The most common cause of gum disease is poor oral hygiene. Other risk factors of gum disease are: smoking, crooked or crowded teeth, breathing through your mouth, food and drinks high in sugar and some medications.
Gum disease is usually pain-free a bit like high cholesterol and blood pressure. However, if left untreated it can lead to Periodontitis (a severe form of gum disease), which results in bone loss and can lead to pain and eventually loss of teeth.