Gingivitis and periodontitis are the two major forms of periodontal disease. Gingivitis is inflammation of the gums (gingiva). It is the first stage of periodontal disease that may or may not progress to more severe forms.

Gingivitis can be divided in a number of ways. In general, the conditions may be classified based on the apparent underlying cause, including:

• Plaque induced. Caused by prolonged buildup of plaque on teeth and gums. This is typically caused by poor oral hygiene. Plaque, a sticky film composed mostly of bacteria that forms on teeth, must be removed daily through brushing and flossing. After two to three days, the plaque hardens or calcifies into tartar (calculus). This rock hard substance must be scraped off with dental instruments.
  
  
• Non-plaque induced. This category includes specific viral, fungal, mechanical or allergic causes. For instance, herpes simplex viruses can cause a painful gingivitis in which the gums turn bright red and there are white or yellow sores inside the mouth. The episodes typically subside in two weeks. Oral thrush (candidiasis) is a fungal infection that can cause gingivitis. A thin film coats the inside of the mouth and the gums bleed when wiped. It is treatable with anti-fungal medications. Poorly fitted dentures, an impacted tooth and similar mechanisms can cause pockets to form in the gums, which may lead to inflammation and infection. On rare occasions, allergies can cause the gums to become inflamed.
  
  
• Related to systemic factors. Gingivitis may be related to a body-wide condition or disease. A wide variety of systemic conditions can affect the development gingivitis, including pregnancy and menopause, which affect hormone levels. Fluctuating hormones can dilate blood vessels in the gums or, in the case of menopause, cause bone loss that can weaken the jaw bones supporting the teeth.
  
  Systemic diseases that can cause gingivitis include diabetes, HIV and leukemia. People with compromised immune systems (such as those infected with HIV) may battle opportunistic infection throughout their bodies, including the gums. Adults and children with cancer of the white blood cells (leukemia) experience gingivitis associated with red bleeding gums when leukemia cells invade the gums. Gingivitis may be one of the first signs of leukemia in many cases.
  
  
• Drug induced. Some medications can cause an overgrowth of gum tissue, making plaque removal more difficult. These include blood pressure and heart rhythm drugs, antiseizure medication and drugs taken to reduce organ rejection. Birth control pills can also cause gum irritation due to a change in hormonal balance.
  
  
• Malnutrition induced. Malnourishment can weaken the immune system so the body is less able to fight off infections, including gum disease. In addition, a rare vitamin C deficiency (scurvy) and niacin deficiency (pellagra) can cause inflamed, bleeding gums. This gingivitis usually clears up with a balanced diet.

A patient’s gingivitis may fall into more than one category. For instance, patients who take medications (or are experiencing menopause) and neglect their oral health increase their chances of developing gingivitis. This classification is more specific than the traditional classification system, which included pregnancy gingivitis, acute necrotizing ulcerative gingivitis (also called "trench mouth") and linear gingival erythema (also called "HIV gingivitis"). Acute necrotizing ulcerative gingivitis is more common in younger patients with poor oral hygiene.

In addition to these classifications, gingivitis may be described as diffuse (patchy), desquamative (peeling), suppurative (pus forming) and hemorrhagic (bleeding).

Periodontitis, the second type of periodontal disease, is inflammation and/or infection of the gums and the surrounding tissues and bones. It is the more severe stage of periodontal disease and typically includes permanent loss of the bone and/or tissue supporting the teeth. The beginning stage of periodontitis may have pockets of 3 to 5 millimeters (mm). The more severe forms can have pockets of 6 mm and up. The classifications of periodontitis include:

• Chronic (or slowly progressive) periodontitis. Occurs over time and can have periodic episodes of infection at one or multiple sites in the mouth. This is also called adult periodontitis. Bone and tissue is slowly lost as the bacterial infection persists.
  
  
• Aggressive (or early onset) periodontitis. Occurs in younger adults, usually before age 35. Hormonal changes in males and females at puberty can trigger gum inflammation that worsens with poor oral hygiene. It starts rapidly and advances quickly, ravaging bone and tissue. There can be periods where the destruction subsides or the condition improves only to be followed by another episode of rapid bone loss. This is also called localized periodontitis, rapid periodontitis or prepubertal periodontitis.
  
  
• Periodontitis caused or influenced by systemic disease. Affects patients with existing diseases such as leukemia, genetic disorders and other disorders where there are not enough white blood cells.
  
  
• Periodontitis associated with pupal infection. Abscesses (painful pockets of pus) in the gums or periodontal tissue caused by acute infection. This is also common in third molars (wisdom teeth) that become impacted.
  
  
• Necrotizing ulcerative periodontitis. Occurs when soft gum and connective tissue die because of uncontrolled infection. Those with compromised immune systems (e.g., HIV, AIDS) or who are malnourished typically have this form. There can be intense jaw pain and rapid destruction of the bone. Necrotic gums turn gray or black as harmful bacteria multiply at rapid rates.
  
  
• Developmental or acquired deformities. Lesions or fractures in the root or tooth or gum deformities causing inflammation and infection. This includes abnormal tooth positions or root fractures and infection around dental restorations and appliances such as implants (periimplantitis).