Does Impression Material Thickness Impact the Accuracy of Addition Silicone Impressions and the Resultant Casts? A 3D Analysis

European Journal of Prosthodontics and Restorative Dentistry (2025) 33, 353–369

3D Analysis Addition Silicone Gypsum Tray Spacer Partially Dentate Dental Impression

Enas E. Negm*

§

(BDS, MSc, PhD)

Mangala Patel *

(BSc (Hons), MSc, PhD)

Paul Ryan *

(BDS, MFDS (RCS Eng), MClinDent (Perio),
MPerio (RCS Ed), FDS (Rest Dent), PGCert
FHEA, PhD)

Address for Correspondence
Enas E. Negm *
Email: e.e.e.negm@qmul.ac.uk
* Institute of Dentistry, Faculty of Medicine and
Dentistry, Queen Mary University of London,
London, United Kingdom
§

Prosthodontics Department, Faculty of Dentistry,
Tanta University

Received: 30.08.2024
Accepted: 22.06.2025

Does Impression Material
Thickness Impact the
Accuracy of Addition
Silicone Impressions and
the Resultant Casts? A 3D
Analysis

Objectives: Conflicting evidence exists regarding the optimal impression thickness and the influence of tray spacing on the accuracy of elastomeric impressions and resulting casts. This study evaluated the effect of three tray spacings (2 mm, 4 mm, and 6 mm) on the dimensional accuracy of three addition silicone impression materials (Aquasil, Panasil, and Elite-HD). Methods: Forty-five impressions of a partially dentate maxillary resin cast were made using standardized custom trays with designated spacer thicknesses. Impressions were scanned using a desktop scanner, and casts were poured into type IV dental stone and subsequently scanned. A digital reference cast was generated and used to superimpose all test scans. Deviations were measured across the full arch, palate, and dentulous-edentulous (horseshoe) regions using digital metrology software. Data were analyzed using multiple regression and Tukey HSD post-hoc tests (α = 0.05). Results: Spacer thickness and material significantly influenced impression and cast accuracy, with higher deviations observed in the horseshoe region compared to the palate (p < 0.001). Conclusions: Panasil at 6-mm spacing produced the most accurate impressions across all regions. Clinical relevance:For cast accuracy, Elite-HD at 4-mm spacing showed the lowest deviation in the palate, while Panasil at 2-mm spacing demonstrated superior accuracy in both full arch and horseshoe regions.

Making an impression is a crucial step in the construction of a fixed or removable dental prosthesis.1 To provide an accurate prosthesis fit, it is essential to accurately capture the tissue surface throughout the impression making procedures.2 Rudd and coworkers3 summarized several potential causes of ill-fitting removable partial denture frameworks, many of which arise from technical errors during the impression-making process. These include improper tray selection, inadequate spacer design, poor material handling, insufficient setting time, and premature removal of the impression.3 Such procedural inaccuracies can lead to distortion of the impression and subsequent inaccuracy in the resultant stone cast.3 The greatest vertical distortion has been observed in the palatal region of poured casts, with deviations up to 302 µm documented.4 Therefore, the accuracy of a removable prosthesis is • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

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