For example, under mechanical properties: fracture toughness/ flexural strength /weibull modulus are tested in vitro on dry flat specimens.
Instead should we use chewing simulators on curved specimens ?
Dear Gali,
The most important property when the subject is ceramic dental parts is Fracture Toughness, not the strength. Therefore you should mind R-Curve (influence of notch dimension in Fracture Toughness).
A brief explanation of why you should mind this property is that in mouth teeth are exposed to impact and compression stresses and this evaluation (R-curve) gives information about the behaviour of the Fracture Toughness under the influence of cracks with different size of "cracks", which are induced by notches.
I'll give some information about it in links within the message (if you cannot accesses then please contact me by message or google "R-curve for ceramic")
I hope it can help you.
Best Regards,
lb
http://link.springer.com/chapter/10.1007%2F978-1-4615-3350-4_14
http://www2.lbl.gov/ritchie/Library/PDF/utility_bridging_ceramics.pdf
I agree, in order to properly assess a material aimed for dental restoration purposes you would have to look at the constitutive law of the material not its linear elastic properties.
Tests to determine this would be preferably performed on plat specimens e.g. nano-indentations or something equivalent.
Gali, Alex and Lucas gave you great advice. Fracture toughness is a standard means of testing dental ceramic restorations and certainly provides great property information about them. However, th there is no pure restorative construct using any intraoral restorative material and few engineered direct replacement materials exist in Dentistry. Ergo, I would like to see a battery of tests used to circum-surround the strengths and weaknesses of our materials so we obtain the individual component information. That way, we might be able to compostize materials to improve performance. That way, we can do theoretical calculations to pre - design potential candidate materials before we create them and create them with some forethought and foresight as to reduce Edisonian engineering efforts by using more Hawking engineering. Bulk and surface properties greatly differ in many engineered materials so this must also be considered as well. Cells feel the hydrated protienacious engineered surface of a Ti6Al4V alloy implant and find a way to colonize the ceramic surface of a metallic implant, grab it tightly and secure it in bone, making it ready to receive a tooth analog and use that construct to chop the meat out of the delectible chicken wing, chomp it into a semi slurry and gulp it down in gustatory satiation. That process required several intefacial interactions to bring a smile to your face and you'll be doing that with three bites for each of the 15 wings you'll be consuming after a hard Fridays work. Don't look for a single, all encompassing single test. Look for a simple battery of easy tests which give you results on which you can depend to be accurately descriptive and somewhat predictive for
I would like to add a few aspects not mentioned so far:
We clinically observe two types of failure of ceramic restorations: early and late failures.
The early failures (within the first one or two years) are mainly due to errors during processing. Examples are faulty processing during conventional or adhesive "cementation", occlusal contacts that are too high, marginal ridges that protrude far into the proximal contact and are not supported by the tooth, processing errors during fabrication, etc.
The early type of failures are hard to investigate in the laboratory. The only approach I see is to use not standardized specimen with simple geometries, but more or less simulate the whole application procedure including the use of human teeth as substrate. But this type of laboratory investigation is not testing a material property, it is testing the process as a whole.
The late failures are due to material fatigue, which is a material property: Under clinical conditions, forces occur during mastication that promote the slow and subcritical growth of an existing crack until it reaches a critical size, resulting in failure at relatively low load levels. In order to investigate on a clinically relevant level, you should apply fatigue simulations to your tests.
In addition to cyclic loading the test environment should at least consider testing under water as well.
Sincerely
Karl-Heinz
I suggest the following references on this subject;
- Kelly JR, Benetti P, Rungruanganunt P, Della Bona A.The slippery slope: critical perspectives on in vitro research methodologies. Dent Mater 2012;28:41-51. doi: 10.1016/j.dental.2011.09.001.
- Kelly JR, Cesar PF, Scherrer SS, Della Bona A, van Noort R, Tholey M, Vichi A, Lohbauer U. ADM guidance-ceramics: Fatigue principles and testing. Dent Mater 2017;33:1192-1204. doi: 10.1016/j.dental.2017.09.006.
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