The Periodontal Ligament
The last dental related structure which we will present is the periodontal ligament. But unlike most ligaments in the body, this connective tissue does more than just attach the tooth to your bone.
By all means, a primary purpose of the periodontal ligament was to provide the network of connective tissue fibers that connect the boney socket to the cementum on the root surface. It also acts as a cushion, a shock absorber of sorts to protect the tooth and the jaw bone from the trauma of chewing. As you will find out when you read about "TMJ/Facial Pain" in that section of this website, the periodontal ligament also provides the important bio-feedback to the brain whenever your teeth touch anything. Lastly, the periodontal ligament provides the nourishment and cells to maintain and repair damage to these important nerves, connective tissue fibers, the cementum, and even the bone itself.
Properties of the Periodontal Ligament
The periodontal ligament space is very small, about 0.2mm in width on average. As everything else in the design of your body, this is for a reason. If the space was any wider, the teeth would be too mobile and wiggle when you chew. If it was any smaller, there would not be enough of a cushion to protect your teeth when you chew.
Inside this space, there is a vast array of fibers that go from the bone on one side to the cementum on the other side. They hold the tooth in the jaw. The same blood vessels that provide nourishment to the pulp supply nutrients to the ligament as well. Similarly, the nerves that provide sensation to the dentinal tubules are the same nerves that provide the feeling of touch to the ligament. They tell the brain when your teeth come into contact with anything.
They have shown that if you touch a tooth with a feather, the brain will register that contact.
An important aspect of the periodontal ligament is the presence of cells that can repair, regenerate, or even destroy the tissues related to this important dental structure. Osteoblasts which make bone, osteoclasts which destroy bone; Cementoblasts and cementoclasts which make and destroy cementum; fibroblasts which make collagen fibers are just a few of these important cells.
Rather than provide all these cells at the same time, the body provides stem cells which can turn into any one of these cells depending on the proper stimulation. The periodontal ligament like the pulp is very rich in stem cells. In fact extracted teeth have become an important source in stem cell research, reducing the reliance on fetal tissue.
How the Periodontal Ligament Helps When Moving Teeth
An example of this stem cell activity happens when you go to the orthodontist and teeth are moved around. As it turns out, when the periodontal ligament is "pulled" stem cells turn into osteoblasts and bone can be created. When the periodontal ligament is "pushed" or "pressed together" the stem cells turn into osteoclasts and destroy neighboring bone.
Now, imagine a tooth being pushing in one direction. The ligament in front of the pushing force eats away at the bone in its path, while the ligament behind the tooth is being pulled and stretched, stimulating the formation of bone in the tooths wake. This makes room for the tooths arrival in its new position, while repairing the boney socket where the tooth used to be.
When Periodontal Ligaments Can Cause Damage
On a final note, if the ligament is stimulated in a certain way, these stem cells can get out of control. Imagine the osteoclasts eating away bone, without the osteoblasts to repair the bone at the same time. Or imagine cementoclasts eating away at the cementum without the opposite repair going on at the same time. Similarly, imagine an osteoblast making too much bone without the balance of its opposing cell being present.
These bizarre actions of this important organ can create some irreparable damage in the process. Roots can become resorbed and dissolved by the clastic cells without the benefit of the blastic cell repair. Bone can take over the ligament and calcify it causing a direct boney connection of the root to the socket. Cementum can be stimulated to form excessive layers, creating a large "blob" of tooth at the end of the root. Look at the images below, see which one fits the description I just gave you.