I Am Between Things; In Teeth, In Time, In Fences

Answer: Gap.  It’s pointing to “gap” because a gap is the space between things. In teeth: a diastema is the gap between teeth. In time: a time gap is the interval between events.  In fences: gaps are openings between slats or posts. “Wide or tiny” fits because gaps can vary in size. So the riddle lists places where “a space between” shows up, and “gap” is the common thread. Source: https://www.riddles.com/index.php/1248