The most reliable criteria in Gustafson method of age estimation is:

Ans. is 'c' i.e. Transparency of root Gustafson's method is method of age determination in adults from physiological changes in teeth.Gustafson devised a microscopic method for age estimation based on the histological examination of ground thin sections of teeth. He evaluated the correlation of six physiological changes with increasing age. These are :Attrition - d/t wear & tear from mastication, occlusal (upper) surface of the teeth is destroyed gradually, first involving the enamel, then dentin and at last the pulp.Paradentosis - with advancing age the gums and peridental tissue surrounding the teeth show regression, gradually exposing the necks, and adjacent part of root of teeth.The amount of secondary dentin - Secondary dentil deposition occurs within the pulp cavity and gradually decreases the size of the cavity.Cementum apposition - Secondary cementum is slowly and continuously deposited throughout life forming incremental lines.Age can be estimated by counting these incremental lines.The degree of root resorption Transparency of root dentine - It is the most reliable of all criteria. It is not seen before 30 yrs of age.