| Abstract|| |
Background and Objectives: An increasing number of different types of commercial cone-beam computed tomography (CBCT) devices are available for three-dimensional (3D) imaging in the field of dental and maxillofacial radiology. When removing impacted or supernumerary teeth, surgical teams often operate adjacent significant anatomical structures such as nerves, vessels, adjacent teeth roots, and paranasal sinuses. It is therefore important to choose the appropriate surgical approach to avoid iatrogenic damage to the essential anatomical neighbouring structures. CBCT, also called digital volume tomography (DVT), can visualize impacted and supernumerary teeth in all standard planes, as well as multisectional 3D views. These devices have shown to be highly beneficial in the assessment of small bony lesions and maxillofacial injuries. However, it is still necessary to determine the effectiveness of such devices in the assessment of impacted and supernumerary teeth, in comparison to the conventional radiological methods of intraoral X-rays and panoramic X-rays.
Materials and Methods: During a period of 2 years, a total of 61 patients of whom majority had impacted teeth or supernumerary elements in the frontal maxillary region were studied with CBCT and treated at the St. Olavs University Hospital. Patients were referred to our Department of Oral and Maxillofacial Surgery with both conventional and digital intraoral X-rays and/or panoramic X-rays. None had any acute infections or odontogenic abscesses, and most presented with asymptomatic impacted tooth. A comparison between the preoperative conventional and the CBCT images, the resulting diagnoses, and the intraoperative findings as "gold standard" were made and recorded in a compiled scoring sheet. The objects of interest were researched with the magnification method. Each patient was identified only with a patient number.
Results: In contrast to the conventional X-rays, the pre-surgical evaluation with the CBCT revealed detailed imaging of significant anatomical structures and objects of interest, with highly accurate anatomical and morphologic imaging, when compared to the intraoperative findings. Furthermore, no diagnostic problems, in relation to the anatomical localization, occurred preoperatively.
Conclusion: The CBCT provides true and precise anatomical information with high surgical predictability without distortion or artefacts, and is superior to conventional radiography. It enables more time-efficient surgeries and reduces costs and surgical complications.
Keywords: Cone beam CT, digital volume tomography, impacted teeth, oral radiology, supernumerary teeth
|How to cite this article:|
Ziegler CM, Klimowicz TR. A comparison between various radiological techniques in the localization and analysis of impacted and supernumerary teeth. Indian J Dent Res 2013;24:336-41
Diagnostic and surgical difficulties resulting from impacted teeth, commonly the wisdom teeth and supernumerary teeth have been the subject of discussion for several years. This is significant as these common anatomical problems can influence other teeth and may be involved in both systemic and local infections as well as inflammatory processes, requiring their removal. Therefore, both clinical and radiological evaluation is necessary for preoperative planning.
|How to cite this URL:|
Ziegler CM, Klimowicz TR. A comparison between various radiological techniques in the localization and analysis of impacted and supernumerary teeth. Indian J Dent Res [serial online] 2013 [cited 2020 Feb 23];24:336-41. Available from: http://www.ijdr.in/text.asp?2013/24/3/336/117998
When removing impacted or supernumerary teeth, surgical teams often operate adjacent to significant anatomical structures, such as nerves, vessels, adjacent teeth roots, and paranasal sinuses. It is therefore important to choose the appropriate surgical approach to avoid iatrogenic damages to the essential anatomical neighbouring structures. ,,,
High-resolution cone-beam computed tomography (CBCT) technique is based on X-ray transmission projections of a sequence of specific offset two-dimensional (2D) absorptions. This technique, also called digital volume tomography (DVT), was originally designed for three-dimensional (3D) diagnostics in the field of dental and maxillofacial radiology: "Dental CT."
The computed tomography (CT) and CBCT can visualize impacted and supernumerary teeth in all standard planes, as well as multisectional 3D views.  Technological advances have allowed the CT to become more and more compact and be more commonly used in diagnostic radiology of traumatology, oncology, and in the study of congenital malformations. ,,,
Because of the drawbacks of CT radiographic technique, such as metal artefacts and limited resolution capacity, the CT is not an ideal tool for imaging of intraosseous details and diseases, such as impacted and supernumerary teeth in oral surgery and dentistry. CBCT, on the other hand, is thought to be more useful for the assessment of small bony lesions and injuries in the maxillofacial region. It also requires less space and has a lower cost than the conventional CT devices. Therefore, CBCTX's are also seen in private medical and dental offices. 
In contrast to conventional helical fan-beam CT scanners, the CBCT systems use a cone beam geometry X-ray source. The high-resolution CBCT technique is based on X-ray transmission projections of a sequence of specific offset 2D absorptions.
It produces 3D images similar to conventional fan beam CT, but in a completely different exposure scanning process. , This sequence of digital lateral cephalograms creates primarily a 2D reconstruction of the skull anatomy in axial, sagittal, and coronal planes. In order to get a 3D high-resolution image, the scanned information has to be run through a special algorithm. Several studies have indicated that the CBCT delivers around 60 μSv radiation dose with each jaw scan. This is a 95% reduction in radiation in comparison with the conventional CT systems. ,,,
Other clinical CBCT benefits possessed by the i-CAT include for example volumetric data acquisition with relatively fast scan time, digital data saving, navigation opportunities and high image definition and resolution for all views. On the other hand, conventional radiological devices for intraoral X-rays and panoramic X-rays are most common, easy to handle, and lower in cost.
Therefore, it was necessary to determine the effectiveness of CBCT devices in the assessment of impacted and supernumerary teeth, in comparison to these conventional radiological methods.
| Materials and Methods|| |
The Department for Oral and Maxillofacial Surgery in Trondheim [Norwegian University of Science and Technology (NTNU), St. Olavs University Hospital] uses an i-CAT (Xoran Technologies, Ann Arbor, MI/Imaging Sciences International, Hatfield, PA, USA) radiological device since 2007 for the investigation of oral and maxillofacial pathologies, such as in traumatology, oncology, airway studies, orthognathic surgery, temporomandibular joint (TMJ) analysis, and dentoalveolar surgery.
After obtaining approval of the regional ethics committee and the Norwegian Commission for patient data protection, over a period of 2 years, a total of 61 patients participated in the study. The majority of the selected patients had impacted and supernumerary teeth located in the maxillary front region and received preoperative CBCT. All patients were referred to the department with a previous intraoral X-ray and/or panoramic X-ray. The study included 38 patients with previous intraoral X-ray and 23 with panoramic X-ray. Eleven of the intraoral X-rays were conventional and 27 were digital. Among the previous panoramic X-rays, 4 were conventional and 19 digital.
The age distribution of patients ranged from 9 to 57 years, with an average age of 15 years. All patients were healthy, and none had any craniofacial malformations. None had any acute infections or odontogenic abscesses. An asymptomatic dens retentus was the main indication for surgery. Patient and relatives received full information about the study and its purpose. Following the patient's or guardian's (depending on age) consensus, they received a scan using the i-CAT radiological device. All patients were scanned in 2D and 3D plans.
The i-CAT cone-beam CT system device is supplied with an X-ray source tube with 120 kV and 3-7 mA. The flat panel image detector with 14-bit gray scale is 23.8 cm wide and 19.2 cm high, allowing an extended field of view (FOV) of 23.2 cm diameter × 17 cm maximal height. The i-CAT chair-side apparatus requires between 9 and 27 s for a 360° rotation during the scanning procedure. Voxels are available in 0.4, 0.3, 0.25, and 0.2 mm sizes.
The smallest digital unit (voxel) involves a 3D cube with an edge length of 0.2-0.4 mm. Due to this, the area of interest can be reconstructed in 2D serial tissue planes or in a 3D point of view. The voxel size determines the image resolution, which depends on the volume tomography system, and varies on an average between 0.125 and 0. 42 (xy).
The regeneration of the initial data (50-80 MB) requires less than 2 min following a 27 s scan for primary reconstruction. According to the manufacturer's information and the study by Roberts et al., this generated an average radiation dose for the patients of about 68 μSv for 20 s scan.
The defaults of the i-CAT tube kilovoltage control system were standardized for the X-ray source tube with 120 kV and 18.54 mA. During the scanning procedure, the voxel size was adjusted by 0.3 mm. The extended FOV was diminished according to the absolute diagnostic necessity.
Every single conventional and CBCT image was analyzed and evaluated pre- and intraoperatively by three independent, both X-ray diagnostically and surgically experienced colleagues. The objects of interest were researched with the magnification method. The superimposition of the critical structures was significant for the localization. The preoperative expected anatomical localization was recorded. The "gold standard" was the intraoperative surgical findings.
Postoperatively, the images were reanalyzed in order to obtain the specificity and precision of the radiography. The evaluation of the preoperative imaging diagnostic and the intraoperative findings was recorded on a compiled scoring sheet, bounded with the patient identification number. Statistical computation and evaluation of the radiological diagnostic image accuracy and certainty, compared to the intraoperative findings, was performed by standard Microsoft Excel software.
| Results|| |
Analysis between the two diagnostic modalities used on the 61 patients showed with statistical significance that the CBCT had a high precision and a lack of unexpected intraoperative findings and complications. In only two cases, unexpected intraoperative findings related to a supernumerary tooth and an impacted tooth were observed. Here, the findings diverged from the preoperative CBCT imaging assessment. In one case, the movement from a patient with attention deficit hyperactivity disorder (ADHD) caused artifacts. Nevertheless, this had no significant effect on the correct localization of the subject of interest. Apart from the patient with ADHD, no problems regarding the scanning process occurred.
The evaluation of the conventional imaging modalities and their preoperative diagnostic benefit in the maxillary front region showed no sufficient diagnostic performance. In 37 cases, the anatomical localization was preoperatively not reliable to define and the intraoperative findings were not identical to the preoperative expectations. Especially in the region with narrow anatomical relations like the maxillary front region, conventional X-ray diagnostic poorly displayed the required exact localization and morphologic relation between the critical structures [Figure 1], [Figure 2], [Figure 3] and [Figure 4] and [Table 1], [Table 2] and [Table 3].
|Table 1: Preoperative anatomical findings from the CBCT versus intraoperative findings|
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|Table 2: Preoperative anatomical findings from the convention X‑ray versus intraoperative findings|
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|Table 3: Dispersion and anatomical localization of the teeth in the study|
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|Figure 1: Preoperative conventional X‑ray of a supernumerary tooth in the maxilla|
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|Figure 2: Preoperative axial slice of the CBCT showing the exact localization of the same supernumerary tooth [Figure 1]|
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|Figure 3: Preoperative sagittal slice of the CBCT showing the localization of a supernumerary tooth in the mandible (the patient with ADHD)|
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|Figure 4: Preoperative coronal slice of the CBCT of the same patient (the patient with ADHD)|
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| Discussion|| |
An increasing number of different types of commercial CBCT devices are available for 3D imaging in the field of dental and maxillofacial radiology. ,,,, The CT and CBCT, also called DVT, can visualize impacted and supernumerary teeth in all standard planes, as well as multisectional 3D views. 
In order to achieve the best diagnostic efficacy, and consequently the best therapeutic results, 3D-CBCT was applied to show critical regions of interest or to clarify uncertain diagnostic questions and indistinct clinical findings, in which conventional 2D radiological diagnosis seemed not to be sufficient. ,
When removing impacted or supernumerary teeth, significant anatomical structures, such as nerves, vessels, adjacent teeth roots, and paranasal sinuses, have to be taken into consideration. It is therefore important to choose the appropriate surgical approach to avoid iatrogenic damages to the essential anatomical neighbouring structures. ,,,
Therefore, it is necessary to determine the effectiveness of CBCT devices in the assessment of impacted and supernumerary teeth, in comparison to the conventional radiological methods of intraoral X-rays and panoramic X-rays.
Especially, the risk/benefit analysis of pretreatment radiological evaluation should always be an important selection criterion. Compared to conventional spiral CT, the radiation dose is one of the most potential advantages of the CBCT technique which exposes the patient to certain lower radiation dose. ,,,,
The absorbed radiation dose can be clearly reduced by individual X-ray beam limitation and collimation. Only special minimized and determinate slices of the area of interest will be scanned. Lower radiation dose values can be additionally achieved by choosing an adequate voxel size. 
Pre-surgical evaluation with the CBCT revealed detailed imaging of significant anatomical structures and objects of interest, with highly accurate anatomical and morphological imaging when compared to the intraoperative findings.
In comparison, conventional intraoral X-ray and panoramic X-ray imaging modalities both magnified and distorted the images of critical structures, often resulting in inadequate diagnostic certainty. Especially in cases of multiple narrow adjacent anatomical structures, the traditional X-ray diagnostic appears unsatisfactorily. ,,
Nevertheless, conventional radiographic methods such as parallax, magnification, status-X radiography and panoramic radiography produce evaluable diagnostic results, but not with the absolute diagnostic information, performance and accuracy of the CBCT X-ray units. ,
The average radiation dose for conventional panoramic radiography varies between 5.5 and 22 μSv. Full mouth series of intraoral X-ray can produce 150 μSv. In comparison, the i-CAT apparatus generates an average radiation dose of about 68 μSv for a 20 s scan. Considering the effective dose radiation the CBCT imaging appears sufficient. ,
In contrast to the conventional radiography, the CBCT displays a complete and detailed 3D overview of the facial skeleton. This overview can greatly help surgeons to visualize and plan the surgical approach, which cannot be replicated with 2D imaging that the conventional radiology offers. ,,
Emission of radiation necessary by using the traditional intraoral X-ray technique appears not reasonable in all indications for gaining an adequate diagnostic, special in effectiveness consideration. ,,
In some cases, the use of conventional oral radiology is technically not feasible, which could be demonstrated on the patient with ADHD in this study. Easy handling of CBCT devices combined with a comfortable seating position for the patient, are both more acceptable for anxious and claustrophobic patients, compared to the conventional CT machine, and the devices are also less space consuming. ,,
Unlike CBCT, the conventional intraoral X-ray radiography can be difficult to perform in puerile patients, patients with iatrophobia, and those with a strong vomit reflex.
However, we found in our investigation some discrepancies also with regard to the expected anatomical localization of the object of interest. To summarize, we observed only in 2 cases of a total of 61 patients a different anatomical localization of the object of interest than expected. In both cases, the proximate cause was not a failure of the DVT technique, but the long interval (of approximately 1 year) between the investigation and surgery with an according to growth processes in a puerile patient.
The evaluation of the conventional imaging modalities and their diagnostic benefit in the maxillary front region showed no sufficient diagnostic performance. In 37 cases, the preoperative expected anatomical localization was not identical to the intraoperative findings. Especially in the narrow anatomical regions of the frontal maxilla, the conventional X-ray diagnostic radiography poorly displayed the required exact localization and morphologic relation between the critical organs.
The conventional radiography in this study was performed not in our department. Most of the digital X-ray images were sent to the department not in the original crude data. This could probably explain the low significance and diagnostic benefit of conventional imaging modalities in this study.
| Conclusion|| |
The CBCT provides true and precise anatomical information with high surgical predictability without distortion or artifacts, and appears superior to conventional radiography, especially in the anterior region of the maxilla. It enables more time-efficient surgery and reduces costs and surgical complications, especially in cases with mixed dentition.
To conclude, we can recommend CBCT diagnostic radiography as an accurate and precise preoperative diagnostic device.
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Thomas R Klimowicz
Department of Oral and Maxillofacial Surgery, Norwegian University of Science and Technology (NTNU), St. Olavs University Hospital, Trondheim
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3]