Self-ligating brackets in perspective of friction: A Review

Newton’s third law of motion states that whenever a force is applied an equal and opposite force occurs in the opposite direction of applied force. Orthodontic tooth movement (OTM) being a biological phenomenon; sound knowledge of biomechanics is required. Sliding mechanics is a common approach in orthodontics to achieve tooth movement for closure and gaining of space.1,2 Sliding mechanics involves sliding of archwire along the bracket slots during the tooth movement. Bracket and archwire combination systems are basically one couple and two couple systems.3 The practitioner can apply orthodontic force systems in three principal orthogonal directions: labio-lingual (LL), mesio-distal (MD), and occluso-gingival (OG). Sum-total of the forces is the vectorial sum of all these forces. Opposing to it are the resistance forces acting along the force and couple in these three principal directions and planes. To achieve better treatment outcome and patient comfort the resistance forces must be controlled by the clinician.