Casting distortion of five-fixture supported implant frameworks fabricated on master casts
Date
2008-10-23T12:23:29Z
Authors
Mitha, Tasneem
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Abstract
Statement of the problem: Conventional techniques for implant framework fabrication
have been shown to produce errors that are inconsistent with the passive-fit requirement
for osseointegrated implant frameworks.
Purpose: The aim of this study was to assess the three-dimensional distortion inherent in
casting of full arch, screw-retained titanium implant frameworks.
Materials and methods: A conventional commercial laboratory one-piece casting, using
the lost-wax technique was used. Five wax patterns were fabricated on a die-stone cast
poured from a plaster impression of a five-fixture brass analogue. A reflex microscope was
used to determine the three-dimensional casting error, by measuring horizontal and vertical
distances for each wax pattern and its corresponding cast titanium framework, as well as
offset distances from the horizontal reference plane.
Results: Significant differences were found in the amount of distortion between wax
patterns and cast frameworks, with the castings being approximately 416 μm to 477 μm
larger than the wax frameworks. The greatest amount of distortion occurred at the terminal
implant abutments, and in the vertical dimension. However, there was inconsistency in
these differences, indicating the three-dimensional nature of the overall distortion of the
cast frameworks.
Conclusions: It is doubtful whether any conventionally cast framework can be made to the
degree of accuracy required to fit passively on its abutments because of the multiple
variables inherent in this process. It is therefore recommended that all full-arch, cast
titanium frameworks be cast in sections, or alternatively be sectioned, indexed and
soldered before being seated intraorally.
Description
Keywords
casting distortion, implant frameworks