Abstract
ObjectivesTo evaluate the dimensional accuracy of impressions taken by use of disposable stock plastic trays and to compare performance with that of metal trays.Materials and methodsFrom a metallic model incorporating three precision balls and three abutment teeth, one-step dual-phase polyether (PE) and vinyl polysiloxane (VPS) impressions were taken using either metal or disposable plastic trays (n = 10 for each of the resulting four test groups). Respective plaster cast scans were aligned with the reference dataset to evaluate global (distance and angle deviations) and local (trueness and precision) accuracy. Analyses of variance (ANOVA) were conducted to determine group differences.ResultsFor all impression tray and material combinations, global accuracy was good (mean distance changes < 100 μm) with greatest deviations being observed for distances exceeding one quadrant of the dental arch. In general, distances measured in the plaster casts were too short. Only VPS impressions with plastic trays showed a different behavior with a large percentage of cross-arch distances exceeding the reference value. Mean local accuracy ranged between 6 and 14 μm (trueness), and 6 and 16 μm (precision). On abutment tooth level, metal trays were associated with a significantly better precision (p = 0.015).ConclusionsThe observed distortions of the studied impression trays and materials are small and should enable satisfying clinical impression-taking.Clinical relevanceCleaning and processing of metal trays before re-use are time-consuming. Especially for patients’ management with single crowns and small fixed dental prostheses, disposable plastic trays can be a viable and cost-effective alternative.
Highlights
In restorative treatment, the reliable communication of the clinical situation to the dental technician is a complex but key process [1]
After the doubled setting time of the impression materials (PE: 12 min, vinyl polysiloxane (VPS): 5 min)—to meet the prolonged setting at room temperature—impressions were demolded with a crosshead speed of 10 mm/min
For each of the test groups differing in impression material and tooth preparation, the median values of the demolding forces were slightly lower for the metal replica when compared with those found for the natural tooth
Summary
The reliable communication of the clinical situation to the dental technician is a complex but key process [1]. There are largely two established elastomeric material classes for impression-taking of abutment teeth prepared for fixed and removal dental prostheses: polyether (PE) and vinyl polysiloxane (VPS) [2,3,4,5]. Both enable excellent dimensional accuracy and the detail. For the sake of completeness, digital impressions by use of intraorally three-dimensional scanners should be mentioned which seem to be—regarding accuracy—comparable if used for the fabrication of single crowns [9,10,11], but are still disadvantageous to conventional impression-taking when it comes to long-span or full-arch restorations [9]. It should be acknowledged that laboratory adjustment of restorations including refinement of fit and occlusal contacts is more challenging without having plaster casts [9]
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