Where is the center of resistance located in a multi-rooted healthy tooth?

The center of resistance in a multi-rooted healthy tooth is typically located 1-2 mm apical to the furcation area. This location is significant because it represents the point within the tooth where the forces applied will produce the most efficient movement of the tooth. In the biomechanics of orthodontics, the center of resistance is where the tooth reacts to forces applied during treatment.

The furcation area is where the roots of the tooth diverge, and since the roots contribute to the overall anchorage and resistance to movement, placing the center of resistance a short distance apical to this area accounts for the effects of the surrounding periodontal tissues and the way the roots interact with the alveolar bone. This positioning allows for consideration of the complex biochemistry and structure of the periodontal ligament (PDL), which influences how forces are translated to tooth movement.

Other locations like the apex of each root, at the center of the crown, or at the cementoenamel junction (CEJ) do not accurately represent the ideal location where the tooth can best resist forces without unintended movement or tipping. Therefore, identifying the center of resistance correctly is crucial for planning effective orthodontic treatments.