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Primer and acid etch
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Acid etch, typically 35-40% phosphoric acid, removes the smear layer AND opens the dentinal tubules. The primer does not open tubules, it "wets" the surface of the dentin to stop the dentin outer layer from collapsing and thus allows better adhesion (at least for traditional etch+prime+bond systems.
Most modern systems that combine etch and prime (Self etching primer, 5-6 the generations) don't fully remove smear layer. Bonding to amalgam isn't generally recommended, as it doesn't increase resistance of the restoration most of the time (Sturdevant's, p. 190).
5th generation agents do not have self-etching primer. They have a primer-bonding agent combination. You're thinking 6th and 7th generation agents, the latter of which combines primer, etch and bonding agent.
ive read those L-pops have as much retention (if not done properly) as placing a composite on unetched dentin. even if done correctly the "all in one" systems just dont seem like a good idea to me as their bond strength is not nearly as well as say 4th generation (yea i know, it takes more time and blah blah blah). newer generations are VERY technique sensitive.
Take a look at the acid concentration of the etchants in the 6th + 7th generation all in one adhesive systems and then compare that to the good 'ol phosphoric acid concentration used for 4th and 5th generation systems (don't think anybody really uses 3rd generation stuff anymore 😉 ) Then you be the judge about the etch potential of each system 😉 And as we all know, the better the etched surface, the better the both quality and quantity of the resin adhesion to the dentin/enamel
