Crown Preparation Dilemmas!?!?!?!?!?!?!

When I am faced with a compromised tooth requiring a crown, I like to use the concept of “TWOs and THREEs” (“2s and 3s”) to help me make treatment decisions. More on that as we read on.

*** Please keep in mind, this “2s and 3s” idea is (or at least was) a University of Minnesota School of Dentistry thing and there are certainly other schools of thought. “2s and 3s” has served me well but many of my colleagues continue to disagree with me (those folks are typically not Minnesota grads).***

1. Big Composite Build-Up and I’m Worried About Adequate Remaining Tooth Structure?

1a. Inadequate REAL tooth structure remaining after a crown preparation will result in crown failure.

1b. Reliance on a bonded restoration without adequate remaining tooth structure AFTER the crown preparation will result in crown failure (composite build-ups work ONLY if there are adequately thick walls of tooth structure surrounding them after the crown preparation).

1c. Stress, strain, shear, and torque (everyday occurrences on every tooth that chews) are real and will cause crown failure if there is not adequately strong REAL axial tooth structure following crown preparation.

1d. Elective endodontics with a core (or a post and core) will help to anchor crowns to compromised teeth (up to a certain point…thankfully we have implants after we’ve reached a threshold of compromised tooth structure).

1e. Bonded crowns are NOT a substitute for a lack of real tooth structure.

1f. Remember “2s and 3s”. In other words:

**After prepping for a crown, if there is 2mm of tooth structure remaining between prep and build-up on 2/3rds of the crown preparation then there likely is adequate tooth structure remaining for long-term strength.**

***If there is less than 2mm tooth structure remaining between prep and build-up on 2/3rds of the crown preparation then consider elective endodontics followed by core placement (more often than not premolars will require a post with a core).***

2. Margin Placement Adjacent to a Composite Build-Up?

2a. Remember “2s and 3s” (again):

**Crown margin must be 2mm gingival to a composite build-up (1mm gingival to an amalgam build-up).**

3. Adequate Axial Height?

3a. Remember “2s and 3s” (again):

**After prepping for a crown there should be 2-3mm of axial height that is REAL tooth structure on 2/3rds of the prepared tooth.**

***If there is LESS than 2-3mm of axial height that is REAL tooth structure on 2/3rds of the crown preparation then place the margin more gingivally to “grow” more axial height.***

****If the gingivally placed margin violates biologic space (falls within 2-3mm of the gingival attachment) then consider crown lengthening surgery.****

4. Crown Lengthening Surgery?

4a. Remember “2s and 3s” (again):

4b. Crown margin must be 2-3mm away from gingival attachment (regardless of bone location).

4c. A crown margin that violates the 2-3mm biologic space (in other words, if the crown margin falls within that 2-3mm space) will cause continuous gum inflammation/irritation and pain.

4d. A crown margin that violates the 2-3mm biologic space should be referred for crown lengthening surgery.

**Crown lengthening will free up space between the gingival attachment and crown margin resulting in long-term healthier gingiva and patient comfort.**

So, this is how I approach compromised teeth requiring crowns. This isn’t the end all and be all philosophy. However, I have confidence in my approach, and each of we practitioners needs to believe in and practice sound principles for the benefit of our patients.