CBCT images provide important information about the presence and extent of bone and/or tooth resorption, cortical expansion, presence of calcifications, tooth displacements, and involvement of anatomical structures [4, 6]. With the different reformats, it is possible to obtain a better view of the bone margins of the lesion in three dimensions [2, 5].
Measurements on CBCT images are acceptably accurate, in addition to revealing the direction in which the expansion is taking place, contributing to the planning of surgical treatment, especially in the early stages of expansion, when it may be difficult to observe the direction of growth by only clinical examination , in contrast to the PR where the image is enlarged .
In the present study, odontogenic keratocyst was more prevalent in the mandible than in the maxilla, in line with previous studies [18–23]. Likewise, ameloblastomas were also located in the mandibular region [18, 20, 22–24]. All dentigerous cysts occurred in the mandible; however, they may be common in the maxillary region . For odontomas, 80% of the cases were observed in the mandible, contrary to previous studies that demonstrated a higher prevalence in the maxilla [18–20, 22, 23].
Among the lesions considered aggressive, odontogenic keratocyst and ameloblastoma caused cortical bone perforation in 71.4% and 50% of cases, respectively. Root resorption and displacement were observed in 22% and 29% of odontogenic keratocyst cases, respectively, and in half of ameloblastoma cases, root resorption of the teeth involved was observed. The main characteristic that differentiated both lesions was the association with unerupted teeth and the expansion of bone cortices, present in all cases of ameloblastoma. As for odontogenic keratocysts, in most cases (64.3%), there was no expansion of the cortices or association with an unerupted tooth (57.1%).
Among the non-aggressive lesions, the dentigerous cyst was not associated with cortical perforation or tooth displacement. However, most cases showed root resorption (66.7%). The margins have always been well defined in non-aggressive lesions, as well as in odontomas, which in 60% of cases, were associated with unerupted teeth or caused tooth displacement without root resorption. Calcifications were observed in ameloblastic fibro-odontoma, adenomatoid odontogenic tumour, and calcifying epithelial odontogenic cyst. CBCT allows the detection of subtle hyperdensities, favouring the orientation of the hypotheses for the diagnosis of calcified lesions, which may also include the calcifying epithelial odontogenic tumour, cemento-ossifying fibroma, and fibro-osseous lesions.
On comparing aggressive and non-aggressive lesions, there was a statistically significant difference only for the perforation of cortical bone, which was more prevalent in aggressive lesions, suggesting that this characteristic is an important indicator of pathological behaviour, guiding the elaboration of diagnostic hypotheses and the plan of treatment.
Oral surgeons can rely on PR if the margins of benign lesions are well defined. However, when the margins are not well defined, CBCT is the best tool for diagnostic assistance . A ‘benign’ lesion appearance in a PR can reveal characteristics of malignancy in thin slices scanned on CBCT. Tomographic images can identify such irregular margins and provide accurate and reliable information in the early stages of a malignant lesion [2, 7]. CBCT is as reliable as MHCT for detecting bone invasion by malignant lesions [26, 27]. However, they are not applicable for the analysis of soft tissue tumours, and in this case is more appropriate acquisition of MHCT in ‘soft tissue windows’ or MRI [7, 28].
The absence of cases of compound odontomas, simple bone cysts, or even the small number of cases of dentigerous cyst, can be justified by the fact that CBCT is not requested in all cases. Generally, the indication for the exam is in more extensive lesions or those close to anatomical structures, to assist in the diagnosis and treatment planning. It is important to note that CBCT, despite its advantages, should not be prescribed indiscriminately because of the relatively high radiation doses when compared to radiographic exams.