basics of gnathology

gnathology, occlusion, bruxism,

1. Gnathology

2. definition Gnathology is the branch of Odontology dealing with the so called " cranio - mandibular" disorders, that's to indicate those disfunctions and pathologies of the masticatory system from a non strictly dental point of view. ” Gnatology ” This difficult word outlines the study of jaw and mandible-related problems. More simply, grathology investigates the problems of proper bite fitting. When extending the field to adjacent areas like articulation of the jaws, head, neck, ears and shoulders, it takes the name of Craniocervicomandibular Disorders (CCMD).

3. overview Gnathology, in fact, concerns about joints and muscles, and in particular, the joint between mandibula and skull ( Temporo Mandibular Joint or TMJ) and about the lowering and elevating muscles of the mandibula. The disorders and the real disfunctions of these anatomical structures, are very common, although they generally go unnoticed because they're not always symptomatic. Unfortunately it must be said that the great majority of the dentists only has a vague powdering about Gnathology, in the best cases on quite uncorrect , not updated and not rational knowledge. For this reason, diagnosis is often vague, therapeutical approach is confusing and results quite mediocre.

4. overwiew Gnatology - The field further extends to other sectors which, at first glance, seem not to be related like posture, balance system, headache, sight, thus embracing a field known as posturology . Gnathology tries to codify what is physiologic, that is to say the models to be adopted for patient's rehabilitation. Opinions are still conflicting and, therefore, the schools of thought are proliferating, in their attempt to find in either direction the truth on dental occlusion . For many people, gnathologic problems mean limited mouth movements, ache, temporomandibular joint sounds; however, the field is much more extended.

5. What is an occlusion ? Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest. Static occlusion refers to contact between teeth when the jaw is closed and stationary, while dynamic occlusion refers to occlusal contacts made when the jaw is moving. The masticatory system also involves the periodontium, the TMJ (and other skeletal components) and the neuromusculature , therefore the tooth contacts should not be looked at in isolation, but in relation to the overall masticatory system.

6. Ideal occlusion When there is an absence of symptoms and the masticatory system is functioning efficiently, the occlusion is considered normal or physiological. It is understood that no such ‘ideal’ occlusion exists for everyone, but rather each individual has their own 'ideal occlusion'. This is not focused on any specific occlusal configuration but rather occurs when the person’s occlusion is in harmony with the rest of the stomatognathic system (TMJ, teeth and supporting structures, and the neuromuscular elements). However, an optimal functional occlusion is important to consider when providing restorations as this helps to understand what is trying to be achieved.

7. Organisation of the occlusion The arrangement of teeth in function is important and over the years three recognised concepts have been developed to describe how teeth should and should not contact: Bilateral balanced occlusion Unilateral balanced occlusion Mutually protected occlusion

8. Bilateral balanced occlusion This concept is based on the curve of Spee and curve of Wilson and is becoming outdated for the restored natural dentition. However, it still finds application in removable prosthodontics. This scheme involves contacts on as many teeth as possible (both on the working and non-working side) in all excursive movements of the mandible. This is especially important in the case of complete denture provision as contacting teeth on the NWS help stabilise the denture bases in mandibular movement. It was believed in the 1930's that this arrangement was ideal for the natural dentition when providing full occlusal reconstruction in order to distribute the stresses. However, it was found that the lateral forces placed on the restored posterior teeth produced damaging effects on the restorations.

9. Unilateral balanced occlusion On the other hand, unilateral balanced occlusion is a widely used tooth arrangement that is used in current dentistry and is commonly known as group function. This concept is based on the observation that NWS contacts were destructive and therefore the teeth on the NWS should be free of any ececntric contacts, and instead the contacts should be distributed on the WS thus sharing the occlusal load. Group function is used when canine guidance cannot be achieved and also in the Pankey -Mann Schuyler (PMS) approach where it was deemed better than canine guidance as it distributed the loading on the WS better.

10. Mutually protected occlusion Mutually protected occlusion - Posterior disocclusion of teeth as the mandible is protruded Studies defines mutually protected occlusion as ‘an occlusal scheme in which the posterior teeth prevent excessive contact of the anterior teeth in maximal intercuspal position, and the anterior teeth disengage the posterior teeth in all mandibular excursive movements’ In eccentric movements, damaging forces are applied to the posterior teeth and the anteriors are best suited to receiving these. Therefore during protrusive movements, the contact or guidance of the anteriors should be adequate to disocclude and protect the posterior teeth. In contrast, the posterior teeth are more suited to accept the forces that are applied during closure of the mandible. This is because the posteriors are positioned so the forces are applied directly along the long axis of the tooth and are able to dissipate them efficiently whereas the anteriors cannot accept these heavy forces as well due to their labial positioning and angulation. It is therefore accepted that the posterior teeth should have heavier contacts than the anteriors in ICP and act as a stop for vertical closure. Additionally, in lateral excursions either canine or group function should act to disclude the posterior teeth on the WS because, as described above, the anterior teeth are best suited to dissipate damaging horizontal forces, as well as the contact being further away from the TMJ, so the forces created are decreased in strength. Group function or canine guidance should also provide disocclusion of the teeth on the NWS as the amount and direction of force applied to the TMJ and teeth can be destructive due to an increase in muscle activity.[19] An absence of NWS contacts also allows smooth movement of the working side condyle as a contact may disengage the guidance of the condyle and therefore cause an unstable mandibular relationship.

11. bruxism Bruxism is excessive teeth grinding or jaw clenching. It is an oral parafunctional activity; i.e., it is unrelated to normal function such as eating or talking. Bruxism is a common behavior; reports of prevalence range from 8% to 31% in the general population. Several symptoms are commonly associated with bruxism, including hypersensitive teeth, aching jaw muscles, headaches, tooth wear, and damage to dental restorations (e.g. crowns and fillings). Symptoms may be minimal, without patient awareness of the condition. There are two main types of bruxism: one occurs during sleep (nocturnal bruxism) and one during wakefulness (awake bruxism). Dental damage may be similar in both types, but the symptoms of sleep bruxism tend to be worse on waking and improve during the course of the day, and the symptoms of awake bruxism may not be present at all on waking, and then worsen over the day. The causes of bruxism are not completely understood, but probably involve multiple factors. Awake bruxism is more common in females, whereas males and females are affected in equal proportions by sleep bruxism. Awake bruxism is thought to have different causes from sleep bruxism. Several treatments are in use, although there is little evidence of robust efficacy for any particular treatment.

12. Occlusal factors of bruxism Malocclusion is a medical term referring to less than ideal positioning of the upper teeth relative to the lower teeth, which can occur both when the upper jaw is ideally proportioned to the lower jaw, or where there is a discrepancy between the size of the upper jaw relative to the lower jaw. Malocclusion of some sort is so common that the concept of an "ideal occlusion" is called into question, and it can be considered "normal to be abnormal". An occlusal interference may refer to a problem which interferes with the normal path of the bite, and is usually used to describe a localized problem with the position or shape of a single tooth or group of teeth. A premature contact is one part of the bite meeting sooner than other parts, meaning that the rest of the teeth meet later or are held open, e.g., a new dental restoration on a tooth (e.g., a crown) which has a slightly different shape or position to the original tooth may contact too soon in the bite. A deflective contact/interference is an interference with the bite that changes the normal path of the bite. A common example of a deflective interference is an over-erupted upper wisdom tooth, often because the lower wisdom tooth has been removed or is impacted. In this example, when the jaws are brought together, the lower back teeth contact the prominent upper wisdom tooth before the other teeth, and the lower jaw has to move forward to allow the rest of the teeth to meet. The difference between a premature contact and a deflective interference is that the latter implies a dynamic abnormality in the bite.

13. Occlusal factors of bruxism People with no teeth at all who wear dentures can still suffer from bruxism, although dentures also often change the original bite. Most modern sources state that there is no relationship, or at most a minimal relationship, between bruxism and occlusal factors. The findings of one study, which used self-reported tooth grinding rather than clinical examination to detect bruxism, suggested that there may be more of a relationship between occlusal factors and bruxism in children. However, the role of occlusal factors in bruxism cannot be completely discounted due to insufficient evidence and problems with the design of studies.

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