Orthodontic Forces and Tissue Changes

Tissue Changes in Orthodontics

• Orthodontic forces can initiate adverse tissue reactions in teeth, supporting structures, sutures, and the TMJ region.
• After orthodontic treatment, a rapid-to-slow relapse occurs during the period of remodeling of the periodontal structures.

Tooth Movement at the Cellular and Molecular Levels

• Orthodontic tooth movement beyond the constraints of the original tooth socket requires the conversion of mechanical forces into biological signals by mechanosensitive cells.
• Mechanotransduction of signals promotes intracellular communication and allows for the coordinated cellular response of alveolar bone modeling.
• Orthodontic forces are perceived by cells as changes in substrate strain, fluid flow shear induced stress, and/or oxygen tension.
• Osteoprogenitor cells, bone lining cells, and osteocytes sense orthodontic forces and initiate signaling pathways through mediators such as Wnt, BMP, TNFα, IL1β, CSF-1, VEGF, and PGE2.

Orthodontic Forces Stimulate Biological Responses

• Changes in the supporting tissues of teeth are necessary for tooth movement beyond the constraints of the original tooth socket upon application of an orthodontic force.
• Theories regarding the biological response to orthodontic forces resulting in tooth movement were initially proposed over a century ago.
• Carl Standstedt's studies in the early 1900s confirmed that bone deposition occurs in areas of tension and bone resorption occurs in areas of pressure following the application of orthodontic force.
• Lighter orthodontic compressive forces lead to rapid bone resorption along the alveolar wall, while heavier compressive orthodontic forces lead to tissue necrosis within the PDL space along the alveolar wall.
• Tooth movement in these hyalinized areas occurs only after bone resorption in underlying bone marrow spaces is sufficient to undermine the supporting alveolar bone.

This chapter discusses the tissue changes that occur in response to orthodontic forces on teeth, supporting structures, and the TMJ region. It covers unfavorable forces, tissue reactions, and remodeling during orthodontic treatment.