Ans. is 'a' i.e. Fluorosis is the most common cause of dental caries in children endemic Fluorosis o Endemic fluorosis occurs when drinking water contains increased amounts of fluorine (3-5 mg/L) o Various toxic manifestations of endemic fluorosis are: a. Dental fluorosis Fluoride is deposited in the enamel of teeth when excess fluoride is ingested during the years of tooth calcification (i.e. during the first 7 yrs of life) q Earliest signs of dental fluorosis is molting of dental enamel. The teeth loose their shine and chalk white patches develop. Later the white patches turn yellow or sometimes brown or black. In severe cases, loss of enamel gives the teeth a corroded appearance. Mottling is best seen on the upper incisors. Mottling is almost entirely confined to the permanent teeth and develops only during the period of formation. b. Skeletal fluorosis Chronic ingestion of excessive amount of fluorine (3.0 to 6.0 mg/L or more) results in skeletal fluorosis. There is a heavy fluoride deposition in the skeleton. Fluoride deposition leads to Osteosclerosis & calcification of the ligaments. In the early clinical stage of skeletal fluorosis, symptoms include pains in the bones and joints; sensations of burning. pricking. and tingling in the limbs; muscle weakness; chronic fatigue: and gastrointestinal disorders and reduced appetite. In the next clinical stage, pain in the bones become constant and some of the ligaments begin to calcify. Osteoporosis may occur in the long bones, and early symptoms of osteosclerosis are present. Stiffness In the back occurs, especially in the lumbar region, followed by dorsal and cervical spines. Restriction of the spine movements is the earliest clinical sign of fluorosis. The stiffness increases steadily until the entire spine becomes one continuous column of bone manifesting a condition referred to as 'poker hack'. The stiffness that first appears in the spine soon spreads to various joints in the limbs owing to the involvement of the joint capsules, the related ligaments, and the tendinous attachments to the bones. The involvement of the ribs gradually reduces the movement of the chest during breathing. which finally becomes mainly abdominal. When that happens the chest assumes a barrel shape. With the increasing immobilization of the joints due to contractures, flexion deformities may develop at hips, knees and other joints, which make the patient bedridden. Despite the fact that the entire bone structure has become affected, the mental faculties remain unimpaired till the last stage is reached. la The stage at which skeletal fluorosis becomes crippling usually occurs between 30 and 50 years of age in the endemic regions c. Genu valgum In recent years, a new form of fluorosis characterised by genu valgum and osteoporosis of the lower limbs has been repoed from some districts of Andhra Pradesh and Tamil Nadu. This form of fluorosis was observed in people whose staple diet was Sorghum (jov*ar). It was found that diets based on sorghum promoted a higher retention of ingested fluoride than do diets based on rice.