Influence of total occlusal convergence and auxiliary retentive features on regional marginal discrepancy in milled and 3D-printed short provisional crowns—an in-vitro study

Abstract

This in-vitro study evaluated the influence of total occlusal convergence (TOC) (10°/20°) and auxiliary retentive features (ARF) (groove, proximal box) on regional marginal discrepancy in milled (CopraTemp PMMA) and 3D-printed (Asiga Dentatooth) short (3 mm) provisional crowns (PC). Eighty PCs were fabricated on standardized mandibular first molar preparations with 3 mm axial height. Preparations varied by TOC (10°/20°) and ARF [none, mid-buccal groove (1.5 × 1.0 mm), or proximal box (2.0 × 2.0 × 1.5 mm)]. Crowns were seated under standardized pre-cementation conditions (50 N, 10 s), and vertical marginal discrepancy was measured at 24 indexed points per crown using 2D stereomicroscopy (40 ×). Descriptive statistics were presented as medians and interquartile ranges, and ART ANOVA was used to evaluate fabrication workflow, preparation design, and their interaction. The marginal discrepancy was surface-dependent, with greater values generally observed at mesial and distal surfaces than at buccal and lingual surfaces. ART ANOVA identified significant workflow effects at the buccal $$(F=6.851,p=0.011)$$ and distal $$(F=5.008,p=0.028)$$ surfaces, while preparation design and workflow-by-preparation interaction were not significant. The 3D-printed 20° groove subgroup (P2G) showed the lowest overall median discrepancy (91 μm), with surface medians of 86 μm, 83 μm, 91 μm, and 111 μm at the buccal, mesial, lingual, and distal surfaces, respectively. Within the limitations of this pre-cementation in-vitro model, surface-specific vertical marginal discrepancy varied between the tested milled and 3D-printed workflows. Several 3D-printed configurations, particularly the 20° groove subgroup, showed a more favorable descriptive pattern; however, these findings should be interpreted as workflow- and geometry-dependent rather than final cemented clinical behavior or a broader superior implication. Under controlled pre-cementation laboratory conditions, the 20° groove printed subgroup showed the most favorable descriptive adaptation pattern; however, these findings do not establish clinical superiority and require validation after cementation, aging, and loading.