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DENTAL ARTICULATION, FACEBOW AND ARTICULATORS
Dr. Waseem Bahjat Mushtaha
Specialized in prosthodontics
1- dental articulation
Dental articulation:
It means the contact relationships of maxillary and
mandibular teeth as they move against each other. This is a dynamic
process.
Articulator:
It is a mechanical instrument that represents the tempomandibular joints
and jaw members, to which maxillary and mandibular cast may be
attached to simulate some or all-mandibular movements.
Occlusion:
It is the static relation ship (process of closure) between the incising or
masticating (occluding) surfaces of the maxillary and mandibular teeth
when they are in contact.
Centric occlusion:
It is the relation of opposing occlusal surfaces which
provides the maximum planned contact and\or
intercuspation.
Centric relation:
It is the relation of the mandible to the maxilla when the
condyles are in uppermost and rearmost position in the
glenoid fossa at a given degree of vertical dimension (jaw
separation). This position may not be recorded in the
presence of dysfunction of the masticatory system.
Centric occluding relation:
It is a term sometimes used to describe the condition in which
the jaws are in centric relation and the teeth or occlusal
surfaces in centric occlusion.
Anatomical articulation:
It is an occlusal arrangement where the posterior artificial teeth have
masticatory surfaces (can make normal masticatory movements with
comfort and efficiency) that closely resemble those of the natural
healthy dentition and articulate with similar natural or artificial
surfaces.
Balanced occlusion:
It means that the artificial teeth are set up so that as many teeth as possible
are in occlusion in any occlusal relationship.
Balanced articulation:
It is bilateral, simultaneous, anterior, and posterior occlusal contact of
teeth in centric and eccentric positions. It means an arrangement of the
teeth so that in any occlusal relationship as many teeth as possible are
in occlusion, and when changing from one relationship to another they
move with a smooth, sliding motion , free from cuspal interference
and maintaining even contact
Curve of Spee (anteroposterior curve):
It is the anatomic curve established by the occlusal
alignment of the teeth, as projected onto the
median plan, beginning with the cusp tip of the
mandibular canine and following the buccal cusp
tips of premolar and molar teeth, continuing
through the anterior border of the mandibular
ramus, ending with the anterior most portion of
the mandibular condyle
Curve of Menson:
It is the curve of occlusion in which each cusp and
incisal edge touches or conforms to a segment of
the surface of a sphere 8 inches in diameter with
its center in the region of the glabella
Curve of Wilson (mediolateral curve):
It means in mandibular arch, that curve , as viewed in frontal plane, which
is concave inferiorly and contacts the buccal and lingual cusps of the
mandibular molars. In the maxillary arch, that curve, as viewed in
frontal plane, which is convex superiorly and contacts the lingual and
buccal cusps of the maxillary molars. The curved is formed by the
facial and lingual cusp tips on both sides of dental arch
Compensating curve:
It is anteroposterior curvature (in the median plane) and the mediolateral
curvature (in the frontal plane) in the alignment of occluding surfaces
and incisal edges of artificial teeth that are used to develop balance
articulation. These curves introduced in the construction of complete
dentures to compensate for the opening influences produced by the
condylar and incisal guidance during lateral and protrusive mandibular
excursive movements, these curves are artificial counterparts of the
curve of Spee and monsoon, which are found in the natural dentition.
The working side:
It is the side on which the chewing is being
done at the movement; it is the side to
which the mandible has moved.
The balancing side:
It is the side opposite to the working side. It is
the side on which, although there is greater
separation of the teeth, there is at least one
point of contact between the upper and
lower teeth. It is also the side on which the
grater condylar movement has occurred
II-FACE-BOW
Def: the face-bow is a caliper-like device that
is used to record the relationship of the jaws
to the temporomandibular joints or the
opening axis of the jaws and to orient the
casts in this same relationship to the
opening axis of the articulator.
Types of face-bow
1-the arbitrary (maxillary) face-bow
2-the kinematic (mandibular, hinge axis
locator) face-bow
1-the arbitrary (maxillary) facebow
A-The maxillary face-bow is one generally used in
construction of complete denture
B-it is used to record the position of the upper jaw
in relation to the hinge axis and transferring the
relation to an articulator. The maxillary face-bow
is simple to use and relatively accurate, and is
based on average computations of an axis
opening of the jaw.
C-it is placed on, the face with condyle rod located
approximately over the
condyles.
D- The condyle rods of one particular model are
positioned on a line extending from the outer
canthus of the eye to the top of the tragus of the
ear and approximately 13mm in front of the
external auditory meatus. The rods of another
commonly used model (ear face bow) are
designed to fit into the external auditory
meatuses (as a posterior reference point).
E-the fork of maxillary face bow is attached to the
maxillary occlusion rim so the record is a simple
measurement from the jaws to the approximate
axis of the jaws.
2-the kinematic (mandibular,
hinge axis locator) face-bow
A-it is used to locate the true terminal hinge axis
and transfer this record to the articulator when
mounting the maxillary cast. However, use of it
can aid in recording centric relation.
B-the fork of kinematic face-bow is attached to the
mandibular occlusal rim.
C-since this is used to orient the casts on an
articulator in the same relation to the opening
axis of the articulator as the jaws are to be the
opening axis of jaws
Functions of a face-bow
1-locate the terminal hinge axis by the use of
kinematic face bow.
2-relate the maxillary cast to the transfer axis
of the articulator in the same relationship as
the maxilla is related to the mandibular
hinge axis.
3-relate the mandibular cast to the hinge axis
by means of a centric relation record.
An arbitrary mounting of the maxillary cast
without a face-bow transfer can introduce
errors in the occlusion of the finished
denture. A face bow transfer is essential
when cusp teeth are used, allows minor
changes in the occlusal vertical dimension
without having to make new maxillomandibular records, and is also most helpful
in supporting the maxillary cast while it is
being mounted on the articulator.
ARTICULATORS
DEF: is a mechanical device which represents the
temporo-mandibular joint and jaw members to
which maxillary and mandibular casts are attached
to simulate jaw movements. The records made
with occlusion rims are used to mount the master
casts and to adjust to articulator. They also help in
maintaining the desired jaw relationships of the
casts during setting up of teeth.
Articulators are classified
according to the instrument
capability and record acceptance
into:
1-simple hinge articulators.
2-mean value or fixed condylar path
articulators
3-adjustable condylar path articulators
A-semi-adjustable articulators.
B-fully adjustable articulators.
1-simple hinge articulators or
plain line articulators
1-They are cold plain line articulators since they
only permit vertical motion i.e. simple opening
and closing or hinge-like movement
2-they accept a single interocclusal record, which is
the centric occluding relation record.
3-Gariot's articulator is a representative for this type
of articulator. It consist of upper and lower
members joined by a simple hinge with a set of
screw against a metal plate posteriorly to serve as
a vertical stop to increase or decrease the distance
between the two members of the articulator.
2-mean value or fixed condylar
path articulators
1-these articulators accept single interoclusal
record the centric occluding relation record, they
permit horizontal as well as vertical movements.
Eccentric movements permitted are based on
average value. For many patients the condylar
path ranges from 30-40 from the horizontal with
an average 32. The inclination of the condylar
guidance of the articulator is fixed to the average
value and cannot be adjusted in any manner.
2-Gysi articulator, Mahdy articulator and Artek.pro
are representive of these types of articulators.
They consist of upper and lower members which
are joined by two vertical posterior posts
"condylar post support" fixed to the lower
member, whereas the upper end of each post has
an inclined groove representing the condylar
path, through which the condylar shafts,
extending from the upper member are located and
moved in this groove allowing horizontal
movement of the upper member.
3-anterior vertical post, "the incisal post"
which is attached to the upper member of
the articulator by a screw , while its lower
end rests on an inclined table, "the incisal
guide table" which is fixed to the lower
member of the articulator.Inclination of the
incisal guide table is fixed at about 30 from
the horizontal plane.
4-in the incisal post there is a hole, through
which the incisal pin passes. The tip of this
pin is designed to touch the midline of the
occlusal rim labially.
5-in Gysi articulator, the upper cast is mounted
according to Bonwill's triangle which is a four
inch (10 cm) equilateral triangle extending
poseriorly from one condyle to the other and
joining the lower incisor's contact point
anteriorly. While the lower cast is mounted
according to the recorded centric occluding
relation record.
6-in Mahdy articulator and Artek pro articulator
face-bow transfer is used to mount the upper cast
while the lower cast is mounted on this
instrument using centric occluding relation
record.
3-adjustable condylar path
articulators
This type of articulators differ from the fixed
condylar path articulators in that they can accept
eccentric records which are used to adjust the
condylar guidance of the articulator, so that the
movements of its jaw members closely resemble
that produced by the patient. According to the
eccentric records accepted by these types of
articulators they are classified into:
A-semi adjustable articulators
B-fully adjustable articulators
A-semi adjustable articulators
This type of articulators can accept the following records:
1-face-bow record to mount the upper cast.
2-centric occluding relation record to mount the lower cast.
3-protrusive record, to adjust the articulator's
horizontal condylar guidance that corresponds to the
patient's horizontal condylar path inclination. Where as the
articulator lateral condylar guidance is adjusted according
to the Hanau's formula
Hanau's formula=L=H\8 + 12
L=the lateral condylar path inclination.
H=the horizontal condylar path inclination
B-fully adjustable articulators
This type of articulator can accept the following records:
1-face bow record to mount the upper cast.
2-centric occluding relation record to mount the lower cast.
3-protrosive record, to adjust the articulator's
horizontal condylar guidance which corresponds to the
patient's horizontal condylar bath inclination.
4-right lateral record, to adjust the left lateral
condylar guidance which corresponds to the
patient's lateral condylar path inclination.
5-left lateral record, to adjust the right lateral
condylar guidance which corresponds to the
patient's right lateral condylar path inclination.
Indexing the cast
Indexing casts prior to mounting them on an
articulator permits removal of the cast and
accurate replacement to the articulator.
Indexing is also important for remounting
procedures made for correcting occlusal
errors after curing a denture. Indexing can
be accomplished by placing grooves or
notches, in the cast or by using remounting
plates
Mounting the master cast on the
articulator
In the process of mounting master casts on a
fixed condylar path articulator the following
steps should be performed:
1-the upper and lower casts are prepared for
laboratory remount by cutting indices on
the under surface of both casts. These
indices are protected by tin-foil.
2-the upper and lower trial denture bases are sealed with
wax to their casts, thus the upper cast, lower cast and wax
rims are all attached together. The arms of the articulator to
be used are lubricated with Vaseline or oil to facilate
cleaning the articulator from the plaster after the case is
finished.
3-the incisal guide pin of the articulator is adjusted until its
top flushes with the top of the upper member.
4-a rubber band is placed on the articulator,
extending from the lower mark of the
guide pin and around
incisal
each condylar post support.
Adjust the rubber band to form a plane that divides the space
between the upper and lower members of the articulator
equally "Bonwell triangle"
5-Three lumps of modeling clay are placed on the
lower mounting plate to serve as an adjustable
cast support
6-with the base plate and occlusion rims sealed
together, place both maxillary and mandibular
casts in the correct relationship on the three clay
supports in the articulators .then align them until
of the occlusal plane of occlusion rim is parallel
to the plane established by the rubber band
7-open the articulator, and paint the base of
maxillary cast with a separating medium.
8-mix, and add plaster to the base of the cast and to
the upper member of the articulator.
9-close the articulator until the incisal guide pin
touches the incisal guide table and then add
plaster as needed to fill any voids. more
10-after the stone has set, invert the articulator, and
open it. Removing the modeling clay cast
supports, paint separating medium on the base of
the lower cast and attach it to the articulator with
plaster.
11-permit the plaster to set, then remove excess
plaster with a knife.
Occlusion rims
An occlusion rim is a wax form used to
establish:
1-the proper lip and cheek support (fullness of
the lips and cheeks)
2-the arch form, which is related to the
activity of the lips, cheeks and tongue.
3-the level of the occlusal plane.
4-accurate maxillo-mandibular jaw relations i.e. Help to determine:
A-vertical dimension and an estimate of the interocclusal distance.
B-horizontal jaw relations (centric occluding relation and condylar path)
5-occlusion rims help to determine the length and width of the artificial
teeth:
A-high and low lip lines are used for determining the length of the
artificial teeth.
B-canine line i.e. corners of the mouth; the distance between the canine
lines determines the width of the six anterior teeth.
C-the distance between the canine line and the posterior end of the
occlusion rim determines the mesiodistal width of the posterior teeth.
6-position of midline of the arch for the correct placement of the central
incisors.
7-arrangement of the artificial teeth to the trial denture (setting up of the
teeth).
Base plate wax is the most commonly used
occluasl rim material. Compound and a
mixture of the plaster and pumice are
sometimes used for constructing occlusal
rims. There are four basic factors that
should be considered in the proper
fabrication of occlusion rims, to assist the
dentist and the dental laboratory technician
throughout the many phases of denture
construction.
These factors are:
1-relationship of natural teeth to alveolar bone:
Since the final goal in the treatment of the edentulous patient is to provide
a functional and esthetic prosthesis, the relationship of the natural teeth
to the alveolar bone must be understood. The fabrication of successful
replacements can be accomplished in most cases only if the artificial
teeth are placed in the same position that was occupied by the natural
teeth they are replacing.
The natural maxillary anterior teeth are inclined slightly forward of the
alveolar bone. They contribute to the support of the upper lip
With the canines providing support for the corners of the mouth. The
mandibular incisors are also inclined forward and tend to support the
lower lip. The maxillary posterior teeth are positioned slightly buccal
to the alveolar ridge, when occluding with the mandibular molars; the
maxillary buccal cusps usually project 2 to 3 mm. beyond the buccal
cusps of the mandibular teeth. The crowns of the lower posterior teeth
are inclined inward
2-relationship of occlusion rims to edentulous
ridges:
The location and dimensions of the occlusion rims in
relation to the edentulous ridge are basically the
same as those for the crowns of the natural teeth
that are to be replaced in their relation to the
alveolar ridge. The occlusion rims simply replace
the natural teeth both in dimension and in their
relationship to anatomic structures. These
relationships should be re-established by the
occlusion rims even if resorption of the residual
ridge has occurred following the removal of the
natural teeth.
3-fabrication technique and
dimensions of occlusion rim:
1-base plate wax (modeling wax):
A sheet of base plat wax is heated over
approximately one half its length until the wax is
soft and pliable. The soft wax is rolled to point to
a point just short of unheated area. The wax is
again heated and rolled until a soft roll has been
formed. The soft wax roll is adapted to a bead of
sticky wax that was previously applied to the
recording base. The roll is further seated to the
base. The roll is further seated to the base with
spatula, with additional molten wax.
The edges of the roll are extended along the lateral surfaces to the border
of the recording base. Additional wax is added to fill any voids in the
contour of the rims. A heated broad bladed knife or plaster spatula is,
used to quickly shape the labial surface of occlusion rim. The anterior
surface should be inclined outward while the posterior surface is
sloped slightly inward.
A hot wax spatula is used to smooth the lingual surface and form a rim
approximately 5mm wide in the anterior area and approximately 810mm in the posterior area.
These basic dimensions are subjected to final chair side changes, since the
dentist uses the rims to determine the proper vertical dimension,
occlusal plane, facial support, as well as the midline of the arch, the
length and width of the anterior teeth, the buccal eminence, the smiling
(high) lip line, and the speaking(low) lip line.
The occlusal surface of the occlusal rim must be smooth and flat. All
surfaces of the rim should be smooth.
2-the composition
(compound impression)
1-May be used and softend in warm water, molded
into a back of the necessary size and placed into
position.
2-a hot wax knife is used to adapt the edge, the
surface is best smoothed with a sand paper.
3-the use of compound is indicated when it is
desired to obtain more than one record of the
occlusion, as with any type of fully adjustable
articulator, or when gothic arch tracing is to be
taken.
3-plaster and pumice
When a functional recording of mandibular
movements is to be made by the patient chewing
on bite rims, these should be made of a mixture of
plaster and pumic. In this technique the patient
goes through the movement of mastication with
the bite blocks in occlusion and so produces the
occlusal plane conforming to those movements.
An acrylic base is the most satisfactory for this
technique. The plaster is mixed with pumic equal
parts of each, to facilate the grinding down in the
mouth.
This plaster-pumic combination is mixed with water
into a thick consistency and a roll of it is placed on
to the base whilst the initial set is taking place. It
can be smoothed with moistened fingers before
setting is completed. A preliminary recording of
vertical dimension is desirable which should be
taken 3mm greater than finally required to allow
for the reduction in grinding down in the mouth.
These plaster rim should be made less than 24 hours
before they are required , otherwise the patient
will have difficulty in grinding them down owing
to the increased hardness of the plaster.