Three-dimensional reconstruction of cone beam CT scan in the planning of the surgery of mandibular impacted third molars

Abstract

Objectives: The aim of this work is to evaluate the possibility that the three-dimensional (3D) reconstruction of a cone beam computed tomography (CBCT) scan may facilitate the technical planning of the surgical extraction of third molars, whose roots are located in proximity of or in contact with the inferior alveolar nerve.

Materials and methods: This article describes the planning process and the extraction of a lower third molar with the inferior alveolar nerve (IAN) entrapped through its roots using the 3D reconstruction of a CBCT scan.

Results: After-surgery clinical examinations showed normal healing of the surgical wound and no neurological symptoms.

Conclusions: The 3D reprocessing of a CBCT allows the construction of a computer-aided design model to investigate the spatial relationships between the wisdom tooth and the IAN. This method makes it possible to reconstruct a virtual model to preview the tooth and its spatial relationships, simplifying the mental processes of reworking and analyzing the existing relationships in the area, an important aid, especially in cases that are difficult to diagnose with a first-level examination. Indeed, it helps in reducing the risk of intra-operative injury to the nerve during extraction procedures.

Keywords: Impacted third molar; inferior alveolar nerve; neurological lesion; pre-operative surgical planning; three-dimensional surgical planning.

Figure 1

Clinical setting. Element 4.8 presents semi-impacted with a large mesial decay

Figure 2

Orthopantomography. The radiographic 2D exam shows a presumable contact between the right mandibular canal and the roots of element 4.8

Figure 3

3D Slicer. Starting from the CBCT scan, the 3D reconstruction is made through the use of the open-source freeware software, marking the tooth and the nerve

Figure 4

3D Visualization. Thanks to the 3D reconstruction, the digital model can be visualized with different angulations, permitting the better analysis of the spatial relationships between the tooth and the nerve

Figure 5

Odontotomy. (a) Coronectomy made through rotatory drills. (b) Separation of the mesial roots from the distal one with a piezoelectric instrument. (c) Separation of the vestibular roots from the lingual one with a piezoelectric instrument

Figure 6

Post-extractive socket. The IAN clinical integrity can be noticed between the wholes leaved by the roots of element