Macroscopic anatomy of the sphenomandibular ligament related to the inferior alveolar nerve block.

We performed macroscopic observations of the sphenomandibular ligaments, and measured the space that is surrounded by the mandibular ramus and the ligament by using computed tomography. The materials used in this study were 40 heads of 40 adult cadavers. The cadaver head was cut on the mid sagittal plane. The medial pterygoid muscles of the cadavers were removed to observe the ligaments. The attaching style of the sphenomandibular ligament to the mandibular ramus was classified into three types: Type I (5 in 40 samples; attached only to the mandibular lingula), Type II (12 in 40 samples; attached to the mandibular lingula and extended toward the rear part of the internal surface of the mandibular ramus), and Type III (23 in 40 samples; attached to the mandibular lingula and toward the posterior border of the mandibular ramus). There was no statistical difference in the length of the ligament among the three types. However, Type III showed the largest width, and the space was approximately eight and three times as large as those of Type I and II, respectively. This indicated that the Type III ligament covered a larger area over the mandibular foramen than Type I. These results suggest that the three-dimensional morphology of the sphenomandibular ligament, as represented by Type III, may affect the effectiveness of anesthesia.