Should You Stop Expanding at 40mm with RPE/IPE?

Introduction

• Dr. Amanda from Straight Smile Solutions addresses a common question: Should expansion stop when the transpalatal width reaches 40mm?
  • Many clinicians use “40mm” as a benchmark after hearing her training material, but it is not a universal stopping point.
  • Tooth size, arch size, and individual anatomy mean that the ideal expansion width varies widely.

Is 40mm the Rule?

• 40mm is not a fixed stopping measurement—it’s a reference point.
  • Actual final width depends on tooth size and arch proportions.
  • Patients with large teeth may reach 42–48mm.
  • Patients with small teeth may finish at 38–40mm.
  • Range typically falls between 38 and 48mm, depending on dentofacial anatomy.

What Clinicians Should Evaluate Instead

• Instead of relying solely on a number, consider full clinical indicators:

• Overall arch form
• Tooth size and spacing
• Symmetry and stability
• Posterior crossbite correction
• Palatal vault development
  • Dr. Amanda’s expansion guidelines and techniques are available in her courses and videos for deeper case review.

Why Overexpansion Matters

• Slight overexpansion is preferred to avoid relapse.
  • Under correction risks arch collapse and retreatment.
  • Some relapse is expected; expansion must account for this.

Clinician Guidance

• Don’t stop just because the caliper reads 40mm.
  • Review functional and structural goals:

• Stable occlusion
• Proper arch coordination
• Skeletal correction vs. dental tipping
  • If uncertain, Dr. Amanda encourages doctors to email or review her course material for step-by-step criteria.

Conclusion

The “40mm rule” is a guideline, not a finish line. True expansion success depends on overall anatomy, tooth size, and clinical stability, not just a single number. When in doubt, aim slightly beyond the visible target to ensure long-term retention and avoid relapse. Expansion should stop when biomechanics and function confirm stability, not when a ruler says so.