Periodontal disease is diagnosed by your dentist during a periodontal examination. This type of exam should always be part of your regular dental check-up.

A periodontal probe (small dental instrument) is gently used to measure the sulcus (pocket or space) between the tooth and the gums. The depth of a healthy sulcus measures three millimeters or less and does not bleed.

The periodontal probe helps indicate if pockets are deeper than three millimeters. As periodontal disease progresses, the pockets usually get deeper.
Your dentist or hygienist will use pocket depths, amount of bleeding, inflammation, tooth mobility, etc., to make a diagnosis that will fall into a category below:

Gingivitis

Gingivitis is the first stage of periodontal disease. Plaque and its toxin by-products irritate the gums, making them tender, inflamed, and likely to bleed.
Periodontitis

Plaque hardens into calculus (tartar). As calculus and plaque continue to build up, the gums begin to recede from the teeth. Deeper pockets form between the gums and teeth and become filled with bacteria and pus. The gums become very irritated, inflamed, and bleed easily. Slight to moderate bone loss may be present.

Advanced Periodontitis

The teeth lose more support as the gums, bone, and periodontal ligament continue to be destroyed. Unless treated, the affected teeth will become very loose and may be lost. Generalized moderate to severe bone loss may be present.

Treatment of gum disease:

If gum disease is caught early and hasn’t damaged the structures below the gum line, a professional cleaning should do. If the pockets between your gums and teeth are too deep, however, scaling and root planing may be needed.

A July 2015 study in the Journal of the American Dental Association finds that scaling and root planing is beneficial to patients with chronic periodontitis (gum disease that has advanced past gingivitis). Chronic periodontitis affects 47.2% of adults over 30 in the United States.

Scaling and root planing:

This deep cleaning has two parts. Scaling is when your dentist removes all the plaque and tartar (hardened plaque) above and below the gumline, making sure to clean all the way down to the bottom of the pocket. Your dentist will then begin root planing, smoothing out your teeth roots to help your gums reattach to your teeth. Scaling and root planing may take more than one visit to complete and may require a local anesthetic.