Biology of Tooth Movement

These flashcards cover the physiologic and orthodontic biology of tooth movement, including theories of eruption, histological changes under different forces, and the phases of tooth movement.

Physiologic Tooth Movement

Naturally occurring tooth movements that take place during and after tooth eruption, including eruption, migration, and movements during mastication.

Tooth Eruption

The axial movement of a tooth from its developmental position in the jaw to its final position in the oral cavity.

Blood Pressure Theory

A theory of eruption suggesting that vascular pressure from the highly vascular tissue around the developing end of the root causes axial movement of the teeth.

Root Growth Theory

A theory stating that the apical growth of roots results in an axially directed force that brings about eruption, though it is often rejected because teeth move further than the increase in root length.

Hammock Ligament

A band of fibrous tissue rich in fluid droplets described by Sicher that spans the alveolar wall below the root apex, applying an occlusally directed force on the tooth.

Periodontal Ligament Traction Theory

The theory that axial movement of the tooth results from the contraction of periodontal fibroblasts, specifically the oblique group of fibers.

Migration (Drift)

Minor changes in tooth position after eruption, usually occurring mesially and occlusally to maintain contact as a result of proximal and occlusal wear.

Pressure Area

A histologic area formed in the direction of orthodontic tooth movement characterized by PDL compression.

Tension Area

A histologic area formed in the opposite direction of orthodontic tooth movement characterized by PDL widening.

Frontal Resorption

Direct resorption of the periosteal bone from the inner socket wall, occurring when mild orthodontic forces are applied.

Hyalinization

A reversible type of tissue degeneration where PDL becomes a clear, cell-free homogeneous mass due to heavy forces and localized ischemia.

Undermining Resorption

Also known as indirect resorption, this occurs when extreme forces cause hyalinization, requiring osteoclasts to resorbing bone from the marrow spaces and peripheral intact PDL.

Secondary Bone Remodeling

Compensatory bone changes involving addition to the endosteal surface beneath pressure areas and resorption from the endosteal surface beneath tension areas to maintain alveolar thickness.

Optimum Orthodontic Force

A force equivalent to the capillary pulse pressure, stated as $20-26\text{ gm/sq. cm}$ of root surface area, which moves teeth rapidly with minimal tissue damage and direct resorption.

Initial Phase

The first phase of orthodontic movement lasting about a week, moving the tooth $0.4\text{ to }0.9\text{ mm}$ through PDL displacement and slight alveolar bone bending.

Lag Phase

A period of little or no tooth movement lasting 2-3 weeks, during which hyalinized tissue must be eliminated before movement can progress.

Post-Lag Phase

The phase following the lag period where tooth movement progresses rapidly as osteoclasts perform direct resorption of the bony surface.

Pressure-Tension Theory

The theory credited to Schwartz stating that orthodontic force creates pressure and tension areas, causing bone resorption in pressure areas and bone deposition in tension areas.

Blood Flow Theory (Fluid Dynamic Theory)

A theory suggesting tooth movement occurs due to alterations in fluid dynamics within the confined PDL space, including the "squeeze film effect" and the formation of aneurysms.

Squeeze Film Effect

A phenomenon described by Bien where sustained orthodontic force causes interstitial fluid in the PDL to be squeezed toward the apex and cervical margins, slowing movement.

Piezoelectric Theory

A theory where distorted alveolar bone generates electrical signals: negative charges in areas of concavity lead to bone deposition, and positive charges in areas of convexity lead to bone resorption.