omparison olydimethyl Robert Daniel

of the physical properties siloxane for fabrication

of two types of facial prost

A. Sanchez, DDS,a Dorsey J. Moore, DDS,b IL. Craz, DDS, MS,C and Robert Chappell, DDSd

University of Missouri-Kansas City, School of Dentistry, Kansas City, MO. The in vitro physical properties of two types of polydimethyl siloxane, MDX 4-4210 and a new material A-2186, were compared. The properties that were investigated in this study were tensile strength, elongation, tear strength, and surface hardness. The properties tested were selected because of their clinical significance for fabricating a facial prosthesis. According to the results obtained in this investigation, the new material, A-2186, had greater tear resistance, tensile strength, and a larger percentage of elongation. A-2186 material, also proved to be softer at the surface than the MDX 4-4210. This combination of physical properties makes this material, A-2186, a better choice than the traditional MDX 4-4210 for the fabrication of facial prostheses. (J PROSTHET DENT 1992;67:679-82.)

he materials used in maxillofacial prosthetics for extraoral prostheses has been a popular subject of research in the past 20 years. Rahn and Boucher,l Beumer and Zlotolow,” and Lewis and Castleberry have described the ideal properties for extraoral prosthesis materials. Many authors have compared and improved the chemical and physical properties of the various materials used for extraoral prosthesis in the search for a better material.4-13 Although each of the available existing materials have advantages and disadvantages, the silicone elastomer MDX 4-4210 (Dow Corning Corp., Medical Products Division, Midland, Mich.) (Fig. l), appears to be the most popular and has most of the properties ideal for use in extraoral prosthesis.14 The purpose of this study was to compare the physical properties of a new material A-2186 (Factor II Inc., Lakeside, Ariz.) (Fig. 2), with those of MDX 4-4210.

MATERIAL

Fig.

1. MDX 4-4210 by Dow Corning Corp.

AND METHODS

A sample group of 90 specimens of each silicone material (MDX 4-4210 and A-2186) was fabricated for each of the tests. The physical properties tested in this study were (1) tensile strength, (2) tear strength, (3) percent elongation, and (4) surface hardness. The test procedures followed the research methods used by Moore et. a1.4 All the specimens were designed and fabricated in accordance with standards established by the American

aAssistantProfessor,Department of Fixed Prosthodontics. bHBG RobinsonProfessorand Chairman,Department of Removable Prosthodontics. Waxillofacial Prosthetics Resident. dProfessor,Department of Oral Biology. 19/l/95258

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2. A-2186 by Factor II Inc.

679

Fig. 3. Diagram of two-part mm). (From Moore et a1.4)

mold design for O-rings (in

Fig. 5. Specimen being tested for tear strength test.

Fig. 6. The Shore A Durometer

testing a sample for sur-

face hardness.

Fig. 4. O-ring sample being tested for tensile strength on Instron

machine.

Society for Testing and Materials (ASTM) designations D412-68 for the tensile strength, D1938-85 for the tear strength, and D2240-68 for the surface hardness test. Aluminum dies were machined to fabricate the O-ring specimens (Fig. 3). To simulate a clinical situation, an impression was made of the master dies and poured in improved stone (two-piece molds). The samples were

anchored on pegs and stretched (Fig. 4) with the Instron machine (No. 1125, Canton, Mass). The pegs were freely rotating Teflon (Du Pont Co., Wi~min~on, Del.) wheels with axles cast in chrome-cobalt alloy. Co&near alignment, absence of torsional forces on the test specimen, and a free-slipping O-ring around the wheel were necessary during stretching. The crosshead speed of the Instron was 50 mm/min with a load cell of 500 kg and a chart speed ratio of 0.2:1 rpm with a 10 kg full scale. All of the O-ring specimens were pulled to the point of rupture (percent elongation and tensile strength). For the tear-strength test, thin rectangular strip (75 mm x 25 mm x 0.5 mm) specimens were fabricated in the

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I. Means and standard deviations of the four tests on facial materials Materials A-2186

MDX 4-4210 Type of test

TI

SD

x

SD

Tensile strength (kg/cm2) Percent of elongation ( W) Tear resistance (kg) Hardness (durometer units)

22.02 329.94 0.19 27.70

2.14 31.34 0.04 0.67

35.45 391.11 0.34 19.90

4.09 24.55 0.04 0.61

same manner as the Q-rings with the use of stone molds. These specimens were sectioned at two thirds (50 mm) of their length, clamped to the Instron machine (Fig. 5), and stretched at a rate of 20 mm/min with a full scale of 500 gm and a load cell of 2 kg (chart head speed [CHS] 0.2:1). Durometer

model No. 340-A2 (The Shore

Instrument and Manufacturing Co., Inc., New York, N.Y.) was used to measure the surface hardness of the two materials (Fig. 6). The specimens consisted of molded disks 30 mm in diameter and 10 mm thick. All sample testings were conducted by one investigator and were done at 23“ C + lo and 50% relative humidity. To eliminate as many variables as possible, the curing and mixing time and the curing temperature were standardized as recommended by the manufacturer. After each mixing, air was removed from the material under vacuum for 30 minutes before it was loaded into the molds. Each sample was carefully examined to ensure the absence of large (macroscopic) air bubbles. RESULTS Table I presents means and standard deviations from the four tests for tensile strength, tear strength, percent elongation, and surface hardness. The Student t-test values comparing the mean for the tensile strength test of MDX 4-4210 (x 22.02) and A-2186 (2 35.45) material were significant at the p < 0.001 level. For the tear resistance study, significant mean differenceswere found between MDX 4-4210 (x0.19) and A-2186 (x 0.34) material at the p < 0.001 level. Significant mean difference were found between MDX 4-4210 (i 329.94) and A-2186 (x 391.11) material

at the

p < 0.001 level for the percent of elongation study. The t-test performed on the sample mean values comparing results for the surface hardness test was significant at the p < 0.001 level for MDX 4-4210 (x 27.70) and A-2186 (X 19.90) material. DISCUSSION The purpose of this study was to compare the physical properties

of these two materials

in their base form (with-

out thinner or color). Moore et a1.4showed an improvement in the physical properties of the MDX 4-4210 material by adding 10% of 360 (manufacturer’s designation) medical

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fluid. This additional variable will be included in the next research project with A-2186 material. During the fabrication of all the samples, there seemed to be fewer air-bubble rejections in the samples fabricated with the A-2186 material than in the samples fabricated with the MDX 4-4210 material. The A-2186 material seems to have less working time than the MDX 4-4210. Its consistency at the time of loading the molds was more viscus than the MDX 4-4210 and thus needed additional force to close the molds, a factor that can present a problem in handling a large mold without a flask. Another difference in handling the two materials was that after the molds were loaded, the residuals were stored in the freezer for use at a later time. This was not possible with the A-2186, because once the catalyst and the base were mixed and stored, there was no way of slowing the reaction so that the material could be used at a later date. The increase in tensile strength, tear strength, and percentage of elongation of the A-2186 material offers a clinical advantage to the marginal integrity of a facial prosthesis. This advantage will increase tbe esthetic quality of a facial prosthesis by permitting a thinner margin with a greater possibility of stretching and less possibility of tearing. The A-2186 material also offers a softer surface than the MDX 4-4210 and simulates a more skinlike feeling. CONCLUSIONS The new silicone material A-2186 has certain advantages in its physical properties over the MDX 4-4210. These advantages are greater tensile and tear strength and a larger percent of elongation, which should clinically increase the usable life of the prosthesis. REFERENCES 1. Rahn AO, Boucher LJ, eds. Maxillofacial prosthodontics. Philadelphia: WB Saunders Co, 1970, 18-30. 2. Beumer J, Zlotolow I. Restoration of facial defects-etiology, disability, and rehabilitation. In: Beumer J, Curtis TA, Firtell DN, eds. Maxillofacial rehabilitation, ed 1. St Louis, CV Mosby, 1979, 311-371. 3. Lewis DH, Castleberry DJ. An assessment of recent advances in external maxillofacial materials. J PROSTHET DENT 1980;43:426. 4. Moore DJ, Glasser ZR, Tabacco MJ, Linebaugh MG. Evaluation of polymeric materials for maxillofacial prosthetics. J PROST~T DENT 1977;38:319.

5. Abdelnnabi MM, Moore DJ, Sakumura JS. In vitro comparison study of MDX 4-4210 and polydimethyl siloxane silicone materials. J PROSTHET D~~~1984;51:523.

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6. Lewis DH, Cowsar DR, Tanquary AC, Tarwater OR. A new RTV silpbenylene maxillofacial prosthetic material [Abstract]. J Dent Res 1976;55(Special issue B):331. 7. Lewis DH, Cowsar DR, Castleberry DJ, Fischer TE. New and improved elastomers for extraoral maxillofacial prosthesis. J Dent Res 1977; 56(Special issue A):174. 8. Gonzales JB, Chao EYS, An KN. Physical and mechanical behavior of polyurethane elastomers formulations used for facial prosthesis. J

12. Bell WT, Chalian VA, Moore BK. Polymethyl siloxane materials in maxillofacial prosthodontics: evaluation and comparison of physical properties. J PROSTHET DENT 1985;54:404. 13. Sweeney WT, Fischer TE, Castleberry DJ, Cowperthwaite GF. Evaluation of improved maxillofacial prosthetic materials. J PROSTHET DENT 1972;27:297.

14. Vergo TJ, Andrews R. Maxillofacial prosthetics: rehabilitation of head and neck cancer patients (III). Quintessence Dent Technol 1984;8:427-

PROSTHET DENT 1978;39:307.

32.

9. Goldberg AJ, Craig RG, Filisko FE. Tear energy of maxillofacial prosthetic materials [Abstract]. J Dent Res 1977;56:(Special issue A):173. 10. Udagama A, Drane JB. Use of medical-grade methyl triacetoxy silane crosslinked silicone for facial prosthesis. 3 PROSTHET DENT 1982;48:86. 11. Wolfaardt JF, Dent M, Chandler HD, Smith BA. Mechanical properties of a new facial prosthetic material. J PROSTHET DENT 1985;53:228.

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Back issues of THE JOURNAI, OF PROSTHETIC DENTISTRY are available for purchase from the publisher, Mosby-Year Book, Inc., at a cost of $7.00 per issue. (Foreign postage is not included.) The following quantity discounts are available: 25 % off on quantities of 12 to 23, and one third off on quantities of 24 or more. Please write to Mosby-Year Book, Inc., Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, or call (BOO)3254177,ext. 4351, or (314)453-4351 for information on availability of particular issues for that period from 1980 to 1991. If unavailable from the publisher, photocopies of complete issues are available from University Microforms International, 300 N. Zeeb Rd., Ann Arbor, MI 48106, (313)761-4700.

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Comparison of the physical properties of two types of polydimethyl siloxane for fabrication of facial prostheses.

The in vitro physical properties of two types of polydimethyl siloxane, MDX 4-4210 and a new material A-2186, were compared. The properties that were ...
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