Wettability of elastomeric gypsum casts

impression

materials

and voids

in

D e n n i s R. Cullen, D D S , a J e s s W. M i k e s e l l , D D S , b and J a m e s L. S a n d r i k , P h D c Loyola University School of Dentistry, Maywood, Ill. Numerous factors are involved in making an accurate void-free dental artificial stone cast or die. The relationship of the wettability of an elastomeric impression material and its interaction with the gypsum slurry is an important factor. This study examined the relative "pourability" of several impression materials by counting the number of resultant voids in artificial stone casts containing 48 point angles. Those elastomers that exhibited the lowest contact angle with w a t e r produced artificial stone casts with the fewest voids. Surfactants applied to the impression material significantly reduced the number of voids in artificial stone casts, as did modified elastomers designated by the manufacturer as hydrophilic. (J PROSTHET DENT 1991;66:261-5.)

The

fabrication of an acceptable fixed or removable prosthesis is dependent upon an accurate void-free cast or die. The interaction of the elastomeric impression material and the gypsum slurry is important in the fabrication of a void-free die. The interaction is determined in part by the hydrophobic nature of the elastomeric impression materials. These materials include elastic polymers (elastomers) such as polysulfide, condensation reaction silicone, addi-

tion reaction silicone (vinyl polysiloxane), polyether, and a recent introduction to dentistry, a light-cured polyether urethane dimethacrylate. These materials are variably hydrophobic, organic polymers of relatively high molecular weight. The hydrophobic nature of these elastomers has resulted in poor wettability and in an increased number of voids in gypsum casts. These voids are probably caused by the inability of the gypsum slurry to readily wet and flow over the surface of the impression. In an effort to improve the wettability of vinyl polysiloxane materials some manufacturers have incorporated surfactants in their formulations. The improved materials have been termed hydrophilic. Pratten and Craig 1 defined the term hydrophilic in this context to apply to those solids that produce a contact angle of 90 degrees or less when the wetting liquid is water. The purpose of this

Presented in part at the annual session of the American Association for Dental Research, San Francisco, Calif. aAssociate Professor, Department of 0ral Diagnosis and Radiology. bprivate practice, Centralla, Ill. cprofessor and Chairman, Department of Dental Materials. 10/1/28251

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Fig. 1. Diagrammatic illustration of aluminum die used in this study. Dimensions are in millimeters.

THE JOURNAL OF PROSTHETIC DENTISTRY

261

CULLEN, MIKESELL, AND SANDRIK

Supplier

Product name

Type

Citricon light body Citricon heavy body Rapid light body Rapid putty Express light body Express hydrophilic (light body) Express hydrophilic (medium body) Express putty Express hydrophilic putty Imprint hydrophilic (medium body) Mirror 3 Extrude (light body) Mirror 3 Extrude (medium body) Mirror q Extrude putty Impregum F Permadyne light body Permadyne heavy, body Genesis light body Genesis heavy body

Condensation silicone Condensation silicone Condensation silicone Condensation silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Polyether Polyether Polyether Polyether urethane dimethacrylate Polyether urethane dimethacrylate

Kerr Mfg., Romulus, Mich. Kerr Mfg.

Coltene, Alstatten, Switzerland Coltene 3M, St. Paul, Minn. 3M 3M 3M 3M 3M Kerr Mfg. Kerr Mfg. Kerr Mfg. ESPE, Seefeld/Oberbay, Germany ESPE ESPE L. D. Caulk, Milford, Del. L. D. Caulk

T a b l e I L Materials used in gypsum cast void m e a s u r e m e n t ,;'i~

',;;,,i~,

,,,

,,

;

,

Product name

Symbol

Type

Supplier

Permlastic light body Elasticon light body Mirror 3 light body Reflect medium body President light body Repr0sit light body Cutter vinyl :light body Methigum medium body Express light body EXpress -hydrophitic light body Mirror 3 Extrude light body Union Broach light body

Per Ela Mir Ref Pre Rep Cut Met Exp Exh Mxd Uni

Polysulfide Condensation silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone Addition silicone

impregum F

Imp

Polyether

Kerr Kerr Kerr Kerr Coltene Caulk Cutter, Berkeley, Calif. DMG, Melville, N.Y. 3M 3M Kerr Union Broach Co. Inc., Long Island City, N.Y. ESPE

study was to determine the contact angle and the wettability of various elastomeric impression materials and to compare this relationship with voids in die stone casts fabricated from etastomeric impressions.

METHODS AND MATERIAL This study was divided into two parts: (1) the first examined the number of voids in stone casts and (2) the ~econd investigated the contact angle of elastomers with water, T h e elastomeric impression materials used in this •~:mdy are Listed in Tables I and II and included polysulfide, ~::ondensation reaction silicone, addition reaction silicone, ~)olyether, and a light-cured polyether urethane ,:limethacrytate. Casts were made using Silky-Rock (Whip-

Mix Corporation, Louisville, Ky.) gypsum die materials vacuum mixed according to the manufacturer's instructions. To determine the ability of the impression material to be poured with a slurry of die stone, an aluminum die containing 48 point angles was constructed (Fig. 1). Acrylic resin custom trays made on the die were filled with impression material. T h e impression material was allowed to cure at room t e m p e r a t u r e for 20 minutes. T h e lightcured elastomer was cured at room t e m p e r a t u r e for twice the a m o u n t of time recommended by the manufacturer. Five impressions were made with each elastomer. Die stone casts were made using conventional methods. Casts were examined under a three diopter lighted magnifier (Luxo

VOIDS IN GYPSUM CASTS

Fig. 2. Elastomer sample with water drop inside fivesided glass box with moist absorbent paper to maintain humidity.

Corp., Sausalito, Calif.) and voids occurring at point angles were counted. Additional impressions and casts were prepared using two commercial surfactants (Delar, Almore International, Inc. Portland, Ore.; and Super Surf, Xentel, San Antonio, Texas). The impressions were sprayed with the surfactant and voids in casts were counted as noted previously. The effect on reduction of voids in casts as a function of each surfactant was compared with baseline counts. Significant differences between baseline and surfactant-treated groups for each elastomer were determined with the t test at p _