Tooth is basically a hereditary unit that is in dynamic interplay with its environment, both affecting and being affected by its adjacent or surrounding tissues and organs. These surroundings, which are also by and large genetically determined, exert influence on the behaviour of tooth movement at all developmental stages, and are termed epigenetic factors. It is difficult, therefore, to make a clear-cut demarcation or draw a line of separation between the effects of environment and heredity. Both these factors act simultaneously and bring out a hybridized effect on their subject, the point of differentiation, however, being in the percentage of contribution.The eruption timing of a deciduous tooth is hence, determined by, firstly the contribution of the genetic constitution of the individual, which in turn depends on the genetic make up of the parents, and the susceptibility of its genetic constitution to alteration by various agents leading to abnormalities. Secondly, it is influenced by the nature of the surroundings in which the tooth develops which in turn depends on numerous factors that turn these surroundings either favourable or unfavourable for timely eruption.