Hypodontia is defined as the developmental absence of one or more teeth excluding the third molars. It is one of the most common dental anomalies, and can have a negative impact on function, and also appearance. It rarely occurs in primary teeth (also known as deciduous, milk, first and baby teeth) and the most commonly affected are the adult second premolars and the upper lateral incisors. It usually occurs as part of a syndrome that involves other abnormalities and requires multidisciplinary treatment. The phenomenon can be subdivided into the following according to the number of teeth concerned: Hypodontia: one to six missing teeth excluding the third molars Oligodontia: six or more missing permanent teeth excluding the third molars Anodontia: complete absence of teeth

Reference
Wiki: Tooth agenesis