If you just did it to raise your GPA, and you actually did raise your GPA, then I believe it will be looked at favorably (inclusive in this is taking higher level sciences, which many schools recommend, another positive aspect).
Admissions at dental schools are not unfamiliar to people working their asses off post-bacc to make themselves look better, it's just another part of the game, and definitely not a bad move unless you started slacking and did worse. As for whether they'll think about the "why didn't he/she do a masters instead?", I doubt it. A masters isn't a norm, a requirement, or an expectation, we're not talking about a lack of shadowing or volunteering. At this point you can't go back and change anything anyway, so just be proud of the hard work you put in thus far.
honestly it depends how bad your GPA is.. If your gpa is below a 3 then I would recommend a masters progam so you would get a clean slate (gpa is calculated separately) now if you had like a 3.1-3.2 and didn't get in last cycle or something then yeah I believe taking some more upper level classes to bring it up .1-.2 would be a better decision because its cheaper I believe but this is just my opinion.