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Medical Forum / General / Dentistry / April 2005Fibre Posts
I don't place many posts but want to know what the regs are using, and a detailed explanation of placement procedure of fibre posts. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com I don't do many posts either. I've been using FiberKor from Pentron for quite a while when I do need one. Gates Glidden to remove gutta-percha. Appropriate post drill (with kit) Etch Wash (I use Microbrush applicators to make sure all of the etchant is gone from the post hole) Damp dry (more Microbrushes) Bond 1/air/cure Cement It or Build It into post hole and on post Place Cure More Build It if needed JME, Fawks > I don't place many posts but want to know > what the regs are using, and a detailed explanation [quoted text clipped - 5 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com The few posts that I use are Fiber-Posts from Whale. I usually will lute them with Unicom. Frequently, I will NOT core up anything around them, just scan and mill. I can set the milling machine to mill some space around the post, and bond the restoration with SO-100 which then becomes my bonding adhesive as well as my core. > I don't place many posts but want to know > what the regs are using, and a detailed explanation [quoted text clipped - 5 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com > I don't place many posts but want to know > what the regs are using, and a detailed explanation > of placement procedure of fibre posts. Fiber 1 (WhaleDent) drill access, Touch 'N Heat, GG's and appropriate drill matched to post size (They give you an acetate with black silhouettes of the posts. You put them against the P/A xray and guage the size you want, as well as the length). Try it in the canal. Cut apical end with Brassler Separating Disk. UltraEtch the post, leave it in dappen dish; UltraEtch the canal; Rinse it well; dry with paper points (shows if any residual etch is present). Single Bond the canal. Wait fifteen seconds with unit light away from work area. Draw off the XS with paper point, blow air till no movement. Cure. Rinse/Dry Fiber one post and paint with SingleBond. Air, cure. Leave in locking college pliers or hemostat. Set Amalgammator to highest speed possible, and its time to 12 secs. Activate Filtek Rely-X Unicem capsule and shake it in Amalgammator. Place in special pliers (exactly like your Fuji 9 pliers), open the little spigot on the capsule and inject it in the canal. DO NOT LENTULO this stuff! Place post at canal opening and release pliers/hemostat. Push/Pull the post gradually but quickly into the canal to evenly distribute the ciment. Hold it in place and cure it. Wait a minute, and spoon off the excess. Wait a couple of minutes again. While waiting, go beat the sh.t out of a few passersby. UltraEtch and SigleBond the supragingival mess. Build up the core in Filtek P-60. Haven't tried the newer autocure core buildups, so can't say. They sure look inviting though. These things are still radiolucid. I'm gonna try the Bertolotti clear light transmitting posts next. They're supposedly radio opaque Cheers SP  SignatureFinally: take out the TRASHH I am using posts with curaray Se bond and flow composite inside.The upper paret I was bilt by photo core mostly.only its important to remember about cleaning and apt application of bonding systems into root canal.You can cure it by light cure transponders tips.Its better when post has machanical retension as best as possible. regards > I don't place many posts but want to know > what the regs are using, and a detailed explanation [quoted text clipped - 5 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com > I am using posts with curaray Se bond and flow composite inside.The upper > paret I was bilt by photo core mostly.only its important to remember about > cleaning and apt application of bonding systems into root canal.You can cure > it by light cure transponders tips.Its better when post has machanical > retension as best as possible. > regards Krzysztof, by 'light cure transponders' do you mean the new SnowPost that Ray Bertolotti talks about? These are supposed to trasmit the light all the way down to the end of the post. Incidentally, <RB> also recommends Photo Core. Thanks SP SignatureFinally: take out the TRASHH When I saw the word, "fibre" I thought this was another Jan Drew dtizy idea for reducing the effects of amalgamitis ......... Post Toasties With Fibre or something like that. (Prevents "nearly dying ....") Joel > I don't place many posts but want to know > what the regs are using, and a detailed explanation [quoted text clipped - 5 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com Thanks to all the regs who responded. >> I don't place many posts but want to know >> what the regs are using, and a detailed explanation [quoted text clipped - 5 lines] >> Take out the G'RBAGE >> wubbabubbazG@RBAGEyahoo.com -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com > Thanks to all the regs who responded. I missed this. When I place posts, I use parallel steel posts, cemented with Durelon, bonded core. I'm just an old fashioned-guy. Steve >>>I don't place many posts but want to know >>>what the regs are using, and a detailed explanation [quoted text clipped - 11 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 >> Thanks to all the regs who responded. > > I missed this. When I place posts, I use parallel steel posts, >cemented with Durelon, bonded core. I'm just an old fashioned-guy. > >Steve Have been doing Dentatus with fugi 2 mmx, but recently switched to fugi 9. Am probably going to switch to a bonded fibre post. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com I prefer the fibre-posts for same reason I don't do ferrules on crowns. I want the restorative material to break before the tooth does. It is much easier to make a post and core than place an implant. Signature~+--~+--~+--~+--~+-- Stephen Mancuso, D.D.S. Troy, Michigan, USA .................................................... This posting is intended for informational or conversational purposes only. Always seek the opinion of a licensed dental professional before acting on the advice or opinion expressed here. Only a dentist who has examined you in person can diagnose your problems and make decisions which will affect your health. ...................... > >>> Thanks to all the regs who responded. [quoted text clipped - 13 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com I don't use fiber posts, but if I did, I'd use Max-Cem. It's a dual-cure, self-etching, self-adhesive resin cement made by Kerr. The syringe is automix, and the kit even comes with special tips that you can place down in the canal and inject the cement as you withdraw it. Since it's a resin, you can do a resin buildup that will bond directly to any excess that expels from the canal while seating the post. 3M makes a similar product called Unicem, but it needs to be triturated...and I don't own a triturator any longer. Pulpdent makes a similar product too, called Embrace. > Thanks to all the regs who responded. >> [quoted text clipped - 13 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com The fundamentals of restoring endodontically treated teeth are something we all know: conservation of tooth structure, adequate post length (if you use a post) good post fit, anti-rotation, ferrule. Most important element, from the viewpoint of longevity of the restoration, is ferrule. Which post material one uses is not very important, with the exception that there seems to be some evidence (there ain't much) showing that custom (not prefab) zirconia posts w/ceramic core might be a bad idea. >The fundamentals of restoring endodontically treated teeth are something we >all know: conservation of tooth structure, adequate post length (if you use [quoted text clipped - 4 lines] >there seems to be some evidence (there ain't much) showing that custom (not >prefab) zirconia posts w/ceramic core might be a bad idea. Whoa! Dump the ferrule. It is responsible for most of the crowns which snap off at the gingival crest .. Stephen Mancuso, D.D.S. Troy, Michigan, USA I am writing on a Tablet-PC,so forgive me if the PC misreads my handwriting. >>The fundamentals of restoring endodontically treated teeth are something >>we [quoted text clipped - 13 lines] > Dump the ferrule. It is responsible for most of the crowns which snap > off at the gingival crest But it prevents root fractures when there's a post. >>>The fundamentals of restoring endodontically treated teeth are something >>>we [quoted text clipped - 15 lines] > >But it prevents root fractures when there's a post. No, it accelerates the fracture. .. Stephen Mancuso, D.D.S. Troy, Michigan, USA I am writing on a Tablet-PC,so forgive me if the PC misreads my handwriting. Now THAT is an interesting concept, Dr. Steve, and I'd really like to hear you expand on it. >>>>The fundamentals of restoring endodontically treated teeth are something >>>>we [quoted text clipped - 17 lines] > > No, it accelerates the fracture. Perhaps you're talking about something different. I'm talking about having the crown margins extend beyond the buildup so that the margin encircles the tooth and root. Saying that a ferrule accelerates root fracture is like saying that a crown accelerates vertical fractures down the central fossa of teeth. It's counterintuitive. Simple physics (statics) can demonstrate why encirclement of the root is beneficial. If that's not convincing to you, then I'd refer you to the study done by Hoag and Dwyer: J Prosthet Dent. 1982 Feb;47(2):177-81. A comparative evaluation of three post and core techniques. Hoag EP, Dwyer TG. An in vitro study was performed evaluating three post and core techniques with and without full crown coverage on extracted mandibular molar teeth. The materials evaluated were amalgam, composite resin, and stainless steel posts, and a combination of cast-gold and stainless steel posts. The results indicate that the method of post and core technique may not be as significant as the placement of full coverage cast-gold crown restorations with sound design and placement of margins beyond the buildup restoration. My point (sorry to repeat for those who are tired of hearing me), is that for the cases where a ferrule would help, you are cutting away too much tooth structure and end up with a thin sliver of tooth holding everything together. In the cases where a ferrule leaves a lot of thickness (of tooth structure) between the pulp canal space and the outer preparation, the tooth would have held up without the ferrule. The average RCT tooth has had a few fillings in it of moderate to big size. Now we cut a big hole down the center to do the RCT. Ream it out a bit bigger for the post. Usually, you will place some core material to have smooth contours you can prep for your retention and resistance form. Of course, now you cannot see the inner surface the residual dentin. A lot of these teeth have some gingival recession and you want your margin 0.5-1.0 mm subgingival. So you reduce the buccal surface just shy of 2.0 mm and the lingual surface a "tad" less. But to get that 2.0 mm reduction at a height just below the gingival crest, you are removing 3-4 mm (sometimes more) of tooth at the height of buccal (and lingual) contour. You get your prep just like we were taught in school and send it off to the lab anticipating your lab tech telling you how perfect that prep looks on the model. If you were to extract that tooth at this stage and section it about 0.5 mm above the margin, you would find that you now have paper thin dentin walls holding the whole thing together. The least little bit of parafunction, or trauma and "S-N-A-P". If you made a really good post, the "snap" occurs at the tip of the post and breaks the root in 2-3 pieces. My recommendation is (except for teeth which are badly discolored), to reduce the vertical height of the tooth 3-4 mm, remove all the filling/core material, make the inner walls about 5-7 degrees of taper so that the occlusal line angles are divergent. Round these occlusal line angles. Round over the transition from the proximal boxes to the buccal and lingual walls, and STOP. Impression or scan time. Make the porcelain and bond in place. The center part of the restoration will be 6-10 mm thick. Horrendously strong. The cervical third of the tooth will be 3-5 mm thick both buccal and lingual--wonderfully strong. The entire occlusal surface will be covered so that parafunctional activity cannot force the cusps apart and cause (or perpetuate existing) fractures. You don't need the post if you have 3 mm of tooth sticking up. If you don't have 3 mm of tooth sticking up, the tooth will probably snap off in the next 5-10 years--regardless of any post. The presence of a post places the vector of forces at the tip of post with lateral parafunctional movement. When (and if) it fails, the root will break. Without the post, should the restoration fail, it will typically just chip (in response to parafunctional activity) in the occlusal third. I know which one I would rather re-treat. I often ask my patients if they would prefer a rigid post going half way down their root which will transmit forces down its entire length and if it fails will break the root, or would they rather skip the post and leave the weakest point somewhere were we can repair it 50 times with damaging the tooth. No one wants a post. Posts are great when you have to play hero and put an existing PFM back on which snapped off at the gingival crest (wonder why?). You tell the patient this is only going to last 1-4 years, set the post, do a reverse-core and cement the PFM back on. Ferrules, are what we were taught in dental school. If you stop, ignore what you were taught in DS, and pretend you were looking at the problem the first time in your life. You are staring down at the tooth from the occlusal view. You have all the filling out of the tooth, the RCT is done and you have trimmed the gutta percha back into to the root. You visualize how much tooth will be cut off for the perfect ferrule at the gingival crest. You look at how much good healthy strong tooth you are cutting away to create paper thin axial walls. You would never choose to do ferrules. Signature~+--~+--~+--~+--~+-- Stephen Mancuso, D.D.S. Troy, Michigan, USA .................................................... This posting is intended for informational or conversational purposes only. Always seek the opinion of a licensed dental professional before acting on the advice or opinion expressed here. Only a dentist who has examined you in person can diagnose your problems and make decisions which will affect your health. ...................... > >>>>>The fundamentals of restoring endodontically treated teeth are [quoted text clipped - 43 lines] > significant as the placement of full coverage cast-gold crown restorations > with sound design and placement of margins beyond the buildup restoration. >You would never choose to do ferrules. Don't think that I have ever done a ferrule, except during plumbing. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com > >You would never choose to do ferrules. R E P L Y A ferrule is a type of cat, right? Joel > >-- > >~+--~+--~+--~+--~+-- > >Stephen Mancuso, D.D.S. > > Don't think that I have ever done a ferrule, > except during plumbing. QUESTION: The cat or something else? > -- > > W_B > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com Hogs too, especially in the Appalachian Mountains. Fawks > R E P L Y > [quoted text clipped - 18 lines] >>Take out the G'RBAGE >>wubbabubbazG@RBAGEyahoo.com > My point (sorry to repeat for those who are tired of hearing me), is that > for the cases where a ferrule would help, you are cutting away too much [quoted text clipped - 11 lines] > 0.5-1.0 mm subgingival. So you reduce the buccal surface just shy of 2.0 > mm and the lingual surface a "tad" less. The amount of reduction on the facial at the margin is 1mm...and a "tad" less on the lingual. I'm doing a lot of Wol-Ceram crowns, and you don't need to do as much reduction at the margin as you do for Cerecs. > But to get that 2.0 mm reduction at a height just below the gingival > crest, you are removing 3-4 mm (sometimes more) of tooth at the height of > buccal (and lingual) contour. More like 1.5mm-2.0mm total reduction buccal-lingually at the margin. >You get your prep just like we were taught in school and send it off to the >lab anticipating your lab tech telling you how perfect that prep looks on [quoted text clipped - 3 lines] >parafunction, or trauma and "S-N-A-P". If you made a really good post, the >"snap" occurs at the tip of the post and breaks the root in 2-3 pieces. The shell is not really that thin on any tooth besides lower incisors or maxillary laterals. Below, you claim that without reduction, the tooth is 3-5 mm thick both buccal and lingual. If you reduce the buccal by 1 mm, and the lingual by 1/2-1mm, then the tooth is 2-4 mm thick on the buccal, and 2 1/2-4 1/2mm thick on the lingual. However, you have much more favorable force vectors. > My recommendation is (except for teeth which are badly discolored), to > reduce the vertical height of the tooth 3-4 mm, remove all the [quoted text clipped - 5 lines] > thick. Horrendously strong. The cervical third of the tooth will be 3-5 > mm thick both buccal and lingual--wonderfully strong. The internal stresses are enormous without the ferrule effect. In the scenario that you just described, you've created a pry-bar with an extra long lever-arm. A ferrule creates a *compressive* force on the wall of tooth that is on the same side that the force comes from. You are creating compression on a cylinder. A tooth without a ferrule creates a compressive force on the wall of tooth that is on the side *opposite* the force. Thus, you are creating tension on a cylinder. A cylinder is much stronger when loaded in compression. > The entire occlusal surface will be covered so that parafunctional > activity cannot force the cusps apart and cause (or perpetuate existing) > fractures. The long prybar is forcing the root apart. > You don't need the post if you have 3 mm of tooth sticking up. Agreed. > If you don't have 3 mm of tooth sticking up, the tooth will probably snap > off in the next 5-10 years--regardless of any post. I don't agree. A ferrule dissipates the lateral forces in such a way that much of tooth is in compression. Brittle materials are very strong in compression. > The presence of a post places the vector of forces at the tip of post with > lateral parafunctional movement. Some of the force, yes. But with a long enough post, you have a small force at the tip due to the long lever arm. With a short post, you have a high force at the tip. With a ferrule, the side of the tooth that the force comes from also shares some of the load with the other side of the tooth, and withthe portion of tooth in contact with the tip of the post. > When (and if) it fails, the root will break. Without the post, should the > restoration fail, it will typically just chip (in response to [quoted text clipped - 4 lines] > post and leave the weakest point somewhere were we can repair it 50 times > with damaging the tooth. No one wants a post. I avoid them as much as possible, but sometimes they're necessary. > Posts are great when you have to play hero and put an existing PFM back on > which snapped off at the gingival crest (wonder why?). Overprepped tooth because that darn Cerec requires a 2 mm shoulder prep all the way around. >You tell the patient this is only going to last 1-4 years, set the post, do >a reverse-core and cement the PFM back on. Pull the tooth and place an implant if it snaps to the gingival crest. I don't do reverse cores anymore because 1-4 years just isn't good enough. > Ferrules, are what we were taught in dental school. If you stop, ignore > what you were taught in DS, and pretend you were looking at the problem [quoted text clipped - 5 lines] > cutting away to create paper thin axial walls. You would never choose to > do ferrules. I graduated Mechanical Engineering and entered dental school. I looked at it from an engineering perspective and deduced that a ferrule helps prevent posts from fracturing roots. The only time that I use a post is when one entire wall of a tooth is gone (buccal or lingual). If I have two walls (even if one is only 2 mm high), I do a bonded core. If I have one wall, and a half wall (one cusp) on the other side, I do a bonded core. If I have zero walls (snapped to the gumline), I send to the surgeon for EXT and implant or bridge. We are on different pages. We don't have to agree when we are done discussing the topic. I don't mind. Kindly scroll. Signature~+--~+--~+--~+--~+-- Stephen Mancuso, D.D.S. Troy, Michigan, USA .................................................... This posting is intended for informational or conversational purposes only. Always seek the opinion of a licensed dental professional before acting on the advice or opinion expressed here. Only a dentist who has examined you in person can diagnose your problems and make decisions which will affect your health. ...................... > >> My point (sorry to repeat for those who are tired of hearing me), is that [quoted text clipped - 18 lines] > reduction at the margin > as you do for Cerecs. I don't reduce the cervical third on a CEREC-- unless I am trying to change the color of the tooth. >> But to get that 2.0 mm reduction at a height just below the gingival >> crest, you are removing 3-4 mm (sometimes more) of tooth at the height of >> buccal (and lingual) contour. > > More like 1.5mm-2.0mm total reduction buccal-lingually at the margin. 2.0 mm reduction at the CEJ requires 3-5 mm of reduction at the height of contour. >>You get your prep just like we were taught in school and send it off to >>the lab anticipating your lab tech telling you how perfect that prep looks [quoted text clipped - 12 lines] > on the buccal, and 2 1/2-4 1/2mm thick on > the lingual. However, you have much more favorable force vectors. I suggest you remove all the filling from the enter of a molar after you have done a full crown prep with 2.0 mm reduction down to the CEJ. The tooth is 3-5 mm thick buccal and lingual if the cervical third of the toothis NOT preped. With the cervical third of the tooth "un-prepped", the lever arm becomes much shorter. IF you prep to the CEJ, the lever arm (ie crown) is longer. >> My recommendation is (except for teeth which are badly discolored), to >> reduce the vertical height of the tooth 3-4 mm, remove all the [quoted text clipped - 15 lines] > creating tension on a cylinder. A cylinder is much stronger when loaded > in compression. You are thinnking of prepping down to the CEJ. Forget that concept. The ferrule does not create any compresion on the tooth. Especially after the lab uses die-separator. What you are doing is moving the fulcrum to the base of the ferrule. All of the crown above the margin is your lever arm. If the tooth is strong enough that parafunctional forces do not create force vectors which cause the post to break the root at the post tip, then there was enough tooth structure present that the post was NEVER needed in the first place. Remember that a post will never strengthen a tooth. It will only weaken it. >> The entire occlusal surface will be covered so that parafunctional >> activity cannot force the cusps apart and cause (or perpetuate existing) >> fractures. > > The long prybar is forcing the root apart. Nothing in the root except gutta percha. >> You don't need the post if you have 3 mm of tooth sticking up. > [quoted text clipped - 6 lines] > much of tooth is in compression. > Brittle materials are very strong in compression. If all your forces are vertical and there is never any parafunction, the restoration you describe will hold up fine (many do in this scenario). IF there is lateral parafunctional vectors of force, forget it. Joel liked to point out that shovel makers all put a ferrule on the end of the shovel blade. Where does a shovel handle break every time? >> The presence of a post places the vector of forces at the tip of post >> with lateral parafunctional movement. > > Some of the force, yes. But with a long enough post, you have a small > force at the tip due to the long lever arm. With a short post, > you have a high force at the tip. The longer the post, the narrower the root is at the tip. The longer the post, the greater force that can be exerted at the post tip when the ferrule weakens. You only need a post to retain a filling on the tooth. Any more post than needed to hld the filling is weakening the tooth. > With a ferrule, the side of the tooth that the force comes from also > shares some of the load with the other side of the tooth, and withthe > portion of tooth in contact with the tip of the post. And all that force is transmitted to the thinnest part of the tooth. >> When (and if) it fails, the root will break. Without the post, should >> the restoration fail, it will typically just chip (in response to [quoted text clipped - 6 lines] > > I avoid them as much as possible, but sometimes they're necessary. Only for heroic measures. They are great when you are trying to sneak some extra life out of a failed restoration. >> Posts are great when you have to play hero and put an existing PFM back >> on which snapped off at the gingival crest (wonder why?). > > Overprepped tooth because that darn Cerec requires a 2 mm shoulder prep > all the way around. I have never had a CEREC crown break a tooth off yet. I see PFM's ehich break the tooth off all the time. Remember, my point is that the cervical third of the tooth is strongest part of the tooth, and should be maintained at all cost. >>You tell the patient this is only going to last 1-4 years, set the post, >>do a reverse-core and cement the PFM back on. > > Pull the tooth and place an implant if it snaps to the gingival crest. I > don't do reverse cores anymore because 1-4 years just isn't good enough. I don't like 1-4 year restorations either, but a) it gets the crown into service while the patient decides, and b) it is the patient's choice what they ultimately get after proper informed consent. >> Ferrules, are what we were taught in dental school. If you stop, ignore >> what you were taught in DS, and pretend you were looking at the problem [quoted text clipped - 9 lines] > it from an engineering perspective and deduced that a ferrule helps > prevent posts from fracturing roots. The ferrule actuallly just keeps the post from loosening as quickly. > The only time that I use a post is when one entire wall of a tooth is gone > (buccal or lingual). If I have two walls (even if one is only 2 mm high), > I do a bonded core. If I have one wall, and a half wall (one cusp) on > the other side, I do a bonded core. If I have zero walls (snapped to the > gumline), I send to the surgeon for EXT and implant or bridge. I used to do the same. I then started looking at every core I did with the intra-oral camera. > We are on different pages. We don't have to agree when we are done > discussing the topic. I don't mind. Kindly scroll. [quoted text clipped - 32 lines] > 2.0 mm reduction at the CEJ requires 3-5 mm of reduction at the height of > contour. But crowns don't snap off the tooth at the height of contour. >>>You get your prep just like we were taught in school and send it off to >>>the lab anticipating your lab tech telling you how perfect that prep [quoted text clipped - 15 lines] > I suggest you remove all the filling from the enter of a molar after you > have done a full crown prep with 2.0 mm reduction down to the CEJ. I do that every time. I got out of the habit of leaving amalgams that "looked OK" because I got burned by decay from microleakage hiding beneath them. I always remove the old buildups/fillings. > The tooth is 3-5 mm thick buccal and lingual if the cervical third of the > toothis NOT preped. With the cervical third of the tooth "un-prepped", > the lever arm becomes much shorter. IF you prep to the CEJ, the lever arm > (ie crown) is longer. The coronal lever arm of the post is the length of the post from the top of the post and core to the point where the post first touches tooth. The radicular lever arm of the post is the length of the post from the tip of the post to the same exact point as mentioned above. Whether or not a tooth is prepped on the buccal at the gingiva or not will not affect the lever arm of the post. >>> My recommendation is (except for teeth which are badly discolored), to >>> reduce the vertical height of the tooth 3-4 mm, remove all the [quoted text clipped - 18 lines] > You are thinnking of prepping down to the CEJ. Forget that concept. The > ferrule does not create any compresion on the tooth. Sure it does...and it occurs on the same side of the tooth from where the force originates. That's the point of the ferrule. Until you can visualize that very important compressive force, you'll have a difficult time conceptualizing why the ferrule is important. > Especially after the lab uses die-separator. The space created by the die-separator is filled with a non-compressible resin or resin-modified glass ionomer cement with a very high compressive strength. Consequently, the space from the die-separator is irrelevent. > What you are doing is moving the fulcrum to the base of the ferrule. For the crown, maybe. The fulcrum of the post is still the point where the post first contacts the tooth. With a ferrule, if you have a load from the lingual, you effectively have three fulcrums: 1)one for the post, 2) one for the crown's buccal contact point, and one for the crown's lingual contact point . Consequently, the stress is dissipated over three different areas. That third area is a compressive force on the tooth/cylinder. With your design, there is one fulcrum...and the stress at that point is enormous. > All of the crown above the margin is your lever arm. With your design too...but all of that force is concentrated at one fulcrum point. Bad news! > If the tooth is strong enough that parafunctional forces do not create > force vectors which cause the post to break the root at the post tip, then > there was enough tooth structure present that the post was NEVER needed in > the first place. Remember that a post will never strengthen a tooth. It > will only weaken it. True. The only reason your design seems to be working OK so far is because of that really thick amount of tooth structurethat you're leaving at the gingival third. However, the lack of ferrule creates a much larger force on the single fulcrum point. The thickness is overcoming the additional load. If there's abfraction, and you put a post in that tooth without a ferrule, that tooth will split down the root...almost guaranteed. >>> The entire occlusal surface will be covered so that parafunctional >>> activity cannot force the cusps apart and cause (or perpetuate existing) [quoted text clipped - 3 lines] > > Nothing in the root except gutta percha. I thought we were talking about posts? >>> You don't need the post if you have 3 mm of tooth sticking up. >> [quoted text clipped - 12 lines] > to point out that shovel makers all put a ferrule on the end of the shovel > blade. Where does a shovel handle break every time? A ferrule provides "encirclement" on a tooth. I don't see the analogy. >>> The presence of a post places the vector of forces at the tip of post >>> with lateral parafunctional movement. And at the coronal contact point, but on the *opposite* side of the tooth in an *opposite* direction. That's really, really bad for teeth...and really, really good at splitting them. >> Some of the force, yes. But with a long enough post, you have a small >> force at the tip due to the long lever arm. With a short post, [quoted text clipped - 4 lines] > ferrule weakens. You only need a post to retain a filling on the tooth. > Any more post than needed to hld the filling is weakening the tooth. If you compare a post that is 9 mm long (from the gingival crest to the tip) to a post that is 3 mm long, the 3 mm post is tranmitting 3 times as much stress on the root of the tooth at the tip than the 9 mm post. That's the definition of a lever arm. Let's say that each post has the same height above the gingiva and that height is 9mm. If you place a 500 N force on the top of each post, then the force on the root with the 9mm post is 500N...and the force on the root with the 3 mm post is a whopping 1500N! I don't care how much thicker the root is at the coronal third vs. the apical third, the huge force from a short post more than negates the thickness advantage. >> With a ferrule, the side of the tooth that the force comes from also >> shares some of the load with the other side of the tooth, and withthe >> portion of tooth in contact with the tip of the post. > > And all that force is transmitted to the thinnest part of the tooth. But it's a much smaller force. >>> When (and if) it fails, the root will break. Without the post, should >>> the restoration fail, it will typically just chip (in response to [quoted text clipped - 18 lines] > I have never had a CEREC crown break a tooth off yet. I see PFM's ehich > break the tooth off all the time. I was just joking about those Cerecs. ;-) > Remember, my point is that the cervical third of the tooth is strongest > part of the tooth, and should be maintained at all cost. Not at the expense of creating a much larger force due to design. >>>You tell the patient this is only going to last 1-4 years, set the post, >>>do a reverse-core and cement the PFM back on. [quoted text clipped - 21 lines] > > The ferrule actuallly just keeps the post from loosening as quickly. No. It drastically changes the force vectors on the tooth. >> The only time that I use a post is when one entire wall of a tooth is >> gone (buccal or lingual). If I have two walls (even if one is only 2 mm [quoted text clipped - 5 lines] > I used to do the same. I then started looking at every core I did with > the intra-oral camera. What did the I/O camera show? >>>> But to get that 2.0 mm reduction at a height just below the gingival >>>> crest, you are removing 3-4 mm (sometimes more) of tooth at the height [quoted text clipped - 6 lines] > > But crowns don't snap off the tooth at the height of contour. Actually they do, because the height of contour for a PFM prep is at the margin. If your crown prep does not extend epically beyond the height of contour, the tooth never snaps off. >> I suggest you remove all the filling from the enter of a molar after you >> have done a full crown prep with 2.0 mm reduction down to the CEJ. [quoted text clipped - 3 lines] > from microleakage hiding beneath them. I always remove the old > buildups/fillings. If you have the filling material totoally removed while you are doing your crown prep, then I commend you for at least paying attention. All too often (because of our good training), we will clean out the caries first, remove all filling material, then core the tooth. After the core is set, we prep for the crown. I want you to be looking at the tooth with the core removed. >> The tooth is 3-5 mm thick buccal and lingual if the cervical third of the >> tooth is NOT preped. With the cervical third of the tooth "un-prepped", [quoted text clipped - 7 lines] > a tooth is prepped on the buccal at the gingiva or not will not affect the > lever arm of the post. Semantics we can agree to. >>>> My recommendation is (except for teeth which are badly discolored), to >>>> reduce the vertical height of the tooth 3-4 mm, remove all the [quoted text clipped - 23 lines] > visualize that very important compressive force, you'll have a difficult > time conceptualizing why the ferrule is important. That is an uneven compression with resultant tension on the opposite side. That would onlly serve to crush dentin. >> Especially after the lab uses die-separator. > > The space created by the die-separator is filled with a non-compressible > resin or resin-modified glass ionomer cement with a very high compressive > strength. Consequently, the space from the die-separator is irrelevent. I thought you ere talking about vertical forces creating compression in a uniform pressure circumpherentially. We were on different pages there. >> What you are doing is moving the fulcrum to the base of the ferrule. > [quoted text clipped - 6 lines] > tooth/cylinder. With your design, there is one fulcrum...and the stress > at that point is enormous. Having worked industrial and commercial construction for eight years, I will tell you that it does really work that way in the world. The strongest of the three points will bear all the stress. If a weaker fulcrum is further out along the lever arm than the stronger one, the weaker one will break before transfering stress to the stronger one. After the first fulcrum breaks, the stress will transfer to the second fulcrum further from the end of the lever arm. If this is not the stronger fulcrum, this too will give way. Once one of the fulcrums you describe give way, movement begins--due to either loosness or (more likelly) flexure. The movement will put greater stress on the remaining fulcrums. If the tooth does not snap, the post will come out and you will find that the post hole is now much wider than the post is (frictional wear). We can certainly discuss cantilevering 300 pound light fixtures over 60 foot drop-offs and discuss where the fulcrum is. The situation is not that different. > > All of the crown above the margin is your lever arm. > > With your design too...but all of that force is concentrated at one > fulcrum point. Bad news! If I have a 100 micron gap across the entire inner surface of the crown/core combination restoration, and have it bonded to place, then I simply have to design in resistance form so as to avoid shear forces to the bonded surface. >> If the tooth is strong enough that parafunctional forces do not create >> force vectors which cause the post to break the root at the post tip, [quoted text clipped - 9 lines] > without a ferrule, that tooth will split down the root...almost > guaranteed. No what I am doing is reporducing what nature created in the first place. You are placing a shovel blade over a wooden handle. (That sounds disrespectful when I re-read it, and please don't take it that way, this debate should be taken for what it truly is, two friends discussing a conflicting topic). >>>> The entire occlusal surface will be covered so that parafunctional >>>> activity cannot force the cusps apart and cause (or perpetuate [quoted text clipped - 5 lines] > > I thought we were talking about posts? Not for my technique. Why do we need a post if we have 1/3 to 1/2 the vertical height of the tooth "un-touched".?? >>>> If you don't have 3 mm of tooth sticking up, the tooth will probably >>>> snap off in the next 5-10 years--regardless of any post. [quoted text clipped - 10 lines] > > A ferrule provides "encirclement" on a tooth. I don't see the analogy. What I am *mostly* trying to get you to see [just so that we both are taking the same thing :-) ], is that cutting away the height of contour and destroying all that good tooth structure to create a ferrule does not make sense--to me. Things (including teeth) break at their weakest point. The weakest point--in the absence of fractures--is the narrowest point. Cutting a ferrule on an endo-tooth creates residual dentin walls which rarely are more than 1.0 mm thick. When you are lucky you have a circle of 1.0 mm thick dentin surrounding your post/core matrix. Along some surfaces you will usually have less than that. 1.0 mm of dentin will not last long when used as a fulcrum. Dentin has lots of flexure to it. Your crown has none. The root which is in bone has little ability to flex. Parafunctional forces will try to bend the tooth half-way between the crest of the bone and apical margin of the crown. If this region is thick, the tooth stays in place, and you may see abfraction and gingival recession in time. If this region is thin,,,,,,,, snap! Going back to our shovel, the handles break when try to do too much with our shovels. On the job site, we would sometimes use tham as pry-bars (since the contractor did not always provide metal pry-bars). We would use the shovel to lift peices of concrete, the lever forms into place for pole-light foundations, to pry a 200 pound piece of pipe over an inch or so, etc. When we did this enough times, the handle would develope a crack. Every crack was in the same place. It would start just inside the ferrule, and extend just outside the ferrule in a oblique direction to the opposite side of the handle. The broken handle is the root and the metal balde is the crown. Some handle would be left in the blade with virtually all of the cut ferrule remaining inside the blade. Encircling the root with a ferrule is what restorative dentists have taught for 50 years. It has been passed on one generation to the next. No one has stopped to say, "hey, is this right or not?" Encircling the tooth with the ferrule simply aplifies the forces so that when it fails, it wil snap off. Again, every tooth will not snap off. Most will survive very well. But, I insist that those which survive never needed the post since there was so much tooth structure remaining. >>>> The presence of a post places the vector of forces at the tip of post >>>> with lateral parafunctional movement. > > And at the coronal contact point, but on the *opposite* side of the tooth > in an *opposite* direction. That's really, really bad for teeth...and > really, really good at splitting them. I think we may be seeing this point in agreement, but am not sure. >> The longer the post, the narrower the root is at the tip. The longer the >> post, the greater force that can be exerted at the post tip when the [quoted text clipped - 11 lines] > the apical third, the huge force from a short post more than negates the > thickness advantage. I think this is a question of whether or not there is movement of crown relative to the tooth. No movement, it does not matter. The entire tooth absorbs all of the shock equally as one peice. If movement is present, then your equation comes into play. As long as your crown/core/post complex has a different modulus of elasticity than the tooth, then parafunctional forces will loosen it (if it does not snap off). Assuming for this part of the discussion that the tooth holds up and does not break off. Also, I want to restrict the discussion to parafunctional forces as I think vertical forces do not cause much harm. Lateral parafunctional forces delivered along an oblique vector will try to bend the tooth at teh center of the most flexible region. If the crown/core is significantly more resilient than the tooth structure, then the crown will come loose or break the tooth at the bse of the ferrule. ONce the crown/core is loose the post is free to abrade the post space or break the root. >>> With a ferrule, the side of the tooth that the force comes from also >>> shares some of the load with the other side of the tooth, and withthe [quoted text clipped - 3 lines] > > But it's a much smaller force. With a ferrule, the side of the tooth opposite the force application will be forced into compression at the base of the crown margin/ferrule. All of the force will accumulate at this point. This is one of "your" fulcom points. This compression will be in a pin-point or alond a narrow line-angle depending on the curve of the margin. This can easily exceed the compressive strength of the dentin with the force concentrated to this small area. There will be light tension force on the opposite side away from the margin, and huge compressive forces right at the fulcrum of the margin. > I was just joking about those Cerecs. ;-) Thanks for teasing me, that implies that I am your friend! >> Remember, my point is that the cervical third of the tooth is strongest >> part of the tooth, and should be maintained at all cost. > > Not at the expense of creating a much larger force due to design. My typical Endo-Crown is strange looking from a dental school point of view. It is shaped much like a mushroom. George W_B sat in with me on a couple of these. What I do is remove all the existing filling material, reduce the occlusal 1/3 of the tooth *flat* (I use a large disk shaped diamond). I then flatten the inner walls of the pulp chamber (after trimming the gutta percha down to the orifices of the root spaces). I try to get as parallel as possible here. I lightly round the line-angles from the axial wall of the pulp chamber to the flat surface of the reduced occlusal height. I am done and ready to scan and mill. The final product looks like a mushroom with an extension wherever a proximal bax was pre-exisiting. The occlusal porcelain is 4.0 mm thick. The center stem is 8-12 mm thick. These things are unbelievably strong. The actual tooth keeps its height of contour intact. When viewed from the occlusal surface, the tooth is 4-6 mm thick on all sides (except for where a proximal box was). If you wish to share an email address, I will forward images. If you choose not to share one, I don't blame you and understand. >> The ferrule actuallly just keeps the post from loosening as quickly. > > No. It drastically changes the force vectors on the tooth. I was taught the same thing. I no longer beleive it. >>> The only time that I use a post is when one entire wall of a tooth is >>> gone (buccal or lingual). If I have two walls (even if one is only 2 mm [quoted text clipped - 7 lines] > > What did the I/O camera show? With the I/O camera, I stop and study the inner surface more. Instead of taking out the old filling, checking for caries, and shoving a core material in right away and running fast to the prep, It slowed me down and made me look closer. Fist off, I found a lot more fractures than I expected to find. I found vertical fractures as well as horizontal ones. But, what I found myself looking at was (in most cases) lots of nice thick tooth structure that would have to be whacked off to make a conventional crown. If I was replacing an existing crown, my eyes opened wider as I saw haw little tooth structure remained with obvious strength. The camera allowed me to see more detail, and forced me to look harder. >> Not at the expense of creating a much larger force due to design. > [quoted text clipped - 12 lines] >intact. When viewed from the occlusal surface, the tooth is 4-6 mm thick on >all sides (except for where a proximal box was). These are kewl. The entire block of milled porcelain is bonded to the remaining tooth structure. Most margins supragingival at the height of contour, except boxes if present. With the solid core of porcelain in the fossae, I just don't see many porcelain fratures happening. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com >>>>> But to get that 2.0 mm reduction at a height just below the gingival >>>>> crest, you are removing 3-4 mm (sometimes more) of tooth at the height [quoted text clipped - 27 lines] > we prep for the crown. I want you to be looking at the tooth with the > core removed. I do that more by accident than anything else. I just got tired of cutting away all of that extra core material while prepping the crown. I remove the filling, prep the crown, remove the decay, and then do the buildup. >>> The tooth is 3-5 mm thick buccal and lingual if the cervical third of >>> the tooth is NOT preped. With the cervical third of the tooth [quoted text clipped - 42 lines] > That is an uneven compression with resultant tension on the opposite side. > That would onlly serve to crush dentin. Dentin doesn't "crush". All materials that we are talking about have better compressive strength than tensile strength. >>> Especially after the lab uses die-separator. >> [quoted text clipped - 4 lines] > I thought you ere talking about vertical forces creating compression in a > uniform pressure circumpherentially. We were on different pages there. Vertical and horizontal forces. We probably are on different pages. That's the limitation of text. If we could draw these out, it'd be easier to explain. >>> What you are doing is moving the fulcrum to the base of the ferrule. >> [quoted text clipped - 10 lines] > will tell you that it does really work that way in the world. The > strongest of the three points will bear all the stress. Not all of, but much of it. > If a weaker fulcrum is further out along the lever arm than the stronger > one, the weaker one will break before transfering stress to the stronger > one. You're talking about completely brittle materials. Teeth have a modulus of elasticity that permits some flexing...which gives it the ability to transfer the stress across a broader area. > After the first fulcrum breaks, the stress will transfer to the second > fulcrum further from the end of the lever arm. If this is not the [quoted text clipped - 6 lines] > over 60 foot drop-offs and discuss where the fulcrum is. The situation is > not that different. >> > All of the crown above the margin is your lever arm. >> [quoted text clipped - 38 lines] > Not for my technique. Why do we need a post if we have 1/3 to 1/2 the > vertical height of the tooth "un-touched".?? Shoot. If I had 1/3 to 1/2 the vertical height un-touched, I wouldn't do a post either. But I thought we're talking about the scenario when a post is needed. If you put a post in a tooth, the core ought to form a ferrule effect around sound tooth. Otherwise, the only thing that resists lateral forces is that post (aka--prybar) sticking down in the root. >>>>> If you don't have 3 mm of tooth sticking up, the tooth will probably >>>>> snap off in the next 5-10 years--regardless of any post. [quoted text clipped - 15 lines] > and destroying all that good tooth structure to create a ferrule does not > make sense--to me. I'm trying to grab hold of both tooth *and* post/core when I do a crown prep on a tooth that *needs* a post. If I grab hold of just the post/core, then I'll end up splitting that root. Just for clarification: When I say "ferrule effect", I'm talking about encirclement of both *tooth structure* and *post/core*. The encirclement of tooth structure is the key element however. > Things (including teeth) break at their weakest point. The weakest > point--in the absence of fractures--is the narrowest point. Cutting a [quoted text clipped - 20 lines] > balde is the crown. Some handle would be left in the blade with virtually > all of the cut ferrule remaining inside the blade. If you designed a shovel the way you are designing a crown, post and core, you'd drill a hole in the end of the handle, weld a spike to the metal shovel portion, and then glue the shovel with spike to the handle. Do you really think that that technique would be stronger than the way they currently make shovels? The spike would split the wood before you could get one boulder out of the ground. > Encircling the root with a ferrule is what restorative dentists have > taught for 50 years. It has been passed on one generation to the next. [quoted text clipped - 42 lines] > discussion to parafunctional forces as I think vertical forces do not > cause much harm. I agree on the vertical forces... > Lateral parafunctional forces delivered along an oblique vector will try > to bend the tooth at teh center of the most flexible region. If the [quoted text clipped - 45 lines] > surface, the tooth is 4-6 mm thick on all sides (except for where a > proximal box was). I've been considering doing exactly this type of restoration on my wife's second molar. She has unbelievably short teeth, and #2 has a prior RCT. There is no way that I can reduce the occlusal 2 mm and also get 3-4 mm of axial wall length without doing major crown lengthening. Retention is impossible in any other scenario except for the one that you present. > If you wish to share an email address, I will forward images. If you > choose not to share one, I don't blame you and understand. >>> The ferrule actuallly just keeps the post from loosening as quickly. >> >> No. It drastically changes the force vectors on the tooth. > > I was taught the same thing. I no longer beleive it. I do. I've sat down and drawn force vector diagrams, and convinced myself that there actually is some sound engineering behind the principles that they're teaching at the dental schools. >>>> The only time that I use a post is when one entire wall of a tooth is >>>> gone (buccal or lingual). If I have two walls (even if one is only 2 [quoted text clipped - 18 lines] > haw little tooth structure remained with obvious strength. The camera > allowed me to see more detail, and forced me to look harder. Thickness certainly translates into more strength. However, prep design trumps thickness. Encirlement of tooth structure creates a more favorable dissipation of lateral forces. Yes, the tooth is thinner/weaker in some spots...but proper prep design greatly reduces the amount of stress seen by those spots. We should send this to one of the senior graduating classes in Mechanical Engineering as a design project. They can do a finite element analysis of the tooth/crown/post complex for each scenario and then we'll know for sure. Perhaps I'll contact my alma mater, Purdue, and see if it's something that they'd like to work into their curriculum. Perhaps you can do the same with your local schools. >> Not for my technique. Why do we need a post if we have 1/3 to 1/2 the >> vertical height of the tooth "un-touched".?? [quoted text clipped - 4 lines] >effect around sound tooth. Otherwise, the only thing that resists lateral >forces is that post (aka--prybar) sticking down in the root. I only use posts to retain the core material., namely fuji 9 which is bonded to tooth structure therefore becomes an integral part of the tooth. 3 - 5 degrees of taper and all is well. I should note that Dr. SM's 'mushrooms' are analogous to a 'dowel' crown, but are bonded in place. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com > I do that more by accident than anything else. I just got tired of > cutting away all of that extra core material while prepping the crown. I > remove the filling, prep the crown, remove the decay, and then do the > buildup. We seem to agree that is the best way to do it. >>>>>> My recommendation is (except for teeth which are badly discolored), >>>>>> to reduce the vertical height of the tooth 3-4 mm, remove all the [quoted text clipped - 30 lines] > Dentin doesn't "crush". All materials that we are talking about have > better compressive strength than tensile strength. Dentinal tubules are hollow. The dentin is flexible. You get microscopic crushing and cracking just as in abfraction. >>>> Especially after the lab uses die-separator. >>> [quoted text clipped - 9 lines] > That's the limitation of text. If we could draw these out, it'd be easier > to explain. I think we are okay here >>>> What you are doing is moving the fulcrum to the base of the ferrule. >>> [quoted text clipped - 12 lines] > > Not all of, but much of it. With multiple fulcroms, you are only as strong as the first one along the lever arm. After (that is "if") it gives out, the stress transfers to the next one down. Only one fulcrom supports the force at one time. >> If a weaker fulcrum is further out along the lever arm than the stronger >> one, the weaker one will break before transfering stress to the stronger [quoted text clipped - 3 lines] > of elasticity that permits some flexing...which gives it the ability to > transfer the stress across a broader area. The flexibilty also alows for abfraction fractures. Also, the crown will focus the stress on the point of pivot. The crown/core matrix is very rigid, so it has a specific rotation relative to the force vector. Point of pivot or fulcrom of the crown/matrix assembly is going to be a very small area, often a point. >> After the first fulcrum breaks, the stress will transfer to the second >> fulcrum further from the end of the lever arm. If this is not the [quoted text clipped - 55 lines] > effect around sound tooth. Otherwise, the only thing that resists lateral > forces is that post (aka--prybar) sticking down in the root. On usenet and in email two people often will carry on a long discussion before realizing they were not comparing the same thing. I am proposing to never cut past the height of contour except for badly discolored teeth, and teeth that are less than 6 mm in height. I am saying this is far preferable to conventional crown preparation with ferrule. I feel conventional crown preparation with ferrule destroys too much good tooth and leads to too many "snaps". >>>>>> If you don't have 3 mm of tooth sticking up, the tooth will probably >>>>>> snap off in the next 5-10 years--regardless of any post. [quoted text clipped - 20 lines] > prep on a tooth that *needs* a post. If I grab hold of just the > post/core, then I'll end up splitting that root. My concept of the ferrule is 2-3 mm of tooth structure beyond the most apical extent of core material. > Just for clarification: > When I say "ferrule effect", I'm talking about encirclement of both *tooth > structure* and *post/core*. The encirclement of tooth structure is the > key element however. I think our definition of Ferrule is the same. >> Things (including teeth) break at their weakest point. The weakest >> point--in the absence of fractures--is the narrowest point. Cutting a [quoted text clipped - 27 lines] > currently make shovels? The spike would split the wood before you could > get one boulder out of the ground. I would rather compare my technique to a screw retained abutment on an implant. You have precesion fit and resistance form, but hold it down with a tiny gold screw. For the shovel, my design would make the handle three times thicker. Of course that would not be too efficient for shoveling dirt and sand. Years ago, I had an ice pick for use on the driveway. One of those small flat blades attached to a wodden handle just like a shovel. When the handle broke, I welded it to a piece of pipe. by cutting off the ferrule and butt-welding it. It lasted about another ten years that way. >> As long as your crown/core/post complex has a different modulus of >> elasticity than the tooth, then parafunctional forces will loosen it (if [quoted text clipped - 60 lines] > axial wall length without doing major crown lengthening. Retention is > impossible in any other scenario except for the one that you present. If you want images of mine so you can create your own design idea based on your personal preferences let me know. You may like a hybred of my thoughts and yours. >> If you wish to share an email address, I will forward images. If you >> choose not to share one, I don't blame you and understand. [quoted text clipped - 8 lines] > that there actually is some sound engineering behind the principles that > they're teaching at the dental schools. I think it boils down to how much tooth structure remains, and that circles back to whether or not a post was indicated in the first place. >>>>> The only time that I use a post is when one entire wall of a tooth is >>>>> gone (buccal or lingual). If I have two walls (even if one is only 2 [quoted text clipped - 24 lines] > spots...but proper prep design greatly reduces the amount of stress seen > by those spots. A natural tooth will flex to some degree along its entire length. Cutting a tooth 1/3 down, then filling it with something which has virtually the same modulus of elasticity creates a structure with *somewhat* similar flex. Covering the entrire tooth in something rigid, eliminates all flex exept between the crown margin and the crestal bone. Instead of spreading the flexing force along the entire tooth, you concentrate it in the thinnest ;art of the tooth. > We should send this to one of the senior graduating classes in Mechanical > Engineering as a design project. They can do a finite element analysis of > the tooth/crown/post complex for each scenario and then we'll know for > sure. Perhaps I'll contact my alma mater, Purdue, and see if it's > something that they'd like to work into their curriculum. Perhaps you can > do the same with your local schools. >> I do that more by accident than anything else. I just got tired of >> cutting away all of that extra core material while prepping the crown. I [quoted text clipped - 40 lines] > Dentinal tubules are hollow. The dentin is flexible. You get microscopic > crushing and cracking just as in abfraction. Yes, dentinal tubules are hollow...but they run parallel to the occluding forces. Ergo, they don't collapse. >>>>> Especially after the lab uses die-separator. >>>> [quoted text clipped - 43 lines] > > The flexibilty also alows for abfraction fractures. > Also, the crown will focus the stress on the point of pivot. The > crown/core matrix is very rigid, so it has a specific rotation relative to > the force vector. Point of pivot or fulcrom of the crown/matrix assembly > is going to be a very small area, often a point. I'm not convinced of that. With a ferrule effect, a force from the lingual creates a compressive force on the lingual wall of tooth, a force at the point where the post contacts the root orifice, a force at the tip of the post, and a force at the buccal edge of the buccal margin. Without a ferrule, you don't have that very important compressive force on the lingual wall of tooth. That's the critical point...and you simply don't have it with your design. >>> After the first fulcrum breaks, the stress will transfer to the second >>> fulcrum further from the end of the lever arm. If this is not the [quoted text clipped - 16 lines] >>> simply have to design in resistance form so as to avoid shear forces to >>> the bonded surface. Where is the resistance form in your design? With a ferrule effect, the resistance form is from the lingual wall of tooth (when there's a lingual force vector). >>>>> If the tooth is strong enough that parafunctional forces do not create >>>>> force vectors which cause the post to break the root at the post tip, [quoted text clipped - 38 lines] > On usenet and in email two people often will carry on a long discussion > before realizing they were not comparing the same thing. ;-) Apples and apple pie. > I am proposing to never cut past the height of contour except for badly > discolored teeth, and teeth that are less than 6 mm in height. I am [quoted text clipped - 73 lines] > implant. You have precesion fit and resistance form, but hold it down > with a tiny gold screw. An implant has ferrule effect! Besides anti-rotation, that's one of the key functions of the internal or external hex, or the spline. How many implants have a flat surface mated to the flat surface of an abutment via only a screw? Answer: none. Even the ITI has a Morse taper that provides the encirclement. > For the shovel, my design would make the handle three times thicker. No. It would just put the spike in a portion of the wood hadn't been shaved down for a ferrule. The spike would still split the wood...unless you put a metal collar around it. But then Voila! You have created a ferrule. > Of course that would not be too efficient for shoveling dirt and sand. > Years ago, I had an ice pick for use on the driveway. One of those small > flat blades attached to a wodden handle just like a shovel. When the > handle broke, I welded it to a piece of pipe. by cutting off the ferrule > and butt-welding it. It lasted about another ten years that way. Wood vs. metal. >>> As long as your crown/core/post complex has a different modulus of >>> elasticity than the tooth, then parafunctional forces will loosen it (if [quoted text clipped - 64 lines] > your personal preferences let me know. You may like a hybred of my > thoughts and yours. Thanks. You've explained it very well however. >>> If you wish to share an email address, I will forward images. If you >>> choose not to share one, I don't blame you and understand. [quoted text clipped - 11 lines] > I think it boils down to how much tooth structure remains, and that > circles back to whether or not a post was indicated in the first place. It's been a heck of debate for two guys who between them probably use posts less than 2% of the time. ;-) > It's been a heck of debate for two guys who between them probably use > posts > less than 2% of the time. ;-) Glad to have the debate on friendly terms. I will try to continue the discussion today and tomorrow. Heading to Chicago for dental meeting Wednesday. If I never change your mind and you never change mine, we will have had fun exercising our minds over the science of this debate :-))) >>>>>> You are thinnking of prepping down to the CEJ. Forget that concept. >>>>>> The ferrule does not create any compresion on the tooth. [quoted text clipped - 15 lines] > Yes, dentinal tubules are hollow...but they run parallel to the occluding > forces. Ergo, they don't collapse. Hollow tubes stacked together very closely have very little stength perpendicular to the axis of the tubes. They have tremendous strength parallel to the long axis of the tubes. Once the force is applied oblique to the long axis, the strength disappears. >> Also, the crown will focus the stress on the point of pivot. The >> crown/core matrix is very rigid, so it has a specific rotation relative [quoted text clipped - 8 lines] > lingual wall of tooth. That's the critical point...and you simply don't > have it with your design. A ferrule will transmitt lateral force into compressive force on the side the force is being applied from. The opposide side will be in tension. If the force is oblique, the rigid metal ferrule will attempt to pivot at the opposite apical margin. If the opposite side is very round, this pivot point will be very small. > Where is the resistance form in your design? With a ferrule effect, the > resistance form is from the lingual wall of tooth (when there's a lingual > force vector). The way I am doing Endo-Crowns, the restoration is shaped like a mushroom with extension laterally from the "stem" into any existing proximal or lateral boxes. There are "tons" of resistance form to the design. I am talking about a restoration which is 3-5 mm thick at its thinnest portion. >>> If you designed a shovel the way you are designing a crown, post and >>> core, you'd drill a hole in the end of the handle, weld a spike to the [quoted text clipped - 12 lines] > only a screw? Answer: none. Even the ITI has a Morse taper that provides > the encirclement. You do understand that I am NOT talking about a flat restoration, but one shaped like mushroom? >> For the shovel, my design would make the handle three times thicker. > > No. It would just put the spike in a portion of the wood hadn't been > shaved down for a ferrule. The spike would still split the wood...unless > you put a metal collar around it. But then Voila! You have created a > ferrule. If we ignore the poor design of trying to dig into something with a wooden shovel "blade", we could discuss the advantage of having a 100% wooken shovel, or one which has a blade fashioned from some material with virtuallly idential modulus of ealsticity, hardness, thermal coefficient of expansion, etc. as the wooden handle. Then, add in a proper joint between the two materials such as many wood-workers are expert at creating. You could bend and flex the handle all day long, so long as you do NOT exceed the modulus of elasticity of either material. The joint would act as if it was part of the original piece of lumber. Exceeding the modulus of elasticity in this example would result in fracture of the handle at the mid-point of the greatest flexure, not at the joint. >> Of course that would not be too efficient for shoveling dirt and sand. >> Years ago, I had an ice pick for use on the driveway. One of those small [quoted text clipped - 3 lines] > > Wood vs. metal. Similar material joined together. >>>>>> The ferrule actuallly just keeps the post from loosening as quickly. >>>>> [quoted text clipped - 8 lines] >> I think it boils down to how much tooth structure remains, and that >> circles back to whether or not a post was indicated in the first place. My opinion is based partlyl on looking at abfraction lesions and giving consideration to how these were created. I am trying to keep the restored tooth as close to the original degree of flexibility/rigidity as possible. > It's been a heck of debate for two guys who between them probably use > posts less than 2% of the time. ;-) And, a nice friendly debate which should be followed by buying each other a round of good single malt Scotch. I owe you the first round. > the method of post and core technique may not be as > significant as the placement of full coverage cast-gold crown restorations > with sound design and placement of margins beyond the buildup restoration. Sounds to me like what we were always admonished to do in Dent School: the finish line must always be on sound TOOTH structure... even if one part of that structure is a proximal box goin' way down to the bone... SP In another post you said that if the crown breaks off at the gumline, you extract it and do implant/bridge. If the tooth snaps off at the gumline, why don't you just do a bit of crown lengthening, make your ferrule prep ( or don't ) and place a fiber post? Thanks SP SignatureFinally: take out the TRASHH Thanks Stove, I think I forgot to respond to the article. The article abstract did look to be merely a statement that restorations do better with the crown totally enclosing all the other filling materials on the tooth. It seemed more a statement of having one finish line between tooth and one restorative material. Signature~+--~+--~+--~+--~+-- Stephen Mancuso, D.D.S. Troy, Michigan, USA .................................................... This posting is intended for informational or conversational purposes only. Always seek the opinion of a licensed dental professional before acting on the advice or opinion expressed here. Only a dentist who has examined you in person can diagnose your problems and make decisions which will affect your health. ...................... > >> the method of post and core technique may not be as [quoted text clipped - 14 lines] > Thanks > SP > > the method of post and core technique may not be as > > significant as the placement of full coverage cast-gold crown restorations [quoted text clipped - 4 lines] > part of that structure is a proximal box goin' way down to the bone... > SP R E P L Y I am not sure that is true today. When restorations were cemented it was absolutely required. Let's say there is a restoration that is bonded in place, and it is absolutely solid with no decay under it. Why end the crown margin BELOW the restoration? Oh its good to end on solid tooth but is it absolutely essential? Maybe not. If the crown design further weakens the tooth in trying to accomplish that, what is gained? Joel > In another post you said that if the crown breaks off at the gumline, > you extract it and do implant/bridge. If the tooth snaps off at the [quoted text clipped - 4 lines] > -- > Finally: take out the TRASHH I agree mostly with Joel. However, each case should be evaluated closely. If getting the margin past the core material margin requires extensive tooth removal, then "skip it". However, I would say this applies for any filling material which you absolutely know is in good condition and well sealed. If you placed an amalgam core 3 weeks before, and you know it will cut away lots of tooth getting the margin of your FGC past it, then make a good judgment call. I take it one step further and make the core part of the restoration and bond the entire thing in place. Signature~+--~+--~+--~+--~+-- Stephen Mancuso, D.D.S. Troy, Michigan, USA .................................................... This posting is intended for informational or conversational purposes only. Always seek the opinion of a licensed dental professional before acting on the advice or opinion expressed here. Only a dentist who has examined you in person can diagnose your problems and make decisions which will affect your health. ...................... > >> > the method of post and core technique may not be as [quoted text clipped - 32 lines] >> -- >> Finally: take out the TRASHH Ouch, ow ow ow, my head hurts. You guys are making me think too much. Great thoughtprovokingness (that's a real word, honest). I teach postgrads and have made the ferrule part of the restorative Torah. But - as has been discussed so very well - I obviously need to revisit the concept. I will say that I'm not aware of any researchers or clinical educators who think that - everything else being equal - the ferrule notion in and of itself is a bad idea. But part of what's being said here is: at what cost? There are some pretty ugly, (is that an oxymoron) crown lengthenings at my school. And I've seen some residents trough through a whole lotta tissue/attachment/bone in the name of finishing on tooth structure. I'll be back. > I take it one step further and make the core part of the restoration and > bond the entire thing in place. Yes.... Filtek Z100 over the bare (but with a layer of bonding) Fiber 1 post ball... it becomes your core buildup/cement all in one. Z100 is a photocure material. This raises the question: How much light do you need to fully polymerize the stuff under the onlay? I would have thought that you'd want a auto/photocure material. It is surprising that you use Z100 here. Thanks SP SignatureFinally: take out the TRASHH >> I take it one step further and make the core part of the restoration and >> bond the entire thing in place. [quoted text clipped - 8 lines] >Thanks >SP Think that dual cure Calibra would work better. -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com >> I take it one step further and make the core part of the restoration and >> bond the entire thing in place. [quoted text clipped - 8 lines] >Thanks >SP The adhesive composite or resin under the porcelain is only 60-150 microns. This porcelain will transmit light amazing well. I use 80 seconds of light on occlusal, and 40 seconds buccal and 40 seconds lingual. I use an LED light. .. Stephen Mancuso, D.D.S. Troy, Michigan, USA I am writing on a Tablet-PC,so forgive me if the PC misreads my handwriting. > Z100 is a photocure material. This raises the question: How much light > >do you need to fully polymerize the stuff under the onlay? I would have [quoted text clipped - 8 lines] > lingual. I use an LED light. > .. OK, thanks. If you were doing onlays with a lab, how thick a space (die spacer) would you leave for your material. I'm guessing you'd ask for 100 microns... I'm asking 'cause one of my patients has a lotta CEREC in his mouth, and I'm gonna do an MO inlay using Z100 as the adhesive. Thanks SP SignatureFinally: take out the TRASHH >> Z100 is a photocure material. This raises the question: How much light >> >do you need to fully polymerize the stuff under the onlay? I would have [quoted text clipped - 15 lines] >Thanks >SP I imagine the die-spacer they use will be more than that. .. Stephen Mancuso, D.D.S. Troy, Michigan, USA I am writing on a Tablet-PC,so forgive me if the PC misreads my handwriting. > >OK, thanks. If you were doing onlays with a lab, how thick a space (die > >spacer) would you leave for your material. I'm guessing you'd ask for [quoted text clipped - 5 lines] > I imagine the die-spacer they use will be more than that. > . Don't think so.... each coat of standard stuff is 25 microns thick. If you can set that parameter on your CEREC, it might be usefull to know what it is, in case you change your bonding style. Thanks SP SignatureFinally: take out the TRASHH >> >OK, thanks. If you were doing onlays with a lab, how thick a space (die >> >spacer) would you leave for your material. I'm guessing you'd ask for [quoted text clipped - 11 lines] >Thanks >SP Yes you can change it .. Stephen Mancuso, D.D.S. Troy, Michigan, USA I am writing on a Tablet-PC,so forgive me if the PC misreads my handwriting. >R E P L Y > >I am not sure that is true today. When restorations were cemented it was >absolutely required. Let's say there is a restoration that is bonded in >place, and it is absolutely solid with no decay under it. Cemented gold does not require a 'ferrule'. I did alot of 3/4 and 7/8 gold. All with knife edge margins. >Why end the crown margin BELOW the restoration? > [quoted text clipped - 3 lines] > >Joel -- W_B Take out the G'RBAGE wubbabubbazG@RBAGEyahoo.com > >R E P L Y > > [quoted text clipped - 3 lines] > > Cemented gold does not require a 'ferrule'. R E P L Y We are talking ending on solid tooth structure as opposed to ending on composite or core buildup. A ferrule is like what holds a decent shovel handle into the shovel itself. Joel > I did alot of 3/4 and 7/8 gold. > All with knife edge margins. [quoted text clipped - 12 lines] > Take out the G'RBAGE > wubbabubbazG@RBAGEyahoo.com < |
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