Ans. is 'd' i.e., Frame method Age from teeth after 20 yearso Teeth eruption is useful for age estimation upto about 18 years, beyond which it is just a guess work. The methods used areGustafson's method : Useful only in persons older than 21 years of age, depending on the physiological changes in each of the dental tissues.1. Attrition - due to wear and tear from mastication, upper surface of teeth destroyed gradually, first involving the enamel - dentine - pulp (depending on the functional use of teeth and hardness of enamel).2. Paradentosis - recession of gums and periodontal tissue surrounding the teeth, exposing the neck and adjacent part of root - teeth fall off (poor hygiene increases paradentosis).3. Secondary dentine formation - develop within the pulp cavity and decrease size of the cavity, start from base - apex, obliterate the cavity, increase with age, caries and paradentosis.4. Cementum apposition - near the end of root, increase cementum, increase thickness, deposited throughout life, and form incremental lines (devised by Boyde).5. Root resorption - because of cementum and dentine, absorption of root start at apex and extend upward (may be pathological).6. Transparency of the root - seen after 30 years of age, canal in the dentine at first widen, increase with age because of deposition of minerals. They become invisible and dentine becomes transparent (Most reliable of all the criteria).Mile's method : Age can be known by changes of root transparency.C) Boyde' method : On enamel of the tooth, there is a line at birth (neonatal line). With increase in age, more lines are added, study of which helps in age determination.D) Stack's method : Age of infant can be known from height and weight of erupting teeth.