A Healthy Occlusion and the Occlusal Analysis
Understanding how to provide a physiologically and mechanically sound occlusion greatly serves the patient’s overall oral health needs, and is a necessary asset for the clinician. As difficult as it has been historically for the profession to understand occlusion, it is a disservice to the patient to ignore it altogether, as occlusal disease continues to destroy dentition and restorations young and old (Figure 13.1). Unfortunately, not only has occlusion been complicated to learn but it has also become one of the most controversial subjects in dentistry. There are many occlusal methods, ranging in complexity from an intricate gnathological approach, a myofunctional approach, or even an overly-simplified naturalbite approach. Each approach has its own following of clinicians, who interpret the literature to back their opinion. Owing to the intense controversy, a large sector of overwhelmed dentists is confused as to which is the correct path and often choose to limit their involvement to single-tooth bite adjustment after a procedure and may choose to avoid occlusal therapy altogether. The literature points to three important rules for a harmonious occlusion, which encompass many other considerations. I call them the three golden rules of occlusion (Box 13.1). These rules are simple to remember and are the scientifically based goals of occlusal therapy. When used, the rules will give the patient a sound bite and will make the process less intimidating for the dentist.
These rules become very important for diagnosis and therapy only when the patient has clear signs and symptoms of occlusal disease, demonstrating that they have not adapted well to their current bite, and corrections would be desirable (Figure 13.2a). Additionally, when extensive dentistry is being planned, or the bite will be altered due to the partial or full rehabilitation (Figure 13.2b). These three rules make for a mechanically and physiologically sound bite.
It is important to remember that many patients may not fulfill one or more of the golden rules and may not show signs and symptoms of occlusal disease. This would suggest that they are well adapted to their current bite and no treatment is necessary or advisable. The mandible and its musculature have dozens of different movements and intricate relationships which govern the way in which the masticatory system functions, and just as when using a computer it is not necessary to know its internal workings, also it is not necessary to memorize all jaw movements and relationships. Fulfilling the three golden rules of occlusion encompasses all elements, and greatly simplifies the approach.
Ideally, all teeth must touch at the same time when a patient is in occlusion, forming bilateral equal contacts (Figure 13.3).Humans, when biting, exert hundreds of pounds of force per square inch, and it only makes sense that equal contacts during occlusion will allow for the forces to be shared among all teeth . When one of the teeth interferes with equal contact, it can lead to severe damage to these teeth, as they will absorb excessive forces . Additionally, the literature shows that if a patient develops or receives an interference in their bite, they will develop transient muscle discoordination and other problems (Figure 13.4) [3,4]. When an interference to the centric bite exists, the patient may develop a deflective interference, which will cause a permanent deviation to the centric bite and lead to uneven destructive wear, similar to the uneven wear that occurs with an unbalanced tire in a car.
All clinicians have had a patient tell them, “That filling we did a while back felt really high at first, but now it feels fine.” It would be important to consider how did the bite adapt to the high contact? Most often what happened is that the deflective interference caused a permanent change in their bite in order for them to adapt and function (Figure 13.5a–c) . This occurs when a patient’s musculature develops engrams to avoid the dangerous interference and permanently changes the position of their mandible, mostly forward, as a defense mechanism . The interference forces the mandible to find a new, safe way to bite, chew and clench without damaging that high spot. Unfortunately, something else in the masticatory system will pay the price for this change . Whatever is the weakest link in the patient’s mouth is what ends up paying the price for this deflective interference. If there is a weak tooth, it will fracture (Figure 13.6). If the patient has weak muscles or joints, they may develop headaches. They can also easily develop any of the other signs and symptoms of occlusal disease, such as hypermobility, abfractions, or wear.
While research is clear that when the patient occludes, all teeth should touch at the same time, there are many opinions as to where the mandible should be while this occurs. The mandible has almost infinite possibilities for movement, so there must be some means of reliably reproducing the location of the mandible in relationship to the maxilla. The centric relationship is a reproducible jaw relationship unrelated to the teeth, as it is the place where both condyles seat high up, tightly against the fossa. The centric relationship is considered to be a physiological position because, when the masticatory muscles are contracting, they will guide the condyle to sit in the fossa as long as there is no dental interference. In extensive rehabilitations and equilibration, it is ideal to adjust the teeth to ensure that the patient’s centric occlusion, or natural bite, coincides with their centric relationship [8,9]. I adopt a non-strict centric relationship philosophy, meaning that as long as the patient has no signs or symptoms of occlusal disease, it is not necessary to adjust or equilibrate the patient into a centric relationship, as they have clearly adapted their natural bite. Additionally, the centric relationship is not a perfect, unmovable place in space .
Posterior disocclusion occurs when the canines and anterior teeth will immediately disclude the posterior teeth in any eccentric movements (Figure 13.7a,b). As previously discussed, humans exert hundreds of pounds of force per square inch when biting. While biting on the centric position where the forces are mostly axial and all the teeth touch at the same time, the forces are shared and any damage to the teeth is minimized. A different scenario occurs when the mandible goes into eccentric movement (forward or to the sides). This is, of course, a natural occurrence when eating, as the mandible goes in the direction of the food, and of course this also happens during parafunctionalmovements. It is in these lateral eccentric movements where only a few teeth touch, mostly in off-center directions (shear), that damage occurs when the full forces of the masticatory muscles are exerted.
Is there a way in which the forces could be minimized or controlled while the mandible is in eccentric movements? Researchers have found that once anterior teeth separate from posterior teeth, the forces are diminished dramatically, and thus the possible damage is decreased [11,12,13]. Ideally, when the mandible swings outside the centric position, the canines and anterior teeth should immediately disclude the back teeth; when this happens, the forces decrease dramatically. This becomes a significant benefit to the patient in protecting their dentition. Therefore, to adhere to the second golden rule, the molars cannot touch anywhere outside the centric relationship (no red outside of blue; Figure 13.8).
For canine guidance to be successful, no posterior interference should be present, and disocclusion must be immediate. This means that a strong palatal ridge must be present on the canines (Figure 13.9a–c). If this is not accomplished,