Answer
(Fatwa: 335/243/L=1431)
For the safety of teeth, it is lawful to use crown and get it plastered with artificial cover if necessary. As far as the matter of wadhu (ablution) is concerned, if crown can be separated from teeth then wudhu and ghusl should be done by taking off the crown and if ghusl was done without taking off the crown and water could not reach up to teeth due to the crown, ghusl will not be valid. And if the teeth are plastered with artificial cover such as they have become the part of teeth, there is no need to take it out at the time of wudhu and ghusl if water is passes over it, the wadhu and ghusl would be complete and valid.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband