A. Line angles were previously defined as the line or angle created by the junction of two crown surfaces of a tooth. The two facial line angles of the anterior teeth and premolars of both arches are normally quite prominent, when compared to the more rounded lingual line angles of the same teeth. Their outline is especially noticeable from the incisal (occlusal) aspect, because they are seen in cross section.
B. These prominent line angles are actually the facial termination of the facial embrasures. For any specific facial embrasure, they are normally located directly adjacent to each other in the faciolingual dimension. For example, the mesiolabial line angle of a lateral incisor should be located directly adjacent (not farther labially or lingually) to the distolabial line angle of the adjacent central incisor. This placement is consistent with the concept of symmetry in embrasure form discussed previously.
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