When you go to Dental Office with pain or decayed tooth, Dentist takes x ray to check depth of decay. Treatment of that tooth depends on depth of decay. Let's see structure of Tooth first. Structure of tooth- To know more about Dental Filling & Root Canal Treatment Click here Enamel - It is outermost layer of tooth. It is hard covering of tooth. Dentin- It lies inside the enamel. It is softer than enamel. Pulp - It is innermost layer. It contains blood vessels and nerves. Now let's see what would be the treatment if the decay lies in Enamel, decay lies in Dentin and decay lies in pulp. Decay lies in Enamel- if decay lies in enamel then treatment would be just Dental Filling or Restoration. Decay lies in Dentin- if decay lies in Dentin then treatment would be Dental Filling or Restoration. Decay involves Pulp-If decay involves pulp then treatment would be Root Canal Treatment.