Gingivitis and periodontitis

With gingivitis, gingiva refers to the gums, and -itis refers to inflammation, so gingivitis is inflammation of the gums.

With periodontitis, peri- means around, and odon-, refers to the tooth, so it’s inflammation and destruction of the supporting structures around the teeth.

Broadly speaking, the two are on a spectrum starting with simple gingivitis on one end, and if the process doesn’t get treated, it can develop into more severe disease - periodontitis, which is on the other end of the spectrum.

Let's start by building a model of a tooth and its surrounding structures.

In the mouth, the bone beneath the bottom row of teeth is the mandible, and the bone above the top row of teeth is the maxilla.

Both bones have an alveolus, or socket, for each tooth.

The socket is lined on the inside by a periodontal ligament.

Protecting the alveolus on the outside, is a layer of soft, supportive tissue called the gingiva, or gums, that sits on top of the bone.

The tooth itself can be roughly divided into two parts.

The first part is the root, and it sits within the alveolus.

The root is covered by a bonelike substance called cementum, and that’s what the periodontal ligament’s fibers attach to.

Next, there’s a short zone called the neck, which is the transition between the root and the crown.

The crown is the visible part of the tooth that protrudes from the gingiva, and it’s covered in enamel.

Enamel has such a high mineral content that it’s the hardest substance in the human body.

The portion of gingiva that sticks up and is not anchored to the tooth is sometimes called the free gingiva, and the space between the free gingiva and the crown is called the gingival crevice or gingival sulcus.

A watery substance called gingival crevicular fluid flows into this space in small amounts.

Gingival crevicular fluid contains various immune proteins and cells like neutrophils, complement proteins, and antibodies.

Within the mouth there are a number of bacterial organisms.

In a healthy mouth, there is a balance of commensal bacteria that compete with each other, and they are all kept in check by immune factors in the mouth.

Gingivitis and periodontitis represent a state of imbalance or dysbiosis.

This is when there’s a relative increase in pathogenic bacteria either because of a lack of competition with other commensal bacteria or because of an ineffective immune response in the mouth.

The pathogenic bacteria form dental plaque which is a sticky collection of bacteria, proteins from saliva, and dead cells from the lining of the mouth.

Individual bacteria multiply and form many small microcolonies that coalesce, creating a layer of dental plaque - which is a type of biofilm.

Compared to a microcolony, the bacteria in a biofilm communicate with each other via chemical signaling and together they create a complex system where some bacteria work on tunneling between the microcolonies and to the surface in order to bring in a steady supply of food.

As an analogy, if bacteria were ants, then a microcolony would be a tiny group of ants, each doing it’s own thing, whereas a biofilm would be an ant farm with complex tunnels and rooms, and each ant carrying out a specialized task.

Some tooth surfaces like the portion of the tooth just outside the gingiva are hard to brush dental plaque away from.

If dental plaque above the gingiva keeps building, the bacteria within that biofilm can invade beneath the gingiva where it becomes very difficult to reach with brushing.