Gum disease is caused by plaque accumilating around your teeth. If it isnt removed by brushing and flossing it can irritate your gums and cause them to become swollen and inflammed.
You may notice you gums bleed very easily. This is known as gingivitis and may be reversed by thorough cleaning. If the plaque is left around your teeth it may cause the gum to come away from your teeth to create "pockets". The plaque can accumilate in these pockets and become very difficult to removed thus making the situation worse.
Over time the bone around your tooth may be broken down and lead ultimately to you needing your tooth extracted. This is known as periodontal disease.
Certain people are particularly at risk of periodontal disease. These include people that smoke and people with diabetes. These each make the problem worse. Once you have periodontal disease there is no way to reverse the effects.
With excellent oral hygiene it is possible to stop the condition getting worse however.
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