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Orthodontics & OcclusionIntermediate

Tooth movement in orthodontics (pressure and tension)

The tooth doesn't force its way through the bone: the bone rebuilds itself around it. It's resorbed on one side and formed on the other.
Metal braces (brackets) with their archwire. The archwire applies a light, continuous force, and the bone is gradually rebuilt around each root.
Metal braces (brackets) with their archwire. The archwire applies a light, continuous force, and the bone is gradually rebuilt around each root.Photo: Suyash Dwivedi · CC BY-SA 4.0, Wikimedia Commons

What you need to know

  • Pressure side: the periodontal ligament is compressed and osteoclasts resorb the bone to clear the way.
  • Tension side: the ligament is stretched and osteoblasts deposit new bone.
  • With light, continuous forces, resorption happens directly on the pressure side.
  • With excessive forces, the ligament gets crushed so much that it's left without cells (it hyalinizes). Then the bone breaks down from behind (undermining resorption) and the movement slows down.
  • After treatment, the bone and fibers take months to reorganize: that's why a retainer is used.

Terms in plain words

OsteoclastCell that resorbs (breaks down) bone. “Clast” comes from the Greek word for “broken”.
OsteoblastCell that forms bone. “Blast” comes from the Greek word for “bud”.
HyalinizationArea of the ligament left without cells due to excess pressure; it delays movement.
Diagram of the pressure side and the tension side of a moving tooth
Study diagram · @dra_iswmi

For the exam

Which cell works on the pressure side?

Show answerHide answer

The osteoclast, which resorbs bone. On the tension side, it's the osteoblast, which forms it.

Sources

  1. Haworth JA, Sandy JR. Contemporary theories of orthodontic tooth movement. Orthodontic Update. 2024;17(2):56–62.
  2. Molecular and Biological Aspects of Orthodontic Tooth Movement: Possibilities for Bioengineering Intervention: A Narrative Review. View source
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