RESUMO
OBJECTIVE: When a dental elastomer is placed in the oral vestibule and the facial muscles contracted while it sets, the functional cast produced frequently shows a deep anteroposterior groove, and marked posterosuperior and smaller anteroinferior bulges. This study investigates whether these features have a structural or a physiological basis. DESIGN: Casts of the right side of the oral vestibule of dissecting room cadavers and living volunteers were made using a polyvinylsiloxane dental elastomer. The volunteers each produced two functional casts in each of the following situations: while the teeth were clenched but the facial muscles inactive, while grimacing, and while swallowing. RESULTS: Grooves and bulges were largely absent in casts from the dissecting room cadavers and of living volunteers with the teeth clenched but the facial muscles inactive. They were present when the elastomer set while the subjects grimaced but most marked when they had been swallowing their saliva. The depth of the grooves varied between individuals and generally was greatest alongside the second molar teeth. We found that the posterosuperior bulge did not coincide with the position of the parotid duct. CONCLUSIONS: The anteroposterior groove represents a well developed horizontal part of buccinator. The regions of the casts bulging superior and inferior to the groove probably represent weaker regions of buccinator towards its maxillary and mandibular attachments. The bulge superior to the groove was not explained by a weakness in buccinator where it is pierced by the parotid duct.
