What makes a Stable Bite?

First requirement of a Balanced Occlusion:

A stable bite begins at the Temporo-mandiblular joints, or TMJ’s. Ideally, each end of your lower jaw seats all the way into its socket under the base of the skull, just in front of your ears. Dentists refer to this position as “Centric Relation”. As you will learn, a stable occlusion requires that your jaw should never need to slide out of the socket (out of Centric Relation) to allow your teeth to fit together. There are three strong muscles on each side that lift your jaw up when you chew. They also function to hold the jaw seated firmly in the socket as your teeth come together. In an ideal situation, the joint will stay in Centric Relation as all your teeth contact at the exact same time, spreading the force of your bite evenly between them. However, if a single tooth touches before the rest, your jaw will automatically, and without your knowledge, shift to find the most even bite it can. This reflex has evolved to help prevent you from breaking that one and only tooth that touches when you close. This functional shift away from a stable joint position can initiate the long term problems of Occlusal Disease. In order for your jaw to move out of Centric Relation, one of the small positioning muscles (there is one at each joint) must fight against the powerful closing muscles to pull the joint away from its resting place deep in the socket. This tug-of-war between the muscles is the primary trigger for clenching and grinding. Since the muscles never have the chance to relax, eventually the weakest part of the system can break down. This is when the signs and symptoms of Occlusal Disease start to appear.

Second requirement of occlusion:

The only time your back teeth should be able to touch is when you bite straight down with the joints fully seated in Centric Relation. This point is critical for a healthy, functional occlusion. In order to slide your jaw to the right, the positioning muscle on the left must pull its joint forward. Sliding to the left requires the opposite movement, and sliding forward means both positioning muscles are working in concert. In a perfected occlusion, when you shift your jaw left, right, or forward (or anywhere in between), your front teeth protect those in the back by acting as a ramp that separates your upper and lower teeth, keeping your molars and bicuspids from hitting at an off-angle. This is accomplished by a slight overlap of your front teeth. As your jaw slides away from Centric Relation, the lower front teeth glide down the back of the uppers, effectively opening your mouth slightly. In a perfect bite, there is no way to rub your back teeth together. Without this protection, you are much more likely to cause damage from clenching and grinding your teeth. Think of chewing forces like hammering a nail. If you hit a nail straight down its long axis, it can take a tremendous amount of pressure. However, if you hit it on an angle, you are likely to bend the nail or split the wood. The same thing happens when you grind your back teeth, directing forces away from the long axis of the teeth. To make matters worse, studies have proven that when back teeth can touch, your brain tells the clenching muscles they can squeeze at full strength. This is fine when all the teeth are touching evenly and the force is directed down the long axis of each tooth, but not when you are shifting your jaw away from Centric Relation. At these moments, anything that gets in the way (including teeth and restorations) is at risk. This is the reason we see so much wear and broken porcelain on teeth, crowns and veneers on patients with unstable occlusions. When muscles and teeth go to war, muscles always win, even to their own detriment. Occlusal interferences like these are the number one cause of muscular headaches, facial pain, and TMJ disorders. When back teeth can rub, muscles are ready for war. However, if we start with the joints seated fully in their sockets and all the teeth touching, the moment you shift away from the full closed bite, the lower front teeth immediately ride down the back of the uppers, and the back teeth come apart. This protects the back teeth, and allows the muscles to relax. This is the secret to a stable, healthy occlusion.