By counting the number of decayed, missing and filled teeth, it is possible to assess the extent of caries in a population. If the DMFT s (s surfaces decayed or filled) is counted, the technique becomes even more specific. (Scores of 1-5 are used For example, a dentist and a nurse survey a class of schoolchildren and record decayed, missing and filled teeth. For children, a def(t) or def(s) index is used, where the 'e' stands for extracted deciduous teeth, rather than those that are exfoliated (fall out) naturally. A filled tooth scores 1. If they count the surfaces filled (e.g. a three-surface filling), the score for that tooth becomes 3. A tooth extracted because of caries scores 5 (five surfaces are missing)