MANDIBULAR THIRD MOLAR

The mandibular third molar (tooth #17 or #32), illustrated in figure 4-47, is the eighth tooth from the midline. It appears in many forms, sizes, and shapes. Since its function is similar to that of the other two mandibular molars, its general appearance is the same. It has smaller surfaces, more supplemental grooves, and four or five cusps, which are not so sharply differentiated as those of the first two molars.

Roots\The roots, generally two in number, are shorter in length and tend to be fused together. In many instances they show a distinct distal curve.

GLOSSARY OF UNIQUE DENTAL ANATOMY

The following list will be helpful to you in understanding some of the anatomical terms used in this chapter.

Cusp\A pointed or rounded elevation of enamel found on cuspids and on the chewing surfaces of bicuspids and molars.

Cingulum\Found on the lingual aspect of an anterior tooth. It is a convex mount of enamel localized to the cervical one-third of the crown.

Fissure\A linear fault that sometimes occurs in a developmental groove by incomplete or imperfect joining of the lobes. A pit is usually found at the end of a developmental groove or a place where two fissures intersect.

Fossa\A rounded or angular depression of varying

Figure 4-47.\Surfaces of mandibular third molar.

_{size found on the surface of a tooth.}

Central fossa\Centrally located depression found on the occlusal surface of molars and mandibular second bicuspids. The other bicuspids have mesial and distal triangular fossa, but do not have a central fossa.

Lingual fossa\Irregular, shallow depression found on the lingual surfaces of an incisor or cuspid.

Triangular fossa\Located adjacent to the marginal ridges on the occlusal surfaces of posterior teeth. Two types of triangular fossae are mesial and distal.

Groove\A small linear depression on the surface of a tooth.

Developmental groove-Fissure between the cusps on the crown of the tooth. Cusp tips are the initial site where enamel develops. As the enamel develops and spreads laterally, it touches enamel developing from other cusps. This junction forms a developmental groove. Such grooves appear on the labial, buccal, and lingual surfaces, and are least apparent on the labial aspect of anteriors.

Supplemental groove\A minor, auxiliary groove that branches off from a much more prominent developmental groove. They do not represent the junction of primary tooth parts and gives the occlusal surface a wrinkled appearance.

Lobe\Is one of the primary divisions of a crown; all teeth develop from four or five lobes. Lobes are usually ^{separated by readily identifiable developmental} they take distal, buccal, or lingual).

_{Cusp ridge\Each cusp has four cusp ridges radiating from its tip. They are named according to the direction} away from the cusp tip (for example, mesial, ^grooves.

Mamelons\Are small, rounded projections of enamel from the incisal edges of newly erupted anterior teeth. The projections wear away soon after eruption.

Ridge\Any linear elevation found on the surface of a tooth, named according to its location or form.

Lingual ridge\The ridge of enamel that extends from the cingulum to the cusp tip on the lingual surface of most cuspids.

Marginal ridge\A linear, rounded border of enamel that forms the mesial and distal margins of anterior teeth as viewed from the lingual, and the mesial and distal borders of occlusal surfaces on posterior teeth.

Oblique ridge\The only tooth on which an oblique ridge is found is the maxillary molar. Consists of an elevated prominence on the occlusal surface and extends obliquely from the tips of the mesiolingual cusp to the distobuccal cusp.

Transverse ridge\The union of a buccal and lingual triangular ridge that crosses the surface of a posterior tooth transversely (roughly 90 to both the buccal and lingual tooth surfaces).

Triangular ridge\Two inclines meet to form a triangular ridge and are located either on a facial or a lingual cusp ridge.

Sulcus\An elongated valley or depression in the surface of a tooth formed by the inclines of adjacent cusp or ridges.