Question: When replacing a crown due to a cavity underneath, why would the dentist cauterize the gum area around the tooth?

Answer: 

Thanks for your enquiry.  Most likely you had decay underneath the old crown and a lot of time this extends down along the root surface of the tooth and below the gum line.  In order for the dentist to access and remove the decay, the gum tissue needs to be removed.  In  our office we use a laser to accomplish this.  This procedure will ensure that we will get a decay free margin for the crown and it will help get a good impression of the prepared tooth to send to the dental laboratory.
Thanks,
Dale J. Brant, DDS
Charles Campbell, DDS
713.795.5905
888.790.0309