Tooth decay starts when cavity-causing bacteria like Streptococcus mutans and Lactobacillus feed on leftover carbs in your mouth. As they grow, they produce acid that breaks down the minerals in your teeth—a process called demineralization, which marks the start of a cavity. Poor brushing and high bacteria levels make decay more likely to develop and spread.

Worn or poorly-fitted fillings

Old or loose silver fillings, or misaligned teeth, can trap food and bacteria, speeding up tooth decay. Snacking on sweets or sipping sugary drinks throughout the day also raises your risk, especially if you don’t clean your teeth regularly.