Visibility of anatomical landmarks in the region of the mandibular third molar, a comparison between a low-dose and default protocol of CBCT.

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.

Web-based educational programme for temporomandibular joint assessment with cone-beam computed tomography.

OBJECTIVES: To develop and evaluate an educational web-based programme for temporomandibular joint (TMJ) assessment using cone-beam computed tomography (CBCT). METHODS: A web-based educational programme 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 programme. Thirty-six undergraduate dental students were invited to test the programme by assessing all cases twice: before and after 2 months of training. Participants submitted written subjective evaluations of the programme. RESULTS: The web-based programme can be accessed on Malmö University webpage (www.cbct-tmj.mau.se). Despite limited CBCT learning in their undergraduate training and not using the programme 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 programme and considered it user-friendly. CONCLUSION: The web-based educational programme that was developed in the present study and tested by dental students could be a useful educational tool for TMJ assessment using CBCT.

Evaluation of a low-dose protocol for cone beam computed tomography of the temporomandibular joint.

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: With the low-dose and processed protocols, visibility of the TMJ anatomical structures and overall image quality were comparable to the default protocol. No significant differences in radiographic findings were found for the two low-dose protocols compared to the default protocol. The area under the curves (Az) 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).

Dose distributions in adult and child head phantoms for panoramic and cone beam computed tomography imaging of the temporomandibular joint.

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.