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A Clear Polycarbonate Face Mask for the Treatment of Hypertrophic Scars

S.Locke, C.P.O.(c)
S. Smith, C.P.(c)
B. Szeliski-Scott, B.Sc.O.T.
E.D. Lemaire, M.Sc.

Introduction

Hypertrophic scarring can be one of the most visual and debilitating results of burn tragedy. The wide, red, elevated, stiff and irritable scars have been found to develop in over 80 percent of the cases where a second- or third-degree burn has occurred and the new skin and grafts have healed (1,2). The main factor contributing to the growth of hypertrophic scars is the large increase in blood flow that occurs at the burn site to form granulation tissue. The granulation tissue, though, contains fibroblasts that produce an excessive amount of collagen fibre (at a rate as much as four times that of collagen production in normal skin). The accumulation of these fibres produces the hypertrophic scar (2,3,4,5,6).

The main treatment for this condition is to apply at least 25 mmHg constant pressure to the immature hypertrophic scar (2,5,6,7). This application of pressure will reduce the vascularity in the scar area and, as a result of the decreased blood flow, decrease the collagen formation and lessen the localized lymphoedema.

Although the pressure method for treating hypertrophic scars has been demonstrated to be effective, the pressure must be applied constantly for as long as six to 12 months, the elastic fabric pressure garments are often uncomfortable, and wearing the pressure garments can lead to psychological problems (5). Elastic pressure garments have also been found to be ineffective in applying the required pressure in areas of high contour or during movement and tend to lose their elasticity over time (4,8,9,10,11).

In order to apply constant pressure to a high contour area, such as the face, various methods have been used (4,11,12,13). These methods involve constructing a partial or full molded mask that directly follows the contours of the face, thereby providing contact with the areas of high relief. These devices were fabricated to be worn under an elastic garment or to be used on their own. Although the use of clear plastic face masks for burns has been documented, the fabrication methods for these devices have not been defined in detail so direct comparison between techniques is not possible. In most cases these techniques used low temperature materials that did not generally maintain their contour and did not require vacuum-forming procedures.

Using clear thermoplastics in the fabrication of a face mask for the treatment of hypertrophic scars has many benefits over treatment using traditional elastic fabric garments. Since the mask is formed over a positive cast of the face, the pressure exertion or pressure relief areas can be easily and accurately formed. This precise control of where the pressure will be exerted and how much pressure will exist is of great clinical benefit to the progressive treatment of the patient. The modification of the positive cast also allows for pressure application to areas of high contour on the face and pressure relief in areas where no scarring will occur (in order to increase comfort). Since clear plastic is used to fabricate the mask, the clinician can see the blanching that occurs at the scar region as a result of the decreased blood flow. This is a useful, quick assessment of mask function. The thermoplastic materials used to construct the mask are also more hygienic than previously used materials.

The following sections outline casting and fabrication procedures for the construction of a polycarbonate face mask for the treatment of hypertrophic scars.

Method

Casting Procedure

The following steps outline the procedures used to obtain the positive cast of the patient, which is used to fabricate the mask. The total casting procedure takes approximately 25 minutes.

  1. Patients who were not able to remain motionless and under control during the procedure were sedated (young children, etc.). This was usually done in conjunction with another surgical procedure. In these cases, the teeth were wired together to keep the jaw in the correct orientation and to maintain jaw closure.

  2. The patient was positioned supine, face up, on an examination table with the chin tilted up so as to expose the neck.

  3. Gauze wrap was applied to hold back the hair, and a parting agent (petroleum jelly) was applied to the facial hair, the ears and the ventilator tube. The remainder of the skin was kept moist with a face cloth soaked with water (Figure 1) .

  4. An airway was provided either by using a piece of gauze coated with petroleum jelly to pack one nostril and inserting a nasotrachial tube into the other nostril or by inserting a flexible straw into each nostril and filling in the space surrounding the straws with petroleum jelly-coated gauze.

  5. A plaster dam was constructed around the face using four layers of six-inch wide plaster of paris strips. The dam enclosed the entire face, including the forehead and the area under the chin, and extended 10-12 cm above the highest facial point. It was helpful to have a second person available to hold the top of the dam in the correct position until the plaster hardened (Figure 2) .

  6. A mix of Jeltrate (alginate, Type II regular set) was prepared, and, with the nasotrachial tube held vertical, the mix was poured into the dammed area. The Jeltrate completely covered the face to a level of two cm above the highest facial point (Figure 3) .

  7. After approximately two minutes, when the mixture had set, a plaster of paris bandage was placed over the top of the Jeltrate to maintain the impression's shape. The plaster cover left an opening for the tube to slide through as the mold was removed (Figure 4) .

  8. When the plaster cover had hardened (approximately five minutes), the base of the dam was loosened, and the plaster/Jeltrate impression was removed from the face. The procedure was performed slowly in order to break the adherence between the skin and the Jeltrate.

  9. A damp paper towel was immediately placed over the impression and the "towel-wrapped impression" was placed in a plastic bag (to avoid shrinkage due to loss of moisture).

  10. Within one hour an extension dam was built up around the impression and the impression was filled with plaster.

Fabrication Procedure

The following steps outline the procedure used to fabricate the face mask. The fabrication procedure should take approximately five to six hours.

  1. Once the positive plaster mold had hardened, the Jeltrate impression was easily removed and the mold was modified as follows:

    Approximately two to five mm of material were removed from the positive mold to apply pressure on hypertrophic scar areas. (Up to 8 mm of material must be removed when working on a "fleshy" area-e.g., the cheek.) If there was no scarring on the nose, the nose area was built up approximately three mm. (It was important not to apply excessive pressure on the bridge of the nose.) This procedure was repeated for any area with little subcutaneous tissue.

    If a loss of contour existed between the chin and the mouth, around thenose, or under the chin, material was removed from the problem area to over-correct for the contoured area. The modification and sanding procedure took approximately one-and-a-half to two hours (Figure 5) .

  2. The positive mold was then polished and put in a drying oven until all moisture was removed from the mold. (The oven was set to 65 degrees Celsius, 150 degrees Fahrenheit.) A higher temperature would, most likely, produce cracks in the mold. This procedure took approximately 10 to 12 hours.

  3. A1/16-inch polycarbonate sheet was cut to the draping frame size and placed in a separate drying oven for approximately 48 hours (the oven was set to 82 degrees Celsius, 180 degrees Fahrenheit). It was imperative to dry the polycarbonate sheet to minimize "bubbling" of trapped moisture during the heating process.

  4. The vacuum platen was prepared as follows:

    A block of scrap material (e.g., Ethafoam) was cut so that the top had the same dimensions as the bottom of the positive mold. This block was placed between the platen and the positive mold to reduce the sharp transition between the mold and the platen in order to prevent wrinkle formation during the vacuum forming.

    An air-wick was provided by covering the platen with dacron felt and/or cotton stockinette. This also prevented adhesion of the plastic to the Ethafoam, thereby facilitating removal from the platen.

  5. The preheated positive mold was placed on top of the Ethafoam insert.

  6. The framed polycarbonate sheet was heated in an oven (set to 218 degrees Celsius, 425 degrees Fahrenheit) until the plastic sagged a distance equal to the height of the mold. NOTE: The plastic sheet is thin and will lose its heat rapidly after being removed from the oven. It is advisable to have a heat gun ready for spot reheating (Figure 6 and Figure 7 ).

  7. The frame was removed from the oven and draped over the positive mold. A 22 kg/cm2 (25 lbs./inch2] vacuum was applied to the layup while heat was applied (using a heat gun) to the undercut areas and any other areas that did not contact the mold. The vacuum and heating were continued until full contact with the mold was achieved. The polycarbonate was maintained under vacuum until it and the mold had cooled (approximately one hour) (Figure 8) .

  8. The perimeter of the facial area was then cut from the mold so that the mask could be removed.

  9. The eyes, nostrils and mouth (to the border of the lips) were cut out of the mask, and the new edges were sanded and buffed (Figure 9) .

  10. With the help of the physician and the occupational therapist, the mask was fit to the patient to make final adjustments to the openings, to determine the anchorage points for the elastic retaining harness and to measure the head circumference for making the retaining harness.

  11. Cyano-acrylate glue was used to adhere 1-inch by 1.5-inch pieces of velcro hook to the surface of the mask in order to anchor the three- or five-point retaining harness. A five-point harness was used whenever possible (Figure 10 and Figure 11 ).

Conclusion

The face mask outlined in this paper is presently being used for the treatment of children and adolescents. The clinical results for these patients are very encouraging in all the cases presently under treatment. The clear plastic materials used in construction of the mask are difficult to mold but retain the contours achieved during molding and allow the clinician to visually examine the effects of the mask on the face. The mask can also be worn under an elastic fabric garment (Jobst, etc.) when additional pressure, beyond that exerted by the harness, is required. The polycarbonate mask appears to be a very useful and functional device for the treatment of hypertrophic facial scars.

Acknowledgments

The authors would like to acknowledge the technical contribution of Mr. Terry Rice to the completion of the fabrication technique and the translation skills of Gordon Clark, as well as the support of Mr. Guy Martel, M.H.Sc., C.P.O.(c), Dr. Anna Drzewiecki, and the Prosthetics and Orthotics Department of The Rehabilitation Centre, Ottawa, Ontario, Canada.


Seth Locke, C.P.0.(c), is senior orthotist at The Rehabilitation Centre, 505 Smyth Road, Ottawa, Ontario, Canada.

Sam Smith, C.P.(c), is senior prosthetist at The Rehabilitation Centre, 505 Smyth Road, Ottawa, Ontario, Canada.

Barbara Szeliski-Scott, B.Sc.O.T., is an occupational therapist at the Children's Hospital of Eastern Ontario, 401 Smyth Road, Ottawa, Ontario, Canada.

Edward Lemaire, M.Sc., is the clinical researcher with the Prosthetics and Orthotic De partment of The Rehabilitation Centre, 505 Smyth Road, Ottawa, Ontario, Canada.

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