The most impoant sign of age determination as per Gustafson's method is:

Ans. a. Root transparency Gustafson's Method The age estimation of adult over 21 years depends on the physiologic age changes in each of the dental tissues. AttritionQ Due to wear and tear from mastication, occlusal (upper) surface of the teeth is destroyed gradually; first involving the enamel, then dentin, and at last, pulp is exposed in the old age. It depends on the functional use of the teeth and also up on the hardness ParadentosisQ Regression of the gums and periodontal tissues surrounding the teeth takes place in the advancing age, gradually exposing the necks and adjacent pas of the roots, due to which the teeth become loose and fall off. Poor oral hygiene increases paradentosis. Secondary DentinQ * It may develop from the walls within the pulp cavity, and decrease the size of the cavity. * First it is deposited at the pulp chamber and gradually extends downwards to the apex, and may completely fill the pulp cavity. Cementum Appositiondeg The cementum increases in thickness paicularly due to changes in the tooth position, especially near the end of the root. Secondary cementum is slowly and continuously deposited throughout life and forms incremental lines. Incremental lines (devised by Boyde) appear as cross-striations on the enamel of teeth due to cementum apposition, and are thought to represent daily increments of growth. They can be seen on histological section. The age can be calculated by counting the number of lines from the neonatal line onwards. This is mainly applicable to infants. This is mainly applicable to infants. Root ResorptionQ It involves both cementum and dentin, which show characteristically sharp grooves. Absorption of the root stas first at the apex and extends upwards. It usually occurs in the late age. It may be due to pathological process. Transparency of the RootQ It is not seen until about 30 years of age. The canals in the dentin are at first wide. With age they are filled by mineral, so that they become invisible and the dentin becomes transparent. It is the most reliable of all criteriaQ.