Marginal Gap Measurement of Pre-Cemented Metal–Ceramic Crowns: A Systematic Review

Background/Objectives: Metal–ceramic crowns may be constructed using different techniques and coping materials. A systematic review analysing the coping material, method of construction, and instruments used for measuring the metal–ceramic crown marginal gap has not been completed. The aim of this systematic review was to appraise the literature relating to the instruments used for the in vitro marginal gap measurement of single pre-cemented metal–ceramic crowns and assess whether the crown coping material and method of coping construction influence the marginal gap. Methods: A systematic search was performed in November 2024 across the EBSCO Host, Scopus, PubMed, and Web of Science databases, adhering to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and specific eligibility criteria. The Joanna Briggs Critical Appraisal Checklist was used to assess article quality. Results: Fourteen studies evaluated marginal gaps in 402 crowns using the following techniques: direct view microscopy (eight studies), replica techniques (three studies), scanning electron microscopy (two studies), and profilometry (one study). The mean marginal gap for all the metal–ceramic crowns across all the studies was 65.97 ± 32.58 µm. The pre-cementation mean marginal gaps showed no significant difference between Computer-Aided Design–Computer-Aided Manufacturing (CAD-CAM) milled copings (87.95 ± 26.35 µm) and conventionally cast copings (90.45 ± 24.37 µm) (t = −0.197, p = 0.847). The mean marginal gaps varied significantly (F = 11.34, p < 0.001) by coping material: cobalt–chromium (Co-Cr) led to 84.28 µm, nickel–chromium (Ni-Cr) led to 70.98 µm, titanium led to 50.18 µm, and noble metal alloys led to 27.90 µm. Six studies addressed confounding factors and followed a standardised approach for measuring marginal gaps. Conclusions: Direct view microscopy was the most commonly used instrument for measuring the marginal gaps of single pre-cemented metal–ceramic crowns, yielding the smallest reported mean marginal gap of 75.00 ± 26.87 µm. Metal–ceramic crowns constructed with noble metal alloys exhibited the lowest mean marginal gaps. Metal–ceramic crowns constructed using conventional casting techniques presented similar marginal gaps to CAD-CAM crowns.