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Laboratory assessment of impression accuracy by clinical simulation

Lookup NU author(s): Dr Robert Wassell


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Some laboratory tests of impression material accuracy mimic the clinical situation (simulatory) while others attempt to quantify a material's individual properties. This review concentrates on simulatory testing and aims to give a classification of the numerous tests available. Measurements can be made of the impression itself or the resulting cast. Cast measurements are divided into those made of individual dies and those made of interdie relations. Contact measurement techniques have the advantage of simplicity but are potentially inaccurate because of die abrasion. Non-contact techniques can overcome the abrasion problem but the measurements, especially those made in three dimensions, may be difficult to interpret. Nevertheless, providing that care is taken to avoid parallax error non-contact methods are preferable as experimental variables are easier to control. Where measurements are made of individual dies these should include the die width across the finishing line, as occlusal width measurements provide only limited information. A new concept of ‘differential die distortion’ (dimensional difference from the master model in one plane minus the dimensional difference in the perpendicular plane) provides a clinically relevant method of interpreting dimensional changes. Where measurements are made between dies movement of the individual dies within the master model must be prevented. Many of the test methods can be criticized as providing clinically unrealistic master models/dies or impression trays. Phantom head typodonts form a useful basis for the morphology of master models providing that undercuts are standardized and the master model temperature adequately controlled.

Publication metadata

Author(s): Wassell RW, Abuasi HA

Publication type: Article

Publication status: Published

Journal: Journal of Dentistry

Year: 1992

Volume: 20

Issue: 2

Pages: 108-114

Print publication date: 01/04/1992

ISSN (print): 0300-5712

ISSN (electronic): 1879-176X

Publisher: Elsevier Ltd


DOI: 10.1016/0300-5712(92)90117-U


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