Slow speed gives us far more tactile feedback for what is caries and what is sound dentin. So it's well worth dragging out. However...
I work with three relevant technologies:
-Surgical Operating Microscope
-Kavo Electrotorque electric handpieces
-Caries Finder dye
Also, there is evidence that composite resin preps are best completed with diamonds, not carbide burs.
So this is where my technique has evolved to, for composite resins. For ceramic onlays or crowns, it's the same except carbide burs are only used to break contact and such.
-Prep at moderate magnification with carbide burs and copious water spray.
-Caries Finder.
-Prep at higher magnification with slightly tapered chamfer diamond with copious water spray. (I employ slightly used diamonds, after they've done a couple of crown preps. They're perfect--they cut and refine on the sides, and barely cut on the ends. Just a little, as the rounded ends are a bit dull by then).
-Rack up the magnification to insanity levels, turn off the water, cut the handpiece speed in half and refine/polish the prep. This isn't going to damage the pulp, it's not cutting dentin significantly or creating lots of heat.
With all that, the low speed becomes redundant. Before the Microscope, however, the tactile feedback was helpful, because I wasn't seeing details as I do now.
And it's not part of your question, but then:
Self-Etch Primers!
Unless we're largely on enamel, as in Class IV anteriors, where Total Etch is preferable. Whenever there's lots of dentin in a prep, meaning Class Is and Class IIs particularly: Self-Etch Primers!
