S h e a r bond s t r e n g t h of two resin a d h e s i v e s for a c i d - e t c h e d metal p r o s t h e s e s F r a n k l i n G a r c i a - G o d o y , D . D . S . , M.S.,* D a v i d A. K a i s e r , D . D . S . , M.S.D.,** W i l l i a m F. P. M a l o n e , D . D . S . , M.S., Ph.D.,*** a n d G r e g o r y H u b b a r d , D.D.S.****
University of Texas Health Science Center, Dental School, San Antonio, Tex. This study compared the shear bond strength of P a n a v i a EX and Comspan Opaque a d h e s i v e r e s i n s with e l e c t r o l y t i c a l l y etched or sandblasted Rexillium III or Litecast B m e t a l s bonded to extracted teeth. An a n a l y s i s of v a r i a n c e r e v e a l e d that there is no difference in bonding strength among etched or sandblasted Rexillium III metal with either P a n a v i a EX or Comspan Opaque resins. With Litecast B metal, s a n d b l a s t i n g produced a greater bond strength than etching with P a n a v i a Ex resin (38.19 MPa sandblasted; 30.53 MPa etched). Conversely, Comspan Opaque resin had a v a l u e of 30.10 MPa etched and 15.40 MPa sandblasted. The etched Rexillium III and P a n a v i a EX r e s i n s recorded a g r e a t e r bond strength (38.38 MPa) than Comspan Opaque resin (27.83 MPa) or s a n d b l a s t e d Rexillium III metal (Rexillium III 34.74 MPa; Comspan Opaque 20.39 MPa) and Litecast B metal ( P a n a v i a EX 38.19 MPa; Comspan Opaque 15.40 MPa). Eighty percent of the failures occurred at the c e m e n t - m e t a l interface with both cements. (J PROSTHET DENT
A c i d - e t c h e d metal prostheses were introduced in 1973.1 Since then, several retentive systems for resinto-metal bonding have been recommended. Perforations in the retainer, 1 silane-coating the metal surface (silicoating system),2, 3 coating the metal surface electrolytically with a thin layer of tin oxide (OVS system), 4,5 electrolytical etching of the retainer, e sandblasting the surface of the retainer, 7 and a network wax pattern s have been described. The three most popular systems are the silicoating, sandblasting, and electrolytical etching. This study compared the shear bond strengths of two adhesive resins with two metals sandblasted or electrolytically etched. MATERIAL
The two adhesive resins selected for this study were Panavia EX dental adhesive (Kuraray Co., Osaka, Japan) and Comspan Opaque (Caulk International, Milford, Del.). The two metals were Rexillium III (Jeneric Industries, Inc., Wallington, Conn.) and Litecast B (Williams Gold, Buffalo, N.Y.). Presented at the American Associationfor Dental Research meeting, San Francisco, Calif. *Professor, Department of Pediatric Dentistry. **Associate Professor and Head, Division of Operative Dentistry, Department of Pediatric Dentistry. ***Professor, Department of Restorative Dentistry, Washington University, School of Dental Medicine, St. Louis, Mo. ****Postgraduate orthodontic student, University of Oklahoma, Oklahoma City, Okla. 10/1/27549
THE JOURNAL OF PROSTHETIC DENTISTRY
Sixty rings 4.8 × 0.8 mm were cast in each metal and the surfaces were sanded to a final grit of No. 600 silicon carbide paper. The specimens were then sandblasted with 50 ~m aluminum oxide for 30 seconds. To simulate porcelain addition, the specimens were fired in a porcelain oven (Ultra-Mat, Unitek, Monrovia, Calif.) under the following conditions: oxidation cycle 1000 ° C with a vacuum, 2 minutes; opaque bake, 960 ° C with a vacuum, 0.5 minutes; first bake, 940 ° C with a vacuum, 0.5 minutes; second bake, 940 ° C, with a vacuum, 0.5 minutes; glaze bake, 950 ° C without vacuum, 0.5 minutes. The metal specimens were randomly divided into four groups of 15 specimens each: group 1: electrolytical etching and cemented with Comspan resin; group 2: sandblasting and cemented with Comspan resin; group 3: electrolytical etching and cemented with Panavia resin; group 4: sandblasting and cemented with Panavia resin. The sandblasted specimens were surface-treated again with a 50 ~m aluminum oxide grit for 0.5 minutes. The electrolytically etched specimens were first cleaned with a 50 ~m aluminum oxide grit for 0.5 minutes. The specimens were spot-welded to electrodes and were then masked from the acid with sticky wax. The sticky wax covered all the surfaces except those to be bonded. The specimens were then electrolytically etched in a 10% solution of H2S04 acid for I minute at a current density of 300 mA with magnetic agitation. The etched specimens were then cleaned in an 18% HC1 acid solution for 10 minutes in an ultrasonic cleaner and were rinsed with deionized water. Dendritic etching was confirmed with a stereomicroscope
GARCIA-GODOY ET AL
Table I. Shear bond strength values Group
1. Rexillium-etched Comspan 2. Rexillium III-sandblasted Comspan 3. Rexillium III-etched Panavia 4. Rexillium IILSandblasted Panavia 5. Litecast B-etched Comspan 6. Litecast B-sandblasted Comspan 7. Litecast B-etched Panavia 8. Litecast B-sandblasted Panavia
Mean (MPa) _+S.D.
27.83 + 8.74
34.74 + 8.21
30.10 _+ 8.26
G r o u p s significantly different at p < 0.05:1 versus 3; 2 versus 4; 2 versus 8; 3 versus 5; 3 versus 7 : 4 versus 6; 5 versus 6; 6 versus 8; 7 versus 8.
at 50 power magnification and the sticky wax coating was removed with two changes of chloroform in the ultrasonic cleaner for 3 minutes each.
Teeth preparation Sixty intact noncarious molars stored in deionized water were used for each metal. They were cleaned with a rubber cup and flour of pumice slurry in a slow-speed handpiece. The facial surface was prepared entirely in enamel with new coarse diamond burs (1DT) to simulate clinical tooth preparation. The teeth were then mounted on polyvinylchloride (PVC) segments and retained by a low melting point metal with a fusing temperature of approximately 85 ° C, and after mounting, were stored in deionized water for 24 hours.
Bonding procedures The teeth were cleaned with flour of pumice in a slow-speed rubber cup, washed, and dried. A 40% phosphoric acid gel was applied for 60 seconds to etch the prepared enamel surface, followed by a 20-second rinse with deionized water. The teeth were dried with oil-free compressed air. When using Panavia resin, one drop of Panavia liquid resin was mixed with one scoop (3.2 gin) of powder and mixed to a creamy consistency for 90 seconds. The adhesive paste was placed on both the metal ring and the prepared tooth surface. The metal was secured with finger pressure for 4 minutes to simulate clinical conditions and the excess paste was removed from the margins with a sharp-tipped brush. An anaerobic environment was provided by placing the Oxyguard gel over the margins of the metal-paste-tooth unit while maintaining finger pressure
for 4 minutes. After the paste had set for 7 minutes from start of the mix, the Oxyguard gel was rinsed for 30 seconds with deionized water. After 7 minutes, the mounted teeth with the metal rings securely adhered were placed in deionized water for a 24-hour period. When using Comspan resin, Caulk self-cure bonding agent base and catalyst were mixed in a 1:1 ratio for approximately 10 seconds. A thin layer of the mix was applied to the prepared enamel surface and to the "conditioned" metal ring surface and distributed with blown compressed air. Simultaneously, the Comspan opaque cement base and catalyst were mixed in a 1:1 ratio for approximately 20 seconds and placed over the bonding agent. The metal ring was then placed on the enamel and held with constant finger pressure for 3 minutes. Excess cement was removed from the margins during the setting and then the unit was allowed to remain undisturbed for 7 minutes. Upon completion of setting, the mounted teeth with the attached metal rings were placed in deionized water for 24 hours. Shear bond strength was tested with the Instron (Instron Corp., Canton, Mass.) testing machine at a crosshead speed of 0.5 mm/min. The statistical analysis was performed with a one-factor analysis of variance (ANOVA) with a StudentNewman-Keuls test for all multiple pairwise comparisons. The level of significance was set at p = 0.05.
RESULTS The results of the study are summarized in Table I.
Comparing etching versus sandblasting Panavia and Comspan resins showed no statistical difference if Rexillium III metal was etched or sandblasted. However, with Litecast B metal and Comspan resin, etching the metal created a superior bond strength compared with sandblasting (p < 0.05). With Litecast B metal and Panavia resin, sandblasting the metal yielded higher bond strength values than metal etching (p < 0.05).
Comparing metals Comspan resin with etched or sandblasted Rexillium III metal exhibited no significantly different bond strengths than Comspan resin with etched or sandblasted Litecast B metal. Panavia resin with etched Rexillium III metal displayed greater bond strengths than Panavia resin with etched Litecast B metal (p < 0.05). Panavia resin with sandblasted Rexillium III metal did not record significantly different bond strengths than Panavia resin with sandblasted Litecast B metal.
Comparing cements with different metals Comspan resin with etched Rexillium III metal exhibited no significantly different bond strengths than Panavia resin with etched Litecast B metal.
J U N E 1991
BOND STRENGTH OF TWO R E S I N A D H E S I V E S
Comspan resin with sandblasted Rexillium III metal recorded lower bond strengths than Panavia resin with sandblasted Litecast B metal (p < 0.05). Panavia resin with etched Rexillium III metal created higher bond strengths than Comspan resin with etched Litecast B metal (p < 0.05). Panavia resin with sandblasted Rexillium III metal exhibited higher bond strengths than Comspan resin with sandblasted Litecast B metal (p < 0.05).
C o m p a r i n g t h e s a m e m e t a l w i t h different cements Panavia resin with etched Rexillium III metal showed superior bond strengths compared with Comspan resin with etched Rexillium III metal (p < 0.05). Panavia resin with sandblasted Rexillium III metal recorded higher bond strengths than Comspan resin with sandblasted Rexillium III metal (p < 0.05). Panavia resin with etched Litecast B metal revealed no significantly different bond strengths than Comspan resin with etched Litecast B metal. Panavia resin with sandblasted Litecast B metal demonstrated higher bond strengths than Comspan resin with sandblasted Litecast B metal (p < 0.05). After shear bond testing, the metal rings and teeth were visually inspected to evaluate the fracture site. Approximately 80% of bond failures occurred at the cement-metal interface with both cements.
DISCUSSION This study revealed that the bond strength of resin bonded to metals depends on the surface treatment of the alloy and the cement. When sandblasted or electrolytically etched Rexillium III metal was used, Panavia resin exhibited a greater bond strength than Comspan resin. However, no significant difference was found between Panavia and Comspan resins using etched Litecast B metal. When Litecast B metal was sandblasted, a higher bond strength was recorded with Panavia resin than if it were electrolytically etched. However, the reverse was evident for Comspan resin; etching ensured a greater bond strength. In a previous scanning electron microscope (SEM) study, 2 sandblasted Rexillium III metal specimens exhibited distinctive retentive morphologic configurations comparable with those of the silicoating technique. The electrolytically etched surfaces in that study displayed greater morphologic retentive features, although silicoating cre-
T H E JOURNAL OF P R O S T H E T I C D E N T I S T R Y
ated superior bond strength. However, resin cements were not evaluated in samples that were merely sandblasted. The bond strengths recorded in this study for metals, treatments, and cements were considered sufficient for success. In clinical practice, dentists could sandblast the metal prosthesis immediately prior to bonding, but additional clinical evaluations are suggested. CONCLUSIONS 1. Panavia resin recorded a greater bond strength than Comspan resin with etched and sandblasted Rexillium III metal. 2. The results of metal etching did not differ from sandblasting using both Panavia and Comspan resins with Rexillium III metal. 3. Sandblasting produced a superior bond strength compared with metal etching using Panavia resin with Litecast B metal. 4. Metal etching created a greater bond strength than sandblasting using Comspan resin with Litecast B metal.
REFERENCES 1. Rochette AL. Attachment of a splint to enamel of lower anterior teeth. J PROSTHET DENT 1973;30:418-23. 2. Re GJ, Kaiser DA, Malone WFP, Garcia-Godoy F. Shear bond strengths and scanning electron microscope evaluation of three different retentive methods for resin-bonded retainers. J PROSTHETDENT 1988;59:568-73. 3. Creugers NHJ, Welle PR, Vrijhoef MMA. Four bonding systems for resin-retained cast metal prostheses. Dent Mater 1988;4:85-8. 4. van der Veen JH, Bronsdijk AE, Slagter AP, van de Poel ACM, Arends J. Tensile bond strength of Comspan resin to six different treated metal surfaces. Dent Mater 1988;4:272-7. 5. van der Veen JH, Jongebloed WL, Dijk F, Purdell-Lewis DJ, van de Poel ACM. SEM study of six retention systems for resin-to-metal bonding. Dent Mater 1988;4:266-71. 6. Livaditis GJ, Thompson VP. Etched castings. An improved retentive system for resin-bonded retainers. J PROSTHET DENT 1982;47:52-8. 7. Thompson VP, Grolman KM, Liao R. Bonding of adhesive resins to various nomprecious alloys [Abstract]. J Dent Res 1985;64:314. 8. Rothermel RA, Kelly JR. Resin-bonded prostheses: micro-leakage and luting agent thickness of etched and cast-mesh-work retainers. J PROSTHET DENT 1986;56:47-50. Reprint requests to: DR. FRANKLINGARCIA-GODOY DENTAL SCHOOL UNIVERSITYOF TEXAS HEALTHSCIENCECENTER 7703 FLOYDCURL DR. SAN ANTONIO,TX 78284-7888
Contributing author James G. E v a n s , M.Ed., Certified Dental Technician, Assistant Professor, Dental Laboratory Technology Education, University of Texas Health Science Center, Dental School, San Antonio, Texas