Evaluation of the effective dose of cone beam CT and multislice CT for temporomandibular joint examinations at optimized exposure levels.

OBJECTIVES: To compare the effective dose to patients from temporomandibular joint examinations using a dental CBCT device and a multislice CT (MSCT) device, both before and after dose optimization. METHODS: A Promax(®) 3D (Planmeca, Helsinki, Finland) dental CBCT and a LightSpeed VCT(®) (GE Healthcare, Little Chalfont, UK) multislice CT were used. Organ doses and effective doses were estimated from thermoluminescent dosemeters at 61 positions inside an anthropomorphic phantom at the exposure settings in clinical use. Optimized exposure protocols were obtained through an optimization study using a dry skull phantom, where four observers rated image quality taken at different exposure levels. The optimal exposure level was obtained when all included criteria were rated as acceptable or better by all observers. RESULTS: The effective dose from a bilateral examination was 184 µSv for Promax 3D and 113 µSv for LightSpeed VCT before optimization. Post optimization, the bilateral effective dose was 92 µSv for Promax 3D and 124 µSv for LightSpeed VCT. CONCLUSIONS: At optimized exposure levels, the effective dose from CBCT was comparable to MSCT.

Comparison of psychophysical properties of two intraoral digital sensors on low-contrast perceptibility.

OBJECTIVES: The psychophysical properties of a new complementary metal oxide semi-conductor-based detector, ProSensor(®) (Planmeca Oy, Helsinki, Finland), in terms of dose response function and perceptibility curve test were performed and compared with those of a charged couple device-based sensor, Dixi(®) (Planmeca Oy). METHODS: Dose response functions at 66 kVp for a Dixi and a ProSensor were determined by means of multiple exposures to a homogeneous X-ray field covering the whole exposure range. The entry dose of each exposure was measured and registered. The mean grey level in each image was plotted as function of the corresponding exposures for both digital systems. Radiographs of a test object containing ten holes of increasing depth were obtained throughout the exposure range of the two digital sensors at 66 kVp. 12 observers were asked to register the number of perceptible holes in each radiograph. Based on the mean value of the observers' evaluation, the perceptibility curves were constructed, and the integral value under the perceptibility curves were compared between two intraoral sensors. RESULTS: The results based on dose response function showed that the ProSensor was more sensitive than the Dixi sensor. Paired t-test showed that the minimal perceptible low-contrast details were significantly higher for the ProSensor than for the Dixi sensor (p < 0.001). The integrals below the two perceptibility curves were 33.4 and 69.2 for the Dixi and ProSensor, respectively. CONCLUSION: Applying the new ProSensor may be beneficial to patients owing to its reduced radiation dose and increased perception for low-contrast details in dentistry.

Comparison of psychophysical properties of two intraoral digital sensors on low-contrast perceptibility.

OBJECTIVES: The psychophysical properties of a new complementary metal oxide semi-conductor-based detector, ProSensor® (Planmeca Oy, Helsinki, Finland), in terms of dose response function and perceptibility curve test were performed and compared with those of a charged couple device-based sensor, Dixi® (Planmeca Oy). METHODS: Dose response functions at 66 kVp for a Dixi and a ProSensor were determined by means of multiple exposures to a homogeneous X-ray field covering the whole exposure range. The entry dose of each exposure was measured and registered. The mean grey level in each image was plotted as function of the corresponding exposures for both digital systems. Radiographs of a test object containing ten holes of increasing depth were obtained throughout the exposure range of the two digital sensors at 66 kVp. 12 observers were asked to register the number of perceptible holes in each radiograph. Based on the mean value of the observers' evaluation, the perceptibility curves were constructed, and the integral value under the perceptibility curves were compared between two intraoral sensors. RESULTS: The results based on dose response function showed that the ProSensor was more sensitive than the Dixi sensor. Paired t-test showed that the minimal perceptible low-contrast details were significantly higher for the ProSensor than for the Dixi sensor (p < 0.001). The integrals below the two perceptibility curves were 33.4 and 69.2 for the Dixi and ProSensor, respectively. CONCLUSION: Applying the new ProSensor may be beneficial to patients owing to its reduced radiation dose and increased perception for low-contrast details in dentistry.

Evaluation of automatic exposure control in a direct digital intraoral system.

OBJECTIVES: The aim of this study was to evaluate the performance of the automatic exposure control (AEC) in an intraoral digital system. METHODS: Three series of radiographs were captured with the activated AEC on seven dry mandibles adhered to different thicknesses of Plexiglas((R)), which represented soft tissue. Exposure times required for each radiograph of the specimens were analysed as functions of the added Plexiglas thickness. Differences in mean grey levels between pairs of the three images obtained from the same specimen were analysed by employing the subtraction technique. Additionally, four radiographs of all seven mandibles were manually exposed with one layer of Plexiglas, which employed one and two steps below and above the registered automatic exposure time. Six observers evaluated the series of radiographs exposed with one layer of Plexiglas in a random order. The observers were instructed to classify the quality of the diagnostic images as unacceptable, acceptable or excellent. RESULTS: The results demonstrated a good correlation between the exposure times determined by AEC and Plexiglas thickness (r = 0.85). Mean grey level values for subtraction images obtained from radiographs exposed with different thickness of Plexiglas with activated AEC indicated that almost identical radiographs were obtained, regardless of the Plexiglas thickness. The subjective observer evaluation of the most satisfactory radiographic image quality as a function of exposure time demonstrated that the highest scores were for radiographs exposed with the AEC function activated. CONCLUSIONS: The AEC function may accurately determine the appropriate exposure times related to object thickness, providing radiographs with satisfactory image quality, and may thus be advantageous in clinical radiographic work.

Marginal bone levels measured in film and digital radiographs corrected for attenuation and visual response: an in vivo study.

OBJECTIVE: To compare the accuracy and precision of measurements on marginal bone levels in differently processed digital radiographs and in film-based radiographs. METHODS: Twenty-one patients with a diagnosis of chronic periodontitis were included in this study. Periapical radiographs were exposed with the Dixi digital intraoral radiographic system (Planmeca Oy, Helsinki, Finland) and the F-speed Film (Insight, Eastman-Kodak Co., Rochester, NY), respectively. Digital radiographs were subsequently processed into two sets: (a) correction for attenuation and visual response and (b) the same correction but with an additional shift in grey levels. Patients had periodontal surgery immediately after the radiographs were exposed. The vertical distance from cementoenamel junction to the most apical part of the marginal bone was assessed. The measurements were then employed as reference standard and subtracted by the vertical distance from radiographs accordingly. Altogether, 47 sites were evaluated. Seven observers were employed for evaluation under the same viewing conditions. ANOVA was employed for statistical analysis. RESULTS: No significant differences were found between the absolute differences of the vertical distance obtained from radiographs to their corresponding reference standards when comparing differently processed digital radiographs, but the absolute differences were significantly smaller in digital radiographs than in films. Interobserver variances were not significant. CONCLUSION: Digital radiographs have a favourable measurement accuracy compared with film radiographs when assessing marginal bone levels.

Evaluation of endodontic files in digital radiographs before and after employing three image processing algorithms.

OBJECTIVES: Two digital image processing algorithms, one aimed at correction for exponential attenuation and one at correction for visual response, have been developed. The aims of the present study were to test whether digital radiographs processed with these algorithms improve determination of the length of endodontic files and whether such processed radiographs are comparable with the radiographs processed with a default image processing method employed by one commercially available digital intraoral system. METHODS: A dried human skull embedded in an acrylic compound was used for exposing radiographs of the upper and lower premolars and molars with endodontic files (Kerr files size 10 and size 15) positioned to the full length of the roots or 1.5 mm short of it. Radiographs were then processed in three sets. In one set, the radiographs were processed to compensate for exponential attenuation and the response of the human visual system. In the second, the radiographs were processed with the same compensation but with an additional shift in grey levels so that the output luminance in dentin at root tips corresponds to the mean of the luminance range of a computer monitor. In the third, the radiographs were processed with the default processing method in the Sidexis program. Ten viewers evaluated all radiographs. Receiver operating characteristic (ROC) curves were obtained and areas under the curves were calculated. RESULTS: For file size 10, ROC curves for processed radiographs were higher than that for originals, while for file size 15, ROC curves for processed and original radiographs were close to each other. Significant differences were found between processed and original radiographs regarding areas under ROC curves for file size 10 but not between the differently processed radiographs. For file size 15, no significant differences were found. CONCLUSION: Radiographs processed to correct for attenuation and visual response may improve determination of the length of thin endodontic files. Such processed radiographs are comparable with the radiographs processed with the default processing method in the Sidexis program.

Dentin formation after corticosteroid treatment. A clinical study and an experimental study on rats.

The overall aim of this series of studies was to determine whether the extensive narrowing of the dental pulp chamber seen in dental radiographs of patients with end stage renal disease was related to the method of treatment of the renal disease. The treatments studied were immunosuppression, renal transplantation and hemodialysis. A strong correlation was found between narrowing of the dental pulp chamber and renal transplantation. In the immunosuppression group and in the renal transplantation group, the patients received immunosuppressive drugs, mainly corticosteroids and azathioprine. Significantly higher doses of corticosteroids had been given to patients showing narrowing of the dental pulp chamber than to patients without such narrowing. The total plasma clearance of the corticosteroids received was measured among transplanted patients. The total plasma clearance was lower in patients with narrowing of the dental pulp chamber than in patients without narrowing. The morphology of the corticosteroid induced dentin in premolars from five deceased patients who had received one or more renal transplants each was compared with that in extracted teeth from five healthy individuals. The results of this study showed that dentin formation after high dose corticosteroid treatment in humans seems to start with a widening of the predentin zone, followed by extensive mineralisation causing substantial reduction of the dental pulp chamber within a few years after the start of treatment. In an experimental study on rats, it was shown that intravenous administration of high doses of corticosteroids induced dentin formation along the pulp chamber walls in the molars. Energy dispersive X-ray microanalysis was used for estimation of the calcium and phosphorus content of the dentin in rat teeth. The calcium and phosphorus composition of the corticosteroid induced dentin was found to be equal to that of normal dentin in control rat molars, which might imply that the mineralisation process was not affected by the corticosteroid treatment and thus the quality of the corticosteroid induced dentin might be equal to normal dentin regarding the calcium and phosphorus composition. In a scanning microscopy study of the morphology of the corticosteroid induced dentin in rat incisors, it was found to be equal to that of normally formed dentin.

Energy dispersive X-ray microanalysis of the dentin in rat molars after corticosteroid treatment.

The aim of this study was to investigate whether the calcium (Ca) and phosphorus (P) composition of corticosteroid induced dentin was the same as in normally developed dentin. Seven rats were given corticosteroids intravenously and three rats served as controls. Energy dispersive X-ray microanalysis (EDX) was carried out on the axially sawn roots of the molars. Measurements were made at 20 sites, equally distributed in the buccal, mesial, lingual and distal direction. The results showed that the Ca/P ratio (weight %) was slightly above 2.0 in both the experimental and the control group, indicating that the corticosteroid induced dentin had a normal Ca/P ratio. However, different degrees of mineralization were found in different directions of the roots.

Effect on human teeth of renal transplantation: a postmortem study.

Extracted teeth from five deceased patients treated by renal transplantation were examined radiographically and histologically, and compared with teeth from healthy persons of approximately the same age. In three of the patients with a renal transplant, the radiographs showed normal pulp chamber sizes, but histologic examination revealed a widened predentin zone, approximately four times greater than in the controls. In two of the patients the radiographs showed marked reduction of the pulp chamber size. The histologic changes of these teeth were mainly an extensive amount of secondary dentin along the pulp chamber walls and the root canals, with a markedly reduced pulp space. One explanation for the difference between the patients was that patients with extensive pulp calcifications were given a higher total amount of corticosteroids than patients with a widened predentin zone.

Surface structure of the temporomandibular joint in normal and steroid-treated rats: a scanning electron microscopic study.

The aim was to study the ultrastructure of the surface of the temporomandibular joint (TMJ) in mature rats. The TMJs from control rats and rats given corticosteroids for 10 days or 38 days were examined. In three joints from the control rats the disk was detached from the condyle before preparation and analysis. Scanning electron microscopy was performed on the condyle, the disk, and the temporal component. Generally, the surface of the three components was predominantly smooth, although the condyle exhibited a more even surface than the disk and the temporal component. In the fossa a pitted or ridged appearance was observed in some areas. There was a striking difference between the surface structure of disks attached to, and that of disks detached from, the condyle during preparation. A prominent undulation of surface was evident in disks detached from the condyle. Below the surface layer of the articular cartilage, a network of collagen fibers and fibrils running in all directions could be observed in all three components. In limited areas there was fibrillation and shallow defects of the surface layer. These changes were seen in all rats given corticosteroids for 38 days but also in some rats given corticosteroids for 10 days and in a few control rats.

Comparison between panoramic and posterior bitewing radiography in the diagnosis of periodontal bone loss.

A study is reported comparing the diagnostic yield of panoramic and posterior bitewing radiographs when used to image periodontal bone disease. It is concluded that there is a high concordance between the findings from the two types of radiographs but that the concordance varies with the degree of bone loss and tooth type. Consequently when panoramic radiography is used in clinical practice, the examination should be supplemented by intraoral radiographs in regions when image quality is poor in the panoramic image and where there are structures of special interest.

Effect of intravenous administration of corticosteroids on dentin formation in the adult rat molar.

This study describes the effects of intravenously given corticosteroids on dentin formation in adult rat molars. Six rats twice a day received corticosteroids 20 mg/kg for 8 days, 10 mg/kg for 13 days, and 5 mg/kg for 19 days. Six rats given a heterotopic heart transplant received 10 mg/kg of corticosteroids twice a day for 40-64 days. Six rats were used as controls. Tetracycline was given at the start of the experiment and after 3 wk of treatment. After 40-46 days the rats were killed. Light microscopic examination of the molars showed no differences in the dentin formation or in the predentin zone between the experimental and control rats. In the ultraviolet light microscope two lines of tetracycline were visible along the root canal walls in both experimental groups. There was an obvious distance between the two lines, which indicated formation of new dentin. In the control group no formation of dentin was visible.

Comparison between panoramic and periapical radiography in the diagnosis of periodontal bone loss.

Panoramic and periapical radiography was performed on 100 patients. Five observers each registered the scores for marginal bone level, presence of bone defects and furcation involvement in the radiographs of 20 patients and the results were compared. The overall concordance in scoring the marginal bone level was high when panoramic and periapical radiography was compared. In the upper arch, 66% of the sites showed concordant scores, 31% deviated by one and 3% by two score-points. In the lower arch, 74% of sites had concordant scores, 25% deviated by one and 1% by two score-points. The panoramic radiographs more often indicated a more severe bone loss than the periapical radiographs. The concordance was related to the degree of bone loss. In sites with no bone loss the concordance was high whereas it was lower in those with severe bone loss. The concordance of the two radiographic methods for the mandibular canine, premolars and first molar was equally as high as the intra-observer overall agreement, but lowest for the mandibular central incisors and the maxillary molars. Bone defects were more easily identified by periapical radiography.

Narrowing of the dental pulp chamber in patients with renal diseases.

Narrowing of the dental pulp chamber was studied radiologically in fifty one patients with renal diseases. Two thirds of the patients were suffering from terminal uremia and were treated either by renal transplantation or with hemodialysis. The remaining patients were nonuremic and were treated with immunosuppressants because of progressive renal disease. There were significantly more patients with narrowing of the dental pulp chamber among the transplant patients than among the other patients. The transplantations included the use of higher doses of corticosteroids than the other treatments. As the median dose of corticosteroids was higher and total plasma steroid clearance was lower in the patients with narrowing of the dental pulp chamber than in the other patients, the amount of this drug received and its pharmacokinetics seemed to be an essential factor in the initiation of narrowing of the dental pulp chamber.