Tooth structure in three layers : Upper layer is protective layer and decay in this layer no sensation found but decay only visible- it is enamel If caries penetrate this layer then cold sensation feel but no pain and no hot sensation- it is dentine layer Above both layer restore with filling. But caries penetrate dentine layer you feel hot sensation and pain, in this penetration  nerves and vessels are exposed, in this condition root canal treatment is only solution. Filling is two types on the basis of location like front/ anterior teeth, in this type of filling aesthetic restoration which are time taking so it's charges much higher in compare of back/ posterior tooth. Charges of filling always depends upon filling material, clinic location and experience of dentist.