ObservationsWill Digital Impressions Eliminate the Current Problems With Conventional Impressions?
Section snippets
SOFT-TISSUE MANAGEMENT
Perhaps the most significant reason for the inadequacy of some impressions made with elastomer impression materials, as observed by dental laboratory technicians, is the lack of visibility of the subgingival margins of tooth preparations (J. Shuck, vice president, sales and marketing, Glidewell Laboratories, oral communication, Jan. 9, 2008). This problem is related directly to inadequate soft-tissue management at the time the impression is made. In a previous JADA column,7 I have outlined the
IMPROPER IMPRESSION TRAY SELECTION
Most dentists use stock double-arch impression trays for their elastomer impressions of one or two units and stock trays for multiple units. Many stock trays are flexible, requiring rigid impression material to provide the stability needed. If the stock tray and the impression material inside it are not adequately rigid, the impression's accuracy will be compromised because of the flexibility of the tray and the material.8, 9, 10 Additionally, stock trays require several times the amount of
SEPARATION OF IMPRESSION MATERIAL FROM THE IMPRESSION TRAY
Problems in separating impression material from the impression tray usually are related to improper use of tray adhesive materials. Polyether and vinyl polysiloxane impression materials require adhesive agents to attach the impression material to the impression tray. Holes in trays further enhance attachment of the impression material to the tray.
Impression trays are not required for digital impressions. Therefore, digital impressions can eliminate this frequently seen problem, thus potentially
DISTORTION OF CONVENTIONAL IMPRESSIONS BEFORE POURING
Polyether and vinyl polysiloxane impression materials are stable for a reasonable time after the impression is made,1, 2, 3, 4, 5 but they can be distorted by inadequate storage or inadvertent force applied to the tray and impression during transportation or shipment to the dental laboratory.
Digital impressions do not involve impression trays, impression materials or shipment to the dental laboratory and so eliminate the associated problems.
STORAGE OF CONVENTIONAL IMPRESSIONS FOR POTENTIAL REMAKING OF CASTS AND DIES
Sometimes, an impression is poured improperly. It may contain bubbles. The stone used for the die material may be too thick or too thin. The impression or the poured dies may be misplaced or lost. The result of each of these problems is a need to remake the dies. When this need arises in the case of an impression made with conventional impression techniques, the impression must be repoured.
The digital impression concept allows retention of the digital information in appropriate computer storage
SUMMARY
Digital impressions appear to be practical, and the concept is being perfected, but the need for further research is clear.12 Digital impressions eliminate some of the negative characteristics of conventional elastomer impressions, but proper soft-tissue management and isolation of tooth preparation margins still is necessary. The relative cost of digital impressions to conventional elastomer impressions is related directly to the number of impressions made by specific practitioners per month,
References (12)
Changes in properties of nonaqueous elastomeric impression materials after storage of components
J Prosthet Dent
(2001)The challenge to conventional impressions
JADA
(2008)The state of fixed prosthodontic impressions: room for improvement
JADA
(2005)- et al.
The effect of tray selection, viscosity of impression material, and sequence of pour on the accuracy of dies made from dual-arch impressions (published correction appears in J Prosthet Dent 2007;97[1]:38)
J Prosthet Dent
(2003) - et al.
A clinical pilot study of the dimensional accuracy of double-arch and complete-arch impressions
J Prosthet Dent
(2002) Now is the time to change to custom impression trays
JADA
(1994)
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2023, Journal of Prosthetic DentistryAccuracy of intraoral scanning methods for maxillary Kennedy class I arch
2023, Journal of Dental Sciences
The views expressed are those of the author and do not necessarily reflect the opinions or official policies of the American Dental Association.
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Dr. Christensen is the director, Practical Clinical Courses, and co-founder and senior consultant, CR Foundation, Provo, Utah. He also is the dean, Scottsdale Center for Dentistry, Scottsdale, Ariz.