligned along the frontal plane (perpendicular to the Frankfort plane) and along the sagittal plane (coinciding with either the cortical bone of the hard palate or the inferior border of the mandible), were compared with images acquired by use of the Centrascan device. The two scans differed substantially. In particular, the cross-sectional images obtained by the conventional procedure showed a distorted anatomy; conversely, the images obtained by the Centrascan procedure showed a better reproduction of the examined area. The Centrascan device seemed to help the radiologist achieve a more correct alignment of the patient's head during CT scan acquisition. Further studies are necessary to fully explore the relative technical merits of the Centrascan device.     

Dimensional accuracy of a binder jet model produced from computerized tomography data for dental implants

A full-scale model produced by multislice helical computerized tomography (CT) was made by using the binder jet method and applied for presurgical diagnosis, surgical simulation, and the production of surgical templates for dental implant treatment. In this study, accuracy of the full-scale model with plaster powder was assessed by shifting the binary threshold values. A step phantom was made from bone-equivalent material. When it was placed in water, the CT imaging was performed with a multislice helical CT unit. Three-dimensional (3-D) images were reconstructed by 3-D visualization software. Using 4 different threshold values, full-scale models were produced by a binder jet method with plaster powder. All sides of the full-scale models were directly measured, and their values were compared with that of the step phantom. The mean difference was approximately 0.1 mm in the axial plane when the setting was 0.75 for the threshold. In total, the mean difference was approximately 0.2 mm when the setting was 0.50 for the threshold. It is suggested this full-scale model could be applied for presurgical diagnosis, surgical simulation, and the production of surgical templates in dental implant treatment.     

Accuracy of magnetic resonance imaging compared with computed tomography for implant planning

Aim: The objective of this study was to evaluate the reliability of magnetic resonance imaging (MRI) compared with computed tomography (CT) for dental implant planning in respect to bone measurements. Methods: Five dry mandibles were submitted to MRI and CT examinations. Each mandible had three specific sites identified with markers, in a total of 15 sites to be studied. The images provided by the MRI and CT examinations were delivered to four specialists in Oral and Maxillofacial Radiology to measure the bone height at the specific sites. Subsequently, the bone height of the dry mandibles was directly measured in the determined sites. The measurements obtained by the specialists in MRI and CT images were compared with the measurements obtained directly from the dry mandibles using the ANOVA test with a 0.05 significance level. Results: The differences between the measurements obtained directly from the dry mandibles and the measurements from the MRI exams varied from 0.13 to 1.67 mm, with 10 sites being overestimated in MRI exams and five sites being underestimated. The differences between the measurements from the dry mandibles and CT exams varied from 0.02 to 1.25 mm, with nine sites being overestimated in CT exams and six sites being underestimated. The differences between the measurements from the MRI and CT exams varied from 0.03 to 1.00 mm, with nine sites giving higher values in MRI exams and six sites giving higher values in CT exams. There were no statistically significant differences between the three grous of measurements (P=0.98). Conclusion: The MRI, when compared with CT, shown to be reliable in respect to bone measurements for dental implant planning.     

Evaluation of voxel values in mandibular cancellous bone: relationship between cone-beam computed tomography and multislice helical computed tomography

Objective: Measurements of bone density in designed sites are important in presurgical imaging for dental implant treatment. However, the pixel or voxel values obtained from cone-beam computed tomography (CT) images are not absolute values. Hence, the relationship between voxel values obtained from cone-beam CT with a limited-volume exposure field and a flat panel detector and bone mineral densities (BMDs) obtained from multislice CT was evaluated in the mandible.
Material and methods: A total of 16 (four males and 12 females) patients who had undergone imaging for mandibular dental implant treatment using cone-beam CT with Alphard VEGA and multislice CT were enrolled in this investigation.
Cross-sectional images of cone-beam and multislice CT were reconstructed, and values of regions of interest (ROIs) in images were calculated.
Results: A high-level correlation between voxel values of cone-beam CT and BMDs of multislice CT was observed ( r =0.965).
Conclusion: It was suggested that voxel values of mandibular cancellous bone in cone-beam CT could be used to estimate bone density.     

The relationship between the incisor position and lingual surface morphology in normal occlusion

This study aimed to investigate the relationship between the morphological characteristics of maxillary incisors and the anterior occlusion. The study materials comprised dental casts and lateral cephalograms of 26 modern Mongolian females with Angle Class I normal occlusion (mean age, 21 years 5 months). Computed tomography (CT) images of the dental casts were taken with an X-ray micro-CT system (SMX-100CT, Shimadzu, Kyoto Japan). The thickness of the marginal ridges and incisal edges, and the overjet and overbite, was measured on the three-dimensional images of the dental casts. On the lateral cephalogram, maxillary incisor to sella–nasion plane angle (U1 to SN angle), maxillary incisor to nasion-point A plane distance (U1 to NA distance), mandibular incisor to nasion-point B plane distance (L1 to NB distance), incisor mandibular plane angle, and interincisal angle were measured by tracing the left incisors of the maxilla and mandible. Spearman’s single rank correlation coefficients were used to investigate any correlation between measurement items for each maxillary incisor. The thickness of the marginal ridges and incisal edges was positively correlated with the overbite. The thickness of the incisal edges was positively correlated with the irregularity index of the maxilla. There were significant negative correlations between overbite and U1 to SN angle, U1 to NA distance, and L1 to NB distance. Significant positive correlations were noted between the overbite and the overjet. In conclusion, there was no strong relationship between the morphological characteristics of maxillary incisors and the anterior occlusion.     

Radiologic measurements of the mandible: a comparison between CT-reformatted and conventional tomographic images

This study was carried out to compare the accuracy of determination of the mandibular contour and the position of the mandibular canal in cadaver mandibles by the multiplanar reconstruction method (MPR-CT), which has recently come to be used widely for preoperative examinations, with those by tomographic techniques and to evaluate the usefulness of MPR-CT. Using three imaging systems, i.e. Quantum CT scanner, Scanora, and OP-100, a total of 6 sites were scanned in the molar regions of 3 cadaver mandibles. The images obtained were measured twice each by 4 radiologists. The anatomic structures measured were the height and thickness of the mandible, distance from the alveolar crest to the mandibular canal, and distance from the buccal cortical bone to the mandibular canal. After scanning, the scanned areas of the mandibles were sliced at a thickness of 2 mm, and soft X-ray images of these slices were obtained. The values of the above 4 anatomic structures obtained by measurements in the soft X-ray radiograms using digital-display calipers were regarded as true values. When compared with the true values, the errors in the distance from the alveolar crest to the mandibular canal were within 1 mm (+/- 1 mm) in 93.7% of the measurements by Direct-CT, 89.6% of the measurements by MPR-CT, 87.5% of the measurements by Scanora, and 47.9% of the measurements by OP-100, and the accuracy of the 4 methods ranked in the order of Direct-CT, MPR-CT, Scanora, and OP-100. A similar tendency was observed in the measurements of other anatomic structures, and statistically significant differences were observed among the methods. Thus, MPR-CT allows more accurate measurements than by the other 2 tomographic techniques,and to be useful as a preoperative examination for implant surgery.     

传统全景片和锥形束CT重建全景片测量牙轴近远中倾斜度的对比研究

目的 比较传统全景片和锥形束CT（CBCT）重建全景片用于测量牙轴近远中倾斜度的准确性。方法 收集15名个别正常志愿者的石膏模型,在模型上确定上下颌从左侧第一磨牙到右侧第一磨牙的牙体长轴和平面的标记点,制作放射显影装置,志愿者佩戴放射显影装置拍摄全景片和 CBCT片。分别在石膏模型、全景片和 CBCT重建全景片上测量牙轴近远中倾斜度。利用多元方差分析和 Dunnett-t检验比较3种测量方法的差异。结果 3种测量方法间的差异有统计学意义（P=0.00）。与模型测量相比,全景片组中12个牙位有2个牙位（上下颌第二前磨牙）测量结果的差异有统计学意义（P=0.00）,CBCT组12个牙位的差异均无统计学意义。结论 评价牙轴近远中倾斜度时,传统全景片存在一定误差, CBCT重建全景片是一种更为有效的评价手段。     

应用CAD/CAM技术进行个体化下颌骨重建

目的:探讨计算机辅助设计和制造技术(CAD/CAM)应用于下颌骨肿瘤切除术后骨缺损的个体化修复重建。方法:选择面部畸形明显的单侧下颌骨成釉细胞瘤4例,术前行下颌骨螺旋CT扫描,三维重建成像,用CAD/CAM数控技术和镜像技术,制成与患者骨组织完全相同的个体化实体模型,根据模型预弯制重建钛板。手术切除病灶下颌骨,切取髂骨节段,植于重建板的舌侧,固定重建板于正常下颌骨端。结果:CT三维重建影像与实体模型测量数据接近;预弯制钛重建板与下颌骨匹配;手术恢复了下颌骨的连续性和功能,面部外形对称,X线片显示重建的下颌骨高度和厚度适中。结论:CAD/CAM技术为术前设计提供了个体化实体模型,提高了手术的精确性,节省了手术时间,降低了手术并发症。     

Precision,reproducibility, and accuracy of bone crest level measurements of CBCT cross sections using different resolutions

Objective:To evaluate the precision, reproducibility, and accuracy of alveolar crest level measurements on CBCT images obtained with different voxel sizes.Materials and Methods:CBCT exams were made of 12 dried human mandibles with voxel dimensions of 0.2, 0.3, and 0.4 mm. Bone crest level was measured directly on the mandibles with a digital caliper and on CBCT images. Images were measured twice by two examiners. Intra- and interexaminer precision and reproducibility were assessed using paired and t-tests, respectively. Accuracy was evaluated using t-tests.Results:Precision and reproducibility of bone crest level tomographic measurements was good for all voxel sizes evaluated. The images with 0.2-mm voxel size showed a decreased number of intraexaminer errors. A high accuracy for measurements of bone crest level was observed for all CBCT definitions, except for the mandibular incisors using the 0.4-mm voxel size.Conclusions:Precision and reproducibility of alveolar bone level measurements were good for various voxel sizes. CBCT images demonstrated good accuracy for 0.2-mm and 0.3-mm voxel sizes. The mandibular incisor region needs better resolution than that provided by 0.4-mm voxel size for bone crest level measurements.     

Tuned aperture computed tomography (TACT®) for cross-sectional implant site assessment in the posterior mandible

PURPOSE: This study was designed to optimize a new radiographic modality known as tuned aperture computed tomography (TACT) for cross-sectional imaging of implant sites in human dry mandibles. MATERIALS AND METHODS: Five imaging modalities were compared for image quality and measurement accuracy: (1) conventional hypocycloidal tomograms, (2) TACT images reconstructed using the average method produced using a linear x-ray source movement, (3) TACT images reconstructed using the average method produced using a multidirectional x-ray source movement, (4) minimally reconstructed TACT images without a fiducial marker at the site of interest, and (5) minimally reconstructed TACT images with a fiducial marker at the site of interest. RESULTS: The extended Mantel-Haenszel mean score statistic was used to investigate the influence of modality on subjective image quality. A statistically significant difference for certain types of TACT images and multidirectional tomography (P < 0.0001) was observed. Linear TACT and multmin TACT were rated as significantly better than other image modalities (P < 0.0009), whereas multidirectional tomography was rated as being significantly worse than other radiographic modalities (P < 0.0001). For the quantitative assessment, data were normalized and analyzed statistically through a paired-comparisons t test. For each modality, the accuracy for maximum height and height was significantly different from ground truth (P < 0.05). CONCLUSION: The qualitative data suggest that visibility of structures important to the choice of implant location and dimension were seen better with certain TACT methods. Quantitative differences from ground truth (actual measurements of the bone-absolute truth) were clinically negligible. TACT appears to offer the potential of superior image quality over the status quo.