Casting distortion of five-fixture supported implant frameworks fabricated on master casts

摘要

Statement of the problem: Conventional techniques for implant framework fabricationudhave been shown to produce errors that are inconsistent with the passive-fit requirementudfor osseointegrated implant frameworks.udPurpose: The aim of this study was to assess the three-dimensional distortion inherent inudcasting of full arch, screw-retained titanium implant frameworks.udMaterials and methods: A conventional commercial laboratory one-piece casting, usingudthe lost-wax technique was used. Five wax patterns were fabricated on a die-stone castudpoured from a plaster impression of a five-fixture brass analogue. A reflex microscope wasudused to determine the three-dimensional casting error, by measuring horizontal and verticaluddistances for each wax pattern and its corresponding cast titanium framework, as well asudoffset distances from the horizontal reference plane.udResults: Significant differences were found in the amount of distortion between waxudpatterns and cast frameworks, with the castings being approximately 416 μm to 477 μmudlarger than the wax frameworks. The greatest amount of distortion occurred at the terminaludimplant abutments, and in the vertical dimension. However, there was inconsistency inudthese differences, indicating the three-dimensional nature of the overall distortion of theudcast frameworks.udConclusions: It is doubtful whether any conventionally cast framework can be made to theuddegree of accuracy required to fit passively on its abutments because of the multipleudvariables inherent in this process. It is therefore recommended that all full-arch, castudtitanium frameworks be cast in sections, or alternatively be sectioned, indexed andudsoldered before being seated intraorally.