Impact of ambient lighting intensity and duration on the signal-to-noise ratio of images from photostimulable phosphor plates processed using DenOptix®and ScanX®systems

OBJECTIVES

To evaluate the impact on photostimulable phosphor (PSP) image signal-to-noise ratio (SNR) of pre-scanning ambient lighting exposures.

METHOD

PSP imaging plates (IPs) were exposed to different radiation exposures to achieve flat field images. The exposed IPs were subjected variously to visible light of different intensities (300, 150 or 20 lux) for durations ranging from < 10 s to 120 s. They were processed using laser scanners from two systems for further comparison (DenOptix versus ScanX). Histogram analysis was performed in each case and mean pixel value and its standard deviation were used as surrogates to assess SNR. Statistical methods applied included analysis of variance with Tukey honestly significant difference test for pair wise comparisons. The a priori alpha was set at P < or = 0.05.

RESULTS

SNR decreased with increased duration and intensity of pre-scanning light exposure. Lower X-ray exposures resulted in decreased signal resulting in reduced SNR, and increased the need to reduce ambient lighting. No statistically significant differences were found comparing ScanX and DenOptix digital imaging systems in terms of SNR.

CONCLUSION

Reduced ambient lighting is preferred for handling IPs prior to processing in the laser scanner.

Array geometry for assessment of mandibular implant position using tuned aperture computed tomography (TACT)

OBJECTIVE

To evaluate observer faciolingual depth and vertical depth reading errors when using various X-ray beam array geometries to make basis images for tomosynthetic reconstruction using tuned aperture computed tomography (TACT).

MATERIALS AND METHODS

Tissue-equivalent models were constructed to replicate the position of dental implants in relation to simulated mandibular canals. X-ray beam geometries used to acquire the basis images for TACT(TM) integration included horizontal linear, vertical linear, and symmetric and asymmetric conical arrays. Twenty-one dentists trained in the use of TACT acted independently as observers. Tasks included: (1) determination of the relative position of the implant in relation to the simulated canal; and (2) measurement of the vertical depth and faciolingual (lateral) depth dimensions between these two structures. As the study did not involve repeated measures (only one measure was obtained from each observer on each of the two dependent variables), data for faciolingual depth and vertical depth reading errors were analysed using a one-way analysis of variance (ANOVA) with Tukey's honestly significant different (HSD) procedure.

RESULTS

Errors in determining the relative position of the implant to the simulated canal were most frequent when the linear horizontal projection geometry was employed for producing basis images (57% error for model #2 where the implant was lingually placed). The mean measurement errors for TACT images constructed using the various different projection arrays depended both on the structural relationship of anatomic features and the employed beam array geometry.

CONCLUSION

Conical beam arrays are preferred over linear beam arrays for constructing basis images used with TACT for the purpose of correlating the position of a mandibular dental implant in relation to the mandibular canal. They more consistently allowed the observers to establish a measurement of the faciolingual relationship of the implant to the canal. For vertical depth measurement of the relationship of a mandibular dental implant to the mandibular canal, TACT does not appear to have any advantage over individual simple transmission radiographic images.

Effect of beam energy and filtration on the signal-to-noise ratio of the Dexis intraoral X-ray detector

OBJECTIVE

To evaluate the signal-to-noise ratio (SNR) of the Dexis charge-coupled device (CCD) intraoral X-ray detector, with special reference to the influence of beam energy and filtration.

MATERIAL AND METHODS

Digital radiographic images were made of a nine-step dental aluminium step wedge using a Dexis intraoral detector. The X-ray generator was a GE 1000 operating at 10 mA with 2.7 mm aluminium filtration. The peak tube voltage settings applied were 50 kVp, 60 kVp, 70 kVp, 80 kVp and 90 kVp. Various exposure times were used at each beam energy and the exposures (in micro C kg(-1)) were determined in each case using a 3 cl beryllium-windowed ionization chamber. SNR was defined using the surrogate measure of mean pixel value (surrogate for signal) divided by the standard deviation of the pixel value (surrogate for noise). SNRs were measured at separate regions of interest (ROIs) at the centre and at both sides of the detector for each aluminium step as well as without the step.

RESULTS

For beam energies of 50 kVp and 60 kVp, the estimated SNR improved both with increased exposure and with increased filtration (thickness of the aluminium step), and image saturation did not occur within the exposure time range permitted by the Dexis software. At 70 kVp and above, the SNR was optimized in the middle of the exposure range: 4 micro C kg(-1) with 290:1 at the ninth step (13.5 mm Al) for 70 kVp; 3.5 micro C kg(-1) with 240:1 at the ninth step (13.5 mm Al) for 80 kVp; 3.5 micro C kg(-1) with 160:1 at the ninth step (13.5 mm Al) for 90 kVp. Saturation did occur at these beam energies within the exposure time range permitted by the Dexis software.

CONCLUSION

For the Dexis intraoral radiographic imaging system, estimated SNR improved both with higher filtration and with lower kVp. The Dexis detector was capable of generating acceptable images of the step wedge at a wide range of kVp settings.

Comparison of complementary metal oxide semiconductor and charge-coupled device intraoral X-ray detectors using subjective image quality

OBJECTIVE

To compare the subjective image quality of the newer generation Schick CDR detector employing complementary metal oxide semiconductor (CMOS) technology with images using the earlier generation charge-coupled device (CCD) Schick CDR detector.

METHODS

All radiographic images were made using the same formalin-fixed adult cadaver maxilla with surrounding natural soft tissues in place. The X-ray generator used was a Villa Sistemi Medicali Diamatic srl AP/Explor X operated at 70 kVp and 8 mA. The source-to-detector distance was set at 38 cm and an optical bench was used to ensure reproducible beam geometry. A range of exposures was applied for both detectors. A panel of nine dentists independently observed and evaluated images made at each exposure. For both detectors, the three images ranked highest were randomized for re-evaluation in panels of six images. Each image was repeated randomly a total of 10 times. Features chosen as observation points were: (1) proximal dental caries; (2) gingival soft tissues; (3) cortical bone; (4) root canal space; (5) root apices; (6) periodontal ligament space; and (7) endodontic instrument tip clarity. Comparisons were made by use of odds ratio analysis applying a 95% confidence level. Interrater and intrarater reliabilities were computed to assess consistency in observer ratings.

RESULTS

The CMOS sensor was rated as outperforming its CCD predecessor for depiction of cortical bone and root apices; the CCD detector was only rated superior for depiction of root canal space. No significant difference was found between the two detectors in perceived depiction of proximal dental caries, gingival soft tissues, periodontal ligament space or endodontic instruments. Combining rating scores from each of the tasks, CMOS and CCD detectors had a similar proportion of image ratings of excellent, acceptable and poor.

CONCLUSIONS

Regarding subjective image quality, the Schick CMOS and CCD detectors were perceived to produce radiographic images of similar overall quality.

Endodontic measurement accuracy and perceived radiograph quality: effects of film speed and density

OBJECTIVES

This study sought to determine the effects of direct exposure x-ray film speed and background density on observer assessment of endodontic working lengths and on perceived radiographic image quality.

STUDY DESIGN

A human cadaver maxilla section with surrounding soft tissues was used for the study. The canal length to the radiographic apex was determined on 4 canals in maxillary posterior teeth by using Trophy RVG images and adjusting the position of a No. 15 file in each canal until the file tip coincided with the radiographic apex in images made at 3 different vertical angulations. The files were measured with a micrometer from the file stop to the file tip to obtain the length to the radiographic apex. Then No. 10 files were placed in the 4 canals at varying lengths short of this previously determined length, and 5 observers assessed the distance from the file tip to the radiographic apex on radiographs made with Kodak D-, E-, and F-speed and Flow D- and E-speed direct exposure x-ray films that were exposed to produce background densities of 1.5, 2.0, and 3.0. Subjective appraisal of radiographic quality was also assessed.

RESULTS

Analysis of variance and Tukey honestly significantly different post-hoc analysis results concerning measurement errors made with each film type revealed significantly less error for Kodak Ektaspeed Plus (E-speed) intraoral x-ray film than for Kodak InSight (F-speed) and Flow E; however, no difference was detected among Kodak Ektaspeed Plus (E-speed), Kodak Ultra-Speed (D-speed), and Flow D. Films with a background optical density of 3.0 received 98% favorable ratings; radiographs with a background optical density of 2.0 received 77% favorable ratings; and those with background optical density of 1.5 received only 18% favorable ratings at the 95% confidence level. Flow D film received the most favorable ratings, but there was no statistically significant difference among other film types at the 95% confidence level.

CONCLUSIONS

Underexposed radiographs are perceived as inferior to slightly overexposed radiographs for endodontic file length assessment regardless of the film speed used. Current Flow and Kodak E-speed and F-speed radiographs appear to be as accurate as other accepted radiographs used in determining endodontic working lengths. Image background density should be kept constant when making comparisons among x-ray films.

Perceived quality of radiographic images after rapid processing of D- and F-speed direct-exposure intraoral x-ray films

OBJECTIVE

We sought to compare the densitometric properties and perceived image quality of InSight (F-speed) and Ultra-Speed (D-speed) film radiographs processed with rapid chemistry. The effects of density, contrast, and film speed on perceived image quality were also studied.

STUDY DESIGN

Images were made of a human cadaver phantom with exposures to achieve background densities approximating 1.5, 2.0, and 3.0. Films were processed in a radiographic darkroom by using Insta-Neg and Insta-Fix rapid chemistry as the manufacturer had recommended. Five endodontic residents independently analyzed images of varying density, speed, and contrast that were presented in a randomized manner. They were required to evaluate the perceived image quality of 5 specifically designated areas on the film, using a labeled photograph as a guide. These areas included root canal obturation, periodontal ligament space, dentinoenamel junction, and crestal bone height. In addition, they were also asked to assess the overall perceived image quality. Statistical analysis consisted of ordinal regression and 2-factor analysis of variance.

RESULTS

No statistically significant differences were proved between F- and D-speed radiographs within the same density group. Higher density and higher contrast resulted in a statistically significant positive impact (P <.01) on the ranking for all 5 subjective determinations. Observers preferred the films exposed to a background density of 3.0 over those of a lower density (P <.01).

CONCLUSIONS

InSight (F-speed film) can be used with rapid chemistry to ensure less radiation exposure to patients than is necessary with D-speed film. The observers participating in this study preferred radiographs from the 3.0 background density group to those from the 2.0 and 1.5 density groups.

Solid-state temporomandibular joint imaging: accuracy in detecting osseous changes of degenerative joint disease and determining condylar spatial relations

The purpose of this study was to evaluate the off-label use of an intraoral charge-coupled device (CCD) for extraoral transcranial radiography of the temporomandibular joint. Corrected linear tomograms and transcranial images made with conventional screen-film combinations and a CCD detector were compared with sectioned cadaver specimens. Radiation dosage, qualitative assessment of condylar degenerative features, and condylar position within the glenoid fossa of the 3 modalities were assessed and compared. The CCD method required special adjustments to achieve adequate quality, and it involved greater exposure than the other methods. This use of this intraoral system for extraoral imaging cannot now be recommended, but future refinements might make it more viable.

Fundamentals of image acquisition and processing in the digital era

OBJECTIVES

To review the historic context for digital imaging in dentistry and to outline the fundamental issues related to digital imaging modalities.

CONTEXT

Digital dental X-ray images can be achieved by scanning analog film radiographs (secondary capture), with photostimulable phosphors, or using solid-state detectors (e.g. charge-coupled device and complementary metal oxide semiconductor). There are four characteristics that are basic to all digital image detectors; namely, size of active area, signal-to-noise ratio, contrast resolution and the spatial resolution. To perceive structure in a radiographic image, there needs to be sufficient difference between contrasting densities. This primarily depends on the differences in the attenuation of the X-ray beam by adjacent tissues. It is also depends on the signal received; therefore, contrast tends to increase with increased exposure. Given adequate signal and sufficient differences in radiodensity, contrast will be sufficient to differentiate between adjacent structures, irrespective of the recording modality and processing used. Where contrast is not sufficient, digital images can sometimes be post-processed to disclose details that would otherwise go undetected. For example, cephalogram isodensity mapping can improve soft tissue detail.

CONCLUSIONS

It is concluded that it could be a further decade or two before three-dimensional digital imaging systems entirely replace two-dimensional analog films. Such systems need not only to produce prettier images, but also to provide a demonstrable evidence-based higher standard of care at a cost that is not economically prohibitive for the practitioner or society, and which allows efficient and effective workflow within the business of dental practice.

Image file interoperability for data protection, communication and trans-system connectivity

DICOM (Digital Imaging and Communication in Medicine) is a set of international imaging standards developed for medicine and extended to incorporate other professions. These standards encompass primary digital and secondary capture images made for dental diagnostic procedures. The standards provide a basis of interoperability for digital system outputs, providing portability and reducing the danger of obsolescence that would render valuable diagnostic information impossible to display. The American Dental Association, through the activities of its Working Group 12.1, is promoting interoperability within DICOM as the industry standard for digital imaging in dentistry.

Tuned-aperture computed tomography versus parallax analog and digital radiographic images in detecting second mesiobuccal canals in maxillary first molars

OBJECTIVE

We sought to evaluate the detectability of second mesiobuccal (MB2) canals in the MB root of maxillary first molar teeth by comparing (1) parallax with pairs of conventional direct-exposure film intraoral radiographs (both D-speed and F-speed), (2) parallax with pairs of charge-coupled device-based digital images acquired through the use of Trophy RVG-ui, and (3) charge-coupled device-based images acquired through the use of a Trophy RVG-ui sensor and tomosynthetically reconstructed by TACT (tuned-aperture computed tomography) Workbench Software.

STUDY DESIGN

Maxillary first molars were mounted in simulated bone. Pairs of images were generated by conventional D-speed and F-speed radiography and digital radiography with a charge-coupled device-based sensor, the RVG-ui. Sequences of images were also acquired for TACT reconstruction by using the digital sensor. Observers viewed sets of images to determine the number of canals present within the MB root of each tooth. Roots were horizontally cross-sectioned and viewed under an operating microscope to determine the actual number of canals present.

RESULTS

The frequency of detection of MB2 canals was remarkably similar across techniques: 39.2% to 39.6% with parallax for both types of film and for RVG-ui images, and 37.9% with TACT. No statistically significant difference was found in the detectability of MB2 canals between the modalities tested. TACT had higher correlation coefficients than the other 3 modalities with respect to intrarater and interrater reliabilities.

CONCLUSIONS

(1) There was a less than 40% chance of locating MB2 canals in the MB root of maxillary first molar teeth by using parallax with pairs of digital or analog radiographs. (2) TACT did not significantly affect the rate of detection of MB2 canals.

CLINICAL VALIDITY OF THE INTERACTIVE AND LOW-DOSE THREE-DIMENSIONAL DENTO-ALVEOLAR IMAGING SYSTEM, TUNED-APERTURE COMPUTED TOMOGRAPHY

Based on technical studies and clinical examinations, the clinical value of a new three-dimensional dento-alveolar imaging system, Tuned-Aperture Computed Tomography (TACT), were examined for dental applications. TACT is a conventional and low-cost tomosynthesis method in which the benefit of digitization is fully utilized. The clinical information yield of TACT has been examined for the detection of dental caries, periodontal defects and radicular fractures, and also for the pre-surgical assessment of implant placement and impacted teeth. In this article, we introduce basic TACT technology, review the literature pertaining to in vitro and in vivo studies, and describe the outline of our study of TACT to determine its clinical value in the assessment of impacted maxillary teeth.

Outcomes of digital X-ray mini-panel examinations for patients having mental retardation and developmental disability

OBJECTIVES

Severely and profoundly mentally retarded and developmentally disabled (MR/DD) patients are unable to communicate disease symptoms, and radiographic examinations are often difficult to perform on non-sedated patients. This clinical trial evaluated the impact on dental treatment planning of radiographic mini-panels for MR/DD patients.

METHODS

With Institutional Review Board approval and informed consent of the legal guardian of each patient, a digital series of six periapical radiographs was achieved without sedation on 72 MR/DD inpatients (the survey was attempted on 74 patients).

RESULTS

The average number of teeth included in each mini-panel was 20.4 compared with 22.2 teeth found clinically and 22.7 teeth determined combining both clinical and radiographic findings. Individual mini-panel images were judged technically excellent in 65% of cases, diagnostically satisfactory in 26% of cases and suboptimal in 9%. The radiographic panels were judged to affect treatment planning for more than 60% of the patients included in the trial. In 32% the detected condition was one or more periapical radiolucency. Several radiographic findings indicated potentially painful conditions that perhaps explained patient actions previously attributed to behavioural problems. Potential sources of dental pain and sepsis were treated by endodontic therapy or dental extractions on a case-by-case basis with or without general anesthesia. The trial also demonstrated a need that has translated into increased state allocations for dental treatment of MR/DD patients resident in the Commonwealth of Kentucky.

CONCLUSIONS

Dental inspections of MR/DD patients are incomplete if radiographs are excluded. Whilst the mini-panel approach could be considered incomplete, it is better than no radiographs at all. 91% of images were excellent to satisfactory in diagnostic quality and a majority of patients' treatments were modified because of the radiographic information.

Diagnostic value of tuned-aperture computed tomography versus conventional dentoalveolar imaging in assessment of impacted teeth

OBJECTIVE

This clinical study compares the diagnostic value of interactive 3-dimensional tuned-aperture computed tomography (TACT) with conventional dentoalveolar radiographic examinations of impacted maxillary incisors.

STUDY DESIGN

TACT was compared variously with conventional intraoral, occlusal, rotational panoramic, and lateral cephalographic examinations. Sixteen dentists independently evaluated the clarity of anatomic structures of impacted anterior maxillary teeth and surrounding tissues. Estimation of confidence in clinical assessment of the patient was made together with a determination of the diagnostic potential of the studied modalities for altering treatment plans.

RESULTS

TACT was found to significantly improve depiction of the buccal/palatal position of the impacted tooth and its relationship with adjacent teeth (P < .0001) irrespective of the availability of lateral cephalograms. Subjective assessments for clinical decision making approximated a 10% increase in confidence ratings with TACT. The added diagnostic value with TACT varied from case to case.

CONCLUSIONS

The interactive 3-dimensional TACT display was perceived to be more informative for assessing impacted teeth and their relation to surrounding tissues than conventional methods in some cases but not in others. TACT altered treatment-option selection in some instances.

A sequential approach to radiological interpretation

A case of large glandular odontogenic cyst of the mandible is presented in which the panoramic radiograph also demonstrated a soft tissue lesion consistent with carotid aneurysm. CT confirmed the bucco-lingual extent of the mandibular lesion and the presence of a soft tissue lesion consistent with an aneurysm of the internal carotid artery. CT angiography, MR angiography and US were used to rule out a carotid artery aneurysm prior to surgery of the mandibular lesion.

Use and implication of the DICOM standard in dentistry

DICOM is an international imaging standard that was developed for medicine and has been extended to support dentistry among other professions. This standard can provide the basis of interoperability for digital system outputs, providing image portability and reducing the danger of obsolescence rendering valuable diagnostic information impossible to display. This paper presents a brief overview of the origins and components of the DICOM standard and reports an ongoing initiative to promote interoperability within the DICOM as the industry standard for digital imaging in dentistry.

A comparison of D-, E-, and F-speed conventional intraoral radiographic films in endodontic measurement

OBJECTIVES

We sought to compare observer measurement error and subjective ratings for International Standards Organization D-, E-, and F-speed direct exposure dental x-ray films used to determine endodontic working lengths.

METHODS

Radiographs were exposed to achieve a standard background density of approximately 2.0. Three human maxillary posterior teeth for which No. 10 K-files had been placed at various lengths within 4 canals were studied in a cadaver section. A total of 30 radiographs were used (10 from each film type). Five licensed dentists excluding all authors viewed the radiographs independently and in random sequence. Distances from the file tips to the radiographic apices were measured and were compared with known lengths for error determination. The observing dentists also subjectively rated the images as desirable or undesirable. Statistical methods included a 3-factor ANOVA with Tukey honestly significant difference post hoc analysis to compare objective measurements and chi-square with respect to subjective ratings.

RESULTS

No significant differences were attributable to film speed grouping or observers (P > .05); however, there was a specimen effect in that a significant difference was found in measurement accuracy among the 4 canals (P < .05). Differences in subjective ratings for the 3 film types were not statistically significant (P > .05).

CONCLUSION

All 3 film types were similar in objective and subjective ratings. This being the case, the faster film is preferred to minimize the radiation dose to the patient.

The role of the dentist in detection of carotid atherosclerosis

Cerebrovascular accidents (CVA), or stroke, afflict 731,000 Americans each year, with 165,000 of these individuals dying. Stroke is a major cause of death and disability throughout the world, including southern Africa. Atherosclerosis-related formation of thrombi and emboli at the bifurcation of the common carotid artery and proximal internal carotid artery represents a common cause of stroke. The detection of carotid atherosclerosis by dentists using panoramic radiographs recently has been presented to the public through television news stories and the press, but many dentists still do not know how to interpret panoramic radiographs for detection of this condition. This communication illustrates examples in which carotid atherosclerosis was detected using panoramic radiography. Differential diagnoses are presented. Since not every carotid plaque calcifies, panoramic radiography should never be used alone to exclude the possibility of carotid atherosclerosis. It should also be remembered that the mere presence of calcified carotid plaque is not necessarily a reflection on the degree of carotid stenosis. Definitive diagnosis and treatment requires referral of patients deemed to be at risk to an appropriate physician. A variety of advanced diagnostic methods, including gadolinium-enhanced MRI, Duplex Doppler sonography and angiography are used to confirm carotid stenosis.

A comparison of image characteristics and convenience in panoramic radiography using charge-coupled device, storage phosphor, and film receptors

This study compared the image layer characteristics, dose requirements, and convenience in use of panoramic radiography using each of four different image receptors including traditional indirect exposure x-ray film, a storage phosphor system, and two solid-state sensors. The OP 100 D (Instrumentarium Imaging, Tuusula, Finland) charge-coupled device (CCD) sensor provided an instant image with a wide focal trough, making patient positioning error unlikely, but at the same time required a patient dose higher than that used with film. While the DigiPan (Trex/Trophy, Marne-la-Vallée, France) CCD significantly reduced the patient dose to radiation and also provided an instant image, the focal trough was narrower making patient positioning error more likely. The storage phosphor system provided high resolution and a reasonable focal trough width, but the procedure took longer than traditional film radiography and did not provide a dose saving.

Sensitometric properties of Agfa Dentus OrthoLux, Agfa Dentus ST8G, and Kodak Ektavision panoramic radiographic film

OBJECTIVES

The purpose of this study was to compare the sensitometric properties of and visualization of anatomical structures with Agfa OrthoLux green-sensitive panoramic radiographic film, Agfa ST8G green sensitive panoramic radiographic film, and Kodak Ektavision green-sensitive panoramic radiographic film used in combination with an Agfa Ortho Regular 400 imaging screen, Kodak Ektavision imaging screen, and Kodak Lanex Regular imaging screen.

METHODS

The density response and resolution of panoramic radiographic film/intensifying screen combinations was evaluated by means of Hunter and Driffield curves, modulation transfer functions, and noise-equivalent number of quanta. Image clarity of selected anatomical structures was rated independently by 6 oral and maxillofacial radiologists.

RESULTS

The ISO speed for the Agfa OrthoLux panoramic radiographic film combinations was the fastest, and the ISO speed for the Kodak Ektavision green-sensitive panoramic radiographic film combinations was the slowest. The average gradient for the Agfa ST8G systems was relatively steep in comparison with those for the other film/screen combinations. The modulation transfer functions for the Kodak Ektavision film were higher than those for the other films, irrespective of the screen combination used, and those for Agfa OrthoLux film were slightly higher than those for Agfa ST8G film. The noise-equivalent number of quanta for the Agfa ST8G film/screen combinations was lower than those for the other film/screen combinations. The noise-equivalent number of quanta for the Kodak Ektavision film/screen combinations was well within the high-frequency range, whereas Agfa OrthoLux combined with either the Kodak Ektavision imaging screen or the Kodak Lanex Regular imaging screen produced a noise-equivalent number of quanta similar to those of the Kodak Ektavision film/screen combinations in the low-frequency range. Agfa OrthoLux was perceived to provide clearer images of the selected anatomical details than Agfa ST8G, and the Agfa OrthoLux/Agfa Ortho Regular 400 combination was not significantly different from the Kodak Ektavision/Kodak Lanex Regular combination in terms of perceived image quality.

CONCLUSION

Agfa OrthoLux is an improvement over Agfa ST8G in film speed, spatial resolution, granularity, and perceived diagnostic image quality. The Agfa OrthoLux/Agfa Ortho Regular 400 combination did not exceed the Kodak Ektavision film/Kodak Ektavision imaging screen combination in resolution, granularity, or perceived image quality.

Array-projection geometry and depth discrimination with Tuned-Aperture Computed Tomography for assessing the relationship between tooth roots and the inferior alveolar canal

OBJECTIVES

The purpose of this study is to compare Tuned-Aperture Computed Tomography (TACT) image sets made with linear vertical, linear horizontal, conical, and x-shaped x-ray projection arrays with regard to observer accuracy in (1) measuring the distance from the apex of a tooth root to the middle of the inferior alveolar canal (IAC), (2) measuring the shortest distance from the surface of a tooth root to the surface of the IAC, and (3) determining whether the root is buccal or lingual to the IAC. The same relationships were also examined by means of pairs of images and the buccal object rule.

STUDY DESIGN

Two artificial mandible sections with simulated IACs were fabricated. The same human mandibular premolar root was used in both models to prevent development of learning cues to differentiate between models. The models were imaged from both sides, resulting in 4 orientations. An optical bench was designed to precisely orient different beam projection arrays for production of TACT image sets and pairs of images for use with the buccal object rule. Twelve dentists participated as observers to independently assess the relationships between the tooth root and the IAC with regard to the 4 orientations.

RESULTS

For measuring the distance from the tooth apex to the middle of the IAC, TACT image sets made from conical and x-shaped arrays proved significantly more accurate than TACT image sets made from linear vertical or linear horizontal projections or pairs of digital images used with the buccal object rule (P <.05). For measuring the shortest distance between the tooth surface and the IAC surface, TACT image sets made from linear vertical, conical, and x-shaped projection arrays were significantly more accurate than measurements made through use of the buccal object rule or TACT image sets made through use of a linear horizontal projection array (P <.05). The following percentages of mistakes were made in determining whether the tooth root was buccal or lingual to the IAC: buccal object rule (58%), linear horizontal array (31%), linear vertical array (2%), conical array (0%), and x-shaped array (0%).

CONCLUSIONS

For TACT, images acquired with conical and x-shaped beam projection arrays are preferred to those acquired with linear arrays for assessing the relationship between tooth roots and the IAC. TACT was found to be significantly more accurate than standard application of the buccal object rule for the relationships investigated.