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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.

Malocclusion is the misalignment of teeth and jaws, or more simply, a "bad bite". Malocclusion can cause a number of health and dental problems. Malocclusion occurs as a result of disturbances in normal occlusal development.^[1]

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. Dynamic occlusion is also termed as articulation. During chewing, there is no tooth contact between the teeth on the chewing side of the mouth.

Centric occlusion is a relationship between upper and lower teeth when they come together, teeth do not need to be in centric relation in order to be in centric occlusion, i.e. the condyle may be anywhere within the glenoid fossa when the teeth are in centric occlusion. Centric occlusion is the first tooth contact and may or may not coincide with maximum intercuspation. It is also referred to as a person's habitual bite, bite of convenience, or intercuspation position (ICP). Centric relation, not to be confused with centric occlusion, is a relationship between the maxilla and mandible.

Concepts of occlusion

Occlusion is defined as the act of opening and closing, while in dentistry its definition is broader and includes the contact of the teeth in the functional and parafunctional movements.^[2] In addition, it includes the development and function of the masticatory system.^[2] Over the course of history there have been several occlusion concepts, which tend to vary based on the specialty of dentistry.^[2] Initially the concepts were based on complete dentures.^[2]

Centric occlusion (CO) is the occlusion, or position, of opposing teeth when the mandible is in centric relation.^[3] Centric relation (CR) is the relationship between the maxilla and the mandible with regards to the position of the mandibular condyle articulating with the thinnest avascular portion of the respective disks in the anterior-superior position.^[3] This position does not require the teeth to be in contact, but it is possible.^[3] Maximal intercuspation (maximal intercuspal position or MIP) is the full intercuspation of the opposing teeth in the dental arches regardless of condylar position.^[3]

The concept of ideal occlusion varies based on a case by case basis, the goal of the dentist is to choose a model that reduces vertical and horizontal stresses, provides MIP during CR.^[4]

Balanced occlusion

Balanced Occlusion is defined as the bilateral, simultaneous, anterior, and posterior occlusal contact of teeth in centric and eccentric positions. Balanced occlusion in complete dentures is unique, as it does not occur with natural teeth.^[5]

This concept of occlusion is based on the efforts of Curve of Spee and Monson's spherical theory and is known also as "fully balanced occlusion" or "bilateral balanced occlusion."^[4] This occlusion concept requires that all the teeth be in contact during both maximum intercuspation and eccentric mandibular movements.^[4] During masticatory movements, there are no vertical forces, just horizontal ones.^[4] The lateral forces that are produced get directed upon the periodontal ligaments and are distributed through the contact area created through the occlusion scheme.^[4]

The concept is ideal for those receiving dentures, but is difficult to obtain on those with normal dentition.^[4] If this occlusal scheme is found in a patient it typically indicates that there is advanced wear on the dentition.^[4] An “ideal” dentition is based on the end goals of restorations involved with orthodontics, dentures and for some, full mouth rehabilitation. The occlusion is therefore not static. It is a continuous functional relationship between the maxillary (upper) and mandibular (lower) teeth. Any disturbances to the masticatory (chewing) system can be due to malocclusion, occlusal dysfunction and conditions such as bruxism (teeth grinding). Patients with bruxism may be treated with preventative therapy including stabilisation with an occlusal bite plane splint.^[1] At present, there is not enough evidence to suggest that non-surgical therapy is effective in patients experiencing teeth during sleep bruxism.^[6]

Unilateral balanced occlusion is a type of occlusion seen on occlusal surfaces of teeth on one side when they occlude simultaneously with a smooth, uninterrupted glide. This is not followed during complete denture preparation. It is more pertained to fixed partial dentures.

Bilateral balanced occlusion is a type of occlusion that is seen when a simultaneous contract occurs on both sides in centric and eccentric positions. Bilateral balanced occlusion helps to distribute the occlusal load evenly across the arch and therefore helps to improve the stability of the denture ^[7]

Mutually protected occlusion

The occlusal scheme was established in 1974 by Dawson that used data study in 1960 revealed a set of patients whose molars did not contact in eccentric movements, while the anterior teeth did not contact in maximum intercuspation.^[4] In order to classify as mutually protected occlusion the following criteria must be met:^[4]

In protrusive movements, the canine and the posterior teeth are protected by the incisors, while in a lateral movement the incisors and posteriors are protected by the canines.^[4] The posterior teeth protect the anteriors in a centric position , which reduces the load onto the temporomandibular joint.^[4]

Mutually protected occlusion is thought to be the best scheme for natural dentition as the cusp-to-fossa relationship provides maximum support for centric relation.^[4] Another reason is that the forces are directed almost completely along the long axis of the tooth.^[4] The scheme is not recommended in patients with compromised periodontium or or if the patient has a horizontal masitcatory cycle.^[4]

Occlusal Development

As the teeth start to erupt at six months, the maxillary (upper) and mandibular (lower) primary (baby) teeth aim to occlude with two teeth of the opposing jaw. The two exceptions to this are the upper left and right central incisor and the lower left and right second molar. Normal alignment and occlusion of the two arches should be achieved after 2 years of age, with the full formation of the roots by the time the child has reached 3 years. The jaws develop in such a way that after one year, a diastema (interdental space) has formed between some teeth. This is more prominent in the anterior teeth as the jaws and permanent teeth grow.^[1]

Assessing Occlusion^[8]

Extra-oral Assessment

• Check for facial asymmetry and skeletal discrepancies


• Measure Lower Face Height

Loss of teeth and occlusal stops can result in over-closure causing a reduced face height. Over-closure is unlikely for patients with tooth wear due to dento-alveolar compensation. Over-eruption may occur for patients due to dento-alveolar development in absence of tooth wear which may result in increased face height.

• Temporomandibular Joints

The maximum extent the patient can open is measured between the incisal edges of the upper and lower incisors. Deviation of mandible on opening or closing should be described. Clicking, crepitus and tenderness of the jaw should be noted as well.

Intra-Oral Assessment

• Intercuspal Position (ICP) / Centric Position

ICP is defined as position of the jaws when there is maximum intercuspation of the maxillary and mandibular teeth. Stability of occlusion in ICP is essential or further dental work will be complicated.

• Retruded Contact Position (RCP) / Terminal Hinge Axis Position

RCP refers to the most comfortable posterior location of the mandible when it is bilaterally manipulated backwards and upwards into a retrusive position. Terminal hinge axis refers to an imaginary axis drawn through the center of the head of both condyles when the mandible opens and closes on an arc of curvature. When the mandible closes in the Terminal Hinge Axis, the first tooth contact refers to RCP.

• Excursive Movements of the Mandible

Protrusion

Condyles move from the glenoid fossa in a forward and downward movement onto the articular eminence when the mandible moves into protrusion. Condylar inclination refers to the angle protrusion makes when the horizontal when the patient is sitting upright

In protrusion, contact between the teeth is governed by incisor relationship and guidance. For instance, the mandibular movement of patients with Class I incisors relationships would be inferiorly resulting in separation of the posterior teeth. This is to overcome the natural overbite of the Class I relationship for the mandible to make a protrusive movement.

Lateral Excursion

The side to which the mandible moves is called the working side and the opposite side is the non-working side. Bennett Movement refers to the lateral movement of the working side condyle when the mandible moves laterally. Bennett’s Angle is measured at the non-working condyle when it moves forward and medially during lateral excursion

Lateral excursion of the mandible is usually governed by Canine guidance or Group Function at the working side. In some cases, teeth at the non-working side can also be in contact when the condylar inclination is shallow or if the tooth guidance on the working side is shallow.

Occlusal problems

Malocclusion is the result of the body trying to optimize its function in a dysfunctional environment. For example, the maxilla (upper jaw) can be placed too far anteriorly compared to the mandible (lower jaw). This would be called a Class II Malocclusion. If the mandible is placed too far posterior compared to the maxilla, it would be a Class III malocclusion. Malocclusion can can also be associated with a number of problems:

• Misaligned ('crooked') teeth


• Gum problems


• The temporomandibular joint (TMJ and jaw muscles.

Malocclusion can cause teeth, fillings, and crowns to wear, break, or loosen, and teeth may be tender or ache.
Receding gums can be exacerbated by a faulty bite.
If the jaw is mispositioned, jaw muscles may have to work harder, which can lead to fatigue and or muscle spasms. This in turn can lead to headaches or migraines, eye or sinus pain, and pain in the neck, shoulder, or even back.
Malocclusion can be a contributing factor to sleep disordered breathing which may include snoring, upper airway resistance syndrome, and / or sleep apnea (apnea means without breath). Untreated damaging malocclusion can lead to occlusal trauma.

Treatment for occlusal problems
Some of the treatments for different occlusal problems include protecting the teeth with dental splints (orthotics), tooth adjustments, replacement of teeth, medication (usually temporary), a diet of softer foods, TENS to relax tensed muscles, and relaxation therapy for stress-related clenching. Removable dental appliances may be used to alter the development of the jaws. Fixed appliances such as braces may be used to move the teeth in the jaws. Jaw surgery is also used to correct malocclusion.^[9]