The clinical anatomy of complications observed in a posterior superior alveolar nerve block

Abstract

The use of anesthetics in dentistry is necessary to prevent pain in precise areas of the oral cavity. This is accomplished by blocking branches of the trigeminal nerve. For treatment of the maxillary molars (with the possible exception of the mesiobuccal root of the 1st maxillary molar) and the buccal soft tissues, a posterior superior alveolar (PSA) nerve block is employed. This injection targets the PSA nerve in the infratemporal fossa. To properly perform the injection, deposition of the anesthetic needs to be placed along the posterior surface of the maxilla. The needle must be advanced approximately 15mm in the following x-y-z plane at the same time to reach the PSA nerve along the posterior surface of the maxilla: medially, superiorly, and posteriorly at a 45 degree angle to the maxillary occlusal plane. Various complications can result from an improperly placed PSA nerve block. The most common complication is a hematoma resulting from trauma to the pterygoid plexus of veins. Another reported complication, although uncommon, is a temporary Bell’s Palsy if the needle is improperly placed into the parotid bed. Although a short needle is recommended for a PSA injection, many clinicians utilize long needles. In this study, an experienced dentist placed a 25 gauge long needle in the oral cavity of fresh tissue cadavers. A 1.8 ml carpule of 10% methylene blue was then injected into the site. To examine the extravasation of the dye in the tissue, dissections were performed and digital images were taken. We observed that using proper technique, the anesthetic would label the PSA nerve. However, improper placement of the needle could lead to damage of the pterygoid plexus, labeling of the inferior portion of the parotid gland with the cervicofacial division of the facial nerve, and labeling in the lateral or medial pterygoid muscles which would result in trismus.