Which toothpaste ingredient produces its caries-preventive effect primarily by decreasing calcium phosphate dissolution at the tooth surface?

Correct answer: D. Fluoride

• A. Chlorhexidine is an antiseptic with broad-spectrum antimicrobial activity; it reduces cariogenic bacteria but does not primarily affect calcium phosphate dissolution.
• B. Xylitol reduces cariogenic bacteria (particularly Streptococcus mutans cannot metabolize xylitol) and promotes salivary flow, but its primary mechanism is not reducing calcium phosphate dissolution.
• C. Triclosan is an antibacterial agent targeting plaque bacteria; its primary action is antimicrobial, not reducing mineral dissolution.
• D. Correct. Fluoride prevents caries by inhibiting demineralization (reducing calcium phosphate dissolution from enamel) and promoting remineralization. It also converts hydroxyapatite to the more acid-resistant fluorapatite.