Influence of Build-Plate Position and Sequential Printing on the Colour Fidelity of Vat-Photopolymerised Microhybrid Resins

<title>Abstract</title> <p>Contemporary vat-photopolymerisation workflows often assume spatial colour uniformity across the build plate and consistent production outcomes across sequential print cycles. This study evaluated these assumptions using two dental microhybrid resin workflows: Saremco Print Crowntec (SPC), a Bis-EMA-based ceramic hybrid resin, and Asiga DentaTooth (ADT), a UDMA-based resin. A total of 216 discs were printed in a 3 × 12 grid across three sequential print runs. Target-referenced intrinsic colour deviation was quantified as ΔE₀₀ in Specular Component Included (SCI) mode and mapped by build position and print run. For each material/run combination, Disc #1 was measured initially to establish the run-specific SCI target L*, a*, and b* coordinates and was subsequently remeasured as one of the 36 samples included in the analysis. Mean ΔE₀₀ was 0.35 ± 0.12 for SPC and 0.23 ± 0.10 for ADT, with maximum values of 0.73 and 0.46, respectively. A combined marginal model with cluster-robust standard errors indicated a significant Material × Run interaction (Wald χ²(2) = 10.41, p = 0.0055), whereas material-specific analyses identified small but statistically detectable run-dependent differences in within-run deviation around separate targets. SPC exhibited local excursions, most notably at Position 33 in Run 1 and Position 24 in Run 2, without evidence of a systematic centre–periphery effect. ADT showed lower overall spatial deviation but a V-shaped profile in within-run deviation. Because a different target-coordinate triplet was established for each run, these profiles do not demonstrate absolute colour drift between runs. All observed values remained below PT₅₀ ≈ 0.8 and well below AT₅₀ ≈ 1.8. Because processing protocols differed between materials, cross-material contrasts were interpreted as material-specific workflow behaviour. Both workflows demonstrated high short-term intrinsic colour consistency, although the observed spatial and run-dependent variation supports attention to resin homogenisation and build-plate process control.</p>