Which chemical can cause mottling of teeth at excess concentrations?

Fluoride is known to cause mottling of teeth when present in excess concentrations. This condition, referred to as dental fluorosis, occurs during the development of teeth when children consume too much fluoride. The excess fluoride affects the enamel of the teeth, resulting in discoloration that appears as white spots or streaks, and in more severe cases, brown stains or a pitted appearance can develop.

This phenomenon underscores the importance of monitoring fluoride levels in drinking water and dental products. Appropriate fluoride concentrations can help prevent tooth decay; however, it becomes detrimental when children ingest fluoride from multiple sources, leading to excessive accumulation.

The other choices, while they may pose health risks or have other effects, do not contribute to dental mottling in the way fluoride does. Chlorine is commonly used for disinfection in water treatment but does not have a known relationship with dental discoloration. Ammonia is primarily associated with water quality issues, particularly toxicity to aquatic life, and hardness refers to the concentration of minerals in water, which generally relates to scaling rather than dental health effects.