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Updated: Sep 19, 2026
Measuring the Complete-arch Distortion of an Optical Dental Impression
Published on: May 30, 2019
Occlusal Adjustment in Free-End Implant-Supported Restorations: Digital Scans Versus Conventional Impressions With
Mohammadreza Nakhaei1, Hossein Dashti1, Arsalan Shahri2
1Department of Prosthodontics, School of Dentistry, Mashhad University of Medical Sciences, Mashhad, Iran.
Objectives:
To quantify the occlusal adjustment required for two-unit, implant-supported polymethyl-methacrylate (PMMA) crowns with either digital or conventional impression techniques, using full-arch and half-arch workflows.
Material And Methods:
An acrylic maxillary-mandibular model carrying two bone-level implant analogs (sites 46-47) was mounted on a semi-adjustable articulator. Twenty impressions were made (n = 5 per group): digital full-arch, digital half-arch, conventional full-arch, and conventional half-arch. PMMA crowns were designed using computer-aided design (CAD) software, milled, and surface-scanned before adjustment. Occlusal contacts were refined on the articulator with 21 µm film while recording adjustment time. Pre- and post-adjustment scans were superimposed and analyzed using three-dimensional surface analysis software to quantify mean material reduction (µm). Data were analyzed with one-way ANOVA and independent-samples t-tests (α = 0.05).
Results:
Digital workflows required significantly less occlusal reduction (146 ± 35 µm vs. 226 ± 35 µm; p = 0.035) and shorter adjustment times (144 ± 36 s vs. 385 ± 36 s; p < 0.001) than conventional, with no effect of arch span (full vs. half; p > 0.05). Within protocols, the digital half-arch group showed the smallest adjustment (127 ± 37 µm) and fastest finishing (98 ± 33 s), whereas the conventional half-arch group required the longest time (456 ± 21 s).
Conclusion:
Fully digital impressions reduce both the amount of occlusal adjustment and the chairside time needed to seat implant-supported crowns compared with conventional silicone impressions. Reducing the scan to a half-arch does not compromise occlusal precision, making the digital half-arch workflow an efficient alternative for posterior, free-end implant restorations.
Clinical Relevance:
In implant posterior PMMA crowns, the impact of impression/workflow choice on occlusal adjustment is unclear. This in-vitro study measured occlusal reduction and chairside time across digital versus conventional and full- versus half-arch workflows. Digital, especially half-arch, required less adjustment and shorter time. Clinically, a digital half-arch approach may streamline delivery and reduce unnecessary material removal, pending confirmation in patient-based settings.