A Guide To Dental Anatomy

 The Permanent Maxillary Premolars

The maxillary premolars are developed from the same number of lobes as anterior teeth—four. The primary difference in development is the well-formed lingual cusp, developed from the lingual lobe, which is represented by the cingulum development on incisors and canines. The middle buccal lobe on the premolars, corresponding to the middle labial lobe of the canines, remains highly developed, with the maxillary premolars resembling the canines when viewed from the buccal aspect.

The buccal cusp of the maxillary first premolar, especially, is long and sharp, assisting the canine as a prehensile or tearing tooth. The mandibular first premolar assists the mandibular canine in the same manner. The second premolars, both maxillary and mandibular, have cusps less sharp than the others, and their cusps articulate with opposing teeth when the jaws are brought together; this makes them more efficient as grinding teeth, and they function much like the molars, but to a lesser degree.

The maxillary premolar crowns are shorter than those of the maxillary canines, and the roots are also shorter. The root lengths equal those of the molars. The crowns are a little longer than those of the molars. Because of the cusp development buccally and lingually, the marginal ridges are in a more horizontal plane and are considered part of the occlusal surface of the crown rather than part of the lingual surface, as in the case of incisors and canines. When premolars have two roots, one is placed buccally and one lingually.

Maxillary First Premolar

The maxillary first premolar has two cusps, a buccal and a lingual, each being sharply defined. The buccal cusp is usually about 1 mm longer than the lingual cusp. The crown is angular, and the buccal line angles are prominent. The crown is shorter than that of the canine by 1.5 to 2 mm on the average.maxillary first premolar

First evidence of calcification 11/2–13/4 yr
Enamel completed 5–6 yr
Eruption 10–11 yr
Root completed 12–13 yr

Maxillary Second Premolar

The maxillary second premolar supplements the maxillary first premolar in function. The two teeth resemble each other so closely that only a brief description of each aspect of the second premolar is necessary. Direct comparison is made between it and the first premolar, and variations are mentioned.

The maxillary second premolar is less angular, giving a more rounded effect to the crown from all aspects. It has a single root.

Considerable variations in the relative sizes of the two teeth may be seen, because the second premolar does not appear true to form as often as does the first premolar. The maxillary second premolar may have a crown that is noticeably smaller cervico-occlusally and also mesiodistally.

First evidence of calcification 2– 21/4 yr
Enamel completed 6–7 yr
Eruption 10–12 yr
Root completed 12–14 yr

The Permanent Mandibular Premolars

The mandibular first premolars are developed from four lobes, as were the maxillary premolars. The mandibular second premolars are, in most instances, developed from five lobes, three buccal and two lingual lobes.

The first premolar has a large buccal cusp, which is long and well formed, with a small, nonfunctioning lingual cusp that in some specimens is no longer than the cingulum found on some maxillary canines. The second premolar has three well-formed cusps in most cases, one large buccal cusp and two smaller lingual cusps. The form of both mandibular premolars fails to conform to the implications of the term bicuspid, a term that implies two functioning cusps.

Mandibular First Premolar

This tooth is situated between the canine and second premolar and has some characteristics common to each of them.
The characteristics that resemble those of the mandibular canine are as follows:
1. The buccal cusp is long and sharp and is the only
occluding cusp.
2. The buccolingual measurement is similar to that of
the canine.
3. The occlusal surface slopes sharply lingually in a
cervical direction.
4. The mesiobuccal cusp ridge is shorter than the
distobuccal cusp ridge.
5. The outline form of the occlusal aspect resembles the
outline form of the incisal aspect of the canine.

The characteristics that resemble those of the second mandibular premolar are as follows:
1. Except for the longer cusp, the outline of crown and
root from the buccal aspect resembles that of    the second premolar.

2. The contact areas, mesially and distally, are near the
same level.

3. The curvatures of the cervical line mesially and distally are similar.

4. The tooth has more than one cusp.

mandibular first premolar

First evidence of calcification 13/4–2 yr
Enamel completed 5–6 yr
Eruption 10–12 yr
Root completed 12–13 yr

Mandibular Second Premolar

The mandibular second premolar resembles the mandibular first premolar from the buccal aspect only. Although the buccal cusp is not as pronounced, the mesiodistal measurement of the crown and its general outline are similar. The tooth is larger and has better development in other respects.

First evidence of calcification 21/4-21/2 yr
Enamel completed 6–7 yr
Eruption 11–12 yr
Root completed 13–14 yr