What is the primary mechanism associated with the role of fluoride in prevention of dental caries? ?

I believe the answer is

Fluoride becomes incorporated into the crystalline structure of teeth, making them less susceptible to decay

Applying fluoride systematically or locally could help prevent the decay of teeth. Fluoride could make a crystal structure that envelop the outer layer of the teeth and protect it. It could also help against acid attack if the process keep going for a long time and make fluorapatite coating.

the electromagnetic energy from the sun arrives in the form of visible and invisible light.