Simply put, this is how the teeth fit together. It is the pressure points the opposing teeth put on each other. It is also how the teeth interact when in function.
The jaw joints (the TMJ’s), are intimately related with this. These ball joints usually sit loosely in a shallow depression in the base of the skull just in front of the ears. Loosely means they are not locked in like an elbow joint is. When the jaws open they can move like a hinge. They can also slide forward. They can also rotate (or “orbit”) as we move our jaws sideways. But the way the teeth maximally mesh will normally dictate where the joints position themselves in relation to the base of the skull. Normally the upper jaw is slightly wider than the lower jaw so the upper teeth overlap the lower teeth. Having them sit further out helps prevent the cheeks from being bitten when the teeth close. Normally when we chew food we do not quite close our teeth all the way together. Normally our teeth only really touch the opposing teeth for 15 – 30 minutes a day – hard to believe.
Normal side view of teeth – Class 1 jaws. Front teeth overlap while back teeth are meshed. Note in this picture the upper and lower jaws are well related to each other. If they are moved too far forward or back the teeth do not fit together. Class 2: the lower jaw is too short – Homer Simpson. Class 3 the lower jaw juts too far forward for the upper - Popeye. Correction for this may involve orthodontics and even oral surgery in order to move the jaws into a better relationship so the teeth can mesh properly.
A good relationship between the upper and lower jaws has it so when we grind sideways (lateral excursion) with our teeth staying in contact, our canine teeth hit immediately and the lower canine slides up the inner ramp of the upper canine and the back teeth are disengaged from each other as this sliding movement against the canines opens them apart.
This is called canine guidance or canine protected rise. If we slide our lower jaw directly forward (protrusion) the lower front teeth should immediately hit the sloping inner back of the upper front teeth and the back teeth again disengage. This is called anterior guidance. When these are working properly the muscles of the face relax. If the canines and front teeth are worn down from intense grinding over the years then all the back teeth stay engaged during all the mouth movements and start getting worn and flattened. When this situation exists, there is all kinds of electrical activity in the muscles of the face. This can have serious long-term consequences.
Theoretically teeth should fit together a certain ideal way. But, most people DO NOT have a “perfect bite.” But humans are great adapters. We make things work in spite of problems. But sometimes the brain decides it does not want to accommodate a non-perfect bite any longer. During the day this is not usually an issue as we are conscious and aware of what our teeth are doing. But at night, the unconscious brain takes over, and it starts trying to find a place where the teeth fit together in a better way. This can be even worse for people that decide to take out their stress on their teeth. A nightly pattern of grinding can become established. The teeth can be clenched and ground across each other for hours at a time during the sleep cycles. This causes overworking of the muscles of the head and neck and the person, especially women, can wake up with some or all of the following Occlusal symptoms, due to excess lactic acid build up:
- Sore face and neck muscles
- Sinus fullness or pain
- Ear pain, full feeling, hearing like they are underwater, tinnitus (ringing)
- Wearing down of the teeth - especially in Men but not exclusively, includes. This is especially bad as it is destructive.
Treatment depends on the extent of the damage and the jaw relationships. The first option is to fabricate a bruxing or night guard (also called a splint).
This leaves the teeth alone and keeps the jaw joints apart at night. It is made so the opposing teeth all hit at the same time against the splint with even pressure distribution combined with a small gentle ramp at the front to simulate anterior guidance with the front teeth and canines. Many people are fine with this. For people with jaws that do not line up this is the only treatment a general dentist can offer in their office. They avoid orthodontics and possible jaw surgery – note the specialists will never guarantee that their treatment will cure clenching/grinding problems although in my experience they usually are cured. With a splint the teeth are not modified. But then the person is stuck wearing this appliance every night. If that becomes unacceptable/intolerable then the only option is a referral to an orthodontist.
The second option for those people we can treat (Class 1 jaws) is to make the teeth fit together in a more harmonious way when normally biting and when sliding around against each other.
We have the person bite on a marking paper that shows where the teeth hit. We will then selectively skim off very tiny bits of enamel in order to make the teeth mesh better together and spread the load out evenly over all the back teeth. The front teeth we like to have just barely out of the bite or minimally touching. We try to get the front teeth only hitting during a forward or sideways slide – anterior guidance. This is called “Occlusal Equilibration” or a “bite harmonization”.
With worn teeth we have to add to the cuspids and anteriors in order to recreate this protected guidance. The first try/test is so simply add composite resin to them. The thought is to make the back teeth fit together better by doing an Equilibration so the person’s unconscious brain does not have to look for a better place for the teeth to mesh during sleep. Then with the add-on to the front teeth, the back teeth will be protected when the jaws do slide. But if this material does not stand up for very long because the person continues to grind – usually because there is a mental stress component the brain has or it is just an unconscious sleep habit that does not want to be broken then further decisions have to be made and these will depend on the extent of the wear.
Sometimes the teeth are so shortened we need to add to them all. This is a complex process. In our office we will usually build them up with composite resin and re-establish anterior guidance with the white build-up material. Ideally all the teeth would then be crowned /capped. But this is very expensive and most people cannot afford to do this immediately. In order to accommodate the finances we try to do two or more opposing crowns per year in order to stabilize our regained bite.