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Medical Forum / General / Dentistry / November 2007Strength of a filled tooth?
How strong (as a function of filling size) is a tooth filled with amalgam or composite compared to the natural tooth? Roughly speaking. > How strong (as a function of filling size) is a tooth filled with > amalgam or composite compared to the natural tooth? Roughly speaking. The bigger the filling, the weaker the combined tooth/filling. This is specifically for internal restorations, as opposed to external (onlays or crowns) regardless of the material. Steve And cracks in the tooth can weaken it more than the size of filling does.  Signature/ Amatus / >> How strong (as a function of filling size) is a tooth filled with amalgam >> or composite compared to the natural tooth? Roughly speaking. [quoted text clipped - 4 lines] > > Steve > And cracks in the tooth can weaken it more than the size of filling does. Well, sure. All other things being equal, the tooth with more structural loss (and correspondingly bigger filling) is going to be more likely to crack. Of course, if there are cracks before the filling is placed, you'd like to know about it. Many would say that amalgam would cause more fractures because of setting expansion. I'm not so sure, but the cracks are more likely to separate since they are generally not bonded. Steve SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 The volumetric change due to expansion of amalgam is less than the volumetric change due to shrinkage in resin. So, the resin should fracture more teeth than the amalgam does. Signature/ Amatus / >> And cracks in the tooth can weaken it more than the size of filling does. > [quoted text clipped - 7 lines] > > Steve > The volumetric change due to expansion of amalgam is less than the > volumetric change due to shrinkage in resin. So, the resin should fracture > more teeth than the amalgam does. Logically this should be the case; how internal stresses caused by resin contraction compare with expansile forces of amalgam--given the bonding of resin to enamel and dentine--I cannot say. I'm not brave enough to do large resin fillings like Fawks, so I don't see that many fractures in the teeth I do resins in. Steve SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 That is because the bond strength is not strong enough. Typically the resin margin opens up and you see recurrent caries instead. Signature/ Amatus / >> The volumetric change due to expansion of amalgam is less than the >> volumetric change due to shrinkage in resin. So, the resin should [quoted text clipped - 7 lines] > > Steve > That is because the bond strength is not strong enough. Typically the resin > margin opens up and you see recurrent caries instead. True, esp. at the gingival seat of Class II restorations. Steve SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 Respectfully disagree (when done correctly). Steve >> That is because the bond strength is not strong enough. Typically the >> resin margin opens up and you see recurrent caries instead. > > True, esp. at the gingival seat of Class II restorations. > > Steve I don't even know what the expansion % of amalgam is. I do know what the contraction of my composite is. IME, teeth are more likely to fracture away from amalgam than composite. That doesn't mean that teeth never fracture from composite. It doesn't mean that a composite cannot cause a crack in a tooth. Whatever tooth structure that may crack around an amalgam has no adhesion at all to the filling material. With composite, the thin portion of enamel that may crack, also has a strong bond to the composite. I have even witnessed a crack (craze line, whatever) form in a tooth as I cured a composite. I have rarely seen one of these teeth come back with that piece missing. Bonding has it's advantages. I think I have gotten better at layering and curing to minimize that occurrence. Steve >> The volumetric change due to expansion of amalgam is less than the >> volumetric change due to shrinkage in resin. So, the resin should [quoted text clipped - 7 lines] > > Steve > I don't even know what the expansion % of amalgam is. I do know > what the contraction of my composite is. IME, teeth are more [quoted text clipped - 13 lines] > > Steve Good point--not curing in bulk should allow for far less internal stress generation. Steve >>> The volumetric change due to expansion of amalgam is less than the >>> volumetric change due to shrinkage in resin. So, the resin should [quoted text clipped - 7 lines] >> >> Steve Think about it. Why would layering change the internal stresses? You still have the same percentage of shrinkage. You still have the same volume of resin which is subject to shrinkage. Eight 1/8 fractions still equal one whole. Internal stresses remain the same. Layering may facilitate getting the contours you want. But, stress due to shrinkage is still the same. Signature/ Amatus / >> >> I don't even know what the expansion % of amalgam is. I do know [quoted text clipped - 31 lines] >>> >>> Steve >Think about it. Why would layering change the internal stresses? You still >have the same percentage of shrinkage. You still have the same volume of >resin which is subject to shrinkage. Eight 1/8 fractions still equal one >whole. Internal stresses remain the same. Layering may facilitate getting >the contours you want. But, stress due to shrinkage is still the same. That's why I line the prep with flowable and cure, then cram the Z-250 in with my thumb. 8^]] I don't cure the flowable separately. I only use it as a "wetting agent" Signature/ Amatus / > >>Think about it. Why would layering change the internal stresses? You [quoted text clipped - 9 lines] > > 8^]] Tried that and found it a bit "messy". Am curing the flowable on the assumption of a good bonded liner. BTW Ross Nash recommends this technic. >I don't cure the flowable separately. I only use it as a "wetting agent" > [quoted text clipped - 10 lines] >> >> 8^]] On large restorations, I do both. I cure a thin layer of flowable on the floor, then place a new smear of flowable and condense the regular composite. Subsequent layers are added in the same fashion. When the last layer goes in, any extra flowable is wiped away over the margins before curing. Some of my early composites would collect stain around imperfect seams of layered material. Since adding a little flowable before the next layer, that is no longer a problem. JME, D > Tried that and found it a bit "messy". > > Am curing the flowable on the assumption of a good bonded liner. > > BTW Ross Nash recommends this technic. >>I don't cure the flowable separately. I only use it as a "wetting agent" I would agree with that technique. Signature/ Amatus / > > On large restorations, I do both. [quoted text clipped - 20 lines] > >>>I don't cure the flowable separately. I only use it as a "wetting agent" An excellent tip. Thanks, I will try it. >On large restorations, I do both. > [quoted text clipped - 19 lines] > >>>I don't cure the flowable separately. I only use it as a "wetting agent" > Think about it. Why would layering change the internal stresses? You still > have the same percentage of shrinkage. You still have the same volume of > resin which is subject to shrinkage. Eight 1/8 fractions still equal one > whole. Internal stresses remain the same. Layering may facilitate getting > the contours you want. But, stress due to shrinkage is still the same. I don't have the research at hand. What I'd heard is that layering allows for stress release between the cured layers. Of course, this is probably done on a laboratory model. For me, I don't like curing through thick layers because I have insufficient confidence that I have depth of cure. I am using Alert for posterior composites--they claim a 5 mm depth of cure, but they don't say if they're using a thermonuclear device or a squirt gun for curing. Mine is closer to a squirt gun, but I give it plenty of time, and I don't assume a 5 mm depth of cure. Steve SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 3M stuff will cure down 8mm and more with an LED light. I have checked it out. 8 X 1/8 is still one whole. Layering loads the stress up in layers. But it is all still there. Signature/ Amatus / >> Think about it. Why would layering change the internal stresses? You >> still have the same percentage of shrinkage. You still have the same [quoted text clipped - 13 lines] > > Steve > 3M stuff will cure down 8mm and more with an LED light. I have checked it > out. > > 8 X 1/8 is still one whole. Layering loads the stress up in layers. But it > is all still there. There seems to be some opinion to the contrary. But like much dental research, it seems pretty seat-of-the-pants stuff: http://www.thejcdp.com/issue028/giachetti/06giachetti.htm Steve SignatureMark & Steven Bornfeld DDS http://www.dentaltwins.com Brooklyn, NY 718-258-5001 I find when I experiment with various composites by light curing a wad of it in a ring of inert material, that 3M resins cure deeper under the same conditions. This is only for the products I evaluated for my own personal use. I find I can cure Z-100 and the newer formulas down to 8mm consistently with my LED lights. Articles like that one are always full of the words "suggested", "recommended" etc. with no detailed basis for that use. Flowable contracts more than a filled resin, therefore, I want it to be as thin as possible. Reminds me of the occlusal lecture telling us that a premature contact on a tooth will cause the lateral pterygoid muscle to contract, therefore resulting in bruxism and clenching. But, try to find a reference proving that point. Signature/ Amatus / >> 3M stuff will cure down 8mm and more with an LED light. I have checked >> it out. [quoted text clipped - 8 lines] > > Steve > I find when I experiment with various composites by light curing a wad of it > in a ring of inert material, that 3M resins cure deeper under the same [quoted text clipped - 9 lines] > resulting in bruxism and clenching. But, try to find a reference proving > that point. That's what I meant by "seat-of-the-pants". ;-) Steve But not with the same vectors of force that would develop from a bulk placement technique. When I am placing composite in *increments* (not just 'layers'), I often place composite in different parts of the prep and on axial walls. I'm not just placing layers from top to bottom. With a material that shrinks 2%, I don't know how important this is, but until they get one that's almost zero, I'll still do it. JMO, D > 3M stuff will cure down 8mm and more with an LED light. I have checked it > out. > > 8 X 1/8 is still one whole. Layering loads the stress up in layers. But it > is all still there. The amount of shrinkage of the material is the same, but the vectors of the shrinkage forces change. Previously cured resin layers can actually strengthen the tooth to make it more resistant to subsequent curing shrinkage. Plus, I use a composite with shrinkage numbers around 2%. When you hit the material with the light it doesn't just shrink equally in all directions. The bond remains intact and I'm not shearing off cusps. D > Think about it. Why would layering change the internal stresses? You still > have the same percentage of shrinkage. You still have the same volume of > resin which is subject to shrinkage. Eight 1/8 fractions still equal one > whole. Internal stresses remain the same. Layering may facilitate getting > the contours you want. But, stress due to shrinkage is still the same. No matter how you put it in, it will shrink towards the greatest volume of resin. Not arguing that the material is not great nor that it will not last as we both know composite resin is a great material. Simply pointing out that careful placement in an environment free of contaminants is the reason for long term success with the modern materials. And,,,,,, that the layering technique is great for getting good contours, and controlling the environment,,,,,,, but does not have good research proving it is superior to just cramming it in. Like many ideas in dentistry and medicine, someone gets on the lecture series and pushes a particular technique, which improves outcomes (often simply because the operator is now paying more attention to what he is doing), and everyone begins to repeat the same mantra. Signature/ Amatus / > > The amount of shrinkage of the material is the same, but the vectors [quoted text clipped - 16 lines] >> facilitate getting the contours you want. But, stress due to shrinkage >> is still the same. I cannot state that I 'know' what the curing forces are within each restoration that I place. I can say that I have seen with my own eyes how bulk placement will often cause fractures of enamel when placed in large restorations. If my results were the same with either technique, I would certainly be using bulk placement. D > No matter how you put it in, it will shrink towards the greatest volume of > resin. [quoted text clipped - 11 lines] > simply because the operator is now paying more attention to what he is > doing), and everyone begins to repeat the same mantra. What can I choose for fillings on back tooth then if composite is not good. Many dentists in my area already stop to use Amalgam, and they say Amalgam is not good for your health. Do you guys here agree with that? Both materials have advantages in particular situations. Signature/ Amatus / > What can I choose for fillings on back tooth then if composite is not > good. Many dentists in my area already stop to use Amalgam, and they > say Amalgam is not good for your health. Do you guys here agree with > that? Properly placed composites can give many years of service (Especially if the restorations are small-medium in size). On posterior teeth with large restorations, gold onlays or crowns have the longest proven track record of success. D > What can I choose for fillings on back tooth then if composite is not > good. Many dentists in my area already stop to use Amalgam, and they > say Amalgam is not good for your health. Do you guys here agree with > that? |
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