Tips On Tooth Preparation

[Dr. Dai Phan]

Hello fellow dentists,

I used to tutor international applicants for advanced studies at Marquette University when I was resident so I now would like to share what I had done for others. Before we look into the details, you need to know the following:

1. Understand the type of margin for that particular type of preparation. Full gold coverage preparation is different from porcelain fused to metal (PFM) is different from all ceramic (AC) is different from veneers (V) etc… That is because of the type of material being used. Gold can be made very thin (0.5mm) in thickness and you will be OK. However, if you make your porcelain that thin, it will be brittle like rice paper and fail even before it is seated in the mouth! So PFM and AC require more reduction to allow for the materials and also for strength. If you prepare a tooth like a FGC and ask for porcelain, the material will either break as you attempt to seat in the mouth or the technician will call you and inform you that it can't be done.

2. Understand the type of finish that the bur you are using will produce. For example, a rounded tip diamond bur will give you a chamfer finish and a blunt or flat ended tip will give you a shoulder finish. Those burs have different shapes because they are designed to serve a particular purpose so use them intelligently!

3. Understand the amount of occlusal reduction for the type of preparation. Gold as mentioned before can be made thin so you do not need to have reduction like you are preparing for PFM or AC coverage. Excessive occlusal reduction is one of major errors that will lower your grade.

4. Take your time and go slow. As you become competent, you can increase your speed. If you end up with a heavy shoulder for a FGC prep, how are you going to correct that?

5. Know what you want to achieve BEFORE you start!

Now, let's look at the FGC criteria for tooth preparation.

a. FGC ( example #19):

Occlusal Reduction for Functional Cusp: 1.5 mm
Occlusal Reduction for Non-Functional Cusp: 1.0 mm
Axial Reduction: at least 1.0 mm but less than 3 mm.
Chamfer Margin of 0.5 mm. That means there are no sharp corners.
Functional Cusp bevel 1.0 mm in width.


b. PFM (example #19)

Occlusal Reduction for Functional Cusp: 2.0 mm
Occlusal Reduction for Non-Functional Cusp: 1.5 mm
Axial Reduction: At least 1.5 mm.
Shoulder Margin ( Radial Shoulder like a "stair" ) of 1.5 mm.
Chamfer Margin for the lingual since this part is in metal. Treat it
like a FGC here.
Functional bevel of 1.0 mm in width.

c. All Ceramic (example # 30)

Think of this as an all around PFM except the lingual is in porcelain.
Just copy what you did on the facial and apply to the lingual. The
reason why porcelain margin require a shoulder is for the support of
the material. Chamfer margin will result in a very thin porcelain layer
that will fail quickly!

TIPS:

1. Make your preparation smooth and free of jagged edges. Use your SLOW SPEED to refine your margin. First, the slow rotation of the bur will smooth out the surface out rather than cutting into the surface. Second, you do not have to fear about "slipping" and cause a gouge in the prep just before you turn the prep in! Start your prep on a high speed and finish your prep on a SLOW speed is my motto!

2. Avoid sharp corners or edges. Use a diamond bur on the SLOW speed will smooth these edges out and give it a "professional" look!

3. Avoid "Flat Top" preparation. In other words, you should be able to see facial and lingual cusps regardless of the type of preparation. Why? That is because you want to maximize the surface area for cement bonding and to prevent rotation of the crown. Plus, it simply looks better!

4. Follow the contour of the gingival in the mesial and distal areas. The margins of the preparation should NOT be straight across but should be higher occlusally in these areas because of the bone morphology and the attachment of soft tissues. What if you ignore this and make it straight across? You will GOUGE the plastic ( a major point reduction) and get into the biological space ( in real life application). Not too nice here.

5. Avoid excessive taper. Your prep should have a slight taper when viewed facial –lingually. How do you prevent overtapering ( another major point killer)? ALWAYS look at your bur on the side when you do the axial reduction. If you look at your bur from the top down (occlusal-gingivally), you may end up with excessive taper and not knowing it until too late!

6. How do you break contact without damaging the adjacent teeth? First use the wedge to push the teeth out. Second, use a matrix band to protect them. Finally, use a smallest diamond bur as these do less damage than a big one and gives you much less risk of over-tapering. Overtapering during breaking contact is a very common rookie mistake!

7. How do you correct minor "nicks" on the adjacent teeth? Swap them out when nobody is watching? No, use composite sandpaper strips to smooth them out.

8. Avoid "knife edge" margin where you can't physically see a definitive margin as this type of preparation has no place for any type of restoration. Guarantee to get your score lowered!

Well, here are the basic reviews of tooth preparation. You need to check what exactly the examiners want for a particular preparation such as bevel on the margin or so forth. Remember that once you know what you are looking for in a preparation, you can make what you want regardless of what type of burs they give you. Don't get fixated on "what burs do I need for this and that" but rather know " the proper criterias that are needed for that type of preparation " . Good luck and let me know if I can be of some help. DP

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[drchai]

Thanks a lot for ur great tips, am sure many will benefit from this.

 

[sweetgal]

hey dr.dai phan,,,this post of urs is really awesome!!!!good job
but i always get stuck with MOD 3/4 VC preparation on maxillary molar,,thats so tricky,,can u plzz give some valuable advice on that..

no words to thank you for ur help,,,

 

[Dushyant]

WOW........
We all appreciate ur help and concern, that was very informative and helpful.
Thanks a lot.

Can u help us contact any institute where we can practice the preprations in the bay area.

Thanks again.

 

[ajex]

thank u...great summery.

2 questions though:

1. where is best to finish the margin? supra-, equal-, or sub-gingival?

2. how best to check for undercuts? i have heard of the close-one-eye technique (personally i find that abit hard to tell); others tips based on ur experience?

many thanks in advance

 

[tummala_p]

hai, u r doing great work ! i have a dought ,does Marquette University conduct practicle exam for the selection of advanced standing programm for foreign trained dentists ? becoz i am planning to apply the unv, if so what would thy ask in the exam to do ? plz respond me as soon as possible thanking u.

 

[smartdentist]

good post, very informative.

 

[dentist79]

We all really appreciate your time and efforts to help us all....looking forward for your support in future too...
thank you

 

[CALALILY]

wow - that was really handy! thankyou for taking the time to write it all out.
much appreciated.

regards and best wishes..

 

[HYDBDS]

Hi Dr. Dai Phan ,
Thanks for such a wonderful post and for your concern for so many aspiring ASP applicants......

You are like an ANGEL among mortal humans.....

God Bless You....
Regards & Best Wishes......

 

[net]

hello Dr. DP,

best post i ever read here. thanks a lot for your help. i got one more question to ask you. could you also summarize how to prep inlay and onlay like you did for crowns? thanks!

btw, could you also post some slides with pictures of the prep or give us a link?

net

 

[manasa]

thx a lot for the thread on tooth prep'n Dr Phan
Please do write on prep tips for gold inlays and composite inlays too.
Thx again..

 

[DENTZY]

Dr.Dai Phan,
That is a wonderful post.Thanks for all the information.
But I have some ques.
Quoting you:-
3. Understand the amount of occlusal reduction for the type of preparation. Gold as mentioned before can be made thin so you do not need to have reduction like you are preparing for PFM or AC coverage. Excessive occlusal reduction is one of major errors that will lower your grade.

How do I check the amount of occlusal reduction done by me in various different planes ?I.E WITH WHICH INSTRUMENT?I end up with more reduction than reqd. each time.

Quoting you:-
4. Follow the contour of the gingival in the mesial and distal areas. The margins of the preparation should NOT be straight across but should be higher occlusally in these areas because of the bone morphology and the attachment of soft tissues. What if you ignore this and make it straight across? You will GOUGE the plastic ( a major point reduction) and get into the biological space ( in real life application). Not too nice here.

This point is not clear to me.Are you saying the mesial & distal marginal ridges shd. be kept higher?Pls. explain.

Thanks a lot,
DENTZY

 

[Dr. Dai Phan]

thank u...great summery.

2 questions though:

1. where is best to finish the margin? supra-, equal-, or sub-gingival?

2. how best to check for undercuts? i have heard of the close-one-eye technique (personally i find that abit hard to tell); others tips based on ur experience?

many thanks in advance

Hello fellow dentists...

I am so glad that I can be of some help. I will do my best to answer all the questions so please be patience. Now, it is important that my answers are based on my preference in some cases and you should evaluate these for yourself rather than taking them "in stone...".

The best location of a margin is the margin that gives you the EASIEST chance of capturing it in the impression as well as providing the best esthetic outcome for the restoration. If you are restoring a tooth say in the posterior areas, put your margin ABOVE the gingival because it is easier to clean, easier to capture in the impression and who cares if the margin is 0.5 mm above the gum line as no one sees it. However, for restrations that are visible such as anteriors, your margins should be subgingival so you do not see the margins when patient smiles. If patient has low smile line, then it is OK to put it at the gingival or even above it. You must consider cleasability as well as esthetically when you make the decision. On your prep on the manakin, put your margin 0.3-0.5 mm above the plastic since the examiner needs to see it.

The best way for undercut is use your perio probe and lay it on the axial wall and watch for "dips"... One eye method sounds ideal but it is much tougher than said. Try it both ways but the perio probe method works well for me. DP

 

[richa sharma]

Hello Dr.Phan,
Thnkyou so much for ur guidance!!
Could u pls add a note about inlays too.
regards,
richa

 

[Dr. Dai Phan]

Dr.Dai Phan,
That is a wonderful post.Thanks for all the information.
But I have some ques.
Quoting you:-
3. Understand the amount of occlusal reduction for the type of preparation. Gold as mentioned before can be made thin so you do not need to have reduction like you are preparing for PFM or AC coverage. Excessive occlusal reduction is one of major errors that will lower your grade.

How do I check the amount of occlusal reduction done by me in various different planes ?I.E WITH WHICH INSTRUMENT?I end up with more reduction than reqd. each time.

Quoting you:-
4. Follow the contour of the gingival in the mesial and distal areas. The margins of the preparation should NOT be straight across but should be higher occlusally in these areas because of the bone morphology and the attachment of soft tissues. What if you ignore this and make it straight across? You will GOUGE the plastic ( a major point reduction) and get into the biological space ( in real life application). Not too nice here.

This point is not clear to me.Are you saying the mesial & distal marginal ridges shd. be kept higher?Pls. explain.

Thanks a lot,
DENTZY

Hi there,

Checking the amount of reduction can be achieved in many ways. First by a " reduction jig" made by putty that is cut in half or by a clear matrix. What it involves is that a silicone putty is pressed over the UNPREPARED tooth then cut in halves (M-D and B-L). By using these jigs one can see the amount of reduction by looking at the empty space between the tooth surface and the inner side of the jig. The second way that is much easier is by using a vacummformed clear plastix shell where it is placed over the preparation. Then the perio probe is poked through the shell and one can measure the amount of reduction. Third method is by using "reference grooves" or depth grooves where the length of the diamond bur is "grooved" into the surface of the tooth. After removing the tooth structures between the grooves, then you are at correct depth. The easiest way is by "eyeballing" it as this is how the preps is graded as using matrix is too time consuming. Of course you need to be experienced to know what looks right and what not. I suggest using a clear shell as this is the most simple and quick. There are other methods of checking but they are more troublesome than worth the efforts.

If you look at the M-D areas say on #19, you will see that the gingival takes a "uphill" curve since the bone morphology is more toward the occlusal than the buccal and lingual. Accurate plastic typodont should reflect that but some don't. If it does, you need to FOLLOW the contour of the gingival so you don't gouge the plastic (major grade killer!). In clinical setting, the most common error of invading the biological width (nicking the junctional epithelium attachment) is total ignorance of the periodontium morpholorgy in the mesial and distal areas. DP

 

[andaljay]

what is the vacummformed plastix shell, is it available at the dental stores?

 

[Dr. Dai Phan]

what is the vacummformed plastix shell, is it available at the dental stores?

The clear shell is the material that dentists use to make bleaching trays for patients. If you are near a dental school, ask a faculty if he can let you have a piece or two. You can buy this at any dental supplier online and since this is dirt cheap for them to manufacture, ask for some free samples. I am sure they would be happy to send you some. DP

 

[Dr. Dai Phan]

The best sourse for understanding the different types of preparations such as FGC, veneers, inlay and onlays comes from quality fixed prosthodontics text books. My favorites are Shillingburg and Rosenstiel. I suggest you buy the Shillingburg since it is very clear and the writting style is very simple to understand. Reading it is one thing but doing it is another animal. As I mentioned before, if you can organize a group I will be willing to help with the practical parts. DP

 

[ivorinedust]

Dear Dr. Phan:

The vacuformed jig is brilliant! But we are not allowed to take perio probes in the Cali exam. I have the Jeela RGS (UCLA)measuring tools that are made to look like amalgam instruments, but non of them is calibrated to 1.0mm from the end. Maybe I'd carve a notch on my explorer 1mm from the tip. BTW, you might like to mention that a poured model cast of the typodont is needed to fabricate the thing, as some of us might not be familiar with the vacuform and make the jig directly from the typodont.

I have a question for you. Which is more important as far as the preclinical/bench exams go? Occlusal reduction or occlusal clearance?

I have observed that most exam typodonts(Columbia SMPVR 860) still have some non contacting surfaces on opposing teeth, even with the best effort to equilibrate them. I see usually them on the distals of opposing molar teeth. If I had one of these typodonts, should I give full reduction on the non-contacting surfaces and risk looking like it was over-reduced, or should I shave it little by little until I get the required clearance but obviously not satisfying the required amount of reduction?

Thanks for your generosity, Doc

Ivorinedust.

"Apolonia, relieve my toothache!"

 

[Dr. Dai Phan]

You have brought up a point that clearly shows the drawbacks of the typodonts. To answer your question, let's look at two different situations. First, in the clinical setting. If the tooth already have adequate occlusal clearance for the particular restoration, then do you still have a need for occlusal reduction? The answer is Yes but for a different reason. The reason is to "prepare" the surface such as smoothing out pits and grooves and not for obtaining adequate clearance because we already have enough space. This procedure is nothing more than a simple enameplasty on the occlusal surface. This procedure is more correctly called "occlusal adjustments" rather than reduction. Before you start to lay your burs on the tooth, ask yourself is tooth reduction is neccessary. You will find that in some cases, you can get by without doing much on the occlusal at all. Now, how about in the practical setting? I believe that you need to do some preparations on the occlusal to demonstate that you know how to do such procedure. Leaving the occlusal surface barely untouched because it "already has adequate occlusal clearance, Mr. Examiner" would certainly won't get you very far at all. So you would certainly need to do occlusal reduction to show that you know how to do such task. But now you are stuck with excessive occlusal clearance that gives the impression of over reduction which that is not the case at all. Well, the way to prevent such situation is to equilibrate your typodont to your best ability. If it cannot be done, bring your concern to the examiners and include a clear shell matrix so they can see the actual reduction for themselves. When I grade my students preps, I take the typodont error into account so I do not deduct points unless it is obviously grossly reduced. I am sure with the experience that the examiners have, they would agree the same thing. DP

 

[DENTZY]

Dr. Dai Phan,
Thankyou for taking the time & answering my queries.

The second way that is much easier is by using a vacummformed clear plastix shell where it is placed over the preparation.Then the perio probe is poked through the shell and one can measure the amount of reduction.

I don't understand this point.Do I adapt a vacummformed clear plastix shell over the "prepared tooth" or unprepared tooth and then gauge the difference using perio. probe???.How do I adapt the shell over tooth?


If you look at the M-D areas say on #19, you will see that the gingival takes a "uphill" curve since the bone morphology is more toward the occlusal than the buccal and lingual. Accurate plastic typodont should reflect that but some don't. If it does, you need to FOLLOW the contour of the gingival so you don't gouge the plastic (major grade killer!).

Thanks for the nice explanation to this.

 

[Dr. Dai Phan]

Dr. Dai Phan,
Thankyou for taking the time & answering my queries.

The second way that is much easier is by using a vacummformed clear plastix shell where it is placed over the preparation.Then the perio probe is poked through the shell and one can measure the amount of reduction.

I don't understand this point.Do I adapt a vacummformed clear plastix shell over the "prepared tooth" or unprepared tooth and then gauge the difference using perio. probe???.How do I adapt the shell over tooth?


If you look at the M-D areas say on #19, you will see that the gingival takes a "uphill" curve since the bone morphology is more toward the occlusal than the buccal and lingual. Accurate plastic typodont should reflect that but some don't. If it does, you need to FOLLOW the contour of the gingival so you don't gouge the plastic (major grade killer!).

Thanks for the nice explanation to this.

The clear shell is vacumm formed over a plaster cast of your tooth. Don't vacummform over your plastic typodont because you will melt it! Then place this matrix over your PREPARED tooth to judge the amount of reduction. You need to do this several times as you prep so you don't end up over reduction. If you place the matrix over UNPREPARED tooth then your reduction will be ZERO since there is no seperation between the tooth surface and the inside of your shell. DP

 

[DENTZY]

The clear shell is vacumm formed over a plaster cast of your tooth.

Dr. Dai Phan,

Please tell me some other way .Some instrument that i can use etc.I don't know where to get the clear shell vacuum formed over a plaster cast of tooth. I need to know some way that I can use at home since I am not familiar with any dental lab. here.I am sure most of us are International dentists who donot have much of link with any dentist/dental lab.Hope you understand and help me out.
Thanks again for your help,
DENTZY

 

[Anushri]

hi Dr. Dai Phan

Thank you very much for starting this thread ! Its a great help for somebody who has nobody around to guide. I have applied to california universities. Yet I have not started practicing for my practical examination. Will you please guide me how to go about it? Importantly, will you please let me know,which all instruments I should buy to practice at home.

Thanks in advance.

Regards
-Anushri

 

[ajex]

what a wonderful thread we have here -- all credits go to Dr. DP. Thank you for doing this =)

 

[ivorinedust]

Quoting Dr. Phan:
...
2. Understand the type of finish that the bur you are using will produce. For example, a rounded tip diamond bur will give you a chamfer finish and a blunt or flat ended tip will give you a shoulder finish. Those burs have different shapes because they are designed to serve a particular purpose so use them intelligently!

Dr. Phan, I have torpedos and gingival curettage/"k" burs in my armamentarium too. They are designed for chamfer finishes too, right? So...when do I use them and when do I use a round tip?

1. Make your preparation smooth and free of jagged edges. Use your SLOW SPEED to refine your margin. First, the slow rotation of the bur will smooth out the surface out rather than cutting into the surface. Second, you do not have to fear about “slipping” and cause a gouge in the prep just before you turn the prep in! Start your prep on a high speed and finish your prep on a SLOW speed is my motto!

I have a U-type friction grip contrangle, so I don't have to buy a separate set of CA or latch burs. Thing is, it chatters a lot and the burs tend to "jump" as I adapt it to my prep. Do you know of a good brand of FG contrangles?

5. Avoid excessive taper. Your prep should have a slight taper when viewed facial –lingually. How do you prevent overtapering ( another major point killer)? ALWAYS look at your bur on the side when you do the axial reduction. If you look at your bur from the top down (occlusal-gingivally), you may end up with excessive taper and not knowing it until too late!

I tried laying my cylindrical bur horizontally as I cut my proximal reduction on a full shell crown on a molar. The cut was nearly parallel. Is this safe to do?

Thanks again for all your comments! I hope I haven't been too annoying with my questions

Ivorinedust

"Apolonia, relieve my toothache!"

 

[rajjos77]

Hello Dr. Dai Phan
Thank you very much for your help.
A very very useful thread.

 

[Dr. Dai Phan]

The clear shell is vacumm formed over a plaster cast of your tooth.

Dr. Dai Phan,

Please tell me some other way .Some instrument that i can use etc.I don't know where to get the clear shell vacuum formed over a plaster cast of tooth. I need to know some way that I can use at home since I am not familiar with any dental lab. here.I am sure most of us are International dentists who donot have much of link with any dentist/dental lab.Hope you understand and help me out.
Thanks again for your help,
DENTZY

Regarding the clear shell, look up in the yellow pages and check for dental lab. Ask them if they can sell you some pieces of materials used to make bleaching trays (clear plastic). If they are not willing to give or sell you some, you can go to hobby shops and buy clear sheets used to vacummform toy parts. There are companies online that you can Google by typing in " Dental Supplies" that sell or give away this stuff. If you still can't find it, just use the putty matrix as the guide. You can see these proven methods in the book called " Fundamentals of Fixed Prosthodontics" by Herbert Shillingburg. DP

 

[Dr. Dai Phan]

...

Dr. Phan, I have torpedos and gingival curettage/"k" burs in my armamentarium too. They are designed for chamfer finishes too, right? So...when do I use them and when do I use a round tip?


I have a U-type friction grip contrangle, so I don't have to buy a separate set of CA or latch burs. Thing is, it chatters a lot and the burs tend to "jump" as I adapt it to my prep. Do you know of a good brand of FG contrangles?



I tried laying my cylindrical bur horizontally as I cut my proximal reduction on a full shell crown on a molar. The cut was nearly parallel. Is this safe to do?

Thanks again for all your comments! I hope I haven't been too annoying with my questions

Ivorinedust

"Apolonia, relieve my toothache!"[/QUOTE]

The torpedo bur can be used for achieving the chamger margin as well as the round-end tapered diamond bur. If you look at the tips, the torpedo has more "pointed" shape than the round-end so this type would give you less of a deep shamfer margin. If you want deep chamfer, use the round-end diamond.

The chatters of the slow handpiece means that it needs to be oiled as older unlubricated handpiece tends to do this. If your bur jumps while cutting, it may mean your bur is bent or your rotation is reversed. Check the setting. Any brand will do the trick just fine.

A pararallel wall is much better than severely tapered walls. However, you should be able to see the walls converging toward the occlusal since this is how the examiners are used to see. If a person cuts the preparation at 6 degree convergence like text book says, you will see that the walls are parallel with each other as the human eyes can't detect a tilt at 3 degrees on each side. If you do this, although "text book" like, you will loose points for not tapering the walls too much! This to show you that what the text book says and what we percieved as ideal don't always go hands in hands with each other. DP

 

[Dr. Dai Phan]

hi Dr. Dai Phan

Thank you very much for starting this thread ! Its a great help for somebody who has nobody around to guide. I have applied to california universities. Yet I have not started practicing for my practical examination. Will you please guide me how to go about it? Importantly, will you please let me know,which all instruments I should buy to practice at home.

Thanks in advance.

Regards
-Anushri

Practicing at home is tough since you need to have a handpiece unit and a pole to support a typodont. The only thing that you can practice at home is making provisionals as you can use a Dremel tool to fabricate your temp. Cutting preps has to be done in the clinic. Start making friends at Dental schools and ask if you can use their lab bench after school hours. For practicals, you need high and slow speed, mirror, perio probe, explorer and fixed/operative burs kit. DP

 

[dentist79]

You have brought up a point that clearly shows the drawbacks of the typodonts. To answer your question, let's look at two different situations. First, in the clinical setting. If the tooth already have adequate occlusal clearance for the particular restoration, then do you still have a need for occlusal reduction? The answer is Yes but for a different reason. The reason is to "prepare" the surface such as smoothing out pits and grooves and not for obtaining adequate clearance because we already have enough space. This procedure is nothing more than a simple enameplasty on the occlusal surface. This procedure is more correctly called "occlusal adjustments" rather than reduction. Before you start to lay your burs on the tooth, ask yourself is tooth reduction is neccessary. You will find that in some cases, you can get by without doing much on the occlusal at all. Now, how about in the practical setting? I believe that you need to do some preparations on the occlusal to demonstate that you know how to do such procedure. Leaving the occlusal surface barely untouched because it "already has adequate occlusal clearance, Mr. Examiner" would certainly won't get you very far at all. So you would certainly need to do occlusal reduction to show that you know how to do such task. But now you are stuck with excessive occlusal clearance that gives the impression of over reduction which that is not the case at all. Well, the way to prevent such situation is to equilibrate your typodont to your best ability. If it cannot be done, bring your concern to the examiners and include a clear shell matrix so they can see the actual reduction for themselves. When I grade my students preps, I take the typodont error into account so I do not deduct points unless it is obviously grossly reduced. I am sure with the experience that the examiners have, they would agree the same thing. DP

The clear shell is vacumm formed over a plaster cast of your tooth. Don't vacummform over your plastic typodont because you will melt it! Then place this matrix over your PREPARED tooth to judge the amount of reduction. You need to do this several times as you prep so you don't end up over reduction. If you place the matrix over UNPREPARED tooth then your reduction will be ZERO since there is no seperation between the tooth surface and the inside of your shell. DP

Hello doc
Its amazing to find thiss great help from you...thanks...
my quest...with what material we take the impression of our prep to judge on the amount of reduction...and do we need to take a impression befor we start ,and then after reducing(at what level should we take first impression for the matrix thing...) and ofcourese with regular plastic trays?
thanks for ur time and patience

 

[Dr. Dai Phan]

Hello doc
Its amazing to find thiss great help from you...thanks...
my quest...with what material we take the impression of our prep to judge on the amount of reduction...and do we need to take a impression befor we start ,and then after reducing(at what level should we take first impression for the matrix thing...) and ofcourese with regular plastic trays?
thanks for ur time and patience

The material used to make a jig to judge the amount of reduction is silicone putty in which two equal parts are hand mixed then hand pressed over UNPREPARED tooth. Then it is cut into labial-lingual half then cut the labial half into gingival and incisal half. As you prepared the tooth, this jig is held against the prepared surface to judge the amonut of reduction. There is no tray needed for this procedure. DP

 

[CALALILY]

Dr. Dai Phan,

thanks for all your posts again.

You mentioned earlier that there may be some slides you could share with us -did you find a method of posting them somewhere (maybe on SDN if they allowed you to do so)?

thanking you for all your support,
regards and best wishes...

 

[futurdentist]

Good Job!!
If anybody knows of any websites that provides demos , please post them here ,too.

Thanks!

 

[dentist79]

The material used to make a jig to judge the amount of reduction is silicone putty in which two equal parts are hand mixed then hand pressed over UNPREPARED tooth. Then it is cut into labial-lingual half then cut the labial half into gingival and incisal half. As you prepared the tooth, this jig is held against the prepared surface to judge the amonut of reduction. There is no tray needed for this procedure. DP

Thank you for answering my question...i understand better now..

 

[drnishpatel]

Practicing at home is tough since you need to have a handpiece unit and a pole to support a typodont. The only thing that you can practice at home is making provisionals as you can use a Dremel tool to fabricate your temp. Cutting preps has to be done in the clinic. Start making friends at Dental schools and ask if you can use their lab bench after school hours. For practicals, you need high and slow speed, mirror, perio probe, explorer and fixed/operative burs kit. DP

dr phan,
i am trying to gather operative kit at home to practice ......can you please ellaborate on what should a typical fixed/operative burs kit should consist of ?? i did tried searching for burs but, the large varieties of burs in catalogues gives me a hard time to decide between necessities and additional burs........ so i thought of geting ur advise on that.....please advice ....thanx

 

[Dr. Dai Phan]

dr phan,
i am trying to gather operative kit at home to practice ......can you please ellaborate on what should a typical fixed/operative burs kit should consist of ?? i did tried searching for burs but, the large varieties of burs in catalogues gives me a hard time to decide between necessities and additional burs........ so i thought of geting ur advise on that.....please advice ....thanx

Hello,

You are right about the massive numbers of burs in the catalogs! This is what I suggest, call the companies (plenty to choose from like Dentsply) and tell them you would like to buy a fixed prosthodontics and operative burs kit. Also ask one for veneer prepration too. They have sets like this that you can buy as they make them for dental students kit. The fixed kit consists of different diamond burs like flat end, rounded end, torpedoes... and operative kit mostly consists of carbides. DP

 

[ivorinedust]

Hi Dr. Phan and friends:

Texts on tooth preps say that a little bit of roughness on the prep surface is actually desirable since it helps in retention after cementation of the crown (of course this does not apply to the prep margins). But examniners tend to grade you down when you present a typodont prep with light scratches on the surface. What gives?

Thanks.

Ivorinedust

"Apolonia, relieve my toothache!"

 

[Dr. Dai Phan]

Hi Dr. Phan and friends:

Texts on tooth preps say that a little bit of roughness on the prep surface is actually desirable since it helps in retention after cementation of the crown (of course this does not apply to the prep margins). But examniners tend to grade you down when you present a typodont prep with light scratches on the surface. What gives?

Thanks.

Ivorinedust

"Apolonia, relieve my toothache!"

I believe that competent examiners will NOT grade you down for roughness on the preps but rather for deep gouges. Common areas of deep gouges are seen on the margin (jagged edges) or in the proximals where the person is overzealous when trying to break contact. Like I mentioned in my earlier posts, use your SLOW speed with the diamond and you will be able to remove some deep gouges without fear. The roughness created by the diamond (NOT the finishing diamonds as these have colored bands on them) burs is what you need. DP

 

[dentaldoc]

I believe that competent examiners will NOT grade you down for roughness on the preps but rather for deep gouges. Common areas of deep gouges are seen on the margin (jagged edges) or in the proximals where the person is overzealous when trying to break contact. Like I mentioned in my earlier posts, use your SLOW speed with the diamond and you will be able to remove some deep gouges without fear. The roughness created by the diamond (NOT the finishing diamonds as these have colored bands on them) burs is what you need. DP

Dr.Dai phan, I really appreciate you sharing your experience with all of us. and I wanted to thank you for that! Goodluck in what ever you do

 

[Dr. Dai Phan]

Dr.Dai phan, I really appreciate you sharing your experience with all of us. and I wanted to thank you for that! Goodluck in what ever you do

You are more than welcomed and I am honored to be at your service. Any questions related to fixed,removable and maxillofacial prosthodontics, fire away... If I don't know the answer, I will try to make them up. DP

 

[DENTZY]

DR. DAI PHAN

I MESS UP THE BOXES ON MOD ONLAYS BADLY.I START OFF IN A GOOD WAY BUT END UP ROUNDING THEM OFF OR GOING TOO DEEP OR JUST CUTTING DOWN TOO BIG A CHUNK OF CUSPS.
WHAT SHOULD BE THE ANGULATION OF BOXES?I LOOKED UP IN STURDEVANT ,BUT I WAS NOT VERY HAPPY BY THE WAY THEY'VE DISCUSSED IT.

ALSO, I AM NOT HAPPY WITH USING THE TAPERED CARBIDE BUR FOR MAKING BOX.I BURN OUT THE TOOTH STR. & BUR WHEN MAKING INITIAL DITCHES(SOMETIMES EVEN WHEN I USE A NEW BUR)AND IF I REDUCE THE SPEED, THE BUR JUST DOESN'T SEEM TO CUT..COULD YOU TELL ME WHY DOES THAT HAPPEN?AM I USING THE BUR IN SOME WRONG WAY?IT DOES NOT HAPPEN WHEN USING A DIAMOND BUR.SO,CAN I USE SOME DIAMOND BUR? OR SOME OTHER TYPE OF BUR?
WHAT DO YOU RECOMMEND I SHOULD DO?
THAT IS TOO ANY QUES,BUT I WOULD APPRECIATE IF YOU CAN HELP ME OUT.

 

[ivorinedust]

Dear Dr. Phan:

Got any tricks to cut parallel grooves on a partial coverage crown? (3/4, 7/8)?

If I mess up my grooves on my posterior 3/4 can I make boxes instead?

Thanks


Ivorinedust

"Apolonia, relieve my toothache!"

 

[DENTZY]

DR. DAI PHAN

I MESS UP THE BOXES ON MOD ONLAYS BADLY.I START OFF IN A GOOD WAY BUT END UP ROUNDING THEM OFF OR GOING TOO DEEP OR JUST CUTTING DOWN TOO BIG A CHUNK OF CUSPS.
WHAT SHOULD BE THE ANGULATION OF BOXES?I LOOKED UP IN STURDEVANT ,BUT I WAS NOT VERY HAPPY BY THE WAY THEY'VE DISCUSSED IT.

ALSO, I AM NOT HAPPY WITH USING THE TAPERED CARBIDE BUR FOR MAKING BOX.I BURN OUT THE TOOTH STR. & BUR WHEN MAKING INITIAL DITCHES(SOMETIMES EVEN WHEN I USE A NEW BUR)AND IF I REDUCE THE SPEED, THE BUR JUST DOESN'T SEEM TO CUT..COULD YOU TELL ME WHY DOES THAT HAPPEN?AM I USING THE BUR IN SOME WRONG WAY?IT DOES NOT HAPPEN WHEN USING A DIAMOND BUR.SO,CAN I USE SOME DIAMOND BUR? OR SOME OTHER TYPE OF BUR?
WHAT DO YOU RECOMMEND I SHOULD DO?
THAT IS TOO ANY QUES,BUT I WOULD APPRECIATE IF YOU CAN HELP ME OUT.

Dr.Dai Phan
Please answer my questions

 

[ivorinedust]

Dr.Dai Phan
Please answer my questions

Hi Dentzy:

With tons of respect for Dr. Phan, allow me to make a few comments:

Burning the teeth with a carbide bur is caused by using a dull bur, too much pressure on the bur or both. If you observe that you over reduce your prep most of the time, or round off the line and point angles, chances are you are to aggresive in using the bur. I used to do that too

I use a hatchet to refine my boxes. I initially cut the boxes straight with a fissure carbide by continuing the isthmus to the proximals. Then I change to a 330 bur and drop my box. Then I go back to the tapered fissure and work on the enlarging box to about 1.0-1.5 deep (depending on tooth size) axially and gingivally. It does not matter if you do not break contact at this time. After you remove the remaining "proximal shell of enamel", start using the hatchet to exit the contact areas on the buccal and lingual at about 45 degree flare. Just shave off the contact a little at a time, starting at the occlusal. It does not pay to be impatient as you cannot cut a huge chunk of a typodont tooth with a hatchet anyway.

Be sure to allow enough space for the lab man's die saw.

Now you have 6 walls to your box: The buccal and lingual proximal walls, the buccal and lingual flares, the axial wall and the gingival floor . Make sure you put a bevel on the gingival floor and blend that in with the proximal flares. See to it that the walls of both mesial and distal boxes make no interference when the crown is seated. That means you have to make them divergent occlusally. Do not undercut the axial walls too.

I make my boxes 1.5mm deep axially at the most, but sometimes on some typodonts, that is deep enough to set the margin subgingivally. So use descretion. It will help if you make the isthmus REALLY shallow to begin with, only about 0.5mm so you can make a full 1.5mm axial wall without ever touching the gingival crest.

I hope this has been helpful. I am sure Dr. Phan has a lot more comments about this.

Humbly,

Ivorinedust

"Apolonia, relieve my toothache"

 

[DENTZY]

Hi Dentzy:

If you observe that you over reduce your prep most of the time, or round off the line and point angles, chances are you are to aggresive in using the bur. I used to do that too

Hi Ivorinedust
Thanks a lot for your help.I still have some doubts, though.
If I am so slow in preparing i wouldn't be able to complete my preps in exam.I got to know we hardly get an hour for each.So how do i make preps faster without burning?Do you use 170L carbide for boxes?

[/QUOTE]I use a hatchet to refine my boxes. I initially cut the boxes straight with a fissure carbide by continuing the isthmus to the proximals. Then I change to a 330 bur and drop my box. Then I go back to the tapered fissure and work on the enlarging box to about 1.0-1.5 deep (depending on tooth size) axially and gingivally. It does not matter if you do not break contact at this time. After you remove the remaining "proximal shell of enamel", start using the hatchet to exit the contact areas on the buccal and lingual at about 45 degree flare. Just shave off the contact a little at a time, starting at the occlusal. It does not pay to be impatient as you cannot cut a huge chunk of a typodont tooth with a hatchet anyway. Be sure to allow enough space for the lab man's die saw.[/QUOTE]

Do you define buccal and lingual walls with hatchet or do you make flares with hatchet?I couldnot follow that one...



Now you have 6 walls to your box: The buccal and lingual proximal walls, the buccal and lingual flares, the axial wall and the gingival floor . Make sure you put a bevel on the gingival floor and blend that in with the proximal flares. See to it that the walls of both mesial and distal boxes make no interference when the crown is seated. That means you have to make them divergent occlusally. Do not undercut the axial walls too.

[/QUOTE]It will help if you make the isthmus REALLY shallow to begin with, only about 0.5mm so you can make a full 1.5mm axial wall without ever touching the gingival crest.[/QUOTE]
Hope you can explain it more as to what that means

Thanks again for your help.

Dentzy

 

[ivorinedust]

Quoting Denzy:

Hi Ivorinedust
Thanks a lot for your help.I still have some doubts, though.
If I am so slow in preparing i wouldn't be able to complete my preps in exam.I got to know we hardly get an hour for each.So how do i make preps faster without burning?Do you use 170L carbide for boxes?[/COLOR]

170L should be good, but I use 169L

Do you define buccal and lingual walls with hatchet or do you make flares with hatchet?I couldnot follow that one...


I do both with the hatchet.



It will help if you make the isthmus REALLY shallow to begin with, only about 0.5mm so you can make a full 1.5mm axial wall without ever touching the gingival crest.[/QUOTE]
Hope you can explain it more as to what that means [/COLOR]

I make my isthmus after I do the occlusal reduction. Some people do the reverse, and that is okay too. Anyway you get the same result. If you cut the isthmus after occlusal reduction, make the pulpal floor very shallow, like 0.5 mm. If you prefer to cut it first, then make it around 1.5mm so, when you make the occlusal reduction, you end up with a 0.5mm deep floor. The reason for this is you'd like to make your boxes as deep/tall as possible for retention of the crown. My teacher says the boxes should be around 1.5mm tall to be effective.

If you begin with a deep pulpal floor, you'd suddenly find yourself too near or beyond the gingival line after you make a 1.5mm deep box. You'd want your margin to be supragingival on the typodont. Besides, you don't need a deep pulpal floor for an MOD as gold is unlike amalgam which could fracture if condensed too thin.

Ivorinedust

"Apolonia, relieve my toothache!"

 

[Dr. Dai Phan]

Exellent replies ! Thanks for helping me out with the answers. Before you spend too much time on 3/4 or 7/8 crowns, ask the schools if these are required. These are done so infrequent in the clinical settings that not many people are aware of their technical specifications. DP

 

[Dr. Dai Phan]

DR. DAI PHAN

I MESS UP THE BOXES ON MOD ONLAYS BADLY.I START OFF IN A GOOD WAY BUT END UP ROUNDING THEM OFF OR GOING TOO DEEP OR JUST CUTTING DOWN TOO BIG A CHUNK OF CUSPS.
WHAT SHOULD BE THE ANGULATION OF BOXES?I LOOKED UP IN STURDEVANT ,BUT I WAS NOT VERY HAPPY BY THE WAY THEY'VE DISCUSSED IT.

ALSO, I AM NOT HAPPY WITH USING THE TAPERED CARBIDE BUR FOR MAKING BOX.I BURN OUT THE TOOTH STR. & BUR WHEN MAKING INITIAL DITCHES(SOMETIMES EVEN WHEN I USE A NEW BUR)AND IF I REDUCE THE SPEED, THE BUR JUST DOESN'T SEEM TO CUT..COULD YOU TELL ME WHY DOES THAT HAPPEN?AM I USING THE BUR IN SOME WRONG WAY?IT DOES NOT HAPPEN WHEN USING A DIAMOND BUR.SO,CAN I USE SOME DIAMOND BUR? OR SOME OTHER TYPE OF BUR?
WHAT DO YOU RECOMMEND I SHOULD DO?
THAT IS TOO ANY QUES,BUT I WOULD APPRECIATE IF YOU CAN HELP ME OUT.

The boxes of the onlays should be divergent toward the occlusal like the angulation of your crown preps. The reason is that you can withdraw the pattern from the cast. Using carbide bur in my opinion in harder than using a small tapered diamond. In the hands of the beginner, you tend to gouge the preps (and opposing tooth) since these cut more efficicient than the diamond. Try the diamond and you will see that your chance of "tooth burning" is reduced. The reason of burning the tooth is you held too long and pressing too hard at the surface. Next time, ease up the pressure and go easy on the pedal too will help. DP