Genetics typically determine the size of a person's teeth. Gender-specific traits affect the size and shape of teeth, and age and lifestyle habits impact the appearance of a person's teeth, according to Carrington College's Department of Dental Health.
Individuals with Down syndrome also typically have smaller teeth, according to the National Down Syndrome Society. It is common for people with Down syndrome to have shorter roots and smaller-than-average teeth. Smaller teeth can also be attributed to delayed eruption for children with Down syndrome. For example, while most babies get their first teeth by 6 to 12 months, babies with Down syndrome may not have tooth growth until 14 or 24 months of age.
Age is also a factor in the size of teeth. The central incisors can indicate the age of a person because older people lose approximately 1 millimeter to 5 millimeters in length, according to Carrington College. Gender also affects the size and shape of teeth. For example, women's teeth are often more rounded and shorter on the outer edge, whereas men's lateral incisors are longer and more square shaped. Excessive teeth grinding can shave off some of the length over time, and alcohol, caffeine and nicotine intake can impact the appearance of teeth.