198 - university of pittsburgh
TRANSCRIPT
Custom-Fabricated Masks for Aeromechanical Measures
CHarRLuiE U. Kastner, D.D.S., M.S.
Anne H. B. Putnam, PH.D.
RaupH L. PH.D.
A technique is described for the construction of custom fabricatedface masks designed for use in aeromechanical studies of individualswith speech disorders, such as those associated with craniofacial de-fects. The wax-elimination method of mask fabrication described hereinis similar to routine dental laboratory procedures. Materials employedare heat-cured acrylic resin for the body of the mask and heat-curedresilient liner for the tissue contacting surface of the mask.
Dentists may be called upon by speech
clinicians and scientists to fabricate spe-
cialized masks which cover the mouth, nose,
or both, so that oral and nasal air flows
and pressures may be measured. These
aeromechanical measurements are useful
when evaluating and managing speech
disorders such as those which may occur
in individuals with craniofacial defects.
Sampling such aeromechanical data is a
twofold problem, however. The mask for
collecting oral or nasal air flow, or both,
must conform to the face under dynamic
conditions oflip, perioral tissue, or man-
dible activity during speech without un-
duly restricting such activity; at the same
time, the mask must be able to accom-
modate the specialized accessories needed
to sample upper airway pressures during
speech. Commercially available masks of
plastic or rubber are often not amenable
to modifications for specific clinical or re-
search requirements. They may not func-
tion satisfactorily even when supple-
mented by use of adhesive putty (see for
example, Gurley and Vig, 1982) to stop air
Dr. Kastner is Associate Professor of RestorativeDentistry at the University of Alberta. Dr. Putnam isan Associate Professor in the Department of SpeechPathology and Audiology at the University of Al-berta. Dr. Shelton is a Professor in the Departmentof Speech and Hearing Sciences at the University ofArizona and was visiting Professor in the Faculty ofRehabilitation Medicine at the University of Albertaduring the course of this work.
leaks. Furthermore, some adhesive putties
may contain asbestos and may be a poten-
tial health hazard. The purpose of this ar-
ticle is to describe a method of individu-
alized face-mask fabrication that is versatile
and safe in its application. Masks can be
constructed to fit the nose, mouth, or both,
of any subject and to couple efficiently with
the aeromechanical measuring instru-
ments.
TECHNIQUE
Mask fabrication involves nine steps as
described below with reference to techni-
cal methods and instruments currently
available in the well equipped dental lab-
oratory.
Step 1
Make a plaster model of the instrument
side of the mask. Determine the salient di-
mensions of the connection to be utilized
in coupling the flow-measuring device and
the mask, e.g., the dimensions of the in-
take cone of a Silverman- or Fleisch-type
pneumotachometer or anemometer. If the
aeromechanical measuring equipment
comes with its own commercial mask (Fig.
1A), make an irreversible hydrocolloid
impression of that mask's opening (instru-
ment side). Otherwise, make an impres-
sion of the connector on the measuring
device. The impression is poured up in
quick-setting plaster and serves as a posi-
197
198
tive model (Fig. 1B) for constructing the
instrument side of the mask. This plaster
cast of the coupling portion of the mask
can then be trimmed with a cast trimmer
to the exact size required (Fig. 2).
Step 2
Create a facial moulage using irrevers-
ible hydrocolloid to make an impression
of the facial anatomy to be covered by the
mask (Morrow et al, 1980). Paper clips orgauze are placed superficially in theimpression material to retain a plasterbacking which is poured over the entireimpression to reinforce it. Remove theimpression from the face and pour the castin dental stone. Paint separating medium!
'Al-cote, LD. Caulk Co.
Cleft Palate Journal, July 1985, Vol. 22 No. 3
FIGURE 1. (A) Commer-cial mask (B) Plaster cast of theinstrument end of the com-mercial mask
FIGURE 2. Plaster masktrimmed to preserve side withopening for instrument cou-pling
on the separated cast (moulage) and out-line the extent of the tissue coverage re-
quired by the mask (Fig. 3).
Step 3
Fabricate a plaster mask using the facialmoulage and the previously prepared castof the instrument opening. Block out anyundercuts on the facial moulage (nares,lips) with modeling clay and make a plas-ter impression following the anatomicaloutline on the moulage. Trim away anyexcess plaster and bond the previouslyprepared cast of the instrument side of themask to the facial section with additionalplaster. Use a plaster knife and wet-drysandpaper to sculpt the external surfaceof the mask as desired (Fig. 4), taking careto preserve the shape and detail of the tis-
Kastner, Putnam, and Shelton, CUSTOM-FABRICATED MASKS 199
sue and instrument surfaces of the plaster
mask.
Step 4
Embed the plaster mask in gypsum
product investment material using cus-
tomary flasking principles and procedures
(Fig. 5). If the external surface of the plas-
ter mask has no undercuts, paint it with
separating medium. Select the proper-sized
investing flask, and use a mixture of im-
proved dental stone" in one-half ofthe flask
to invest the plaster mask. Position the
narrow surface of the plaster mask toward
the bottom of the flask. If the external
surface of the plaster mask has undercuts
*Vel-Mix Corporation
FIGURE 3. Mask out-lines on facial moulages
FIGURE 4. (A) Sculp-tured plaster mouth mask po-sitioned on facial moulage (B)nose mask
between the instrument and tissue sur-
faces, it is necessary to determine the height
of contour (the greatest convexity of the
plaster mask) and cut the mask into two
parts (Fig. 6). The two parts are then in-
vested as described above (Fig. 7).
Step 5
Remove the plaster mask from the in-
vestment material. The improved dental
stone should have been allowed to set
completely before removing the plaster
mask from the investment with an air chisel
(Fig. 8). This will leave the investment flask
with a mold ofthe external surface ofthe
plaster mask. Examine and repair any de-
fect of the mold with improved dental stone
and sandpaper. Then, line the mold evenly
200
FIGURE 5. Plaster mouth mask invested
FIGURE 6. -Plaster nose mask cut at the greatestconvexity (height of contour)
Cleft Palate Journal, July 1985, Vol. 22 No. ©
with two layers of baseplate wax (Fig. 9).
The second layer applied should be as
smooth as possible as this will be the in-
ternal surface of the mask.
Step 6
Complete the flasking procedure by in-
vesting the wax mask in a mix of dental
stone with both halves ofthe flask in place.
Step 7
Separate the two halves of the flask.
Proceed with boilout, wax elimination and
the application of separating medium (Fig.
10) in the usual manner.
Step 8
Pack the mask by filling and compress-
ing acrylic resin and resilient liner into the
mold in the flask. Follow the manufactur-
er's specifications in handling and mixing
clear, heat-cured acrylic resin. For the first
step of the packing procedure, cellophane
paper is used between the two halves of
the flask to allow them to be separated.
Examine and repair any deficiencies and
cut away excess material (flash). Remove
1'/; to 2 cm of packed acrylic resin from
the periphery of the facial side of the
packed mask with a sharp scalpel (Fig. 11).
Replace the cutaway portion with very soft
ethylmethacrylate® (resilient liner) which
Co, Essinton PA
FIGURE 7. Investedhalves of the plaster nose mask
Kastner, Putnam, and Shelton, CUSTOM-FABRICATED MASKS 201
FIGURE 8. Use of air chisel to remove the plas-ter mask from the investment
will form the pliable facial interface ofthe
mask. This resilient material stays quite
sticky; eight to ten minutes after mixing it
has a runny consistency and is easier to
handle. However, care must be taken not
to incorporate air bubbles when applying
the ethylmethacrylate and it should be
overfilled since it does not lend itself to a
ae
FIGURE 9. Mold lined evenly with two layers ofbaseplate wax
trial pack procedure. When the ethyl-
methacrylate has been applied to the acrylic
resin body of the mask, the two halves of
the flask are realigned without cellophane
paper and slowly pressed together. The two
halves of the flask do not have to make
100 percent contact since flash of the re-
silient liner is desirable. Clamp the flask
and place it into a curing unit for eight
hours at 165° Fahrenheit. An equivalent
heat-cured resilient denture liner, Softic
49", has recently become available and can
also be used to make the pliable tissue con-
tacting border of the mask.
*Kerr Corporation
FIGURE 10. Applicationof separating medium afterboilout of wax
202
Step 9
Separate the flask and retrieve the pro-
cessed mask for finishing and final polish-
ing. An air chisel, used carefully, is help-
ful during the deflasking procedure.
Trimming and polishing of the mask is
done with the customary dental instru-
ments and equipment. Ice water can be
used to facilitate trimming and polishing
of the resilient border of the mask. If the
mask has to be sectioned, as was the case
with the nose mask shown in Figure 6, the
processed sections can be joined with self-
curing clear acrylic resin. The joints can
be rendered even and smooth with rou-
tine trimming and polishing procedures
(Fig. 12).
DIscUssION
The technique which has been de-
scribed here yields custom-fabricated face
masks (Fig. 13) which are useful to the
study of aeromechanical events in speech
in several ways. The clear, firm acrylic resin
which forms the body of the mask consti-
tutes a stable structure for coupling to air
flow monitoring devices and a stable base
for the soft ethylmethacrylate resilient liner
which interfaces with the subject. Further-
more, the clear acrylic body of the mask
may be modified by drilling orifices
through it or securing attachments to it
which allow for simultaneous observation
or experimental manipulation of several
aeromechanical events. Two such modifi-
Cleft Palate Journal, July 1985, Vol. 22 No. 3
FIGURE 11. Removal of1'/ to 2 cm of packed acrylicresin to be replaced with verysoft ethylmethacrylate (resili-ent liner)
cations are illustrated in Figure 14. Item
"a" in the figure is a patent bipolar nipple
which has been sealed into the left wall of
the mask, transversing it and facilitating
the attachment of tubing used to sense in-
traoral or nasal air pressures in a subject
during speech production. In the example
shown, a short sleeve of polyethylene tub-
ing serves as a coupling receptacle on the
FIGURE 12. Completed nose mask
Kastner, Putnam, and Shelton, CUSTOM-FABRICATED MASKS 203
inner pole ofthe nipple for a short length
ofslender tubing. With the mask in place
over a subject's oral airway, the slender
tubing can be inserted translabially into the
subject's mouth to sample intraoral air
pressure during bilabial consonant pro-
duction. The slender, short length can be
easily removed and replaced with a com-
parable piece ofclean tubing for each new
subject. The outer pole ofthe nipple can
be seen on the exterior of the mask in Fig-
ure 13 where it provides continuity for the
pressure-sensing line by coupling to tub-
ing connected to a differential pressure
transducer.
A second modification to which this mask
design lends itself is exemplified by item«6055
c" in Figure 14. In this case, the mask has
FIGURE 13. Mouth maskon subject depicting instru-mentation attachment and re-silient liner (a)
FIGURE 14. Internalview of mouth mask showingfrom left to right (a) pressuresensing tube, (b) coupling toflow meter, and (c) oral pres-sure release attachment
been customized for a research project to
include a special receptacle secured to its
inner right wall by self-curing acrylic. The
receptacle was designed to hold a transla-
bial pressure-release device in optimal po-
sition for insertion between a subject's lips
with the mask in place over the oral air-
way. The pressure-release device is shown
inserted in the receptacle with its mouth
piece in the foreground of Figure 14; it
was used experimentally to introduce
translabial air leaks during subjects' pro-
ductions of voiceless bilabial stop conso-
nants while intraoral air pressures and oral
air flows were monitored simultaneously.
The versatility of the mask in this inves-
tigation facilitated the manipulation and
observation of multiple aeromechanical
204
events during speech-like tasks.
A final and especially versatile feature
of this mask design is its soft tissue border
of ethylmethacrylate resilient liner. The
pliability of this material is increased by
submerging it in warm water. At body
temperatures the liner tends to conform
to the contour of a subject's face and
maintains a tenacious interface in spite of
motions of the subject's mandible or per-
ioral tissues during speech. This obviates
the need for the use of additional adhe-
sive putties between the subject and the
mask and precludes the potential health
hazard of some conventionally used put-
ties which may contain asbestos. Finally,
Cleft Palate Journal, July 1985, Vol. 22 No. 3
masks designed according to the steps out-
lined here can be made to fit faces of all
shapes and sizes and can be cold sterilized
for use on a large number of subjects.Acknowledgement. The authors thank Mr. Jim
Perry, Mr. Phil Perry, and Dr. Frank B. Wilson fortheir contributions to this project.
REFERENCES
GURLEY WH, V1G PS. A technique for the simulta-neous measurement of nasal and oral expiration.Am J Orthod 1982; 82:33.
Morrow RM, RUDD KD, EISSMANN HF. Dental Lab-oratory Procedures Complete Dentures, Vol I, St.Louis: CV Mosby Co, 1980: