Classification of impacted mandibular third molars on cone-beam CT images

Abstract

Background Neurological involvement is a serious complication associated to the surgical removal of impacted mandibular third molars and the radiological investigation is the first mandatory step to assess the risk of a possible post-operative injury to the inferior alveolar nerve (IAN). The aim of this study was to introduce a new radiological classification that could be normally used in clinical practice to assess the relationship between an impacted third molar and mandibular canal on cone beam CT (CBCT) images. Material and Methods CBCT images of 80 patients (133 mandibular third molars) were independently studied by three members of the surgical team to draw a classification that could describe all the possible relationships between third molar and IAN on the cross-sectional images. Subsequently, the study population was subdivided according to this classification. The SPSS software, version 15.0 (SPSS® Inc., Chicago, Illinois, USA) was used for the statistical analysis. Results Eight different classes were proposed (classes 0-7) and six of them (classes 1-6) were subdivided in two subtypes (subtypes A-B). The distribution of classes showed a prevalence of buccal or apical course of the mandibular canal followed by lingual position and inter-radicular one. No differences have resulted in terms of anatomic relationship between males and females apart from a higher risk of real contact without corticalization of the canal when the IAN had a lingual course for female group. Younger patients showed an increased rate of direct contact with a reduced calibre of the canal and/or without corticalization. Conclusions The use of this classification could be a valid support in clinical practice to obtain a common language among operators in order to define the possible relationships between an impacted third molar and the mandibular canal on CBCT images. Key words:CBCT, classification, inferior alveolar nerve, third molars.

Classification of impacted mandibular third molars using cone beam computed tomography based on neurological risks: N.R.C.

“…The reduced thickness of the lingual bone plate compared to the buccal plate could be an explanation of this ascertainment. This finding agrees with the observation of Maglione et al [17] concluding that the patients at high risk of developing an IAN damage are patients with a lingual course of the mandibular canal. Particular attention should be taken for the cases with lingual course of the mandibular canal during CBCT examination and third molar removal.…”

“…This result is in accordance with the majority of the consulted literature [17,34,35]. The K value revealed a moderate agreement for the entire classification (0.598), which could be explained by the fact that this classification was composed by three elements, so it is unexpected to have an excellent agreement.…”

“…Since a preoperative evaluation of the exact relationship between the roots of the mandibular third molar and the IAN would aid in predicting, and potentially avoiding sensory impairment [14], newer classifications focusing on the relationship between the third molar and the mandibular canal have been presented [3,[15][16][17]. The newer classifications have some drawbacks.…”

“…The newer classifications have some drawbacks. In fact, they are a little blurry and they examined the general course of the mandibular canal not the closest relationship, given that the course of the mandibular canal in relation to the third molar could have various situations [17]. Moreover, these classifications do not present all the anatomical situations and they are adapted to the main objective of their studies.…”

Necessity of CBCT - examination in assessment of the surgical approach for the extraction of impacted lower third molars

“…The incidence in the different populations is between 9.5% (1) and 25% (2). The belief is that the main reason for retention of these teeth is insufficient space in the retromolar area (3,4).…”