tooth form and occlusion2(351)
TRANSCRIPT
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Tooth form and occlusion
Part II
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OCCLUSAL ANATOMY OF
RESTORATIONS
Occlusion is defined in dictionary as being
closed or the act of closure,
while in dentistry the term denotes the static
opposing teeth contact relationship.
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On the wider scale, the modern concept of
occlusion describes the term as themultifactorial functional relations between
teeth in contact and the other components of the masticatory system (condyles, glenoids,
ligaments, muscles and jaws).
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The teeth are the elements of the
masticatory system that are directlyinvolved in the act of closure and any
disturbance in the occlusal anatomy orphysiology can result in serious damaging
effects in the other components of the whole
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TYPES AND PHYSIOLOGIC
ASPECTS OF OCCLUSION I- Centric occlusion:
When the jaws are in a closed position
with the maxillary and mandibular teeth
are in maximal interdigitated contact
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Malocclusion.
It is a term describing the abnormal or
malpositioned relationship of maxillary
and mandibular teeth when they are in
centric occlusion .
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The centric relation:
describes the relation between the
mandible and maxilla when the
mandibular condyles are in the most
retruded functional unstrained position in
the glenoid fossae with the articular disc
ro erl inter osed.
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The centric occluding relation
Combines the status of both teeth and
jaws in centric i.e. centric occlusion and
centric relation.
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Eccentric occlusion :
describes the relation between teeth whenthe mandible is moved from centricposition.
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This occurs in cases of :1) lateral or protrusive functional occlusion(contact in the functioning region)2) nonfunctional disclusion (balancing
contacts occurring during jaw movementslike lateral nonfunctional contacts orprotrusive nonfunctional contacts).
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During lateral movement of the mandible,the working side contacts could be either:
1) canine guided lateral functionalocclusion pattern ( as in cases of unworndentition) or
2) grouped lateral functional occlusionwhere there is a dominant guidance by thecanines plus a share of posterior teeth cusp
inclines guidance.(in older age and worn
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OCCLUSAL DIAGNOSIS
The anatomical landmarks present on the
occlusal aspects of posterior teeth and the
incisal and lingual surfaces of posterior
teeth must be restored back during
construction of individual or multiple
restorations.
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The posterior teeth are provided with cusps
with tip and inclined planes, fossae, ridgesto present with the formers the action of
mortars and pestles for grinding food.
Pits, fissures and grooves act as spillways
during mastication.
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Meanwhile, the canines are provided withpointed cusps for tearing of food while the
incisors are provided with horizontal edgesfor incision.The prominence of such landmarks depends
on the age, the type of occlusion and thechewing habits present in the mouth
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Articulation of teeth in centric occlusion on
a carbon paper gives the chance to detectthe sites of centric holding areas prior to
designing of a cavity preparation andselecting the type of restoration.
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The eccentric movement of the mandible in
lateral right, left, and protrusive movementswill give the operator the chance to detect
the range of functional and nonfunctional
contacts.
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Recently, computerized occlusal analysis is
helpful for accurate diagnosis and detectionof occlusion criteria prior to the restorative
procedures.
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The universal key of occlusion known todetect the normality of centric occlusion is
the articulation of the mesio buccal cusp of the upper first molar with the buccal grooveof the lower first molar with the upper
overlapping the loweri.e. the lingual surface of upper cusp
contacts the buccal aspect of the lower
molar buccal groove.
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b) Determinants of Occlusion:
These factors are involved in the control of
articulation of teeth during movement of themandible in response to the action of the
muscles.
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They are:
1. Posterior condylar guidance.(pathway of head of condyle on the articular eminence).
2. Anterior incisal guidance (pathway of incisal edges of lower incisors on thelingual surface of uppers)
3. The arrangement and morphology of teeth (vertical dimension, horizontal overlapor over jet, vertical overlap alignment and
topography of teeth).
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N; B:
The first factor is not under the control of
the operator because it is a fixed anatomicalfactor while the latters can be changed by
the dentist and thus they are termed the
variable factors.
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c) Inter-occlusal records:
They are determined and transferred to
articulators with a variety of typesaccording to the data they can accommodate
in order to carry on the procedure of
analyzing the occlusion or constructing an
inlay restoration.
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A face bow record is needed to mount the
upper model and then the lower model ismounted by determining the relation in
centric and the limits of eccentric
movements.
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Various methods can be utilized to relatethe mandible to the maxilla such as;
1- mounting full mouth casts.2- occlusion blocks.3- wax bites and arch tracing.
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Then, the occlusion is studied on the
mounted models and a removable die isconstructed to enable the accurate re-
orientation of the tooth on which the
restoration will be performed.
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FUNCTIONS OF THE OCCLUSAL
ANATOMY1. Mastication of food.
Each tooth is designed to perform certainfunction, incisors for incision, and canines
for tearing and posterior teeth for grinding.
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2. Intercuspation between upper and lower
teeth preserves the relation between theupper and lower jaws and consequently
between the condyle of the mandible to the
glenoid articulation of the maxilla.
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3- Stabilization of jaw movements by
determination of the limits of protrusive andlateral movements.
4- Prevents drifting , over-eruption andmovement of teeth and preserves theiralignment.
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Food cycling and spillway action (pits,
fissures, fossae and grooves as well as thespillways created by the intercuspation in
cases of quadripoded, tripoded and dipoded
contacts of antagonistic cusps with the
corresponding fossae). This is essential for
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GUIDELINES FOR THE RESTORATIONOF OCCLUSAL ANATOMY
1- During restoration of the anatomicalmarkings, the operator should be aware of
the correct anatomy and the physiologicaspects of the dentition.2- The landmarks (pits, fissures, grooves,
cuspal form and inclined planes, fossae, andridges) must be restored in the same size,form and location.
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3- This is performed by correct carving of
plastic restorations inside the mouth andmore precisely restored with indirect
restorations via the appropriate mounting
procedures and the meticulous carving of
the wax pattern.
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4- The precision of the various steps of
impression making, model and dieconstruction, inter-occlusal records and
mounting models is required to assure the
perfect restoration as an ultimate objective.
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SQULAE OF IMPERFECT RESTORATION OFANATOMICAL LANDMARKS
1. Detrimental stresses on the teeth and
supporting structures due to prematurecontacts resulting from misplacement of
structures or undercarving of restorations as
well as the faulty management of inter-
occlusal records.
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The premature contacts in centric andeccentric movements must be checked and
corrected before dismissing the patient.These stresses may cause fracture of restoration, post restoration pain and pulpal
inflammation and damage to supportingstructures.
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2. Inefficiency of mastication and foodstagnation by incorrect restoration of the
spillways and anatomical landmarks.This will prevent correct cycling and escapeof food and may cause recurrent caries and
periodontal problems.
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3. Drifting, over-eruption and malalignment
of teeth may occur due to failure to securethe inter-arch relations provided by the
occlusion of antagonistic teeth.
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4. Articular and temporo-mandibular
problems may result due to unstable jaw
movements and abnormal chewing habits.