Final answer:
Fluoride in plaque converts hydroxyapatite to fluorapatite, creating a more acid-resistant enamel and exerting a bacteriostatic effect that slows the progression of tooth decay.
Step-by-step explanation:
Fluoride present in plaque biofilm plays a crucial role in oral health by combating tooth decay. When toothpaste containing fluoride is used, the fluoride becomes incorporated into the hydroxyapatite of tooth enamel, transforming it into fluorapatite, Ca₅(PO₄)₃F. This compound is more resistant to acid attacks and less soluble than hydroxyapatite, hence providing stronger enamel protection. The presence of fluoride in the plaque also has a bacteriostatic effect, meaning it inhibits the growth of bacteria such as Streptococcus mutans, which are known to produce acids that contribute to tooth decay. Further, fluoride enhances the remineralization of the enamel by promoting the uptake of calcium and phosphate ions.