If force is applied to the crown of the tooth instead of the center of resistance, what type of movement occurs?

When force is applied to the crown of a tooth rather than directly to its center of resistance, the type of movement that occurs is rotation or tipping. This is due to the fact that the crown of the tooth acts as a lever point. When force is applied to the crown, it creates a moment arm that results in the tooth tilting or rotating around its center of resistance, which is generally located within the periodontal ligament and the root of the tooth.

For instance, if you imagine pushing the top of a seesaw (analogous to the crown of a tooth), it will pivot around its midpoint, which corresponds to the center of resistance. The result is a rotational movement rather than a straightforward translational movement.

In contrast, other movements such as intrusive (moving the tooth down into the bone) or extrusive (moving the tooth up out of the bone) require forces that act through the center of resistance to achieve perpendicular movements that do not cause tipping. Translation typically involves equal forces applied to both the crown and the root, moving the entire tooth in a straight line without tipping. Thus, the nature of the force application significantly impacts the movement patterns observed in orthodontic practices.