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The Montgomery 3MM Rule

administration case acceptance continuing education dentistry relationships workplace Jan 30, 2024


In the intricate world of dentistry, I often found myself at a crossroads, wondering whether a case would be a breeze or a challenge. This uncertainty led me to develop a guiding principle that has significantly enhanced my treatment planning – introducing The Montgomery 3MM Rule.

Over the years of learning different techniques and systems, I quickly realized that we needed a reliable decision-making tool. I wanted a way to distinguish between hard and easy cases, preventing myself from getting in over my head. The Montgomery 3mm rule was born out of this necessity.

Understanding the 3mm Rule

So, what exactly is the Montgomery 3mm rule? It started as a method to differentiate between dental and skeletal problems, evolving into a comprehensive guide for treatment planning.

Let's explore some scenarios where this rule comes into play:

Dental Midline Correction:

  • Less than 3mm off: Correct with prep and restore.
  • More than 3mm off: Orthodontics is needed before restorative treatment.

Diastema Closure:

  • Diastema greater than 3mm: Consider orthodontic movement before restoration.

Crowding Issues:

  • Mesial AND distal crowding over 3mm in one tooth: Include orthodontics.
  • Total crowding from canine to canine over 3mm: Ortho becomes part of the plan.

Cross Bite Correction:

  • If 3mm or more movement is needed in the upper or lower tooth: Combine ortho with restorative correction.

Vertical Dimension Increase:

  • CEJ to CEJ dimension more than 3mm closed: Include VDO increase in the plan.

Class I Malocclusion:

  • Canine or molar more than 3mm away from Class I: Consider restorative, interproximal reduction, or arch expansion.

Intermolar Width and Airway Evaluation:

  • Arch form more than 3mm too narrow: Evaluate for airway problems.

Gingival Contours:

  • If tooth position is more than 3mm away from final position: Assess additional treatment needs.

Crowding and Papilla Display:

  • Total crowding less than 3mm: Ortho only if teeth are gorgeous.
  • Contact point more than 5mm from osseous crest: Risk of open "black triangle" in the papilla display.

Applying the Rule in Practice

I've found that the Montgomery 3mm rule accelerates decision-making, by creating a straightforward plan without the need to be a hero with a single modality. It streamlines processes, to avoid wasting time with trial and error.

So, whether you're navigating midline corrections, diastema closures, or complex malocclusions, have some fun implementing the Montgomery 3mm rule in your practice. It might just be the game-changer you've been looking for!

You can download your FREE copy here!

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