Effective dose of dental CBCT-a meta analysis of published data and additional data for nine CBCT units.

OBJECTIVES: This article analyses dose measurement and effective dose estimation of dental CBCT examinations. Challenges to accurate calculation of dose are discussed and the use of dose-height product (DHP) as an alternative to dose-area product (DAP) is explored. METHODS: The English literature on effective dose was reviewed. Data from these studies together with additional data for nine CBCT units were analysed. Descriptive statistics, ANOVA and paired analysis are used to characterize the data. RESULTS: PubMed and EMBASE searches yielded 519 and 743 publications, respectively, which were reduced to 20 following review. Reported adult effective doses for any protocol ranged from 46 to 1073 µSv for large fields of view (FOVs), 9-560 µSv for medium FOVs and 5-652 µSv for small FOVs. Child effective doses from any protocol ranged from 13 to 769 µSv for large or medium FOVs and 7-521 µSv for small FOVs. Effective doses from standard or default exposure protocols were available for 167 adult and 52 child exposures. Mean adult effective doses grouped by FOV size were 212 µSv (large), 177 µSv (medium) and 84 µSv (small). Mean child doses were 175 µSv (combined large and medium) and 103 µSv (small). Large differences were seen between different CBCT units. Additional low-dose and high-definition protocols available for many units extend the range of doses. DHP was found to reduce average absolute error for calculation of dose by 45% in comparison with DAP. CONCLUSIONS: Large exposure ranges make CBCT doses difficult to generalize. Use of DHP as a metric for estimating effective dose warrants further investigation.

3D osteoarthritic changes in TMJ condylar morphology correlates with specific systemic and local biomarkers of disease.

OBJECTIVE: To assess 3D morphological variations and local and systemic biomarker profiles in subjects with a diagnosis of temporomandibular joint osteoarthritis (TMJ OA). DESIGN: Twenty-eight patients with long-term TMJ OA (39.9 ± 16 years), 12 patients at initial diagnosis of OA (47.4 ± 16.1 years), and 12 healthy controls (41.8 ± 12.2 years) were recruited. All patients were female and had cone beam CT scans taken. TMJ arthrocentesis and venipuncture were performed on 12 OA and 12 age-matched healthy controls. Serum and synovial fluid levels of 50 biomarkers of arthritic inflammation were quantified by protein microarrays. Shape Analysis MANCOVA tested statistical correlations between biomarker levels and variations in condylar morphology. RESULTS: Compared with healthy controls, the OA average condyle was significantly smaller in all dimensions except its anterior surface, with areas indicative of bone resorption along the articular surface, particularly in the lateral pole. Synovial fluid levels of ANG, GDF15, TIMP-1, CXCL16, MMP-3 and MMP-7 were significantly correlated with bone apposition of the condylar anterior surface. Serum levels of ENA-78, MMP-3, PAI-1, VE-Cadherin, VEGF, GM-CSF, TGFßb1, IFNγg, TNFαa, IL-1αa, and IL-6 were significantly correlated with flattening of the lateral pole. Expression levels of ANG were significantly correlated with the articular morphology in healthy controls. CONCLUSIONS: Bone resorption at the articular surface, particularly at the lateral pole was statistically significant at initial diagnosis of TMJ OA. Synovial fluid levels of ANG, GDF15, TIMP-1, CXCL16, MMP-3 and MMP-7 were correlated with bone apposition. Serum levels of ENA-78, MMP-3, PAI-1, VE-Cadherin, VEGF, GM-CSF, TGFß1, IFNγ, TNFα, IL-1α, and IL-6 were correlated with bone resorption.

Correlating cone beam CT results with temporomandibular joint pain of osteoarthritic origin.

OBJECTIVES: The purpose of this study was to determine whether bony changes in temporomandibular joint (TMJ) osteoarthritis (OA) is correlated with pain and other clinical signs and symptoms. METHODS: Clinical data and cone beam CT (CBCT) images of 30 patients with TMJ OA were analysed. The criteria of Koyama et al (Koyama J, Nishiyama H, Hayashi T. Follow-up study of condylar bony changes using helical computed tomography in patients with temporomandibular disorder. Dentomaxillofac Radiol 2007; 36: 472-477.) and Ahmad et al [Ahmad M, Hollender L, Anderson Q, Kartha K, Ohrbach R, Truelove EL, et al. Research diagnostic criteria for temporomandibular disorders (RDC/TMD): development of image analysis criteria and examiner reliability for image analysis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009; 107: 844-860.] were used to classify the condyles observed on the CBCT. Clinical measures included self-reported pain, mandibular range of motion, TMJ sound, pain on palpation of the TMJ and masticatory muscles, and pain on jaw function. Generalized linear modelling was used to correlate the clinical and radiographic findings and Spearman's rho was used to correlate the two classification systems. RESULTS: There was poor correlation between the maximum condyle change and pain rating (Koyama: r² = 0.1443, p = 0.3995; Ahmad: r² = 0.0273, p = 0.9490), maximum mouth opening (Koyama: r² = 0.2910, p = 0.0629; Ahmad: r² = 0.2626, p = 0.0951), protrusion (Koyama: r² = 0.0875, p = 0.7001; Ahmad: r² = 0.1658, p = 0.3612), right lateral motion (Koyama: r² = 0.0394, p = 0.9093; Ahmad: r² = 0.0866, p = 0.6877) and left lateral motion (Koyama: r² = 0.0943, p = 0.6494; Ahmad: r² = 0.1704, p = 0.3236). Strong correlation was observed between Koyama et al's and Ahmad et al's classifications for average (r = 0.9216, p < 0.001) and maximum (r = 0.7694; p < 0.0001) bony change. CONCLUSIONS: There was poor correlation between condylar changes (as observed on CBCT images), pain and other clinical signs and symptoms in TMJ OA.

A manufacturer's role in reducing the dose of cone beam computed tomography examinations: effect of beam filtration.

OBJECTIVES: The dosimetry of the Kodak 9500 cone beam CT (CBCT) unit (Carestream Health, Rochester, NY) was measured before and after installation of copper filtration. METHODS: Dosimetry of a pre-production Kodak 9500 CBCT unit was compared with a current production unit with 0.4 mm of added filtration and increased kVp. Thermoluminescent dosimeter 100 chips were placed at 24 locations in a RANDO (radiation analogue dosimetry) head phantom (Nuclear Associates, Hicksville, NY). Small, medium and large adult default exposure settings were used in separate dosimeter runs for large and medium field of view (FOV) examinations with both units. Equivalent dose and effective dose were calculated using International Commission on Radiological Protection (ICRP) 1990 and 2007 tissue weights. RESULTS: Estimations of risk using 2007 ICRP calculations increased by an average of 77% for large FOV scans and 125% for the medium FOV scans in comparison with 1990 calculations. With added filtration, effective dose for medium FOV examinations for default settings were: small adult 76 µSv, medium adult 98 µSv, and large adult 166 µSv. Effective doses for large FOV examinations were: small adult 93 µSv, medium adult 163 µSv, and large adult 260 µSv. Effective dose was reduced by an average of 43% in examinations made with increased filtration and adjusted kVp. CONCLUSION: The manufacturer's installation of additional filtration with the adjustment of kVp in the Kodak 9500 CBCT unit resulted in significant patient dose reductions for examinations at all adult default settings.

Quantification of condylar resorption in temporomandibular joint osteoarthritis.

OBJECTIVE: This study was performed to determine the condylar morphologic variation of osteoarthritic (OA) and asymptomatic temporomandibular joints (TMJs) and to determine its correlation with pain intensity and duration. STUDY DESIGN: Three-dimensional surface models of mandibular condyles were constructed from cone-beam computerized tomography images of 29 female patients with TMJ OA (Research Diagnostic Criteria for Temporomandibular Disorders group III) and 36 female asymptomatic subjects. Shape correspondence was used to localize and quantify the condylar morphology. Statistical analysis was performed with multivariate analysis of covariance analysis, using Hotelling T(2) metric based on covariance matrices, and Pearson correlation. RESULTS: The OA condylar morphology was statistically significantly different from the asymptomatic condyles (P < .05). Three-dimensional morphologic variation of the OA condyles was significantly correlated with pain intensity and duration. CONCLUSION: Three-dimensional quantification of condylar morphology revealed profound differences between OA and asymptomatic condyles, and the extent of the resorptive changes paralleled pain severity and duration.

Comparison of conventional and cone beam CT synthesized cephalograms.

OBJECTIVES: To compare cephalometric measurements from synthesized cone beam CT (CBCT) lateral cephalograms using orthogonal and perspective projections with those from conventional cephalometric radiographs and dry skulls. METHODS: Ten skulls were imaged using CBCT and conventional cephalometry. CBCT volume data were exported in DICOM format and imported in Dolphin 3D (pre-release version). Orthogonal and perspective lateral cephalometric radiographs were created from 3D virtual models. Nine linear and five angular measurements were made in Dolphin at three different times. Three calliper measures of midsagittal landmarks were made directly onto skulls. Perspective and conventional image measurements were corrected for known magnification. Reproducibility of measurements was assessed using multivariate analysis of variance (MANOVA). Linear and angular measurements were compared between image modalities by measurement using a repeated measures MANOVA model. Differences and absolute value of differences between image measurements and skull measurements were assessed using analysis of variance (ANOVA). RESULTS: Measurements were not different between the imaging modalities (P>0.05), except for the mandibular unit length (P=0.01). Linear midsagittal measurements were significantly greater than skull measurements for perspective CBCT and significantly less than skull measurements for conventional images (P=0.003). Precision of orthogonal CBCT midsagittal linear measurements was significantly better than the other modalities (P=0.007). Orthogonal CBCT projections provided more accurate midsagittal skull measurements than perspective CBCT or conventional cephalometric radiographs. CONCLUSIONS: CBCT can reproduce conventional cephalometric geometry with similar precision and accuracy. Orthogonal CBCT projections provided greater accuracy of measurement for midsagittal plane dimensions than perspective CBCT or conventional cephalometric images.

Dosimetry of 3 CBCT devices for oral and maxillofacial radiology: CB Mercuray, NewTom 3G and i-CAT.

OBJECTIVES: Cone beam computed tomography (CBCT), which provides a lower dose, lower cost alternative to conventional CT, is being used with increasing frequency in the practice of oral and maxillofacial radiology. This study provides comparative measurements of effective dose for three commercially available, large (12'') field-of-view (FOV), CBCT units: CB Mercuray, NewTom 3G and i-CAT. METHODS: Thermoluminescent dosemeters (TLDs) were placed at 24 sites throughout the layers of the head and neck of a tissue-equivalent human skull RANDO phantom. Depending on availability, the 12'' FOV and smaller FOV scanning modes were used with similar phantom positioning geometry for each CBCT unit. Radiation weighted doses to individual organs were summed using 1990 (E(1990)) and proposed 2005 (E(2005 draft)) ICRP tissue weighting factors to calculate two measures of whole-body effective dose. Dose as a multiple of a representative panoramic radiography dose was also calculated. RESULTS: For repeated runs dosimetry was generally reproducible within 2.5%. Calculated doses in microSv [corrected] (E(1990), E(2005 draft)) were NewTom3G (45, 59), i-CAT (135, 193) and CB Mercuray (477, 558). These are 4 to 42 times greater than comparable panoramic examination doses (6.3 microSv [corrected] 13.3 mSv). Reductions in dose were seen with reduction in field size and mA and kV technique factors. CONCLUSIONS: CBCT dose varies substantially depending on the device, FOV and selected technique factors. Effective dose detriment is several to many times higher than conventional panoramic imaging and an order of magnitude or more less than reported doses for conventional CT.

Accuracy of measurements of mandibular anatomy and prediction of asymmetry in panoramic radiographic images.

OBJECTIVES: Measurements of ideally positioned and systematically mis-positioned skulls were used to evaluate errors in linear measurements and symmetry ratios made with panoramic X-ray images. METHODS: Digital panoramic images of 30 skulls placed in ideal, shifted and rotated positions, were assessed by measuring distances between anatomic points and fiducial references. Differences between photographic measurements (control) and radiographic measurements were compared. Horizontal measurements included a 20 mm wire and the distance from gonion to mental foramen (G-MF). Vertical distances measured included a 40 mm wire, condyle to sigmoid notch length, and condyle to gonion (posterior mandibular height or PMH). A relative symmetry ratio comparing the difference between right and left PMH was also calculated. Distances measured in panoramic images were corrected using the left vertical wire distance or the panoramic unit's stated magnification factor (1.25x). RESULTS: Greatest differences were noted for horizontal measurements and shifted skull positions. Use of an arbitrary magnification correction was consistently less accurate than use of an internal calibration and resulted in general underestimation of actual dimensions. Measures of PMH varied significantly from expected values for each of the three skull positions (P<0.005). Panoramic accuracy for detecting asymmetry was 67% for ideal, 70% for rotated, and 47% for shifted skull positions when an internal reference was used. CONCLUSIONS: Panoramic radiographs should be used with caution in making absolute measurements or relative comparisons. Even when internal fiducial calibration for image distortion of anatomy is used, measurements such as those assessing posterior mandibular facial symmetry may be unreliable.

Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit.

OBJECTIVES: This study provides effective dose measurements for two extraoral direct digital imaging devices, the NewTom 9000 cone beam CT (CBCT) unit and the Orthophos Plus DS panoramic unit. METHODS: Thermoluminescent dosemeters were placed at 20 sites throughout the layers of the head and neck of a tissue-equivalent RANDO phantom. Variations in phantom orientation and beam collimation were used to create three different CBCT examination techniques: a combined maxillary and mandibular scan (Max/Man), a maxillary scan and a mandibular scan. Ten exposures for each technique were used to ensure a reliable measure of radiation from the dosemeters. Average tissue-absorbed dose, weighted equivalent dose and effective dose were calculated for each major anatomical site. Effective doses of individual organs were summed with salivary gland exposures (E(SAL)) and without salivary gland exposures (E(ICRP60)) to calculate two measures of whole-body effective dose. RESULTS: The effective doses for CBCT were: Max/Man scan, E(ICRP60)=36.3 micro Sv, E(SAL)=77.9 micro Sv; maxillary scan, E(ICRP60)=19.9 micro Sv, E(SAL)=41.5 micro Sv; and mandibular scan, E(ICRP60)=34.7 micro Sv, E(SAL)=74.7 micro Sv. Effective doses for the panoramic examination were E(ICRP60)=6.2 micro Sv and E(SAL)=22.0 micro Sv. CONCLUSION: When viewed in the context of potential diagnostic yield, the E(ICRP60) of 36.3 micro Sv for the NewTom compares favourably with published effective doses for conventional CT (314 micro Sv) and film tomography (2-9 micro Sv per image). CBCT examinations resulted in doses that were 3-7 (E(ICRP60)) and 2-4 (E(SAL)) times the panoramic doses observed in this study.

Effect of data compression on proximal caries detection: observer performance with DenOptix photostimulable phosphor images.

OBJECTIVES: To study the effect of lossy image compression on caries detection. Null hypothesis states no difference in caries detection efficacy among observers using original digital images versus images compressed at various rates of compression. METHODS: Digital images of 41 extracted posterior teeth were obtained with a storage phosphor DenOptix (Gendex DenOptix Imaging system) system. Images were exported in Tagged Image File Format (TIFF) and compressed with Joint Photographic Experts Group File Interchange Format (JFIF), as provided by the software of the imaging system. The compressions options JFIF100%, JFIF75% and JFIF50% resulted in reducing the image size to 1:2, 1:11 and 1:16, respectively. Eight observers evaluated the presence or absence of caries on a 5-point confidence scale. The actual caries status of each proximal surface was determined by ground section histology. Responses were evaluated by receiver operating characteristic (ROC) analysis. Areas under the curves (Az) were assessed using analysis of variance (ANOVA). RESULTS: The mean Az scores were 0.85 for original/uncompressed images, and 0.89 for JFIF100%, 0.88 for JFIF75% and 0.88 for JFIF50% images. These differences were not statistically significant (P = 0.26). Differences between observers were also not statistically significant (P = 0.12). CONCLUSIONS: JFIF compression at the level of 1:16 can be used without significant deterioration in diagnostic accuracy for proximal caries detection.

Influence of the number of basis images and projection array on caries detection using tuned aperture computed tomography (TACT).

OBJECTIVES: to determine if the number of basis images and spatial distribution of the projection array used for TACT slice generation influence observer performance in caries detection. METHODS: In the first experiment, 2, 4, 8 and 12 basis projections of each of 40 teeth were acquired using a CMOS digital radiography sensor. Projections were distributed radially in space using a 20 degree angular disparity. TACT slices were generated from the four subgroups of images, presented to eight observers, and viewed on a high-resolution monitor. Observers scored the presence/absence of caries using a 5-point confidence scale. Gold standard was histological examination of tooth sections. ROC curves measured observer diagnostic performance. ANOVA tested for significant differences between observers and experimental conditions. In the second experiment, the number of basis projections judged to be satisfactory for TACT slice generation was used. Horizontal and vertical linear arrays of projections were compared to the circular projection array. RESULTS: There was a statistically significant difference between the numbers of basis projections in the detection of both occlusal (P=0.006) and proximal caries (P=0.005). No significant difference was found between projection arrays in the detection of either occlusal (P=0.065) or proximal (P=0.515) caries. CONCLUSIONS: The number of TACT basis projections significantly influences caries detection. Eight or more images should be used. Either linear-vertical, linear-horizontal or circular arrays of basis projections may be used for TACT slice generation in caries detection tasks.

Generation of TACT image slices using different reconstruction algorithms: effects on natural caries detection.

OBJECTIVE: The purpose of this study was to determine whether the method of reconstruction of tuned-aperture computed tomography (TACT) slices has an influence on observer performance in caries detection. STUDY DESIGN: Eight images of each of 40 extracted posterior teeth were acquired by using a solid state intraoral detector. Stacks of tuned-aperture computed tomography slices were generated by using the minimum and average reconstruction methods. Slices of the 2 experimental conditions were presented to 8 observers in a balanced order. Images were viewed on a high-resolution 21-in color monitor. Observers scored the presence/absence of caries by using a 5-point confidence scale. Observers' assessments were compared with histologic examinations of tooth sections. Receiver operating characteristic curves measured observers' diagnostic performance. Analysis of variance was used to test for possible significant differences between observers and between experimental conditions. Sensitivity, specificity, accuracy, and interobserver reliability were also calculated. RESULTS: No statistically significant differences between the 2 methods of reconstruction were found for the detection of either occlusal (P =.07) or proximal (P =.52) caries. Interobserver reliability was similar for both experimental conditions. CONCLUSIONS: The minimum and average methods of TACT reconstruction provide comparable performances for caries detection tasks.

Evaluation of tuned aperture computed tomography (TACT) in the localization of simulated periodontal defects.

OBJECTIVES: To compare the diagnostic efficacy of tuned aperture computed tomography (TACT) with the application of the 'buccal object rule' (BOR) in the localization of simulated periodontal defects. METHODS: Thirty interproximal sites were selected in fifteen cadaver segments of maxillae and mandible. Artificial periodontal defects were created using round burs and 40% formic acid in the buccal, lingual or mid-buccolingual areas. Eight basis projections were obtained and TACT slices were reconstructed for each region of interest. Two of the basis images were used in application of BOR for localization of the defect. Eight observers scored the location of defects using TACT slices and the paired radiographs separately. Data were analysed using the kappa statistic and ANOVA. RESULTS: A mean weighted kappa of 0.14 for localization was obtained with both BOR and TACT. Using ANOVA, there was no significant difference between modality and observer. There was however, a significant difference (P=0.019) between different defect sizes. Both modalities performed better with larger defect sizes. TACT performed slightly better than BOR when the smaller lesions were included; however, with larger lesions, this trend was reversed. CONCLUSIONS: The results confirm the relationship between correlation distance (the resultant slice width) and object size in the application of TACT for localization. BOR remains a simple yet effective tool for localization. The clinical significance is not clear considering the low kappa scores obtained with both the modalities.

The effect of the number of iterative restorations on tuned aperture computed tomography for approximal caries detection.

OBJECTIVES: To determine whether the number of iterative restorations performed on TACT images affects observers' ability to detect dental caries. METHODS: Eight TACT basis images of 40 extracted human posterior teeth were acquired using a CCD sensor. TACT slices of each tooth were generated and subsequently submitted to 1, 2 or 3 iterative restorations. Stacks of images from the three experimental conditions were presented to six observers in a balanced order, on a high-resolution 21' color monitor. Observers scored the presence or absence of approximal caries using a 5-point confidence scale. Observers' assessments were compared with the results of histological examination. Receiver operating characteristic (ROC) curves were generated and possible significant differences between observers and between modalities tested by ANOVA. The level of significance was set at alpha=0.05. Interobserver reliability was calculated as intraclass correlation. RESULTS: Mean areas under the ROC curves (A(z)) for the three experimental conditions were 0.791 (one iterative restoration), 0.81 (two iterative restorations), and 0.778 (three iterative restorations). ANOVA did not demonstrate any significant difference between modalities (P=0.25) but did so between observers (P=0.031). Interobserver reliability was similar for all experimental conditions tested. CONCLUSIONS: Varying the number of iterative restorations from one to three does not affect observers' ability to detect approximal caries with TACT slices.

Effect of angular disparity of basis images and projection geometry on caries detection using tuned-aperture computed tomography.

OBJECTIVE: The purpose of this study was to determine whether projection geometry and angular disparity of basis images used for tuned-aperture computed tomography (TACT) slice generation influence observer performance in caries detection. STUDY DESIGN: Four sets of 8 projections of each of 40 teeth were acquired by using a digital sensor. Each set was radially distributed and subtended angular disparities of 10 degrees, 20 degrees, 30 degrees, and 40 degrees, representing strict projection geometries. A fifth set of images was acquired by using unconstrained geometry. TACT slices were generated from all experimental conditions and presented to 8 observers who viewed the images on a high-resolution monitor. Observers scored the presence/absence of caries with a 5-point confidence scale. Ground truth was achieved by histologic examination of tooth sections. Receiver operating characteristic curves measured observers' diagnostic performance. Analysis of variance was used to test for significant differences among observers and between experimental conditions. RESULTS: No statistically significant difference between angular disparities was found for the detection of either occlusal (P =.105) or proximal (P =.052) caries. No statistically significant difference between unconstrained and stringent projection geometries was found for the detection of either occlusal (P =.879) or proximal (P =.130) caries. CONCLUSIONS: Angular disparities ranging from 10 degrees to 40 degrees provide comparable performance in caries detection with TACT. Both unconstrained and stringent projection geometries may be used when reconstructing TACT slices for caries detection tasks.

Fractal dimension analysis of weight-bearing bones of rats during skeletal unloading.

Fractal analysis was used to quantify changes in trabecular bone induced through the use of a rat tail-suspension model to simulate microgravity-induced osteopenia. Fractal dimensions were estimated from digitized radiographs obtained from tail-suspended and ambulatory rats. Fifty 4-month-old male Sprague-Dawley rats were divided into groups of 24 ambulatory (control) and 26 suspended (test) animals. Rats of both groups were killed after periods of 1, 4, and 8 weeks. Femurs and tibiae were removed and radiographed with standard intraoral films and digitized using a flatbed scanner. Square regions of interest were cropped at proximal, middle, and distal areas of each bone. Fractal dimensions were estimated from slopes of regression lines fitted to circularly averaged plots of log power vs. log spatial frequency. The results showed that the computed fractal dimensions were significantly greater for images of trabecular bones from tail-suspended groups than for ambulatory groups (p < 0.01) at 1 week. Periods between 1 and 4 weeks likewise yielded significantly different estimates (p < 0.05), consistent with an increase in bone loss. In the tibiae, the proximal regions of the suspended group produced significantly greater fractal dimensions than other regions (p < 0.05), which suggests they were more susceptible to unloading. The data are consistent with other studies demonstrating osteopenia in microgravity environments and the regional response to skeletal unloading. Thus, fractal analysis could be a useful technique to evaluate the structural changes of bone.

Comparison between PAI and quantitative digital radiographic assessment of apical healing after endodontic treatment.

OBJECTIVE: The purpose of this study was to compare both subjective (Periapical Index, PAI) and objective (densitometric) radiographic evaluation of healing after endodontic treatment for apical periodontitis. STUDY DESIGN: Standardized radiographs of 103 teeth taken at baseline (immediately after endodontic treatment) and at 1, 4, 12, 26, and 52 weeks were evaluated. Consensus PAI scores obtained from 7 calibrated observers served as "true scores." Densitometric estimates of periapical status were obtained from digitized radiographs as the ratio of mean gray value of an area of radiolucency (AR) to an adjacent and similar-sized normal (N) area (AR/N). The selected regions of interest on baseline images were automatically superimposed on postoperative images. All estimates of change were measured with respect to baseline. The subtraction estimate was expressed as AR(S)-N(S). Linear regression was used to analyze longitudinal changes against baseline and to assess the relationship of PAI and AR/N and of change in PAI with respect to baseline and AR(S)-N(S). RESULTS: Five hundred fifty-six PAI scores were generated, with 547 AR/N values and 444 subtraction estimates. PAI, AR/N, and AR(S)-N(S) demonstrated statistical significance for change (P < or = .05) starting at 12 weeks. PAI was significantly correlated with AR/N (P < .0001), as was CHPAI with AR(S)-N(S) (P < .024). CONCLUSION: The PAI and 2 densitometric estimates (AR/N and AR(S)-N(S)) detected healing of apical periodontitis at 12 weeks after treatment. No difference could be observed among the methods.

Analysis of fractal dimensions of rat bones from film and digital images.

OBJECTIVES: (1) To compare the effect of two different intra-oral image receptors on estimates of fractal dimension; and (2) to determine the variations in fractal dimensions between the femur, tibia and humerus of the rat and between their proximal, middle and distal regions. METHODS: The left femur, tibia and humerus from 24 4-6-month-old Sprague-Dawley rats were radiographed using intra-oral film and a charge-coupled device (CCD). Films were digitized at a pixel density comparable to the CCD using a flat-bed scanner. Square regions of interest were selected from proximal, middle, and distal regions of each bone. Fractal dimensions were estimated from the slope of regression lines fitted to plots of log power against log spatial frequency. RESULTS: The fractal dimensions estimates from digitized films were significantly greater than those produced from the CCD (P=0.0008). Estimated fractal dimensions of three types of bone were not significantly different (P=0.0544); however, the three regions of bones were significantly different (P=0.0239). The fractal dimensions estimated from radiographs of the proximal and distal regions of the bones were lower than comparable estimates obtained from the middle region. CONCLUSIONS: Different types of image receptors significantly affect estimates of fractal dimension. There was no difference in the fractal dimensions of the different bones but the three regions differed significantly.