某老年人牙龈退缩的牙面中未患龋牙面有40个,患根面龋的牙面10个,因根龋充填的牙面10个。该老年人根龋指数为()
A:20%
B:25%
C:33%
D:37%
E:40%
出自:口腔执业医师