Hello , my name isXXXXX and I will try my best to provide you with the answer to your question.
Well, there are cracks and there are cracks!1 No two are alike so depending on the degree and angle and whether there is pulpal involvement will dictate the eventual treatment.
For example. the tooth that was cracked and had a crown put on , may have just had a cusp
crack and or a hairline crack that has been able to be held together adequately with a crown.
The one that has had a root canal must have involved the pulp
. Once that happens, saliva is introduced into the pulp chamber and will eventually infect the tooth. A root canal is the only option.
With this latest racked tooth, you will need to have an x-ray and a bite test to see if there is pulp involvement. If you already have pain
or experience pain on biting, the pulp is involved and you will need a root canal most likely.
Diagnosing a cracked tooth, by the way, is very difficult as some don't even show on x-ray. If you can visualize the crack or chip yourself, it does not mean it is through and through.
I would advise you to get this tooth x-rayed and have your dentist
check it out. I cannot say for sure whether you need one treatment or the other as I have limited information from here.
I hope this helps. Please ask more if I can help further.