Statement of problem
Anterior cantilever resin-bonded prostheses fail as a result of a labio-lingual peeling
action, which creates a stress concentration within the adhesive layer.
Purpose
The purpose of this study was to identify the factors that determine the retention
of an anterior resin-bonded prosthesis and to seek to eliminate the stress concentration
within the adhesive layer by fundamentally altering the prosthesis design.
Material and methods
The first experiment involved 40 Ni/Cr (Wiron 99) beams with a width of 5 mm, thickness
of 0.5 mm, and lengths ranging from to 13 to 22 mm. The beams were cemented onto a
block of the same material using an adhesive resin luting agent (Panavia 21). The
length of the beam that was bonded ranged from 1 to 10 mm, resulting in a bonded area
ranging from 5 to 50 mm2. A load was applied onto the cantilevered portion of the beam 2 mm from the end,
causing a peeling action. The force (N) required to debond these beams was measured
using a pull-to-fracture test. Subsequently, a second experiment was undertaken, and
7 beams with an altered point of attachment (new design) were tested. The new design
had the point of attachment of the cantilevered portion located centrally on the bonded
area of the beam. Implementing this new design clinically would result in a cantilevered
resin-bonded fixed partial denture that would have the connector arm attached more
centrally on the retainer wing. The data were analyzed using a 1-way analysis of variance
(α=.05), and a Tukey pairwise comparison test was used when the results was statistically
significant. Two finite element analysis (FEA) models, one simulating the first experimental
design and the other simulating the new design, were created. A load was then applied
on the cantilevered portion of the beams similar to the experimental models, and the
stress patterns were examined. The numerical values of these resultant stresses were
plotted graphically.
Results
The direction of load application, which may be transferred to a clinical setting
as labio-lingual forces, was identified as the dominant force responsible for debonding.
The new design, which addressed this problem, showed a significant increase (P<.001) in retention. The FEA models identified the stress concentrations within the
adhesive layer of the traditional design, which were eliminated when the new design
was tested.
Conclusions
For the in vitro model, loads that may be interpreted clinically as labio-lingual
forces resulted in the lowest forces required to cause debonding, and these forces
were independent of the surface area of bonding. Altering the point of attachment
of the cantilevered portion onto the retainer caused a significant increase in the
forces needed to cause debonding.
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Article info
Publication history
University of Sheffield, Sheffield, United Kingdom
Footnotes
Presented at the British Society for Dental Research (BSDR) Annual Conference, Birmingham, UK, April 2004.
Identification
Copyright
© 2006 The Editorial Council of The Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
