Pre-dental dental students begin taking prerequisite science courses their freshman year of college. A student of any major can apply to dental school as long as they take the required courses (listed below). The Dental Admissions Test (DAT) is generally taken in the late spring/early summer at the end of a student's junior year of college. However, it can be taken as soon as all necessary prequisite courses are completed. In fact, students may do better taking it after their sophmore year, having just finished organic chemistry, as opposed to waiting an extra year and forgetting material.
Dental schools begin accepting applications on June 1st of the year prior to matriculation. Interviews usually take place from the following August through February. The first round of acceptances are sent out on December 1st. Most dental schools require a four-year college degree for admission. However, many will allow students to matriculate if they have 90 credit hours and have fulfilled all prerequisite courses. It is very difficult to gain admission this way. If a student wishes to attempt entry to a dental school with only three years of college, then they would take the DAT and apply the summer after their sophmore year.
Visit https://www.adea.org/GoDental/Application_Prep/The_Admissions_Process/Timeline_to_apply.aspx for more information.