Importance of Occlusion in fixed prosthodontics

Noreen Mohammed Naguib5212322

G.11

Mandible to Maxilla relationships and terminologies: Centric occlusion It is the most closed complete

interdigitating of mandibular and maxillary teeth irrespective of condylar position or centricity .

Centric relation :maxillo-mandibular relationship in which the condyles articulate with the thinnest avascular portion of the disk and being in the most anterior-superior position against the articular eminencies.Rest position : Purely Muscle-guided position when the mandible is at physiologic rest without any tooth contacts, there will be a 1-3 mm space the freeway space.

Maximum opening : maximum separation between arches about 40-50 mm

Centric Relation of TMJ •Its repetitive reproducible and recordable position

•Independent of presence and absence of teeth •The final act of masticatory stroke ends in centric relation

•It is a border position and the posterior limit of the envelope of motion

•Can resist maximum loading by muscles with no sign of discomfort

•Note: maximum intercuspation may or may not coincide with centric occlusion

•if MI occurs with the condyles out of centricity, then both positions would not coincide, the MI in this case, called habitual closure, and is considered as an eccentric position

Vertical dimensions :Vertical dimension of occlusion (VDO): at maximum intercuspation Vertical dimension of rest (VDR): at rest with freeway space Plane of occlusion:

refers to an imaginary surface that theoretically touches the incisal edges of the incisors and the tips of the occluding surfaces of the posterior teeth

Curves of occlusion: Two areas constitute the occlusal plane and should be

addressed separately .1 -the anterior teeth, Their position is determined by :

Esthetics -demand for anterior guidance

-phonetic considerations.2 -Posterior teeth, position is determined by two

curves .-curve of Spee

-curve of Wilson.

Curve of SpeeThe anterior/posterior curve of maxillary and mandibular occlusal surfaces It is designed so that the posterior teeth can be separated in protrusion, by the affects of condylar guidance and anterior guidance. This phenomenon reduces posterior interference

Curve of Wilson “It is the mediolateral curve that contacts

the buccal and lingual cusp tips on each side of the arch it is always related to the lower arch Allows for the lingual cusps (working cusps) of maxillary teeth to function with the lower occlusal scheme without interference.

Mandibular movements TMJ and articular eminence (posterior guidance) Occlusion curves Teeth shapes &surfaces Cusp heights Central fossa Marginal ridges occlusal table -Wilson -Spee Neuro-musculature -masticatory muscles --ligaments PDL and perioception occlusion Teeth (anterior) guidance: -Anterior teeth guidance -Canine guidance -Group function Occlusal interrelationship Mandible to maxilla relation in 3 planes mainly horizontal and vertical

The guidance systems There are two systems that provide hard guidance during mandibular movements; they are interrelated and part of one system .

Posterior guidanceThe temporomandibular joint ; made up of the head of the condyle, articular eminence, the intra-articular disc and the glenoid fossaThe anterior guidance system is provided by which ever teeth naturally touch during function to guide the mandible movements; happens during dynamic occlusion or functional occlusion, and any other contact that happens prematurely, or inhibits harmony is referred to as Occlusal interference

Tempromandibular joint complex It is a synovial joint but differs from most synovial joints in that the articular surfaces of the bony components are covered with dense fibrous connective tissue, instead of hyaline cartilage. In addition, the TMJ has a fibrous articular disc, to which muscle fibers are attached. This disc divides the joint into two compartments, upper and lower, thereby giving the mandible a wide range of movement.

Mutually Protected Occlusion An occlusal scheme in which the anterior teeth protect the posterior teeth, and vice versa .

The anterior teeth protect the posterior teeth by providing guidance during excursions thus allowing the cusps of the posterior teeth to disocclude rather than strike one another during lateral or protrusive

movements from centric relation ;To prevent this from happening, the anterior teeth of each arch will, ideally, be situated so as to come into contact before the cusps of the posterior teeth do, thus preventing wear on the posterior teeth .

The posterior teeth protect the anterior teeth by providing a stable vertical dimension of occlusion. While anterior teeth may retain their natural position even after loss of posterior teeth, the masticatory forces will eventually cause the single-rooted anterior to splay, thus leading to a collapsed bite

Balanced occlusion It’s a type of occlusion used in dentures and artificial teeth For lateral movement of the mandible When the mandible moves laterally all posterior teeth with the canine on both sides ;the working and non-working ;contact, unlike functional guidance where contact on the non-working side doesn’t happen Compensating curves:

When artificial teeth have balanced occlusion the curvetures of the teeth occlusal surfaces said to have compensation curves; instead of curve of Spee and curve of Wilson

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