Novel hybrid resin-ceramic crowns in dentistry – a comparison of the internal and marginal fits achieved for additively versus subtractively manufactured permanent crowns

Limited information exists regarding the internal and marginal fits of hybrid resin–ceramic crowns when using subtractive or additive manufacturing workflows. Excessive marginal fit discrepancies can lead to biological complications, while poor internal fit may impact retention and mechanical stability. The objective of this study was to compare the marginal and internal fits of hybrid resin–ceramic crowns fabricated using additive and subtractive manufacturing and to assess directly the level of agreement between a digital evaluation workflow and the silicone replica technique, given that these tools may yield different results. A standardized crown design was prepared on a customized metal model and used to fabricate, using either a subtractive milling process (Voco Grandio Disc) or an additive 3D-printing process (Bego VarseoSmile TriniQ), 10 crowns per group. The internal and marginal fits of the crowns were assessed using both a digital analysis and the conventional silicone replica method. Fit values were compared across manufacturing and measurement methods. The silicone replica method gave significantly lower internal fit values for additively manufactured (AM) crowns (mean: 103.1 μm, SD: 58.3), as compared with the subtractively manufactured (SM) crowns (mean: 181.8 μm, SD: 102.9), corresponding to β = –78.7 μm (95% CI: –111.9 to –45.5; p < 0.001). AM crowns also exhibited smaller marginal gaps (–89.5 μm, 95% CI: –135.3 to –43.7; p = 0.001). However, both the AM and SM crowns presented marginal and internal fit values did not meet clinically acceptable thresholds for permanent restorations. When comparing measurement techniques, the largest differences in fit was observed in the absolute marginal and occlusal regions, whereas cervical and axial discrepancies were minimal (<15 μm). Neither manufacturing method achieved clinically acceptable fit values, although the AM crowns demonstrated statistically smaller internal and marginal gaps than the SM crowns. These findings emphasize that the choice of measurement technique (digital versus silicone replica) strongly influences the results, with the digital workflow showing unresolved alignment limitations. Within the limitations of this in vitro study, additive manufacturing yields lower gap values than subtractive milling manufacturing. The marginal gaps for both materials were significantly larger than the upper gap limit established for acceptable clinical outcome. • Both AM and SM fabrication techniques produce internal fit values that highlight certain limitations for permanent use under current workflows. • Additively manufactured (AM) crowns show lower internal and marginal fit values as compared to subtractively manufactured (SM) crowns, although neither technique meets clinical acceptability thresholds. • Direct comparison of evaluation techniques reveals that the silicone replica method has greater reliability than the digital workflow.