Evaluation of the diagnostic efficacy of two cone beam computed tomography protocols in reliably detecting the location of the inferior alveolar nerve canal

In vitro accuracy of ultra-low dose cone-beam CT for detection of proximal caries

OBJECTIVES

This study aimed to assess the accuracy of ultra-low dose (ULD) cone-beam CT (CBCT) for detection of proximal caries.

METHODS

This in vitro study evaluated 104 molar and premolar teeth. The teeth were mounted in dry skulls and underwent CBCT with 4 protocols of high-resolution (HR), normal (NORM), ULD-HR, and ULD-NORM; 78 CBCT images were scored by 3 observers for the presence and penetration depth of caries twice with a 2-week interval using a 5-point Likert scale. The teeth were then sectioned and observed under a stereomicroscope (gold standard). The 4 protocols were compared with each other and with the gold standard. The receiver operating characteristic curve was drawn, and the area under the curve (AUC) was calculated and compared by the Chi-square test (alpha = .05).

RESULTS

The interobserver agreement ranged from 0.5233 to 0.6034 for ULD-NORM, 0.5380 to 0.6279 for NORM, 0.5856 to 0.6300 for ULD-HR, and 0.6614 to 0.7707 for HR images. The intra-observer agreement ranged from 0.6027 to 0.8812 for ULD-HR, 0.7083 to 0.7556 for HR, 0.6076 to 0.9452 for ULD-NORM, and 0.7012 to 0.9221 for NORM images. Comparison of AUC revealed no significant difference between NORM and ULD-NORM (P > .05), or HR and ULD-HR (P > .05). The highest AUC belonged to HR (0.8529) and the lowest to NORM (0.7774).

CONCLUSIONS

Considering the significant reduction in radiation dose in ULD CBCT and its acceptable diagnostic accuracy for detection of proximal caries, this protocol may be used for detection of proximal carious lesions and assessment of their depth.

The in-vitro accuracy of fiducial marker-based versus markerless registration of an intraoral scan with a cone-beam computed tomography scan in the presence of restoration artifact

OBJECTIVES

To determine the effect of restoration artifact ('metal artifact') on registration accuracy of an intraoral scan and cone-beam computed tomography (CBCT) scan, comparing fiducial marker-based registration with markerless registration.

MATERIALS AND METHODS

A maxillary model was fitted with multiple configurations of zirconia crowns to simulate various states of oral rehabilitation. Intraoral scans and CBCT scans (half and full rotation) were acquired. Registration was performed using markerless (point-based registration with surface-based refinement) and fiducial marker-based registration. Each experimental condition was repeated 10 times (n = 320). The absolute deviation was measured at the canines and first molars, and the average and maximum values were analysed using multiple linear regression.

RESULTS

R2 was 0.874 for average error and 0.858 for maximum error. For markerless registration, there were 0.041 mm (p < .001) and 0.045 mm (p < .001) increases in average and maximum error per crown, respectively. For fiducial marker-based registration, the effect of additional crowns was not statistically significant for average (p = .067) or maximum (p = .438) error. For a full arch of crowns, the regression model predicted average and maximum errors of 0.581 and 0.697 mm for the markerless technique, and 0.185 and 0.210 mm for the fiducial marker-based technique. Overall, the fiducial marker-based technique was more accurate for four or more crowns. The half rotation scan increased average error by 0.021 mm (p = .001) and maximum error by 0.029 mm (p < .001).

CONCLUSIONS

Under the present study's experimental conditions, the fiducial marker-based technique should be considered if four or more full-coverage highly radiopaque restorations are present.

Comparative Evaluation of a Lower-Dose CBCT Acquisition Protocol for Preoperative Implant Site Assessment in Dry Human Skulls: A Proof-of-Concept Study

Restoration of edentulous sites with dental implants is increasingly becoming a popular choice. Cross-sectional 3-dimensional imaging using cone-beam computed tomography (CBCT) provides a better depiction of the implant site to help the clinician plan the procedure better. In spite of the advantages, radiation dose will always remain a concern. The evolution of lower-dose protocols is ongoing, but whether those acquisition protocols yield comparable diagnostic information is still not well established. The objective of this study was to evaluate the diagnostic efficacy of a low-dose, 180° rotational CBCT acquisition protocol for evaluating a potential implant site in comparison with a conventional 360° rotational acquisition. Ten dentate and partially edentulous dry human skulls providing 82 randomized implant sites-40 in the maxilla and 42 in the mandible-were chosen for this study. Each skull was imaged using a 360° and a 180° rotational acquisition on a J. Morita Accuitomo CBCT scanner. Evaluation of cortical and trabecular bone, height, width, and proximity to critical structures, such as the inferior alveolar nerve canal and the maxillary sinus, were measured. An oral surgeon and an oral radiologist rated the diagnostic efficacy of the scans by evaluating the above characteristics. Statistical evaluation of the data with linear regression showed significant agreement between both protocol measurements. Kappa analyses yielded a good interobserver agreement. In this proof-of-concept study, CBCT imaging using the lower-dose, modified arc, and 180° acquisition protocol shows comparable results to the conventional 360° protocol for preoperative implant assessment.

Effective doses of dental cone beam computed tomography: effect of 360-degree versus 180-degree rotation angles

OBJECTIVES

The aims of this study were to compare radiation absorbed dose (AD) and effective dose (ED) to tissues from cone beam computed tomography (CBCT) scans with 360-degree versus 180-degree rotations with use of different fields of view (FOV), to compare EDs calculated from measured ADs versus dose area product (DAP) values, and to compare doses to the lens of the eye (LOE) from different scan parameters.

STUDY DESIGN

ADs for each protocol were measured in tissues, including the LOE, by using an anthropometric phantom. EDs were calculated on the basis of dosimetry (EDm) and DAP values (EDd). Dose differences were determined with analysis of variance (ANOVA).

RESULTS

ADs and EDs were substantially lower for 180-degree rotation scans compared with 360-degree rotation scans (P < .01). Remainder tissues had the greatest effect on effective dose for most FOVs. Doses were generally lower with small FOVs compared with large FOVs. Most EDm values were lower than EDd values in large FOVs but higher in small FOVs. Differences in EDm and EDd were variable and unpredictable. LOE doses were smaller with the 180-degree scans and smaller FOVs.

CONCLUSIONS

Radiation doses were generally lower with 180-degree rotation scans and smaller FOVs. These parameters should be used for CBCT acquisitions, whenever possible, and should be made available in all units.

Doses, Benefits, Safety, and Risks in Oral and Maxillofacial Diagnostic Imaging

Diagnostic imaging is essential in dentistry. Doses range from low to very low, benefits to patients can be immense, and safe techniques are well known but widely ignored. Doses range from very low with properly executed intraoral, cephalometric, and panoramic imaging to higher than multidetector computed tomography with cone-beam computed tomography. Benefits are substantial: imaged dental disease, often obscured from direct vision by size and anatomy, can pose a mortal threat to the patient. Additionally, imaging is often central in planning complex dental procedures. Safe imaging in dental environments is straightforward; the means for minimizing dose and maximizing diagnostic efficacy have been widely and inexpensively available for decades. Such techniques reduce patient dose by some 80% over traditional techniques but are infrequently used. Digital panoramic equipment reduces doses markedly. For cone-beam computed tomography imaging, selection criteria are critical in defining appropriate fields of view and presets; several publications address this. It is treacherous to discuss risk in oral and maxillofacial radiology. There are more than 330 million dental x-ray examinations annually, the majority being intraoral examinations, with steady increases in panoramic and cone-beam computed tomography. Radiation carcinogenesis from conventional imaging is unlikely, while large field-of-view, high-resolution preset cone-beam computed tomography can be comparable in carcinogenesis risk to craniofacial multidetector computed tomography. Uncertainties in risk estimation from low doses coupled with the huge numbers of dental images taken annually and the rapid growth of cone-beam computed tomography dictate that safe oral and maxillofacial imaging is in the interests of patients, staff, and the public. As low as reasonably achievable (ALARA) practices and linear no-threshold risk modeling continue to be prudent and appropriate.