Measurement of pressure ulcer volume using dental impression materials: suggestion from the field.

Measurement of Pressure Ulcer Volume Using Dental Impression Materials: Suggestion from the Field

[Covington JS, Griffin JW, Mendius RK, et al: Measurement of pressure ulcer volume using dental impression materials: Suggestion from the field. Phys Ther 69:690--694, 1989]

Key Words: Decubitus ulcer; Electrotherapy, electrical stimulation; Tests and measurements, volume; Wound healing. Chronic wounds such as pressure ulcers constitute a problem in rehabilitation. To determine the amoung of healing in response to treatment, sequential assessments of changes in ulcer size are essential. When ulcers involve only the epidermis and the dermis, repeated measurements of wound perimeter or wound surface area (WSA) can furnish a good index of the amount of healing that has occurred. When ulcers are deep enough to involve subcutaneous tissue and muscle, however, measurements of both internal configuration of the wound (ie, depth and volume) and WSA are necessary to assess completely the amount of healing that has occurred. Various satisfactory methods of WSA measurement have been described. These methods include length and width measurements of the wound with a ruler[1,2] and analysis of photographic records[3] or tracings of wound perimeters.[4-6] Internal wound dimensions are commonly measured by placing a depth gauge at the "deepest" aspect of the wound[6] or by determining the volume of saline needed to fill the wound.[1] Neither of these methods is entirely satisfactory. Use of a depth gauge leaves considerable room for measurement error because the value obtained from each measurement depends on the technician's determination of the "deepest" portion of the wound. Although the volumetric method appears to be more accurate than the depth-gauge method, the use of this method is sometimes not feasible. We have encountered two patient situations in which the volumetric method could not be performed. Both patients had Grade IV (subcutaneous or deeper tissue involvement) pressure ulcers. One patient with a sacral ulcer could not be turned for volumetric measurements because of respiratory complications. The other patient had an ulcer over the ischial tuberosity that could not be filled with saline because of its location. Although healing rates of pressure ulcers in response to various therapeutic interventions have been reported for WSA measurements,[2-4] healing rates for changes in volume have not. Furthermore, little information exists concerning the correlation between changes in depth and volume and changes in WSA as healing progresses in deep pressure ulcers. It has been our experience that changes in internal wound dimensions and changes in WSA may not always be parallel during the healing process. For example, the patient with the ischial ulcer showed what seemed to be a satisfactory healing rate according to WSA measurements, with little apparent change in wound depth. Although a change in internal wound configuration seemed to be occurring as determined by digital probing, this internal change could not be quantified. In the patient with the Grade IV sacral ulcer, we observed granulation tissue beginning to fill the wound, although WSA measurements showed little change. Thus in these two patients, WSA measurements did not seem to provide a complete description of the healing that seemed to be occurring, and volumetric measurements with saline were impossible to perform. We therefore sought an alternative method for quantification of changes in ulcer volume. This report describes 1) fabrication of a model of a pressure ulcer using dental impression-making techniques and 2) use of the model to provide a quantitative measurement of the wound space. Such a measurement of wound volume could furnish important additional information to WSA measurements in describing healing rates of deep pressure ulcers.

Background

In construction of fixed and removable dental prosthetic devices, dentists use a variety of impression materials to produce an exact duplicate of the patient's oral cavity. Most impression materials are two chemical forms that react when mixed together; the reaction mechanism takes place intraorally. The final product is a dimensionally accurate "negative" impression of the tooth or oral structure. A gypsum material is then poured around the impression and allowed to set. The resulting "positive" cast duplicates the patient's oral cavity with an accuracy of approximately 0.4%.[7] This accuracy is maintained even though the impressions are often made in a field having saliva or blood present. In making impressions of the pressure ulcer, we used a high-viscosity, addition-type silicone material known as Reprosil [R] (*) (vinyl polysiloxane). This material is classified by the American Dental Association as an elastomeric impression material that produces a polymer of excellent dimensional stability with high strength in thin sections.[8] Vinyl polysiloxane produces no objectionable odor or molecular by-products, is stable in a moist field, is nonirritating to wound tissue, and is available in a variety of viscosities. Vinyl polysiloxanes are also easy to mix and clean up, have little permanent deformation following compressive strain, have acceptable rheological properties that allow thin sections to be removed from the impression area without tearing, and have excellent elastic recovery and detal reproduction.[7]

Procedure

The ulcer used for these measurements was located over the right ischium of a patient with C6 quadriplegia (Fig. 1). The patient was positioned side-lying for the measurements. Equal lengths of the base and catalyst material were extruded onto a mixing pad and mixed (Fig. 2). After mixing, an impression syringe with a lumen tip opening of approximately 2 mm in diameter was loaded and the remaining material was placed onto a square 0.02-in([dagger])-thick piece of polystyrene to form a flat and stable impression base. The syringe was placed into the base of the wound, and the impression material was slowly expelled from the syringe, filling the wound as the syringe was withdrawn (Fig. 3). After expressing material around the wound orifice, the polystyrene square was gently placed over the wound and held steady until the material was set (Fig. 4). The polymerization reaction is usually complete approximately 5 to 7 minutes after mixing begins. As the impression is being made, the edge of the material can be touched to gauge the degree of setting. After polymerization was completed, the negative impression was withdrawn, rinsed off with tap water, and placed in a 2% solution of glutaraldehyde to disinfect it. To construct a positive impression of the wound, we used a reversible hydrocolloid impression material. Reversible hydrocolloid material is used in dentistry to replicate various casts by surrounding them with hot liquid hydrocolloid material that gels upon cooling. The negative impression was placed in a hydrocolloid flask, and the flask was filled with hot liquid hydrocolloid (Fig. 5). When the hydrocolloid cooled, we inverted the flask and removed the bottom to reveal the base of the original impression (Fig. 6). The original impression can be removed, showing a view of the original wound. The flask can be tilted in any manner to allow the wound orifice to be uppermost. Volumetric measurements of the wound were made by titrating colored water into the wound replica. The original impression should remain reasonably stable for several weeks. If a permanent model of this negative impression is desired, a gypsum product (plaster or dental stone) can be used to fill the positive impression (Fig. 7). Reversible hydrocolloid is not a stable long-term product because of its tendency to desiccate. If a permanent model of the positive impression is desired, the original impression can be lubricated with petroleum jelly and dental stone or plaster can be poured around the impression. The permanent models can be retained for future analyses.

Clinical Considerations

The ideal type of ulcer for this measurement procedure is one of craterlike configuration, without extensive undermining or sinus formation. The wound orifice must be large enough to permit removal of the impression material after it has set; a wound with a small orifice and large interior would not be suitable for this technique. If the wound orifice is in an area with high-density body hair, the area can be lubricated using petroleum jelly to minimize hair removal as the impression is withdrawn. The patient should be able to remain still so the procedure can be continued to completion. A disadvantage of this procedure is apparent if it becomes necessary to remove the material before polymerization is complete. The unset material has the consistency of mud or pudding, and complete removal of unset material is difficult. If the procedure must be halted before polymerization is complete, the polystyrene base can be withdrawn, the impression material covered with a cloth, and the patient repositioned. The remaining material will continue to polymerize and can be removed when set. We have not encountered instances in which impression material leaked into sinuses, fragmented, or remained unpolymerized. An advantage of this method is that the patient does not have to be in any particular position for the procedure because of the high viscosity of the impression material. The use of impression materials for this purpose is analogous to intraoral use by dentists, in which an impression is taken of an area (often a wound created by dental surgery) that is frequently contaminated with blood and saliva. We consider the risks associated with this procedure to be minimal. The time involved for creation of the negative impression (ie, time involved with the patient) is approximately 15 minutes. The time involved in creation of the positive impression and determination of wound volume is approximately 45 minutes. The cost of materials required for one ulcer measurement is approximately $3. Access to a dental laboratory and dental personnel would be required for the measurement procedure following creation of the negative impression. Materials for this technique can be obtained from a dental laboratory or dental office.

Summary Understanding of the healing rates of deep pressure ulcers may be enhanced in future studies by relating changes in wound volume to changes in WSA. In this report, a type of dental impression material, vinyl polysiloxane, was used to produce a model of the internal topography of a pressure ulcer. This model was used to obtain volumetric measurements of the wound cavity. A permanent replica (cast) of the wound was also fabricated. Further clinical trials investigating the reliability of this method for measuring the volume of deep pressure ulcers are indicated.

(*)L D Caulk Co, Div of Dentsply International, Inc, Milford, DE 19963. ([dagger])1 in = 2.54 cm.

PHOTO : Fig. 1. Grade IV pressure ulcer before measurement.

PHOTO : Fig. 2. (A) Materials needed for making an impression include the impression material

PHOTO : extruded on a mixing pad, a mixing spatula, and disassembled impression syringe to ease

PHOTO : loading; (B) after mixing, impression material is loaded into syringe, and syringe is

PHOTO : reassembled.

PHOTO : Fig. 3. Loaded impression syringe is placed into wound, and impression material is

PHOTO : expelled into ulcer.

PHOTO : Fig. 4. When wound cavity is filled, remaining impression material is placed on a stiff

PHOTO : polystyrene sheet, placed over wound, and held gently in place until impression material

PHOTO : is set.

PHOTO : Fig. 5. Positive replication of wound is made using reversible hydrocolloid impression

PHOTO : material. Impression (on base of left flask) is placed in hydrocolloid flask and filled

PHOTO : with liquid hydrocolloid (right flask).

PHOTO : Fig. 6. (A) Hydrocolloid cools and gels, and the impression is removed; (B) impression

PHOTO : represents wound topography.

PHOTO : Fig. 7. Resulting plaster cast of wound (A) matches original "negative" impression and (B)

PHOTO : can be used for further study or stored indefinitely.

References [1]Wolcott LE, Wheeler PC, Hardwicke HM, et al: Accelerated healing of skin ulcers by electrotherapy: Preliminary clinical results. South Med J 62:795-801, 1969 [2]Carley P, Wainapel S: Electrotherapy for acceleration of wound healing: Low intensity direct current. Arch Phys Med Rehabil 66:442-446, 1985 [3]Akers T, Gabrielson A: The effect of high voltage galvanic stimulation on the rate of healing of decubitus ulcers. Biomed Sci Instrum 20:99-100, 1984 [4]Kloth LC, Feedar JA: Acceleration of wound healing with high voltage, monophasic, pulsed current. Phys Ther 68:503-508, 1988 [5]Bohannon RW, Pfaller BA: Documentation of wound surface area from tracings of wound perimeters: Clinical report on three techniques. Phys Ther 63:1622-1624, 1983 [6]Sinacore DR, Mueller MJ, Diamond JE, et al: Diabetic plantar ulcers treated by total contact casting: A clinical report. Phys Ther 67:1543-1549, 1987 [7]American Dental Association Specification #19 for Dental Impression Materials. Chicago, IL, Council on Dental Materials and Devices, American Dental Association, 1984 [8]Phillips RW: The Science of Dental Materials, ed 8. Philadelphia, PA, W B Saunders Co, 1982, pp 144-149

J Covington, DDS, is Chairman, Department of Dental Hygiene, College of Related Health Professions, and Associate Professor, College of Dentistry, The University of Tennessee, Memphis, 847 Monroe Ave, Rm 430, Memphis, TN 38163 (USA). J Griffin, MS, PT, is Associate Professor, Department of Rehabilitation Sciences, The University of Tennessee, Memphis. R Mendius, MSCRRN, is External Rehabilitation Coordinator, Baptist Memorial Hospital Regional Rehabilitation Center, 1025 E H Crump Blvd, Memphis, TN 38104. R Tooms, MD, is Professor, Department of Orthopaedic Surgery, The University of Tennessee, Memphis. J Clifft, MS, PT, is Assistant Professor, Department of Rehabilitation Sciences, The University of Tennessee, Memphis.