Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain as you have a deeply decayed tooth with almost complete loss of the crown of tooth there has been infection in the area below the root tips of the tooth due to through and through communication of the inside of tooth with the mouth which has led to bacteria reaching below the rot tips causing pus formation and the condition is known as
DENTAL ABSCESS..
At times the pus and infection perforates the bone and accumulates in the soft tissues leading to swelling and in your case there is formation f a draining
sinus over the gums...
The best treatment for this kind of condition is Extraction of the tooth followed by a
prosthesis like Implant or Bridge..
As of now you need not to go to ER and just start taking broad spectrum antibiotic like
Augmentin 625 mg three times a day [only if not allergic to penicillin group],
Ibuprofen 400mg thrice daily for pain,and
Pantoprazole 40mg every morning once empty stomach..
Take for three days and by then consult your
dentist and get the treatment done..
Hope this information helps..
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Thanks and regards..
Dr.Honey Nandwani Arora..