Ill not argue with you one the requirements for a printed part within dentistry...there is no astm standard to reference....I think everyone has their own ideas as to the requirements....
but in response to your other points...
The roland is subtractive not additive...so there is a significant difference in the application.
While a .6mm burr is twice the diameter of the formlabs beam, a bur is capable of removing less material than its diameter....so its EXTERNAL or INTERNAL feature size is limited less by tool then by movement. This is the same benefit I am describing with the formlabs machine but in reverse. These areas are as smooth as the machine movement. In areas of plunge or pencil operations then the subtractive feature is limited in the same way wall thickness and minimum feature is with the formlabs machine....restricted by tool/beam size.
Now as to the trident...
A US Quarter is 31/32"
After adjusting scaling this means......
the center tines barb would then measure where it expands from the tine a width of .08", 2032 microns, and .14" , 3556 microns in length to its tip.
My invisionhr does 656dpi xy, so ~38 microns is the smallest possible single point of deposition...but because its method is "raster" rather than "vector" it cannot edge smooth for higher apparent resolution. So while this model printed on the Invision would not be as smooth along planar borders, the tip of the trident would, in my print, be approximately 1/8th the dimension of their tip. Significantly sharper.
There is no reason that the beam diameter HAS to be 300 microns. They could have reduced beam diameter significantly but doing so would dramatically increase their build time. I think their machine is a great design. I think its very capable...of what its intended to do. Their machine has an intended audience, its an alternative/upgrade to reprap/makerbot etc marketed to that level of user, hobbyists. Id love to see their FORM2, should it happen, include a zero aperture iris to allow beam dimension to be varied to allow fast fill at their 300 micron and a second fine feature pass at a smaller beam diameter....but as it stands...
Its resolution is significantly beneath MY requirements...ymmv