Can extreme sinusitis have anything to do with periodontal disease?

There is a connection between your dental health and your sinuses. The big molars you have towards the back of your mouth have roots so deep, dentists sometimes accidentally open a hole to their patients' sinuses when they extract them. If the roots of one of these teeth is infected, it most certainly can infect your sinuses in turn. Periodontal disease is different, though. It is disease of the gums, and not of the teeth's roots. In any case, have your dentist take some x-rays if you think your dental and sinus problems are connected.

I would say no. Sinus could however still cause bad breath.

yes.... go to a doctor....

Very likely since all that stuff is in the same area and your whole body is connected. If you are suffering from this see your doctor and dentist.

HELLO,
SINUSITIS CAN DEFINITELY CAUSE DENTAL PAIN IN UPPER TEETH. THERE CAN ALSO BE PAIN FROM PERIODONTAL DISEASE, BUT THE TWO ARE NOT RELATED TO EACH OTHER AS A REASON FOR EXISTING.

Your sinuses are located directly above your mouth. In some cases there can be a small leak from them into your gums. This would cause them to become inflamed and sometimes infected. an x-ray of the sinus cavities could probably detect any leakage.

Unlikely. Sinusitis is more of a danger to the BRAIN than the mouth, since there is a very short distance behind the sinuses to the brain. However periodontal disease is also a high risk factor for an infection of the heart called pericarditis, which requires 6 weeks of IV antibiotics to treat, because the veins from the head drain directly to the vessels which enter the top of the heart's right side.
First, start working on those gums-brush and floss at least twice a day followed by a low alcohol mouthwash used as directed. See a dentist for evaluation and further treatment.
Second-see an ear, nose and throat specialist for the sinusitis. Treatment can range from antibiotics to surgical drainage/repair of damaged structures.
Third, don't fool around with this. The nose is the first line of defense for airborne infections such as TB, anthrax, MRSA, memingitis, etc. Even people who have had their tonsils removed still have some immune tissue in place at the back of the throat. There is no magic 'ju-ju' in herbs, etc. that will be an effective substitute for the modern medicine that I have described.

Periodontal disease is when the bone that holds the root in, for your teeth is breaking down, it has allot to do with brushing and flossing and having your teeth cleaned. Plaque gets under your gums and starts to break down that bone, its over time. Its more your own health regiment for brushing then your sinuses.