Lecture 2

Maxillary central incisor

The deciduous tooth appears in the mouth at 3–18 months of age, with 6 months being the average and is replaced by the permanent tooth around 7–8 years of age.

The size of permanent tooth is larger than the deciduous tooth.

There are gender differences in the appearance of this tooth. In males, the size of the maxillary central incisor is larger usually than in females.

Gender differences in enamel thickness and dentin width are low.

Generally

There are some minor differences between the deciduous maxillary central incisor and that of the permanent maxillary central incisor.

The maxillary central incisors contact each other at the midline of the face. The position of these teeth may determine the existence of an open bite or diastima. Systemic disease, such as syphilis, may affect the appearance of teeth.

Variations of size, shape, and color of teeth exist among people, as with all other teeth.

Age differences in the gingival-incisal length of maxillary central incisors are seen and are attributed to normal attrition occurring throughout life. Thus, younger individuals have a greater gingival incisal length of the teeth than older individuals.

Maxillary central incisor

Development

The aggregate of cells which eventually form a tooth are derived from the ectoderm of the first branchial arch and the ectomesenchyme of the neural crest. As in all cases of tooth development, the first hard tissue to begin forming is dentine, with enamel appearing immediately afterwards.

Maxillary central incisor

The deciduous maxillary central incisor begins to undergo formation or mineralization 14 weeks in utero, and at birth 5/6ths of the enamel is formed.[The crown of the tooth is completed at around 1.5 months after birth and erupts into the mouth at around 10 months of age, making these teeth usually the second type of teeth to appear. The root completes its formation when the child is 1.5 years old.

Development

Maxillary central incisor

The permanent maxillary central incisor begins to undergo formation or mineralization when a child is 3–4 months of age. The crown of the tooth is completed at around 4–5 years of age and erupts into the mouth at 7–8 years of age. The root completes its formation when the child is 10 years old.

Development

Maxillary central incisor

Permanent incisors

They are eight in number.

Their major function is to punch and cut food material during the process of mastication (chewing).

They play important role in supporting the lips and maintaining a desirable esthetic appearance and they are important in phonetics (speech).

Characteristic features of incisor’s crown

Incisal ridge and edge.

The incisal ridge is that portion of the crown which makes up the complete. The incisal edge exist on an incisor after occlusal wear has created a flattened surface linguo-incisally

incisal portion..

Presence of mammelons.

Marginal ridge are longitudinally positioned.

Lingual fossa.

Cingulum.

The permanent maxillary central incisor is the widest tooth mesiodistally in comparison to any other anterior tooth.

It is larger than the neighboring lateral incisor and is usually not as convex on its labial surface. As a result, the central incisor appears to be more rectangular or square in shape.

The mesial incisal angle is sharper than the distal incisal angle. Straight mesial outline and rounded distal outline.

When this tooth is newly erupted into the mouth, the incisal edges have three rounded features called mammelons. Mammelons disappear with time as the enamel wears away by friction.

Well marked marginal ridges, lingual fossa and well developed cingulum.

Single tapered root.

Principal identifying features

Permanent maxillary central incisors

Labial view

The mesial outline of the tooth is straight or slightly convex, whereas the distal outline is much more convex.

The crest of curvature is closer to the mesio-incisal angle on the mesial side, while it is at the junction between the incisal and middle thirds.

The incisal outline in newly erupted teeth has elevations called mammelons, and with age they will wear off and result in straight incisal outline.

Labial view

The cervical line appears as a semicircle in shape with the curvature directed towards the root.

From this view, the root is blunt and cone-shaped and is usually 2–3 mm longer than the length of the crown.

A line is drawn through the center of the root and crown tends to parallel the mesial outline of the crown and root.

The crown and the root are tapered lingually, so the mesio-distal dimension of the lingual surface is narrower than that of the labial surface.

Below the cervical line, the lingual side of the maxillary central incisor has a small smooth convexity, called a cingulum which is confluent with raised marginal ridges mesially and distally.

Incisally, there is the lingual portion of the incisal ridge. Between this ridge and the marginal ridges and the cingulum there is a shallow concavity called the lingual fossa .

Developmental grooves are found on the cingulum and lying into the lingual fossa.

Lingual view

The crown is triangular in shape with the apex at the incisal ridge and the base at the cervix.

The root appears cone shaped with a blunt apex. Unlike most other teeth, a line drawn through the center of the incisal edge will also cross through the center of the root apex. This also occurs in maxillary lateral incisors.

The crest of curvature for the palatal and labial surfaces is located directly incisally to the cervical line.

Mesial view

The labial surface of the crown is convex from the crest of curvature to the incisal edge. The lingual surface of the crown is convex at the cingulum and slightly convex at the incisal edge, but it is concave at the mesial marginal ridge.

More than any other tooth in the mouth, the cervical line from this view curves tremendously, about 3 to 4 mm, toward the incisal.

Mesial view

This side of the tooth is similar to the mesial side, with little difference.

The curvature of the cervical line is less distally than mesially.

Distal view

The incisal edge is centered over the root.

The labial outline of the crown is broad and flat.

The incisal edge and incisal ridge are well-defined.

The lingual outline tapers lingually to the cingulum.

The mesio-distal dimension is greater labially than lingually.

The crown has triangular shape, as the root shape in cross-section.

Incisal view

Permanent maxillary central incisors

Contact with adjacent teeth in the same arch is referred to as interproximal contacts.

The central incisors contact each other at the incisal third and contact the lateral incisor nearly at the junction between the incisal and middle thirds of the crown.

Interproximal contacts

Pulp anatomy

The pulp is the location of the nerve and blood supply of a tooth.

In the deciduous maxillary central incisor, endodontic treatment is less frequent. In the permanent maxillary central incisor, root canal treatment can be effective.

There are three pulp horns in this tooth. In nearly all maxillary central incisors, there is one canal with one apex.

During root canal therapy, access into the pulp is frequently located centrally on the lingual surface between the incisal edge and the cingulum.

At the level of the cervical line, the shape of the canal is triangular but becomes circular at the middle level of the root.

Although the root is generally straight, the most common points of curvature is near the apex, and their direction is more common toward the distal and lingual.