diphyodonty

Diphyodonty is a dentition pattern in which an individual develops two successive sets of teeth over its lifetime: a first, deciduous (baby) dentition and a second, permanent dentition. This contrasts with monophyodonty, a single set of teeth, and polyphyodonty, multiple successive sets. Diphyodonty is common among most mammals, including humans, but not universal across all vertebrates; some lineages show different patterns such as teeth that are retained only temporarily or replaced continuously.

In humans and many other mammals, the deciduous dentition begins forming during embryonic development and erupts in early childhood. The deciduous set contains 20 teeth (four per quadrant: two incisors, one canine, two molars). Eruption typically starts around six months and continues until about three years of age. Deciduous teeth generally serve during early feeding and guiding the development and eruption of the permanent teeth.

Replacement of deciduous teeth by permanent teeth involves the development of permanent successors from the dental lamina. Roots of deciduous teeth are gradually resorbed as the permanent teeth erupt, creating pathways for occlusion with the opposing dentition. In humans, the permanent dentition comprises 32 teeth (including the third molars). Each quadrant standardly contains two incisors, one canine, two premolars, and three molars, though third molars may be absent in some individuals. Notably, the first permanent molars erupt without preceding deciduous predecessors, behind the last deciduous molar.

Evolution and clinical relevance: diphyodonty reflects a balance between early functionality and later full occlusion, with implications for dental development, growth, and pediatric dentistry. Variations exist across species, influencing tooth timing, replacement, and jaw development.