MMPA et FMA

Marcello M. | July 8, 2025

Understanding Vertical Skeletal Relationships in Orthodontics

Orthodontic diagnosis involves evaluating both horizontal and vertical skeletal relationships. Two essential angular measurements used to assess vertical growth patterns are the Maxillary-Mandibular Plane Angle (MMPA) and the Frankfort-Mandibular Plane Angle (FMA).

Although both assess vertical facial proportions, they use different reference planes and provide complementary diagnostic insights. Understanding their roles and differences is crucial for comprehensive treatment planning.


Why Measure MMPA and FMA?

Both angles help orthodontists:

  • Determine the patient's growth pattern (horizontal, vertical, or balanced)
  • Predict potential occlusal challenges such as open bite or deep bite
  • Design appropriate orthodontic mechanics for better treatment outcomes
  • Improve the accuracy of skeletal diagnosis and facial aesthetics evaluation

By evaluating both angles, orthodontists get a complete and reliable view of the patient's vertical proportions. This dual assessment allows better-informed treatment decisions.


Key Differences Between MMPA and FMA

Criteria MMPA FMA
Full Name Maxillary-Mandibular Plane Angle Frankfort-Mandibular Plane Angle
Reference Planes ANS–PNS (Maxillary plane) and Go–Me (Mandibular plane) Po–Or (Frankfort plane) and Go–Me (Mandibular plane)
Craniometric Base Maxilla Base of the skull
Main Use Evaluates relationship between upper and lower jaws Assesses mandibular position relative to cranial base
Typical Application Intermaxillary divergence analysis Assessment of mandibular orientation
Normal Value 27° ± 5° 27° ± 5°

How to Interpret the Angles

  • Low values (< 22°): Suggest a horizontal growth pattern (hypodivergent)
  • Normal values (22°–32°): Indicate a balanced growth direction (normodivergent)
  • High values (> 32°): Reflect a vertical growth tendency (hyperdivergent), often associated with long-face syndrome or open bite tendencies

Why Use Both?

Though both MMPA and FMA assess vertical dimension, they approach it differently:

  • FMA gives a cranial base reference, helping assess how the mandible is inclined relative to the skull.
  • MMPA offers a more jaw-to-jaw relationship analysis, useful for evaluating intermaxillary divergence.

There are clinical cases where using one angle alone could be misleading. For example, a patient might have a normal FMA but a high MMPA, indicating vertical maxillo-mandibular divergence. Using both values provides a more accurate diagnosis and avoids underestimating skeletal imbalances.


Conclusion

MMPA and FMA are powerful diagnostic tools in orthodontics. Their combined use allows for a thorough assessment of facial vertical proportions, leading to more precise diagnoses and better treatment planning.

By integrating both angles into your cephalometric analysis, you ensure a comprehensive understanding of each patient’s skeletal structure. Ready to explore how OrthoAnalyser simplifies these measurements?