endodontist vs tooth doctor

endodontist and tooth doctor both are nouns.

Word	Noun	Adjective	Verb	Adverb
endodontist	Yes	No	No	No
tooth doctor	Yes	No	No	No

As nouns, tooth doctor is a hypernym of endodontist; that is, tooth doctor is a word with a broader meaning than endodontist:

endodontist: a dentist specializing in diseases of the dental pulp and nerve
tooth doctor: a person qualified to practice dentistry

Other hypernyms of endodontist include dental practitioner, dentist.

endodontist (noun)	tooth doctor (noun)
a dentist specializing in diseases of the dental pulp and nerve	a person qualified to practice dentistry