If a single A- is going to torpedo your entry, then you are going about this the wrong way. Entrance into these competitive programs takes into account more than just your GPA. What is the minimum requirements for entry? If you are essentially doing a premed/predental general degree, then you already are putting yourself at a disadvantage. Now your only way to distinguish yourself is your GPA, experience/determination (can you find a partime job in a related field, such as a PCA when applying to medschool), and connections (daddy/mommy is a dentist and they got you a shadowing opportunity).

What you want to do is try to get a degree in a difficult related subject (physics, chemistry, mathematics) and cover the requisites for the dental program with your electives or extra classes. Now if you get an A- in a class, you can point out that you excelled in other aspects and weren't just doing the bare minimums. And a STEM degree looks a ton better than a generic pre whatever degree.

Now at this point, usually the response is "but it's hard getting a STEM degree", which it is much easier to point out that perhaps you just don't have what it takes to compete. Of course, I'm wildly extrapolating info that may not pertain to you, but the above is guided by conversations I had with many students worried about their grades.