This is the ValueSet that contains all the codes in Dental Observation Codes (http://hl7.org/fhir/us/dental-data-exchange/ValueSet/dental-observation-codes) and Dental Observation Codes (http://hl7.org/fhir/us/dental-data-exchange/ValueSet/dental-observation-codes). E.g. what you have to deal with if you get resources containing codes in either of them