Enhanced M1/M2 macrophage ratio promotes orthodontic root resorption

Area of Science:

• Oral biology
• Immunology
• Orthodontics

Background:

• Orthodontic root resorption is a common challenge during tooth movement.
• Macrophages are involved in root resorption, but the precise mechanism is not fully understood.

Purpose of the Study:

• To investigate how the M1/M2 macrophage polarization ratio influences root resorption during orthodontic treatment.

Main Methods:

• Applied nickel-titanium coil springs to rat molars for 3-14 days to induce orthodontic force.
• Analyzed macrophage polarization markers (CD68, iNOS, CD163), inflammatory cytokines (interferon-γ, TNF-α), and anti-inflammatory cytokines (IL-4, IL-10).
• Administered TNF-α inhibitor (etanercept) or IL-4 to assess their effects on root resorption.

Main Results:

• M1-like macrophages and pro-inflammatory cytokines (TNF-α) increased on the compression side, correlating with root resorption.
• Removing orthodontic force led to increased M2-like macrophages and anti-inflammatory cytokines (IL-4, IL-10), partially rescuing resorption.
• Inhibiting TNF-α or administering IL-4 reduced root resorption severity and the M1/M2 ratio.

Conclusions:

• The M1/M2 macrophage polarization balance is a critical factor in orthodontic root resorption.
• Elevated M1/M2 ratios exacerbate root resorption, whereas a decreased ratio can mitigate it.
• Targeting macrophage polarization presents a potential therapeutic strategy for managing orthodontic root resorption.