Final answer:
The statement that fluoride is not a naturally occurring mineral is false. Fluoride is indeed a naturally occurring mineral found in the earth's crust and in water at varying levels, contributing to dental health when present in appropriate amounts. Overexposure, however, can lead to fluorosis, highlighting the need for regulated fluoride levels in water supplies.
Step-by-step explanation:
All of the statements about fluoride are true except for D. fluoride is not a naturally occurring mineral. Fluoride is a mineral that naturally occurs in the earth's crust and is released from rocks into the soil, water, and air. While fluorides are indeed safe and effective when used as recommended, and chronic overexposure can lead to dental fluorosis, and acute overdosing can result in poisoning or even death, fluoride is naturally found in various concentrations in drinking water around the world.
Excess fluoride can lead to skeletal fluorosis, where the joints stiffen and bones thicken, severely impacting mobility and negatively affecting the thyroid gland. This is why the US Environmental Protection Agency sets a maximum level of 4 ppm of fluoride in drinking water. In areas with high levels of natural fluoride in groundwater, both dental and skeletal fluorosis can be a problem.
It's important to note that fluoride plays a critical role in preventing tooth decay by reacting with hydroxylapatite in teeth to form a less soluble and more acid-resistant substance. Community water fluoridation is a cost-effective method to deliver fluoride and reduce tooth decay significantly among all age groups.