Download Facebow Manual - Advance Dental Designs

AD2 FACEBOW
RECORDING MANUAL
Dr. Jorge Ayala Puente, DDS*
Dr. Gonzalo Gutiérrez Álvarez, DDS*
Dr. José Miguel Obach M., DDS
Translation: Dr. Barbara Fernández Lübbert, DDS
Edited: Dr. Robert E. Williams
* Roth Williams Center for Functional Occlusion Instructors
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Facebow recording
The facebow is an indispensable part of the semi or completely adjustable
articulator, because the upper cast is mounted in the same position as the maxilla, with
respects to the cranium.
Facebows are classified in two types:
a) Anatomic
b) Cinematic
Anatomic (AD2, Panadent, Whip Mix, Dentatus, etc.) facebows position the
upper maxilla based on the axis-orbital plane which is determined by average values and
will be described later. .
Cinematic facebows are sophisticated instruments such as axiographs and/or
pantograghs that help determine the individual values of different parameters measured in
our patients, such as, exact hinge axis, condyle eminence, Bennett angle, and immediate
side shift provides more information to program the articulator.
For a better understanding of these concepts, we will begin with the basics, which
is a description of an anatomic facebow which is used to obtain initial screening records. .
The facebow used by the AD2 system.
Components of the AD2 System facebow (Fig. 1)
1)
2)
3)
4)
5)
6)
Facebow
Bite fork stem assembly
Bite fork
Nasion relator
Hex wrench
Oribital pointer (not numbered)
1
4
3
5
5
2
Figure 1. Components of the AD2 facebow
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Facebow (Fig.2)
a)
b)
c)
d)
e)
Comprised of:
Two lateral arms (1)
Central screw (2) that joins both lateral arms & allows change in width
Cross bar with rotation screws (1 a) designed to:
1) Position the nasion relator in the slot (3a)
2) Position the bite fork stem through a hole and fixation screw (3b)
External ear pieces (4)
Orbital pointer (5) with fixation screw used with the axiograph.
2
1a
3
1
3a
3b
5
3a
3b
4
Figure 2. Elements that make up the Facebow.
Bite-Fork Stem
Of all the facebow components, the bite-fork stem is probably the most unique
one incorporated by the AD2 System. Its function is to support the bite-fork and it
replaces the facebow when mounting the upper cast on the articulator in the lab.
The bite-fork stem is made of two round metal and perpendicular rods joined by a
simple connector.
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Components of the bite-fork stem (Fig. 3):
1)
2)
3)
4)
5)
6)
Vertical arm
Horizontal arm
Simple connector
Short end
Long end
Double connector (toggles)
4
2
3
1
6
5
Figure 3. Parts of the bite fork stem
The vertical arm presents two ends: an upper short one (4) and a lower long one
(5). The upper end is inserted in a hole found on the facebow cross bar while the lower
end is used when mounting the upper model by being inserted in the mounting fixture.
Both ends have a flat surface which prevents it from rotating once the thumbscrew positions it on the facebow or mounting fixture.
The horizontal arm has a double connector (toggles) that supports and fixes the
bite fork. Never tighten the toggles (6) without the bitefork in place. The toggles will
be distorted!
The simple connector, as well as joining the horizontal and vertical arms,
regulates the height of the horizontal arm and the height of the bite fork.
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Bite Fork
Before using the facebow, the bite fork that will be placed in the patient’s mouth
must be prepared. For that it is necessary to apply Godiva (Kerr green stick compound)
impression material (Figure 4) in three places: in the midline and the area of the first
molars (Figure 5). Ideally, the surface of the compound must be smooth, without
irregular areas to allow for the most accurate impression of the upper incisal edges and
the cusps of the upper bicuspids and molars.
Figure 4. Godiva sticks (Kerr green stick compound)
The bitefork comes with several holes so that the compound has good retention.
There is a line in the center of the bitefork which must coincide with the patient’s skeletal
midline when placing the bitefork. (Figure 6)
Figure 5. Bite fork with compound.
Figure 6. Perforated Bite fork. The
central line represents the facial midline.
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Nasion Relator
Consists of the following :
1. Nasion relator. Once in position, it must be well adapted to the nasal bridge and not
uncomfortable for the patient.
2. Vertical column with two fixation screws. It is used for the following:
a) Supports the nasion relator and regulates its antero posterior position by
means of the upper screw (2a). Sets the orbital height (third reference height).
b) Connects the nasion relator to the facebow cross bar through the slot (2b) and
sets it in place with the lower screw (2c)
Components of the Nasion relator (Fig.7)
2a
1) Nasion pad
2) Vertical column
2a) upper screw
2b) slot to place it on the facebow
cross bar
2c) lower screw
2b
1
2
2c
Figure 7 Nasion relator.
In figure 8, the nasion relator is shown together with the facebow.
Figure 8
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Basic concepts of facebow recording.
It is important to explain certain theoretical concepts so that there is a better
understanding of why the use of the facebow is so important in diagnosis.
This step is necessary to mount the upper cast and reproduce the three
dimensional position of the maxilla. It also provides:
a) an estimated mandibular rotating axis or hinge axis
b) a reference plane, called axis-orbital plane
What is the hinge axis and the axis-orbital plane? Are they really important for an
orthodontic diagnosis?
The facebow uses three reference points, two posterior and one anterior. The
posterior ones represent the rotation axis (or hinge) of each condyle, which are arbitrarily
recorded in the patient’s external auditory canal with the ear pieces on the face-bow.
The anterior reference point or orbital point (3rd reference point) (not necessarily
coincides with the cephalometric orbital point) is also arbitrary and is determined by a
specific distance from the nasal bridge by the nasion relator.
With the three reference points, an axis-orbital plane is established. The upper
cast is mounted on the upper member of the articulator on the axis-orbital plane. (Fig.9).
Figure 9. Axis-orbital plane recorded by the facebow. The hinge axis is determined by
the ear pieces and the orbital point by the nasion relator.
In summary, the use of a semi-adjustable articulator with a facebow will estimate
the position of the maxilla in the skull as well as the relation of the mandible with the
cranium, or its hinge or rotating axis.
Once the lower cast is mounted on the articulator the distance between the hinge
axis and the lower teeth is established so that a mandibular closing arc can be established
for each lower tooth (Fig.10).
This is one of the reasons why the hinge axis is so important. The mandibular closing arc
of the patient on the articulator shows the tooth contacts in closure.
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Fig. 10. Mandibular closing arc where the distance between the hinge axis and the dental
arch are duplicated (or each individual tooth).
Since the reference points are determined arbitrarily, this mandibular closing arc
is not 100% exact, but for diagnosis it is still considered a convenient and useful system.
However, there are certain therapeutic procedures where vertical dimension will be
changed (orthognatic surgery, selective grinding, etc.) and it will be necessary to use a
true hinge axis (cinematic), determined by an axiograph or pantograph that will
accurately determine the true mandibular closing arc.
The following are the steps to use the facebow. Seat the patient in a horizontal
position. However, for practical reasons, the photographs have been taken with the
patient in a vertical position.
Steps for facebow recording.
Step 1
Place the bite fork with the green stick
compound in a water bath at 60ºC (140ºF)
until it softens.
Step 2
Frequently, the bite fork tends to overheat
and cause discomfort for the patient. After
the compound is shaped before it is put in
the mouth run cold water over the bottom
of the bitefork. This will cool the bitefork
and it will cause the base of the compound
to become more firm. This helps to prevent
overseating of the bitefork touching the
teeth.
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Step 3
Place the bite fork in the patient’s mouth
aligning the center mark with the facial mid
line. Lightly press the bite fork upwards so
the teeth indent the compound but making
sure no teeth come in contact with the
bitefork. Remove the bite fork and cool it
in ice water.
Step 4
With a scapel eliminate all compound
excess until the indentation is only 1 mm
deep. There should be only cusp tip
indexing.
Step 5
Place the bite fork in the mouth to check
that the mid-lines coincide and that it is
stable and no teeth touch the bitefork.
Step 6
Place the nasion relator in the slot of the
facebow cross bar and tighten the screw,
which must always be under the cross bar.
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Step 7
Insert and lock the short end of the bite fork
stem to the facebow. The flat surface of the
short end must face the fixation screw.
Step 8
With the hex wrench, loosen the simple
connector on the bite fork stem.
Step 9
With the hex wrench, loosen the double
connector (toggles) on the bite fork stem.
Observation:
(steps 6, 7, 8 and 9 are generally done by a
dental assistant before the facebow
recording begins).
Step10
Take the facebow and loosen the central
manual screw (located on the anterior end
of the face-bow). Turn only ½ turn.
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Step 11
Instruct the patient to separate the lateral
arms of the facebow and to place the ear
pieces in the ear – to push in and forward.
This can be done by an assistant.
Tighten the central screw to lock the width
of the facebow.
Step 12
While the patient (or assistant) is still
holding the facebow arms, place the nasion
relator on the patient’s nasion. Use the
nasion relator like a plunger and put gentle
pressure to push the relator against the
patient. This will move the earpieces more
forward to approximate the condyles. Set
this position with the respective screw.
Step 13
Check that the simple and double
connectors of the bite-fork stem are
loosened and that the double connector is
facing down and is on the right side of the
patient.
Step 14
Slide the bite fork through the hole in the
double connector and put it in the patient’s
mouth seating the teeth in the indentations.
Make sure it seats firm and there is no
movement.
Another method will be shown for
placing the bitefork and the facebow.
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Step 15
Maintain the bite fork stable with the index
and middle fingers of one hand, and firmly
screw the simple and double connectors
with the hex wrench with the other hand,
checking that the lateral arm of the bite fork
stem is at 90º with respect to the vertical
arm. Once the connectors are firmly
tighten, check again the stability of the bite
fork. Another method will be shown.
Step 16
Loosen the central screw of the facebow
and ask the patient (or assistant) to open the
lateral arms and remove it from the ears.
Remove the facebow down and forward.
Step 17
Loosen the thumb screw that joins the bite
fork assembly to the facebow.
Step 18
Remove the bitefork assembly and send it
to the lab so the upper cast can be mounted.
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