Prevalence of an unusual hypoplastic defect of the permanent maxillary lateral incisor in great apes

Abstract

In this article, I describe a previously unreported maxillary lateral incisor defect (MLID) of the enamel in great apes and evaluate potential general causes (genetic, systemic stress, or localized disturbance), as well as examine differences in prevalence among the represented taxa. This defect occurred only on the labial surface of the maxillary lateral incisor and extended from the cervical-mesial quarter of the crown to the mesial edge of the cementoenamel junction (CEJ). The study sample consisted of 136 great ape specimens, including 41 gorillas, 25 chimpanzees, and 70 orangutans from the Smithsonian's National Museum of Natural History great ape collection. I used logistic regression to assess the prevalence of this defect in the sample and a binomial probability test for bilaterality. This defect of the maxillary lateral incisor is the second most common defect I observed in the study sample (30.1% of individuals affected), and was more likely to occur in individuals with linear enamel hypoplasia (LEH) and pit defects than those without these defects. Among specimens with both maxillary lateral incisors present, the defect was mostly bilateral. Pan and Pongo were significantly more likely to exhibit the defect than Gorilla. Between Pongo species, Pongo pygmaeus was significantly more likely to exhibit the defect than Pongo abelii. Between subspecies of Gorilla, although Gorilla gorilla gorilla exhibited the defect and Gorilla gorilla beringei did not, the difference was not significant. No sex differences were evident in this sample. The prevalence of this defect indicates it is not hereditary. The bilateral trend indicates a systemic cause, although the high inter-tooth specificity suggests a local disturbance and a combination of both is possible.

Orangutans, enamel defects, and developmental health: A comparison of Borneo and Sumatra

“…Abnormal dental formation provides a record of developmental stress in young hominoids. In an evaluation of three types of dental defect (repetitive linear enamel hypoplasia (rLEH), localized hypoplasia of the primary canine (LHPC), maxillary lateral incisor defect (MLID)) among five large apes (orangutans, mountain and lowland gorillas, chimpanzees, and bonobos), orangutans have the highest or second highest prevalence (Guatelli‐Steinberg, Ferrell, & Spence, ; Guatelli‐Steinberg & Skinner, ; Hannibal, ; Skinner, ; Skinner, ; Skinner & Hopwood, ; Skinner & Newell, ; Skinner, Skinner, Pilbrow, & Hannibal, ; Tsukamoto, ). These findings suggest that, albeit for unknown reasons, orangutans are remarkably stressed in infancy.…”

“…The second crypt fenestration defect, MLID, is attributed to abnormal contact of the labial surface of the somewhat less‐formed upper lateral incisor crown with the incisal edge (or fenestration margin) of the more mineralized central incisor through a fenestrated inter‐crypt boney septum in under‐developed jaws with pre‐eruptive dental crowding (Hannibal, ; Skinner et al, ). MLID is created in the first few years of an orangutan's life (ca.…”