Need help with class I and II amalagam prep

[ayaska]

Hello. I'm having a very annoying problem with my first preparations- class I and II for amalgam. I have no idea what burs to use in order to make flat the pulp floor of the preparation. So far I've done 1 prep for class I and 1 for II and they've turned out too wideq covering more than half of the occlussal surface. The problem is that i always go back in order to flatten the floor of the cavity and in the process make the walls wider and wider and in the final shape is too wide. Can you give me any advice on how to avoid that and what bur to use? We're working on the Fresco plastic models.

---

Members don't see this ad.

 

[Screwtape]

Do you have a #57 bur (straight fissure bur?) ? I would use that along with a hatchet hand instrument. You should also ask your faculty. They know what burs you have available and which ones are better for certain things.

PS: If you end up using the #57, use it in the slow speed hand piece, or very slow speed on the high speed hand piece.

 

[jmh018]

I would also recommend a 57. The H can also be good for really refining some areas after going over it with a 57, especially the interproximal on a class II.

Do your professors not tell you what burs to use when first describing the prep?

 

[yappy]

330, 329 for initial prep depth & outline. Then 57 slow speed @ 10k; if you're really careful you can try it dry. It's so easy it will make you feel like you're cheating. It will perfectly smooth walls too.

 

[ayaska]

Thank you very much for the help I'll try the 57 and 330 329 combo with slow speed and see how it goes.

 

[dentalprodigy]

Here's how I tackle class 1's... If working on 19 for example. I'll make 3 holes along central fossa with a 1/2 round bur. This ensures I'm exactly in the middle of the occlusal and not too buccal/lingual. Then I'll connect these 3 dots with a 169. I prefer this because it's very pointy and accurate. After connecting the 3 dots with the 169, I'll make my buccal and lingual dove tails. Prep should look like a cross now (with central groove and buccal and lingual groove). Now I'll extend prep distally/mesially following the triangular fossas of the distal/mesial aspect. Be careful not to go too deep with the 169 because then you might go deeper than they ideal 1.5mm pulpal depth.

Now take a 56 carbide (straight fissure bur) and basically widen your outline into you can fit a small end of the condensor in & through whole prep. You can use 556 also for this (more flutes/cutting surfaces hence easier to cut).

Once you're happy with the width of prep(ideally should be width of condenser), take 331(inverted cone) and run it along cavosurface margins on buccal and lingual only. Then 169 for mesial and distal to create divergence.

My method to flatten and smoothen pulpal floor is to use a 35 bur. After you have 1.5mm pulpal depth (using 56/556), take brand new new 35 on a slow speed and using just the weight of hand piece run it along pulpal floor. This should make it smooth.

For class 2's, after I'm done my class 1prep portion, I take a high speed with 56(I prefer 556) and go straight from mesial aspect of the class 1> to the interproximal contact/ marginal ridge. Thin marginal contact until u can break it with hand instruments(hatchets). Make your reverse s curve, extend width, adjustments with 556 again followed by 35 to match the pulpal floor smoothness.

Now some ppl drop the box (of class 2 prep) with 56 but I find a 33. 1/2 to do the job better because it sinks in better. You can use any small but pretty much... 34, 1/2 round bur. One box is dropped, I'll switch to 35 to make its floor smooth. Use 34 for those corners of the gingival box that the 35 can't reach in.

Try these and see what works for you.

I have faculty who use 330 for the whole thing. Another professor uses just 56. Some classmates of mine prefer the “floor bur” to make pulpal floor smooth. Use whatever works for you

Sent from my HTC One_M8 using Tapatalk

 

[ayaska]

Thank you

 

[Bis-GMA111]

i personally use a 1556 for the whole thing and don't touch the slow speed. with that said, when i started off, i used a 330, simply because a 330 measures to be ~2mm which is how deep your prep should be. as the first poster suggested, if you were to drill on #19 for instance...i would start in the central fossa and go down the full cutting length of the 330and extend this dot mesially. make sure this part is level. then from the dot that you made in the central fossa extend the preparation distally. then make the ''dove tails'' along the central fossa faciolingually (for retention). also keep in mind that you don't want to extend the preparation into the marginal ridges for a class 1. only slightly into the mesial and distal fossas.

theoretically the 2 spots that are of concern depth wise are these dovetails. but, professors like to see a uniform depth of 1.5 (or 1.7mm depending onw hat school you go to)-2mm throughout the prep or 1mm into dentin.

should you use a 330 bur, you would have to flatten the floor using a slow speed due to the pear shape of the 330. i would personally use the fissured 56 slow speed and lightly smoothen everything out. if it turns out you've gone too far pulpally, (i.e. are at about 2mm already), very very carefully go over your pulpal floor without adding too much pressure with the slow speed. another trick is to go over it again with the slowspeed on reverse to smoothen everything out. the bur doesn't cut when on reverse. **note that this is not ideal for a patient since reverse on a slowspeed would cause a lot of ringing and discomfort to the patient** so only use for a typodont.

what else....the prep (as i'm taught in my school--using modified g.v. black aka minimal preparation) is to keep the preparation about 1mm faciolingually for an 'ideal' prep. if you've been introduced to hand instruments, try using a hoe to measure the FL width. it should fit snugly. also you can use that to scrape and unsupported enamel from your prep. another way to check the width is to use a 1mm amalgam plugger.

class II: same concept, except you just extend the respective area over the marginal ridge. we're taught to keep this extension in a relatively straight line to hit the adjacent contact. i've seen work from other students from diff schools where they have their proximal boxes in a ( ) sort of fanned out shape, which from what i understand is classic g.v. black. same general concept though--break gingival contact and have a converging proximal box. get rid of unsupported enamel by using a combo of angled hatchets/hoes or just use a flame bur or a slow speed.

in real life though--just chase the decay.

not to worry though. it took me a while to prep my first teeth, but with a lot of practice, i was able to do a class one in about 5 minutes by the end of my first year. just keep at it and do not be afraid to ask for help. good luck!

 

[yappy]

Thank you very much for the help I'll try the 57 and 330 329 combo with slow speed and see how it goes.

Sorry. Just to be clear I always use 330 or if it's a small prep 329 in my high speed handpiece. I have a latchkey 57 that I use on slow speed to smooth everything else out. GL

 

[Bis-GMA111]

oh and another tip. for class I, (or the class 1 portion of a class 2), make sure your facing walls on the occlusal are at a slightly acute angle. remember, for amalgam preparations you have to create retention so the filling stays in.

 

[Bis-GMA111]

how does it work with dropping the proximal box with a 33 1/2 (just curious if i'm thinking about the same bur) the cutting surface is just way too small if i'm thinking of the right bur. often times i've found a 1556 to do the job, as it takes ~ 3mm to drop the box on a typodont tooth and the length of the cutting edge of the bur is 3.8 . i mean i know there is no set depth, as you're supposed to keep going to break gingival contact, but i was just wondering

@dentalprodigy

 

[dentalprodigy]

how does it work with dropping the proximal box with a 33 1/2 (just curious if i'm thinking about the same bur) the cutting surface is just way too small if i'm thinking of the right bur. often times i've found a 1556 to do the job, as it takes ~ 3mm to drop the box on a typodont tooth and the length of the cutting edge of the bur is 3.8 . i mean i know there is no set depth, as you're supposed to keep going to break gingival contact, but i was just wondering

@dentalprodigy

I'll start sinking my proximal wall with 33 1/2 (by going back and forth until I'm happy with a decent depth), I'll switch to 34 later and repeat same back and forth motion. Now I'll be deeper and wider. Now I'll go to 35 and repeat.



Sent from my HTC One_M8 using Tapatalk

 

[doc toothache]

Hello. I'm having a very annoying problem with my first preparations- class I and II for amalgam. I have no idea what burs to use in order to make flat the pulp floor of the preparation. So far I've done 1 prep for class I and 1 for II and they've turned out too wideq covering more than half of the occlussal surface. The problem is that i always go back in order to flatten the floor of the cavity and in the process make the walls wider and wider and in the final shape is too wide. Can you give me any advice on how to avoid that and what bur to use? We're working on the Fresco plastic models.

You have done one of each and you are disappointed that you couldn't frame them? The level of the pulpal floor is more a function of the steadiness in holding the handpiece as you move around the prep than on the type or size of the burr that you use.

 

[THS]

I second the 329/330. Pear-shaped burs prevent sharp angles in the prep, which may cause cusp fracture or amalgam failure in the future. I use the 329 for initial prep, then the 330 to smooth the walls and floors.

 

[Bis-GMA111]

I second the 329/330. Pear-shaped burs prevent sharp angles in the prep, which may cause cusp fracture or amalgam failure in the future. I use the 329 for initial prep, then the 330 to smooth the walls and floors.

true, 330s are good for those reasons but they don't give you flat floors. it is a rounded ''pear shaped'' end

 

[THS]

true, 330s are good for those reasons but they don't give you flat floors. it is a rounded ''pear shaped'' end

I just finished reading your post above, and I'll have to try the 56 in operative tomorrow. So far we have only done Class 1s, so my experience is limited. Hopefully this advice will put me ahead of my classmates!

 

[Msmouth]

I have tried a bunch of burs and my favorite is the 556 cross cut, high speed. For Class 2 I start my prep very near the proximal surface and outline the area where I need to open contact without actually breaking contact just yet. Then I follow the groove and make and complete the class 1 prep that leads to the proximal area. When I'm ready to open the contact area I wedge the tooth. At this point I should know how wide to go since I already outlined it. I continue with the same bur at the same level as the class I. Once that's done then I drop the box with a 169L (long). I drill down an additional 1 mm and then work my way in to form the axial wall. If I need more smoothing I use a 34/35 to smooth pulpal floors or a finishing diamond for the walls.
At first I barely used high speed but once you practice with it a lot and gain that hand control it clicks.
HTH