Denshi Jisho — Online Japanese dictionary

虫歯 むしば cavity; tooth decay; decayed tooth; caries
Common word, Noun, No-adjective 

You can also

Look up kanji details for 虫歯.

Try a Yahoo Jisho search for 虫歯 .
Try a Goo Jisho search for 虫歯 .
Try a Google search for 虫歯 .