Cone beam computed tomography devices in the evaluation of buccal bone in anterior teeth.

OBJECTIVE: To determine the accuracy of various cone beam computed tomography (CBCT) devices in assessing the buccal bone in anterior teeth. MATERIAL AND METHODS: A skull encased in tissue equivalent material was imaged with six CBCT devices: 3D Accuitomo 170 (J. Morita, Japan), CS 9000 3D (Carestream Dental, France), CS 9300 (Carestream Dental, France), Eagle 3D (Dabi Atlante, Brazil), i-CAT Classic (Imaging Sciences International, USA) and Orthophos XG 3D (Sirona Dental System, USA). The exposure and acquisition protocols were determined using the manufacturer's guidelines, the voxel size adjusted as close as possible to 0.2 mm. Cross-sectional images were evaluated randomly, and the buccal bone was assessed. RESULTS: The statistics were calculated based on a logistic regression model with the significance level set at 5%. All CBCT devices showed high accuracy; however, observers noted that the accuracy and sensitivity of CS 9300 device were slightly superior. CONCLUSION: The diagnostic performance of all CBCT devices was high for the evaluation of buccal bone in anterior teeth. When the clinical usefulness of an imaging modality is equivalent, the choice of appropriate imaging should be directed towards the modality that delivers the least radiation dose to the patient for a specific diagnostic task.

Cone Beam Computed Tomographic imaging in orthodontics.

Over the last 15 years, cone beam computed tomographic (CBCT) imaging has emerged as an important supplemental radiographic technique for orthodontic diagnosis and treatment planning, especially in situations which require an understanding of the complex anatomic relationships and surrounding structures of the maxillofacial skeleton. CBCT imaging provides unique features and advantages to enhance orthodontic practice over conventional extraoral radiographic imaging. While it is the responsibility of each practitioner to make a decision, in tandem with the patient/family, consensus-derived, evidence-based clinical guidelines are available to assist the clinician in the decision-making process. Specific recommendations provide selection guidance based on variables such as phase of treatment, clinically-assessed treatment difficulty, the presence of dental and/or skeletal modifying conditions, and pathology. CBCT imaging in orthodontics should always be considered wisely as children have conservatively, on average, a three to five times greater radiation risk compared with adults for the same exposure. The purpose of this paper is to provide an understanding of the operation of CBCT equipment as it relates to image quality and dose, highlight the benefits of the technique in orthodontic practice, and provide guidance on appropriate clinical use with respect to radiation dose and relative risk, particularly for the paediatric patient.

Comparison of digital scanning and polyvinyl siloxane impression techniques by dental students: instructional efficiency and attitudes towards technology.

INTRODUCTION: With increasing use of digital scanning with restorative procedures in the dental office, it becomes necessary that educational institutions adopt instructional methodology for introducing this technology together with conventional impression techniques. OBJECTIVE: To compare the time differences between instructing dental students on digital scanning (DS) (LAVA C.O.S. digital impression system) and a conventional impression technique (CI) (polyvinyl siloxane), and to compare students' attitudes and beliefs towards both techniques. MATERIALS AND METHODS: Volunteer sophomore dental students (n = 25) with no prior experience in clinical impressions were recruited and IRB consent obtained. Participants responded to a pre-and post-exposure questionnaire. Participants were instructed on the use of both DS and CI for a single tooth full coverage crown restoration using a consecutive sequence of video lecture, investigator-led demonstration and independent impression exercise. The time necessary for each step (minutes) was recorded. Statistical significance was calculated using dependent t-tests (time measurements) and 2-sample Mann-Whitney (questionnaire responses). RESULTS: The time spent teaching students was greater for DS than CI for video lecture (15.95 and 10.07 min, P = 0.0000), demonstration time (9.06 and 4.70 min, P = 0.0000) and impression time (18.17 and 8.59 min, P = 0.0000). Prior to the instruction and practice, students considered themselves more familiar with CI (3.96) than DS (1.96) (P = 0.0000). After the instruction and practice, participants reported CI technique proved significantly easier than expected (pre-instruction: 3.52 and post-instruction: 4.08, P = 0.002). However, overall participants' perception of ease of use for DS was not influenced by this instruction and practice experience (pre-instruction: 3.84 and post-instruction: 3.56, P = 0.106). Despite the results, 96% of participants expressed an expectation that DS will become their predominant impression technique during their careers. CONCLUSIONS: Dental students with no clinical experience have high expectations for digital scanning, and despite their initial difficulty, expect it to become their primary impression technique during their professional futures. The instructional time necessary for introducing DS into the curriculum is significantly greater than CI in both classroom (lecture) and clinical simulation settings (investigator-led demonstration).

Accuracy of CBCT images in the assessment of buccal marginal alveolar peri-implant defects: effect of field of view.

OBJECTIVES: To investigate the reliability and accuracy of cone beam CT (CBCT) images obtained at different fields of view in detecting and quantifying simulated buccal marginal alveolar peri-implant defects. METHODS: Simulated buccal defects were prepared in 69 implants inserted into cadaver mandibles. CBCT images at three different fields of view were acquired: 40 × 40, 60 × 60 and 100 × 100 mm. The presence or absence of defects was assessed on three sets of images using a five-point scale by three observers. Observers also measured the depth, width and volume of defects on CBCT images, which were compared with physical measurements. The kappa value was calculated to assess intra- and interobserver agreement. Six-way repeated analysis of variance was used to evaluate treatment effects on the diagnosis. Pairwise comparisons of median true-positive and true-negative rates were calculated by the χ² test. Pearson's correlation coefficient was used to determine the relationship between measurements. Significance level was set as p < 0.05. RESULTS: All observers had excellent intra-observer agreement. Defect status (p < 0.001) and defect size (p < 0.001) factors were statistically significant. Pairwise interactions were found between defect status and defect size (p = 0.001). No differences between median true-positive or true-negative values were found between CBCT field of views (p > 0.05). Significant correlations were found between physical and CBCT measurements (p < 0.001). CONCLUSIONS: All CBCT images performed similarly for the detection of simulated buccal marginal alveolar peri-implant defects. Depth, width and volume measurements of the defects from various CBCT images correlated highly with physical measurements.

Comparative diagnostic yield of cone beam CT reconstruction using various software programs on the detection of vertical root fractures.

OBJECTIVES: To evaluate the effect on diagnostic yield in the detection of experimentally induced vertical root fractures on cone beam CT images using four dental software program. METHODS: 190 single-rooted extracted human teeth were divided into three groups according to the pulp canal status: unrestored (UR), filled with gutta-percha (GP) and restored with a metallic custom post (Post). One-half of the sample of each group was artificially fractured and the segments repositioned. All teeth were scanned on a cone beam CT device at 0.2 mm nominal voxel resolution (i-CAT Platinum; Imaging Sciences International, Hatfield, PA). The data were exported as digital imaging and communications in medicine files and imported into Dolphin Imaging & Management Solutions, v. 11.5 (Patterson Dental Supply Inc., St Paul, MN), InVivoDental, v. 5.0 (Anatomage Inc., San Jose, CA) and Kodak Dental Imaging Software 3D module, v. 2.1.11 (Carestream Health Inc., Rochester, NY) software. Cross-sectional images in the acquisition (using Xoran CAT™, v. 3.0.34 software; Xoran Technologies, Ann Arbor, MI) and additional software were presented to three calibrated oral radiologists who rated the presence or absence of root fracture on a five-point scale. Receiver operating characteristic analysis was performed, and treatment comparisons compared by analysis of variance and pairwise comparisons were performed using Tukey's test at an a priori value of α < 0.05%. RESULTS: All dental software performed equally at detecting fractures. Fractures were significantly more difficult to detect when posts were present. CONCLUSIONS: The diagnosis of root fracture is software-independent. The presence of an intracanal metallic post significantly decreases the detection of artificially created root fractures.

Ex vivo detection of mesiobuccal canals in maxillary molars using CBCT at four different isotropic voxel dimensions.

AIM: To study observers' ability to detect mesiobuccal (MB) canals in maxillary molars using iCAT cone-beam computed tomography (CBCT) at different voxel dimensions and to assess the impact of clinical experience on accuracy of detection. METHODOLOGY: Using 12 experimental models with two molars each, CBCT scans were acquired at four different voxel dimensions. From the cross-section view of these scans, 96 videos were generated. Five endodontic postgraduate students and two endodontic staff watched the videos and counted the MB canals in each root. Horizontal sections of the roots were evaluated under magnification to determine the true canal numbers. The detection of MB canals within the four resolutions was compared by odds ratio, and the weighted χ(2) test compared detection accuracy to raters' clinical experience. Rater agreement was measured by kappa statistics. RESULTS: Overall, 92% of the maxillary molars had two MB canals upon analysis of horizontal cross-sections. The CBCT detection increased from 60.1% at 0.4 mm voxel size to 93.3% at 0.125 mm voxel size. Significant differences (P < 0.01) were observed between the different resolutions except for the 0.2 and the 0.125 voxel scans. Second-year trainees were significantly (CI = 0.2929-0.712) more accurate than first-year trainees and endodontic staff at MB canal detection (87.9% against 77.1% and 76.8%). Intra-rater reliability increased with higher-resolution scans (41.1% to 96.4%). CONCLUSIONS: The reliability of detection of maxillary molar MB2 canals in CBCT scans increased as the resolution improved. Accuracy of MB2 canal detection among observer groups could not be correlated with the observers' level of clinical experience.

Evaluation of web-based instruction for anatomical interpretation in maxillofacial cone beam computed tomography.

OBJECTIVES: To evaluate the effectiveness of a web-based instruction in the interpretation of anatomy in images acquired with maxillofacial cone beam CT (CBCT). METHODS: An interactive web-based education course for the interpretation of craniofacial CBCT images was recently developed at our institution. Self-evaluation modules on correlative anatomical features were also included to support the learning process. Three e-learner groups were selected to evaluate the effectiveness of the educational modules. The three groups were (1) oral health specialists (OHSs) (comprising periodontologists, prosthodontists, orthodontists and maxillofacial surgeons); (2) third grade (DS3) and (3) first grade (DS1) undergraduate dental students. The assessment modules that were part of the interactive web-course content were administered after delivery of the course material. In addition, each group received a computer affinity questionnaire to quantify the extent of knowledge about computers and a perception questionnaire to assess their attitudes toward the web-course. RESULTS: The OHS group yielded significantly better scoring results in the post-course test than the pre-course test. However, no statistically significant differences in test scores were found for both undergraduate student groups (DS1 and DS3). All groups presented a highly positive attitude towards the web-course, as was demonstrated by the post-course perception questionnaire. CONCLUSIONS: The present CBCT educational course is an effective didactic method for teaching OHSs the anatomical interpretation of CBCT multiplanar reformatted images and, for undergraduate students, it was found to be as effective as conventional educational methods in dentistry. The efficacy of a web-based educational course requires further evaluation.

A web-based instruction module for interpretation of craniofacial cone beam CT anatomy.

OBJECTIVES: To develop a web-based module for learner instruction in the interpretation and recognition of osseous anatomy on craniofacial cone-beam CT (CBCT) images. METHODS: Volumetric datasets from three CBCT systems were acquired (i-CAT, NewTom 3G and AccuiTomo FPD) for various subjects using equipment-specific scanning protocols. The datasets were processed using multiple software to provide two-dimensional (2D) multiplanar reformatted (MPR) images (e.g. sagittal, coronal and axial) and three-dimensional (3D) visual representations (e.g. maximum intensity projection, minimum intensity projection, ray sum, surface and volume rendering). Distinct didactic modules which illustrate the principles of CBCT systems, guided navigation of the volumetric dataset, and anatomic correlation of 3D models and 2D MPR graphics were developed using a hybrid combination of web authoring and image analysis techniques. Interactive web multimedia instruction was facilitated by the use of dynamic highlighting and labelling, and rendered video illustrations, supplemented with didactic textual material. HTML coding and Java scripting were heavily implemented for the blending of the educational modules. RESULTS: An interactive, multimedia educational tool for visualizing the morphology and interrelationships of osseous craniofacial anatomy, as depicted on CBCT MPR and 3D images, was designed and implemented. CONCLUSIONS: The present design of a web-based instruction module may assist radiologists and clinicians in learning how to recognize and interpret the craniofacial anatomy of CBCT based images more efficiently.

Diagnostic accuracy of film-based, TIFF, and wavelet compressed digital temporomandibular joint images.

The purpose of this research was to determine if digitization and the application of various compression routines to digital images of temporomandibular joint (TMJ) radiographs would diminish observer accuracy in the detection of specific osseous characteristics associated with TMJ degenerative joint disease (DJD). Nine observers viewed 6 cropped hard-copy radiographic films each of 34 TMJs (17 radiographic series). Regions of interest measuring 2 in x 2 in were digitized using an 8-bit scanner with transparency adapter at 300 dpi. The images were placed into a montage of 6 images and stored as tagged image file format (TIFF), compressed at 4 levels (25:1, 50:1, 75:1, and 100:1) using a wavelet algorithm, and displayed to the observers on a computer monitor. Their observations regarding condylar faceting, sclerosis, osteophyte formation, erosion, and abnormal shape were analyzed using ROC. Kappa values were determined for relative condylar size and condylar position within the glenoid fossa. Indices were compared using ANOVA at a significance level of P < .05. Although significant and substantial observer variability was demonstrated, there were no statistically significant differences between image modalities, except for condylar position, in which TIFF and wavelet (at all compression ratios) performed better than the original image. For faceting, wavelet 100:1 performed better than radiographic film images. Little actual image file reduction was achieved at compression ratios above 25:1.

In vivo accuracy and reliability of color-coded image enhancements for the assessment of periradicular lesion dimensions.

OBJECTIVE: The purpose of this study was to compare dimensions on charge-coupled device-acquired images under various enhancements with dimensions on film radiographs and in vivo dimensions with respect to the linear measurement of periradicular radiolucent lesions. STUDY DESIGN: The dimensions of 25 lesions imaged by means of a charge-coupled device-based digital receptor and Ektaspeed Plus radiographic film were measured and compared with dimensions as actually measured on impressions of the lesions taken during surgery. Digital images were displayed in unenhanced, equalized, and equalized/color-coded modes. The color-coding protocol was repeated to determine the method error, and each image treatment was also remeasured to determine intrarater reliability. Differences were compared through use of a Friedman 2-way analysis of variance with a follow-up Wilcoxon signed rank test (alpha = 0.01). RESULTS: Actual lesion dimensions were larger than dimension estimates obtained with digital images (range, 23% to 35%) and film radiographs (range, 29% to 43%). Color-coded images were significantly less accurate than equalized images and unenhanced images. Images equalized through use of the measurement algorithm of the resident software provided estimates that were more accurate than estimates made with film radiographs and a standard millimeter rule. Intrarater variability was low. The application of color coding was found to be unreliable. CONCLUSIONS: When applied to intraoral images, color-coded image processing of digital images had limited value in the estimation of periradicular lesional dimensions.

Panoramic radiographic patterns of the infraorbital canal and anterior superior dental plexus.

OBJECTIVE: To describe and classify the presentations of the infra-orbital canal/groove (IOC/G) complex and anterior superior dental plexus (ASDP) on panoramic radiographs. METHODS: The frequency of occurrence and variations in appearance of the IOC/G were determined on 246 random panoramic radiographs. A classification system consisting of Types I, II and III was developed to describe the radiographic patterns of the IOC/G. RESULTS: Two hundred radiographs (81.3%) demonstrated evidence of the IOG/C. The most frequent appearance of the IOC was Type III (44.75%) closely followed by Type I (42%) and Type II (13.25%), with only minor differences in prevalence between right and left sides. Sixty one percent were bilateral. Radiologic evidence of the ASDP was noted in 29% of radiographs demonstrating an IOG/C with 12% of cases being bilateral. Three distinct radiographic patterns of the anterior superior dental plexus (ASDP) were also observed. CONCLUSION: A classification of the appearance of the IOC/G and ASDP on panoramic radiographs has been presented.

Characteristics of the Orthopantomograph OP 100.

OBJECTIVE: To investigate empirically the imaging characteristics of the Orthopantomograph OP 100 and compare them to the average form of the dental arch. METHODS: Repeatable radiographs were taken of a lead resolution grid positioned at 1 mm increments along known angular intervals of the projected X-ray beam. Focal trough thickness was determined by visibility of the 1.5 lp mm-1 resolution limits. The path of the effective rotation center was determined using a film positioned at right angles to the slit beam. The vertical magnification and horizontal magnification and distortion index, corrected for the position of the tomographic layer, were calculated using a reference object placed at various resolution limits of the focal trough. The beam projection angle was calculated with respect to the central plane of the focal trough and the average dental arch shape compared with the average proximal contact angle. RESULTS: The maximum resolution observed at the central plane of the focal trough was 5 lp mm-1. The width of the focal trough varied from 17 mm in the anterior region to 44 mm in the posterior region. The path of the effective rotation center was found to translate between three fixed centers of rotation, with the effective anterior projection radius of 24 mm. The vertical magnification factor within the focal trough showed a linear increase along the beam path from 1.24-1.37 and the horizontal magnification varied from 1.01-1.63. The distortion index varied from 0.84-1.24. The beam projection angle increased from 90 degrees anteriorly to 115 degrees in the premolar area with respect to the central plane of the focal trough and from 90 degrees anteriorly to 110 degrees in the premolar area compared with the average dental arch. CONCLUSIONS: The OP 100 provides a focal trough conforming well to the overall geometry of the dental arch and provides adequate spatial resolution.

In vivo comparison of Visualix-2 and Ektaspeed Plus in the assessment of periradicular lesion dimensions.

UNLABELLED: Accurate assessment of intraosseous lesion dimensions is useful in determining strategies for treatment of periradicular pathoses of dental causation. OBJECTIVES: To compare the efficacy of digital versus analog imaging for the measurement of mesiodistal and vertical dimensions of periapical lesions in patients that require apical surgery. METHODS: Fourteen examiners assessed the dimensions of 28 lesions with a millimeter ruler and Ektaspeed Plus radiographs (Eastman Kodak, Rochester, N.Y.), and with the Visualix-2 (Gendex/Dentsply, Milan, Italy) in unenhanced, contrast-stretched and equalized modes with proprietary software mouse-driven measurement algorithm. Impregum F (Premier Dental Products) impressions at surgery were used as the "gold standard." Ten randomly chosen images were reread 2 weeks later to assess intra-operator reliability. As the Mauchly sphericity test was significant for all tests, a multivariate analysis of variance was used to assess accuracy. To explain the exact difference between means, the Bonferroni test was applied. Intra-observer reliability was assessed with Friedman's two-way analysis of variance; inter-observer effects were determined with Cronbach's alpha. RESULTS: For accuracy in measurement, the closest to the "gold standard" were achieved with the Visualix-2 with image equalization. The contrast-stretched Visualix-2 and unenhanced Visualix-2 measurements were less accurate; conventional film was consistently the least accurate (p < 0.002). On the other hand, subjective preference placed film radiographs above the unenhanced Visualix-2 images; contrast-stretched Visualix-2 images were preferred over all other modalities. CONCLUSIONS: Charge-coupled device-based images with the Visualix-2 are preferable to film-based radiographs for measuring periapical lesion dimensions.

A meta-analysis of mandibular intercanine width in treatment and postretention.

The meta-analysis technique of literature review was applied to a total of 26 previous studies to assess the longitudinal stability of postretention mandibular intercanine width. Weighted averages and standard deviations for the means of 1,233 subjects were compared for linear changes in intercanine transverse dimensions during treatment (T1), immediately after treatment (T2), and after removal of all retention (T3). Net change was defined as the difference between means at T3 and T1. Dimensional changes were also evaluated on the basis of patient pretreatment Angle classification, extraction, and nonextraction treatment modalities of each group. Paired two-tail t-tests were performed between T3 and T1 means on all groups at the a priori level of significance set at a < or = 0.05. Statistically significant differences were observed for the following groups: all patients; nonextraction; extraction; Class I; Class I extraction; Class II extraction; and, Class I Division 1 nonextraction. The findings of this study indicate that regardless of patient diagnostic and treatment modalities, mandibular intercanine width tends to expand during treatment on the order of one to two millimeters, and to contract postretention to approximately the original dimension. While statistically significant differences could be demonstrated within various groups, the magnitudes of the differences were not considered clinically important.

A common sense approach to TMJ and implant imaging.

During the last two decades, computer-based imaging technology has contributed significantly to our assessment of patients with head and neck anomalies. For instance, magnetic resonance imaging has given us a modality for visualizing the hard and soft tissues of the temporomandibular joint. We are fortunate that this has led to the refinement of the concepts of normality and the characterization of non-normal conditions. In the pre-surgical assessment of alveolar bone prior to implant placement, tomography in its various forms has provided the possibility of three dimensional bony assessment thus potentially optimizing fixture placement and minimizing potential failure. Unfortunately, there has been a reluctance to employ these techniques as they are either not available or both the equipment and the cost of image acquisition time is too expensive. Until recently, there has been a lack of consensus as to the selection of imaging modalities appropriate to patient presentation and the clinical value of the information obtained. The more recent development of computer-controlled panoramic imaging has made available to us many special projections which are capable of producing hard tissue images of either the TMJ or a potential implant site in multiple dimensions at lower cost (both financially and in terms of X-ray dose) than the more advanced modalities. These projections can now be incorporated into a clinically determined patient-based protocol and thus provide the clinician with both an economical and common sense approach to diagnostic imaging.

Tissue radiation dosages using the RVG-S with and without niobium filtration.

Tissue doses for a modified Rando head- and-neck phantom were measured for imaging with speed group E film with standardized aluminium filtration and the RVG-S both with and without added niobium filtration. Cylindrical holes drilled into the phantom's tissue-equivalent material permitted the placement of a small ionization chamber into anatomically correct sites representing the thyroid, parotid, submandibular and sublingual glands. To establish the necessary cone positions, angulations and time settings for each exposure, diagnostically acceptable images of six teeth, representative of different intraoral regions, were made for a DXXTR mannequin. Entrance and exit points were marked and transferred to the phantom to allow reproducible repeat exposures. The RVG-S provided reductions in average skin entrance dose of 31 per cent to 39 per cent with standard aluminium filtration and 51 per cent to 60 per cent with the addition of niobium filtration to attenuate the beam. While dose reductions relative to E-speed film usage were found for deep tissue sites, these were site and projection specific. The cumulative reduction from use of the RVG-S without niobium filtration was 32 per cent. It was 42 per cent with additional niobium filtration. It should be noted, however, that adding niobium filtration resulted in increased dosages to the deeper soft tissues such as the thyroid gland.

Sensitometric effects of varying the intensifying screens used with Agfa Dentus ST8G and RP6 panoramic radiographic films.

OBJECTIVES: To compare the sensitometric effects and information yield of varying the intensifying screens used with both Dentus ST8G and RP6 Agfa Gevaert, Dormagen, Germany panoramic radiographic films. MATERIAL AND METHODS: Four screen-film combinations were employed for each of the two film types. The screens used were blue fluorescing PX-III (Kasei Optonix, Tokyo, Japan) and Special (Siemens AG, Bensheim, Germany), as well as green fluorescing Lanex Regular (Eastman Kodak, Rochester, NY, USA) and Trimax T16 (3M, Mineapolis, Minnesota, USA). The density response for each screen-film combination was evaluated using the characteristic curves generated. Information yield, as determined by the radiographic detection of defects in an aluminium test object, was evaluated by nine observers. RESULTS: The characteristic curves for ST8G were different when green and blue fluorescing screens were used; however, those for RP6 varied little irrespective of the choice of intensifying screens. Observers were able to perceive defects at significantly lower radiation exposures for ST8G combined with green fluorescing screens compared with blue emitting screens. RP6 with all screen combinations provided similar image detail perceptibility at comparable exposures with ST8G with green-fluorescing screens. CONCLUSIONS: RP6 is suitable for use with either the spectrally matched blue emitting screens or green-emitting screens. ST8G radiographic film should always be matched to rare earth screens.

Evaluation of XD/A Plus and ST8G films for cephalometric radiography with Grenex G8 and BH-III screens.

OBJECTIVES: Sensitometric properties, clinical image quality, and patient dose requirements are important considerations when selecting film for cephalometrics. Two recently released films, XD/A Plus and ST 8G green sensitive films, were studied. METHODS: The films were each combined with Grenex G8 (Fuji Medical) green-fluorescing matched and BH-III (Kasei Optonix) blue-fluorescing mismatched intensifying screens. The density response and resolution for each screen-film combination were evaluated by use of the characteristic curve and modulation transfer function. The kilovoltage settings providing clinically acceptable images were assessed individually by 12 observers. Clinically acceptable images for each combination were also compared, and the skin entrance doses in the temporomandibular joint region were determined. RESULTS: The average contrast at the most effective density range was found to be slightly higher for the BH-III group than for the G8 group. The modulation transfer function for the BH-III group was inferior to that for the G8 screens. There were no significant differences in diagnostically acceptable image quality among the four combinations; nevertheless the BH-III screen group required two to three times more exposure than the G8 screen group. CONCLUSIONS: XD/A Plus and ST8G films provide acceptable image detail for cephalometrics. To minimize the patient dose they should be used with green-emitting screens.

Measurement algorithm accuracy of the RVG-PCi in vertical and diagonal assessments at various beam energies.

The Trophy RadioVisioGraphy model PCi was compared to Kodak Ektaspeed Plus film for accurate recording and estimation of the length of size 15 files placed vertically and diagonally across the receptor surface. Variations in kilovoltage (50, 70, and 75) and exposure were also factored. Eight observers estimated file lengths using the proprietary software measurement algorithm for the RVG-PCi and a millimeter rule for the film-based radiographs. Both modalities resulted in slight magnification for vertically oriented files; however, the RVG-PCi caused overestimation in the order of 6 to 8% with diagonally oriented instruments. Measurement interobserver variability was least when using the RVG-PCi. It was concluded that the proprietary software supplied with RVG-PCi is not sufficiently accurate for endodontic assessment. Furthermore, exposures above 0.15 s at 75 kVp resulted in pixel saturation resulting in apparent shortening of the instrument; hence, length calculations are particularly sensitive to overexposure when using the RVG-PCi.

Identification of the temporomandibular joint and adjacent cephalometric landmarks using a dual sensitivity screen-cassette system.

OBJECTIVES: Clinical evaluation of a cassette with dual speed screens for cephalometric radiography. METHODS: Two lateral cephalometric radiographs were taken on 20 consenting subjects using the TMJ Orthoceph Slimline Cassette System (TOSCS), incorporating circular Trimax 12 screens in the area adjacent to the temporomandibular joint, and a control cassette (Trimax 8 screens). Ten pairs of radiographs with optimal image quality were randomly presented to 10 observers trained in cephalometric interpretation. Observers rated the overall diagnostic quality of each radiograph and of the TMJ region on an ordinal scale. They then located specific landmarks and traced the TMJ anatomy using acetate overlays. Overlays were digitized by a single operator who repeated tracing placements and digitizations to determine the error of recording method. Landmark variability was compared in the x- and y-axis by the Wilcoxon matched-pairs signed ranks test (p < 0.05). Six repeat tracings were performed and assessed by percentage of repeated observations above the maximum affordable error. Fossa space values were analyzed by the coefficient of variation (CV). The variability of the angular and linear values was also compared. RESULTS: TOSCS image quality was perceived as significantly better than the control. Method error was 0.34 mm in the x-axis and 0.4 mm in the y-axis. Interobserver variability was 2 to 3 times greater than intraobserver. There was less variability with TOSCS for identification of basion (x-axis), center-of-rotation (x-axis) and condyle (posterior) (x-axis). However, this was clinically insignificant. Accurate determination of the fossa space was not possible as CV varied from 23 to 84%. No differences in the variability of angular or linear values variability were found. CONCLUSIONS: While observers preferred TOSCS, no significant clinical differences could be demonstrated between the two systems.