Comparison of three intra-oral storage phosphor systems using subjective image quality

OBJECTIVE

To compare the subjective image quality of three intra-oral storage phosphor systems.

METHODS

DenOptix (Dentsply/Gendex, Chicago, IL, USA), Digora (Soredex, Helsinki, Finland), and CD-Dent (DigiDent Digital Imaging Technologies, Nesher, Israel) were compared. Two different imaging plates (IPs), BAS300 and HR300 (Fuji Photo Film Co., Tokyo, Japan) were used with the DenOptix system. The specimen was the maxilla and surrounding soft tissues of an adult cadaver. Imaging was at 70 kVp and 8 mA with a focus-detector distance of 38 cm using an optical bench. The exposure times were varied and a panel of five dentists independently evaluated the images produced with each system/IP receptor for seven features; proximal caries, gingival soft tissues, cortical bone, root canal space, root apices, periodontal ligament space and endodontic instrument clarity on a three-interval confidence scale. The best three exposures were chosen according to the highest scores for each system. These images were re-read in random order a total of 10 times. Pair-wise comparisons were made by use of odd's ratio analysis. A 95% confidence interval was applied.

RESULTS

Images made with the DenOptix system/BAS IP combination were perceived to have the best overall image quality. The DenOptix/HR IP combination and Digora were rated almost equally in second place. The DigiDent system was ranked inferior. The Digora was considered to be the best for demonstrating gingival soft tissues (P < 0.05) and the DenOptix/HR300 combination the best for clarity of endodontic instruments (P < 0.05).

CONCLUSIONS

While the DenOptix/BAS 300 combination was rated highest overall, the ranking of image quality by modality was found to be task-dependent. Digora was rated best for demonstrating gingival soft tissues.

Comparison of observer performance in determining the position of endodontic files with physical measures in the evaluation of dental X-ray imaging systems

OBJECTIVE

To examine the feasibility of substituting observers determining the accuracy of endodontic measurements for measurements of physical qualities in comparison of digital imaging systems.

METHODS

Sensors from six digital imaging systems were compared for signal-to-noise ratio (SNR), modulation transfer function (MTF) and detective quantum efficiency (DQE). A total of 45 canals in teeth from human cadavers were instrumented to their apical foramina. Endodontic files, ranging in size from size 8 to size 20, were glued in place at random distances from the apical foramina spanning a range of +/- 3 mm. The teeth were imaged with the six digital systems and dental X-ray film. Fifteen dentists independently measured the distance from the end of the file to the apical foramen. Results were expressed as the measurement error. Measurement error was compared to SNR, MTF and DQE for each digital system.

RESULTS

CDR (Schick, New York, NY, USA), Digora (Sordex, Helsinki, Finland) and Dexis (Provision Dental Systems, Palo Alto, CA, USA) produced the highest SNR values followed closely by RVG-4 (Trophy, Croissy-Beavborg, France). Sens-A-Ray (Dent-X/Regam Medical Systems, Sundsvall, Sweden), Dexis and the RVG-4 produced the best MTF results. Dexis had the greatest DQE. The mean measurement errors (in mm) were: Film 0.65, Dexis 0.69, CDR 0.71, RVG-4 0.74, Digora 0.89, Sens-A-Ray 0.97, and Visualix-2 (Gendex, Monza, Italy) 0.98.

CONCLUSIONS

Digital systems closely approximate film in their accuracy when used for endodontic measurement providing that the assessment instruments have similar resolving power. DQE was the best physical predictor of system accuracy when compared with endodontic length measurements. MTF and SNR alone did not accurately predict observer precision.

Evaluation of tuned-aperture computed tomography depth discrimination for image series acquired variously with linear horizontal, linear vertical, and conical beam projection arrays

OBJECTIVE

To compare depth discrimination by using tuned-aperture computed tomography (TACT) variously with linear horizontal, linear vertical, combined linear horizontal and linear vertical, and conical beam projection arrays.

STUDY DESIGN

The first test object was a metallic mesh angled at 30 degrees to the surface of a computed dental radiography size No. 1 x-ray sensor. The second test object was a dry human mandible. The sensor was mounted on an optical bench constructed to permit free and precise geometrical settings for the horizontal and vertical angulations of the x-ray beam. The extent of blurring of horizontal and vertical wires in each TACT reconstructed image slice was observed for each of the tested beam projection arrays.

RESULTS

With a linear horizontal beam projection array, it was not possible to determine the depth of structures parallel to the horizontal dimension, such as the mandibular canal. With a linear vertical beam projection, it was not possible to determine the depth of structures parallel to the vertical dimension. A conical array of beam projections was best suited to the task of depth discrimination of objects in all planes. The best second alternative was a combination of linear vertical and linear horizontal projections.

CONCLUSIONS

Beam projection geometry is important for the accurate depth discrimination of TACT reconstructed images. A conical beam projection array is ideal.

A 3-D reconstruction system for the human jaw using a sequence of optical images

This paper presents a model-based vision system for dentistry that will assist in diagnosis, treatment planning, and surgical simulation. Dentistry requires an accurate three-dimensional (3-D) representation of the teeth and jaws for diagnostic and treatment purposes. The proposed integrated computer vision system constructs a 3-D model of the patient's dental occlusion using an intraoral video camera. A modified shape from shading (SFS) technique, using perspective projection and camera calibration, extracts the 3-D information from a sequence of two-dimensional (2-D) images of the jaw. Data fusion of range data and 3-D registration techniques develop the complete jaw model. Triangulation is then performed, and a solid 3-D model is reconstructed. The system performance is investigated using ground truth data, and the results show acceptable reconstruction accuracy.

Associations in 425 patients having temporomandibular disorders

OBJECTIVES

Chronic facial pain in general and temporomandibular disorders (TMD) in particular are among the most common conditions affecting mankind. The objective of this study was to retrospectively evaluate standardized data on patients having TMD in order to seek trends and cross-correlations.

METHODS

The patients' records were reviewed for 425 consecutive patients having TMD, examined and treated in one clinic by one dentist. Demographic information and signs and symptoms of TMD were tabulated and the features were cross-correlated to find underlying trends.

RESULTS

TMD primarily affects women, as more than 84% of those affected were female. The most common feature (found in 84% of subjects) was facial muscular pain in the vicinity of the TMJ. In 42%, this pain was bilateral. Unilateral pain was almost equally distributed on the right or left side. Headaches were reported in 78% of patients with TMD. "Popping" noises in the TMJ on opening (54%) or closing (31%) the mouth, or stiffness of the neck (33%) were the next most frequent associations.

CONCLUSIONS

The demographics for the studied population of TMD patients closely agrees with previous studies reported in the literature. This study reinforces the fact that pain associated with TMD primarily affects women.

Extraoral and panoramic systems

Digital solutions for extraoral and panoramic radiology have been available for more than 15 years. The costs, however, have been too high for adoption in private dental practice. The past 2 years have seen tremendous growth in the number of relatively cost-effective digital options available to the dentist and dental specialist. Furthermore, computer speed and data storage capacities have progressed. This article presents an overview of systems available at present, and their enabling technologies and enhancement capabilities.

Evaluation of a new F speed dental X-ray film. The effect of processing solutions and a comparison with D and E speed films

OBJECTIVE

To compare the properties of a new speed group F intra-oral X-ray film with those of three well established types both from groups D and E, and evaluate the impact of six commercially available processing solutions.

METHODS

Four types of dental X-ray film, Flow (Flow X-ray, West Hempstead, NY, USA), speed group F, Ektaspeed Plus (Eastman Kodak, Rochester NY, USA) and M2 Comfort (AgfaGevaert, Morstel, Belgium), both speed group E, and Ultra-speed (Eastman Kodak), speed group D, were exposed under standardised conditions and processed in six different processing solutions. Base plus fog density, characteristic curves, film density, speed, average gradient, contrast and latitude and spatial resolution were calculated.

RESULTS

The choice of processing chemistry affected radiographic characteristics including speed grouping. The new F film was consistently the fastest. M2 Comfort could achieve F speed and Ultra-speed achieved E speed using Automat XR chemicals. The speed of Ektaspeed Plus was independent of the automatic processing solution used. Ultra-Speed film had the lowest base plus fog density and the widest latitude. Film contrast was similar irrespective of the film and solution combination.

CONCLUSIONS

The choice of processing chemistry can affect radiographic characteristics. The new F film reduces patient exposure by one-half compared with E speed film with no detriment to image quality.

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.

An electronic survey of opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems

OBJECTIVES

To assess opinions on the compatibility of current X-ray generators with intra-oral digital X-ray systems.

METHODS

A questionnaire was posted in both English and in Japanese on oral and maxillofacial radiology electronic bulletin boards. The questionnaire was also mailed to selected researchers and manufacturers in oral and maxillofacial radiology. The replies were evaluated to determine opinion on the current and future status of digital intra-oral imaging with special reference to their compatibility with current X-ray generators.

RESULTS

Seventy-one replies were received from 19 countries: 39% from Japan and Korea, 27% from North America, 25% from Europe and 8% from the rest of the world. Eighty per cent of respondents were from academia, 15% from industry and the remainder largely in private practice. Respondents' experience was equally divided between solid state, mainly charge-coupled devices (CCDs) and photostimulable phosphor (IP) technologies. Sixty-eight per cent considered that current X-ray generators are compatible with intra-oral digital systems and many believed this was due to their gray scale flexibility. Twenty-eight per cent believed that existing X-ray generators are inconsistent with low exposure times. Many of the replies suggested that in future pixel size would decrease and bit depth and receptor sensitivity increase.

CONCLUSIONS

Most respondents are happy to use existing X-ray generators with digital X-ray systems. However, they also believe that increased sensitivity of receptors could lead to more stringent designs of X-ray generators to ensure more reliable outputs in the low exposure range.

RVG-ui: a sensor to rival direct-exposure intra-oral x-ray film

The RVG-ui is a solid-state system for dental x-ray imaging combining a charge-coupled device (CCD) of small pixel size (19.5 microns) with a caesium iodide (CsI) scintillator. It features two sizes of sensor with receptive areas that approach the size of No. 1 and No. 2 periapical x-ray films. The spatial resolution of the RVG-ui exceeds 20 lp/mm, rivaling direct-exposure intra-oral x-ray film when the latter is optimally exposed and processed. The recording latitude of the RVG-ui for clinically acceptable images is 25:1, making exposure error unlikely. In features such as speed of image acquisition, reduction in radiation dose, retrieval of data, and organization and storage of images, the RVG-ui system surpasses traditional x-ray film. Furthermore, it is possible to make accurate length measurements very quickly, and to apply an artificial intelligence program to determine the probability of proximal dental caries in enamel and dentin.

Effect of number of projections on accuracy of depth discrimination using tuned-aperture computed tomography for 3-dimensional dentoalveolar imaging of low-contrast details

OBJECTIVE

The purpose of this study was to test the hypothesis that the number of projections influences the accuracy of a simple depth discrimination task when tuned-aperture computed tomography is used.

STUDY DESIGN

In each of 4 partially edentulous mandibles, 2 radiopaque steel spheres were attached to the facial and lingual surfaces and 1 ceramic sphere was place in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned ceramic sphere relative to the 2 steel spheres were determined from 3-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently by means of an optical micrometer. Multiple projections were produced from radially symmetric exposures bearing an angular disparity of 15 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction was varied systematically (2, 4, 8, 12, and 16 projections). The consequences of this variable, as well as specimen and observer effects, were evaluated in a balanced factorial experimental design. Depth estimates were performed by 10 trained observers. The depth reported was that corresponding to the tuned-aperture computed tomography slice perceived to yield the image of the ceramic sphere in sharpest focus. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance.

RESULTS

No statistically meaningful effects were found for the number of projections (P = .607) or for different observers (P = .093), but a significant specimen effect was demonstrated (P = .006).

CONCLUSIONS

Factors other than high contrast limit the perception of image sharpness under these conditions. Depth may be estimated accurately from relatively small numbers of projections.

Temporomandibular joint pantomography using charge-coupled device, photostimulable phosphor, and film receptors: a comparison

Our objective was to compare the accuracy and practicality in use of three available imaging receptors for temporomandibular joint (TMJ) imaging; namely, two computer-assisted and one traditional analog x-ray film system. A standardized tissue-equivalent encased human skull specimen was imaged using lateral and posteroanterior (PA) pantomographic projections with the Orthopantomograph OP 100 (Instrumentarium Imaging, Tuusula, Finland) and three different receptor modalities: (1) Ektavision film with Ektavision screens (Eastman Kodak, Rochester, NY); (2) DenOptix photostimulable phosphor screens (Dentsply/Gendex, Chicago, IL); and (3) the charge-coupled device (CCD) receptor, DigiPan (TREX/Trophy Radiology, Marne-la-Vallée, France). The effective focal trough was found for each receptor using lead resolution grids placed at fractional millimeter distances along empirically determined beam projection angulations. The time to acquire and process images was also established. We found that the CCD system permitted real-time display, whereas the use of traditional film took 2 minutes to load the cassette in a darkroom and perform the exposure, and then a further 2 minutes to unload and process. The storage phosphor took 3 minutes to unload the cassette and process the image and a further 20 seconds to clear the plate following laser scanning. Film produced the greatest maximum resolution followed by the storage phosphor and the CCD. In conclusion, CCD-based TMJ pantomography provided an instant image. The photostimulable phosphor system used was the least satisfactory in terms of the time expended to obtain an image, but provided better spatial resolution than the CCD. Ektavision film/screens provided the best spatial resolution in this investigation.

Intraoral radiographic storage phosphor image mean pixel values and signal-to-noise ratio: effects of calibration

OBJECTIVE

The DIGORA intraoral radiographic storage phosphor system needs to be calibrated before images are made. Calibration involves inputting of the maximum exposure to be used. This investigation studied the effects of different maximum exposure calibration settings on the mean pixel value for selected regions of interest and the signal-to-noise ratio for images of a test phantom.

STUDY DESIGN

A dental phantom containing a step wedge made of different thicknesses of homogeneously radiopaque bone-equivalent material was imaged at 70 kVp with exposures ranging from 12.8 to 105.2 microC.kg-1. Images were displayed through use of imaging software, and a region of interest was set for each bone-step. The mean pixel values and their standard deviations were measured.

RESULTS

Except for very low exposures (< 10% of the calibrated maximum), there was a linear relationship between exposure and the pixel values within the regions of interest irrespective of the calibrated maximum exposure. Low exposures resulted in underexposed low-contrast images. Low calibrated maximum exposures (< 54.5 microC.kg-1) resulted in low-density images with poor signal-to-noise ratios.

CONCLUSIONS

Because of the very wide image latitude of the DIGORA system, loss of image quality was not observed as a result of adjustments in the calibration setting over the range of exposure commonly used in dental practice. The highest accepted exposure was limited by prior calibration; hence, if diligence is applied, patient exposure can be minimized without detriment to image quality.

Observer differentiation of mechanical defects versus natural dental caries cavitations on monitor-displayed images with imaging plate readout

OBJECTIVE

The purpose of this study was to compare the ability of dentists to detect mechanically created defects vs natural dental caries cavitations on the proximal surfaces of extracted teeth by means of storage phosphor imaging plate technology.

STUDY DESIGN

Fifty-two extracted molar and premolar teeth were blocked into sets for bitewing radiographs through use of the DIGORA digital imaging system. Sixteen natural caries cavities and 28 artificial lesions were present in the 80 proximal surfaces included in the study. A group of 16 dentists assessed proximal lesions on unenhanced images on the monitor and 1 month later on contrast-enhanced images. A different group of 16 dentists assessed proximal lesions on contrast-enhanced images and 1 month later on unenhanced images. The Mann-Whitney U test was used to check for a reading-order effect. The Zelen test of odds ratio was used to test for homogeneity, and the Mantel-Haenszel analysis or stratified logistic regression was used for inference about the common odds ratio. Alpha was set at P < .05.

RESULTS AND CONCLUSIONS

With the DIGORA system, there was little difference between the detection rates of mechanical defects and natural carious cavities with unenhanced images, but the mechanical defects were more readily detected when contrast-enhanced images were used. Cavity depth positively affected the odds of diagnosis of lesions, with deeper lesions being more readily detected than more superficial ones irrespective of whether they were natural or artificial. In comparison with findings of previous studies in which film and a charge-coupled device detector were used, the overall detection rate for natural dental caries was remarkably constant across the modalities.

Panoramic dental radiography using a charge-coupled device receptor

Panoramic radiography using a slit beam and film/screen receptor is standard for the emergency room evaluation of mandibular fractures and also in dentistry. This study compared the spatial resolution, area distortion factors, and the dosage considerations for a panoramic system where standard film/screen and a charge-coupled device were alternatively employed as the image receptor. Resolution and image contours were determined using a lead resolution grid positioned at selected beam projection angulations. Exposure measurements were carried out using a RANDO average man phantom and a 3 cc beryllium-windowed ionization chamber. The maximum spatial resolution with film approached 5 lp mm-1 whereas with the CCD the maximum resolution was just above 4 lp mm-1. Consequently, the image layer was reduced slightly in width when using the CCD receptor. The use of the CCD resulted in skin exposure reduction exceeding 70%.

Clinical trial of panoramic dental radiography using a CCD receptor

The objective of this study was to evaluate the perceived clinical efficacy of a charge-coupled device (CCD) detector for panoramic radiography by comparing the images produced to conventional film/screen radiographs using the same machine and patient population. For clinical evaluation, 18 criteria were selected. These included overall assessment of the area of coverage, clarity of dental structures, clarity of bony outlines, specific anatomic details such as the maxillary sinus floor, mandibular canal and mandibular condyle, and region-by-region assessment of the dentition. Observers acted independently using identical optimal viewing conditions. Film and digital radiographs were evaluated separately. A five interval Likert rating scale was used. Digital images were rated superior to the conventional film radiographs for 14 criteria. Film radiographs marginally outperformed digital images for three criteria. For one criterion (periodontal bone status) the two modalities showed no difference in terms of the means ratings. It was concluded that digital images are clinically equivalent to conventional film/screen images for panoramic dental radiography.

A sensitometric comparison of Kodak Ektavision and Fuji Super HR-S panoramic radiographic films

OBJECTIVES

The purpose of this study was to compare the combination of Ektavision film and Ektavision intensifying screen with the combination Super HR-S panoramic radiographic film and HR-4 intensifying screen with respect to sensitometric properties and the visualization of anatomic structures.

METHODS

The density response and resolution of both panoramic radiographic film/intensifying screen combinations were evaluated through use of the generated characteristic curves and the modulation transfer function. The diagnostic clarity was evaluated by five oral and maxillofacial radiologists who used a rating scale to evaluate the image clarity of selected anatomic structures.

RESULTS

The film speed and radiographic contrast, respectively, were 1.3 and 1.2 times higher for Ektavision than for Super HR-S. The image resolution with Ektavision was similar to that with Super HR-S. Ektavision was perceived to provide clearer images of the selected anatomic details than did Super HR-S.

CONCLUSION

With respect to the clarity of anatomic structures, Ektavision film, with its higher speed and higher contrast, proved superior to Super HR-S film.

Effects of projection geometry and number of projections on accuracy of depth discrimination with tuned-aperture computed tomography in dentistry

OBJECTIVE

The purpose of this study was to determine the degree to which the number and angular disparity of component projections influence depth discrimination with tuned-aperture computed tomography.

STUDY DESIGN

Groups of three tiny steel spheres served as fiducial references on and in four partially edentulous mandibles. Two spheres were attached to the facial and lingual surfaces of each mandible, and the third was fixed in the apical region of an open tooth socket. Errors in estimates of the depth of the apically positioned sphere relative to the other two spheres were determined from three-dimensional tuned-aperture computed tomography reconstructions. These data were compared with actual measurements produced independently with an optical micrometer. Multiple projections required by the tuned-aperture computed tomography reconstruction algorithm were produced from radially symmetric exposures bearing angular disparities of 5, 15, 30, and 45 degrees. The number of symmetrically dispersed projections per tuned-aperture computed tomography reconstruction likewise was varied systematically (2, 4, 8, 12, and 16 projections). These variables were manipulated through the use of a balanced factorial design. Depth estimates were performed by trained observers; the estimates were based on the determination of tuned-aperture computed tomography slices perceived as imaging the respective apical spheres in sharpest focus. Specimen and observer effects were also considered as independent variables. Resulting data were normalized by logarithmic transformation and analyzed statistically by analysis of variance.

RESULTS

Significant differences (p < 0.005) were demonstrated for angular disparity and specimen effects, but the number of projections and the effect of the observer were not found to be statistically significant.

CONCLUSIONS

In dentistry, angular disparities of 15 degrees or greater should be used when tuned-aperture computed tomography is being applied to diagnostic tasks requiring maximal depth discrimination accuracy.

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

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.

Teledentistry: protocols for the transmission of digitized radiographs of the temporomandibular joint

Tomograms of the temporomandibular joint were digitized in three different formats using a PC-based system. The image resolution for various projections was determined at different camera-film distances. Three series of images were transmitted by telephone, and transmission times were measured. The original radiographs, the digitized images, the transmitted images and the transmitted-and-printed images were presented to 10 observers, who were asked to rate image quality. No difference in image quality was found between the initial digitized and the transmitted images. However, transmitted and transmitted-and-printed images were of significantly lower quality than the original radiographs or the digitized images viewed on a computer monitor. Transmission time was reduced significantly (50%) by cropping the images before transmission. The image quality of individual radiographs was better than radiographs formatted as a series.

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.