noun
decayed baby tooth; carious milk tooth
Refers specifically to a decayed or cavity-ridden baby tooth, often with a soft, crumbly texture likened to miso paste. Used in informal, often child-related contexts.
子供の味噌っ歯を早めに治療したほうがいい。
It's better to treat a child's decayed baby tooth early.
甘いものばかり食べていると味噌っ歯になりやすい。
If you eat only sweets, you're likely to get decayed baby teeth.
虫歯 is the general term for a cavity or decayed tooth, applicable to both baby and permanent teeth. 味噌っ歯 is a colloquial, somewhat dated term specifically for a decayed baby tooth with a soft, miso-like consistency.
Compound of 味噌 (miso, fermented soybean paste) + っ (epenthetic consonant) + 歯 (tooth). The name comes from the resemblance of a severely decayed baby tooth's soft, brownish texture to miso paste.