Commentary

Considering that maxillary canines are the second most common impacted teeth, determining their exact location has an important role in orthodontic and surgical treatment planning. Adequate localisation may help avoid future complications including ankylosis, resorption of the adjacent teeth and formation of pathologic lesions.1 Also, it helps establish the prognosis and duration of the treatment.2

Traditionally, 2D radiographic images in different angulations (periapicals (PAs), occlusal, panoramic and lateral or posterior anterior cephalometric radiographs) have been used to localise these impacted teeth. Newer cone beam CT machines offering multiple customisable features together with the ability to manipulate the image in different views and the lack of superimposition provide an attractive option.

This systematic review and meta-analysis focused on the use of conventional radiography versus cone beam radiography for visualisation of the impacted maxillary canine. One of the limitations for evaluation of the impacted teeth is the absence of a gold standard for each imaging system.

The two studies that reported accuracy were in vitro. The risk of bias was assessed using the QUADAS-2 tool and the authors rated as having high bias risk for patient selection (both) and index test (one) while the rest of the categories were rated as low bias risk. The QUADAS-2 is a tool for quality assessment of clinical diagnostic accuracy studies so it is uncertain how it can be of use for in vitro studies. From those accuracy studies one compared CBCT to horizontal PAs and CBCT to panoramic together with occlusal views, the other compared CBCT against a panoramic plus two PAs and two occlusal views. Each study used different units and settings.

The modifications to the Newcastle-Ottawa scale add to the uncertainty of the authors' conclusions. This tool assesses risk of bias for observational studies but does not include cross-sectional studies, making the results difficult to understand and reproduce.

Since all the cross-sectional studies were done using seven different units using unique settings it very challenging to make any specific recommendations.

Most patients requiring the location of an impacted canine are children or young adults. Considering that the risk of radiation exposure to children or young adults is more than, and can be twice that of adults,3 careful consideration of the risk benefits should be done before acquiring any image.

Current advances in digital dental radiographs as well as progress with techniques in different types of small field CBCT scan helped drastically reduce the exposure. Still, in the majority of cases, a considerable number of conventional images, using different angulations, are obtained before creation of a treatment plan.

The effective dose of small field of view cone beam CT scans for children varies between 7-521 μSv and from 5-652 μSv for adults.4 However, the radiation exposure for a panoramic image varies between 2.7-24.3 μSv, a cephalometric image between 2-6 μSv and a full mouth series with rectangular collimation and CCD sensor is estimated 17 μSv.5, 6 Based on this important information a small field CBCT scan may provide the most benefits considering the radiation exposure compared to multiple conventional radiographs.

At the present time, small field CBCT scans are not readily available and when considering the cost to the patient, its use may be limited.

As stated in American Academy of Oral and Maxillofacial Radiology position statement regarding use of CBCT scan in orthodontic treatment, the use of CBCT scan should be based on the patient's history, clinical examination, previous radiographic imaging, and the presence of a clinical condition that the exposure to the radiation, especially in children or young adults, can be justified.7

To the main question of this review: considering the limited number of in vivo studies in accuracy of imaging systems and the lack of discussion of the treatment outcome, the answer remains unclear.