Application of cone beam computed tomography in oral and maxillofacial surgery

Authors

  • M Ahmad,

    1. Associate Professor and Director, Division of Oral and Maxillofacial Radiology, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA; Director, American Board of Oral and Maxillofacial Radiology.
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  • J Jenny,

    1. Partner, Twin Cities Oral and Maxillofacial Surgery PA, Minneapolis, Minnesota, USA; President, Advanced Head and Neck Imaging LLC, Minneapolis, Minnesota, USA.
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  • M Downie

    1. Partner, Twin Cities Oral and Maxillofacial Surgery PA, Minneapolis, USA; Vice President, Advanced Head and Neck Imaging LLC, Minneapolis, Minnesota, USA.
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Associate Professor Mansur Ahmad
Division of Oral and Maxillofacial Radiology
School of Dentistry
University of Minnesota
Minneapolis MN
USA
Email: ahmad005@umn.edu

Abstract

In the past decade, the utility of cone beam computed tomography (CBCT) images in oral and maxillofacial surgery has seen continuous increase. However, CBCT images are not always able to replace other imaging modalities. Based on the current published knowledge, this paper discusses advantages and limitations of CBCT images in the diagnosis and surgical planning of dentoalveolar procedures, odontogenic cysts, benign and malignant tumours, inflammatory changes, orthognathic surgery, maxillofacial trauma, sinus disorders, and systemic and osseous conditions that manifest in the maxillofacial area. This paper also suggests alternative imaging modalities when CBCT images are not adequate for surgical planning.

Abbreviations and acronyms:
BRONJ

bisphosphonate-related osteonecrosis of the jaws

CBCT

cone beam computed tomography

MDCT

multi-detector CTs

MRI

magnetic resonance imaging

OMS

oral and maxillofacial surgery

Introduction

The introduction of cone beam computed tomography (CBCT) has dramatically changed how an oral and maxillofacial surgeon conducts his or her practice. This technology has improved the efficiency of oral and maxillofacial surgeons in private offices, where access to cross-sectional imaging has now become quicker and easier than in a hospital-based practice. Prior to the introduction of CBCT, panoramic radiography was the most common imaging tool in private oral and maxillofacial surgery (OMS) offices. Only limited cases were evaluated with cross-sectional imaging. While oral and maxillofacial surgeons have successfully practised using panoramic radiography, the limitations of this imaging technique include variable magnification, distortion, superimposition of structures, and suboptimal imaging of structures not located in the focal trough. CBCT has overcome these limitations. Depending on the field of view, CBCT scans show a large area of the facial skeleton beyond the limits of a panoramic radiograph or a small area of focused clinical interest. As the CBCT slices can be reformatted and viewed in multiple possible orientations (multiplanar views), anatomic structures are not superimposed (Fig. 1).1 Within the last decade, the technology and design of CBCT scanning machines has made the placement of the machines both physically and financially possible. Greater access to interoffice scanners allows for a greater ease of patient acceptance and use for the treating surgeon.

Figure 1.

 (a) A panoramic radiograph revealed a suspicious radiolucent bony defect (arrow) in the region of the missing right maxillary canine. The first premolar root is displaced distally, and the lateral incisor is displaced mesially. (b) and (c) Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software and OnDemand 3D, a third-party software. The labial cortical plate is well defined and smoothly corticated in the edentulous region of the canine. The 3-D reconstruction shows this ‘bony defect’ being a prominent canine fossa.

Prior to the introduction of CBCT, multiplanar views were obtained primarily with multi-detector CTs (MDCT) and magnetic resonance imaging (MRI). Physical dimensions and cost of MDCT and MRI equipment are prohibitive for installation in a typical OMS office. Smaller physical dimension, lower cost and easier operation have led to rapid acceptance of CBCT units. There are many instances where an oral and maxillofacial surgeon may reliably use a CBCT scan where an MDCT may otherwise have been chosen to provide diagnostic information. However, the need of MDCT and MRI examinations in oral surgery is not obsolete, even though the quality of CBCT images may be better than MDCT scans.2 A study that evaluated the image quality of bone structures acquired by five different CBCT machines and one MDCT machine showed that the image quality of one CBCT machine was superior to that from the tested MDCT machine while images from other CBCT units were comparable to the test MDCT images.2 However, soft tissues are better displayed on MRI and soft-tissue window CTs. Currently, neither MDCT nor CBCT can replace the MRI where soft tissue diagnosis is the primary aim. These situations include analysis of soft tissue tumours, extension of intraosseous tumours into surrounding soft tissue and position of the disc in temporomandibular joints.

Major uses of CBCT examination in oral surgery practice include surgical extraction of third molars and impacted teeth, tracing of the inferior alveolar canals, implant planning, evaluation of cysts and tumours, fracture diagnosis, orthognathic surgical planning and follow-up, inflammatory conditions of the jaws and the sinuses, evaluation of the temporomandibular joints, and as an aid in diagnosing unexplained symptoms of pain. The following subsections provide utility of CBCT in different surgical situations.

Evaluation of impacted teeth

Dentoalveolar surgery for impacted teeth is a common procedure in an OMS office. Location of the inferior alveolar canal and its close contact to the third molar root structures are risk factors in dentoalveolar surgery. Therefore, image analysis principles were developed for panoramic or periapical radiographs to identify the canal location.3 However, the inferior alveolar canal may follow a tortuous path, and may not be reliably interpreted on a 2-D image. Multiplanar views from a CBCT are useful not only in tracing the canal, but also in assessing a bifurcated or trifurcated canal (Fig. 2).4 In addition, knowledge of the location of the canal allows the surgeon to develop a safer surgical plan related to the access to the tooth and root elevation. Ankylosis of impacted teeth adds another layer of complication in dentoalveolar surgery. Plain films are not reliable in revealing ankylosis of teeth.5 Compared to panoramic radiography, CBCT images allow better risk assessment of third molar removal.6 Panoramic or periapical radiographs are often inadequate to locate impacted maxillary canines and to identify their relationship to the roots of the lateral incisors. Surgical exposure of the canine crowns for orthodontic bracket placement may require multiple periapical radiographs obtained at differing horizontal or vertical angles. Application of image shift principles is complicated and time consuming. A surgeon can eliminate the complication of guess-work when CBCT scans are available (Fig. 3). The use of 3-D reconstructions also allow for a more complete visual picture for the treating orthodontist to provide proper vectors of tooth movement.

Figure 2.

 Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) and (b) Coronal sections of the left mandibular third molar region from the same patient. (a) The third molar root has branches of inferior alveolar canal on the buccal and lingual aspects. (b) Bifurcated inferior alveolar canal is visible distal to the left mandibular third molar region. (c) A thin slice in the left mandibular edentulous third molar area shows a roughly vertical accessory branch of the inferior alveolar canal.

Figure 3.

 (a) Multiple impacted teeth, 12-year-old male. The panoramic radiograph was acquired on an orthodontic patient to evaluate delayed eruption of the right maxillary canine, premolars and second molar. (b), (c) and (d) Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software and OnDemand 3D, a third-party software. (b) A maximum intensity projection view shows the relationships of the impacted teeth. (c) and (d) Manipulation of the 3-D images and cine mode (not shown) help in locating the impacted teeth and their relationship to each other.

Use of CBCT for benign lesions and cysts

In evaluating cysts or benign tumours, intraoral or panoramic radiographs show only the two dimensions of the lesion. Observation of the third dimension, i.e. bucco-lingual extension of a lesion, requires additional radiographs obtained at 90 degrees from the original view. In contrast, all three dimensions are recorded by the multiplanar (axial, coronal and sagittal planes) imaging of CBCT (Fig. 4). Such multiplanar views provide important information on the presence and extent of bone resorption, sclerosis of neighbouring bone, cortical expansion and internal or external calcifications, and proximity to other vital anatomy (Fig. 5).7 Multiplanar sections are preferred when examining cysts or tumours deep in the tissues.8,9 If the lesion borders can be clearly seen, then multiple extraoral plain film radiographs, oriented at 90 degrees to each other, can provide adequate information of the size of a lesion. Information on the spatial relationship of the lesion with other anatomic landmarks on such images is limited, and often difficult to interpret. Because of superimposition of large tissue volume, extraoral plain film radiographs often cannot provide reliable information on the internal structure of a lesion.

Figure 4.

 Radicular cyst, 60-year-old male. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) Reconstructed panoramic view shows well-defined lucent lesion in the left maxillary canine premolar area. The wall of the sinus is displaced. (b) Axial section shows destruction of the palatal bone. (c) Coronal section shows disruption of the floor of the nasal cavity, hard palate, and the buccal cortical plate of the alveolar bone. (d) Sagittal section shows disruption of the floor of the nasal cavity and expansion of the palatal cortical plate.

Figure 5.

 Ameloblastoma, 39-year-old female. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) Reconstructed panoramic view shows multilocular lesion in the mandibular right molar area. The inferior border of the mandible is thin and slightly expanded. (b) Axial maximum intensity projection view shows buccal and lingual expansion. The lingual cortical plate is thin and partially resorbed. (c) Coronal section through the third molar area. Compared to the normal left side the right side shows expansion in the bucco-lingual aspect and lower border of the mandible.

Newer CBCT units allow slice thickness to be as low as 0.1 mm. These thin slices allow better visualization of the bony margins of a lesion. Oral and maxillofacial surgeons may depend on panoramic radiography if the margins of cystic or benign lesions are well defined.10 If the margins are ill-defined, CBCT is a better option for diagnosis.11 Apart from presurgical evaluation of aggressive benign cysts or tumours, CBCT is also helpful in post-surgical follow-up of the margins of lesions that may have a high recurrence rate (Fig. 6). A surgeon may find CBCT scans acquired in their own OMS office more convenient and diagnostically sufficient compared to MDCT scans (Fig. 7).

Figure 6.

 Recurrent ameloblastoma, 59-year-old female. (a) Periapical radiograph acquired in 1997. The well-defined corticated radiolucent lesion superimposed over the second molar root was missed by a general dentist. (b) Panoramic radiograph acquired in April 2010 shows multiple radiolucent lesions in the mandibular third molar area. The lesion superimposed over the second molar root appears to be larger than the lesion in 1997. The patient reports that the third molar was extracted about 30 years ago and a ‘cyst’ was removed. (c) and (d) Data acquired using an iCAT CBCT machine in April 2010. Images are reformatted in iCATVision software. The radiolucent defects are separated by normally appearing bone (arrow).

Figure 7.

 Recurrent keratocystic odontogenic tumour, 18-year-old female. (a), (b) and (c) were acquired by a MDCT machine in 2007. Images are reformatted using OnDemand 3D, a third-party software. The reformatted panoramic view shows keratocystic odontogenic tumours in the right maxillary sinus area and left mandibular second premolar first molar area. (b) and (c) The keratocystic odontogenic tumour occupies almost the whole right maxillary sinus. The third molar is displaced superiorly and anteriorly. The lateral wall of the maxillary sinus is displaced and partially resorbed. (d), (e) and (f) Follow-up examination was acquired in 2009 using an iCAT CBCT machine. Images are reformatted in iCATVision software. (d) On the reformatted panoramic view, the right maxillary sinus area is sclerosed. The keratocystic odontogenic tumour in the left mandible is now healed. (e) and (f) Sagittal and coronal views show recurrence of the maxillary keratocystic odontogenic tumour. The margins of the lesion are well-defined, smooth and corticated.

For surgical planning, a lesion may need to be measured from different angles. For osseous components, when compared to the gold standard dry skull, the measurements on CBCT images are acceptably accurate with less than 1% error.12,13 In comparison, panoramic radiographs are not reliable for size measurement due to variable magnification error.14

Use of CBCT for malignant lesions

The limitation of plain films in depicting the margins of a benign lesion is also encountered in diagnosing malignant lesions. A lesion that may have a ‘benign’ appearance on a panoramic radiograph could reveal ominous features in thin slices of CBCT scan (Fig. 8). Compared to smooth margins of cysts and benign tumours, the margins of malignant tumours are irregular. CT images can identify such irregular margins and provide information in the early stages of a malignant lesion (Fig. 9). The advantage of CBCT over MDCT lies in the lower radiation dose and low cost.15 Whenever a malignancy is suspected to involve osseous components, cross-sectional imaging with CT or CBCT must be obtained (Fig. 10). CBCT images are as reliable as MDCT images in predicting bone invasion by malignant lesions.16 CBCT images are not useful in analysing soft tissue tumours, rather MRI or soft tissue window MDCT is a better diagnostic tool. Multiple examinations using CBCT, MDCT, MRI or nuclear medicine may be needed for a complete diagnostic work-up of a patient with a malignant lesion.

Figure 8.

 Squamous cell carcinoma, 72-year-old male. (a), (b) and (c) were acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. A periapical radiograph (not shown) of the mandibular third molar area suggested a dentigerous cyst associated with the third molar. Thin slice (b) showed loss of lamina dura of the second molar. (c) Coronal views show resorption of the lingual cortical plate. A dentigerous cyst is likely to expand the cortex. (d) The panoramic radiograph was acquired immediately after extraction of the third molar and before the histopathologic examination. (e) Follow-up examinations after surgical resection and grafting are being done with panoramic radiographs.

Figure 9.

 Metastatic cancer, 81-year-old male. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) Reconstructed panoramic view shows irregular lesions in the mandibular right second molar area and the vertical ramus. The second molar was extracted a few months before this scan. (b) Coronal view of the left ramus shows multiple radiolucent areas and disruption of the buccal and lingual cortical plates.

Figure 10.

 Chondrosarcoma of the nasal septum, 59-year-old female. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. The scan was requested based on a finding on a panoramic radiograph. (a) Axial view shows a roughly oval soft tissue density mass present in the anterior part of the nasal septum. (b) The sagittal views show the soft tissue density mass is at the floor of the nasal cavity. The floor is disrupted. Presence of thin calcifications in the mass suggest high grade lesion. Low grade lesions are usually uniformly dense.

Use of CBCT for inflammatory changes in the bone

As mentioned in the previous paragraph, irregular margins are a common radiographic feature of malignancy. Interestingly, osteomyelitis has similar irregular margins. However, a malignant lesion is less likely to develop a new layer of periosteal bone, while chronic infection frequently results in such layering. Periosteal reaction and cortical destruction, as viewed on multiplanar images, can be useful in differentiating these radiographically similar lesions of widely different prognosis (Fig. 11).17,18 If the infection is acute, neither plain film radiography nor CBCT scan is useful, as early infection does not cause enough bony change to be radiographically detectable. If an aggressive infection persists for two weeks or more, the primary finding on a radiograph is a lytic lesion with irregular margins. If the infection is chronic or moderate to low grade, the bone appears of mixed density. The margin of a chronic infection is often sclerotic and can be adequately viewed on plain film radiographs. To identify periosteal bony reactions, oral and maxillofacial surgeons traditionally used occlusal radiographs. However, wrong exposure factors or angulation can limit the utility of an occlusal radiograph to demonstrate a thin periosteal bony layer. With CBCT images, where multiplanar slices are easy to adjust, thin layers of periosteal bones are better viewed compared to occlusal radiographs. In addition, small bony sequestra associated with osteomyelitis are better identified with cross-sectional imaging.

Figure 11.

 Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) and (b) Chronic osteomyelitis, 71-year-old female. (a) Mixed density appearance in the left mandibular posterior region. The inferior border of the mandible is partially disrupted. (b) On the coronal view at the level of the first molar area, the arrow points to periosteal new bone formation. (c) and (d) Bisphosphonate-related osteonecrosis of the jaw, 59-year-old female. (c) The scan was acquired to evaluate failing implants in the right mandible. Compared to the normal left side, the right molar area has increased sclerosis. (d) Follow-up examination three months post-implant removal, the lingual cortical plate is disintegrating. Periosteal new layer of bone is visible in the lingual aspect of the third molar area.

Features of osteomyelitis are also seen in bisphosphonate related osteonecrosis of the jaws (BRONJ). Although BRONJ is a debilitating condition, fortunately the incidence of this disease is low. In 2004 and 2005, a survey of Australian oral and maxillofacial surgeons identified 158 cases of BRONJ.19 Since that time, the prescriptions of bisphosphonate have increased. In evaluating BRONJ, CBCT images are better than panoramic radiography.20 Currently, all these imaging modalities have limited values in detecting early stages of the disease.21,22 BRONJ may also be associated with failing dental implants. In South Australia, seven BRONJ-related implant failures were reported in a population of 16 000 patients.23 In implant cases, MDCT is likely to produce image artefacts arising from metal implants. CBCT can be used to evaluate the status of alveolar bone adjacent to the implants and also as a follow-up examination (Fig. 11C and 11D).

Orthognathic surgical planning and follow-up studies

For orthognathic surgery, DICOM data from CBCT can be used to fabricate physical stereolithographic models or to generate virtual 3-D models.24–26 Such 3-D reconstructions are most useful for morphological analysis and spatial relationship of the neighbouring structures as well as for growth and developmental anomalies, gross tumour development or fracture displacement.8,27 These 3-D surface models generated from CBCT data may be slightly inferior to that from MDCT, but are usually of acceptable quality.28 The 3-D reconstructions are extremely useful in the diagnosing and treatment planning of facial asymmetry cases. Airway measurement techniques are improving with newer software options.29,30 These data are being used for surgical orthodontic cases as well as for sleep apnoea patients.31 Follow-up CBCT imaging is useful in evaluating the success of orthognathic surgery (Fig. 12), as well as to measure the displacement of the surgical segments in all three orientations.25

Figure 12.

 Follow-up of orthognathic surgery. (a)–(f) are from the same patient, 54-year-old female. Panoramic radiograph acquired in May 2005, three months after orthognathic surgery. Both the condylar heads are partially visible. (b)–(f) Data acquired in October 2009 using an iCAT CBCT machine. Images are reformatted in iCATVision software and InVivo, a third-party software. (b) Axial view shows absence of lateral and medial pterygoid plates on the left side (arrows). (c) 3-D reconstruction shows satisfactory anterior occlusion, although the patient reports that her lower jaw deviates to the right side during opening. (d) and (e) The left condylar head and neck is completely resorbed, possibly because of lack of adequate pterygoid muscle strength due to missing pterygoid plates. (f) The right side of the condyle (not completely shown) is present and has a flattened superior margin. (g)–(i) Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. Bilateral sagittal split osteotomy and grafting. (h) Incomplete integration of the graft materials on the buccal cortical plates. (i) Disrupted inferior alveolar canal margin (arrow).

Fracture of dentomaxillofacial structures

The diagnosis of a simple dental or jaw fracture can be achieved with periapical or panoramic radiographs. Initial assessment of a complex jaw fracture may also be performed with plain films. However, vertical root fracture or multiple jaw fractures with bone displacement may be better evaluated with CBCT images. Compared to periapical radiographs, CBCT images are significantly better for diagnosing root fractures.32,33 For complex jaw fractures, CBCT may be a valid alternative imaging tool to MDCT, considering radiation dose and image quality.34 Non-displaced fractures of the mandibular condyle can be very difficult to diagnose with conventional radiographs. Multiplanar views of CBCT scans allow much better assessment of interarticular fractures of the condylar head. Currently, most dental CBCT units require the patient to be in an upright sitting or standing position during image acquisition. Therefore, a CBCT unit in its current configuration may not be appropriate where trauma to the cervical vertebra is also suspected and the neck is stabilized. In addition, involvement of cranium and leakage of cerebro-spinal fluid cannot be studied with CBCT. The role of CBCT in fracture diagnosis, therefore, appears to be limited to fracture of teeth and jaw fractures from fall, sports-related injury (Fig. 13) or minor assault. MDCT with or without MRI is a better imaging choice in automobile or industrial accidents involving jaws and other parts of the body.

Figure 13.

 Multiple jaw fracture, 22-year-old female, professional basketball player. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. The patient fell on the basketball court and fractured the left condyle and the symphysis area. (a) Maximum intensity projection shows bone plates and the symphysis region and the left condylar and neck area. (b) A thin layer of periosteal new bone formation (arrow) on the lingual aspect of the left ramus is consistent with remodelling.

Use of CBCT for diseases of paranasal sinuses

In addition to dental offices, ENT practitioners are also using CBCT units as an efficient in-house examination tool. Likewise for oral and maxillofacial surgeons, identifying the condition of the maxillary sinuses is important for implant planning and to rule out sinus disease as a cause for orofacial pain (Fig. 14). Sinusitis, a common inflammatory disease involving the maxillofacial skeleton, is often of odontogenic origin.35,36 In some cases with sinusitis, endodontic therapy of the offending tooth may fail, requiring a surgical intervention.37 CBCT not only provides diagnostic information of the status of extension of periapical lesions into the maxillary sinuses,38 but also provides reliable information on the septa of the sinus and presence of exostoses, useful presurgical information when planning sinus floor augmentation in preparation for implant placement.39

Figure 14.

 Ewing’s sarcoma, 8-year-old male. (a) Panoramic radiograph was taken to evaluate right-sided jaw pain. The crown of maxillary right second molar is rotated posteriorly and superiorly. This rotation was significant compared to a previous panoramic radiograph (not shown) acquired about 2 weeks prior to this radiograph. (b)–(e). Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (b) Reformatted panoramic view shows soft tissue density mass occupying the posterior part of the maxillary sinus and displacement of the wall of the sinus. (c) Axial view showed bowing (arrow) of the posterior wall of the right maxillary sinus. (d) Thin slice through the molar area shows disruption of the pterygopalatine fossa and displacement of the posterior wall. The posterior part of the orbital floor is partially resorbed. (e) The right pterygoid canal is obliterated (compare with the unaffected left side, arrow).

Waters’ sinus view, a traditional sinus examination, is now considered inadequate in detecting maxillary sinus opacification and ‘very poor’ in detecting masses in the ethmoid, frontal and sphenoid sinuses.40,41 CBCT images are helpful in identifying mucous retention phenomena, antral polyps, sinonasal polyposis and malignant tumours of the sinuses. In addition, an oral and maxillofacial surgeon should consider a CBCT scan if there is a suspicion of oro-antral fistula formation or if an implant is displaced into the sinus (Fig. 15).

Figure 15.

 Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) and (b) are from the same patient. (a) Oro-antral fistula (arrow). (b) Displaced root fragment into the sinus. Note the opacity of both the maxillary sinuses. (c) Oro-antral fistula (arrow) and polypoid tissues in the left maxillary sinus, nasal cavity and ethmoid air cells.

A limitation of CBCT is its poor resolution of soft tissues.42 Sinus masses can be composed of different types of soft tissues with or without fluid accumulation. In addition, the fluid may be thin watery secretion blood or a mix with pus. On a CBCT scan, a mass in the sinus usually has a uniform density. Therefore, differentiation of the density into a fluid or soft tissue mass is often not reliable. CBCT data can be relied on for the size and margin of the sinus mass, status of the sinus wall, and blockage of the ostium. Some software allows measurement of the air space, which can be accurate.43,44 Fungal sinusitis often accumulates calcified materials. On a CBCT scan, these calcified materials can be easily differentiated from the soft tissue component of the sinusitis.

Craniofacial disorders

Frequently, patients with developmental disturbances require surgical treatment. CBCT images are invaluable in patient education, treatment planning and as a follow-up study to evaluate growth, development and function. For a cleft palate patient, use of a panoramic radiograph is limited to identifying an alveolar cleft only. Cross-sectional imaging, such as with CBCT, assists in the assessment of the width of the cleft, tooth proximity to the cleft, deviation of the nasal septum and its degree of fusion to the palate, as well as the location of supernumerary teeth and the visualization of the entire osseous defect. Thorough evaluation of the maxillofacial structures with cleft or other developmental defects and syndromes can be achieved with cross-sectional imaging and 3-D reconstruction (Fig. 16).

Figure 16.

 Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software and OnDemand 3D, a third-party software. (a)–(c) are from the same patient. Unilateral cleft palate and Class III jaw relationship. The coronal slice shows deviation of the nasal septum. (d)–(e) are from the same patient. Treacher-Collins syndrome. Note prominent antegonial notch, steep mandibular angle, partially missing zygomatic arch, and incompletely developed external ear.

Use of CBCT in detecting foreign bodies in the maxillofacial complex

One of the limitations of using MDCT scans in the maxillofacial area is artefacts arising from metal restorations. Extensive bridgework or metal restorations can make a MDCT scan virtually non-diagnostic. Such artefacts from metal objects are lower on CBCT images (Fig. 17A and 17B).45,46 Therefore, CBCT is a better imaging modality to assess metal objects in the face, such as fragments embedded from a gunshot,45,47 following automobile or industrial accidents and for localizing retained broken dental needles or surgical wires (Fig. 17C, 17D and 17E).

Figure 17.

 (a) and (b) are from the same patient. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software and OnDemand 3D, a third-party software. Maxillectomy of the right side and presence of rib graft. Note absence of metal artefacts arising from bone plates. (c)–(d) are from the same patient. Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. The patient complained of bilateral facial pain, localized to the temporomandibular joints. A CBCT scan shows presence of twisted metal wires in the soft tissues bilaterally. The temporomandibular joints were unremarkable. The patient does not recall any surgical procedure in this area.

Use of CBCT scans in soft tissue calcifications

Although CBCT images have low contrast (soft tissue) resolution, they can be better than MDCT in depicting soft tissue calcifications, such as carotid atherosclerosis.42 Other calcifications, such as tonsilloliths and sialoliths (Fig. 18A and 18B), are adequately viewed on CBCT images.48 Ossification of the stylohyoid ligament can impinge the cranial nerves (classic Eagle syndrome) or the carotid artery (carotid artery syndrome). Surgical correction of the ossified ligaments can provide relief of the symptoms.49 Although an ossified stylohyoid ligament can easily be diagnosed on a panoramic radiograph, the relationship of the ligament to other structures is better evaluated by 3-D reconstruction of CBCT (Fig. 18C).

Figure 18.

 Data acquired using an iCAT CBCT machine. Images are reformatted in iCATVision software. (a) and (b) are from the same patient. Sialolith (arrow) of the submandibular gland. (c) Ossified stylohyoid ligament bilaterally (arrow). Note pseudo-articulation on the right side.

Conclusions

In the last decade, CBCT has become an important diagnostic tool for oral and maxillofacial surgeons. The benefit of this imaging modality can be better utilized by realizing its capacities and limitations. As the technology now stands, with respect to evaluating maxillofacial disease, CBCT is mostly a tool for diagnosing diseases of the osseous structures. Currently, it is not useful for the study of lesions limited to soft tissues. Practitioners should exercise caution to avoid over-interpretation of the findings on a CBCT scan. A combination of clinical information, signs, symptoms, and radiographic findings should be considered to determine the need for surgery or follow-up examinations. On many occasions, follow-up examination can simply be a clinical examination or a single periapical radiograph. The practice of oral and maxillofacial surgeons has become more efficient and successful with CBCT, and will continue to benefit OMS offices if CBCT is judiciously used based on expected diagnostic gain, cost to the patient and the radiation dose.

Ancillary