Can a Tooth That's Been Prepared for a Crown Keep Getting a Crown on It?

Crowns can be remade on a tooth indefinitely as long as there is tooth structure to attatch them too.  They can last many years as long as you take care of your teeth and get your checkups.  One should always keep restorations to the minimum size so that when they need to be replaced that there is enough tooth to continue to use them.  Sounds like the 3/4 crowns were a way to be more conservative and save more of the teeth and that is good.  Always keep your restorations small.  There are so many ways to keep things small nowdays.  Talk to your dentist or find one that believes in minimally invasive dentistry.

Crowns are some of the longest lasting restorations but a number of factors are involved in terms of when they need to be replaced.  Each time a tooth is crowned more tooth structure is removed.  At some point enough tooth may not be there and you would probably be better off with an implant at that point . Considering you said that they were just placed hopefully you have many years before you even have to worry about it

You are 19. That is a bit young for getting crowns. It is not unheard of, but a bit too young, If you take good care of your restorations, and teeth, you do not have to routinely replace them. They can last for 20-30 years if they are made well and you take care of them by going to get them cleaned 3-4 months and  having a great hygiene. 

Fortunately, crowns are among the longest lasting restorations we have, and you may find some last up to 20-30 years.  Some, much less.

There are many factors to longevity of crowns, not limited to if a person clenches, grinds their teeth while they sleep, hygiene habits, periodontal condition, material of the crown, and so on.

Each time the tooth is worked on, some tooth structure is removed.  It is a good idea for the dentist to be as conservative as possible to allow future work if needed and to avoid the pulp/nerve.

At age 19, you are wise to be aware that these are not the last crowns these teeth will have, perhaps 2 or 3 more times.  It is good that they are only 3/4 crowns now, which will allow future work to be done.

Great question-Dentists try hard to do excellent work.  How you take care of your oral health will aid in the longetivity and maintenance of your dentistry.  You must have regular cleanings and check-up visits.  Brushing and flossing and overall good sense will help keep your smile healthy.  Watching your diet, eating healthy and not abusing the work you have is also important.  No chewing of ice or hard foods so you don't get chipping.  Consider wearing a bite protector as well.  Nothing lasts forever-everything will eventually need replacing-especially if you are blessed with long life.  BUT recurrent decay and other unexpected events can result in revisions.  Modern dentistry is always evolving and you never know what will be the state of the art when you need to redo your teeth.  Enjoy and be careful-

I think that the answer to your question depends on several factors.  Do you see a dentist regularly for cleanings and exams?   Is your hygiene excellent including flossing daily?  Do you have an ideal bite? Are you a grinder?  All of these things play a factor in the lifespan of a tooth after having a crown.  Typically, a crown can be replaced when the existing one breaks or gets recurrent decay.  Only if the problem has been present for a while before seeking treatment are you in jeopardy of losing the tooth and then needing an implant.  Hope this helps.