Title The Altered Cast Impression Technique Does Not Offer Significant Advantages Over Conventional Single Impression Techniques
Clinical Question In the fabrication of distal extension removable partial dentures, does the altered cast technique result in improved outcomes compared to conventional single-cast impression techniques?
Clinical Bottom Line The altered cast impression technique has been demonstrated in multiple studies to produce statistically significant improvements in edentulous ridge adaptation and reduced forces to abutment teeth. However, most authors agree that these minor improvements are not clinically significant. Some studies demonstrate no clear superiority of the altered cast over a single cast technique. Furthermore, any slight advantage conferred by the altered cast may be outweighed by the advantages of simplicity, reduced materials cost, and reduced chair time offered by one-piece cast techniques.
Best Evidence  
PubMed ID Author / Year Patient Group Study type
(level of evidence)
31034543Sayed/20197 in-vivo studies (n=98 individuals)Systematic Review
Key resultsAll seven articles included in this systematic review reported less vertical movement of distal extension RPD bases fabricated through the altered cast technique compared with other one-piece cast techniques. Different measurement techniques were employed by the included studies to measure denture base fit to the edentulous ridge. Included studies reported differences in tissue displacement (1.170, 0.960, 0.885mm vs. 0.345, 0.315, 0.340mm), differences in denture base movement (mean differences 0.19mm and 0.06mm), ridge adaptation distance (0.15mm mean difference), and tissue placement (7.547mm vs 7.2110mm vs 5.856mm). While some of the included studies reported that the observed differences were statistically significant, most studies maintained that these differences were not likely to be clinically significant.
29617037Jayaraman/2018Nine studies of varried qualityCochrane Database Systematic Review
Key resultsThis Cochrane Review analyzed literature comparing impression techniques and materials used in the fabrication of complete dentures and removable partial dentures. It included a 2004 randomized controlled trial by Frank, et al. that focused on distal extension RPDs. Frank compared outcomes of one-piece cast and altered cast techniques and found no clear difference in patient reported overall satisfaction at one year follow-up and no significant difference in number of border and intaglio adjustments one month after insertion (RR 1.43, 95% CI 0.61-3.34). Additionally, at one year follow-up there was no significant difference in gingival health of the right abutment (RR 1.05, 95% CI 0.56-1.98) and theleft abutment (RR 1.10, 95% CI 0.46-2.64) and no significant difference in mobility of the right abutment (RR 2.90, 95% CI 0.87- 9.61) and left abutment (RR 1.16, 95% CI 0.40 to 3.37). At one year follow-up, denture base adaptation to the ridge for one-piece cast was poor compared to altered cast, but there was no clear difference in the buccal shelf area (MD ‐0.11, 95% CI ‐0.18 to ‐0.04).
Evidence Search Altered cast impression (Pubmed)
Comments on
The Evidence
The Sayed review employed robust inclusion/exclusion criteria and performed a thorough review of available literature using PRISMA guidelines to answer a focused clinical question. An appropriate number of studies were included, however, the total sample size remained small. The author maintains that many of the results were statistically significant but fails to mention how this was determined or any statistical values associated with these determinations. The included studies all used different metrics and compared the altered cast method to different impression techniques and materials, which reduces the validity of the review. Sayed maintains that the advantage gained by the altered cast technique is probably not clinically significant. While this may be true, this recommendation is based on expert opinion rather than clinical data, such as long-term follow up studies of the altered cast technique. Long-term studies of clinical outcomes are necessary to make a definitive recommendation on clinical significance. The Cochrane review also employed robust inclusion/exclusion criteria and only a single study met the strict criteria. The lack of available studies meeting the stringent Cochrane criteria highlights the fact that few well-controlled studies of the altered cast technique have been performed. Indeed, Jayaraman points out that Frank’s findings are “low to very-low” in quality and at high risk of bias, and that more high quality RCTs are necessary to confirm advantage of one technique over another.
Applicability Distal extension removable partial dentures require adequate tissue support in order to minimize stress to abutment teeth. Clinicians need to be aware of how different fabrication techniques may affect treatment outcomes.
Specialty (General Dentistry) (Prosthodontics)
Keywords Distal extension, altered cast, removable partial denture
ID# 3431
Date of submission 05/02/2020
E-mail robert.stabio@cuanschutz.edu
Author Robert Stabio
Co-author(s) e-mail
Faculty mentor Walter Daniels, DMD
Faculty mentor e-mail walter.daniels@cuanschutz.edu
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?)
None available
Comments and Evidence-Based Updates on the CAT
None available