In public health, mottling and brownish staining of dental enamel is most commonly caused by which condition in drinking water?

Introduction / Context:
This question is from public health and dental science. It asks about the cause of mottling or discoloration of dental enamel, a condition often seen in areas with certain mineral imbalances in drinking water. Understanding this relationship helps in topics such as water quality, fluoridation, and dental health campaigns.

Given Data / Assumptions:

• The symptom is mottling of dental enamel, often called dental fluorosis when linked to fluoride.
• The possible causes are high chlorine, nitrate, fluoride, or calcium levels in water.
• Basic awareness of water chemistry and its effects on teeth is assumed.

Concept / Approach:
Dental fluorosis is a condition that arises when children are exposed to excessive fluoride while their teeth are forming. The enamel develops white streaks, brown stains, or a mottled appearance. In severe cases, the enamel becomes pitted and fragile. This usually occurs in regions where the natural fluoride content of drinking water is significantly higher than recommended levels. Chlorine in water is mainly used for disinfection and does not typically cause enamel mottling. Nitrates may cause other health problems but are not directly linked to mottled enamel. High calcium makes water hard and can lead to scaling but not the specific brown mottling associated with fluorosis.

Step-by-Step Solution:

Verification / Alternative check:
Public health and dental hygiene sources describe dental fluorosis as a visible marker of excessive fluoride exposure. They often include photographs of mottled teeth from high fluoride regions and explain that the underlying water contains fluoride above recommended limits. These texts emphasise that while fluoride is beneficial at low concentrations, excessive levels cause enamel defects. Chlorine, nitrate, and calcium are discussed in other contexts, such as disinfection, blue baby syndrome, and water hardness, with different symptoms. This confirms that the correct answer points to high fluoride levels in drinking water.

Why Other Options Are Wrong:

High levels of chlorine in drinking water is incorrect because chlorine is primarily a disinfectant and is not typically linked to mottled enamel.

High levels of nitrate in the water supply is wrong because nitrates are more associated with health problems such as blue baby syndrome, not with enamel discoloration.

High levels of calcium in the water, making it hard, is incorrect because hardness causes scale deposits and soap inefficiency but not the characteristic mottling of enamel described.

Common Pitfalls:
Students may confuse fluoride, chloride, and chlorine due to similar sounding names. Another mistake is to assume that any excess mineral in water will produce similar visible symptoms in teeth. In reality, dental fluorosis is specifically tied to fluoride exposure during tooth formation. Remember this clear link: mottled enamel and brown stains on teeth strongly suggest excess fluoride in drinking water over a long period, especially in childhood.

Final Answer:
Mottling of dental enamel is most commonly caused by High levels of fluorides in the water over a long period.