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.
Eventually, it can form a hard mass, called a dental calculus.
Dental calculus creates a nice space for bacterial plaque formation, because it’s hard to remove,
and from there bacteria can enter the gingival sulcus and cause gingival inflammation, or
gingivitis.
Damaged gingival cells release inflammatory signals that recruit neutrophils to the area,
and those neutrophils can release harmful chemicals that kill bacteria, as well as damage
the nearby tissue.
Fortunately, simple gingivitis is a reversible condition, and the damaged tissue can heal
over time as long as the infection is stopped and treated.
In periodontitis, the process of dysbiosis is often more extreme - with even more disease-causing
bacteria flourishing in the mouth.
One classic hypothesis suggests that the first step in periodontitis is the presence of the
so-called orange-complex of bacteria, which includes gram-negative anaerobic bacteria
like Fusobacterium nucleatum and Prevotella intermedia.
Once these orange-complex bacteria are established, the next step is the presence of the so-called
red-complex of bacteria, which includes Tannerella forsythia, Treponema denticola and, its most
notorious member, Porphyromonas gingivalis or P. gingivalis for short.
Another line of thinking suggests that rather than these red-complex bacteria being the
specific culprits, it’s the overall change in the bacterial community that these bacteria
trigger that tips the scale toward periodontitis.
Either way, the pathogenic bacteria within the subgingival dental plaque create a periodontal
pocket and damage gingival cells in the process.
Local mast cells and nerves release chemicals like histamine and substance P which cause
dilation of local blood vessels, resulting in swelling of the gingiva.
Damaged gingival cells release additional cytokines like interleukin-1, which brings
more immune cells to the area, like neutrophils and macrophages.
The body’s immune response causes even more damage to the gingiva and periodontal ligament,
ultimately loosening the tooth.
That one notorious bacterium P. gingivalis, is also known for impairing the immune cells
from effectively killing bacteria.
This helps other pathogenic bacteria to overgrow as well - kind of like a thief that destroys
the police station and allows other thieves to flourish in a city.
The immune response also delivers more blood flow to the damaged tissue, and that provides
nutrients for the bacteria.
Together, the bacteria and immune response end up in a positive-feedback loop where the
expanding infection causes an increased immune response, which doesn’t destroy the bacteria
but provides the bacteria with more fuel to grow.
The immune response also activate osteoclasts in the bone, which start to dissolve the bone
supporting the tooth, loosening it even more.
Symptoms of gingivitis typically include redness, swelling, and bleeding - especially after
brushing or flossing.
Some people though experience no symptoms, especially in the early stages of infection.
Severe disease that progresses to periodontitis can result in tooth loss.
Diagnosis of gingivitis and periodontitis are usually made by looking for swollen or
bleeding gums, probing of each gingival sulcus to determine how deep it is, and X-rays to
evaluate the bone level.
With inflammation and destruction, the sulcus becomes deeper as the periodontal pocket expands.
Treatment depends on how severe the infection is.
Daily brushing and flossing, and use of antimicrobial agents like mouthwashes, can help prevent
the formation of dental plaque, but in severe cases antibiotic and surgery might be needed.
All right, as a quick recap…
Gingivitis is caused by infection and inflammation of the gingiva that can grow to involve the
tooth supporting structures, which is called periodontitis.
When dental plaque builds up near the gumline, it can allow bacteria to invade toward the
root of the tooth.
Diagnosis is done via visual inspection, X-rays, and probing the gums, and treatment of severe
cases may include removal of the infected tissue, antibiotics, and surgery.