The tooth located in the primary dentition of the mandible distal to the primary first molar tooth. It is succeeded by the mandibular second premolar. The form of the crown is similar to but smaller than that of the first permanent mandibular molar. It has four cusps but the central pit (fossa) is significantly more extensive. The mesial and distal surfaces are strongly convex and there is a pronounced bulge on the buccal surface. It has a mesial and a distal root which diverge markedly to make room for the tooth germ of the mandibular second premolar. The mesial root may show some partial buccal and lingual division. The root apices may converge towards each other, further embracing the permanent tooth germ, which can result in its unintentional removal if extraction is attempted when the roots are fully formed. Calcification of the tooth begins at about 6 months of foetal life. The tooth erupts at about 20 months after birth and the calcification of the root is complete at about 3 years.