Gold Crown Prep on #30 (Preclinical Practical)

[DrTacoElf]

Hey,

Was wondering if anyone had tips for my first crown prep practical. Its on #30 for a gold crown (chamfer margin - ideal reduction 1.5mm). I'm having somewhat of a hard time getting the proper reduction (I always seem to be underreduced)....

Thanks 🙂

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[Motown]

DrTacoElf,
I personally prefer the brassler 6878k for both the chamfer and occlusal reduction. This link might be helpful:
http://www.brasselerusa.com/documents/crown1.pdf
Slightly different prep - but the technique is the same.
A bite impression in red wax is also an effective evaluation technique for occlusal reduction - check thickness of bite impression after occlusal preparation.
Good luck on your practical.

 

[crazy_sherm]

#30's not too bad, hardest part is getting the mannequin cheek outa the way. Make two putties, section one down the buccal groove and section the other one along the cusps. Check marginal ridge height with the adjacent teeth. Also check cusp reduction by holding and instrument straight along the cusps of 29 and 30, using that to measure. Use depth cuts when starting your prep, I usually go about 3/4 the intended reduction. Once you get it reduced down that far, all you'll need to do is refine the prep. You really only need 1.5mm reduction on the occlusal and the functional bevel. The axial reduction should be 0.8mm at the margin and gradually move up to 1.5mm occlusally. You should be able to do the whole prep with a 878-16 diamond. I sometimes use a football on slow speed to take out the sharp ridges, but not so important for gold.

 

[nothen2do]

Use those strips of wax that when folded 3 times, equal 1.5 mm. Take a bite impression, anywhere that light shines thru or theres a big hole, means you didnt reduce enough in that area

 

[DrTacoElf]

Use those strips of wax that when folded 3 times, equal 1.5 mm. Take a bite impression, anywhere that light shines thru or theres a big hole, means you didnt reduce enough in that area

Good Idea!!

Ill have to see what wax this is but i'm sure i can come up with something

 

[Rezdawg]

You can check occlusal reduction by taking out a ball burnisher...one of the sizes is about 1.6 mm in diameter (You can use an Iwanson gauge to accurately measure or just used your probe and eyeball it). So, when the jaws are occluded, you can try to run the burnisher inbetween number 3 and 30 and see how it fits in there. If it doesnt go in, just reduce a little more...if it goes in with no problems, then you overreduced...you want it to barely squeeze through.

 

[JavadiCavity]

At Pacific, we were not allowed to use wax to check the bite during preclinical practicals. In clinic, wax is the ideal way to check occlusal reduction.

Taco, watch the marginal ridge heights closely. That is there are where I usually ran into trouble. Initially, I always seemed to reduce too much there. Took me one or two practicals to get the hang of it.

 

[ItsGavinC]

I'm having somewhat of a hard time getting the proper reduction (I always seem to be underreduced)....

Thanks 🙂

Well, at least consider yourself lucky in this aspect. That's a problem that can be fixed. Screwing the chamfer or always overreducing by 1 mm would be much more difficult to fix.

 

[Mach band]

Hey,

Was wondering if anyone had tips for my first crown prep practical. Its on #30 for a gold crown (chamfer margin - ideal reduction 1.5mm). I'm having somewhat of a hard time getting the proper reduction (I always seem to be underreduced)....

Thanks 🙂

If I remember correctly, chamfer margin is 0.5mm and occlusal reduction is 1 and 1.5 depending on whether it's non-functional or functional. For the chamfer margin, I use the tip of 812 bur to measure it. The tip is about 0.6 mm which is close enough to 0.5 spec.
For the occlusal reduction, if buccal, I would use a hoe or a hatchet to check. If lingual, I would use the technique nothen2do mentioned (2 for non-functional and 3 for functional). I would cut the buccal half first, then base on that to cut the lingual half. If you keep your bur stable, you won't need too much of checking on the lingual half. Another way of doing the occlusal reduction is to cut several cuts at different locations. This way you know how much you cut. Then just use the bur to even out the reduction. Remember to check often. Good luck!

 

[tinker bell]

the strip wax is the red wax that you use to box your impression and pour the cast. Fold it three times, close the typodont. Voila

In the worse scenario, if you look at your temp and see that the occlusal area super thin, you need to reduce some more.

Look at the temp is the best way to check in my opinion. Also, Brasseler has some depth cutting bur. Or the diameter of the 856 016 is 1.6 mm. If you just cut accross the occlusal surface a few lines, then follow those depth cut. You are pretty sure that you have enough reduction.