Statement of problem
There is currently no protocol for managing endodontic access openings for all-ceramic
crowns. A direct restorative material is generally used to repair the access opening,
rendering a repaired crown as the definitive restoration. This endodontic procedure,
however, may weaken the restoration or initiate microcracks that may propagate, resulting
in premature failure of the restoration.
Purpose
The purpose of this in vitro study was to evaluate how an endodontic access opening
prepared through an all-ceramic crown altered the structural integrity of the ceramic,
and the effect of a repair of this access on the load to failure of an all-ceramic
crown.
Material and methods
Twenty-four alumina (Procera) and 24 zirconia (Procera) crowns were fabricated and
cemented (Rely X Luting Plus Cement) onto duplicate epoxy resin dies. Twelve crowns
of each were accessed to simulate root canal treatment therapy. Surface defects of
all accessed specimens were evaluated with an environmental scanning electron microscope.
The specimens were repaired with a porcelain repair system (standard adhesive resin/composite
resin protocol) and were loaded to failure in a universal testing machine. Observations
made visually and microscopically noted veneer delamination from the core, core fracture,
shear within the veneer porcelain, or a combination thereof. A Kruskal-Wallis test
was used to determine if a significant difference (α=.05) in load to failure existed
between the 4 groups, and a Mann-Whitney test with a Bonferroni correction (P<.0125) was used for multiple comparisons. A Weibull analysis was also used to estimate
the Weibull modulus and characteristic failure for each group.
Results
All specimens exhibited edge chipping around the access openings. Some displayed larger
chips within the veneering porcelain, and 4 zirconia crowns showed radial crack formation.
There was a significant difference in load to failure among all groups with the exception
of the alumina intact and repaired specimens (P=.695). The alumina crowns generally showed fracture of the coping with the veneering
porcelain still bonded to the core, whereas the zirconia copings tended not to fracture
but experienced veneering porcelain delamination.
Conclusion
Endodontic access through all-ceramic crowns resulted in a significant loss of strength
in the zirconia specimens but not in the alumina specimens.
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Article info
Publication history
Marquette University School of Dentistry, Milwaukee, Wis; US Army Dental and Trauma Research Detachment, Great Lakes, Ill; Baylor College of Dentistry, Dallas, Tex
Footnotes
This investigation was supported by Marquette University School of Dentistry and the American Academy of Fixed Prosthodontics Tylman Research Grant Program, 2004.
Identification
Copyright
© 2006 The Editorial Council of The Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.
