Fixed Prosth Crown Prep Tips???

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QTpieDMD

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Hey Folks,

I have my first fixed prosthodontics practical this week. I wanted to know does anyone have any tips? We are going to be doing a full gold crown prep with a chamfer margin on #19. Any pointers on how to keep decent anatomical form when reducing the occlusal surface would be greatly appreciated. Thanks so much ;) .

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Cut narrow depth guides both on the heights of triangular ridges & in the primary grooves. Make sure you get the depths & angles both right, not too shallow or deep, steep or flat. If you take a few minutes to make sure those guides are right, occlusal reduction is just a matter of playing connect-the-lines with your diamond, and the varying-height guides make it almost impossible to lose your anatomy short of conscious effort.
 
If you guys are doing it on ivorine teeth, i recommend using a slow speed for occlusal reduction. On real patients, use high speed, but for the sake of a practical, take your time, and do a good job.
 
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I would make a suck down matrix of the tooth before you prep it. During the exam you can place the matrix over the prep and pierce it with an explorer to measure the occlusal reduction and the axial inclinations. I would start with proximal reductions using a 169. this isolates the prep from the other teeth. Some people like to start with the occlusal reduction, but this increases your chances of dinging adjacent teeth.
Next: depth cuts. and finally axial reductions. Check every so often with you matrix to make sure you don't over prep. Check your margins with an explorer and refine them with a slow speed. There is a bur with an end cutting tip only and this is good eliminate J hook margins.
I would start with a high speed and refine with a slow speed. I don't think there is enough time to prep the tooth using only a slow speed. Get a game plane. 5 min for interproximal reductions, 15 occlusal reduction, 15 for Buccal Lingual and 10 for margins etc...
If you have to make a temp, I would slightly overprep the tooth. it is difficult to get a good provisional if you have thin chamfer margin.
Practice you weakness. like getting a margin on the DL of the prep. good luck.
 
Something I've learned since being in clinic is that you really don't need or want much anatomical form to the crown prep. For the most part, you want to keep everything nice and smooth without any sharp edges. Those sharp edges will be stress points that you don't want.

As one adjunct faculty (a graduate of Temple two years ago!) told me, you've got to play it safe and reduce lab bills. Redoing crowns because you did a crappy prep is a waste of chair time and a lab bill you don't need. He makes all his preps dome shaped on the occlusal. I've taken to doing that as well.
 
Hey Guys,

Thanks soooo much for the tips! I can't tell you how much I appreciate it.
 
Do you guys do 7/8 or 3/4?
And cast gold?
 
ecdoesit said:
Do you guys do 7/8 or 3/4?
And cast gold?

Ahh the 7/8ths. I don't think you'll see that much outside UCLA. :)
 
ItsGavinC said:
Something I've learned since being in clinic is that you really don't need or want much anatomical form to the crown prep. For the most part, you want to keep everything nice and smooth without any sharp edges. Those sharp edges will be stress points that you don't want.

As one adjunct faculty (a graduate of Temple two years ago!) told me, you've got to play it safe and reduce lab bills. Redoing crowns because you did a crappy prep is a waste of chair time and a lab bill you don't need. He makes all his preps dome shaped on the occlusal. I've taken to doing that as well.

Flat top crowns do not go over well at my school. Plus, it would be a quick way to fail boards.
 
12YearOldKid said:
Flat top crowns do not go over well at my school. Plus, it would be a quick way to fail boards.

My school too.

Making the crown flat may be considered too aggressive or may result in nicking a pulp horn.
 
What do you guys use in clinic to cement temps (or provisionals for the pros guys)? I hear TempBond is pretty weak, which has been my experience. I've begun using IRM instead. Durelon, anyone?
 
Tempbond at UNC and I've only had one fall off in my 4 years here. I think a big part of it is educating your patient about not eating stick/chewy/crunchy stuff on that side.
 
drhobie7 said:
What do you guys use in clinic to cement temps (or provisionals for the pros guys)? I hear TempBond is pretty weak, which has been my experience. I've begun using IRM instead. Durelon, anyone?
I use aluminum or polycarb crown shells, relined with Snap, and cemented with IRM. They're working great so far, including one active business traveller who's had the temp in place for about 2 months with no problems.
 
DcS said:
Tempbond at UNC and I've only had one fall off in my 4 years here. I think a big part of it is educating your patient about not eating stick/chewy/crunchy stuff on that side.

And actually prepping a tooth correctly with walls that are reasonably parallel (not teepee'd) never hurts. I've also only lost one with Tempbond in 4 years, and that was cause my prep was a bit dodgy...of course, it was my first one... :)
 
jpollei said:
And actually prepping a tooth correctly with walls that are reasonably parallel (not teepee'd) never hurts. I've also only lost one with Tempbond in 4 years, and that was cause my prep was a bit dodgy...of course, it was my first one... :)

My thoughts exactly! As I think back as to how my Full Coverage Crown preps have "evolved" over the years, I've gone from a DEEP chamfer with convergent axial walls in the 10-15 degree range and practically tertiary anatomy on the occlussal surface to where I am today(and have been for the last 4 or 5 years) with a 90 degree 1.5mm wide butt joint, parallel axial walls, and a very smooth occlussal surface. I've always been a rounded edge guy :oops: :D .

One of the main reasons that I love the 90 degree butt joint, and one of the part time faculty in my residency who I learned a ton from showed me this, is that with a 90 degree butt joint, it's literally a very quick glance 100% yes or no if you got the margin on your impression and it's much easier to identify the margin as your trimming the temp :thumbup:

I also use temp bond (non eugenol version) and rarely have any retention issues(most common reason if I have to recement one is the patient was eating something as sticky as a tootsie roll :eek: :rolleyes: , or if the prep is really short vertically)

As for tips on preps, the best thing I can tell anyone, is get a routine and follow it. It doesn't really matter if your a butt jointer, a chamferer, or a feather edge fiend, just make the same steps over and over. For example, my routine is as follows:

#1) occlussal/incisal depth cuts

#2) Gross occussal/incisal reduction

#3) Interproximal reductions

#4) buccal/lingual reduction

#5) Verify adequate reduction of all surfaces

#6) Smooth finish lines/round angles

The burs I use vary depending on anterior/posterior tooth(I've got some really small diameter burs for the mandibular anteriors! :D )

Total handpiece running time from start to finish will take me a little under 4 minutes depending on how much chit-chatting I'm doing :rolleyes: :D
 
As one adjunct faculty (a graduate of Temple two years ago!) told me, you've got to play it safe and reduce lab bills. Redoing crowns because you did a crappy prep is a waste of chair time and a lab bill you don't need. He makes all his preps dome shaped on the occlusal. I've taken to doing that as well.[/QUOTE]

Dome shaped occlusals???!!! On a posterior crown?! I wonder what some of the the premier lab technicians thoughts are on that sort of nonsense. Are dental students spending any time doing lab work these days?

Gavin: I suggest you ask some of the premier dentist-laboratory teams out there what they think about this idea. Some suggestions might be David Garber-Pinhas Adar, John Kois-Steve McGowen, Tom Trinker-Matt Roberts, Edward McLaren-Chang, Alan Sulikowski-Aki Yoshida, Gerard Chiche-Hitoshi Aoshima, Fradeani-Barducci, etc.

These are dentist-technician teams respected in the dental world -- and I suspect all of them would laugh at the idea of dome shaped occlusals.

Rounded edges and corners are great, but to try make an esthetic looking crown on a dome--especially with poor occlusal reduction--and the technician is doomed to fail. Is this really the type of dentistry they are teaching you at ASDOH??? Wow!
 
Thanks for the advice. Yeah the one that I used TempBond on that fell off was an old crown that was super short and way overtapered. So I guess with poor retention a stronger cement would have been better. Glad to hear it's ok for normal preps.

My instructor gave me a tip today that makes sense. He said to do the hardest part of a prep first. That way you'll have an easier time making the rest draw. For example, if the DL will be the toughest spot to do on #3, do that one first and then make the other walls draw to that. Made sense to me.
 
Great tips.

The dentist I worked for used Durelon if the retention was weak - onlays, maybe short crowns (can't remember), and sometimes when the patient had to come back to the office for re-cementation.

You can also give your patient single dose Tempbond with a disposable spatula and basic instructions if you feel the temp is at risk of popping off or going on vacation/business trip.
 
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