Deciduous Teeth

Primates, like most eutherian mammals are diphyodont (have two generations of teeth) although some mammals have deciduous teeth that are not replaced (usually the first post-canine tooth), some have lost a few or all of their deciduous teeth, and others shed them all before birth. All deciduous teeth are small enough to begin to form before birth but small immature jaws cannot accommodate large permanent teeth (one reason for diphyodonty). In all Hominids there are 20 deciduous teeth (di2: dc1: dm2 in each quadrant of the mouth). Deciduous molars are, perhaps more correctly, sometimes referred to as deciduous premolars. A successional permanent tooth develops beneath and lingual to each one. Deciduous tooth crowns are whiter, have larger pulp chambers, have thinner enamel, are more bulbous than permanent tooth crowns and lack a sinuous cervical margin. Deciduous tooth roots are proportionately longer than permanent tooth roots relative to their crown height and deciduous molars have more widely splayed roots with little common root trunk. Great ape deciduous incisors are, like their permanent counterparts, larger than human deciduous incisors. Deciduous ape canines are much taller and have a concave posterior border that extends onto a distal talon or talonid, whereas human deciduous canines are narrowest at the cervix and broaden out to become widest in the mid-crown. Deciduous ape canine crowns project beyond the occlusal plane and create a space (diastema pl. diastemata) in the opposing tooth row. This diastema is pre-canine in the upper tooth arch and post-canine in the lower tooth arch. Deciduous molar teeth tend to have more pointed and, in the case of dm2, more equally sized cusps than permanent molars. Their more equal size may reflect the fact that each cusp begins its initial mineralization closer together in time than permanent molar tooth cusps do.