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One of the main driving forces of a change in direction from opposing models produced from alginate to opposing
models derived from alginate substitutes in fixed prosthodontics is the severe mismatch of accuracy between modern
bite registration materials and alginate-driven stone models. Boksman 26 looked at PVS bite registration materials and
the need for extensive occlusal adjustments on crown & bridge prostheses, showing the severe open-bite mounting
that can result when using a highly accurate PVS bite registration with a poorly detailed alginate-driven stone model
(Fig. 7). Using PVS for the final impression, for the bite registration and for the opposing models eliminates the dimensional
mismatch between materials, resulting in more accurate mounting of the case and less clinical necessity for occlusal
adjustments (Fig. 8−11).
The surface replication of the casts is also much smoother than models derived from alginate impressions. Even though
the cost of the PVS alginate substitutes is higher than the irreversible hydrocolloid alginate materials, the impression is
easier to take due to the thixotropic nature of these materials, the time and cost of pouring up the opposing model can
be eliminated, the impression can be repoured if the model is broken or chipped, there is increased office efficiency,
the opposing model is more accurate, the bite registration actually fits, and the time and frustration of adjusting the
final prosthesis is minimized. These many benefits more than compensate for the extra cost. In addition, the clinician
can now (in some cases) bill this as part of the laboratory procedure. CM
References
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Dr. Len Boksman is adjunct clinical professor at the Schulich School of Medicine and Dentistry and maintains a private practice in London, Ontario, Canada. He is also a
paid part-time consultant to Clinical Research Dental Inc. and Clinician’s Choice. Contact him at lboksman@clinicalresearchdental.com or 519-641-3066, ext. 292.
Gregg Tousignant, CDT, is technical support manager for Clinical Research Dental Inc. E-mail him at gtousignant@clinicalresearchdental.com.
Reprinted by permission of Dentistry Today, ©2009 Dentistry Today. “DOCTOR-TECHNICIAN PERSPECTIVES: Alginate Substitutes: Rationale for Their Use,” by
Leendert Boksman, DDS, and Gregg Tousignant, CDT: Dentistry Today, Vol. 28, No. 4, 04/09, pp 104−105.
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