SECTION EDITORS

M i c r o l e a k a g e at the r e s i n - a l l o y i n t e r f a c e of c h e m i c a l l y r e t a i n e d c o m p o s i t e r e s i n s for c a s t r e s t o r a t i o n s H. S t r y g l e r , D . D . S . , * M . S . D . , J. I. N i c h o l l s , Ph.D.,** a n d J. D. T o w n s e n d , D . D . S . , M.S.D.***

University of Washington, School of Dentistry, Seattle, Wash. N e w r e t e n t i v e m e c h a n i s m s b e t w e e n v e n e e r i n g resins and c a s t i n g alloys are c l a i m e d to h a v e a c h e m i c a l bond that results in a high bond s t r e n g t h c o m b i n e d w i t h l o w m i c r o l e a k a g e b e t w e e n the v e n e e r i n g resin and cast restoration. This study c o m p a r e d the m i c r o l e a k a g e o f four c h e m i c a l bonding m e c h a n i s m s w h e n three v e n e e r i n g r e s i n s w e r e bonded to t w o dental casting alloys. R e s i n - v e n e e r e d alloy d i s k s w e r e i m m e r s e d in red India ink and k e p t at 37 ° C for 72 hours. The d i s k s w e r e then bench dried for 24 hours. The resin v e n e e r w a s sectioned into eight sectors in an e n g i n e e r i n g milling m a c h i n e and t h e s e resin sectors w e r e r e m o v e d to d i s p l a y the m i c r o l e a k a g e pattern. It w a s concluded that (1) no m i c r o l e a k a g e w a s found in t w o combinations, and (2) the h i g h e s t m i c r o l e a k a g e w a s w i t h Sr-IsositN / P a n a v i a EX/Firmilay combinations. (J PROSTHET DENT 1991;65:733-9.)

S i n c e the introduction of light-cured resins, the universal application of porcelain has been strongly challenged. Composite resin veneers are convenient, compatible with the various casting alloys, and permit intraoral repair. Resin alloy adhesion originally required mechanically retentive beads or electrochemical etching, 1-3 but retentive beads, despite their popularity, required additional space and tooth reduction. This nonadhesive system commonly resulted in poor marginal sealing, with seepage of oral fluids between the resin and the alloy, causing discoloration. 4,5 Electrochemical etching resolved some of these limitations by providing high bond strength and acceptable esthetics. 6 Unfortunately, chemical etching is presently limited to the Ni-Cr alloys because of the etching unpredictability of the other dental casting alloys. 3 Several studies have reported that chemical bonding had a bond strength superior to mechanical retention. 7-1° Chu et al. 7 demonstrated that Silicoater (Kulzer, Wehrheim, Germany) bonding agent used to provide chemical retention for Dentacolor (Kulzer) and Visio-Gem (ESPE/Premier, Norristown, Pa.) resin to a Ni-Cr alloy surface, recorded significantly greater tensile bond strengths than small beads with compact spacing. Laufer et al. s evaluated

Presented before the Pacific Coast Society of Prosthodontics meeting, Napa, Calif. *Private Practice, Mexico City, Mexico. **Professor, Restorative Dentistry. ***Lecturer, Restorative Dentistry. 10/1/24210

THE J O U R N A L OF PROSTHETIC D E N T I S T R Y

the bond strength of composite resins bonded to cast dental alloys and concluded that the application of Silicoater adhesive to the alloys resulted in a composite resin bond strength twice that of etched Litecast B alloy (Williams, Chicago, Ill.). Thompson et al. 9 illustrated improved bond strengths for Panavia EX (Kuraray Co. Ltd., Osaka, Japan) bonding agent applied to air-abraded (50 ~m aluminum oxide) Ni-Cr-Be and Cr-Co alloys. Tanaka et al. 1° studied a new adhesive resin, MMA/PMMA, with 5% weight 4-methacrylyoxyethyl trimellitate anhydried (4-Meta) (Sun Medical Co., Kyoto, Japan). Their results confirmed a high bond strength for this resin when applied to Ni-Cr and Cr-Co alloys, after blasting with alumina, and oxidation. Since the resins are chemically bonded to the alloys, microleakage should be reduced, preserving bond strength and esthetics. This study compared the microleakage of four different chemical bonding mechanisms and a sandblasted control used to bond three veneering resins to two dental casting alloys. METHODS

AND

MATERIAL

The materials used in this study are listed in Table I. Seventy-five alloy disks were cast in each of the two alloys. The dimensions of these alloy specimens are given in Fig. 1. Initial alloy preparation. The test surfaces of the alloy disks were machined on an engineering lathe with an attached slow-speed handpiece. An aluminum oxide abrasive wheel (Shofu, Menlo Park, Calif.) and a Brownie wheel (Shofu) were used to create a smooth fiat test surface on these disks. The disks were next abraded with 50 ~m alu-

733

STRYGLER, NICHOLLS, AND TOWNSEND

13 mm

2mm 2ram

2mm

15mm

15mm

Cast allo'

3mm dia.

F i g . 3. Cast alloy disk with resin component. F i g . 1. Cast alloy disk.

16mm 4mm t

~

~

T a b l e I. Materials, composition, and manufacturer

t

Product

[ 16mm

Ni-Cr-Be Au-Ag-Pd

Williams, Chicago, Ill. J. F. Jelenko, Amherst, N. J.

Bonding agent Silicoater

SiOx-C

Kulzer, Wehrheim, Germany Kuraray Co., Ltd., Osaka, Japan Sun Medical Co., Kyoto, Japan Ivoclar, Schaan, Liechtenstein

Panavia-EX

Veneering resin Dentacolor F i g . 2. Cylindrical brass mold.

Visio-Gem

minum oxide particles at 80 psi and finally cleaned in an ultrasonic cleaner in distilled water for 10 minutes. Silieoater alloy preparation. After the initial alloy preparation, 30 alloy disks (five for each resin/alloy combination) were cleaned with Siliclean (Kulzer) material for 10 minutes in an ultrasonic cleaner and coated with an SiO~C layer (Siliflam, Kulzer) for 5 minutes. After cooling for 2 minutes, these disks were immediately treated with the silane coupling agent (Silicoup, Kulzer), and the veneering opaques were applied within 5 minutes of Silicoup application.

SR-Isosit-N

was applied on 15 alloy disks (five disks for each veneering

734

Manufacturer

Metal alloy Litecast B Firmilay

Superbond C&B ABC

Ni-Cr-Be preparation for Panavia E X adhesive. After initial alloy preparation, Panavia E X material

Major element

Phosphorylated Bis-GMA 4-META Bifunctional urethane Multifunctional methacrylic Bifunctional methacrylic silicon dioxide Diurethane dimethacrylate and silica

Kulzer ESPE/Premier, Norristown, Pa. Ivoclar

resin). Two drops of liquid were dispensed for each scoop of powder ("two-drop" scoop used). All of the measured powder was incorporated simultaneously into the liquid, mixed for 60 seconds, and painted uniformly on the disks with a brush. Because of the anaerobic properties of Panavia E X material, Oxyguard (Kuraray Co. Ltd.) material was applied to prevent oxygen contact with the resin. After 3 minutes, the Oxyguard material was rinsed off with

J U N E 1991

VOLUME 65

NUMBER 6

MICROLEAKAGEAT RESIN-ALLOYINTERFACE

1E~'~~-~"Resinsectors

R

R

i~oleakag e I

l

Microleakage

F i g . 4. Resin sectioned into eight sectors.

F i g . 5. Computation of microleakage area for one sector. R1 = R - (a + b)/2. Area = 1/2 (R 2 - R12).

T a b l e IL Opaque and resin application Opaque Veneering resin

Visio-Gem Dentacolor SR-Isosit-N

Resin

Curing method

Curing time (min)

P/L ratio

No. of layers

Alpha light Dentacolor xs light

1 3

1:1 1:1

3 3

Air dry

3

3

Curing method

Beta light Dentacolor xs light Ivomat 120 C/6 bar pressure

Curing time (min)

15 3 7

P/L, Powder-to-liquidratio.

distilled water and the specimens dried before opaque application.

Au-Ag'Pd alloy preparation for Panavia E X adhesive. After initial alloy preparation, 15 alloy disks were tin plated in a Multiplater (Unitek, Monrovia, Calif.) instrument. After tin plating, the disks were cleaned in distilled water for 2 minutes, then dried. Tin plating was needed to avoid natural oxidation, to increase the adhesive bond, and to provide water resistance, n Panavia E X adhesive was applied to the disks as specified earlier.

Alloy preparation for Superbond C & B adhesive. After initial alloy preparation, 15 disks of each alloy were immersed in an oxidizing solution containing 3 % sulfuric acid and 1% potassium permanganate. Immersion times were 10 seconds for the Ni-Cr-Be alloy and 30 seconds for the Au-Ag-Pd alloy. This solution precipitated an oxidation effect in an acidic environment and controlled the oxidation rate by varying the pH. This oxidation of the surface of the alloys improves the adhesion of Superbond C & B material. 1° Disks were washed in an ultrasonic cleaner with distilled water for 1 minute, then dried. One drop of S u p e r b o n d C & B catalyst was a d d e d to four drops of monomer and mixed for 15 seconds, creating an activated liquid. One cup

(0.07 gm) of polymer was then a d d e d to the activated liquid and mixed for 30 seconds. This mixture was applied uniformly to the disks with a brush. A curing time of 15 minutes was allowed before application of the opaque. Alloy preparation for ABC adhesive. After initial alloy preparation, two coats of ABC metal primer were painted with a brush on 15 disks of each alloy. The opaques and veneering resins were applied within 15 minutes of the application of primer. Control specimens. After initial alloy preparation, the veneering opaques and resins were applied to 15 disks of each alloy. No additional alloy surface t r e a t m e n t was provided for these controls. Opaque and veneering resin application. Opaques and veneering resins were applied as outlined in Table II. A cylindrical brass mold 16 m m in diameter with an internal hole 13 m m in diameter and 4 mm deep was used to form the veneering resin portion of the alloy-resin specimen (Fig. 2). A glass slab placed over the top of this mold was used to create a flat, smooth surface during the initial polymerization. After removal of the specimen from the mold, final polymerization was achieved by placing specimens in the appropriate veneering resin curing unit. A uniform 2 m m thickness of resin was obtained by using this

STRYGLER, NICHOLLS, AND TOWNSEND

Conn.). The resin sectors were detached with a hemostat plier No. 2 (Hu-Friedy, Chicago, Ill.), thus exposing the alloy surface (Fig. 4). Measurements of the dimensions a and b (Fig. 5) were made directly on the alloy surface from the external edge of each sector to the point where the trail of red ink was indiscernible (Fig. 5). A X40 power microscope equipped with a calibrated scale (Carolina Biological, Gladstone, Ore.) was used to determine the values of a and b and, thus, the microleakage. Values of a and b (Fig. 5) were measured to 0.001 mm accuracy, and measurement error was determined to be +_0.004 mm. With the values of a and b known, the microleakage in each of the eight sectors was calculated by use of the formula given in Fig. 5. The total microleakage formula was modified to compensate for the different patterns (Fig. 6). Thirty separate categories of five specimens were evaluated in this study, requiring 150 cast alloy disks (75 for each of the two alloys).

Statistical a n a l y s i s All microleakage data were subjected to a one-way analysis of variance, and the Student-Newman-Keuls test was used to compute statistically significant differences between the test groups. RESULTS The mean microleakage areas and standard deviations in square millimeters are given in Table III and Figs. 7 through 9. Table IV contains the statistically significant subsets (p --

Microleakage at the resin-alloy interface of chemically retained composite resins for cast restorations.

New retentive mechanisms between veneering resins and casting alloys are claimed to have a chemical bond that results in a high bond strength combined...
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