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Title Limited Evidence Supports Using The Altered Cast Impression Technique For Partial Removable Dental Prostheses (PRDP)
Clinical Question Is there a clinically significant difference in the outcome of the distal extension PRDP made with an altered cast impression technique as opposed to a one-piece cast technique?
Clinical Bottom Line An accurate and properly extended cast is necessary for an optimal clinical result. The limited evidence demonstrates a measurable advantage for the altered cast impression procedure. However, the advantage realized may not be clinically significant. Single definitive impressions can provide acceptable results provided that the framework fits well, and the cast is properly extended. (See Comments on the CAT below)
Best Evidence (you may view more info by clicking on the PubMed ID link)
PubMed ID Author / Year Patient Group Study type
(level of evidence)
#1) 15153855Frank 2004n=72, patients receiving mandibular bilateral distal extension PRDPRandomized Controlled Trial
Key resultsThere was 0.15 mm less space between tissue at ridge crest and denture base in the altered cast group at time of placement and 0.11 mm one year after placement. This was statistically significant but not deemed to be clinically significant. 22% of the one-piece casts were under extended. No under extension was found with the altered cast procedure. Although the altered cast impression procedure provided a measurable advantage in tissue adaptation, this did not have a significant effect on the other parameters evaluated (number of follow-up appointments needed, occlusion, detectable denture base movement, abutment mobility, sulcus depth measurement, gingival index, subsequent treatment of natural teeth, and patient satisfaction).
#2) 1501177Leuphold 1992N=7 patients receiving mandibular bilateral distal extension PRDPComparative Study
Key resultsThree PRDPs were made for 7 patients using three different impression techniques: irreversible hydrocolloid with stock metal tray, border molded custom tray with polysulfide, and an altered cast impression with polysulfide. A device was used to measure vertical displacement of the denture base toward the tissue. Mean displacement for the irreversible hydrocolloid was 1.48 mm bilaterally, 0.78 mm and 0.81 mm for right and left side for the border molded custom tray, and 0.6 mm bilaterally for the altered cast. A statistically significant difference of 0.19 mm was observed between the custom tray and altered cast groups. Although statistically significant, the authors questioned the clinical significance of this difference.
Evidence Search "Denture, Partial, Removable"[Mesh] AND "altered-cast"[All Fields] OR "altered cast"[All Fields]
Comments on
The Evidence
Very limited evidence that addresses the clinical question is available. One randomized controlled trial was found. That study followed a limited number of patients for one year. A single experienced provider made all impressions. Less experienced clinicians may not have the same results. In the single comparative study found, only a single clinical measurement was made at the time of placement of the PRDPs. The anatomic form of the edentulous spaces being treated was not well defined in either study. From the evidence available it is not clear if the altered cast impression procedure offers a discernible clinical advantage over a single definitive impression. It is possible that the procedure could be more beneficial to some patients than others.
Applicability The altered cast impression procedure can produce measurable advantages to a single impression technique. However, the clinical advantage may not be discernible. Clinicians must decide if the additional steps involved in the altered cast impression will produce significantly improved clinical outcomes. The ability of the clinician to make an acceptable single impression and the anatomic form of the edentulous area being treated are factors to consider.
Specialty/Discipline (General Dentistry) (Prosthodontics) (Restorative Dentistry)
Keywords removable partial dentures; altered cast impressions
ID# 2165
Date of submission: 01/05/2012spacer
E-mail walter.daniels@ucdenver.edu
Author Walter C. Daniels, DMD
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Basic Science Rationale
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Comments and Evidence-Based Updates on the CAT
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by Christine Fortmann, Russell Johnson, Kirk Sutton (San Antonio, Texas) on 08/07/2012
A review of the literature reveals recent publications regarding the benefits and methodology of the Altered Cast Impression Technique, however, there is no further evidence discussing the clinical advantage this technique provides. As a result, we agree with the clinical bottom line in the CAT above.

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