RESEARCH

AND EDUCATION JOHN J. SHARRY

Effect of varying one semiprecious

surface texture on bond strength of and one nonprecious ceramo-alloy

Michael A. Carpenter, D.D.S., M.S.,* and Richard J. Goodkind, D.M.D., University

of Minnesota,

School of Dentistry,

Minneapolis,

P

reparation of the ceramo-alloy surface prior to porcelain bonding has been a subject of coniroversy among dental ceramists. The literature is replete with theories regarding the effects of surface texture on bond strength. The results of previous studies seem to have depended upon the ceramo-alloy system evaluated and the test design used. Lavine and Custer’ found that a roughened surface increased bond strength by 13% to 15% for ceramo-alloys with high gold content. Lubovich2 noted that surface roughness slightly enhanced bond strength for semiprecious and nonprecious metals but not for precious metals. Shell and Nielsen’ concluded that the effect of surface roughening on bond strength was minimal. They said that a fine degree of roughening would be beneficial if it produced edges and corners in a profusion that would increase the driving force toward wetting ceramo-alloys by the ceramic employed. Surface texturing is inherent in the preparation of ceramo-alloy copings, which are usually ground with noncontaminating aluminum oxide stones to remove casting oxides and refine contours. This procedure often results in some burnishing of the alloy, leaving metal tags and casting voids covered by burnished metal. To obviate these potentially bond-weakening conditions, aluminum oxide abrasives of various particle sizes have been used to eliminate alloy tags and uncover surface voids. The proposal by Shell and Nielson’ that a uniform matted surface can be Presented and Prosthodontists NW. Condensed

placed first Research

from

a thesis

requirements University *Graduate **Professor,

86

JULY

for the of Minnesota.

Student, Director

1979

in the Award

presented degree

1978 American Competition, in partial

of

Master

fulfillment of

42

NUMBER

Science

of the from

the

Minn.

created which may enhance the wettability of ceramo-alloys by molten porcelain is subject to question. This investigation evaluated the effects of varied surface textures created by aluminum oxide air abrasion upon a gold-silver-palladium ceramo-alloy, Games,* and a nonprecious nickel chrome ceramoalloy, N/P II.? The objectives were (1) to determine how these variations in surface texture affect the bond strength of the two ceramo-alloy systems studied and (2) to evaluate the resultant surface area and re-entrant angles created by air abrasion within the limited scope of available instrumentation. The data obtained should be beneficial to the understanding of this procedure and contribute information that might help control one of the many variables inherent in ceramo-alloy fabrication.

MATERIALS

AND METHODS

A total of 120 test samples were cast and standardized to size: 60 rectangular ceramo-alloy strips were evaluated by a four-point flexural bend test (test 1) designed by Caputo,’ and 60 cylindrical pullthrough ceramo-alloy test specimens were evaluated by a pull-rod test (test II) developed by Boettcher$ Before mechanical testing began, each ceramo-alloy system was divided into three surface texture groups (smooth, medium, and rough) for each test method. The surface textures were created as follows: (1) smooth-O.05 pm aluminoxide particles in a waterbase suspension, using metallurgic lapping procedures outlined by Buhler Ltd.; (2) medium and

*J.F. Jelenko tHowmedica,

& Company, Inc., Dental

New Rochelle, N. Y. Division, Chicago, 111. R. A. Boettcher, Manager,

$Personal Communication: and Development Prosthetic

Division of Prosthodontics. of Graduate Prosthodontics.

VOLUME

College of Las Vegas,

M.S.**

Monrovia,

I

Laboratory,

tinitek

Research Corp.,

Calif

0022-3913/79/070066

+ 10SO1.00~00

1979 The C. V. Mosby

Co.

SURFACE

TEXTURE

AND

BOND

STRENGTH

12.5m-o

rodws

Alignment marks

Sample

Fig.

1.

Test I-Flexural

four-point

rough-50 and 280 pm aluminum oxide air abrasive particles, respectively, using a laboratory air abrasive blasting unit. Air abrasive particle sizes were determined by sedimentation analysis. Before porcelain was applied, surface profile evaluations were performed on a representative number of test I samples from each ceramo-alloy system investigated. The procedures were: (1) surface topography analysis using a Talysurf Model 3 metrology instrument,* (2) surface area analysis using a topomeasuring device, (3) re-entrant angle determination, and (4) scanning electron microscopy to evaluate surface topography. Figs. I and 2 show completed sample geometries for each test method design prior to mechanical testing by an Instron testing machine. Each sample was fired three times: (1) opaque porcelain application, (2) body porcelain application, and (3) glazing. Completed test samples were loaded into their respective test fixtures for each test method used with the Instron. Test I samples were loaded in compression using a cross-head speed of 0.05 inch per minute. Test II samples were loaded in tension using a cross-head speed of 0.02 inch per minute. A load deflection stress-strain curve resulted for each test method design. The load at failure was used to calculate the pounds per square inch necessary to shear the porcelain-metal bond for test II samples. Shear stress determinations for test I samples were not made because information was lacking concerning several parameters necessary to perform the analysis by Hatfield.’ Scanning electron microscopy was used to evaluate the surface topography of test samples before the application of porcelain and after mechanical testing.

*Taylor

Holsson,

THE JOURNAL

L&ester,

OF PROSTHETIC

England.

DENTISTRY

bend test. Fixture with sample in place.

9.5mm Plotinum +--I h L

J-Lzi f

r

IOmm .l

.

3.25mm

\ Felt

Pad

i

Fig. 2. Test II-Completed for testing.

pull-rod

test. Specimen

ready

RESULTS The data from test I and test II for each ceramoalloy system were subjected to a one-way analysis of variance. The recorded test II data were used to compute bond shear strength values on which oneway analysis of variance tests were performed. Test I analysis of variance for the N/P II ceramoalloy system and the Cameo ceramo-alloy system demonstrated no significant difference among smooth, medium, and rough textures (N/P II-F (2,24) = 0.92, p > .25; Cameo-F (2,24) = 1.135, p > 0.25, respectively) (Fig. 3). Test IT analysis of variance for the N 11’ II ceramoalloy system demonstrated that there were significant differences among the bond shear strengths of the three surface texture modes as reflected by a p < .OOl. The analysis of variance for the Cameo ceramo-alloy system showed no significant diRerence between smooth, medium, and rough textures (F (2,27) = 0.64, p > .50) (Fig. 4). Test I and test II could not be compared statistically because of inherent differences in design and

87

CARPENTER

TEST I-N/P II-MICROBOND “I-LIFE PORCELAIN, ANALYSIS VARIAHCE OF MEAX INITIAL FRACTURE

OF STRENGTHS

TEST II-N/P II-II HI-LIFE PORCELAIN, OF MEAN BOKD SHEAR

“ARIA!,CE

SOUl-CC? of Yarlt3tlO” Among B,fh,n Total

y-9 x - 5.72 - 3.48 s = 1.86

H-9 x = 5.14 - 3.71 s - 1.92

-

s2

s.2 Degrees of Freedom 2 24 52

Sum of SOUilreS

Veall Squares

6.980741 90.933333 97.914074

3.490370 3.78889

F Ratio 0.92

Probabi

1 ity

0.25ePcO.50 P>O.25

10 5630.53 = 655855.55 s = 609.85

z = IO 2

3= s =

source Of var1arion AmOnK WIthIn Total

s

3.88 2.49 1.57

.9

Degrees of Freedom 2 26 28

-

: s =

SUlll Of SqUal-.?S 6.758927 100.295556 109.054483

Rough

10

wan squares 4.379464 3.85752:

F Rai~o 1.135

? = $

Probabillfy

Yal-lEltlO”

I s -

.25