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# Optimisation strategies of different VAT photopolymerization printers

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Timothy FASHAM<fnref n="1" />, Philippe FRANCOIS<fnref n="1" />, Nicolas LEBON², Floriane LAVERNE<fnref n="3" />

**Objective 1:** Create a protocol to compare the **closeness** of 3D printed models, with different VAT printers & post-processed while considering various resin types and layer thicknesses.

**Objective 2:** Assess the **efficiency** of printing and post-processing 10 models, printed two by two on the platform.

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STL of printed models with dental lab scanner (n = 110)

Mesh processing:
support removal

Chebyshev plane
selection

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Parallel cutting
plane (+0.4mm)

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Closeness
comparison based on
"area of valid surface"

Best fit
superimposition
digital master vs
printed model

Valid surface
threshold = 10 µm

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Deviations in
blue > green area
grey = deviation < threshold

## Results

<table><caption>**Printing efficiency:** total printing and production (printing + post-processing) time of 10 models for each resin & layer thickness</caption><thead><tr><th>Resin & layer thickness</th><th>Total printing time</th><th>Total production time</th></tr></thead><tbody><tr><td>Draft 200µm (DR200)</td><td>3h40</td><td><strong>4h08</strong></td></tr><tr><td>Draft 100µm (DR100)</td><td>7h45</td><td><strong>8h13</strong></td></tr><tr><td>Grey 100 (GR100)</td><td>12h35</td><td><strong>13h35</strong></td></tr><tr><td>Grey 50 (GR50)</td><td>22h00</td><td><strong>23h00</strong></td></tr><tr><td>Fast Model 200µm (FM200)</td><td>1h05</td><td><strong>2h45</strong></td></tr><tr><td>Fast Model 100µm (FM100)</td><td>3h05</td><td><strong>4h45</strong></td></tr><tr><td>Precision Model 50µm (PM50)</td><td>9h00</td><td><strong>9h50</strong></td></tr><tr><td>Die and Model 170µm (DM170)</td><td>2h35</td><td><strong>3h35</strong></td></tr><tr><td>Die and Model 100µm (DM100)</td><td>3h10</td><td><strong>4h10</strong></td></tr><tr><td>Die and Model 50µm (DM50)</td><td>5h25</td><td><strong>6h25</strong></td></tr><tr><td>Aqua-Gray 50µm (AG50)</td><td>8h40min</td><td><strong>12h30</strong></td></tr></tbody></table>

<figure><img src="image_7.png" /><figcaption>**Closeness:** "area of valid distance" between the various resin types and layer thicknesses</figcaption></figure>

Resin & layer thickness

Values with the same superscript letter are not significantly different at p <0.05.

**Capacity** (2 models vs 10 models in a go (DR + GR group)) and **parameters** (wash time & cure time) of post-processing units respective to the

manufacturer parameters and the established protocol **influence the total production time** of 10 printed models. e.g. post-processing time is 28 min for all 10 models within DR group versus 3h50 for AG50 group

## Discussion

Closeness can be affected by the parameters related to the **hardware** of the VAT printer and the post-processing units:

* Platform speed + VAT temperature need to be adapted to the resin's rheology for optimising resin flow

→ avoid separation of the layers (e.g. DM50)

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* Pixel smoothening in the new-gen "optimised LCD" could reduce the closeness with the original STL model

* Inappropriate curing time & temperature may lead to part warpage (i.e. distortion)

## Conclusion

New-gen "optimised LCD" matches DLP and surpasses "low-cost LCD" in printing closeness depending on the resin type and layer thickness

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**Automated SLA printer** (i.e. FormAuto) and large post-processing (wash & cure) units are promising to optimise both closeness and efficiency

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**SLA VAT printer** present a better closeness overall

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Reducing layer thickness does not necessarily increase the closeness

<footnote n="1">¹Innovative Dental Materials and Interfaces Research Unit (URB2i, URP 4462), University Paris Cité, ²Léonard de Vinci Pôle Universitaire, Research Center, 92916 Paris La Défense, France</footnote>

<footnote n="3">³Innovative Dental Materials and Interfaces Research Unit (URB2i, URP 4462), University Sorbonne Paris Nord</footnote>