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

This study demonstrates that while two dental microhybrid resin workflows (SPC and ADT) exhibit high short-term intrinsic colour consistency with deviations well below perceptibility thresholds, they display material-specific spatial and run-dependent variations that highlight the need for attention to resin homogenisation and build-plate process control.

Original authors: Frank Alifui-Segbaya, Muna Syafawati Binti Saruji, Joanne Choi, Andrew Cameron, Ismail Fidan

Published 2026-08-18

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Frank Alifui-Segbaya, Muna Syafawati Binti Saruji, Joanne Choi, Andrew Cameron, Ismail Fidan

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the world of modern dentistry, the difference between a perfect smile and a noticeable mismatch often comes down to a single, subtle quality: colour. When a dentist needs to replace a broken tooth or restore a damaged one, the goal is to create a restoration that is indistinguishable from the natural teeth surrounding it. This requires more than just matching a shade guide; it demands that the material itself remains consistent, whether it is printed in the centre of a machine or at the very edge, and whether it is the first item made in a batch or the last. For years, manufacturers of dental materials have relied on a comforting assumption: that if you print a series of identical objects using the same machine and the same liquid resin, every single piece will come out with the exact same colour. This belief underpins the efficiency of mass production, where hundreds of crowns might be printed at once. However, the process of creating these objects is complex. It involves a machine that shines light onto a liquid resin, hardening it layer by layer, while the liquid is constantly replenished and the newly formed object is peeled away from the base. Each of these steps introduces tiny variables—changes in light intensity, the flow of the liquid, or the temperature of the material—that could theoretically cause one part of the print to look slightly different from another.

A team of researchers from Griffith University and the University of Otago set out to test whether this assumption of perfect uniformity holds true in the real world. They focused on two popular types of dental resins, one based on a ceramic hybrid formula and the other on a urethane dimethacrylate system, both designed to mimic the look and feel of natural teeth. To investigate, they did not simply print a few samples and hope for the best. Instead, they created a rigorous experiment involving 216 small, disc-shaped samples. These discs were arranged in a precise grid on the printer's build plate, covering the entire surface from the corners to the centre. They then ran the printer three times in a row for each type of resin, carefully controlling the environment and the machine settings to see if the position of the disc or the order in which it was printed made any difference to the final colour.

The researchers measured the colour of every single disc using a highly sensitive device that captures the intrinsic colour of the material, ignoring surface shine or texture. They compared each disc against a specific colour target established at the very beginning of each printing run. The results were reassuring for the dental industry but revealed a more nuanced reality than the simple assumption of uniformity suggested. Both materials performed exceptionally well, with every single disc falling well within the range of what a human eye would perceive as identical. The average difference in colour was so small that it was far below the threshold where a person could notice a change. In fact, the largest deviation observed in the entire study was still less than half the limit at which a colour difference becomes noticeable to the average observer. This confirms that, for practical purposes, these printing workflows are highly reliable and capable of producing consistent results.

However, the study did uncover subtle patterns that suggest the process is not perfectly uniform. While the overall colour was consistent, the researchers found that the two materials behaved differently depending on where they were placed on the printer. One of the resins showed a few isolated spots where the colour drifted slightly more than expected, particularly in specific corners of the build plate during certain runs. The other resin was even more consistent across the entire plate, showing a very smooth distribution of colour. Interestingly, the researchers found no evidence that the centre of the printer was inherently better or worse than the edges, a common concern in manufacturing. The variations they did see were not a simple case of "centre versus edge" but rather specific, localised quirks that appeared in certain spots at certain times. Furthermore, the colour consistency within a single printing run changed slightly from one run to the next, but this was not a sign that the machine was drifting out of control over time. Instead, it reflected the natural, small fluctuations that occur as the resin is used, replenished, and processed.

The study concludes that while these dental printing systems are robust enough to produce colour-perfect restorations for clinical use, the assumption that every part of the build plate is identical is not entirely accurate. The variations are so small that they do not pose a risk to the final appearance of a dental crown, but they are significant enough to warrant attention from manufacturers and technicians. The findings suggest that to maintain the highest level of quality, especially for colour-critical applications, it is important to pay attention to how the resin is mixed and how the machine is managed between runs. The research highlights that colour fidelity is not just a property of the liquid resin itself, but a result of the entire workflow, from the moment the resin is poured into the machine to the final curing process. By understanding these subtle spatial and temporal variations, dental professionals can better manage their production processes, ensuring that every restoration, whether printed in the first batch or the last, meets the exacting standards required for a natural-looking smile.

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

Problem Statement
Contemporary vat-photopolymerisation (VPP) workflows for dental applications often operate under the assumption that colour uniformity is spatially consistent across the build plate and that production outcomes remain stable across sequential print cycles. However, the layer-by-layer nature of VPP introduces process variables—such as optical irradiance non-uniformity, resin replenishment dynamics, and time-dependent rheological changes—that may compromise reproducibility. While previous research has addressed the influence of printing orientation and post-curing on optical properties, there is limited validation regarding whether build-plate planar position and the sequence of print runs affect short-term intrinsic colour fidelity within controlled VPP workflows. This uncertainty is clinically significant, as colour-critical dental devices are frequently manufactured in batches where uniformity assumptions may not hold.

Methodology
The study evaluated two dental microhybrid resin workflows:

Saremco Print Crowntec (SPC): A Bis-EMA-based ceramic hybrid resin.
Asiga DentaTooth (ADT): A UDMA-based resin system.

Experimental Design:

Sample Generation: A total of 216 disc-shaped samples (15 mm diameter, 2.0 mm thickness) were printed in a 3 × 12 rectilinear grid (36 samples per run) across three sequential print runs for each material.
Process Control: Resin was homogenized prior to the first run and manually stirred between runs. All builds utilized manufacturer-defined profiles on a digital light processing (DLP) printer with a 385 nm UV source. Post-processing protocols differed by material (ethanol wash/UV curing for SPC; isopropyl alcohol wash/flash curing for ADT).
Colour Measurement: Samples were measured using a Konica Minolta CM-700d spectrophotometer in Specular Component Included (SCI) mode to assess intrinsic chromaticity. An inverted-stage, air-backed configuration was used to minimize background influence.
Target-Referenced Analysis: Unlike studies comparing against a global standard, this study established a unique target-coordinate triplet ( $L^*, a^*, b^*$ ) for each material and run combination based on the initial measurement of Disc #1. Colour deviation was quantified as $\Delta E_{00}$ (CIEDE2000) relative to these run-specific targets.
Statistical Analysis: Linear mixed-effects and marginal models with cluster-robust standard errors were used to assess the effects of build position (centre vs. periphery) and print run order. Global spatial autocorrelation was evaluated using Moran's I.

Key Results

Overall Deviation: Both materials demonstrated low intrinsic colour deviation. SPC had a mean $\Delta E_{00}$ of $0.35 \pm 0.12$ (max 0.73), while ADT showed a mean of $0.23 \pm 0.10$ (max 0.46). All values remained below the 50:50 perceptibility threshold ( $PT_{50} \approx 0.8$ ) and the acceptability threshold ( $AT_{50} \approx 1.8$ ).
Spatial Patterning: No systematic centre–periphery effect was observed; distributions for central (positions 14–23) and peripheral (positions 1–13, 24–36) areas overlapped substantially. However, Moran's I indicated significant positive spatial autocorrelation, particularly for SPC. SPC exhibited "local excursions" (e.g., Position 33 in Run 1, Position 24 in Run 2), whereas ADT displayed a more homogeneous spatial profile.
Sequential Run Effects: A significant Material × Run interaction was detected ( $p = 0.0055$ $p = 0.0055$ ).
- SPC: Showed a modest increase in deviation around the Run 3 target compared to Run 1.
- ADT: Exhibited a "V-shaped" profile, with the lowest deviation in Run 2 and higher deviations in Runs 1 and 3.
- Interpretation: Because each run utilized a distinct target triplet, these variations represent within-run dispersion around different targets rather than absolute temporal colour drift relative to a single standard.
Directional Components: SPC variation was primarily associated with the $b^*$ axis (yellow-blue), while ADT showed shifts in $L^*$ and $b^*$ across runs.

Key Contributions

Methodological Rigor: The study introduces a target-referenced approach using run-specific baselines to isolate within-run spatial and sequential variability, distinguishing it from absolute shade drift.
Workflow-Specific Insights: It demonstrates that colour fidelity is a function of the entire material–printer–post-processing workflow rather than resin chemistry alone. The distinct post-processing protocols for SPC and ADT preclude direct cross-material comparisons of resin chemistry effects.
Spatial Characterization: The research challenges the assumption of a simple centre–periphery colour gradient, revealing instead complex local excursions and spatial autocorrelation patterns that vary by material.
Quality Control Framework: The findings provide a baseline for interpreting $\Delta E_{00}$ values in VPP manufacturing, suggesting that observed variations are often process-control signals rather than clinical failures.

Significance and Claims
The paper concludes that while both tested workflows achieve high short-term intrinsic colour consistency suitable for clinical applications (all values below perceptibility thresholds), the assumption of perfect spatial and temporal uniformity is not supported. The observed variations, though statistically detectable, are small relative to clinical acceptability limits.

The authors assert that these findings support a quality-control interpretation rather than a clinical failure interpretation. The study suggests that for colour-critical applications, manufacturers should prioritize:

Consistent resin homogenisation.
Standardisation of idle times between runs.
Monitoring of environmental and vat temperatures.
Cautious planning of sequential production runs.

The paper explicitly states that its findings are specific to the tested workflows and measurement configurations (including the novel air-backed measurement setup) and should be generalized cautiously to other materials, printers, or extended production periods. The study does not claim to have identified the exact causal mechanisms (e.g., specific irradiance gradients or filler redistribution rates) but posits that rheology, thermal exposure, and post-processing response are plausible contributors to the observed patterns.

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

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