Yes, it is possible to have RCT without replacing the tooth with crown but it is advisable to have crown. The reason is that during RCT, the nerves from the root canal will be taken out due to which tooth becomes weak and brittle and won't be able to bear the masticatory stress. Gradually you will notice the tooth pieces coming out in pieces.
Crowning not only increases the shelf life of tooth but will also give RCT treated tooth natural appearance. If you are worrying about esthetics, than there is nothing to worry as crowns come in various shades which can exactly match the natural tooth.
Various things to be taken care after RCT are:
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