How would you clean the smear layer completely without etching the dentin? There are several issues associated with cleaning that would probably jeopardized your bond strength.

Haitham Elafifi Ebeid, a smear-layer free dentin is an acid-etched dentin. If so, there's no indication to use self-etch adhesives, because the mineralized content for the adhesive to react would be removed. The primer of 2 step self-etch adhesives would be out of mineralized contact to react.

That's the advantage when using self-etch or universal adhesives, when adhering to dentin substrates - since no acid-etching is needed, the organic portion remains sustained by the smear layer that will be incorporated in the adhesive interface by the reaction with self-etch and universal adhesives.

However, when only etch-and-rinse adhesives are available, we have to etch the dentin and this procedure is not as predictable since dentin humidity can't be objectively assessed, depth of etching can't be fully controlled and it's hard to make sure that a proper cleaning of the dentin surface is achieved after etching. This makes adhesion with etch-and-rinse adhesives clinically less reproducible.

You can give it a try when you use fractured dentin. I would assume that it bonds even better than with smear layer.

It depends on what kind of smear layer you want to compare.

Smear layer prepared by SiC paper is easily dissolved by acidic monomer.

I used to test the bond strength on the dentin surface with the metallurgic polishing. Clearfil SE bond can bond well with the surface.

But smear layer created from diamond bur is more difficult to remove due to its denseness. So, the bond strength is compromised.

It must be better tensile bond strength because all your primer is in contact directly with the dentin and specially with your mineralized portion of dentin. But is hard to know because you must acid etch and this step will jeopardize your bond strength because you are eliminating 7-12 microns of HAP required to chemical bond with MDP leaving only the effect of HEMA (microretention) to bond the structure