when you make amalgam preps, the margins are usually considered the dirtiest place for bacterial and plaque accumulation , so you extend the margin(make the prep bigger) in order to place the margin where it's easier to clean. Is this concept still widely used in private practices?
If you are talking about the buccal and lingual margins for an interproximal box, the answer is yes. There is considerable debate on the merits of extension for prevention on occlusal grooves though. Classic G.V. Black calls for extending the prep along all the grooves and also serves to dovetail the prep so the amalgam can mechanically lock in, but lately there are dentists who advocate if the grooves do not have a deep fissure and is well-coalesced, it shouldn't be breached. All I know is that two weeks from now when I take my NERB, I will have to do extension for prevention on my class-II patient.
But don't you think that's a way of taking away too much healthy tooth structure just to remove interproximal caries? how about when you are making prep for posterior composite? I heard you can be more consertive when you work with composite, but i am not sure. Thanks, and good luck with NERB.
The major reason for making the amalgam prep at least 2 mm deep is so that the amalgam can have adequate bulk to resist any occlusal forces exerted.......if the thickness of the amalgam is say 1.1 mm, it will be very prone to fracture. Composite restorations do not require the bulkiness to stay intact. I personally think that extension for prevention is malpractice all in itself. A lot of dentists also consider using an explorer to check for caries also malpractice (we'll argue about that at another time). Even if the lesion is a pinpoint incipient lesion in the distal of #5, you would have to remove all the good and healthy tooth structure on the occlusal and marginal ridge for an amalgam restoration. But what do I care right? I want to yank out teeth in the furture......think of how much healthy tooth structure I'd be wasting.
Anything more than 2mm is too aggressive for the initial outline form (this is from Sturdevant's Operative Dentistry text). 1.5mm depth is good enough for bulk strength, at least with the more modern high-copper Amalgam formulations that has been condensed properly. The reason why lots of dentists out there love using the #330 bur (particularly the Peds guys who have to work with young permanent teeth with large pulp chambers and extended pulp horns) is precisely because the cutting head is 1.5mm long. Cut along the grooves to just when the cutting head disappears, and you got yourself the perfect depth for an amalgam prep. All the licensing boards will require you to do extension for prevention. I don't agree with some of the rationale behind it either (to quote one of my instructors, "G.V. Black don't know ****!" ), but I guess that's the price we have to pay to get our foot in the door.
Maybe I'm wrong, but I believe the cutting surface of a #330 is 1.75mm? I couldnt find the size in sturdevant's, but I might have heard it in one of my pediatrics courses.
Bitecys and Doggie, it actually depends on the brand. They are technically listed at 1.5, but ours are 1.6. 1.75mm may be a stretch, but I don't think it's completely unfathomable.
Hmm... I wonder if there is a standards body that sets the dimensions for these burs...? Ever since I finished all my clinical requirements to graduate, I have too much time on my hands to ponder obscure questions like that! NERB next Wednesday... I've ran through the preps countless times on a typodont already in the past few weeks (makes me feel like a freshman LOL) with the Brasseler #330 establishing the perfect 1.5mm amalgam depth then cleaning things up with a #55L and planing the floor smooth... And I have a patient with the perfect board lesion lined up too! Damn I hate the waiting... Can't wait to get it over with.
Gavin, you learn something new every day...although I'd have to agree that 1.75 seems like a serious stretch considering the 330 is suppsed to give ideal depth. OH well, i seriously need to get back to learning my bony lesions for my oral path final tomorrow!
my school teaches that extension for prevention is unneccesary in most cases, we follow the technique in Summitt's "fundamentals of operative dentistry" - but we have to go back to (GV) Black for the WREB if it were my tooth i would want the most conservative prep possible, right?
