Origin of the Cusps and Crests of the Tribosphenic Molar

Abstract

During the sessions, the question of exactness in identifying and comparing homologues was discussed by several participants. Professor Butler stated that the thought held by some, that differences arise in going back along the jaw, might also be viewed alternatively to represent structures on anterior teeth as degenerate forms of those on the posterior ones. Patterson also thought that he could not place any great trust in premolar analogy and that, as he stated in the Brussels Conference in 1956, "it is a dangerous tool."Butler and others also questioned identification of cusps by their relationship to crests. Butler asked, "How sharp does a convex surface have to be before it becomes a crest? . . . On a photograph a highlight on a slope is difficult of identification . . . in some cases I would say that there is not a crest where one is claimed." He also went on to say that having crests running across a tooth in the upper and lower jaws does not make the crests homologous, "Nor does it make the cusps at their lingual ends homologous." -A.A.D.

What lies beneath? An evaluation of lower molar trigonid crest patterns based on both dentine and enamel expression

“…A variety of ridges may form on these cusps, and crests of enamel may even join them. These ridges and crests have received various names in the literature [see Remane (1921), Vandebroek (1967), and Grine (1984)]. Korenhof (1982) recognized three trigonid crests on the dentine surface of the lower deciduous second molar, the names of which reflect their different origins: mesial marginal ridge, middle trigonid, and distal trigonid crest (see Fig.…”

“…The middle trigonid crest was described by Vandebroek (1967: 799) as the “first step in the process of “molarization” of the primitive tribosphenic molar. Functionally, he suggested that it facilitated the shearing ability of the tooth by adding a “cutting unit.” In humans, Zubov (1992b) reported its highest frequency in contemporary Africans.…”

Modular Wear Facet Nomenclature for mammalian post-canine dentitions

“…During the last century, various attempts were undertaken to refine the nomenclature in order to better reflect mammalian dental evolution (e.g. Vandebroek 1967;Crompton & Jenkins 1968;Szalay 1969;Hershkovitz 1971;Butler 1978;Maier & Schneck 1981;Van Valen 1982). However, describing the occlusal surface in detail is a challenging task, because various factors influence their formation and there is a wide variation among different taxa.…”