Cone beam computed tomography (CBCT) in paediatric dentistry

Dose considerations in children

The relative risk of radiation is higher for children since the cells are more susceptible to the stochastic effects of radiation. In addition, the child is more likely to live long enough to see the detrimental effect develop. For children aged under 10 years there is a three times greater relative radiation risk, and for adolescents a two times greater risk than that for an adult aged 30.⁸ It has also been found that, due to childhood anatomy, the radiation dose to the thyroid can be four times greater in a 10-year-old child than in an adult.⁸

Once the CBCT examination has been justified, the examination should then be fully optimized. This can be achieved by simply reducing the FoV or volume size as shown in Table 1. However, other ways of optimizing effective dose include adjusting the exposure factors and the arc of rotation. Regarding the exposure factors, the main way in which the dose can be reduced without losing diagnostic information is through reducing the mA (current).^9,10 The arc of rotation can be adjusted on some units. For instance, reducing the arc of rotation from 360 degrees to 180 degrees reduces the dose by 50%.¹¹

The European Commission has provided guidance on CBCT for dental and maxillofacial use, which include 20 basic principles based on expert consensus. These include the advice that all CBCT imaging must be preceded by a thorough history and clinical examination, must be justified, and should have the potential to provide new information to aid in patient management.¹²

Uses of CBCT in children

A multi-centre audit in Leeds, Manchester and Sheffield found that the most common reasons for CBCT to be taken in children was for the localization of teeth (106/313) and the presence of root resorption (60/313).¹³ The most common region scanned was the maxillary canine and incisal region. A service evaluation, again in the UK, examining CBCT use in Liverpool, Manchester and Newcastle found that the most common reason for CBCT to be carried out in children was to assess the localized developing dentition.¹⁴ However, it should be noted that this service evaluation only included CBCTs requested by paediatric dentists, and not by other clinicians who may have been involved in the child's care. Encouragingly, the review did show that most CBCTs affected treatment decisions.¹⁴ Another study has shown that there is greater confidence in treatment plans when CBCT is used,¹⁵ however this cannot necessarily be interpreted as leading to better patient outcomes.

The following section outlines the current guidance for CBCT for the common/important clinical conditions.

Caries

For caries assessment, an in vitro study showed that digital radiography systems and CBCT behave similarly in the detection of proximal caries.¹⁶ Another study has shown that CBCT is better than conventional radiography at the detection of proximal caries.¹⁷ CBCT and digital radiography are similar for the detection of occlusal caries.¹⁸ Examples of occlusal and proximal caries lesions are shown in Figure 2.

Two studies have demonstrated that CBCT may be better than both film and photostimulable phosphor plates (PSPs) in assessing proximal lesion depth, which, in theory, suggests it could be used for the monitoring of disease.^17,19 Wenzel, in her review, concluded that CBCT was fairly accurate in determining whether cavitation had taken place.²⁰ However, amalgam restorations produce significant artefact that reduces diagnostic accuracy. CBCT should not be used for caries detection when there are amalgam restorations in the region of interest.²¹ An example of the artefact produced by amalgam restorations is shown in Figure 3.

Other authors have investigated whether imaging parameters affect caries diagnosis. The voxel size seems to have little effect on caries detection.^17,22 There is some evidence that the number of frames, or exposures acquired during the rotation, can be successfully reduced without loss of diagnostic quality, thus delivering the same diagnostic yield at a lower dose.²³

The European Commission review concluded that the available evidence did not support the use of CBCT for caries diagnosis.¹² However, if a CBCT has been carried out for other purposes the teeth should be evaluated for the presence of caries.

Periodontal disease

The European Commission guidelines published in 2004 advise that existing radiographs, such as bitewings taken for caries assessment, should be used in the first instance to assess periodontal bone levels.²⁴

The British Society of Periodontology, in conjunction with the British Society of Paediatric Dentistry, have produced radiographic guidelines for children.²⁵ The guidance suggests radiographic examination is required for BPE codes of 3, 4 or *. The recommended radiographic examinations include horizontal bitewings, selected peri-apical radiographs and panoramic radiographs, but do not include CBCT. The attraction of 3D imaging for periodontal assessment is that it may visualize irregular bony defects, and buccal/lingual attachment that would not be seen clearly on 2D imaging. Laboratory studies have found CBCT is more accurate in diagnosing periodontal defects and periodontal bone loss than conventional intra-oral imaging.²⁶ A clinical study also found CBCT to be accurate in estimating the size of furcation lesions.²⁷

Although CBCT may be useful in managing complex and surgical periodontal cases, the European Commission does not recommend CBCT as a routine imaging modality for periodontal bone support.¹² High-resolution limited-volume CBCT may be justified in cases of furcation lesions and infra-bony defects, where there is insufficient information from clinical and conventional imaging. However, it should be remembered that CBCT is generally a higher-dose examination than conventional radiography, and movement artefacts are likely to be more common in children, which will reduce diagnostic yield. An example of severe movement artefact is shown in Figure 4.

Whenever reporting on a CBCT taken for other reasons, attention should be paid to assessing the periodontal bone levels.

Peri-apical disease

The literature suggests that high-resolution CBCT may be more sensitive at detecting peri-apical lesions compared to conventional radiography, with no loss in specificity.²⁸ More peri-apical lesions have been identified as being associated with posterior teeth by CBCT than by conventional radiography.¹² Further, following apicectomy, greater quantities and larger-sized peri-apical lesions were identified when CBCT was used compared with conventional radiographs.²⁹ However CBCT is not recommended as a standard method of diagnosing peri-apical inflammatory disease. Its use should be limited to selected cases when conventional radiographs give a negative finding, yet there are contradictory positive clinical signs and symptoms.^12,30,31 If indicated, small-volume CBCT should be used to keep the radiation dose as low as possible. An example of a peri-apical infection demonstrated on CBCT is shown in Figure 5.

Endodontics

3D imaging does have clear advantages over conventional 2D imaging in endodontics. However, it must be remembered that CBCT has a lower resolution than intra-oral imaging.

When assessing root canal anatomy, it has been shown that in up to 70% of cases, the use of a CBCT gave additional, relevant clinical information,³² although the influence on patient management is unclear. CBCT has been shown to be of particular use in identification of a second mesio-buccal canal in maxillary first permanent molars, with good sensitivity and specificity (Figure 6).³³

Owing to the overall lack of evidence in the application, CBCT is not indicated as a standard method for identification of canal anatomy, but limited-volume high-resolution CBCT may be indicated for cases when inadequate information is gained from conventional intra-oral imaging, particularly in those teeth with complex root canal systems.^12,30 It must be considered that the use of an operating microscope may give the required information with no radiation exposure.

CBCT has been used in assessing both internal and inflammatory external resorption. Teeth that have suffered dental trauma are at increased risk of external resorption, and the use of CBCT to provide early diagnosis and aid prompt treatment of this rapidly progressing condition would afford an advantage.³⁴ The European Society of Endodontology suggests CBCT may be useful in the assessment and/or management of root resorption that clinically appears to be potentially amenable to treatment.³⁰ An example of root resorption is shown in Figure 7. Other justifiable potential applications relevant to children include aiding in management of dens invaginatus (Figure 8).³⁵

Dental trauma

It has been reported that when used in assessing dental trauma, a significantly higher diagnostic accuracy was found when using CBCT compared with conventional radiography.³⁶ For children who have sustained acute dental trauma, CBCT may not be achievable at initial presentation, therefore, it is recommended that conventional intra-oral radiographs are taken and that limited-volume, high-resolution CBCT is carried out only when adequate information for management is not gleaned from conventional imaging.^12,30 An example of a CBCT scan taken following trauma is shown in Figure 9.

Orthodontics

The British Orthodontic Society advises against the routine use of CBCT in orthodontics.³⁷ In the hospital setting, large-volume CBCT may be useful in patients with significant craniofacial deformity, for whom both orthodontics and surgical intervention or surgery only is envisaged as a treatment plan.¹² However, large-volume CBCT should never be undertaken if the sole purpose is to produce a cephalometric image.³⁷ The British Orthodontic Society suggests small-volume CBCT may be useful in the following scenarios.³⁷

Pathological lesions of the jaws

There is a role for CBCT for bony diseases of the jaws where soft tissue detail is not required. It can be used to help with the diagnosis, but is not recommended as the first-line investigation in cases of suspected malignancy.¹² CBCT is useful is assessing the full extent of a lesion, particularly when the maxillary antrum is involved (Figure 13), and when planning surgery where the lesion is close to important neurovascular structures.

Conclusion

CBCT has proven to be valuable in diagnosing and managing dental disease in children. However, the decision to undertake CBCT must always be justified, with routine taking of CBCT scans absolutely contraindicated. The increased radiation risk should be outweighed by the benefit that the additional information provides in terms of decisions affecting management of the child and, ultimately, the outcome for the patient.