Basic Question About Waxing/Labwork

[DrTacoElf]

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[gryffindor]

From this model they are able to create a crown out of procelain, gold, etc.(Any Special Steps Involved In Creating These Crowns From The Cast?)

To get from the model to the final gold crown, the lab has to recreate the tooth structure the dentist removed off the tooth in wax, this is a "wax-up" of the tooth. This wax pattern is carefully removed off the model and cast into gold using the "lost wax process" - google this, it's too much to try and explain to someone who hasn't seen it done. Basically there are a lot of steps between the model step you described and getting to the final product.

Each tooth has an ideal occlusal anatomy that the lab will probably try to emulate in the final restoration. This anatomy may however be lost when the crown is adjusted for occlusion into the patient's mouth - it will either be ground away by the lab when they fit and adjust the final crown on the models they have, or it will be ground away by the dentist when s/he fits it chairside in the patient's mouth.

We learned wax-ups at my school because we had to cast several crowns, onlays, and inlays in our preclinical courses. I think the benefit to doing a wax-up is that you really learn the intricate anatomy of the tooth you are working on and it is really a great way to learn dental anatomy and have it become second nature to you (rather than memorizing it out of a textbook). I personally liked wax-ups because I could bring them home and do them in front of the TV since they require little brain power, but you will have plenty of classmates who despise them too.

 

[DrTacoElf]

To get from the model to the final gold crown, the lab has to recreate the tooth structure the dentist removed off the tooth in wax, this is a "wax-up" of the tooth. This wax pattern is carefully removed off the model and cast into gold using the "lost wax process" - google this, it's too much to try and explain to someone who hasn't seen it done. Basically there are a lot of steps between the model step you described and getting to the final product.

Each tooth has an ideal occlusal anatomy that the lab will probably try to emulate in the final restoration. This anatomy may however be lost when the crown is adjusted for occlusion into the patient's mouth - it will either be ground away by the lab when they fit and adjust the final crown on the models they have, or it will be ground away by the dentist when s/he fits it chairside in the patient's mouth.

We learned wax-ups at my school because we had to cast several crowns, onlays, and inlays in our preclinical courses. I think the benefit to doing a wax-up is that you really learn the intricate anatomy of the tooth you are working on and it is really a great way to learn dental anatomy and have it become second nature to you (rather than memorizing it out of a textbook). I personally liked wax-ups because I could bring them home and do them in front of the TV since they require little brain power, but you will have plenty of classmates who despise them too.

Thanks for the info, if anyone else has anything to add feel free

 

[aphistis]

So I'm wondering why we are taught waxing of teeth. Is it simply become more familiar with their anatomy in a hands-on sort of way or is it an inexpensive way to mimic clinical restorations (i.e. composite).

Correct Me If I'm Wrong Here....
Lets say a dentist has prepped a mandibular molar for a crown. He takes an impression of the lower arch or lower 1/2 which contains the prepped tooth and then sends this out to the lab after he casts a temporary from the impression. Then the lab has this impression and casts from it a whole arch using plaster (?). Then then they have recreated the mouth (prepped tooth, which is now called a die and adjacent teeth are also present). From this model they are able to create a crown out of procelain, gold, etc.(Any Special Steps Involved In Creating These Crowns From The Cast?)

Another question I have is about the occlusal surface anatomy of a crown. How does the lab know what to make this like or is variation within the population so minimal that they can use a preset pattern, and let the dentist adjust occlusion from this?


Thanks!

Griffin did a good job explaining, but I just saw a couple small points worth responding to.

You don't "cast" temporary impressions--casting is defined as making the final metal restoration (think of the little die-cast cars you played with as a kid, they were all metal). Also, there are two general ways to make a temporary, direct & indirect.

Direct temporaries involve taking a putty impression of the individual tooth/teeth in question before you start preparing them, fill it with provisional material, and then squishing it back down over the prepped teeth. Then you clean off the extra, adjust the occlusion, and you're done. Alternately, instead of the putty impression you can use a pre-fabricated crown form and just reline the inside so it fits, then adjust the occlusion.

Indirect temporaries are essentially the same thing, except that instead of creating the provisional back into the mouth, you make it on your dies, & working models (additional stone models which help in establishing proximal & occlusal contact).

Hope that helps some.

 

[ItsGavinC]

Both excellent posts. Waxing is blah, IMO, however.

 

[JesseBrad3]

I think a lot of labs now use computers to simulate what would be done with wax, and then mill it from a block of porcelain (ie. Cerec). It's probably a lot quicker and easier than waxing up by hand. I'm not sure how schools teach students how to make crowns and inlays, but I'm assuming most do it the olde-fashioned way.

 

[tinker bell]

Most of the time, now, dentists use PVS to take impression. Putty is extra-good, but it is more expensive.
Dentist send the impression to the lab, and the lab pour a full arch cast (not totally plaster), and mount both the max & man arches up to stimulate real mouth movement, check occlusion. They also pour another cast of the prep tooth, using die stone this time, to make a die. Once the stone is harden, you saw off the die out, trim it. So, wax up is done on the full arch cast, the die is used to trim the margin of the tooth after wax up is done.

If you still want to hear about casting:

The wax up is then carefully removed, and margin trim and carefully checked like 5 times. Then, you put in in a casting ring, pour some investment stone in to fill the ring. Put this ring in 500F for an initial burn out, then 1100F oven for a real burn. At this point, all the wax is burned, the space is empty now. (the whole thing takes like 1.5hr for both oven). So, you remove the burn out wax in casting ring, and with some melted, hot gold, you cast the tooth(the melted gold now occupies the space that is formerly occupied by wax). After that, quench the whole ring so the grain of gold will shrink, crack the investment and retrieve your gold crown.

I really like doing those real gold crown. If you seriously like to do your gold work, go to UCSF or USC. You'll get to do plenty of gold crowns and bridges. I just did a gold bridge, and I think you learn a lot once you have done it, rather than just preping the teeth, send to the lab.

 

[DrTacoElf]

Most of the time, now, dentists use PVS to take impression. Putty is extra-good, but it is more expensive.
Dentist send the impression to the lab, and the lab pour a full arch cast (not totally plaster), and mount both the max & man arches up to stimulate real mouth movement, check occlusion. They also pour another cast of the prep tooth, using die stone this time, to make a die. Once the stone is harden, you saw off the die out, trim it. So, wax up is done on the full arch cast, the die is used to trim the margin of the tooth after wax up is done.

If you still want to hear about casting:

The wax up is then carefully removed, and margin trim and carefully checked like 5 times. Then, you put in in a casting ring, pour some investment stone in to fill the ring. Put this ring in 500F for an initial burn out, then 1100F oven for a real burn. At this point, all the wax is burned, the space is empty now. (the whole thing takes like 1.5hr for both oven). So, you remove the burn out wax in casting ring, and with some melted, hot gold, you cast the tooth(the melted gold now occupies the space that is formerly occupied by wax). After that, quench the whole ring so the grain of gold will shrink, crack the investment and retrieve your gold crown.

I really like doing those real gold crown. If you seriously like to do your gold work, go to UCSF or USC. You'll get to do plenty of gold crowns and bridges. I just did a gold bridge, and I think you learn a lot once you have done it, rather than just preping the teeth, send to the lab.

Tinkerbell thanks for this great info

Two Questions
1) PVS = PolyVinylStyrene?
2) I'm a little confused about the die part highlighted in red above, specifically how the die is used to trim the margin of the tooth after wax up is done.

 

[aphistis]

Tinkerbell thanks for this great info

Two Questions
1) PVS = PolyVinylStyrene?
2) I'm a little confused about the die part highlighted in red above, specifically how the die is used to trim the margin of the tooth after wax up is done.

PVS is polyvinylsiloxane, a silicone impression material. It produces the best impressions, but it's pretty expensive. You might see "vinyl polysiloxane" "poly (vinyl siloxane)" or any number of other word arrangements depending on who you talk to, but it's all the same stuff.

As for the part in red, it sounds like Tink waxes differently than I do (no big surprise, everyone develops their own technique). I use the full-arch stone models (= working casts) to check proximal & occlusal contacts, but I do most of my waxing on a die. The method for perfecting margins is called margination, and it basically involves taking a heated fine wax instrument and tracing the entire margin on the waxup. This melts the wax and makes sure you have a perfectly-fitting transition from crown to natural tooth.

After that, like she said, you check it about 34,000 times to make sure everything looks good (if you have an open margin on the actual gold casting, it's back to the drawing board to start waxing all over again), then you invest it, burn the wax out in an oven, and cast your gold. If all has gone well, at this point you have a gold crown ready to polish & deliver.

 

[ItsGavinC]

It's all about sending the stuff to a lab (but a *very* good lab).

 

[tinker bell]

Dr. Taco,

You just pour a stone cast for the die. Once you remove it, you saw off the other parts that don't have your prep tooth on it. So, at this point, the die is only your prep tooth. In your example, it would be the mandibular molar. Since this is the free one tooth that you can hold it in your hand, go around the margin, you can use it to trim the margin of your wax up

One more thing, if you have loads of time, some readings will help you since you are so interested. Fundamental of fix prosthodontics by Dr. Shillinburgh is a required reading for almost every dental school. It has super details of everything you can ever think of.

I hope my answer didn't confuse you even more.

 

[DrTacoElf]

Wow, thanks guys I actually understand the process now . Are solid porcelain crowns and/or PFM crowns done in the same way (lost wax method) or is that a whole new process?

 

[tinker bell]

Porcelain is similar, but you don't use wax, use porcelain, painted on the prep tooth, then bake it, and also cast.

 

[psiyung]

Wow, thanks guys I actually understand the process now . Are solid porcelain crowns and/or PFM crowns done in the same way (lost wax method) or is that a whole new process?

Taco,

If you're interested, I can send you a powerpoint regarding the lost wax method. Just pm me or reply to this thread if you are

 

[DrTacoElf]