This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Forensic Medicine
The most reliable criteria in Gustafson method of age estimation is: 
Select and explain. 
A. Attrition, B. Secondary dentin deposition, C. Transparency of root, D. Cementum apposition
C: Transparency of root
Answer: C: Transparency of root 
Explanation: 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.