198 - University of Pittsburgh

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


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-


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


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,


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:

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