Tensile bond strength of resin-bondednon-preciousalloys with chemically and mechanically roughened surfaces F. IsidoP N.M. Hassna ~ K. Josephsen 2 S. KaabeP 1Dept. of Prosthetic Dentistry and Stomatognathic Physiology 2Dept. of Oral Anatomy, Dental Pathology and Operative Dentistry Royal Dental College Vennelyst Boulevard DK-8000 Aarhus, Denmark Received May 14, 1990 Accepted June 14, 1991

Dent Mater 7:225-229, October, 1991

Abstract--The present study was carried out for investigationof the tensile bond strength of resin-bonded non-precious alloys after their surfaces were roughened by sandblasting, chemical etching, or sugar crystal impressions. Fifty test specimens were cast in a Ni-Cr (Wiron 88) alloy and 50 in a Co-Cr (Wirobond) alloy. Twenty specimens of each alloy were surface-treated according to the sugar crystal impression method. The remaining specimens were first sand-blasted, and 20 specimens of each alloy were thereafter allocated for chemical etching and divided into subgroups with different etching conditions. The samples were chemically etched in strong inorganic acid solutions. After being etched, the specimens were bonded together in pairs by a chemicallycuring resin cement (Panavia EX) with a force of 2 kg/cm2. After cementation, the specimens were stored under humid conditions at 37~Cfor three wk. Priorto being tested, the specimens were subjected to 1000 thermal cyclings at temperatures between 10°C and 55~C. The tensile bond strength tests showed that Ni-Cr specimens sand-blasted and thereafter etched with a 50% conc. of HNO3 and a 50% conc. of HCI for two min and Co-Cr specimens sandblasted and etched (conc. HCI for 15 rain or three h) or sand-blasted alone resulted in similar high bonding values ranging between 33.3 and 37.2 MPa. Surface roughening with use of the sugar crystal impression method resulted in statistically significant lower bond strength values for both alloys (Ni-Cr, 17.9 MPa; Co-Cr, 10.2 MPa).

ince the introduction of resinbonded bridge constructions into clinical dentistry (Howe and Denehy, 1977), this concept has gained widespread use due to the simplicity of the clinical and laboratory work procedures comparedwith conventionalbridge work, and due to its economical advantages, especially when non-precious alloys based on Ni, Cr, Co, and Be are used. Although the period of clinical experience with the bonding of a metal framework to the sound enamel of abutment teeth is still short, clinical investigations have demonstrated that resin-bondedbridges during function are liable to loosen from masticatory stress (Synnott, 1984). In vitro studies have demonstrated that the critical part in the retention of a resin-bonded bridge is the contact zone of the luting agent to the metal framework rather than to the etched enamel (see reviews by Synnott, 1984, and Zidan, 1985). Inorder for this problem to be eliminated, several techniques have been introduced for the creation of sufficient retention for the luting agent to the framework. These include creation of micro-irregularities or porosities through sand-blasting of the precious alloy surfaces or by electrolytical etching of non-precious alloys (Thompsonet al., 1983; Livaditis, 1986; Creugers et al., 1988). Another technique is the creation of holes, meshes, or indentation marks from water-soluble crystals in the wax pattern prior to casting (Baylis and Thomas, 1985; Moon, 1987). A third approach has used a combination of mechanical and chemical retention b~ silicoating or tin-plating the prepared metal framework(Bronsdijkandvan derVeen, 1986). At the present state of knowledge, most ofthese methods suffer from one or more serious drawbacks. The mechanical retention obtained by the creation of holes has normally proved to be unsatisfactory. Some ofthe alternatives, such as the electrolytical etching technique, have proved to be complex and sensitive in practical use. Other methods, e.g., the silicoating procedure, re-

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quire specialized and highly expensive equipment. The aim of the present study, therefore, was to investigate three methods • for the creation of surface irregularities in two different base-metal alloys for resin-bondedbridgework, namely, sandblasting, the crystal impression method, and chemical surface etching, in order to test their ability to ensure surface retention aider being bonded with resin composite cement. MATERIALS AND M E T H O D S

Standardized disc-shaped specimens were used to test the tensile bond strength of resin bonding. Th~ specimens were fabricated on stone dies made from a brass block with a cylindrical hole having a diameter of 8.69 mm and a depth of 2 mm. A total of 100 wax patterns was made on the stone dies and cast in two different non-precious alloys. Fii~y specimens were cast from a commercial Ni-Cr alloy (Wiron 88, Bego Company, Germany). The other 50 specimens were cast from a commercial Co-Cr alloy (Wirobond, Bego Company, Germany). Twenty specimensfrom each alloy were allocated for sand-blasting and etching. Each of these groups was divided into two subgroups. Twenty specimens of each alloy were made according to the sugar crystal retention method, and the last 10 specimens of each group were sand-blasted only. Wax patterns for specimens with surface irregularities according to the sugar crystal retention method were fabricated in the following way: A special water-soluble adhesive (Bonding Traps, Benzer Dental, Ziirich, Switzerland) was painted over the required area of the dry stone die. The sugar crystal granules (Bonding Traps, Benzer Dental) were applied over the prepared area and then covered with inlay wax. After the disc had been waxed up, the stone die with the wax pattern was placed in water, which dissolved the adhesive gel and the sugar crystals. The wax pattern was then removed from the die and prepared for the casting procedure. Casting was m~de at a commercial

Dental Materials]October 1991 225

F i g , I. A SEM micrograph of a Ni-Cr (Wiron 88) test specimen after being only sandblasted, The bars represent 10 I~m.

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