I just had dentals done on two of my pups...one is 12 and the other 13. They did lose teeth....both always do each year, so it was not unexpected. They both had abscesses, neither of which was know about prior to the dental. The reason they were caught? Because my vet does dental xrays which is VERY important for vets to do! Many do the dentals without, but the best practice is to do the xrays. There is absolutely no way for a vet to know what is going on under the gum line unless they are done.
Unless a dog is terribly ill and not likely to survive another year, I do them because the risk of the infection is worse than the risk of anesthetic issues. If a vet is following recommended protocols, there is no real reason to fear anesthesia. And when I say recommended protocols I am not just referring to the type of anesthesia, I am referring to the proper amount of people in the room during the dental. There should always be a person sitting and doing nothing but monitoring vital signs during the procedure.
Here are some helpful links:
https://www.avdc.org/ownersinfo.html American College of Veterinary Anesthesia and Analgesia
As to proper protocol here is a link I use as a baseline to check out vets. I personally only use vets who have AAHA accreditation. When they inspect a vet clinic they look for things like what I mentioned above about proper monitoring of pets during anesthesia.
https://www.aaha.org/default.aspx