Research
Research experience is not a requirement for admission to dental school, but may add an extra layer to your application if the institutions you are applying to have a research focus, or if you are particularly interested in research.
Most schools recognize that it is not possible for all students to have research experience prior to dental school, as not all undergraduate institutions have research opportunities available to students. You should do research if you are interested by it, not solely to enhance your application to dental school. While many students think that lab research is most important, experience with social science research is just as fascinating and valuable.