I’m not happy with my crown preps

[DOCI3]

I’m a 3rd year and I’ve done 3 crown preps so far (on patient). My 1st prep was mandibular molar and it went perfectly. My 2nd was maxillary molar and I over reduced interproximally and my margins were rough and inconsistent. My faculty was pretty hard on me and wouldn’t let me do anymore till I practiced on manikin for over a month. This put me back schedule wise and took up a lot of my time outside clinic, but I did it. I did my 3rd prep on maxillary premolar a week ago and again over reduced interproximals with inconsistent rough margins. I don’t know what to do. I’m feeling discouraged and scared of being stopped from prepping but I also think patient preps are the only way I will get better. It doesn’t help that I’m scared of my faculty banning me again and that I’m worried I’m doing my patients more harm than good. Any thoughts, comments, tips or advice is welcome.

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[AppalachianDentalBoy]

What burrs are you using to reduce proximally?

 

[DOCI3]

What burrs are you using to reduce proximally?

break contact w flame, follow through with 1/2 DT

 

[AppalachianDentalBoy]

break contact w flame, follow through with 1/2 DT

Have you tried different approaches? We initially break contact with a 169L then follow it with one of the skinnier diamond burs (blanking rn). Stevenson Dental Solutions on youtube has some good content if you'd like to see some different ways from your instructors

 

[knewstance]

I like to use a large chamfer bur with no water at a low speed to finish and provide a final "set point" on my margins. I will usually do this with direct vision if possible as the final thing that I do for my preparation.

Interproximal on maxillary molars is tough, I will spend some time finding the perfect position with the mirror if direct vision isn't an option.
Another thing that I find helpful sometimes is to brace the head of the handpiece with my opposite hand, adding some additional stability.

 

[TanMan]

I’m a 3rd year and I’ve done 3 crown preps so far (on patient). My 1st prep was mandibular molar and it went perfectly. My 2nd was maxillary molar and I over reduced interproximally and my margins were rough and inconsistent. My faculty was pretty hard on me and wouldn’t let me do anymore till I practiced on manikin for over a month. This put me back schedule wise and took up a lot of my time outside clinic, but I did it. I did my 3rd prep on maxillary premolar a week ago and again over reduced interproximals with inconsistent rough margins. I don’t know what to do. I’m feeling discouraged and scared of being stopped from prepping but I also think patient preps are the only way I will get better. It doesn’t help that I’m scared of my faculty banning me again and that I’m worried I’m doing my patients more harm than good. Any thoughts, comments, tips or advice is welcome.

Try not to work with that faculty ever again. Sounds like a powertripping faculty that decreased your confidence and making you doubt yourself. You should do some research on which faculty are easier and take a more real world approach to restorative.

Define overreduced interproximals. Were you anywhere near the pulp? Did you compromise your ferrule or coronal structure? Why was the crown indicated in the first place? Ideal preps rarely happen because ideal lesions/fractures are not too common. There's almost always deviation from ideal preps (besides building the tooth back up and prepping, but even that has its own limitations). Ask any labtech, overreduction is better than underreduction. Underreduction tends to lead to restorative failure or unnatural contours.

Rough margins can be prevented/fixed with larger shoulder burs. With larger shoulder burs, the working end of the bur prevents you from slipping/roughening of the margin, whereas a larger bur prevents you from gouging your axial wall. I like coarse/extracoarse burs for improved micromechanical retention, even though that idea is up for debate. If available, always use high speed, avoid the slow speed. Slow speed chatters too much and as the name implies, it is slow. If you're afraid of interprox damage, use a wedge guard or when prepping, follow the adjacent tooth ridge, not the DEJ. This should help reduce overprepping of interprox and keep your eye on preventing adjacent tooth damage.

 

[schmoob]

Do your occlusal reduction first, it will make breaking contact much easier and easier to see. You can use a flame, thin diamond or even a thin carbide to break the contact it doesn’t matter.
Definitely use a coarse bur for your margins. Ease up on the grip, finger rest, and use your opposite finger for stability if you need to.
Refine your margins with a fatter, fine chamfer. Go nice and smooth WITH WATER and you should feel it glide along the margin. Never use a smaller chamfer because you will always end up with a J-lip.

like to use a large chamfer bur with no water at a low speed to finish and provide a final "set point" on my margins.

Do NOT do this. It’s one thing on a typodont, but not on a patient.

 

[knewstance]

Do NOT do this. It’s one thing on a typodont, but not on a patient.

This is debatable. Not something I'm going to argue online.

 

[schmoob]

This is debatable. Not something I'm going to argue online.

Nothing wrong with some friendly academic discussion.

But no, it’s not debatable:

Effect of cooling water temperature on the temperature changes in pulp chamber and at handpiece head during high-speed tooth preparation - PubMed

The temperature changes in the pulp chamber and at the handpiece head were above harmful thresholds when tooth preparation was performed without cooling water. However, cooling water of all temperatures prevented harmful critical temperature changes even though water at 35°C raised temperatures...

pubmed.ncbi.nlm.nih.gov

In vitro assessment of temperature change in the pulp chamber during cavity preparation - PubMed

Within the limitations of this in vitro study, the results indicate that reducing the amount of water cooling or increasing air pressure and load during cavity preparation increased the temperature of the pulp chamber in extracted teeth.

pubmed.ncbi.nlm.nih.gov

You shouldn’t be able to smell your prep or be covered in dust. If you cause pulpitis and get sued or reported to the board, you don’t have a leg to stand on when they find out you didn’t use water. Actually even if you didn’t cause it, if the board or expert witnesses find out you didn’t use water you will be held liable because the most logical explanation is the damage is iatrogenic.

 

[TanMan]

Besides preventing the overheating of the pulp, cutting efficiency is higher with water. Multiport spray that sprays directly onto your bur is the best, since it is extremely hard to clog the bur. Slicing through a point contact v. broad contact makes a world of difference in whether your bur will stall or not and how much friction/heat you will generate. Heat makes us inefficient for a few reasons. One is potential for postop pain that you will probably have to deal with as a postop visit, second is slower cutting due to flutes/bur getting clogged with dentinal and carious debris, and finally, with heat, the debris becomes stickier and harder for your bur to advance. Heat doesn't matter so much when IF the tooth is endo treated and/or you are cutting in fractions of a second.

I'm all for efficiency and prepping with cool water is the way to go for the aforementioned reasons. Time = money, anything that slows you down costs you money. Doesn't matter if you have impeccable margins if you have postop pain afterwards.

 

[dPseh]

Do your occlusal reduction first, it will make breaking contact much easier and easier to see. You can use a flame, thin diamond or even a thin carbide to break the contact it doesn’t matter.
Definitely use a coarse bur for your margins. Ease up on the grip, finger rest, and use your opposite finger for stability if you need to.
Refine your margins with a fatter, fine chamfer. Go nice and smooth WITH WATER and you should feel it glide along the margin. Never use a smaller chamfer because you will always end up with a J-lip.


Do NOT do this. It’s one thing on a typodont, but not on a patient.

Learned my lesson the hard way in school. Prepping #15 alone and the water was killing me.
Prepped a bit without water, patient expressed sudden pain. Came back later with pulpitis and complaints of cold sensitivity.

OP: One thing that wasn’t mentioned was to refine your margins with an end cutting bur.
All other advice with bur selection is sound and all about preference.
I also agree with starting with occlusion reduction first for better visualization of what you’re working with.

 

[DrJeff]

My personal sequence that works for me.

#1 - lots of water running through my handpiece

#2 - occlussal/incisal reduction depth cuts

#3 - Open up the interproximal contacts - I typically just a 90* cyclinder diamond for this as I'll set my proximal wall tapers a step or 2 down my sequence

#4 - Occlusal reduction

#5 - Buccal and lingual wall reduction

#6 - set margins/taper proximal walls with a chamfer diamond of various sizes depending on the clincal situation

#7 - verfify all areas of reduction and prep for desired surface finish and adjust if needed before taking the scan of the prep, and then re verify that there is adequate reduction and no undercuts once I see my prep on the screen of the scanner

 

[Rambunctious]

I’m a 3rd year and I’ve done 3 crown preps so far (on patient). My 1st prep was mandibular molar and it went perfectly. My 2nd was maxillary molar and I over reduced interproximally and my margins were rough and inconsistent. My faculty was pretty hard on me and wouldn’t let me do anymore till I practiced on manikin for over a month. This put me back schedule wise and took up a lot of my time outside clinic, but I did it. I did my 3rd prep on maxillary premolar a week ago and again over reduced interproximals with inconsistent rough margins. I don’t know what to do. I’m feeling discouraged and scared of being stopped from prepping but I also think patient preps are the only way I will get better. It doesn’t help that I’m scared of my faculty banning me again and that I’m worried I’m doing my patients more harm than good. Any thoughts, comments, tips or advice is welcome.

You're coming on a forum asking what to do, you have to realize every dentist has a different opinion. Just do what your faculty says, we are not the ones that are going to pass or fail you, they are. If you go in there with a new technique you learned from here (not using water, different bur, etc) against what they said then you will continue to be punished at school. Just know that we all went through what you're going through with ridiculous faculty. Grow thick skin and take your medicine. Once you pass dental school you can start listening to what other dentists do as far as shortcuts or whatever.

 

[TanMan]

You're coming on a forum asking what to do, you have to realize every dentist has a different opinion. Just do what your faculty says, we are not the ones that are going to pass or fail you, they are. If you go in there with a new technique you learned from here (not using water, different bur, etc) against what they said then you will continue to be punished at school. Just know that we all went through what you're going through with ridiculous faculty. Grow thick skin and take your medicine. Once you pass dental school you can start listening to what other dentists do as far as shortcuts or whatever.

You definitely have a point. If you want to maximize your dental school experience, do the absolute bare minimum of doing things the "dental school way". It's almost like you have a parallel education system in that you have to learn for the school, and you have to learn what's efficient and profitable.

What I did was that I made sure to work with faculty that didn't really care so much about how to do things but the results. Results oriented instructors tend to be better and dentists who keep it real. The worst ones are the full time academics who have no idea about real world dentistry. If you frame your thought processes and gear it up for efficiency, you will be miles ahead of your colleagues when you get out into the real world. Otherwise, good luck with doing 30min-1 hour fills, 10 appt dentures, hour long endos, and so on...

Anyway, here's a primer on fast crown prepping:
1. Use a wheel bur that has a height of 2mm. Instant 2 mm occlusal reduction with no depth cuts and nothing getting in your way. Should take a few seconds
2. Strip all the axial walls with a gross reduction bur. Slice through the interproximals with either a push or pull (whatever you have more control over). This will give you the view of the DEJ at the line angles. Strip the buccal lingual walls by following DEJ. What will slow you down here is the height of contour, so don't just move your bur from mesial to distal or distal mesial, since the buccal and lingual walls have a higher tendency to slow your cutting efficiency down. Cut with an upward stroke (towards the occlusal) to keep the bur clean, the tooth cooled, and less resistance. This step should take 30 seconds or less
3. Refine all the axial walls, line angles, and margins with an 847 bur. This one may take an extra minute or two.

Prep should take a few minutes at most. Keep your margins supragingival or equigingival. If you can't, use epi + surgical 557/round to trough and maintain a dry field. If you're going to prep first then endo afterwards, keeping it as supragingival as possible is preferred for the rubber dam clamp

 

[GoldMouth]

You definitely have a point. If you want to maximize your dental school experience, do the absolute bare minimum of doing things the "dental school way". It's almost like you have a parallel education system in that you have to learn for the school, and you have to learn what's efficient and profitable.

What I did was that I made sure to work with faculty that didn't really care so much about how to do things but the results. Results oriented instructors tend to be better and dentists who keep it real. The worst ones are the full time academics who have no idea about real world dentistry. If you frame your thought processes and gear it up for efficiency, you will be miles ahead of your colleagues when you get out into the real world. Otherwise, good luck with doing 30min-1 hour fills, 10 appt dentures, hour long endos, and so on...

Anyway, here's a primer on fast crown prepping:
1. Use a wheel bur that has a height of 2mm. Instant 2 mm occlusal reduction with no depth cuts and nothing getting in your way. Should take a few seconds
2. Strip all the axial walls with a gross reduction bur. Slice through the interproximals with either a push or pull (whatever you have more control over). This will give you the view of the DEJ at the line angles. Strip the buccal lingual walls by following DEJ. What will slow you down here is the height of contour, so don't just move your bur from mesial to distal or distal mesial, since the buccal and lingual walls have a higher tendency to slow your cutting efficiency down. Cut with an upward stroke (towards the occlusal) to keep the bur clean, the tooth cooled, and less resistance. This step should take 30 seconds or less
3. Refine all the axial walls, line angles, and margins with an 847 bur. This one may take an extra minute or two.

Prep should take a few minutes at most. Keep your margins supragingival or equigingival. If you can't, use epi + surgical 557/round to trough and maintain a dry field. If you're going to prep first then endo afterwards, keeping it as supragingival as possible is preferred for the rubber dam clamp

Hey TanMan, thanks for detailing your workflow! Just wondering if you do any depth cuts or anything to help ensure you're not under or overprepping the crown. I've also seen a video on the 'reverse crown prep' where you prep the margin first with a ~1mm round bur and then prep occlusally/all walls (I've had some graduated dentists report good efficiency with this technique, but I've yet to try it on a patient).

Also, is the wheel bur you mention just a diamond wheel? Do you mean the wheel has a thickness of 2mm (so using the flat side to reduce) or that the diameter of the wheel is 2mm (so using it perpendicularly to the occlusal surface to reduce)?

And I 100% agree with picking the more 'real world' instructors... so much easier to work with and oftentimes, a hell of a lot nicer

 

[Rambunctious]

You definitely have a point. If you want to maximize your dental school experience, do the absolute bare minimum of doing things the "dental school way". It's almost like you have a parallel education system in that you have to learn for the school, and you have to learn what's efficient and profitable.

What I did was that I made sure to work with faculty that didn't really care so much about how to do things but the results. Results oriented instructors tend to be better and dentists who keep it real. The worst ones are the full time academics who have no idea about real world dentistry. If you frame your thought processes and gear it up for efficiency, you will be miles ahead of your colleagues when you get out into the real world. Otherwise, good luck with doing 30min-1 hour fills, 10 appt dentures, hour long endos, and so on...

Anyway, here's a primer on fast crown prepping:
1. Use a wheel bur that has a height of 2mm. Instant 2 mm occlusal reduction with no depth cuts and nothing getting in your way. Should take a few seconds
2. Strip all the axial walls with a gross reduction bur. Slice through the interproximals with either a push or pull (whatever you have more control over). This will give you the view of the DEJ at the line angles. Strip the buccal lingual walls by following DEJ. What will slow you down here is the height of contour, so don't just move your bur from mesial to distal or distal mesial, since the buccal and lingual walls have a higher tendency to slow your cutting efficiency down. Cut with an upward stroke (towards the occlusal) to keep the bur clean, the tooth cooled, and less resistance. This step should take 30 seconds or less
3. Refine all the axial walls, line angles, and margins with an 847 bur. This one may take an extra minute or two.

Prep should take a few minutes at most. Keep your margins supragingival or equigingival. If you can't, use epi + surgical 557/round to trough and maintain a dry field. If you're going to prep first then endo afterwards, keeping it as supragingival as possible is preferred for the rubber dam clamp

The wheel bur is what i use but it will straight flatten the occlusal. It works in the real world for what we do but if we did that back in dental school without following the occlusal anatomy, instant failure. Maybe it was just UOP but man they were extremely anal

 

[TanMan]

Hey TanMan, thanks for detailing your workflow! Just wondering if you do any depth cuts or anything to help ensure you're not under or overprepping the crown. I've also seen a video on the 'reverse crown prep' where you prep the margin first with a ~1mm round bur and then prep occlusally/all walls (I've had some graduated dentists report good efficiency with this technique, but I've yet to try it on a patient).

Also, is the wheel bur you mention just a diamond wheel? Do you mean the wheel has a thickness of 2mm (so using the flat side to reduce) or that the diameter of the wheel is 2mm (so using it perpendicularly to the occlusal surface to reduce)?

And I 100% agree with picking the more 'real world' instructors... so much easier to work with and oftentimes, a hell of a lot nicer

When we think about prepping, we think about the absolute reduction of tooth structure, but I prefer to see it with the relative distance to the opposing tooth and in excursives as well. You can meet your minimum thickness in MIP, but depending on the steep curvatures, canine/group guidance and slopes, you may not meet your minimum thickness standards in excursives. When designing the crown, I like to try and maintain the cuspal heights of the adjacent teeth and following the cuspal inclinations of the opposing teeth. The height of a 909 bur comes in different heights. I prefer 2.0 since it is way safer than a 1.5 reduction and you use the flat side to reduce. To maintain your slopes, there's two ways, either just use the flat end parallel to the slope OR flatten it then use a rounded football diamond to increase central groove depth and create new slopes. For suspected fractures, I prefer flattening first since I can visualize fractures a LOT more easily than if I were to prep parallel to the slope in hopes of maintaining the existing cuspal inclinations.

My philosophy is that the less time you spend cutting the tooth, the less trauma you're inflicting on it. And of course, the more productive you are.

The wheel bur is what i use but it will straight flatten the occlusal. It works in the real world for what we do but if we did that back in dental school without following the occlusal anatomy, instant failure. Maybe it was just UOP but man they were extremely anal

Yeah, that's school for you. You can still maintain the slopes with a wheel bur, but it makes more sense to flatten initially to see the extent of the fractures. That's why I say dental school is like doing school twice. You have to learn their way and the real way.

 

[Rambunctious]

When we think about prepping, we think about the absolute reduction of tooth structure, but I prefer to see it with the relative distance to the opposing tooth and in excursives as well. You can meet your minimum thickness in MIP, but depending on the steep curvatures, canine/group guidance and slopes, you may not meet your minimum thickness standards in excursives. When designing the crown, I like to try and maintain the cuspal heights of the adjacent teeth and following the cuspal inclinations of the opposing teeth. The height of a 909 bur comes in different heights. I prefer 2.0 since it is way safer than a 1.5 reduction and you use the flat side to reduce. To maintain your slopes, there's two ways, either just use the flat end parallel to the slope OR flatten it then use a rounded football diamond to increase central groove depth and create new slopes. For suspected fractures, I prefer flattening first since I can visualize fractures a LOT more easily than if I were to prep parallel to the slope in hopes of maintaining the existing cuspal inclinations.

My philosophy is that the less time you spend cutting the tooth, the less trauma you're inflicting on it. And of course, the more productive you are.



Yeah, that's school for you. You can still maintain the slopes with a wheel bur, but it makes more sense to flatten initially to see the extent of the fractures. That's why I say dental school is like doing school twice. You have to learn their way and the real way.

i agree