I did three years of extensive research in biochemistry projects and published more than once. It helped a little bit and I'm sure it looked good on the application, but my extracurriculars and service really generated much more interest from my interviewers than research. Honestly, most dentists do not want to spend time in a research lab (there are exceptions), and became dentists because of the human interaction. I had a vivid experience during one interview when I was asked to explain my research. I tried to describe it as intelligently and brief as I could, but I knew there was no way my interviewers could have understood half of what I said because of the specific background knowledge required. I asked if they wanted any clarification and they both shook their heads and said "no, please, we just wanted to see if you knew what you were talking about!"
Research won't hurt, but there are certainly other things that will boost your app. much more effectively to get into dental school. It is not that remarkable to get into dental school with no research at all, but try that with no shadowing or no extracurriculars and your chances are slim to none.