The Dental Morphology Of Anterior Teeth

Morphology Of Permanent Incisors And Canines

Incisors

There are 4 maxillary incisors — two central incisors and two lateral incisors, and 4 mandibular incisors — two central incisors and two lateral incisors. The incisors are marked by the symbols 12, 11, 21, 22, 32, 31, 41, 42 according to the International Numbering System.

Functions

The mandibular incisors function with the maxillary incisors in cutting food; enabling articulate speech; helping to support the lip and maintain appearance; Their fourth function is to help guide the mandible posteriorly during the final phase of closing just before the posterior teeth contact. In this way the anterior teeth protect the posterior teeth from overloading.

Description

From the facial aspect, the crowns of incisors are relatively rectangular, longer incisogingivally than wide mesiodistally. They are narrowest in the cervical third and broader toward incisal third. They are more convex on the distal than on the mesial sides, except the mandibular central incisor which is symmetrical. The mesioincisal corner nearly forms a right angle, although this angle is slightly rounded.

The distoincisal corner is more rounded. This is a very important marker for distinguishing the incisors from other teeth. The cervical line is convex toward the apex on the facial and lingual sides.

A Mamelon is one of the three tubercles sometimes present on the incisal edge of an incisor tooth that has not been subjected to wear. Mamelons are usually present on newly emerged teeth and they are soon worn off by functional contacts against the incisors of the opposite dental arch — a phenomenon named attrition.

The roots are wider faciolingually than mesiodistally, except for the maxillary central incisor, and when they bend in the apical third, it is usually to the distal.

N.B. The central incisor root is the only maxillary tooth that is as thick at the cervix mesiodistally as faciolingually. This is the reason for its conical shape. Because of its shortness and conical shape, the maxillary central incisor is generally considered to be a poor support for any fixed bridge, due to its low mechanical stability.

The two shallow vertical depressions on the labial surface of incisors divide this surface into three portions, usually called the mesial, middle and distal lobes. These depressions are named developmental depressions. The crowns have a narrower lingual surface because the mesial and distal sides converge lingually. When viewed from the proximal, the crowns are wedge shaped.

The labial and lingual crest of curvature is in the cervical third, close to the cervical line. The lingual outline is S-shaped, being convex over the cingulum and concave from the cingulum nearly to the incisal edge. The labial outline is broader and less curved than the lingual outline.The functional wear of the incisal edges of incisors is an important mark for identification. Due to the contacts between upper and lower incisors in function their incisal edges are subjected to wear in a specific pattern — maxillary incisors demonstrate wear on the lingual side, and the mandibular incisors — on the facial side of the incisal edge.