Arrangement of the Posterior Teeth

8/13/2019 Arrangement of the Posterior Teeth

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Dr.Mohammad Al Sayed

4/5/2008


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The arrangement of the posterior teeth involves theapplication of principles similar to those followed inthe arrangement of anterior teeth. The artificialposterior teeth should be placed as nearly as possiblewhere the natural teeth were .Orientation of the occlusal plane:

* The anterior end of the occlusal plane is orientedaccording to esthetics. The vertical level at whichthe anterior teeth are set is the level of the anterior endof the occlusal plane. This level is usually1-2 mm below the resting upper lip.

* The posterior end of the occlusal plane should belocated so that it would be in level with the junctionbetween themiddle and the distal third of the

retromolar pad. This guideline will place the occlusalplane that is familiar to the tongue.


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* The inclination of the occlusal plane is an importantfactor in stability or instability of dentures. Ideally, theocclusal plane should be parallel to both ridges.

* The vertical orientation and inclination is alsogoverned by the relative amount of bone lost from thetwo ridges. The occlusal plane should be placed at

a level that would favor the weaker of the two ridges. ( Ifmore bone has been lost from the maxilla than from themandible, the occlusal plane must be closer to themaxilla than the mandible. If more bone has been lost

from the mandible than from the maxilla, the occlusalplane must be closer to the mandible than the maxilla).However the level of the occlusal plane must be placedas nearly as possible to the position of the occlusal plane

of the natural teeth.


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:Buccolingual position of posterior teeth

* The buccolingual position of the posterior teeth and the

posterior arch form are determined anteriorly by thepositions of the anterior teeth. Posteriorly, it is determinedby the shape of the basal seat provided by the maxilla andmandible. The mandibular posterior teeth should beplaced so that the antero-posterior groove (central) isplaced on the crest(centre) of the residual ridge.The crest of the mandibular residual ridge is marked on theedentulous cast by a line drawn from the crest of the ridgein the 1stpremolar and canine area up to the mesial of theretromolar pads.If the teeth are placed buccal to the ridge, the dentures maytip on the opposite side when pressure is applied to theseteeth. The teeth should not be placed lingual to theresidual ridge because this will cause lack of space for thetongue, and the dentures will be displaced when thetongue moves.


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* The posterior part of the arch form will bedetermined to a great extent by the neutral zone

between the cheeks and the tongue.Neutral zone is the area between the tongue on one sideand the cheeks and lips on the other, where opposingsoft tissue displacing forces create a zone of neutral orminimal muscular force, the teeth should be placed as

far as possible with respect for these muscle forces. * Post extraction changes may lead to a gradualshifting of the neutral zone with the tongue spreadinglaterally. In other words the buccolingual space

available for placing teeth is reduced. This is ofparticular importance in the case of the lowerdenture. The artificial teeth used are considerablynarrower than the natural teeth and this allows themto be placed so that the denture is stable.


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Position of maxillary posterior teeth:

st premolar:1The maxillaryThe maxillary first premolar is placed with itslong axis perpendicular to the occlusal plane

(vertically upright).The buccal cusps are raised0.5mm from the occlusal plane.

premolar:nd2The maxillary

The long axis is perpendicular to the occlusal

plane ( parallel to the vertical axis). The buccalcusp is 0.5 mm above the occlusal plane andthe palatal cusp touches the occlusal plane.


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molar


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molar:st1The maxillary

The long axis (viewed from side ) may slightlyincline mesially. When viewed from thefront the tooth slopes buccally. The

mesiobuccal cusp of the first molar is raised0.5 mm above the occlusal plane. Themesiopalatal cusp is in contact with theocclusal plane. The distobuccal cusp israised about 1 mm above the occlusal plane.


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molar:nd2The maxillary

The long axis ( viewed from side, cervicalarea) may slightly incline mesially. Themesiobuccal cusp of the 2ndmolar is raised

1 mm above the occlusal plane. Thedistobuccal cusp 1.5 mm above the occlusalplane. No cusp touches the occlusal plane.

When viewed from the front the toothslopes buccaly (more than the 1stmolar).


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The maxillary teeth viewed from the occlusal

surface should follow the following guidelines:- The distobuccal surface of the canine, thebuccal surfaces of the premolars and themesiobuccal surface of the 1stmolar should

follow a straight line. Buccal surfaces of the 2ndmolar are slightly inwards and are placed sothat all buccal surfaces of the 1st and 2ndmolarsfollow a straight line.The posterior teeth shouldbe placed so that the central grooves of themaxillary posterior teeth follow the line of thecrest of the mandibular residual ridge.


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The position of the mandibular posterior

teeth:The placement of the mandibular posterior teethdetermines how well the teeth occlude, both in

centric occlusion and in lateral and protrusiveexcursions. The mandibular 1stmolar is firstplaced in position followed by the 2ndmolar,and then the two bicuspids. After placing each

mandibular tooth in the correct position theincisal guide pin should be checked to insurethat it is in contact with the guide table.


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molar:st1Position of the mandibularThe mesibuccal cusp of the maxillary 1stmolarfits into the buccal groove of the mandibular

1stmolar. The mesiolingual cusp of themaxillary 1stmolar fits into the centralgroove of the mandibular 1stmolar. This

provides proper buccal overjet.


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molar:nd2Position of the mandibular

The mandibular 2ndmolar is placed with themesiobuccal cusp fitting between themaxillary 1stand 2ndmolars and contact with

their marginal ridges. The lingual cusps ofthe maxillary 2ndmolar fit into the centralgroove of the mandibular 2ndmolar.


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premolar:nd2Position of the mandibular

The mandibular 2ndpremolar is placed withthe buccal cusp fitting between themaxillary 1stand 2ndpremolars and in touch

with their marginal ridges. The lingual cuspfits in between the palatal cusps of themaxillary bicuspids.


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premolar:st1Position of the mandibular

The buccal cusp of the mandibular 1stpremolar fits between the maxillary canineand the 1stpremolar. Usually this tooth is

not placed until the anterior and posteriorteeth are placed. If there isnt sufficientspace for the placement of this tooth it maybe trimmed and made narrower to fit intothe available space rather than alter theplacement of anteriors.


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the buccal cusps of the mandibular teethIn centric occlusioncontact the central fossae of the maxillary teeth while the

lingual cusps of the maxillary teeth fit into the central fossaeof the mandibular teeth.

Occlusal contacts during lateral movements:Contacts on the working side i.e. the side to which the mandible

is moving.Working or functional occlusion occurs when the buccal cuspsof the maxillary teeth meet the buccal cusps of themandibular teeth, and the palatal (lingual) cusps of maxillaryteeth meet the lingual cusps of the mandibular teeth.

However the relationship is not cusp tip to cusp tip, but cusptip into cusp valley with each maxillary cusp distal to thecorresponding mandibular cusp.There should be contact of anterior maxillary and mandibularteeth on the working side.


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The balancing side is theBalancing occlusion:

opposite side to the side which the mandiblehas moved.

Balancing occlusion occurs simultaneously onthe opposite side from the workingocclusion.`In balancing occlusion, thepalatal cusps of the maxillary teeth contact thebuccal cusps of the mandibular teeth.Balancing occlusion functions to maintain thedentures in position during excursivemovements. There will be no contact of theanterior teeth on the balancing side.


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Balancing contacts in protrusive occlusion:

Balancing contacts in protrusive excursionspermit the posterior teeth to touch when theanterior teeth are in contact. The distal

inclines of the maxillary buccal cuspscontact the mesial inclines of themandibular buccal cusps.


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Compensating curve of spee:

Anatomic curvature of the occlusal alignmentof the natural teeth beginning at the tip ofthe lower canine and following the buccal

cusps of the natural premolars and molars iscalled curve of spee.

The anterior height of the lower posteriorteeth can be checked clinically. The heightof the 1stmandibular premolar usuallycoincides with the height of the restinglower lip at the corner of the mouth.


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Curve of spee

Curve of wilson


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Documents

Arrangement of the Posterior Teeth