André Mol

In Vivo Comparison of Conventional and Cone Beam CT Synthesized Cephalograms

OBJECTIVE To compare measurements from synthesized cone-beam computed tomography (CBCT) lateral cephalograms using orthogonal and perspective projections with those from conventional cephalometric radiographs. MATERIALS AND METHODS Thirty-one patients were imaged using CBCT and conventional cephalometry. CBCT volume data were imported in Dolphin 3D. Orthogonal and perspective lateral cephalometric radiographs were created from three-dimensional (3D) virtual models. Twelve linear and five angular measurements were made on synthesized and conventional cephalograms in a randomized fashion. Conventional image measurements were corrected for known magnification. Linear and angular measurements were compared between image modalities using repeated measures analysis of variance. Statistical significance was defined as an alpha level of .01. RESULTS With the exception of the Frankfort-mandibular plane angle (P < .0001), angular measurements were not statistically different for any modality (P > .01). Linear measurements, whether based on soft or hard tissue landmarks, were not statistically different (P > .01). CONCLUSIONS Measurements from in vivo CBCT synthesized cephalograms are similar to those based on conventional radiographic images. Thus, additional conventional imaging may generally be avoided when CBCT scans are acquired for orthodontic diagnosis.

Precision of cephalometric landmark identification: Cone-beam computed tomography vs conventional cephalometric views

INTRODUCTION In this study, we compared the precision of landmark identification using displays of multi-planar cone-beam computed tomographic (CBCT) volumes and conventional lateral cephalograms (Ceph). METHODS Twenty presurgical orthodontic patients were radiographed with conventional Ceph and CBCT techniques. Five observers plotted 24 landmarks using computer displays of multi-planer reconstruction (MPR) CBCT and Ceph views during separate sessions. Absolute differences between each observers plot and the mean of all observers were averaged as 1 measure of variability (ODM). The absolute difference of each observer from any other observer was averaged as a second measure of variability (DEO). ANOVA and paired t tests were used to analyze variability differences. RESULTS Radiographic modality and landmark were significant at P <0.0001 for DEO and ODM calculations. DEO calculations of observer variability were consistently greater than ODM. The overall correlation of 1920 paired ODM and DEO measurements was excellent at 0.972. All bilateral landmarks had increased precision when identified in the MPR views. Mediolateral variability was statistically greater than anteroposterior or caudal-cranial variability for 5 landmarks in the MPR views. CONCLUSIONS The MPR displays of CBCT volume images provide generally more precise identification of traditional cephalometric landmarks. More precise location of condylion, gonion, and orbitale overcomes the problem of superimposition of these bilateral landmarks seen in Ceph. Greater variability of certain landmarks in the mediolateral direction is probably related to inadequate definition of the landmarks in the third dimension.

Interproximal tissue dimensions in relation to adjacent implants in the anterior maxilla: clinical observations and patient aesthetic evaluation.

OBJECTIVES This clinical study aimed to assess (i) interproximal tissue dimensions between adjacent implants in the anterior maxilla, (ii) factors that may influence interimplant papilla dimensions, and (iii) patient aesthetic satisfaction. MATERIAL AND METHODS Fifteen adults, who had two or more adjacent implants (total of 35) in the anterior maxilla, participated in the study. The study design involved data collection from treatment records, clinical and radiographic assessment, and a questionnaire evaluating aesthetic satisfaction. RESULTS The median vertical dimension of interimplant papillae, i.e., distance from tip of the papilla to the bone crest, was 4.2 mm. Missing papilla height (PH) at interimplant sites was on average 1.8 mm. Median proximal biologic width at interimplant sites was 7 mm. The most coronal bone-to-implant contact at implant-implant sites was located on average 4.6 mm apical to the bone crest at comparable neighbouring implant-tooth sites. The tip of the papilla between adjacent implants was placed on average 2 mm more apically compared with implant-tooth sites. The contact point between adjacent implant restorations extended more apically by 1 mm on average compared with implant-tooth sites. Median missing PH was 1 mm when an immediate provisionalization protocol had been followed, whereas in the case of a removable temporary it was 2 mm. Split group analysis showed that for missing PH<or=1 mm, the median horizontal distance between implants at shoulder level was 3 mm. Patient satisfaction with the appearance of interimplant papillae was on average 87.5%, despite a Papilla Index of 2 in most cases. CONCLUSIONS The apico-coronal proximal biologic width position and dimension appear to determine papilla tip location between adjacent implants. There was a significant association between the provisionalization protocol and missing PH, which was also influenced by the horizontal distance between implants. Patient aesthetic satisfaction was high, despite a less than optimal papilla fill.

Three-dimensional quantification of mandibular asymmetry through cone-beam computerized tomography

OBJECTIVE The aim of this study was to determine if 3-dimensional (3D) shape analysis precisely diagnoses right and left differences in asymmetry patients. STUDY DESIGN Cone-beam computerized tomography (CT) data were acquired before treatment from 20 patients with mandibular asymmetry. 3D shape analysis was used to localize and quantify the extent of virtually simulated asymmetry. Two approaches were used: 1) mirroring on the midsagittal plane determined from landmarks; and 2) mirroring on an arbitrary plane and then registering on the cranial base of the original image. The validation presented in this study used simulated data and was applied to 3 clinical cases. RESULTS For mirroring on the midsagittal plane, there was a >99% probability that the difference between measured and simulated asymmetry was <0.5 mm. For mirroring with cranial base registration, there was a >84% probability of differences <0.5 mm. CONCLUSIONS Mandibular asymmetry can be precisely quantified with both mirroring methods. Cranial base registration has the potential to be used for patients with trauma situations or when key landmarks are unreliable or absent.

The performance of projective standardization for digital subtraction radiography.

OBJECTIVE We sought to test the performance and robustness of projective standardization in preserving invariant properties of subtraction images in the presence of irreversible projection errors. Study design Twenty bone chips (1-10 mg each) were placed on dentate dry mandibles. Follow-up images were obtained without the bone chips, and irreversible projection errors of up to 6 degrees were introduced. Digitized image intensities were normalized, and follow-up images were geometrically reconstructed by 2 operators using anatomical and fiduciary landmarks. Subtraction images were analyzed by 3 observers. RESULTS Regression analysis revealed a linear relationship between radiographic estimates of mineral loss and actual mineral loss (R(2) = 0.99; P <.05). The effect of projection error was not significant (general linear model [GLM]: P >.05). There was no difference between the radiographic estimates from images standardized with anatomical landmarks and those standardized with fiduciary landmarks (Wilcoxon signed rank test: P >.05). Operator variability was low for image analysis alone (R(2) = 0.99; P <.05), as well as for the entire procedure (R(2) = 0.98; P <.05). The predicted detection limit was smaller than 1 mg. CONCLUSIONS Subtraction images registered by projective standardization yield estimates of osseous change that are invariant to irreversible projection errors of up to 6 degrees. Within these limits, operator precision is high and anatomical landmarks can be used to establish correspondence.

Comparison of two methods for quantitative assessment of mandibular asymmetry using cone beam computed tomography image volumes

OBJECTIVES The aim of this study was to compare two methods of measuring mandibular asymmetry. The first method uses mirroring of the mandible in the midsagittal plane; the second uses mirroring of the mandible and registration on the cranial base. METHODS Surface models were constructed from cone beam CT (CBCT) scans of 50 patients with asymmetry. For the first approach, a midsagittal plane was defined for each patient as the plane passing through nasion, anterior nasal spine and basion. Mirrors for both halves of the mandible were created. The second approach consisted of mirroring the image volume by flipping the left and right sides and then registering the mirrored image onto the cranial base using a mutual information maximization method. Surface distances between hemimandibles and mirrors were calculated for nine regions. RESULTS There was no statistically significant difference between the mean surface distance measurements obtained with the two approaches and when comparing both halves in most areas. CONCLUSION Both mirroring techniques provided similar quantification of mandibular asymmetry in this cohort.

Stationary intraoral tomosynthesis for dental imaging

Despite recent advances in dental radiography, the diagnostic accuracies for some of the most common dental diseases have not improved significantly, and in some cases remain low. Intraoral x-ray is the most commonly used x-ray diagnostic tool in dental clinics. It however suffers from the typical limitations of a 2D imaging modality including structure overlap. Cone-beam computed tomography (CBCT) uses high radiation dose and suffers from image artifacts and relatively low resolution. The purpose of this study is to investigate the feasibility of developing a stationary intraoral tomosynthesis (s-IOT) using spatially distributed carbon nanotube (CNT) x-ray array technology, and to evaluate its diagnostic accuracy compared to conventional 2D intraoral x-ray. A bench-top s-IOT device was constructed using a linear CNT based X-ray source array and a digital intraoral detector. Image reconstruction was performed using an iterative reconstruction algorithm. Studies were performed to optimize the imaging configuration. For evaluation of s-IOT’s diagnostic accuracy, images of a dental quality assurance phantom, and extracted human tooth specimens were acquired. Results show s-IOT increases the diagnostic sensitivity for caries compared to intraoral x-ray at a comparable dose level.

Imaging of the TMJ

There are a number of techniques available for imaging the temporomandibular joint (TMJ), including conventional and panographic radiography, computed tomography (CT), and magnetic resonance imaging (MRI). The optimal imaging strategy in a patient with TMJ disease will depend largely on the clinical scenario and the questions to be answered. In general, radiography and CT are preferred for assessment of hard tissues, while MRI is more suited for evaluating the soft tissues, including the articular disc. In this chapter, we review the most commonly used techniques for TMJ imaging, with a focus on their indications, relative strengths and weaknesses, image interpretation, and common findings in patients with TMJ dislocations.

Stationary digital intraoral tomosynthesis: Demonstrating the clinical potential of the first-generation system

Stationary intraoral tomosynthesis (sIOT) is an experimental imaging approach using a fixed array of carbon nanotubeenabled x-ray sources to produce a series of projections from which three-dimensional information can be reconstructed and displayed. Customized to the dental workspace, the first-generation sIOT tube is compact, easy-to-operate, and designed to interface with standard digital intraoral detectors. The purpose of this work was to explore the utility of the sIOT device across a range of dental pathologies and thereby identify limitations potentially amenable to correction through post-acquisition processing. Phantoms, extracted human teeth, and cadaveric specimens containing caries, fractures, and dilacerated roots, often associated with amalgam restorations, were imaged using tube settings that match the kVp and mA used in conventional clinical 2D intraoral imaging. An iterative reconstruction approach generated a stack of image slices through which the reader scrolls to appreciate depth relationships. Initial experience demonstrated an improved ability to visualize occlusal caries, interproximal caries, crown and root fractures, and root dilacerations when compared to 2D imaging. However, artifacts around amalgam restorations and metal implants proved problematic, leading to the incorporation of an artifact reduction step in the post-acquisition processing chain. These findings support the continued study of sIOT as a viable limited-angle tomography tool for dental applications and provide a foundation for the ongoing development of image processing steps to maximize the diagnostic utility of the displayed images.

Automatic quantification framework to detect cracks in teeth

Studies show that cracked teeth are the third most common cause for tooth loss in industrialized countries. If detected early and accurately, patients can retain their teeth for a longer time. Most cracks are not detected early because of the discontinuous symptoms and lack of good diagnostic tools. Currently used imaging modalities like Cone Beam Computed Tomography (CBCT) and intraoral radiography often have low sensitivity and do not show cracks clearly. This paper introduces a novel method that can detect, quantify, and localize cracks automatically in high resolution CBCT (hr-CBCT) scans of teeth using steerable wavelets and learning methods. These initial results were created using hr-CBCT scans of a set of healthy teeth and of teeth with simulated longitudinal cracks. The cracks were simulated using multiple orientations. The crack detection was trained on the most significant wavelet coefficients at each scale using a bagged classifier of Support Vector Machines. Our results show high discriminative specificity and sensitivity of this method. The framework aims to be automatic, reproducible, and open-source. Future work will focus on the clinical validation of the proposed techniques on different types of cracks ex-vivo. We believe that this work will ultimately lead to improved tracking and detection of cracks allowing for longer lasting healthy teeth.