Characterization of a retromolar foramen in a Chinese population: A radiographic study.

Background: Retromolar canal (RMC) arises from the mandibular canal (MC) behind the second or third molar and travels anterosuperiorly to a retromolar foramen (RMF). RMCs and RMFs have generally been ignored in anatomical textbooks and have rarely been reviewed or studied in the anatomical and dental literature until the last decades.

Objective: This study aimed to characterize RMF in a Chinese population concerning its incidence, origin, and classification via anatomical study and periapical radiography.

Methods: 123 dry adult Chinese mandibles were collected to observe the incidence of RMFs. RMFs were determined using a steel wire 0.5 mm in diameter. The passways or origins of the retromolar canal (RMC) were determined and classified via periapical radiography. For each RMF, two dentists independently measured the diameter and its distances to the lingual cortex, the buccal cortex, and the distal edge of the last tooth (or the alveolar fossa) using a vernier caliper.

Results: The incidence of RMFs was 31.71%. The average RMF diameter was 0.78 ± 0.27 mm. From RMF, the distance was 4.27 ± 1.87 mm to the lingual cortex, 8.61 ± 2.23 mm to the buccal cortex, and 7.84 ± 3.87 mm to the distal edge of the last tooth (or the alveolar fossa). RMCs were classified into MC type originating from the mandibular canal and AF type originating from the alveolar fossa. The diameters of MC ones were more significant than those of AF ones. There was no apparent correlation between the existence of the third molar and the presence of an RMF.

Conclusion: The incidence of RMFs in Chinese may be about one-third, which is a potential factor in the onset of surgery accidents. RMCs can be classified into two types by their origins. One of them is MC, which originates from the mandibular canal, and the other is AF, which originates from the alveolar fossa.