Have you ever had “that call” from your technician? You know-that one where he or she wanted to touch base, complement you on your excellent impression… & Oh yes:
“Would it be okay if I sent you a reduction coping?”
“Um-sure… How much room do you need?”
“Oh-about 2 mm…”
“WHAT?!?!!?” How could this be?? You KNOW that you had enough reduction! You KNOW that you prepped enough! You KNOW…you think you know…do you know?! Let’s think about that. Have you ever gotten a crown back from the lab, tried it in… & adjusted…& adjusted…& checked…& adjusted. Oh-there’s the coping! Have you ever cut off “someone else’s crown” only to find a 1/4mm of porcelain and-being generous, a 1/4mm of metal coping? Or how about this: have you had the patient come back with a hole in the occlusal of the temporary crown…& they are occluding on the prep? But you KNOW that you reduced enough? How could this have happened? Was it “second molar rebound”? Was there some sort of supra eruption following relief of traumatic occlusion? Perhaps-distortion from those pesky triple trays!
Whether we realize it or not or are aware of the causes, this is happened to all of us… & will continue to do so. In many if not all cases however, this can be foreseen and avoided. The use of a simple leaf gauge screen prior to preparing 2nd molar crowns can give great insight into the possible or likely loss of occlusal clearance.
1) Use a leaf gauge to screen to determine the 1st contact
2) Count the number of leafs. 8 leafs at the incisors equals 1mm. 1mm at the incisors equals about 1/3rd of a mm at the second molar.
This means you could possibly take 1/3rd of a mm off of the second molar and still be in contact! 16 leafs at the incisors = 2mm…which could equal a loss of 2/3rd’s of a mm of reduction!
The leaf gauge screen is a great tool to help us realize when the occlusion may change during our preparation…and allow us to be PREpared to compensate with just a bit more reduction.
I hope that is helpful. I think that posting an article or a video of the concept may be even more so. Please let me know and I would love to hear your feedback!
As always-we would love to hear your comments & please feel free to share using the link buttons below!
Great article. I’ve been trying to learn more about this problem. And using the leaf gauge to load the TMJ is useful to know if the second molar is interfering with centric relation. But what is the solution to this dilemma? What do you do to solve this problem? Thanks.
Thank you for the kind words-I am glad that you enjoyed it!
For day to day applications, the screen can let us know if we will potentially need to reduce more. We are not equilibrating everyone for every second molar crown. This is just a practical, everyday tool to help us provide consistent and efficient restorative care.