Find another dentist--ANY dentist who will tell you that the life of a tooth will not be shortened when they drill/cut/sand/shape it is flat lying.
Fact is, any object touching another object has a "micro gap"--be it a brick wall, or a mouth full of teeth.
You don't need a bridge that outlasts you & everything else in your mouth. You need a solution that will allow you to both bite normally enough to eat like a regular person, and something you feel is physically acceptible.
You just learned there is no such thing as a permanent root canal--meaning they do not last--nothing in the mouth environment lasts forever-bridges can break, so can filling, implants, regular teeth, dentures, veneers--it is a harsh and volatile environment.
Think about what goes on in your mouth, just for a moment...chewing, smashing, crunching, grinding, pressure exerted from the jaw...then the beginning stages of digestion-enzymes & bacteria that are doing their job--their job is to break down the stuff you are eating.
RUN from that dentist--he is trying to sell you unnecessary & ridiculous things & using scare tactics.
If you want some honest answers where someone isn't trying to sell you their treatment--go to a dental school & get an appointment and ask questions about your options--THEY LOVE QUESTIONS--there are plenty of dentists there teaching their students several methods--Dental schools offer great discounts & are supervised by the dentists teaching them--they're not making $$ from you-and you can get several opinions & options all in 1 place.
If you want some ideas from outside of the dental community, find some OLD OLD people who still have their own teeth--ask them what type of dental procedures they've had--and how long they lasted.