I think that you are asking how frequently a tooth that is to be used as a retainer for a fixed dental prosthesis or a tooth that requires a full veneer crown should have prophylactic root canal therapy prior to the prosthetic intervention. The question seems to be asking about risk reduction or risk modification.

Before asking a question like this the author of the question needs to identify a few factors.

One factor relates to the frequency with which a vital tooth becomes devital after crown preparation?  Unfortunately there is no one definitive answer to this question. It is very much based upon the preparation technique that was used, the original pulp of the tooth, the skill of the clinician performing the preparation and ultimately the type of restoration is being made for that individual tooth. Certainly a single tooth with a healthy pulp, no history of trauma but now needing to be restored with a full veneer crown that is required after biologic complications usually in the form of dental caries will be less likely to undergo necrosis of the pulp then wooded tooth that had had cusp of fracture secondary to trauma or a tooth that had been restored many times previously because of multiple caries and episodes of recurrent disease.

We don't see that many reports of a vital tooth becoming divital although we certainly do see these data from time to time. As you might expect given the number of disclaimers above the rate of hope necrosis has been described as low as 5% of the time and as high as 25% or more.

So if the first factor that you determine is the frequency with which it tooth loses vitality and you keep careful track of your own data in your own experience then you might say that in your hands this type of restoration experiences pulp necrosis of let's say 8%. So if you know which of those 8% of the teeth are going to experience necrosis you should indeed perform prophylactic root canal therapy. Of course there's no way that you would be able to predict those 8% with a high degree of accuracy. You might be able to create an algorithm that would be used to determine relative risk. A series of factors may be considered for each tooth with some teeth being at very high risk while other teeth are much lower risk. If you have no idea what the pulp necrosis rate is or the expectation that the pulp will necrosis at some point in the future it's awful difficult to answer the question regarding prophylactic root canal therapy.

The other thing to realize is that not every root canal treatment that is planned can be performed and remain successful indefinitely. Obviously you would never ask this question if you knew that the tooth was already devital.  so you're only considering root canal treatment on teeth that are in this question zone. If the tooth lacks pulp vitality or tooth has a periapical lesion or a tooth is symptomatic before intervention then those teeth require root canal therapy prior to restorative intervention because ignoring the infected tooth is certainly not a way to make the tooth somehow heal. That will not happen. Performing the root canal on such a tooth has a lower success rate following root canal treatment than a vital tooth would if it undergoes prophylactic root canal treatment.

Root canal treatment on teeth that have a vital pulp when done by someone with skills in root canal treatment, an endodontist, who thoroughly scrutinizes the tooth for accessory canals (using a microscope) succeed somewhere between 90 and 95% of the time. The problem with that number is that it probably does not count teeth that required root canal treatment but had nonnegotiable canals or fractures or some other complication that made the tooth not restorable. Those teeth that were otherwise nonrestorable should be counted as root canal failures because the intent is to perform the root canal treatment is a precursor to restorative care so the 5 to 10% failure rate of root canals when vital prophylactic root canal therapy is performed might be a few percent higher although once again in the hands of a skilled endodontist those numbers should be relatively low.

So here you have a situation where 5 to 10% of teeth being treated with root canal therapy will fail at sometime in the future meaning that the tooth will develop a peri-apical lesion at some time in the future. Add a couple additional percent to this number as teeth that could not be negotiated meaning that obscuration capacity was diminished because the canals could not be extirpated, debrided and obturated so now were taking this group of vital teeth that when treated for crown preparation would become necrotic at some time in the future somewhere between 5% of the time and 30% of the time and were doing a prophylactic procedure on those teeth to address this 5 to 30% risk with a treatment that is unsuccessful somewhere between five and 13% of the time in the hands of the highly skilled endodontist

I guess you could say that another algorithm could be developed to determine the riskiness of the type of restoration that is being performed. Certainly a single crown that is necessary because of erosion that occurs because of endogenous sources is that much less risk following tooth preparation and would be a tooth that a patient fractured when they landed on their face after a motorcycle accident.

This is a long preamble to an answer that I probably could've given in the first sentence and that answer is that there is not nearly enough information in the question to give an intelligent answer to the question. There are myriad of concerns that need to relate to the quality of the root canal treatment, the prosthetic demands of the treated tooth and a linking of the two.  these factors combine to create that algorithm. I doubt however that we have such high quality, well populated, logical duration and appropriately powered randomized controlled clinical trials that we could answer these questions with a high degree of certainty.

I second Steven E Eckert's response. It is very thorough.

https://munirgomaa.com

I would recommend you read the article in the J. PROS. DENT . 1985 BY MAUREN  ABDUL ROSS ON THE " THE STRESSED  PULP". THIS IS A VERY IMPORTANT ARTICLE ON ACCESSING WHEN TO CONSIDER ENDODONTIC TREATMENT

Ascertaining whether or not a tooth would become non-vital after preparing and placing an abutment crown in the future is not possible within 100% accuracy. In this case, the best we can do is inform the patient of the slight possibility. 

Dentists performed electric pulp test, cold test, hot test, drilling test combine with xray (apical radiolucency) and clinical sign and symptoms (pain to percussion and palpation) and the degree of damage (due to caries/ trauma/ erosion/ abrasion etc) to conclude whether the pulp is vital or not.

We never put crown or bridge or any fixed prosthesis of a non-vital tooth (i.e. pulpal death confirmed), however, there is a chance of "delay death" (due to deep caries, that the bacteria and toxin enter the dentinal tubules of thin dentine remained, long term cold and hot irritation, toxic nature of cement etc)  or wrong conclusion of the pulp vitality, patient did not tell the response of EPT correctly (e.g. when we apply the very mild electricity, we touch the tooth, the touch/ pressure of the tooth was perceived as sensitivity of the tooth by patient), therefore the tooth was found non-vital later, or the irreversible pulpitis was confirmed after the cementation.

Therefore, it is a good practice to check the vitality of the pulp before the tooth preparation and again before the cementation of the crown or bridge etc if not in same visit. Ask patients to sign that we make it according to the tests result. There is a chance of delay death, when it happens and is confirmed, we will drill through the crown/ inlay/ onlay etc to perform root canal treatment.       

If the tooth being taken for abutment of an FPD is confirmed to be vital and the expertise of the prosthodontist is adequate, there is no necessity to do a root canal treatment. If at a later date it becomes non vital, RCT can be done through the retainer. Also, as told by Jenkins, patient can be informed of the slight possibility of RCT at a later date

Totally endorse the view of MR Dhakshaini. None of the standard textbooks of fixed Prosthodontics written/edited by stalwarts like Shillinburgh, Rosensteil, Tylman, Dykema recommend prophylactic endodontic treatment of prospective abutments of fixed dental Prostheses. 

prophylatic endodontic treatment prior to crown or FDP preparation is not the right thing to do! as you already can read above the % of teeth that become non vital after prosthetics is low and is mentioned in several papers eg by dr I Sailer, dr B Pjeterson, etc....

in most of the cases an RCT is posible through the retainer.

in fact I think you do a lot of harm with prophylactic endodontics.

I agree with most of the answers here and want to adress that prophylactic endodontics is obsolete and probably can be considered as malpraxis. Following Steven Eckerts statement we can identify two risks:

1. The risk that an abudment tooth or crowned vital tooth is becomming non-vital. This risk is explained by Steven, and is depending from many factors. however, the consequence of a non-vital case presenting with apical problems or painfull pulpitis is an endodontic treatment and the tooth can be saved. Maybe the retention of the restoration is at risk, but then a new restoration can be made in most cases.

2.The risk for tooth and restoration failure on a non-vital tooth is increased compared to vital teeth. due to failing root-canal treatments, weakended tooth structure leading to vertical fractures etc. In our research based on longevity of teeth  and restorations on practice data from general practitioners as well as more controlled populations. the Hazard ratio for tooth failure and restoration failure can be twice as high for endodontically treated teeth as when vital teeth are involved. Maybe people can argue that endodontics on vital pulps are more succesful, but isn't that very strange considering the risk for a pulp becomming non-vital is limited and the risk for failure of an endodontically treated tooth is considerable? 

3. As dentists we have the obligation to preserve oral health for the patient, our purpose is not to do as much dentistry as possible in a mouth. Therefore, those considering making a crown on a vital tooth should also consider if a less invasive option including monitoring is probably biologically advantageous and more beneficial to patients. Especially in dental magazines I see so much unnecassary dentistry on still functional (but imperfect) restorations leading to invasive restorative therapy without the consideration what the risk of such a treatment is.

Let's put it like this (as I say often to my students): more dentistry, more trouble....