Quality of preimplant low-dose tomography

OBJECTIVES: The aim of this study was to test the influence of radiation dose on image quality in mandibular preimplant computed tomographic examinations and to compare the quality of computed and conventional spiral tomographic images. STUDY DESIGN: Cross-sectional images were obtained on 17 patients with conventional spiral tomography (Scanora technique) and reformatted computed tomography at 40 and 80 mAs. Observers graded the acceptability of images for implant planning and traced the contour of the mandibular body and canal. RESULTS: Conventional spiral tomographic images scored significantly higher than computed tomographic images whereas mean score differences between computed tomographic techniques were not statistically significant. Anatomic structures, in particular the mandibular canal, were more frequently untraceable in high-dose than in low-dose computed tomography but always traceable in conventional tomograms. CONCLUSION: Conventional spiral tomograms were subjectively preferred over computed tomographic images. For mandibular implant planning, computed tomography examinations can be performed with lower-than-standard mAs. Quantum noise seems to contribute to the visibility of anatomic structures in reformatted computed tomographic images.     

Measurement accuracy of reconstructed 2-D images obtained by multi-slice helical computed tomography

The present dental reconstructed computed tomography (CT) images consist of continuously piled-up axial CT images that are perpendicular to the axial CT plane. In the mandibular posterior region, the angles of designed implants frequently differ from the angles perpendicular to the axial CT plane and the measurement of mandibular height is inaccurate. This study was performed to clarify the measurement accuracy of double-oblique reconstructed images in multi-slice helical CT, using dried mandibles. The mandibular height was measured from the alveolar crest immediately below the aluminum tube to the superior border of the mandibular canal using the double-oblique reconstructed images and the micro-CT average images of three semi-lateral dried mandibles. The mean of the differences between the double-oblique reconstructed images with a table pitch of 1.5 in a helical scan and the micro-CT average images was 0.31 mm. It is concluded that the accuracy of the double-oblique reconstructed image measurements with helical scan is high. So this double-oblique program can be applied to the imaging diagnosis in dental implant treatment.     

The use of 3 different imaging methods for the localization of the mandibular canal in dental implant planning

PURPOSE: The purpose of this study was to investigate the efficiency of panoramic radiography, conventional (cross-sectional) tomography, and computerized tomography for location of the mandibular canal before implant placement in the posterior region of the mandible. MATERIALS AND METHODS: Edentulous mandibles from 6 dry adult human skulls were used in this study. Four measurements (D1, D2, D3, D4) were made of 12 areas, one on each side of each mandible. Panoramic radiographs, conventional tomograms, and computerized tomograms were obtained. On each image, measurements were made for localization of the mandibular canal by one researcher. All measurements were repeated 3 times within a period of 3 weeks. Upon completion of imaging, the mandibles were surgically sectioned to provide direct measurements. The measurements obtained from the images were compared with direct measurements. Pearson correlation coefficients were calculated to detect statistical correlations between repeated measurements. The Dunnett t test was performed for statistical comparison of measurements from images and direct measurements. RESULTS: Pearson correlation coefficients showed strong linear correlation for all measurements (P < .01). No statistically significant difference was observed between direct measurement and D1, D2, or D4 (P < .05), but a statistically significant difference for D3 (buccolingual width 5 mm under mandibular crest; Dunnett t test; P > .05) between measurements was obtained from the images and direct measurements. CONCLUSION: The measurements obtained from computerized tomographic images were more consistent with direct measurements than the measurements obtained from panoramic radiographic images or conventional tomographic images.     

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.     

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.     

Spiral tomography for measuring bone width at different levels from the crest to the inferior border of the mandible in vitro

Introduction Tomography images provide sufficient detail for estimating the vertical and horizontal dimensions of alveolar bone and reducing surgical injuries. This study evaluated the role of spiral tomography in measuring mandibular alveolar bone width. Methods Cross-sectional tomography slices were taken using a Cranex Tome unit at three or four different locations on each side of three chosen mandibles, such that all the locations were distal to the mental foramen. In addition, artificial soft tissues were reconstructed using Play-Doh modeling clay. On the tomography image, a line was drawn from the crest to the inferior border of the mandible (MC), and the bone height to the mandibular canal and bone width were measured at one-third, two-thirds, and one-half MC, and the mandibular canal levels. Then, the mandibles were sectioned at the same sites, and the bone sections were measured. For statistical analysis, the sign test analysis was used. Results There was a statistically significant difference between the tomographic and real anatomical bone width at one-half and one-third MC, and the canal level (P < 0.05), while the difference between tomography and bone section measurements were not significant at two-thirds MC, or, the bone height to the mandibular canal (P > 0.05). Conclusions The bone width on tomographic images was overestimated by between 2.3 and 0.1 mm. Therefore, caution should be exercised when evaluating bone width measured from tomography images. In most locations, the measured height to the canal was underestimated by between 0.1 and 2.7 mm, which confirmed the safety of spiral tomography for estimating the distance related to the mandibular canal.     

Accuracy of mandibular cross-sectional imaging with tuned- aperture computed tomography (TACT), iteratively reconstructed TACT, and multidirectional, linear, and transverse panoramic tomography

OBJECTIVE: This study was designed to compare 5 modalities with respect to accuracy in mandibular cross-sectional imaging. The modalities tested were tuned-aperture computed tomography (TACT), iteratively reconstructed TACT, multidirectional tomography, linear tomography, and transverse panoramic tomography. STUDY DESIGN: Twenty sites were selected from 3 dry human mandibles, and cross-sectional views were imaged through use of each of the 5 modalities. A quantitative analysis included measurements of 2 linear distances; a qualitative study included image evaluation by 6 observers. A nested mixed analysis of variance model was used to control for mandibles and locations within mandibles for the quantitative analysis; the Cochran-Mantel-Haenszel test was used for the qualitative analysis. RESULTS: There was a significant difference in measurement error for maximum height but not for width. There was also a significant difference in qualitative image evaluation results. CONCLUSIONS: Of the 5 modalities tested, the narrow-layer multidirectional tomographic technique produced the greatest diagnostic accuracy and quality in cross-sectional imaging. The transverse panoramic tomographic technique produced the least diagnostic accuracy and quality. Linear tomography, TACT, and iteratively reconstructed TACT were intermediate in accuracy and quality.     

Accuracy of computerized tomography for the evaluation of mandibular sites prior to implant placement

The objective of the present study was to observe the effect of positioning of the mandible on the accuracy of cross-sectional images obtained by reformatting computerized tomographic (CT) scans. An additional aim was to evaluate the ability of a software program (DentalVox, Era Scientific) to reconstruct these measurements on the reformatted images, regardless of the positioning of the mandible, accurately and without distortion. The test was carried out by examining a partially edentulous dry human mandible with an acrylic radiologic template. Through the use of an acrylic glass support, the mandible was positioned at angles of 0, 10, 15, 20, and 30 degrees relative to the scanning gantry, and a series of CT scans was performed that provided five sets of axial images. Each set of original axial images was reformatted by the DentalVox software, used first in its basic function, which is typical of all software for axial CT measurement (control group), and again in its function of site-specific multiplanar reconstruction (test group). The results showed that the position of the mandible in relation to the CT gantry can influence the precision of the linear measurements. The error ranged from 2% to 51%. The DentalVox software allowed the reconstruction of cross-sectional images with very little distortion regardless of the mandibular position.     

Selected cephalometric angular norms in Kikuyu children

Fifty-six standardized lateral head radiographs of Kikuyu children, represented equally by sex and aged nine to 15 years, were evaluated to determine norms for six dentoskeletal angles. The mean values obtained for the measured variables in the two sexes were: SNA = 84.4 degrees (+/- 4.0 degrees); SNB = 79.3 degrees (+/- 4.1 degrees); ANB = +5.1 degrees (+/- 2.0 degrees); FMA = 34.0 degrees (+/- 5.1 degrees); IMPA = 96.2 degrees (+/- 5.0 degrees) and 1/1 = 111.6 degrees (+/- 7.7 degrees). Angle SNB was found to be significantly larger in females. A comparison of the means of the cephalometric angles for the Kikuyu children with those of black American children demonstrated a steeper Frankfort-mandibular plane angle and a more acute lower incisor to mandibular plane angle in Kikuyu children. The Kikuyu children were also noted to have a more prognathic maxilla relative to the cranial base and mandible, a greater inclination of the lower incisors to mandibular plane and a more acute interincisal angle when compared to white children. The study emphasizes the need for use of group specific norms for orthodontic diagnosis and treatment planning.     

Craniofacial growth in untreated skeletal Class II subjects: A longitudinal study

Eighty-five (45 male and 40 female) skeletal Class II untreated subjects with low (< 27 degrees ), average (27 degrees - 36 degrees ), and high (> 36 degrees ) mandibular plane angles (MP-SN) were selected from the Bolton-Brush and the Burlington Growth Studies. Cephalograms of each subject at ages 9 and 18 were traced, and 28 parameters were measured. The difference in each parameter from ages 9 to 18 was calculated, and comparisons were made between the groups with low, average, and high angles. Results showed that for children at age 9, the high-angle group showed greater convexity, larger Y-axis and gonial angles, and greater anterior facial height, and the low-angle group had larger SNA and SNB angles, and greater posterior cranial base, mandibular body, ramus height, and posterior facial height. From ages 9 to 18, all the low-, average-, and high-angle groups showed a decrease of convexity (more flattened face) and a mandibular forward rotation (decreased MP-SN). The low-angle group displayed significantly more facial flattening and more mandibular forward rotation than did the high-angle group. Moreover, the mandibular incisors became more retroclined in the low-angle group and more proclined in the high-angle group with age. Comparisons between males and females showed similar skeletal growth patterns in angular measurements. However, a significant sex difference was noted in some linear measurements.     

Radiation absorbed from dental implant radiography: a comparison of linear tomography, CT scan, and panoramic and intra-oral techniques

Absorbed radiation dose in bone marrow, thyroid, salivary gland, eye, and skin entrance was determined by placement of lithium fluoride thermoluminescent dosimeters (TLD's) at selected anatomical sites within and on a human-like x-ray phantom. The phantom was exposed to radiation from linear tomographic and computer-assisted tomographic (CT) simulated dental implant radiographic examinations. The mean dose was determined for each anatomical site. Resulting dose measurements from linear tomography and computer-assisted tomography are compared with reported panoramic and intra-oral doses. CT examination delivered the greatest dose, while linear tomography was generally lowest. Panoramic and intra-oral doses were similar to those of linear tomography.     

The effect of vertical and horizontal head positioning in panoramic radiography on mesiodistal tooth angulations.

The purposes of this study were to examine the effect of potentially common patient positioning errors in panoramic radiography on imaged mesiodistal tooth angulations and to compare these results with the imaged mesiodistal tooth angulations present at an idealized head position. A human skull served as the matrix into which a constructed typodont testing device was fixed according to anteroposterior and vertical cephalometric normals. The skull was then repeatedly imaged and repositioned five times at each of the following five head positions: ideal head position, 5 degrees right, 5 degrees left, 5 degrees up, and 5 degrees down. The images were scanned and digitized with custom software to determine the image mesiodistal tooth angulations. Results revealed that the majority of image angles from the five head positions were statistically significantly different than image angles from the idealized head position. Maxillary teeth were more sensitive to 5 degrees up/down head rotation, with 5 degrees up causing mesial projection and 5 degrees down causing distal projection of maxillary roots. Mandibular anterior teeth were more sensitive to 5 degrees right/left head rotation, with the projected mesiodistal angular difference between 5 degrees right and 5 degrees left rotation ranging from 4.0 degrees to 22.3 degrees. Maxillary teeth were relatively unaffected by 5 degrees right/left head rotation, and mandibular teeth were relatively unaffected by 5 degrees up/down head rotation. It was concluded that the clinical assessment of mesiodistal tooth angulation with panoramic radiography should be approached with extreme caution with an understanding of the inherent image distortions that can be further complicated by the potential for aberrant head positioning.     

A preliminary report on a computer-assisted dental cast analysis system used for the prosthodontic treatment

To accomplish computerized 3D morphological analyses of maxillary and mandibular casts with malocclusions on the same co-ordinate system, a new reference co-ordinate located on soft tissue has been proposed consisting of the top of maxillary bilateral tubercles and incisive papilla on the maxillary cast. To test the validity of this co-ordinate system, the angles of the occlusal plane in this system were examined on 10 subjects with normal occlusion. In addition, to analyse maxillary and mandibular casts on the same co-ordinate system, a bite block was made under the intercuspal position. The maxillary cast was measured by 3D measuring system, then, the bite block was placed on maxillary casts, and measured similarly. To examine the position reproducibility of this method, 3D co-ordinates of the apex of the buccal cusp of the mandibular pre-molar in five bite blocks were determined. The angles formed of the occlusal plane were 1.3 +/- 1.3 degrees and 0.2 +/- 1.1 degrees on the sagittal and frontal base plane, respectively. This co-ordinate system had enough stability to replace the occlusal plane. By the measurement of bite blocks, the co-ordinates of the mandibular cusp tips were determined within the deviation of 0.2 mm.     

The effects of positioning variations in transcranial radiographs of the temporomandibular joint: a laboratory study

The relationship of the mandibular condyle to the articular fossa and eminence as seen on transcranial oblique lateral (TOL) radiographs of the temporomandibular joint is used by some clinicians as an important diagnostic sign and indicator of treatment. The literature is divided on the validity of this. The aim of this study was to consider the effects of variations in both the position of the joint and the X-ray beam orientation on the image seen on TOL radiographs. TOL radiography of a mounted block specimen of a human temporomandibular joint and associated tissues was carried out using a range of specimen rotations (+20 degrees to -20 degrees with respect to the sagittal plane) and X-ray beam angulations (20 degrees, 25 degrees, 30 degrees). Analysis of tracings of the joint images showed that most of the parameters measured varied by statistically significant amounts with changes in either specimen rotation or beam angulation. It is concluded that any convention which purports to evaluate the position of the mandibular condyle in relation to the articular fossa from TOL radiographs is invalid when the orientation of the condyle to coronal and horizontal planes is unknown.     

Three-dimensional computed tomographic evaluation of morphologic airway changes after mandibular setback osteotomy for prognathism

OBJECTIVE: To observe changes in the pharyngeal airway and the hyoid bone position after mandibular setback osteotomy in 30 patients with mandibular prognathism by means of 3-dimensional computed tomography (3DCT). STUDY DESIGN: Preoperative and postoperative computed tomography (CT) examinations were performed on 17 patients treated by sagittal split ramus osteotomy with rigid osteosynthesis and on 13 patients treated by intraoral vertical ramus osteotomy without osteosynthesis. The amount of mandibular setback was measured by the preoperative to postoperative difference of the mandibular position in axial CT images. The sizes of the preoperative and postoperative pharyngeal airway were evaluated from semitransparent and crosscut 3DCT images. Postoperative displacement of the hyoid bone was evaluated by a technique to superimpose a postoperative hard tissue 3DCT image on the preoperative image. The helical scan technique was used in the CT examination. The volume rendering technique was used to create 3DCT images. RESULTS: The mean mandibular setback was 7.8 +/- 2.1 mm with a range of 5 to 11 mm. Three months after surgery, the lateral and frontal widths of the pharyngeal airway had decreased significantly in comparison with the preoperative width. The mean reduction rates of the lateral and frontal width were 23.6% and 11.4%, respectively. The diminished airway did not recover by either 6 months or 1 year after surgery in most cases. Downward and posterior displacement of the hyoid bone was seen postoperatively. There were positive correlations between the amount of mandibular setback and reduction of the lateral width of the pharyngeal airway (r = 0.54) and the amount of hyoid bone displacement (r = 0.42). There were no significant differences between the two surgical techniques. CONCLUSION: Three-dimensional computed tomography was a practical imaging technique to evaluate the morphologic airway changes. The pharyngeal airway may have irreversible narrowing after mandibular setback surgery.     

A study on reliability of the tomographic image of the temporomandibular joint

Summary For this study, seven different types of phantom were made simulating the condyle. The phantoms attached to a human dry skull were tomographed using the Polytome-U, under identical conditions to those of tomography for patients. There was no significant difference of the images between tube side and film side of the mandible. The images of the medial part of the TMJ were clearer than that of the lateral part. A discrepancy of contours on the focal plane between the phantom and the tomographic image occurred when the inclination of the phantom surface was larger than the maximum exposure angle. Concerning the influence of focal movements to image quality, the images obtained from hypocycloidal movements were superior with minimum superimposition, although the contrast of the image varied when the phase of the hypocycloidal movements were altered. Any sectional images were not manifested with the phantoms when the inclination of the phantom surface was larger than 23 degrees. Furthermore, 106 condyles from human dry skull were examined on the area of which the inclination of the condylar surface was less than 23 degrees. The mean latero-medial distance of the area was 14.1mm, which corresponded to 75% of whole latero-medial distance of the condyle.     

Frequency domain analysis of cross-sectional images of the posterior mandible

The Siemens Orthophos (Siemens, Mu¨nchen, Germany) is a panoramic machine that uses a microchip to control the movements of the radiation source and film. Several programs are available for different views of the facial skeleton and associated structures. Program 16 is dedicated to cross-sectional imaging of the posterior mandible. Three millimeter cross-sections were cut from 12 cadaver specimens of the mandible. These sections were imaged separately by contact radiography, 48° hypocycloidal tomography of Philips Polytome (Philips-Massiot, Paris, France), and program 16 of the Orthophos panoramic machine. Program 16 of the Orthophos was also used to image the cross-sections after they were glued back together with the surrounding parts of the specimens. Four different images of the cross-sections were thus obtained. The contact radiographs were used as gold standards. Frequency domain analysis, which was used to compare the images resulting from each imaging modality, demonstrated that useful diagnostic information was in the range of 0.12 to 0.60 cycles/mm for the contact radiographs. In spite of differing tomographic angles for the Orthophos program 16 and the hypocycloidal tomography, the images of the 3 mm cross-sections showed similar frequency distribution. However, the Orthophos Program 16 did not produce diagnostically useful images when the cross-sections were imaged with the surrounding parts of the specimens probably because of the narrow tomographic angle used for this program. These images had strong low to medium frequency components compared with the gold standard images. These results suggest that diagnostically more useful images with the Orthophos might be obtained by increasing the tomographic angle.     

基于锥形束CT影像对下颌管解剖变异的系统评价

目的 基于锥形束CT(cone beam computed tomography,CBCT)影像进行解剖学研究的系统评价,以评估下颌管变异及其解剖学发生率.方法 在PubMed、Cochrane、CNKI数据库中搜索2005年1月至2019年12月关于成年人群下颌管解剖变异的相关文章,并采用随机效应模型对其进行分析.通...     

Transverse growth of the maxilla and mandible in untreated girls with low, average, and high MP-SN angles: A longitudinal study

INTRODUCTION: The purpose of this study was to investigate maxillary and mandibular transverse growth in untreated female subjects with low, average, and high mandibular plane angles longitudinally from ages 6 to 18. METHODS: Eighty-one untreated white girls with low (< or = 27 degrees , n = 16), average (> 27 degrees to < 37 degrees , n = 41), and high (> or = 37 degrees , n = 24) mandibular plane angles at age 6 were selected from the Bolton-Brush and Burlington Growth Studies. For each subject, longitudinal posteroanterior cephalograms at different ages (from ages 6 to 18) were traced, and the widths of maxilla and mandible were measured. All the measurements were converted by using a magnification factor of 8.5% (the subject-to-film distance was set at 13 cm). RESULTS: At age 6, the high-angle group had narrower maxillary and mandibular widths than the low-angle group, and this trend continued until age 18. From ages 6 to 14, maxillary width showed a steady and similar rate of increase for all 3 groups (0.90-0.95 mm per year), yet a plateau was reached at age 14 for all groups. Mandibular width increased at a steady rate (about 1.6 mm/year) for all 3 groups until age 14, and a plateau was reached for the high-angle group. For the low- and average-angle groups, mandibular growth continued from ages 14 to 18 but at a slower rate (0.85 mm and 0.39 mm per year, respectively). CONCLUSIONS: Vertical facial patterns (with low or high mandibular plane angles) might play a strong role in the transverse growth of the maxilla and the mandible.     

Relationship between jaws and the masseter muscle by superimposing MR images on the cephalogram

The purpose of this study was to observe the morphological relationship between maxillofacial skeleton and masseter by superimposing the masseter image constructed by MR image scanning on the cephalogram. Sixteen subjects with different mandibular plane angle were examined in this study. Cephalogram and MR images of each subject were taken, and the images were input to a computer by using a digitizer. The areas of masseter were selected in each MR scan image which were projected to the mid-sagittal layer of the MR scan images. The synthesized image of cephalogram and masseter was obtained by completely superimposing sagittal images of the masseter with the mid-sagittal-plane MR image on the cephalogram. The inclination of masseter was determined by the center of gravity on the cross-section of masseter. These synthesized images of cephalogram and masseter showed various shapes of masseter according to different mandibular plane angle. The inclination of masseter had a close correlation with some skeletal parameters (mandibular plane angle, ANB, Y-axis, facial angle, saddle angle) of cephalometric analysis. The volume of the masseter also had a close correlation with skeletal parameters (mandibular plane angle, gonial angle, Y-axis). These results revealed that morphometric analysis using synthesized images of cephalogram and masseter is useful, and that the inclination and the volume of masseter may have an influence on the shape of the mandibular bone and its vertical and anteroposterior development.