Intro: History of anchorage
Orthodontic anchorage, deﬁned as the ability to avoid unwanted tooth movements that is provided by other teeth, by the palate, head, or neck, or implants in bone¬¬¬¬ (1)
The fundamental of orthodontic anchorage is based on Newton's third law of motion which states that for every action there is an equal and opposite reaction. An understanding of this law is necessary to produce desired types of tooth movement and anchorage. (7)
Anchorage is composed of units of resistance. This may be a single tooth, a group of teeth, or any available anatomic areas. Together with the use of appliances, anchorage can be made to offer resistance to movement. (7)
It is generally accepted that unless an additional posterior force is…show more content… With such an anchorage preparation the direction of pull from the Class II elastics would be greater than 90° during function. Such a pull will further depress rather than elongate the terminal molars.
Third degree or total anchorage preparation was reserved for cases which had an ANB angle of more than or equal to 5° and the total discrepancy was 14- 20mm.
The anchorage preparation was such that all the molars and premolars were tipped distally with the distal marginal ridge of the second molar being located below the gum level.
Such anchorage preparation is usually not required nowadays. (3)
The edgewise bracket eliminated the sim-ple anchorage potential of the anterior teeth. Tweed and others applied differential anchor-age concepts with the edgewise appliance by using a series of archwires with tipback bends in the buccal segments—thereby enhancing anterior retraction as well as anchorage preservation
Tweed modified these tipping mechanics slightly for use in nonex-traction treatment. Tweed used tipback bends to facilitate anterior retraction by tipping teeth distally toward extraction sites.
A. Before extraction of bicuspids.
B. Initiation of retraction, with vertical loops to close