OBJECTIVE: Optimization of radiographic examinations is essential for radiation protection. The objective of the study was to investigate the clinical applicability of a low-dose CBCT protocol as compared to the default for pre-surgical evaluation of mandibular third molars.

MATERIAL & METHODS: Forty-eight patients (62 teeth) referred for pre-surgical mandibular third molar investigation were recruited after justification for CBCT. Two CBCT scans of each site were made using a default protocol and a low-dose protocol (Veraviewepocs 3D F40, J Morita Corp, Kyoto, Japan). The low-dose protocol had the same tube potential (90 kV) and exposure time (9.4 s) as the default, but with reduced tube current, from 5 mA to 2 mA. Four observers evaluated the visibility of five relevant anatomical variables. Image quality was ranked on a 3-point scale as diagnostically acceptable, doubtful, or unacceptable. The Wilcoxon signed-rank test compared differences between the two protocols. The significance level was set at p ≤ .05.

RESULTS: No significant differences were found between the two protocols for any observer regarding the visibility of the relationship and proximity between the roots and the mandibular canal; root morphology; and possible root resorption of the second molar. The periodontal ligament differed significantly in visibility between the two protocols (p ≤ .05).

CONCLUSIONS: This study indicates that a low-dose CBCT protocol with a 60% reduction of the tube current provides, in most cases, acceptable image quality for pre-surgical assessment of mandibular third molars. Optimization of CBCT protocols should be a priority according to recommended guidelines.

OBJECTIVES: The aim of this study was to map and compare the distributions of absorbed doses with Gafchromic film for panoramic radiography and cone beam computed tomography (CBCT) examinations of the temporomandibular joint (TMJ) by using adult and child phantoms.

STUDY DESIGN: Gafchromic films were placed at 5 selected levels of anthropomorphic head phantoms of an adult and a child. Clinical protocols for panoramic and CBCT imaging of the TMJ were used for three 2-dimensional or 3-dimensional dental x-ray units. Mean absorbed doses in a set of radiosensitive tissues within the oral and maxillofacial regions were estimated.

RESULTS: The absorbed doses varied considerably among and within radiosensitive tissues. The bone surface and the salivary glands received the highest absorbed doses compared with other tissues, in both panoramic and CBCT examinations of the TMJ. The radiation burden to the adult phantom was generally higher than that to the child phantom. Small right and left fields of view were associated with lower amounts of radiation, in contrast to a single larger field of view.

CONCLUSIONS: The absorbed dose within all radiosensitive tissues varied considerably in relation to examination type, x-ray unit, clinical settings, and patient age. The mean doses were smaller when using 2 (bilateral) 4 × 4 cm volumes than with use of one 14 × 5 cm volume.

OBJECTIVE: Evaluation of cone beam CT (CBCT) examination with a low-dose scanning protocol for assessment of the temporomandibular joint (TMJ).

METHODS: 34 adult patients referred for CBCT imaging of the TMJ underwent two examinations with two scanning protocols, a manufacturer-recommended protocol (default) and a low-dose protocol where the tube current was reduced to 20% of the default protocol. Three image stacks were reconstructed: default protocol, low-dose protocol, and processed (using a noise reduction algorithm) low-dose protocol. Four radiologists evaluated the images. The Sign test was used to evaluate visibility of TMJ anatomic structures and image quality. Receiver operating characteristic analyzes were performed to assess the diagnostic accuracy. κ values were used to evaluate intraobserver agreement.

RESULTS: ) averaged for the low-dose and processed protocols, according to all observers, were 0.931 and 0.941, respectively. Intraobserver agreement was good to very good.

CONCLUSION: For the CBCT unit used in this study, the low-dose CBCT protocol for TMJ examination was diagnostically comparable to the manufacturer-recommended protocol, but delivered a five times lower radiation dose. There is an urgent need to evaluate protocols for CBCT examinations of TMJ in order to optimize them for a radiation dose as low as diagnostically acceptable (the as low as diagnostically acceptable principle recommended by NCRP).

Cone-beam computed tomography (CBCT) is one of the most revolutionary innovations in dentistry, and was introduced into the dental field two decades ago as a three-dimensional (3D) imaging modality. Since then, it has gained general clinical acceptance, and is widespread among many dental specialties. The CBCT examination is a fast and user-friendly technique that provides multiplanar images with high spatial resolution, providing information that is unattainable with two-dimensional (2D) imaging in many diagnostic tasks. Thus, CBCT is an essential examination tool that can replace or complement other examinations. CBCT imaging plays a valuable role when hard tissue abnormalities are suspected in the temporomandibular joint (TMJ) by providing diagnostic information on cortical and subcortical boneintegrity or destruction/production changes.

The growing availability and use of CBCT at dental clinics has led to concerns as to whether the information obtained by CBCT imaging justifies the additional exposure of the patient to radiation and the training required to examine and interpret the images. The radiation protection principles: justification and optimisation, should always be applied as the basis for protection. This thesis presents four studies on TMJ imaging using CBCT. In line with recent trends towards digital online education, two CBCT educational tools were developed for the interpretation of CBCT images of the TMJ and published on the Malmö University web site. The first was an educational tool including 35 CBCT examinations of TMJ, presented as 2D multiplane CBCT images. The second was a web-based programme containing 15 CBCT examinations of TMJ, presented as 3D multiplane CBCT images. Both tools included the image analysis criteria of the Diagnostic Criteria for Temporomandibular disorder (DC/TMD) as an assessment module, and were tested by dental students. It was found that they could be useful educational tools for TMJ assessment using CBCT images.

The aim of the third study was to map and compare the distribution of absorbed doses using radiochromic film dosimeters in panoramic radiography and CBCT examinations of the TMJ using adult and child anthropomorphic head phantoms. Sheets of Gafchromic film (XR-QA2)were placed at five levels, corresponding to the radiographic examination, in the phantoms. The clinical protocols for panoramic and CBCT imaging of the TMJ of three dental X-ray units were used. The mean absorbed doses to a number of radiosensitive tissues within the oral and maxillofacial regions were estimated. The absorbed doses varied considerably among and within the radiosensitive tissues with examination type, X-ray unit, clinical setting, and patient age. The bonesurface and salivary glands received the highest absorbed doses in both radiographic examinations. The radiation burden was lower when using two small right and left fields of view (FOVs) than when using a single larger FOV. Accurate measurements of the absorbed dose in small dental radiation fields is challenging due to steep dose gradients. The use of Gafchromic film has shown promising results, allowing dose comparisons between different radiographic imaging.

The last study was carried out to investigate the possibility of dose optimisation in CBCT examinations of the TMJ, in line with there commendations of the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP). Thirty-four adult patients referred for CBCT imaging of the TMJ underwent two examinations with different scanning protocols, a manufacturer-recommended protocol (default), and a low-dose protocol in which the tube current was reduced to 20% of that in the default protocol. Three image stacks were reconstructed: the default protocol, the low-dose protocol, and the low-dose protocol processed using a noise reduction algorithm. Four radiologists evaluated the visibility of TMJ anatomic structures, image quality and radiographic findings. It was found that the visibility of the TMJ anatomical structures, the overall image quality and the radiographic findings using the low-dose protocol were comparable to those in the default protocol, indicating that diagnostically comparable results could be obtained with a five times lower radiation dose.

Finally, this thesis highlights the diagnostics of TMJ imaging using CBCT in the context of image interpretation, imaging dosimetry and dose optimisation, all with the purpose of improving and optimising radiological TMJ diagnostics.

OBJECTIVES: To develop and evaluate an educational web-based program for temporomandibular joint (TMJ) assessment using cone-beam computed tomography (CBCT).

METHODS: A web-based educational program was designed for TMJ assessment using CBCT images. Fifteen CBCT cases of the TMJ (three-dimensional reconstructed volumes) and an assessment module based on image analysis criteria in the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) were added to the program. Thirty-six undergraduate dental students were invited to test the program by assessing all cases twice: before and after 2 months of training. Participants submitted written subjective evaluations of the program.

RESULTS: The web-based program can be accessed on Malmö University webpage (www.cbct-tmj.mau.se). Despite limited CBCT learning in their undergraduate training and not using the program in the 2-month interval, the students were able to correctly diagnose 80% of the cases at the second assessment. Their diagnoses, however, did not differ significantly from the first assessment. Overall, the students were satisfied with the program and considered it user friendly.

CONCLUSION: The web-based educational program that was developed in the present study and tested by dental students could be a useful educational tool for TMJ assessment using CBCT.

Introduction To measure absorbed dose with high spatial resolution we have used Gafchromic film which gives an analog-looking dose distribution image compared to point measurements, e.g. TLDs. CBCT examinations of TMJs will produce dose distributions with very steep dose gradients. Over a distance of 2 mm, the absorbed dose can increase/decrease more than a factor of 10. Point measurements using 3x3 mm TLDs will give dose values with high uncertainty when placed in areas with steep dose gradients. Aim The aim was to map the absorbed dose distributions with Gafchromic film, for TMJ investigations using adult and child phantoms. Another aim was to analyze the difference of dose distributions in sensitive organs/tissues between the phantoms. Material and methods Gafchromic films were placed between selected layers of the two head phantoms. The number of films was chosen to well cover the height of the CBCT volume used. The films were scanned in a flatbed scanner and the net pixel values were converted to absorbed dose using a calibration curve. Clinically used examination protocols were applied for three different CBCT units. Outlines of organs/tissues considered at risk were superimposed on the dose distributions. Maximum, minimum and mean doses were calculated. Also, the integrated dose in the phantom was calculated to reflect the total radiation load. Preliminary results and conclusion For CBCT examinations, dose gradients are steep in many organs/tissues considered at risk. Measuring dose distributions with high spatial resolution will give a solid foundation for calculating mean doses in those organs/tissues both for children and adults and will also facilitate comparisons of different examination protocols and of different CBCT units.

Objectives Osseous changes in temporomandibular joint disorders (TMD) are common indications for cone beam computed tomography (CBCT). The number of such cases is increasing while a number of qualified oral radiologists is limited. This study investigated the usefulness of a training programme for general dental practitioners (GDPs) regarding temporomandibular joint (TMJ) osseous changes detection in CBCT images. Methods We selected CBCT images of 35 TMD cases and chose 5 of them to use in training 7 GDPs on detecting osseous changes in the TMJ. In evaluation directly following training, GDPs assessed the 30 remaining cases. Three qualified radiologists served as reference standard. A 2-month follow-up of training comprising evaluation of the same cases. The cases are assessed according to Ahmad etal (Oral Surg Oral Med Oral Pathol Oral Radiol Endod, 107, 2009, 844) protocol of TMJ osseous changes in CBCT images. ResultsSensitivity and specificity of the CBCT protocol were high, except for some criteria that did not appear in the cases. Average observer sensitivity was 65% while specificity was 87%. Average correct individual response rate was 84%. Mean agreement among the GDPs was 73%. Observer performance had improved at the 2-month follow-up. Conclusion The present educational programme could be a helpful material on recognising possible osseous changes of TMJ and it can be used as a part of a training programme for GDP and for specialist candidates.