Schreger lines are visual artifacts that are evident in the cross-sections of

ivory Ivory is a hard, white material from the tusks (traditionally from elephants) and teeth of animals, that consists mainly of dentine, one of the physical structures of teeth and tusks. The chemical structure of the teeth and tusks of mammals is ...

. They are commonly referred to as cross-hatchings, engine turnings, or stacked chevrons. Schreger lines can be divided into two categories. The easily seen lines which are closest to the

cementum Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.Illustrated Dental Embryology, Histology, a ...

are the ''outer Schreger lines''. The faintly discernible lines found around the tusk nerve or pulp cavities are the ''inner Schreger lines''. The intersections of Schreger lines form angles, which appear in two forms: concave angles and convex angles. Concave angles have slightly concave sides and open to the medial (inner) area of the

tusk Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share c ...

. Convex angles have somewhat convex sides and open to the lateral (outer) area of the tusk. Outer Schreger angles, both concave and convex, are acute in extinct

proboscidea The Proboscidea (; , ) are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. From ...

and obtuse in extant proboscidea.U.S. Fish & Wildlife Services , Forensics Laboratory
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Notes

Ivory