610 the journal of prosthetic dentistry volume 81 number 5

TOLEDANO ET AL
THE JOURNAL OF PROSTHETIC DENTISTRY
MAY 1999
615
27. Crim GA, García-Godoy F. Microleakage: the effect of storage and cycling
duration. J Prosthet Dent 1987;57:574-6.
28. Mixson JM, Eick JD, Chappell RP, Tira DE, Moore DL. Comparison of two-
surface and multiple-surface scoring methodologies for in vitro
microleakage studies. Dent Mater 1991;7:191-6.
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Copyright © 1999 by The Editorial Council of 
The Journal of Prosthetic
Dentistry.
0022-3913/99/$8.00 + 0. 10/1/96694
Shear stresses in the adhesive layer under porcelain veneers
Troedson M, Derand T. Acta Odontol Scand 1998;56:257-62.
Purpose. 
In vitro studies into which part of the enamel-resin–composite-porcelain laminate sys-
tem breaks have shown that the luting interface is the weakest part of the lamination and that it
will fail due to sheer stresses. This study calculated sheer stress in the composite cement and
enamel bond with the facing loaded in the incisal area under different angles and adhesive con-
ditions.
Material and methods. 
Two-dimensional finite element models of veneers on teeth with an
intermediate layer of resin were designed according to the size of an average maxillary central
incisor. The abutment was considered to be homogenous, and the remaining enamel layer under
the buccal surface of the veneer and the pulp were treated as dentin with regard to material prop-
erties. Three models of the tooth were created with different margin designs, while all designs
had preparations that covered the incisal edge. Porcelain facings were made to be 0.5 mm thick:
composite cement layer, 25 
µ
m; enamel bond layer, 1 
µ
m. Three adhesive conditions were test-
ed: (1) lack of polymerization in the facing’s periphery, (2) lack of polymerization in the middle,
and (3) total bonding of the facing. All models were loaded at 0, 30, and 60 degrees to the long
axis of the tooth.
Results. 
Rather extensive tables presented the numeric results of the study. Maximum sheer
stresses did not exceed the stress level for debonding, but great differences in maximum shear
stress appeared with varying loss of bond and different loading angles. Fully laminated facing
showed stress levels in the composite cement to be only 
1
⁄
5
of those in the facing with a lack of
adhesion in the periphery and 
1
⁄
15
of those in the enamel bond. Maximum stresses increased about
4 times when the load angle was 30 degrees compared with 0 degrees, and increased 1.5 times
from 30 to 60 degrees.
Conclusions. 
A porcelain veneer that is kept inside the enamel, with full lamination, demon-
strated fairly low shear stresses in the enamel bond and composite cement and thus should indi-
cate good long-term prognosis. 13 References.—ME Razzoog
Noteworthy Abstracts
of the
Current Literature