The process whose specific outcome is the formation of dentin, the mineralized tissue that constitutes the major bulk of teeth. Dentin may be one of three types: primary dentin, secondary dentin, and tertiary dentin. [ GOC:sl GOC:cjm http://www.ncbi.nlm.nih.gov/pubmed/10206335 http://www.ncbi.nlm.nih.gov/pubmed/21196346 ]