Objectives: The aims of the present study were to clarify the anatomy of impacted mandibular third molars in relation to surrounding structures and to investigate the pathway of infection originating from pericoronitis of this tooth.
Study design: Computed tomography (CT) images were evaluated in 87 patients with uninfected mandibular third molar impaction and in 12 patients with infection originating from an impacted mandibular third molar. In uninfected patients, bony features around the impacted crown were investigated together with the relationship between the crown and surrounding muscles. In infected patients, involvements of bony and soft tissue structures were evaluated according to the disappearance of cortices and lateral asymmetry of density and shape in the spaces and muscles.
Results: In uninfected patients, the disappearance of the lingual cortical plate was observed in 48 (35.3%) impacted molars, while only in 11 (8.1%) teeth for buccal cortices. The cortical thickness was thinner on the lingual side than the buccal side. Sixty-five percent of the masseter muscle horizontally overlapped the crown, while almost all of the medial pterygoid muscle was posteriorly situated apart from the crown. The mylohyoid muscle horizontally overlapped the crown at below or intermediate vertical positions. In infected patients, the involvement of lingual structures was more frequently observed than that of buccal structures. The mylohyoid muscle was involved in 10 (83.3%) of 12 patients. Among them, 8 showed submandibular space involvement.
Conclusion: CT findings supported the clinical observations of infection spread in patients with pericoronitis of the impacted mandibular third molar. CT appeared to be an effective tool for investigating the pathway of infection originating from the pericoronitis of impacted mandibular third molars.