The correct answer is option 1: Tooth caries. Deficiency of fluoride, a mineral found in water and certain foods, can lead to tooth decay or tooth caries. Fluoride plays a crucial role in preventing tooth decay by strengthening the tooth enamel, which is the outer protective layer of the teeth. When there is a deficiency of fluoride, the enamel becomes weaker and more susceptible to the acids produced by bacteria in the mouth. As a result, cavities or tooth decay can occur.
Option 2, mottling of tooth, is not a health problem caused by fluoride deficiency but rather an excessive intake of fluoride, known as dental fluorosis. Dental fluorosis can cause white or brown spots on the teeth but does not lead to tooth caries.
Options 3 and 4, bending of bones and stiffening of joints, are not directly related to fluoride deficiency. These health problems are more commonly associated with other conditions such as osteoporosis or arthritis.
Therefore, the correct health problem associated with fluoride deficiency is tooth caries.