Higher quality dentist? Depends on your definition. If you are thinking of a dentist as being limited to working on patients from 9 to 5, then yeah, go ahead and graduate, start working.
I am 5-year DMD student @ Harvard; my 5th year is being completed at the Harvard School of Public Health. Will I be a higher quality dentist? In my eyes, yes. Having a second degree from Harvard is sweet, especially considering the connections and opportunities that are available to me. I have friends that have spent the year doing research, getting an MBA, Master of Public Policy from the other Harvard schools, too. One student actually spent her year creating a dental clinic for HIV patients in Haiti. It's a tremendous opportunity to get funding to push the envelope for what you can do with your dental career. And if you are considering continuing in that particular line of work after dental school, you've already jumped the gun so to speak. More of the MD students at Harvard med spend an extra year getting another degree or doing research (about 50%). In my incoming class 5/35 students (14%) of the students took advantage of opportunities like this to expand their horizons.
Point said, consider what you want to do after dental school, what your CAREER will be.