A baby’s teeth are not visible at birth, but already exist underneath the gums. Children's primary teeth begin forming at about the sixth week of pregnancy, and start mineralizing — building the bonelike inner tooth layer (called dentin) and the super-hard enamel layer that covers it — around the third or fourth month.

A mother's nutrition during pregnancy affects the development of her child's teeth. Adequate intake of calcium, phosphorus, vitamins A, C, and D, and protein is essential.