David Hatcher

Radiation absorbed in maxillofacial imaging with a new dental computed tomography device

OBJECTIVE The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the effective dose for the NewTom 9000, a new generation of computed tomographic devices designed specifically for dental applications. Comparisons are made with existing reports on dose measurement and effective dose estimates for panoramic examinations and other computed tomographic imaging modalities for dental implants. STUDY DESIGN Thermoluminescent dosimeters were implanted in a tissue-equivalent humanoid phantom at anatomic sites of interest. Absorbed dose measurements were obtained after single and double exposures. The averaged tissue-absorbed doses were used for the calculation of the whole-body effective dose. RESULTS The effective dose for imaging of maxillomandibular volume with a NewTom 9000 machine is 50.3 muSv. CONCLUSION The effective dose with the NewTom 9000 machine is significantly less than that achieved with other computed tomographic imaging methods and is within the range of traditional dental imaging modalities.

Comparison of airway space with conventional lateral headfilms and 3-dimensional reconstruction from cone-beam computed tomography

INTRODUCTION Changes in the normal pattern of nasal respiration can profoundly affect the development of the craniofacial skeleton in both humans and experimental animals. The orthodontist is often the first clinician to notice that a child is breathing primarily through the mouth, either at the initial examination or later during treatment. The lateral headfilm, part of the patients normal records, might show increased adenoid masses, suggesting that these could be part of the problem. Previous studies have, however, questioned the validity of the information from lateral headfilm. METHODS Our aim was to compare imaging information about nasopharyngeal airway size between a lateral cephalometric headfilm and a 3-dimensional cone-beam computed tomography scan in adolescent subjects. The nasopharyngeal airway area and volume were measured in 35 subjects (8 boys, 27 girls; average age, 14 years). RESULTS Volumetric measurement errors ranged from 0% to 5% compared with known physical airway phantoms used to calibrate. A moderately high (r = 0.75) correlation was found between airway area and volume; the larger the area, the larger the volume. However, there was considerable variability in the airway volumes of patients with relatively similar airways on the lateral headfilms. Nine of the 35 patients had over 25% of the potential nasopharyngeal airway volume occupied by inferior turbinate protuberances, leading to significant airway restriction in some patients. CONCLUSIONS The cone-beam 3-dimensional scan is a simple and effective method to accurately analyze the airway.

Comparison of cone beam computed tomography imaging with physical measures

OBJECTIVES The goal of this study was to determine the accuracy of measuring linear distances between landmarks commonly used in orthodontic analysis on a human skull using two cone beam CT (CBCT) systems. METHODS Measurements of length were taken using volumetric data from two CBCT systems and were compared with physical measures using a calliper applied to one human adult skull. Landmarks were identified with chromium steel balls embedded at 32 cranial and 33 mandibular landmarks and the linear measures were taken with a digital calliper. The skull was then scanned with two different CBCT systems: the NewTom QR DVT 9000 (Aperio Inc, Sarasota, FL) and the Hitachi MercuRay (Hitachi Medico Technology, Tokyo, Japan). CT data including the landmark point data were threshold segmented using CyberMeds CB Works software (CB Works 1.0, CyberMed Inc., Seoul, Korea). The resulting segmentations were exported from CB Works as VRML (WRL) files to Amira software (Amira 3.1, Mercury Computer Systems GmbH, Berlin, Germany). RESULTS The error was small compared with the gold standard of the physical calliper measures for both the NewTom (0.07+/-0.41 mm) and CB MercuRay (0.00+/-0.22 mm) generated data. Absolute error to the gold standard was slightly positive, indicating minor compression relative to the calliper measurement. The error was slightly smaller in the CB MercuRay than in the NewTom, probably related to a broader greyscale range for describing beam attenuation in 12-bit vs 8-bit data. CONCLUSIONS The volumetric data rendered with both CBCT systems provided highly accurate data compared with the gold standard of physical measures directly from the skulls, with less than 1% relative error.

Craniofacial imaging in orthodontics: Historical perspective, current status, and future developments

Rapid and substantial advances in imaging methods and technology have not always been expediently or adequately communicated to the practicing orthodontist. In this review we highlight contemporary imaging techniques and innovations in imaging that, in the future, are likely to greatly improve the depiction of craniofacial structures for use in diagnosis and treatment planning. In order to provide an appropriate background for this topic, we first discuss the evolution of craniofacial imaging in orthodontics and review the limitations of current methods, including the two-dimensional representation of three-dimensional anatomy, depiction as a patchwork of site-specific images, associated geometric errors, and images that have a limited point of view and are static in space and time. Three-dimensional computed tomography can be considered a partial solution to these limitations, but imaging costs, radiation exposure, and lack of soft tissue representation may make it unacceptable for routine orthodontics. A more complete solution might be achieved through digital processing of contemporary imaging technologies that would extend their capabilities, overcome many of their limitations, and result in an increase in the amount of relevant information obtained. Digital processes are currently being developed that create accurate multidimensional models that integrate form and function. These models will be interactive, linked to knowledge databases, and will provide the clinician with answers to pertinent questions. These advances in imaging are likely to enhance the accuracy and reliability of orthodontic diagnosis and treatment planning, and will be of importance in both clinical practice and research.

Radiographic findings in bisphosphonate-treated patients with stage 0 disease in the absence of bone exposure.

PURPOSE Radiographic features in patients with bisphosphonate-related osteonecrosis of the jaw (BRONJ) are well described, but less is known in bisphosphonate-exposed individuals with stage 0 disease (clinical symptoms without exposed necrotic bone) considered at risk for BRONJ. We sought to characterize radiographic findings in a subgroup of patients with concerning clinical symptoms and bisphosphonate exposure to identify imaging features that may presage development of BRONJ. MATERIALS AND METHODS A dental symptom survey was returned by 8,572 Kaiser Permanente Health Plan members receiving chronic oral bisphosphonate therapy, and 1,005 patients reporting pertinent dental symptoms or complications after dental procedures were examined. Those without BRONJ but with concerning symptoms were referred for clinical evaluation, including imaging. Among the subset who received maxillofacial imaging, we identified those with stage 0 disease and abnormal radiographic features. RESULTS There were a total of 30 patients without exposed bone but with concerning symptoms who received maxillofacial imaging (panoramic radiography or computed tomography) in the context of clinical care. Among these 30 patients, 10 had stage 0 disease with similar radiographic features of regional or diffuse osteosclerosis in clinically symptomatic areas, most with extension beyond the involved site. Other findings in these 10 patients included density confluence of cortical and cancellous bone, prominence of the inferior alveolar nerve canal, markedly thickened and sclerotic lamina dura, uniform periradicular radiolucencies, cortical disruption, lack of bone fill after extraction, and a persisting alveolar socket. None had exposed bone develop during 1-year follow-up. The remaining 20 patients had normal or localized radiographic findings consistent with odontogenic pathology. CONCLUSION In 10 of 30 symptomatic patients referred for clinical evaluation and imaging, a consistent finding was conspicuous osteosclerosis in clinically symptomatic areas characteristic of stage 0 disease. These data support the need to better understand radiographic features associated with bisphosphonate exposure and to determine whether osteosclerosis is a specific finding indicative of the risk for progression to BRONJ.

Mesiodistal Root Angulation Using Panoramic and Cone Beam CT

OBJECTIVE To determine if the panoramic projection can accurately determine mesiodistal root angulations. MATERIALS AND METHODS A plaster study model of the dentition of each of five patients was prepared. A radiographic stent containing radiopaque markers was fabricated for each of the models. Panoramic and cone beam computed tomography (CBCT) scans were taken on each patient with the radiographic stent seated on the dentition. Root angulations for each of the radiographic images were measured and compared. RESULTS Root angulation was measured by three independent individuals and good reliability between measurements was demonstrated. Compared to plaster model measurements (the gold standard), the CBCT scan produced very accurate measurements of root angulation. Compared to CBCT images, panoramic projections did not provide reliable data on root angulation. CONCLUSION Panoramic images did not accurately represent the mesiodistal root angulations on clinical patients.

Evaluation of the human airway using cone-beam computerized tomography

OBJECTIVE The goal of this project was to define and measure human airway space with radiographic volumetric 3-dimensional imaging and digital reconstruction of the pharynx using cone-beam computerized tomography. STUDY DESIGN This was a randomized retrospective study. Ten patient scans were selected randomly from a pool of 196 subjects seeking dental treatment at the University of California, San Francisco. Digital Imaging and Communications in Medicine-format volume images were captured using a low-radiation rapid-scanning cone-beam computerized tomography system (Hitachi MercuRay). RESULTS Detailed progressive rostrocaudal cross-sectional area histograms indicated that 8 of the 10 subjects demonstrated a region of maximum constriction near the oropharynx level. The most restricted cross-sectional area varied from 90 mm(2) to 360 mm(2). CONCLUSIONS The maximum constriction of the airway in 10 subjects quietly breathing for 10 seconds indicated variation in the level of the pharynx and the extent of the rostrocaudal zone of restriction.

Anthropometric analysis of the human mandibular cortical bone as assessed by cone-beam computed tomography.

PURPOSE The purpose of this study is to assess cortical thickness, height, and width with cone-beam computed tomography (CBCT), and determine the relationship of these parameters with age. PATIENTS AND METHODS A total of 113 subjects from the University of California at San Francisco Orthodontic Clinic with a CBCT scan were enrolled. Subjects were stratified by age in decades. Thickness of buccal and lingual cortices and mandibular height and width were evaluated in 5 regions (13 sites). A single factorial ANOVA was used to compare the parameters among age groups. P less than or equal to .05 was statistically significant. RESULTS There were 44 (38.9%) males; 69 females. For all groups, the thickest to the least thick cortical plates were: base of the mandible, lower buccal one third, upper lingual one third, upper buccal one third, and lower lingual one third. In all groups, the mandible increased in height as the midline was approached, and the width of the upper third of the mandible decreased from the second molar to the symphysis whereas the reverse occurred in the lower third. Comparison of the age groups showed that subjects 10 to 19 years old had thinner cortical plates than other age groups (P <or= .05) with peak thickness in subjects 40 to 49 years old. The subjects 10 to 19 years old also had lower posterior mandibular height (P <or= .05). There was no statistical difference in width among the groups. CONCLUSIONS The mandibular cortical bone is thickest at the base, on the buccal side. Subjects who are 10 to 19 years old have thinner cortical bone and decreased mandibular height compared with all other age groups. The mandible continues to mature through 40 to 49 years of age and then decreases in thickness after this period.

Quantitative assessment of temporomandibular joint disk status

The purpose of this study was to quantify temporomandibular joint disk-slice information produced by magnetic resonance imaging by means of a stepwise discriminant analysis. One hundred ninety-four adolescents consented to magnetic resonance imaging evaluation of their temporomandibular joints. Sagittal magnetic resonance imaging slices of each joint were assigned to one of six subjective categories of disk position by an experienced maxillofacial radiologist. Standardized reference planes transferred to each magnetic resonance image from corresponding lateral cephalometric radiographics facilitated the measurement of disk length and disk displacement and the computation of ratio values of these measurements. Discriminant analysis revealed that all three quantitative variables were descriptive and discriminant for grouping slice data into pre-established subjective categories. Cross-validation and misclassification error calculations showed a 69.3% agreement between subjective and discriminant classification. Therefore quantification of disk displacement can be used in place of subjective evaluation. In addition, discriminant analysis disclosed a reduction in disk length associated with increased severity of disk displacement.

Three-Dimensional Assessment of the Eruption Path of the Canine in Individuals With Bone-Grafted Alveolar Clefts Using Cone Beam Computed Tomography

Objective To evaluate the eruption path of the permanent maxillary canine during a 1-year period after secondary alveolar bone grafting and to (1) compare the canine eruption path on the cleft and noncleft side, (2) examine the number of congenially missing lateral incisors and the rate of canine impaction, and (3) examine the relationship between the eruption status of the canine and timing of alveolar bone grafting relative to age and canine root development using cone beam computed tomography (CBCT). Methods Cone beam computed tomography scans for 17 nonsyndromic unilateral cleft lip and palate (UCLP), and four bilateral cleft lip and palate (BCLP) consecutive cases of alveolar bone grafting surgery were obtained after orthodontic expansion and before alveolar bone grafting and at least 1 year postsurgery on the Hitachi MercuRay CBCT machine. The DICOM files were imported into Dolphin 3D Imaging 10.5 and reoriented for consistency. The X, Y, and Z coordinates were determined for the canine cusp tip and root tip on both the cleft and noncleft sides. The direction of movement of the canine in 1 year was determined. Results Most canines on both the cleft and noncleft sides moved incisally, facially, and mesially. Twelve percent of the canines on the cleft side appeared to require surgical exposure. Eighty percent of the canines had less than half root development at the time of bone grafting. The amount of root development did not affect the outcome in terms of eruption amount or direction. Conclusions Most canines on both the cleft and noncleft side moved incisally, facially, and mesially.