1. Dental school is getting harder and harder to get into every single cycle. There is no denying that. You may be getting more competitive, but so is everyone else. An M.S. may be what you need, but not want, at this point.
2. You must look deeply into your life motivations to determine ultimate self-satisfaction - would you be 100% content knowing you never became a dentist, but became something else successful in another career? If the answer is no, keep applying. If the answer is yes (or you're > 60/40 at this point), do yourself a favor and drop the journey now for something else you're passionate about. There is absolutely nothing wrong with not being a dentist in this country.
3. There is a huge myth here on SDN about the aura of being a DMD or MD in 2017. Dentistry is not some automatic gateway for financial freedoms (at least, it isn't anymore, despite naive pre-dents' misconceptions of wealth in this occupation relative to crippling debt loads), and there will be plenty of future US dentists with below average salaries/high debt obligations, simply because they're not very good clinicians and business owners. You will have to work extremely hard as a dentist (smart marketing, more operating hours, leaner financial waste and more efficient workflow, proper health insurance balance for repayments) to pull a > 200k salary after overheads, debts, etc., especially in a saturated clinician area.
EDIT: If the answer above is also no, you can also apply next cycle with a better profile *and* start searching for another healthcare job that interests you - apply for medical sales, pharmaceuticals, biotech, anything that pays decently in your gap year to support yourself, and use that job to finance any potentiality for a Masters degree. Many people take 2 roads at once in hopes that the ultimate one eventually pulls through. Now, if you have family commitments and require more money or a high-paying career, there's nothing any of us can say here on that matter; those industries typically require experience and a complete 180 on your life.