During orthodontic uprighting of tooth #18 (mandibular left second molar) using an uprighting spring coil, what movement does the crown undergo?

An uprighting spring applies a force to move the crown distally while moving the root mesially — correcting the mesial tipping (forward lean) that commonly occurs when #18 (or any molar) tips mesially after premature loss of a tooth anterior to it. When the spring delivers force: the crown of the molar moves distally (tips distally), the root moves mesially, and the tooth uprights to a more vertical position in the alveolus. This is used to create sufficient space for implant placement or to improve the axial alignment of a tilted molar before prosthetic restoration. The movement follows Newton's third law: the tooth rotates around the center of resistance, with crown and root moving in opposite directions.