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Occlusion (dentistry)

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Occlusion, in a dental context, means simply the contact between teeth.[1] 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.[1] 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.

Anatomical Basis of Occlusion

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Occlusal Terminology

Intercuspal Position (ICP), also known as Habitual Bite, Habitual Position or Bite of Convenience , is defined at the position where the maxillary and mandibular teeth fit together in maximum intercuspation. This position is usually the most easily recorded and is almost always is the occlusion the patient closes into when they are asked to 'bite together'. This is the occlusion that the patient is accustomed to, hence sometimes termed the Habitual Bite.[1]

Centric relation (CR) describes a reproducible jaw relationship (between the mandible and maxilla) and is independent of tooth contact. This is the position in which the mandibular condyles are located in the fossae in an antero-superior position in against the posterior slope of the articular eminence.[2] In CR, the muscles are in their most relaxed and least stressed state.

When the mandible is in this retruded position, it opens and closes on an arc of curvature around an imaginary axis drawn through the centre of the head of both condyles. This imaginary axis is termed the terminal hinge axis. The first tooth contact that occurs when the mandible closes in the terminal hinge axis position, this is termed Retruded Contact Position (RCP).[3]  RCP can be reproduced within 0.08mm of accuracy due to the non-elastic TMJ capsule and restriction by the capsular ligaments, thus it can be considered a ‘border movement’ in Posselt’s envelope.[4]

Posselts Envelope of Border Movements

Posselt’s Envelope of Border Movement is a schematic diagram of the maximum jaw movement in three planes (sagittal, horizontal and frontal).  This encompasses all movements away from ICP, and includes:

  • Protrusive movements: When the mandible moves forward from ICP, this is considered as protrusion. The predominant contacts occur on the incisal and labial surfaces of the mandibular incisors and the incisal edges and lingual fossa areas of the maxillary incisors.[5]
  • Lateral movements: When the mandible moves to the left or right, the mandibular posterior teeth move laterally across their opposing teeth in different directions.  For example, when the mandible moves to the right, the right mandibular posteriors move laterally across their opposing teeth and this is termed the working side (the side to which the mandible is moving).  In contrast, the left mandibular posteriors move medially across their opposing posteriors and this is called the non-working side (the side to which the mandible is moving away from).
  • Retrusive movements: This is when the mandible moves posteriorly from ICP. Compared with protrusive and lateral movements, retrusive movements are generally considerably smaller with a range of movement around 1 or 2 mm due to restriction by the ligamentous structures.[6]

Curvatures of Occlusal Planes

The occlusal plane tends to be curved in order to permit simultaneous functional contact in several areas of the arch and utilise the maximum number of tooth contacts.  This would not achievable should the occlusal plane be flat due to the complexity of the jaw movements and constantly shifting centres of rotation.[6]

Curve of Spee

  • The occlusal (biting) surfaces of the dental arch generally display a curved alignment from the lower canine tip, through the premolars and molars and then continues as an arc through the condyle.  If this arc was to be extended, it would form a circle around 4 inches in diameter. This is referred to as the curve of Spee [7] or the compensating curve, and plays a role in occlusion, with suggestions that this curve increases the efficiency of occlusal forces during mastication.[8]  An exaggerated curve may lead to malocclusion with a deep overbite and improper functional occlusion.

Curve of Wilson

  • When viewed from a frontal view, the maxillary arch can be seen to have a slight buccal inclination in the posterior region which results in a convex curve, should you draw a line through the buccal cusp tips of the right and left molars.

On the other hand, the mandibular arch shows a slight posterior lingual inclination and when a line is drawn through the buccal cusp tips of the posterior teeth, a concave curve is seen.  If the mandibular and maxillary arch are brought together into occlusion, the curvatures will match perfectly and this is called the curve of Wilson.[9] This curve is thought to align the teeth along a parallel axis to the muscles of mastication (medial pterygoid) which helps to optimise the masticatory forces. The overlap of the upper and lower buccal cusps also helps to protect soft tissues and keep food within the occlusal table.

Curve of Monson

  • If the curve of Spee and the curve of Wilson were to be extended over all cusp tips and incisal edges, the curve of Monson is obtained.  Dr. George S Monson proposed in 1920 that the curve of Monson is an ideal curve of occlusion in which each cusp and incisal edge touches the surface of an imaginary 3D sphere 8 inches in diameter.[10]

See also

References

  1. ^ a b c Davies, S; Gray, R M J (2001-09-08). "Occlusion: What is occlusion?". British Dental Journal. 191 (5): 235–245. doi:10.1038/sj.bdj.4801151. ISSN 0007-0610.
  2. ^ "The Glossary of Prosthodontic Terms". The Journal of Prosthetic Dentistry. 117 (5): C1 – e105. May 2017. doi:10.1016/j.prosdent.2016.12.001.
  3. ^ David., Ricketts, (2014). Advanced Operative Dentistry : a Practical Approach. Elsevier Health Sciences. ISBN 9780702046971. OCLC 1048579292.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  4. ^ Ulf, Posselt, (1952). Studies in the mobility of the human mandible. OCLC 252899547.{{cite book}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  5. ^ author., Nelson, Stanley J.,. Wheeler's dental anatomy, physiology, and occlusion. ISBN 9780323263238. OCLC 879604219. {{cite book}}: |last= has generic name (help)CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  6. ^ a b P., OKESON, JEFFREY (2019). Management of temporomandibular disorders and occlusion. MOSBY. ISBN 0323582109. OCLC 1049824448.{{cite book}}: CS1 maint: multiple names: authors list (link)
  7. ^ Spee, Ferdinand Graf; Biedenbach, Maria A.; Hotz, Margaret; Hitchcock, H. Perry (May 1980). "The Gliding Path of the Mandible along the Skull". The Journal of the American Dental Association. 100 (5): 670–675. doi:10.14219/jada.archive.1980.0239. ISSN 0002-8177.
  8. ^ S., Monson, George (November 1932). Original Communications: Applied Mechanics to the Theory of Mandibular Movements. Philadelphia. OCLC 658039296.{{cite book}}: CS1 maint: multiple names: authors list (link)
  9. ^ Wilson, George H (1911). A manual of dental prosthetics. Philadelphia: Lea & Febiger. pp. 22–37.
  10. ^ Monson, George S. (May 1920). "Occlusion as Applied to Crown and Bridge-Work". The Journal of the National Dental Association. 7 (5): 399–413. doi:10.14219/jada.archive.1920.0071. ISSN 0097-1901.
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