Occlusion in an Adult Male Gorilla with a Supernumerary Maxillary Premolar

Supernumerary teeth, or teeth that develop in addition to the normal number of deciduous and permanent dentition, have been widely described in human and nonhuman primates. Most studies have focused on the morphology and on the etiology of supernumerary teeth, and little is known about their occlusal relationships with adjacent and antagonistic teeth, and their effects on individuals’ masticatory efficiency. We analyzed the occlusal wear pattern of an adult male Western lowland gorilla (Gorilla gorilla gorilla) with a fully erupted extra maxillary right premolar. We used a virtual method, occlusal fingerprint analysis, to reconstruct the major mandibular occlusal pathways responsible for the creation of wear facets on the tooth crowns. This approach is based on analysis of facet parameters such as inclination, directions, and areas, all measured using high-resolution 3-D virtual models of dental crowns. The results show unusual wear patterns in the supernumerary premolar and on its antagonist contacts (lower P4 and M1) that cannot be associated with a normal masticatory behavior. Occlusal simulation and kinematic analyses reveal a high level of directional overlapping combined with the absence of common occlusal contacts. This indicates a case of malocclusion that must have caused discomfort in this gorilla when biting or chewing, and may represent the first evidence of bruxism (grinding the teeth and clenching the jaw) in wild great apes.