Techniques and materials for final impressions when making complete and partial removable dentures

Review question

In this review, conducted through Cochrane Oral Health, our aim was to evaluate which technique and material should be used for the final impression when making complete and partial removable dentures, to increase the quality of the denture, and improve oral health-related quality of life for the individual.

Background

It is common for elderly people to have lost some, or all of their teeth (edentulism). This has a significant impact on their quality of life. There are several steps to making complete and removable partial dentures. The final impression is a very important step for ensuring the quality of the denture in terms of satisfaction, comfort, stability of the denture, and chewing ability. There are a number of different techniques and materials used for making the final impression for complete dentures or removable partial dentures. There is no consensus on which are the best.

Study characteristics

The evidence in this review is current to 22 November 2017. We found eight studies with a total of 485 participants for complete dentures, and one study with 72 participants for removable partial dentures. The participants ranged from 45 to 75 years old, and had been without their teeth for 10 to 35 years. The studies compared different materials used to make the final impression for dentures (alginate, zinc-oxide eugenol, wax, and addtional silicone, polysulfide or polyether) and different techniques for making the final impression (open-mouth versus closed-mouth, single-stage versus two stage-two step), or both.

Key results

For most comparisons and outcomes, there was no evidence of a clear difference between the techniques or materials compared.

Very low quality-evidence from one study (10 participants) suggested that making dentures with an additional silicone elastomer biofunctional prosthetic required fewer adjustments than conventional methods.

Low-quality evidence from another study (144 participants) suggested that complete dentures made with silicone elastomer in a two stage–two step final impression, may be better than those made with alginate, in terms of oral health-related quality of life, stability of the denture, and chewing efficiency.

With the limited evidence available, we are unable to draw any conclusions about the best impression techniques and materials for complete and partial removable dentures. There is a need for further research in this area.

Quality of the evidence

The quality of the evidence base overall is low to very low. Only one or two studies assessed each intervention and comparison, and most of the studies were at high risk of bias. Many of the studies did not measure our key outcomes. For both complete and partial removable dentures, we conclude that we have no reliable findings.

Authors' conclusions: 

We conclude that there is no clear evidence that one technique or material has a substantial advantage over another for making complete dentures and removable partial dentures. Available evidence for the relative benefits of different denture fabrication techniques and final-impression materials is limited and is of low or very low quality. More high-quality RCTs are required.

Read the full abstract...
Background: 

Edentulism is relatively common and is often treated with the provision of complete or partial removable dentures. Clinicians make final impressions of complete dentures (CD) and removable partial dentures (RPD) using different techniques and materials. Applying the correct impression technique and material, based on an individual's oral condition, improves the quality of the prosthesis, which may improve quality of life.

Objectives: 

To assess the effects of different final-impression techniques and materials used to make complete dentures, for retention, stability, comfort, and quality of life in completely edentulous people.

To assess the effects of different final-impression techniques and materials used to make removable partial dentures, for stability, comfort, overextension, and quality of life in partially edentulous people.

Search strategy: 

Cochrane Oral Health’s Information Specialist searched the following databases: Cochrane Oral Health’s Trials Register (to 22 November 2017), the Cochrane Central Register of Controlled Trials (CENTRAL) (Cochrane Register of Studies, to 22 November 2017), MEDLINE Ovid (1946 to 22 November 2017), and Embase Ovid (21 December 2015 to 22 November 2017). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. No restrictions were placed on language or publication status when searching the electronic databases, however the search of Embase was restricted by date due to the Cochrane Centralised Search Project to identify all clinical trials and add them to CENTRAL.

Selection criteria: 

We included randomised controlled trials (RCTs) comparing different final-impression techniques and materials for treating people with complete dentures (CD) and removable partial dentures (RPD). For CD, we included trials that compared different materials or different techniques or both. In RPD for tooth-supported conditions, we included trials comparing the same material and different techniques, or different materials and the same technique. In tooth- and tissue-supported RPD, we included trials comparing the same material and different dual-impression techniques, and different materials with different dual-impression techniques.

Data collection and analysis: 

Two review authors independently, and in duplicate, screened studies for eligibility, extracted data, and assessed the risk of bias for each included trial. We expressed results as risk ratios (RR) for dichotomous outcomes, and as mean differences (MD) or standardised mean differences (SMD) for continuous outcomes, with 95% confidence intervals (CI), using the random-effects model. We constructed 'Summary of findings' tables for the main comparisons and outcomes (participant-reported oral health-related quality of life, quality of the denture, and denture border adjustments).

Main results: 

We included nine studies in this review. Eight studies involved 485 participants with CD. We assessed six of the studies to be at high risk of bias, and two to be at low risk of bias. We judged one study on RPD with 72 randomised participants to be at high risk of bias.

Overall, the quality of the evidence for each comparison and outcome was either low or very low, therefore, results should be interpreted with caution, as future research is likely to change the findings.

Complete dentures

Two studies compared the same material and different techniques (one study contributed data to a secondary outcome only); two studies compared the same technique and different materials; and four studies compared different materials and techniques.

One study (10 participants) evaluated two stage–two step, Biofunctional Prosthetic system (BPS) using additional silicone elastomer compared to conventional methods, and found no evidence of a clear difference for oral health-related quality of life, or quality of the dentures (denture satisfaction). The study reported that BPS required fewer adjustments. We assessed the quality of the evidence as very low.

One study (27 participants) compared selective pressure final-impression technique using wax versus polysulfide elastomeric (rubber) material. The study did not measure quality of life or dentures, and found no evidence of a clear difference between interventions in the need for adjustments (RR 0.81, 95% CI 0.38 to 1.70). We assessed the quality of the evidence as very low.

One study compared two stage–two step final impression with alginate versus silicone elastomer. Oral health-related quality of life measured by the OHIP-EDENT seemed to be better with silicone (MD 7.20, 95% CI 2.71 to 11.69; 144 participants). The study found no clear differences in participant-reported quality of the denture (comfort) after a two-week 'confirmation' period, but reported that silicone was better for stability and chewing efficiency. We assessed the quality of the evidence as low.

Three studies compared single-stage impressions with alginate versus two stage-two step with elastomer (silicone, polysulfide, or polyether) impressions. There was no evidence of a clear difference in the OHIP-EDENT at one month (MD 0.05, 95% CI -2.37 to 2.47; two studies, 98 participants). There was no evidence of a clear difference in participant-rated general satisfaction with dentures at six months (MD 0.00, 95% CI -8.23 to 8.23; one study, 105 participants). We assessed the quality of the evidence as very low.

One study compared single-stage alginate versus two stage-two step using zinc-oxide eugenol, and found no evidence of a clear difference in OHIP-EDENT (MD 0.50, 95% CI -2.67 to 3.67; 39 participants), or general satisfaction (RR 3.15, 95% CI 0.14 to 72.88; 39 participants) at six months. We assessed the quality of the evidence as very low.

Removable partial dentures

One study randomised 72 participants and compared altered-cast technique versus one-piece cast technique. The study did not measure quality of life, but reported that most participants were satisfied with the dentures and there was no evidence of any clear difference between groups for general satisfaction at one-year follow-up (low-quality evidence). There was no evidence of a clear difference in number of intaglio adjustments at one year (RR 1.43, 95% CI 0.61 to 3.34) (very low-quality evidence).

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