Transcript Arrangement of the posterior teeth

Dr.Mohammad Al Sayed
4/5/2008
The arrangement of the posterior teeth involves the
application of principles similar to those followed in
the arrangement of anterior teeth. The artificial
posterior teeth should be placed as nearly as possible
where the natural teeth were .
Orientation of the occlusal plane:
* The anterior end of the occlusal plane is oriented
according to esthetics. The vertical level at which
the anterior teeth are set is the level of the anterior end
of the occlusal plane. This level is usually
1-2 mm below the resting upper lip.
* The posterior end of the occlusal plane should be
located so that it would be in level with the junction
middle and the distal third of the between the
retromolar pad. This guideline will place the occlusal
plane that is familiar to the tongue.
* The inclination of the occlusal plane is an important
factor in stability or instability of dentures. Ideally, the
occlusal plane should be parallel to both ridges.
* The vertical orientation and inclination is also
governed by the relative amount of bone lost from the
two ridges. The occlusal plane should be placed at
a level that would favor the weaker of the two ridges. ( If
more bone has been lost from the maxilla than from the
mandible, the occlusal plane must be closer to the
maxilla than the mandible. If more bone has been lost
from the mandible than from the maxilla, the occlusal
plane must be closer to the mandible than the maxilla).
However the level of the occlusal plane must be placed
as nearly as possible to the position of the occlusal plane
of the natural teeth.
Buccolingual position of posterior teeth:
* The buccolingual position of the posterior teeth and the
posterior arch form are determined anteriorly by the
positions of the anterior teeth. Posteriorly, it is determined
by the shape of the basal seat provided by the maxilla and
mandible. The mandibular posterior teeth should be
placed so that the antero-posterior groove (central) is
placed on the crest(centre) of the residual ridge.
The crest of the mandibular residual ridge is marked on the
edentulous cast by a line drawn from the crest of the ridge
in the 1st premolar and canine area up to the mesial of the
retromolar pads.
If the teeth are placed buccal to the ridge, the dentures may
tip on the opposite side when pressure is applied to these
teeth. The teeth should not be placed lingual to the
residual ridge because this will cause lack of space for the
tongue, and the dentures will be displaced when the
tongue moves.
* The posterior part of the arch form will be
determined to a great extent by the neutral zone
between the cheeks and the tongue.
Neutral zone is the area between the tongue on one side
and the cheeks and lips on the other, where opposing
soft tissue displacing forces create a zone of neutral or
minimal muscular force, the teeth should be placed as
far as possible with respect for these muscle forces.
* Post extraction changes may lead to a gradual
shifting of the neutral zone with the tongue spreading
laterally. In other words the buccolingual space
available for placing teeth is reduced. This is of
particular importance in the case of the lower
denture. The artificial teeth used are considerably
narrower than the natural teeth and this allows them
to be placed so that the denture is stable.
Position of maxillary posterior teeth:
The maxillary 1st premolar:
The maxillary first premolar is placed with its
long axis perpendicular to the occlusal plane
(vertically upright).The buccal cusps are raised
0.5mm from the occlusal plane.
The maxillary 2nd premolar:
The long axis is perpendicular to the occlusal
plane ( parallel to the vertical axis). The buccal
cusp is 0.5 mm above the occlusal plane and
the palatal cusp touches the occlusal plane.
molar
The maxillary 1st molar:
The long axis (viewed from side ) may slightly
incline mesially. When viewed from the
front the tooth slopes buccally. The
mesiobuccal cusp of the first molar is raised
0.5 mm above the occlusal plane. The
mesiopalatal cusp is in contact with the
occlusal plane. The distobuccal cusp is
raised about 1 mm above the occlusal
plane.
The maxillary 2nd molar:
The long axis ( viewed from side, cervical
area) may slightly incline mesially. The
mesiobuccal cusp of the 2nd molar is raised
1 mm above the occlusal plane. The
distobuccal cusp 1.5 mm above the occlusal
plane. No cusp touches the occlusal plane.
When viewed from the front the tooth
slopes buccaly (more than the 1st molar).
The maxillary teeth viewed from the occlusal
surface should follow the following guidelines:
- The distobuccal surface of the canine, the
buccal surfaces of the premolars and the
mesiobuccal surface of the 1st molar should
follow a straight line. Buccal surfaces of the 2nd
molar are slightly inwards and are placed so
that all buccal surfaces of the 1st and 2nd molars
follow a straight line.The posterior teeth should
be placed so that the central grooves of the
maxillary posterior teeth follow the line of the
crest of the mandibular residual ridge.
The position of the mandibular posterior
teeth:
The placement of the mandibular posterior teeth
determines how well the teeth occlude, both in
centric occlusion and in lateral and protrusive
excursions. The mandibular 1st molar is first
placed in position followed by the 2nd molar,
and then the two bicuspids. After placing each
mandibular tooth in the correct position the
incisal guide pin should be checked to insure
that it is in contact with the guide table.
Position of the mandibular 1st molar:
The mesibuccal cusp of the maxillary 1st molar
fits into the buccal groove of the mandibular
1st molar. The mesiolingual cusp of the
maxillary 1st molar fits into the central
groove of the mandibular 1st molar. This
provides proper buccal overjet.
Position of the mandibular 2nd molar:
The mandibular 2nd molar is placed with the
mesiobuccal cusp fitting between the
maxillary 1st and 2nd molars and contact with
their marginal ridges. The lingual cusps of
the maxillary 2nd molar fit into the central
groove of the mandibular 2nd molar.
Position of the mandibular 2nd premolar:
The mandibular 2nd premolar is placed with
the buccal cusp fitting between the
maxillary 1st and 2nd premolars and in touch
with their marginal ridges. The lingual cusp
fits in between the palatal cusps of the
maxillary bicuspids.
Position of the mandibular 1st premolar:
The buccal cusp of the mandibular 1st
premolar fits between the maxillary canine
and the 1st premolar. Usually this tooth is
not placed until the anterior and posterior
teeth are placed. If there isn’t sufficient
space for the placement of this tooth it may
be trimmed and made narrower to fit into
the available space rather than alter the
placement of anteriors.
In centric occlusion the buccal cusps of the mandibular teeth
contact the central fossae of the maxillary teeth while the
lingual cusps of the maxillary teeth fit into the central fossae
of 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 cusps
of the maxillary teeth meet the buccal cusps of the
mandibular teeth, and the palatal (lingual) cusps of maxillary
teeth meet the lingual cusps of the mandibular teeth.
However the relationship is not cusp tip to cusp tip, but cusp
tip into cusp “valley” with each maxillary cusp distal to the
corresponding mandibular cusp.
There should be contact of anterior maxillary and mandibular
teeth on the working side.
Balancing occlusion: The balancing side is the
opposite side to the side which the mandible
has moved.
Balancing occlusion occurs simultaneously on
the opposite side from the working
occlusion.`In balancing occlusion, the
palatal cusps of the maxillary teeth contact the
buccal cusps of the mandibular teeth.
Balancing occlusion functions to maintain the
dentures in position during excursive
movements. There will be no contact of the
anterior teeth on the balancing side.
Balancing contacts in protrusive occlusion:
Balancing contacts in protrusive excursions
permit the posterior teeth to touch when the
anterior teeth are in contact. The distal
inclines of the maxillary buccal cusps
contact the mesial inclines of the
mandibular buccal cusps.
Compensating curve of spee:
Anatomic curvature of the occlusal alignment
of the natural teeth beginning at the tip of
the lower canine and following the buccal
cusps of the natural premolars and molars is
called curve of spee.
The anterior height of the lower posterior
teeth can be checked clinically. The height
of the 1st mandibular premolar usually
coincides with the height of the resting
lower lip at the corner of the mouth.
Curve of spee
Curve of wilson