Dimensional accuracy of three techniques for full-arch implant impressions: orthodontic elastomeric chain versus...

Accurate transfer of implant positions is critical for achieving passive fit in full-arch prostheses. Although splinting of impression copings enhances accuracy, the optimal chairside splinting method remains uncertain. Orthodontic elastomeric chains have been proposed as a practical alternative to floss-resin splinting, but their dimensional accuracy has not been quantitatively validated.

The purpose of this in-vitro study was to compare the accuracy of full-arch implant impressions made with three techniques non-splinted (NS), dental-floss with light-polymerizing resin (FR), and orthodontic elastomeric chain with light-polymerizing resin (CR) and to determine whether the chain-resin technique provides comparable or superior trueness.

A mandibular master model with six parallel implants (Bio3 GmbH, Pforzheim, Germany) and multiunit abutments torqued to 25 N cm was used to fabricate 21 casts (n = 7 per group). Open-tray impressions were made with polyvinyl siloxane (Zhermack, Italy). In the FR and CR groups, copings were splinted with dental floss or a closed-type orthodontic chain, respectively, reinforced with light-polymerizing pattern resin (Motif, Dokuz Kimya, Turkey), sectioned with a 0.3-mm diamond disk, and rejoined before impression making. Definitive casts with gingival masks were produced in type IV stone. Digital scan bodies were attached, and casts were scanned with a laboratory scanner (3Shape, Denmark). Linear inter-implant distances (positions 1-6) and inter-axis (3D) angulations were measured in Geomagic Design X 2022.0 (3D Systems, USA). Examiner reliability was ensured by repeating 10% of the measurements (intraclass correlation > 0.95). Normality was assessed using the Shapiro-Wilk test, and homogeneity of variances was evaluated using Levene's test. According to the results of these assumption checks, global comparisons were performed using either one-way ANOVA or the Kruskal-Wallis test. Thereafter, false discovery rate (FDR) correction was applied to the global-test P values. Finally, a power analysis was conducted to evaluate the effect sizes and achieved power associated with the obtained results. All statistical analyses were performed at a significance level of [Formula: see text].

Significant differences (P < 0.05) were observed for 6 of 10 metrics (Distance 1-3, 1-4, 1-5, 1-6; Angulation 1-2, 1-6). The CR group exhibited the lowest pooled deviation (8.549) compared with FR (9.106) and NS (9.914). FR achieved the highest number of per-metric wins (4 of 6 significant comparisons). The non-splinted technique consistently produced the largest deviations.

Within the limitations of this in vitro study, splinting implant impression copings with an orthodontic elastomeric chain reinforced with light-polymerizing resin showed favourable performance in the pooled absolute deviation analysis, whereas the floss-resin method demonstrated comparable consistency by performing better in the per-metric winner assessment. In contrast, the non-splinted technique did not show favourable performance compared with the other groups. Therefore, both the orthodontic elastomeric chain reinforced with light-polymerizing resin and the floss-resin techniques may be considered practical chairside alternatives for full-arc h implant impressions. In particular, the chain-resin splinting approach may represent a simplified, time-efficient, and clinically feasible option for achieving accurate full-arch implant impressions.