Role of CBCT in OMFS

 

Introduction

The introduction of cone-beam computed tomography (CBCT) imagining technique in the detection and diagnosis of head and neck lesions had a revolutionary effect on surgical and dental practice. CBCT provides practitioners 3-dimensional and multi-planar views for a more precise diagnosis and treatment planning less expensively with much lower radiation exposure compared to conventional 3D radiographic imagining technique. The availability of 3-dimensional analysis of head and neck anatomy enables clinicians to plan aptly, treat patients with confidence, and evaluate postoperative outcomes. Nowadays, CBCT machines are routinely available in almost every dental practice that carries out surgical procedures.

 

An overview

Historically, the demand for a higher resolution 3D imaging technique of hard tissues had lead to the invention of CBCT. However, soft tissue resolution had to be sacrificed in the process as CBCT lacks the detailed depiction of soft tissue pathological conditions. CBCT served as a replacement method of cross-section image production to fan-beam computed tomography (CT), applying relatively a much lower radiation dose and using less expensive radiation detectors than conventional CT.

CBCT has initially been introduced for its essential role in the field of dental implantology, and later on, was implemented in other dental and medical areas. The projection of the CBCT images can be made through many available image viewing software, and while many protocols have been suggested to serve this purpose, a standard protocol aims to examine the anatomy of concern in all planes and reconstruction of the images into a 3D model.

 

1.Cysts and tumors

In the broad purview of cysts and tumors encompassed within the head and neck, there are several odontogenic and non-odontogenic lesions that can be examined adequately using CBCT.  Detection or suspicion of these lesions is usually first seen on a conventional radiograph. However, to further examine the nature, borders, size, shape, internal structures, and damage to surrounding structures of the abnormality, a CBCT image is ordinarily taken. Evaluation of these imperatives will aid the clinician to differentiate between benign and malignant lesions and help in determining the best approach to be taken onwards.

CBCT image showing a large lesion in anterior mandible with perforation of the buccal cortical plates

 

In dentistry, cystic lesions surrounding impacted or erupting teeth such as dentigerous cysts are routinely examined using CBCT. In fact, when suspicion of odontogenic keratocysts, dentigerous cysts, or periapical cysts is evident, detection and evaluation are best to be carried out using CBCT. Moreover, precise assessment of these bony lesions and determining their border and expansion is an essential part of formulating an accurate treatment plan. Furthermore, it is believed that CBCT is a superior diagnostic tool in the radiographic assessment of bony cancerous lesions. However, there is a quantitative lack of data in the literature to support this statement. In fact, there is no standardized protocol to support the use or repeated use of CT or CBCT in the detection and treatment of bony cancerous lesions.

The main issue with all the current available radiographic imaging techniques is the fact that accurate evaluation of the nature of cysts and tumors is not possible. Therefore, the clinical biopsy and postoperative histopathological results are the main confirmatory tests of the nature of the lesion. Notwithstanding the foregoing, but when comparing CBCT to other radiographic techniques as a preoperative diagnostic tool, we find that the clinical significance of the findings on CBCT is more accurate and reliable.

CBCT images showing case 2A suspicion of granuloma on CBCT and histopathology confirming the diagnosis. However, case (2B) was also thought to be a granuloma but histopathology confirmed a cystic lesion. (a) Sagittal view (b) coronal view (c) axial view (d) three-dimensional view

 

Furthermore, the density of the lesion (either radiolucent or radiopaque, or a combination of the two) can be analyzed and better understood using CBCT, which helps in the diagnosis of osseous lesions such as cemento ossifying fibroma. Moreover, evaluation of bone density is the main concern when planning for implants for grafting. However, not all abnormalities are considered pathological or require treatment, and CBCT permits accurate comparison of one side to the other. Thus, the clinician has to be familiar with the features of image view software in order to determine the nature and importance of the condition detected. The application of this imaging technique is highly recommended for diagnosis and treatment planning of cysts and tumors of the head and neck. In fact, the overall diagnostic reliability of CBCT in the diagnosis of bony malignancies was shown to be superior to other 3D imagining techniques.

 

2. Inflammations and infections

As a general rule, acute inflammatory lesions in the head and neck area are challenging to find on any type of radiograph. However, that is not the case with chronic inflammations, as CBCT grants examination of many bone reactions, especially ones that include periosteal layering and disruption of the bony cortices.

Diagnosis of osteosclecrosis using CBCT, showing thickening of cortical plate and focal region of medullary bone density on the left body of the mandible.

 

Delayed or non-healing bony lesions such as bisphosphonate-related osteonecrosis of the jaw bone is another example of a  pathological condition that can be evaluated efficiently in early stages even where necrosis is minimal using CBCT. Additionally, osteomyelitis, which is a rare but serious bone infection, can be seen and diagnosed accurately using 3D imaging.


CBCT showing region of extensive necrosis involving the upper border of the mandibular canal.

 

Additionally, maxillary sinusitis of odontogenic origin, which often poses a diagnostic challenge for the clinician, is now easily diagnosed using 3D radiographs and easily distinguished from non-odontogenic infections. Thickening of the maxillary sinus membrane can be due to periodontal bone loss, periapical infections, root canal treatment, the position of the maxillary teeth in relation to the sinus, and many other pathologies. CBCT not only helps in determining origin but also in grading and measuring the extension of the pathology in all dimensions. Furthermore, symptomatic pathologies of the maxillary sinus like retention cysts, polyps, and tumors, which are smaller than 3 millimeters, are unlikely to be diagnosed using conventional 2D radiographs.

 

CBCT images showing (a) antrolith within the maxillary sinus and (b) a mucous retention cyst within the maxillary sinus.

 

3. Head and neck trauma

Due to limitations of conventional 2-dimensional imaging in assessing orbital and maxillofacial fractures, CBCT became an essential investigation tool for precise examination of the location, size, degree of fractures, presence of fragments, and foreign bodies as a result of trauma. Fractures can be interpreted in a radiograph by the presence of radiolucent line, an alteration in the normal anatomic layout, an irregularity in the cortication, or an increase in the radiopacity of the bone, which could be a result of the overlapping of two fragments of bone. These interpretations can sometimes be seen on a panoramic radiograph of a mandibular fracture; however, coronoid and condylar fractures will often be superimposed by the zygomatic process, maxillary tuberosity, and the pterygoid process of the sphenoid bone.

 

CBCT images showing condylar fracture from different angles

 

Also, CBCT has the ability to present gunshots wounds, orbital fractures, condylar and coronoid fractures, and many other facial fractures with high accuracy, thus, making it the radiograph of choice for maxillofacial surgeons.

 

Evaluation of complex facial fractures due to road traffic accident using CBCT

 

4. Temporomandibular joint (TMJ) osseous pathology

Although magnetic resonance imaging (MRI) is known as the "gold standard" for TMJ imaging and diagnosis due to superiority in soft tissue examination, many cases can be diagnosed accurately using CBCT, especially those with osseous pathologies. CBCT aids in the analysis of TMJ function by capturing images of the condyle and surrounding structures in a 3-dimensional manner. It allows examination of the joint space and the true position of the condyle within the fossa, which aids in the diagnosis of a dislocated joint disk. Moreover, quantifying the roof of the glenoid fossa and estimation of the thickness of the soft tissues nearby the TMJ can be done using CBCT, which can replace the need for MRI. These advantages mentioned above have made CBCT the favorable imaging technique for TMJ cases associated with osseous pathologies such as ankylosis, fractures, and dislocations, developmental anomalies of the condyle, and rheumatoid arthritis.

 

 

CBCT images showing medial and lateral poles of the condyle from different angles.

 

Comparison between MRI and CBCT in the detection of condylar osteophyte. MRI (A, B and C) showing no sign on abnormality, while CBCT revealed osteophyte in the condylar head.

 

5. Developmental and congenital facial deformities

While facial deformities are generally linked with genetic disorders and syndromes that affect other parts of the body, they often require early diagnosis and intervention, especially when obstructing respiratory function. CBCT aids in the diagnosis of these syndromes, any associated skeletal discrepancies, and many correlated pathologies of the head and neck. Additionally, the features and anomalies of hemifacial microsomia, which commonly affect the mandible, ear, and spine, are best manifested using 3D radiography.

 

CBCT images of an 18 years old patient with hemifacial microsomia, showing (a) hypoplasia on the left side of the mandible and (b) calcified left stylohyoid ligament on the same side.

 

In addition, developmental defects and calcifications of the salivary gland and tonsils can also be identified in terms of location and distinguished from possibly conspicuous pathologies. Moreover, volumetric analysis of bony defects and prediction of the graft amounts needed, the stability of the post graft arch, and prolonged effect on growth can be seen using CBCT.

 

Panoramic and CBCT images showing developmental salivary gland depression of the left ramus

 

6. Impacted and supernumerary teeth

Cessation of an eruption of a tooth or presence of supernumerary teeth juxtaposition to the maxillary sinus or sensory nerves may result in several adverse effects on surrounding healthy structures; and oftentimes require CBCT to evaluate the lesion and the risks involved with the treatment plan. Additionally, the density of the bone around impacted teeth, and the buccolingual dimension of the tooth cannot be determined using conventional radiographs and often necessitates the use of 3-dimensional imaging, which can considerably alter the overall treatment plan. In addition, evaluation of the crown-root angulations of buccally and palatally impacted teeth prior to their extraction is essential to ensure safety and smoothness of flow during the procedure. The application of CBCT serves the purpose in this field, as shown in the pictures below.

 

3D teeth model using CBCT data and Mimics Research software representing palatal (A and B) and buccal (C) views of impacted teeth

 

Furthermore, assessment of nerve canals and their branches is a huge part of surgical pre-operative planning. Sundry of radiographic techniques are possible to determine the canal location and its relations to surrounding structures which include periapical radiography, panoramic radiography, CT, and CBCT imaging. However, the known advantages of CBCT in terms of better image production, reproducibility, higher accuracy, and resolution with lesser radiographic artifacts, making it the technique of choice for the detection of nerve canals. Also, since complications are no stranger when it comes to complicated extraction of impacted lower mandibular third molars, to which most common is inferior alveolar nerve (IAN) injury. A glimpse at the relationship between IAN and lower wisdom teeth can be felt on panoramic and periapical radiographs. However, it can never be absolute without the use of 3-dimensional imaging. The precise delineation of the inferior dental nerve can be done using CBCT in high-risk cases where communication is noted in the 2D radiograph. Based on its' results, the treatment plan can change from extraction to coronectomy or even no treatment.

Furthermore, simulation of the procedure to be carried out can be done by inserting the radiographic image of the CBCT into computer software. Moreover, complications such as displaced roots or fragments in the maxillary sinus or submandibular area are more meticulously depicted using CBCT. Damage to adjacent teeth and structures during the extraction of an impacted tooth can be significantly reduced or, in some rare cases, inevitably accepted. Hence, the original treatment plan is often altered after an accurate analysis of the CBCT and radiology reports.

 

Multiple CBCT slices showing root fragment in the nasolacrimal canal from axial (A), coronal (B) and sagittal (C) views

 

7. Assessment of the airway and supporting structures

Airway related disorders such as obstructive sleep-disordered breathing and upper airway resistance syndrome are often associated with obstruction or increased airway resistance and are diagnosed mainly with Polysomnograms and the aid of CBCT. The primary role of CBCT lies in the assessment of the size and shape of airway anatomy and surrounding structures. CBCT provides cross-sectional images of the airway and is often shown to be constricted in patients with an obstructive sleep disorder.

 

 

CBCT images showing constricted airway in patients with obstructive sleep apnea.

 

Furthermore, the restriction of normal nasal respiration and oxygen intake during facial growth can have an impact on the development of the craniofacial skeleton. Hence, it is crucial to continue monitoring the progression and growth of these patients post-surgical or non-surgical intervention. CBCT provides accurate measurements of the airway dimensions and capacity, and therefore, making it a suitable diagnostic method for monitoring growth. Additionally, enlargement of the surrounding structures such as the tongue, tonsils, or soft palate can significantly reduce the airway dimension, and hence, a CBCT image might be necessary to formulate an accurate treatment plan.

 

CBCT image showing restriction of airway space due to a hemangioma enlarging the soft palate and extending posteriorly to impinge on the airway space.

 

In addition, the presence of nasal polyps, which are benign hyperplastic growth of nasal mucosa and can lead to nasal obstruction, can be located and measured using CBCT. The use of CBCT by ENT surgeons is more common nowadays and has proven to be an advanced diagnostic tool in this field. 

 

8. Dental endodontic lesions

Utilizing CBCT in diagnosis and treatment of endodontic lesions is more commonly adopted by endodontists in this day and age. The precision in locating and differentiating periapical lesions from maxillary sinuses and nerve foramen and other surrounding structures is far superior to conventional 2-dimensional imaging. Furthermore, in complex endodontic cases, this imagining technique yields an adequate amount of information about the number of canals and roots and their morphology. Additionally, detection and measurement of the depth, type, and extensions of root fractures, internal and external root resorptions, pulp stones, and root canal calcification can be done effectively without the burden of structural superimposition using CBCT.

 

CBCT images detecting different types of C-shaped canals; type C1 (a and b); type C2 (c and d); and type C3 s (e and f).

 

9. Dental periodontic lesions

The dimensions of the alveolar bone establish a vital prognostic element in discerning the success of periodontal surgeries and implants. Acknowledging the level of buccal and lingual bony defects in dentate and edentulous areas using CBCT imagining provides an advanced and better understanding of the case and aids in formulating precise treatment plans. Moreover, dynamic evaluation of furcation involvements, periodontal cysts and pathologies, intrabony defects, and dehiscence is another advantage of this 3-dimensional imagining.

 

(a and d) Periodontal surgery and measurement of bony defects around the mandibular canine; (b and c) 3-dimensional images of bony defects around the mandibular canine.

 

Progression and Post-operative evaluation

Monitoring the healing of a treated or removed lesion is an essential aspect of postoperative care. CBCT, with its low radiation intensity, is clearly suitable for postoperative follow-up. CBCT is favored for follow up of benign lesions surgeries; however, CT and MRI still have the edge when it comes to postoperative follow-up of malignancies. Furthermore, the presence of serious post-operative complications such as prolonged paresthesia warrants the use of CBCT. Additionally, disparate osseous lesions have a high recurrence rate, and routine postoperative re-imaging is essential for early detection and management. Notwithstanding the foregoing, but depending on the nature of the planned treatment, the additional benefit of 3D analysis may not be needed in all post-operative cases, and a 2D radiograph may be sufficient.

 

Recommendations

Numerous recommendations about the correct use of CBCT have been proposed by researchers to help clinicians during their daily practice. Generally, despite the impeccable role of CBCT in understanding the anatomic relationship between lesions and surrounding structures, experienced surgeons can decide on the treatment modality without the use of CBCT. Furthermore, the clinical significance and improvements in outcome after the additional use of CBCT remains unclear, and therefore, complete dependency on CBCT as a radiographic imaging tool cannot be recommended.

There is a controversy in regards to the use of CBCT for exploration outside of the region of interest, and despite the high frequency of incidental findings in CBCT images, yet most of these findings are not life-threatening and do not compel urgent treatment. Therefore, can CBCT be recommended as a replacement for conventional 2D radiographs for examination purposes?. The primary weakness of CBCT lies in the detection and characterization of soft tissue lesions, and current literature does not support its use in that field. Lastly, the use of CBCT in the pediatric age group should be carried on cautiously and can only be advocated when the adequate conventional radiographic examination has failed to answer the question for which imaging was initially requested.

 

Conclusion

In conclusion, cone beam computed tomography is a suitable examination tool for regular use in the dental practice where financial cost and radiation dose considerations are paramount. Moreover, the assets of CBCT should be recognized not only by dental professionals but also by medical clinicians. Coherently, the rapid advancement in radiographic imaging technology will undoubtedly increase the practitioner’s access to 3D x-rays.

Despite the availability of numerous research and data in the literature about the role of CBCT in the head and neck region, there is yet no current evidence-based guideline or protocol to support the necessity of its use in each speciality. The knowledge and experience of the clinician is ultimately the deciding factor in each case. Conceivably, a standardized guideline supporting the use of CBCT would constringe the possibility of unnecessary radiation, inaccurate diagnosis, and treatment plan.