A transpalatal arch is a rigid wire that connects the left and right upper molars across the palate. Typically, it has a U loop in the middle that allows for adjustments in width. The transpalatal arch can be adjusted to rotate a molar, push a molar backwards, or restrain both molars from moving forwards. It adds stability to the upper molars; this is important when we do not want the upper molars to move or shift out of position while other teeth in front are being moved.
See also: rapid maxillary expander