b. Angles (Junctions).
(1) Line angle. The line angle is a line formed by the junction of two
surfaces. A specific line angle is often named to indicate the surfaces it joins. For
example, the junction between the distal and lingual surfaces of an anterior tooth is
called the distolingual line angle. The junction between the mesial and the occlusal
surfaces of a posterior tooth is called the mesio-occlusal line angle. There are eight line
angles per tooth.
(2) Point angle. The point angle represents the junction of three surfaces.
For example, mesiolabioincisal for an anterior tooth point angle (mesial, labial, incisal
surfaces) or distolinguo-occlusal for a posterior tooth point angle (distal, lingual, occlusal
surfaces). There are four point angles per tooth.
c. Rounded Elevations.
(1) Lobe. Lobes are one of the primary anatomical divisions of a crown. All
teeth develop from either four or five lobes. Each lobe was the center of calcification in
the developing tooth. Lobes are usually separated by readily identifiable developmental
(2) Mamelon (scallop). A mamelon (see figure 4-9) is one of three small,
rounded projections of enamel (thought to resemble a scallop shell) sometimes present
on the cutting edge of a newly-erupted incisor tooth. The projections wear away soon
Figure 4-9. Mamelons.