UpStudio refuse to print a flat first layer ob dental model

Hi I am printing dental study model , with a flat first layer. After leveling the bed correctly, I can print without raft (for material and time saving).
But Upstudio design the first layer of some models with a step or half the layer, thought the models are prepared in meshmixer to assure their horizontality.
What is this issue ?

By the sounds of it, the model must not be flat in UP Studio then. You might have made too many modifications to the underside of the design for it to not be flat some how.
If the problem persists, you’ll have to use a raft by the sounds of things.

What material are you printing in? If you’re printing in ABS, pretty much 90% of the time you’ll be wanting to use a raft so that it’s prints properly without warping etc anyway.