Current Applications

Abstract

With the introduction of cone beam computed tomography (CBCT), the practice of dentistry has taken a new approach. Before the emergence of this technology, most of the dental professionals depended on the conventional two-dimensional (2-D) radiographic imaging for treatment planning and evaluation. Previously, the multi-detector computed tomography or medical CT scanners were utilized for assessment of pathology and trauma cases in dentistry. CBCT technology has found its way into the dental offices and offers many advantages and specific clinical applications for both specialist and general dentists. CBCT image quality is superior as compared to 2-D as structures can be viewed without superimposition and distortion, in three dimensions.

1 Utilization of Cone Beam Computed Tomography in Orthodontics and Oral Surgery

Since the discovery of X-rays, without a doubt, the conventional two-dimensional (2-D) radiographic imaging has remained an integral part of the diagnostic process in dentistry and also in its specialties like orthodontics, oral surgery, periodontics, and implantology. For the practice, depending on the need and the treatment stage of the patient, the appropriate radiographic imaging modality should be selected and used, if there is adequate reason to believe that this exposure will effectively aid the clinician in the initial diagnosis, better treatment planning, on-going evaluation, and also with the posttreatment assessment of the cases. Imaging serves as an important adjunctive tool and provides baseline information about the patient. Pretreatment understanding of the relationships of underlying osseous structures, soft tissues, and dentoalveolar components is essential in order to form a treatment plan of the various craniofacial abnormalities, malocclusion, and other dental anomalies. During the treatment phase, the follow-up imaging allows to evaluate the effectiveness of the treatment administered. After the completion of the treatment, with appropriate radiographic imaging, the clinician is able to assess the outcome.

With the introduction of cone beam computed tomography (CBCT), the clinicians were faced with new challenges in terms of usage, effectiveness, benefits, and financial issues. It was especially difficult as initially no evidence-based systemic guidelines or position papers were available.

The American Academy of Oral and Maxillofacial Radiology (AAOMR) [1] published a position paper in 2013. Both board-certified orthodontists and oral and maxillofacial radiologists contributed in development of this paper to establish orthodontic-specific clinical guidelines for practice. According to this published position paper, the utilization of CBCT in different phases of orthodontic treatment should be justified on an individual basis and should be based on clinical signs and presentation of the patient. The panel established that “there was no clear indication to support the routine use of ionizing radiation in standard orthodontic diagnosis and treatment planning, including the use of CBCT.” This position paper by AAOMR supported the position of the American Dental Association Council of Scientific Affairs [2] in the selection of CBCT imaging, which suggested that imaging should be based on clinical examination and must be decided on the individual patient needs.

Hodges et al. [3] evaluated the impact of CBCT on the orthodontic diagnosis and treatment planning. They reported that changes in the diagnosis and treatment plan varied widely with patient characteristics. The results supported obtaining a CBCT scan before orthodontic diagnosis and treatment planning when a patient had an unerupted tooth with delayed eruption or a questionable location, suspected severe root resorption, or a severe skeletal discrepancy. They also concluded that “CBCT scans should be ordered only when there was clear, specific, individual clinical justification.” No advantage was found in terms of changes in treatment plan for patients when the reason for obtaining a CBCT scan was to assess the temporomandibular joint abnormalities or airway analysis. However, the participating orthodontists in the study who used the CBCT imaging frequently in practice were more confident in the diagnostic process and in forming a treatment plan after viewing the CBCT scans during the study [3].

This new 3-D technology made it possible, in a dental office setting, to have superior quality structural images in three planes (axial, sagittal, and coronal) without superimposition and with a radiation dose much less then medical CT units at a lesser expenditure.

According to some practicing orthodontists, most of the orthodontic practices are no longer using full-mouth intraoral radiographic surveys. Even the conventional extraoral posterior-anterior cephalometric views are not made as CBCT provides all the needed information required for outcome assessments for orthodontic and oral surgery procedures. Thus, it has been suggested that conventional 2-D images may not be needed, if CBCT imaging is available and the radiation dose of CBCT is similar to conventional imaging, as CBCT provides more in-depth information.

For the needs of the oral surgery and the orthodontic procedures, typically CBCT machines with a larger sensor or image detector are used to capture the craniofacial region. A smaller sensor or a more collimated smaller region of interest is sometimes utilized for localized problems such as impacted teeth. Most common uses of CBCT would include diagnosis and treatment planning, skeletal evaluation, tooth localization for impacted teeth, assessment of root shape and condition in suspected external apical root resorption, evaluation of alveolar bone thicknesses, treatment planning for alveolar bone grafting in cleft lip and palate, pre-orthognathic surgery, and evaluation of airway patency and size.

2 Tooth Impactions

Most common impacted teeth are third molars and permanent maxillary canines. CBCT imaging is often done to localize the position, angulation, and effect of the impacted teeth on the surrounding structures, as the technology has been shown to improve diagnosis and contribute in treatment modifications in such cases in a significant number of subjects [4, 5].

CBCT is considered very helpful in planning surgical access and assessing the direction of extrusion of the impacted canines in the oral cavity and provides a 3-D insight for proximity of these impacted canines to adjacent teeth and structures, extent of resorption of adjacent teeth, size of the follicular space, and the presence of pathology [6, 7].

Visualization of 3-D root structure of a tooth with CBCT is substantially superior as compared to the conventional 2-D radiographic imaging (Fig. 2.1). It has been suggested that the small field of view may be used for CBCT imaging of impacted maxillary canines if the canine inclination in the arch on a conventional 2-D panoramic radiograph exceeds 30° relative to a perpendicular midline and also in cases where adjacent root resorption and/or dilaceration of the root is in question [8].

Fig. 2.1

CBCT-reconstructed panoramic image (a) and cross-sectional views (b and c). Impacted tooth is noted on the right mandibular premolar region (black arrow). Idiopathic osteosclerosis also noted periapical to tooth # 19 (arrowhead)

3 Osseous or Bony Evaluation

Condition of the buccal and lingual alveolar bone and thickness is determined by the dentoalveolar anatomy prior to start of the treatment and by the bone’s morphology and adaptability during tooth movement during the treatment and its morphology following the final positioning of teeth after completion of the process. Kapila et al. [9] described alveolar boundary conditions in orthodontics, which included the depth, height, and morphology of alveolar bone relative to tooth root dimensions, angulation, and spatial position. They stated that for orthodontic tooth movements, alveolar boundary conditions can be considered dynamic and determined by the patient’s pretreatment bone condition and gingival biotype as well as bone physiology (see Chap. 10 and 11).

Alveolar bone is not static in shape as remodeling of the alveolar bone occurs, without which the orthodontic tooth movement would not be possible. However, use of excessive orthodontic forces to a tooth can affect alveolar boundary conditions unfavorably and may result in dehiscences and fenestrations. The cross-sectional views from the CBCT are very useful in verifying the thickness of the buccal and lingual cortex (Fig. 2.2) not visualized on conventional 2-D radiographic images, both before and after the treatment.

Fig. 2.2

CBCT-reconstructed panoramic image (a) and axial (b) and cross-sectional view (c) images show buccally located impacted mandibular right canine (black arrow). Thinning of the buccal cortex is evident (black arrowhead)

CBCT can also be a useful tool for evaluation of the bone quantity, quality, the underlying trabecular bone pattern, and thus stability of the bone [10]. Temporary Anchorage Devices (TADs) have been used in orthodontic procedures to provide a stable anchor for the application of orthodontic forces. TADs can be placed nearly anywhere in the oral cavity, but it is important that there is no impingement on the complex surrounding anatomical structures, such as roots or vessels and nerves. CBCT may be used to determine the optimal site and treatment plan for the placement of TADs, as the proximity and relationship to the surrounding structures such as roots, nasal fossa, maxillary sinuses, and vasculature can be visualized beforehand to avoid complications.

4 Orthognathic Surgery

CBCT 3-D volumetric reconstructions provide detailed information for treatment planning of orthognathic surgery (Fig. 2.3). Volumetric analysis can help predict the procedure. CBCT data can be used to create stereolithic models of the area of interest as well (Fig. 2.4). One cannot emphasize enough the usefulness of this 3-D technology in orthognathic surgery to visualize the relationship between hard and soft tissues [11]. To a large extent, CBCT has replaced lateral cephalometric imaging for diagnosing skeletal and dental deformities like hemifacial macrosomia and Treacher Collins syndrome.

Fig. 2.3

(a) Large field-of-view CBCT coronal image (a) and a 3-D view (b). Changes after the orthognathic surgery are seen. Images show disruption of the bone due to surgery (black arrow) and opacification of the maxillary and ethmoid sinuses (black arrowhead). Surgical pins are also noted in the maxilla in the 3-D view

Fig. 2.4

Three different stereolithic models (a–c) are shown, which were fabricated to simulate the surgical treatment planning. Courtesy Dr. Kevin Smith and Dr. Steven Sullivan

4.1 Cleft Lip and Palate

This anomaly is commonly encountered and adversely effects the involved human beings. CBCT provides unique useful information for patients with cleft lip and palate. It is very useful in pretreatment and posttreatment planning phases, providing information about the cleft defect site, eruption status and position of the canines in the involved sites, and pre- and post-graft bone width and height. Timing of alveolar cleft repair is often determined based on conventional panoramic and occlusal imaging. In such cases, CBCT allows better evaluation of dental age, arch segment positioning, and cleft size compared with traditional radiography. Volumetric analysis with CBCT provides better prediction in terms of the cleft defect morphology (Fig. 2.5) as well as the volume of graft material needed for repair. After the surgery, the stability of the arch after grafting, the quality of the bone graft over time, and the effect on overall facial growth can be evaluated with CBCT [12]. Other uses include evaluation of impacted teeth for potential complications such as root resorption of adjacent roots. With CBCT the relationship between the impacted and supernumerary teeth and the surrounding structures such as the walls of the maxillary sinuses, cortical borders of the inferior alveolar canals, and mandibular cortices can be studied before the actual procedures to avoid potential postsurgical complications. Surgical prediction and treatment planning have become easier. However, it is important to understand the data manipulation, software tools along with normal anatomy, and anatomical variations for maximum treatment planning and surgical accuracy (see Chap. 13).

Fig. 2.5

CBCT-reconstructed panoramic image (a) and axial (b) and sagittal cross-sectional views (c) made along the axis of the impacted canine are shown. Cleft palate is visible on the left anterior maxilla on reconstructed panoramic image and axial image (red arrows). Buccal-lingual position of the impacted canine within the arch is visible on the images

4.2 Temporomandibular Joints (TMJ)

If included in the field of view, TMJ region can be visualized in detail, without superimposition on CBCT. Cortical outline and the position of the condyles, glenoid fossae, articular eminence, and joint spaces can be evaluated. Radiographic progressive changes include condylar flattening (Fig. 2.6), irregular and/or thickened cortical outlines, osteosclerosis, cortical erosions, osteophyte formation, subchondral cysts, and narrowing of the joint space [13]. Referring the patients to the appropriate specialists prior to commencing orthodontic treatment is recommended [7].

Fig. 2.6

CBCT sagittal cross sections show degenerative joint disease in a 52-year-old female. Severe flattening of the condylar head (red arrow) and possibly a small osteophyte formation are observed on the anterior aspect (red arrowhead)

It has been emphasized that although CBCT provides diagnostic information about the TMJ disorders, it does not reveal if the disease process is active or not. Kapila et al. [7] stated that “CBCT images allow the concurrent visualization of the TMJs and assessment of the maxillo-mandibular-spatial relationships and occlusion and provide the opportunity to visualize and quantify the local and regional effects associated with the TMJ abnormalities” [7].

4.3 Airway Analysis

Factors like mandibular growth, function of the soft tissues and the jaw musculature, dentoalveolar development, and airway morphology affect development of vertical malocclusions. It has been reported that in children with mouth breathing issues, vertical malocclusions may develop with a constricted pharyngeal airway considered a potential contributing factor [14]. Although constricted airways, especially in children with enlarged adenoids and tonsils, are often diagnosed clinically with conventional 2-D lateral cephalometric images [15], the volume or cross-sectional area without superimposition may be a better measure of airway narrowing, which requires CBCT, rather than conventional 2-D images [16].

Earlier it was suggested that a constricted pharyngeal airway may contribute to mouth breathing and to the development of a steep mandibular plane angle with anterior open bite tendency, [14] but later studies have generated conflicting results with one study showing no relationship between facial pattern and airway volume, while the other study demonstrated the existence of such a relationship [16, 17]. Kapila et al. [18] stated that the discrepancies in the findings of the two studies highlight the need to use a standardized protocol for measuring airway volumes. An example of visualization of narrow airway is shown from a CBCT scan in Fig. 2.7.

Fig. 2.7

Airway analysis shows narrow airway (region outlined in red on coronal and sagittal images). Axial image also shows the narrow airway. Outline of the airway is also observed in the 3-D model

5 Incidental Findings

In addition to the diagnostic information from the region of interest, CBCT scans can present with a variety of incidental findings. A thorough knowledge of anatomical structures and their variations is of utmost importance. It is the responsibility of the clinician to evaluate and interpret the complete CBCT data set to rule out any abnormalities and potentially pathology. Clinician must also recognize incidental findings encountered in these images. Incidental findings are abnormal findings, unrelated to the problem in question, encountered in images unintentionally as the image was not made for that purpose. Findings should be reported and discussed with the patient. Appropriate actions or recommendations should be made as needed.

The frequency of incidental findings on CBCT images has been reported in several research papers with a high range between 25% and 54% by Cha et al. [19] They evaluated the location, nature, and occurrence of incidental findings in maxillofacial structures on 500 CBCT scans done for various diagnostic reasons. They also assessed association between these findings and symptoms in orthodontic patients. They reported the overall rate of incidental findings as 24.6%, and the highest was in the airway area (18.2%), followed by TMJ findings (3.4%), endodontic-related findings (1.8%), and others (1.2%). Specifically in the orthodontics, the airway-related incidental findings were 21.4%, TMJ findings 5.6%, and endodontic lesions 2.3%. However, only 22% of the airway findings, such as mucosal thickness, polyps, and retention cysts, were correlated with clinical signs and symptoms. It was recommended that for clinical diagnosis, the CBCT data should be interpreted with a full history of clinical signs and symptoms and with detailed communications with specialists to comprehensively evaluate possible underlying diseases.

Another study [20] reported the incidental findings in CBCT scans done for orthodontics. They reported at least one such finding in 66% of the patients; most common were retained primary root tips, followed by periapical disease. According to the results of this study, the overall orthodontic treatment was not altered. However, a high proportion of these cases required further follow-up or intervention (72.5%). Orthodontic treatment was altered in two cases. The first case involved root resorption of a premolar due to an ectopic maxillary permanent canine, which changed the proposed extraction plan. Dilaceration of the poorly positioned central incisor was also detected. In the other case, resorption and pulpal involvement were observed that changed the prognosis of the tooth and thus the extraction pattern.

Avserver et al. [21] evaluated 691 CBCT scans for incidental findings outside the primary region of interest. They reported 1109 incidental findings in the paranasal sinuses in 79.3% of the scans. The majority of the findings were in the maxillary sinus (mucosal thickening, polypoid mucosal thickening, air-fluid level, partial to complete opacification, hypoplasia mucus retention pseudocyst, aplasia, and tooth in the sinus), followed by the nasal cavity (deviated nasal septum, concha bullosa, and onodi cells). Most of the incidental findings required no treatment, but the authors recommended that the clinicians should be aware of the incidental findings and possible anatomic variations. Corrective action should be taken if needed to avoid future complications.

Edwards et al. [22] evaluated the rater agreement between the orthodontic clinicians in the assessments of reported incidental findings with regard to both the need for additional follow-up and the impact on future orthodontic treatment in large-field maxillofacial CBCT scans. Raters demonstrated higher levels of agreement for dentoalveolar findings as compared with all other extragnathic regions when assessing clinical significance of the findings. Fair to excellent rater agreements were discovered for the need for further follow-up and their potential impact on future orthodontic treatment.

Allareddy et al. [23] assessed the number of incidental findings on CBCT scans inside and outside the primary region of interest. The review of 1000 scans showed that 943 (94.3%) scans had findings within and outside the primary regions of interest. They reported 77 different conditions that were observed in these scans, both in the primary region of interest and outside the area. Larger study samples of this paper have provided a better clarification of the importance of analyzing the CBCT data completely to rule out any significant disease.

Edwards et al. [24] reported a higher frequency of incidental findings in large field of view maxillofacial CBCT scans of an orthodontic sample. The majority of the finding may be outside the regions of interest of many dental clinicians. Specifically, incidental findings in the airway and paranasal air sinuses were the most frequent. Other findings were found in the dentoalveolar region and the surrounding hard and soft tissues. This study underscores the importance for comprehensive review of the entire CBCT volume and the requisite to properly document all findings, regardless of the region of interest. The authors emphasized the importance of comprehensive review of the entire CBCT volume and documentation of the findings, regardless of the area of interest.

In orthodontics and oral surgery practices, often a larger field of view is used, and thus the probability of the incidental findings is somewhat more. Price et al. [25] also evaluated the type and prevalence of incidental findings from CBCT of the maxillofacial region. For reporting, the findings were divided into the following groups: (1) needed intervention/referral, (2) monitoring only, and (3) no further evaluation. Assessment of 300 CBCT revealed findings that were categorized into airway, soft tissue calcification, bone, temporomandibular joint (TMJ), endodontic, dental developmental, and pathological findings. A total of 272 scans revealed 881 incidental findings, and the most prevalent were airway findings (35%) followed by soft tissue calcification (20%), bone related (17.5%), TMJ (15.4%), endodontic (11.3%), dental developmental (0.7%), and pathological findings (0.1%). Intervention/referral was needed for 16.1% cases, 15.6% required monitoring. and the remaining (68.3%) required neither. This study also underscored the need to thoroughly examine all CBCT volume for significant findings within and beyond the area of interest.

Mutalik and Tadinada [26] reported a high prevalence (58%) of pineal gland calcifications in patients who were referred for CBCT for implant therapy. The pineal gland is located between the two cerebral hemispheres and produces a hormone called melatonin that affects sleep patterns. With age, the pineal gland calcifications increase. However, calcifications in the pineal gland have been reported in younger population as well. Most studies have considered these calcifications as physiologic, but a thorough medical history and clinical exam are recommended to rule out neurodegenerative disorders.

Incidental findings are listed according to the region where they are more commonly detected (Table 2.1). Paranasal sinuses and nasal fossae: Very common incidental findings in the paranasal sinuses are the mucosal thickening (Fig. 2.8) and mucus retention pseudocyst (Fig. 2.9). These changes can occur due to chronic inflammation. These findings may be suggestive of chronic sinusitis. When only sinuses are involved, the term sinusitis may be used. The term rhinosinusitis is used when the changes also extend to the nasal cavity. Inflammation can be viral, bacterial, or fungal. Clinical symptoms associated with chronic sinusitis are nasal congestion, discharge, and pain and discomfort. The diagnosis of chronic sinusitis is based on endoscopy or if the radiographic findings have been present for longer than 12 weeks.

Table 2.1 Region of occurrence and common incidental findings

Fig. 2.8

Coronal CBCT views. (a) shows mild unilateral mucosal thickening on the left floor of the left maxillary sinus (red arrow) and large frontal sinuses (red arrowheads). Some deviation of the nasal septum is also noted. (b) shows opacification/air-fluid level in the right maxillary sinus (yellow arrow)

Fig. 2.9

CBCT images show a relatively large homogeneous rounded opacity, possibly a mucus retention pseudocyst, in the left maxillary sinus (yellow arrows). Concha bullosa (pneumatization of the middle concha) is noted on the right side (red arrow)

Mucosal thickening can lead to obstruction of the passages between the paranasal sinuses and nasal cavity, and this causes a blockade. If other findings such as moderate to severe opacification within the paranasal sinuses and air-fluid levels are noted, acute sinusitis may be suspected. Mucosal thickening can be noted in any of the sinuses. Attention should be paid to the frontal sinus due to its proximity to the brain. While interpreting the images, one should look for any signs of bone changes such as sclerosis or erosion. Rosenfeld et al. [27] have recommended that acute bacterial rhinosinusitis must be distinguished from acute rhinosinusitis caused by viral upper respiratory infections and noninfectious conditions. Clinician should confirm a clinical diagnosis of acute bacterial rhinosinusitis with objective documentation of sinonasal inflammation, which may be accomplished using anterior rhinoscopy, nasal endoscopy, or computed tomography. Although rare, complications may arise like osteomyelitis, orbital and periorbital cellulitis, and intracranial abscesses. Other abnormal radiographic findings associated with the sinus disease include air-fluid level and nonhomogeneous opacification (Fig. 2.10). Less common incidental finding associated with the maxillary sinus is hypoplasia of the maxillary sinus (Fig. 2.11).

Fig. 2.10

CBCT axial (a), coronal (b), and sagittal (c) images show inflammatory changes in the right maxillary sinus (red arrow). Note the bubbly-appearing (dark) fluid in the right maxillary sinus. No inflammatory changes are visible in the left maxillary sinus. Cortical outline of the maxillary sinuses appear to be within normal limits. Normal nasal septum is also noted

Fig. 2.11

A comparison of the right and left maxillary sinuses shows unilateral hypoplasia of left maxillary sinus (red arrows)

Other incidental findings include concha bullosa (Fig. 2.9), asymmetry of the nasal structures (Fig. 2.12), opacity in the ethmoid sinus such as osteoma and mucosal thickening (Fig. 2.13), and mucosal thickening in the sphenoid sinus (Fig. 2.14). While using larger fields of view in CBCT images, the cervical spine is often captured. Degenerative changes in the cervical spine can be noted as osteosclerosis, pseudocysts, and flattening and ligament calcifications (Fig. 2.15).

Fig. 2.12

Coronal view (a) shows mild mucosal thickening on the floor of the left maxillary sinus (yellow arrow), hyperplastic left inferior nasal turbinate (red arrow). Left inferior nasal meatus appears minimized. Axial (b) view shows deviation of the nasal septum to the left side (green arrow)

Fig. 2.13

CBCT coronal (a), axial (b), and sagittal (c) images show a well-defined small opacity, possibly an osteoma (red arrows) and mucosal thickening (yellow arrows) within the ethmoid sinuses

Fig. 2.14

Sagittal view shows mucosal thickening in the ethmoid (yellow arrows) and sphenoid sinuses (red arrow)

Fig. 2.15

CBCT views show normal unobstructed airway on sagittal view (a) and axial view (b). Enlarged adenoids causing narrowing of the airway are shown by the yellow arrow on sagittal view (c). Cortical changes (red arrow) are also noted in the cervical vertebrae (C1 and C2) with possibly a calcification of a ligament (green arrow)

Maxillary and mandibular arches can also have pathologic conditions not related to the primary region of interest. A case of incisive canal cyst vs. large incisive or nasopalatine foramen is shown in Fig. 2.16. The presence of incisive canal cyst is presumed if the width of the foramen is greater than 1 cm or enlargement is noted on successive radiographic images. Oral-antral communication or fistulae can also be found (Fig. 2.17). Incidental calcifications in the maxillary sinus have also been reported (Fig. 2.18). Intrasinus calcifications can be idiopathic in nature or due to chronic inflammatory or fungal diseases.  Calcifications may appear as dense and well-defined masses, with irregular, nodular or linear shapes. Differential diagnosis may include dystrophic calcifications, anthrolith, osteoma, polyp or foreign material. Stafne’s bone defect or lingual salivary gland depression may also be visualized. This is extraosseous and is located often below the inferior alveolar canal and anterior to the angle of the mandible (Fig. 2.19).

Fig. 2.16

Coronal (a), axial (b), and sagittal (c) images show midline incisive canal cyst vs. enlarged incisive foramen in a 62-year-old male. CBCT scan was taken for implant treatment planning. Diameter of the well-defined corticated entity was more than 5 mm. Lingual cortex was partially missing (red arrow). Recommendation was a clinical examination to determine the need for biopsy and to rule out pathology

Fig. 2.17

Coronal (a) and sagittal (b) images show an oroantral communication (red arrows) with mucosal thickening on the floor of the right maxillary sinus. Coronal image (c) also shows displaced root into the maxillary sinus

Fig. 2.18

Linear calcifications / foreign material is shown by yellow arrows in the maxillary sinus on coronal (a) and sagittal (b) CBCT images. Irregularly shaped high-density structure appears to be embedded in the thickened mucosal covering on the floor of the left maxillary sinus. Discontinuity of the bone is also noted in the left lateral aspect of the maxilla maybe due to previous surgical procedure

Fig. 2.19

Stafne bone defect is shown by the yellow arrows on reconstructed panoramic (a), axial (b), and coronal (c) images, which is well-defined, unilateral rounded area extending from the medial surface of the mandible or on the lingual aspect of the mandible. Red arrow on image b shows loss of mandibular buccal cortex due to an osseous inflammatory lesion

Airway: Narrowing and asymmetry of the airway or the pharyngeal space can be noted on the CBCT images. Hypertrophy of the adenoids can lead to narrowing (Fig. 2.20). Causes may include sleep apnea, asymmetry of structures, and tumors. One must keep in mind, like other scenarios, imaging findings should be correlated with the clinical evaluation for a more definitive diagnosis.

Fig. 2.20

Sagittal CBCT view shows the narrowing of airway due to enlarged adenoids (yellow arrow)

Carotid artery calcifications: Plaque formation can occur within the artery due to disease. These calcifications with the vessel lumen can diminish in the size, causing reduction of the blood flow. Loose plaque deposits can cause conditions such as pulmonary embolism. The end result can be life-threatening and debilitating conditions, such as myocardial infarction or stroke. This can occur extracranially and intracranially.

Calcifications of the carotid artery can present as single or multiple, high-density structures, with generally defined outline. Extracranially, the calcifications can occur at the bifurcation point of the common carotid artery (C3–C4 vertebrae level). The appearance may be ringlike on axial CBCT images and may appear linear on sagittal and coronal images. In the axial CBCT images, the calcifications are located medial and anterior to the sternocleidomastoid muscle. Within the cranium, these calcifications may be located on either sides of the sella turcica or the sphenoid sinus area. Other structures that may be confused with calcified carotid atheromas may include calcified triticeous cartilage, superior cornu of calcified thyroid cartilage, and greater cornua of the hyoid bone due to the location of these structures. Further medical evaluation is recommended as this may be an indicator of arterial stenosis and stroke (Fig. 2.21).

Fig. 2.21

Carotid artery calcifications are noted bilaterally (yellow arrows) as circular high densities on the axial image (a). Sagittal view (b) shows somewhat linear appearance of the calcifications. Coronal image (c) also shows irregular calcification at the level of C3–C4 (yellow arrow) on the left side of the partially visible cervical spine. Courtesy: Dr. Hui Liang

Tonsilloliths: Dystrophic calcifications, possibly due to previous inflammation and infection, are present in the crevices of the palatine and pharyngeal tonsils and are often seen radiographically. On CBCT images, these calcifications may appear as single or multiple small high-density somewhat rounded structures (Fig. 2.22).

Fig. 2.22

CBCT images show smaller multiple tonsilloliths (yellow arrows)

Sialoliths: Calcification or mineralization can occur in the salivary glands. On CBCT images, single or multiple, unilateral or bilateral high-density calcifications can be noted within the salivary glands (Fig. 2.23). Further evaluation is recommended.

Fig. 2.23

CBCT coronal (a), axial (b), and sagittal (c) images show sialoliths (yellow arrows). Courtesy: Dr. Hui Liang

Pineal gland calcifications: The pineal gland is located in the center intracranially between the two hemispheres of the brain. It is also known as pineal body or pineal organ. This small gland produces melatonin hormone that regulates sleep patterns and body metabolism. In large field of view CBCT scans, calcifications may be noted in the pineal gland region. These calcifications may present as single opacification or a group of small higher density rounded to irregular structures (Fig. 2.24). The size is variable. However, if the calcifications appear larger than 1 cm in size, further evaluation for pathology is recommended. Presence of sleep disorders has been also linked to presence of calcifications, especially in very young children.

Fig. 2.24

Pineal gland calcifications are noted on sagittal (a), coronal (b), and axial (c) views by the red arrows. Narrow airway is also noted on the sagittal view (a)

Extradermal and intradermal opacifications and calcifications: Facial jewelry, soft tissue esthetic implants, cosmetic surgery, and foreign bodies may be seen on CBCT images. Obtaining a clinical history would certainly guide the clinician in better radiographic interpretation. Calcifications within the skin may be seen on CBCT images due to various reasons such as idiopathic or dystrophic conditions, trauma, previous surgical procedure, systemic diseases, or metastatic condition. Elevation of serum calcium or phosphate levels should be considered. On CBCT images, high-density single or multiple calcifications of various shapes may be observed. Examples of smaller dispersed extradermal calcification are seen in Fig. 2.25.

Fig. 2.25

Extradermal calcifications are shown on the CBCT images (yellow arrows). Axial, coronal and sagittal images show multiple smaller rounded calcifications on the buccal aspect of the mandible within the soft tissue

Intradermal shunts and catheters: For management of various systemic diseases, shunt systems and catheters are used. Shunts provide alternative pathways through which cerebral-spinal fluids bypass obstructions and may run from the subarachnoid spaces or the ventricles within the brain. Shunts and catheters divert CSF to another body region where it will be absorbed to restore the physiological balance between CSF production, flow, and absorption when one or more of these functions have been impaired. These are used to relieve the pressure on brain due to fluid accumulation. These tubes appear hyperdense on CBCT images (Fig. 2.26).

Fig. 2.26

Catheter is shown by the red arrows on sagittal (a) and axial (b) views (sagittal view shows the length and axial view shows the diameter of the catheter tunneled under the skin within neck tissues). Sagittal image (c) shows intracranial ventricular catheter (red arrow) and calcification of the falx cerebri (green arrows). Sagittal image (c), axial image (d) and coronal image (e) show calcification of the falex cerebri (green arrows) and intracranial catheter (red arrow). Courtesy: Dr, Kevin Smith and Dr. Steven Sullivan

Soft tissue calcification of external auditory canal (EAC): The EAC is an important part of the temporal bone and is involved in conduction of the sound waves. It is approximately a 1-in.-long, slightly (S-shaped) curved dermal-lined passageway from the outside of the head or auricle toward the tympanic membrane or the eardrum, which separates it from the middle ear; the outer one-third is cartilaginous and inner two-third osseous. Soft tissue abnormalities or growths that may be incidentally seen on CBCT images, taken for dental needs, in the EAC, include cerumen or earwax, atresia (narrowing), posttraumatic or infection-caused keloid, external otitis (infection), hemangioma, lymphangioma, papilloma, keratosis obturans, acquired cholesteatoma, adenoma, fibroma, mixed tumor, and carcinomas. The most common lesion is congenital atresia. Wax accumulation is considered a physiological process unless clinical symptoms are reported. Cholesteatomas are not common in EAC but arise as a result of ingrowth of the stratified squamous epithelium of the EAC into the middle ear. Cholesteatoma can involve the tympanic membrane, the middle ear, and mastoid process. On the CBCT, the soft tissue lesion within EAC will show as hypodense asymmetric growth of variable size. Differential diagnosis must be made to avoid complications, and thus a consultation with otolaryngologist is recommended (Fig. 2.27). As emphasized earlier, a thorough medical history will aid in radiographic interpretation. If unsure, communication with the medical team is essential.

Fig. 2.27

Calcification are noted on CBCT images in ear canal with an opaque foreign object

 Elongated styloid process: The styloid process projects down and forward from the inferior aspect of the temporal bone, below the ear. Elongated styloid process is a common radiographic finding. The normal length of styloid process ranges from 20 to 30 mm. Elongation may be unilateral or bilateral. Example of an elongated styloid process is shown in Fig. 2.28. Foreign material: Nowadays, several injectable midface augumentation materials are available in the market. Facial filler may be visualized on radiographic images incidentally and should not be mistaken as a disease process. These materials appear as hyper-attentuated numerous rounded foci or as linear opaque structures dispersed within subcutaneous facial tissues (Fig. 2.29).

Fig. 2.28

3-D model of elongate styloid process is visible (yellow arrow)

Fig. 2.29

Cheek filler material is noted buccal to the zygomatic arches on axial and coronal images bilaterally (yellow arrows). Maxillary sinuses also show moderate to advanced mucosal thickening and asymmetry of the nasal structures.Courtesy: Dr. Kevin Smith and Dr. Steven Sullivan

It is essential for the clinician, obtaining a CBCT scan, to have proper training for interpretation of normal anatomy, variation of anatomy, and other abnormalities in these images. Most incidental findings are encountered in larger field of view scans. Entire data volume should be comprehensively evaluated. It is vital to understand the importance of identification of the incidental findings, frequency of occurrence, and the medicolegal implications. It is also worth stating that the clinician or diagnostician who opts to interpret those radiographic images carries the medicolegal and ethical responsibility for identification of all variations and abnormalities in the entire data set of images. The need for further follow-up or assessment should be recognized when incidental findings are encountered that appear to be outside the area of expertise of the practicing dentist or specialist (Kapila SD book [28], Turpin [29]). Some cases may require referral for further clinical assessment and follow-up imaging to confirm the diagnosis or to rule out pathology. Although the type and frequency of the follow-up imaging vary, many clinicians advise a 6- to 12-month period. It is not justified to expose the patient for the purpose of identifying incidental findings. It should be noted that while dental clinicians are not expected to treat conditions outside of their professional expertise, it is their responsibility to identify abnormalities and deviations in the complete CBCT data set. If there are concerns, then the patient should be referred to the relevant specialist [30].