The relative importance of environment and heredity in the development of various diseases and conditions is still a debatable topic. Most of the dental problems are found to have an interaction of these two factors. Many of the genetic disorders involve orofacial region and it is therefore of utmost importance for the dental surgeons to understand the normal development and mechanism involved in the development of abnormalities. We can consider hereditary head and neck pathology in a traditional sense as being either simple or complex consideration.

• Simple considerations are those resulting from single gene defect.
• Complex considerations are those which result from a collection of altered genes interacting with environmental influences.

Simple hereditary conditions:
Normal development and maintenance of the craniofacial complex is highly regulated at the molecular level. Odontogenesis can thus have simple gene disorders.

Congenitally missing teeth:
Hypodontia is the most common simple hereditary trait affecting oral cavity with maxillary lateral and premolar being most commonly involved excluding 3rd molars. Several genetic mutations resulting in hypodontia have been identified. The missense mutation in MSX1 gene causes an autosomal dominant trait of variably missing lateral incisors, second premolars and 3rd molars. Mutation in PAX 9 gene has been associated with unusual pattern of hypodontia converting of missing mandibular incisors, molars premolars.