Marisa Panchim. Bond strength of 8 base metal alloys with 3 porcelains . Master's Degree(Prosthodontics). Mahidol University. : Mahidol University, 2003.
Bond strength of 8 base metal alloys with 3 porcelains
Abstract:
Base metal alloys have replaced noble alloys in the fabrication of porcelain fused
to metal restorations since the price of noble alloys has risen rapidly. Nowadays there
are many types of base metal alloys and porcelains in Thailand, and the proper
matching between porcelain and alloy will increase the longevity of the restorations.
A modified shear bond strength test was developed to evaluate compatibility
between 8 base metal alloys and 3 porcelains. Four cast metal discs (6.8x2.0 mm) of
each base metal alloy were prepared and fused with each type of porcelain cylinder
(5.2x9.0 mm). The porcelain cylinders were then embedded in 20 mm cubes of an
autopolymerizing acrylic resin in PVC pipes. The specimen was fixed on a Universal
Testing Machine to allow pull loading of the cast metal disc in a vertical direction
until failure of the bond occurred.
The bond strength ranged from 14.2-25.7 MPa. There were no significant
differences of the mean shear bond strength among each porcelain-alloy composite
and among each alloy group. However, a significant difference was found only
between the Noritake porcelain group (21.0 MPa) and the Shofu group (16.4 MPa)
(p<0.05), while the Vita group (19.0 MPa) did not significantly differ from the other
two groups. Failure of almost all specimens (93 out of 96) were cohesive failures in
the porcelain cylinders and the rest were partially adhesive failures.
The results implied that the recorded values reflected the strength of the porcelain
itself rather than the strength of the interfacial bond. So, the bond strength seemed to
be higher than what the recorded values showed. This indicated that the pull shear test
used in this study was not the ideal test as expected. Matching of porcelain and base
metal alloy could not be determined because most of the failures occurred in the
porcelain. Good bond strength of the porcelain and the alloy was one of many factors
that controlled the success of the restorations.