Dental imaging has been dramatically enhanced by cone beam computed tomography (CBCT) over the past decade. By allowing the accurate visualization of anatomy and pathology at considerably less radiation and cost than conventional CT scans, CBCT imaging has become the standard of care when 3D radiographic images are required in dentistry.1 Some of the more common dental applications of CBCT technology today include planning for implant placement, complex extractions, or other surgical procedures, as well as the evaluation of temporomandibular joints and suspected pathological lesions.2
The field of orthodontics has many uses for the information gathered by CBCT scans. These include detection and location of impacted or supernumerary teeth, studying mixed dentitions, planning temporary orthodontic anchorage devices, identifying and locating pathological lesions, evaluating growth and development of the craniofacial complex, analyzing the airway, and orthognathic surgery planning.3 Additionally, as the dental patient can now be imaged in three dimensions at resolutions approaching a tenth of a millimeter, CBCT scans are increasingly being used to digitize the dentition.4 By generating digital models this way, CBCT technology has eliminated the need for impressions for the production of orthodontic study models.
Successful orthodontic treatment has always relied heavily on accurate and informative imaging. Currently, the primary images used to plan orthodontic treatment are panoramic and lateral cephalometric radiographs. These images are not optimal, however, due to the presence of distortion, magnification, superimposition of the left and right sides of the dentition, and presence of other projection artifacts.5 Images produced by CBCT scans are superior to the traditional “pan and ceph” in all these aspects. Indeed, as stated by Miles,6 “visualization of anatomy and pathology has now replacedradiographic interpretation”. This improvement in imaging, however, can come at the cost of increased radiation exposure. The orthodontic profession continually concerns itself with the dilemma of radiation dose to the patient versus quality of images for diagnosis and treatment planning. This is especially true considering that adolescents comprise the majority of the orthodontic patient population. The dosimetry of many CBCT scanners (including the next generation i-CAT machine used in this study) is below that of a full mouth series taken with D speed film and with round collimation. Unfortunately, the radiation dose remains higher than the radiation dose delivered by a combined digital panoramic and lateral cephalometric radiographic examination.7
When a CBCT scan is performed, the field of view (FOV) often extends beyond the specific anatomic area of interest. The current literature8,9,10 would suggest that it is the responsibility of the treating clinician to analyze all of the information obtained in the FOV for occult pathology, not just the information critical for a specific treatment plan. As such, the clinician may be required to analyze regions of anatomy outside his or her area of comfort or expertise, thus warranting referral of the scan to an oral and maxillofacial radiologist for review.
Given the increased use and availability of CBCT machines in dentistry, having a better understanding of the prevalence and characteristics of incidental findings in CBCT scans would be of clinical interest to the profession. Therefore, the purpose of this study was to characterize the incidence of occult pathology in CBCT scans of patients seeking routine orthodontic treatment
Materials and Methods
The sample population comprised 194 patients (110 females, 84 males) starting orthodontic treatment at the Graduate Orthodontic Department of the University of Minnesota School of Dentistry from July 2008 to July 2009, in which radiology reports were available. The average patient was 13.0 years old, with a range of 8 to 63 years of age. The CBCT scans were performed using a Next Generation i-CAT scanner (Imaging Sciences International, Hatfield, PA), and were part of the routine records protocol used for orthodontic diagnosis and treatment planning. The machine was set at 120 kVp and 37.10 mA. The resolution was set at 0.3 mm voxels enhanced scan, and scan acquisition time was 17.8 s.
All scans were screened by one of two board certified oral and maxillofacial radiologists. The resulting radiographic reports were then reviewed for findings, whichwere categorized by patient gender and age and lesion location (airway, TMJ, endodontic, or other). The findings were further classified as incidental, requiring continued monitoring, or as significant, requiring immediate follow-up. The statistical analysis performed on the information gathered included Fisher’s Exact Test and a simple logistic regression for continuous independent variables.
Of the patients in the population studied, 65.5 % (127/194) had incidental findings reported. Airway findings were most commonly observed, followed by the TMJ, other, and endodontic categories (Table I). In terms of significant findings, it was found that 37.6% (73/194) of the patients had findings that required immediate follow-up, with TMJ and endodontic concerns being most frequently cited.
Examples of the most common incidental findings include retention cysts, sinusitis, and flat condylar margins. The most common significant findings were signs of degenerative joint disease, osteophytes, apical periodontitis, and undiagnosed periapical radiolucencies. This sample population also included findings of an ameloblastoma, dentigerous cysts, a possible giant cell granuloma, and a sialolith. Please see Table II for a detailed listing of findings as described in the radiology reports.
Statistical analysis of the data revealed significant correlations between age and number of findings. As age increased so did the rate of incidental findings in the TMJ (p =0.0156) and endodontic groups (p< 0.001). There was no correlation between age and airway or “other” findings. No significant relationships were found between gender and the number or location of findings.
As CBCT imaging transitions from the cutting edge to the standard of care in many areas of dentistry, the prudent clinician will want to fully understand the implications in adopting this new technology. The present study provides information on the incidence and significance of findings in CBCT scans of a mixed patient population seeking orthodontic treatment. Overall, 73 of 194 patients (37.6%) had findings deemed significant enough to warrant further evaluation.
Patient age correlated positively with the number of incidental findings (p = 0.0053). Regarding location, a significant relationship was found with age and findings in the TMJ (p= 0.0156) and endodontic groups (p< 0.001). There was no correlation between advancing age and airway or “other” findings. These results might be expected considering the often degenerative, “wear and tear”, nature of TMD. Similarly, with increasing age comes increased time for teeth to develop endodontic problems, either through new decay or the failure of previous restorations.
A review of the recent dental literature demonstrates incidence rates similar to those of the present study. After examining CBCT scans of endodontic, implant, TMJ, and orthodontic patients, Cha et al11 found that 24.6% of patients had incidental findings. These most commonly involved the sinuses or airway, followed by the temporomandibular joints. In a study examining the additional information provided by the enhanced detail and greater FOV of CBCT, Scanlon12 and colleagues reported findings that excluded those visible on a panoramic or full-mouth series of films. Of the 95 patients evaluated, 65% had potentially clinically significant incidental findings. This can be compared to a retrospective review of panoramic radiographs taken for orthodontic treatment planning, where Bondemark et al13 observed pathology in 8.7% of an adolescent sample of patients. The differences in incidence rates between studies can largely be attributed to the author’s definition of what is significant enough to report. For example, in a review of 381 cases, Miles14 described 701 “reportable findings”, ranging from deviations of normal (tori) to serious (various non-odontogenic lesions). For this reason, in the present study all findings were reported, then those requiring additional examination or follow-up were further quantified (Table II).
It would appear that incidental findings of varying significance should be expected when capturing CBCT images of our patients, especially when the FOV is large, as in scans for orthodontic purposes. It is critical that clinicians do not simply review the information that they were seeking when performing a radiographic interpretation. If the remainder of the data volume is neglected, there is a high risk that important information concerning the treatment of the patient could be missed. As previously stated, this information may simply require that the clinician monitor the pathology, but it may require follow-up with an appropriate health care professional. As the ethical15 and legal10 implications of CBCT imaging are further discussed, the prudent clinician will weigh the benefits against the risks of enhanced 3D imaging for each patient.
Of the 194 patients in this study scanned for the purposes of orthodontic diagnosis and treatment planning, 73, or 37%, demonstrated findings deemed significant enough to require a follow-up evaluation or appropriate referral.
When characterized by location, the majority of findings could be classified as being outside the orthodontic treatment domain.
This study adds support to the notion that regardless of the purpose of a CBCT scan, the entire data volume should be reviewed by a clinician competent to do so.
Dr. Mansur Ahmad and Dr. Mohammad Islam are acknowledged for their help in interpreting CBCT scans.
This study was supported by the University of Minnesota School of Dentistry Summer Research Program.
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