蛀牙 (zhù yá): tooth decay; dental cavities; CL:顆|颗[ke1],個|个[ge4]

My little brother loves eating candy, so he already had several cavities by age six. The doctor said he should eat fewer sweets and brush his teeth carefully every day.

Yesterday I went to the dentist. After examining me, he told me I had a cavity that needed to be filled. Fortunately it was found early; otherwise it would have gotten worse.

My mom often reminds me that I must brush my teeth before bed; otherwise I'll easily get cavities, and when they hurt, it's really uncomfortable.