Premolars (dentes praemolaris: prae = in front of / before, mola = mill[stone]; dentes bicuspidati: bi = two, cuspis = eminence or cusp, bicuspid tooth).
Premolars (and molars) are located in the lateral areas of the dental arch, ie, in the cheek area (bucca), and are known as posterior, back, or lateral teeth. The premolars have a chewing or masticatory surface instead of a chewing edge. This surface is formed by the pronounced development of the dental tubercle into a genuine cusp. Cusps are referred to as buccal or lingual. Premolars are used to roughly chew food. With tough food, they are instinctively used to hold and bite the food.
The maxillary first premolar (dens praemolaris medialis) (Fig 4-44) usually has a divided root apex, and in some cases there may be two roots. Very rarely three root apices may be found. A buccal and palatal (lingual) root can be distinguished with independent, very branched root canals, which makes root canal treatment very difficult.
The average dimensions of the maxillary first premolar are:
- Crown width (mesiodistal): 6.5 mm
- Crown depth (buccolingual): 7.8 mm
- Crown length: 8.0 mm
- Total apicocoronal length: 20.5 mm
The vestibular (buccal) surface strongly resembles the labial surface of the canine but is slightly smaller. Curvature and angle characteristics are reversed. The medial ridge is displaced distally, the mesiobuccal cusp ridge is longer than the distal, and the mesial facet is larger than the distal. The cervical margin is curved apically, and cervical grooves are present.
The lingual surface is smaller than the vestibular surface and more curved; the horizontal curvature is more pronounced and more rounded. The medial ridge and the lingual cusp are displaced mesially so that the distolingual cusp ridge appears longer. The cervical line is curved buccally.
The approximal surface is almost rectangular. The contours of the buccal, lingual, and occlusal surfaces can be seen. The vestibular surface contour displays the vertical curvature characteristic: The greatest curvature is at the cervix in order to protect the marginal periodontium. The lingual surface contour is evenly rounded. The occlusal surface contour shows the higher, more angular buccal cusp and the smaller, rounded lingual cusp. The contact points lie directly below the marginal ridges. The cervical line runs slightly toward the masticatory surface.
The occlusal surface (masticatory or chewing surface) has an oval outline and is wider buccally and rounded and narrower palatally. The horizontal curvature characteristic is reversed. The cusps are located on half of the buccal and lingual portions of the masticatory surface. The buccal cusp is larger, higher, and more angular, with prominent triangular ridges, cusp ridges, and crests, whereas the lingual cusp is rounded and looks more delicate. There may be displacement of the tip of the lingual cusp distally and the central developmental groove lingually. The central developmental groove branches before the marginal ridges into two small supplemental developmental grooves running crosswise, giving the whole groove formation the appearance of a broad H. Growth-related fossae are formed in the branching points of the central developmental groove; these are the deepest parts of the occlusal surface.
The mesial approximal marginal ridge is concave for contact with the canine, whereas the distal ridge is convexly shaped. Growth-related depressions form on the triangular ridges, which can sometimes reach the same depth as a supplemental developmental groove.
The maxillary second premolar (dens praemo-laris lateralis) (Fig 4-45) is smaller, more compact, and more symmetric than the first premolar; the cusps are almost of the same height and virtually the same size, and the central developmental groove lies in the middle. The second premolar is a rudimentary tooth. It has only a single developed root.
The average dimensions of the maxillary second premolar are:
- Crown width (mesiodistal): 6.3 mm
- Crown depth (buccolingual): 8.3 mm
- Crown length: 7.5 mm
- Total apicocoronal length: 20.0 mm
The vestibular (buccal) surface is similar to that of the first premolar but smaller and without pronounced angle and curvature characteristics. It contains two identical facets that are separated by a slightly prominent medial ridge.
The lingual surface is also similar to that of the first premolar, although the middle ridge lies centrally.
The approximal surface shows cusps of unequal height, the buccal cusp being more angular than the rounded lingual cusp. The central developmental groove lies in the middle and is very deep, which indicates a risk of caries. Buccal and lingual curvatures are normal.
The occlusal surface is more symmetric than on the first premolar but with the same characteristics: prominent buccal and rounded lingual cusps. The central development groove lies in the middle of the occlusal surface.