Why It's Important for Dentists to Pay Attention to Physical Properties and Testing Methodology of Dental Ceramics (ISO Standards)

You're listening to The Dr. Phil Klein Dental Podcast from Viva Learning.com. Welcome to the show. I'm Dr. Phil Klein. Today we'll be discussing ways to ensure our clinical success by using dental materials that give us the best results. In order to do this, we really need to have some understanding of what ISO is and how their recommendations affect how our products are tested and the claims made by the manufacturers. we should understand the basics behind flexural strength versus fracture toughness, testing methodology, and utilizing data to make the right material selection for our restorative cases. To help us make this all relevant to the dental clinician, I'm pleased to welcome our guest, Dr. Jason A. Griggs. Dr. Griggs is the global head of ISO, the International Organization for Standardization, workgroup on dental ceramics. He has served as principal investigator of various grants and authored over 80 peer-reviewed articles, six book chapters, and two patents. He is currently associate dean at the University of Mississippi School of Dentistry. Dr. Griggs, it's a pleasure to have you on Dental Talk. Phil, it's a pleasure to be here. Tell us what ISO means and stands for, and how is it relevant to the dental manufacturer and ultimately, of course, the dental clinician? The ISO is an international organization for standardization and it's a group of product manufacturers and academic scientists and even end users. Some dentists are members of the group and what they try to do is make sure that all the products we use in our modern life are safe and reliable and that the terms that we use to describe the performance of those products are consistent in the same from one lab to another and from one manufacturer to another. For example, one thing that would be important for them that the ISO would tell them what types of information about the product need to be included in the instruction card that goes in the box and is shipped to the dentist. And in addition, the ISO would tell the manufacturer how to conduct the test methods to measure the information the product performance that they put on that card and would give them suggested minimum limits for important material properties like strength or fracture toughness and would also tell them maximum permissible limits of undesirable things like radioactivity uh cytotoxicity how much uh the dental product may leach out into the patient's saliva uh to set maximum safe limits for those things if i'm a manufacturer and i'm making a dental ceramic i pretty much need to be totally on board with iso right i need to work with them or be involved with them You would need to follow the ISO standards, and the regulations would vary from one country to the next, but I think most countries would have a regulation requiring the manufacturer to follow ISO standards. Right. So even if I make it in the United States, I'm only asking this question because I want to make sure our audience understands the importance of ISO, that it's important for them as clinicians to purchase products that have rigorous testing. And let's get into testing. So what are some of the proper testing protocols regarding dental ceramics that a dental clinician should understand? And also answer the question, why should they be concerned with that? Probably one of the most important tests, important ceramic material properties is strength. of the material because ceramics have a problem that they are more brittle than other classes of materials and their strength or lifetime is a little bit more variable than other classes of materials. So when we think of ceramics strength is one of the most important properties and it would be important to measure that strength using a consistent test method. For example, you would need to shape and polish strength test specimen from the dental ceramic. And if you choose to polish and polish and provide an ultra fine finish on the surface, you can make the strength of that test specimen go higher and higher, the finer you polish it. So there's a standard test method that tells what fineness of abrasive media should be used to grind the specimen flat, how much material should be removed from the surface, and what fineness of surface polish should go through. The standard tells what rate of speed to bend the specimen when breaking it because the faster you bend the specimen, the higher strength you're going to measure. It prevents accidental mistakes in testing, and the standard also prevents manipulation of the test method to make the product appear stronger than it actually is. Right. So it keeps everybody on an even playing field when they make their claims about their physical properties of the material. How is that enforced, though? Does ISO have any influence on enforcing or role in enforcing any of this? when these manufacturers do these tests, or are these just recommendations, which are very important, of course? Well, these are recommendations, and then it would be up to individual governments to enforce whether or not to follow the recommendations if you're selling a product in their market. I see. Okay, so it's an international kind of a consensus of experts in each one of these fields. You're one of the experts in ceramics, for dental ceramics. That's correct. I've been doing dental ceramics research for about 30 years now, and I'm the convener or the head of the ISO work group on dental ceramics. That's impressive. We're really talking to someone who knows just about everything there is to know about dental ceramics from the standpoint of engineering. How challenging is it to meet all of these protocols for the manufacturer, and is there a governing body that checks, and I asked you that before, manufacturers for these standards? It's a complicated structure because there's so many different type of dental products and products we use in our everyday lives. So the ISO has a TC 106 or Technical Committee 106 is in charge of all aspects of dental products. And you can tell from the name of that technical committee that there's a lot of other areas other than dentistry that the ISO is regulating. But within the Committee 106, we have hundreds of scientists working together to make sure that the standards are good and consistent. And so we have to break that down. And there are a lot of subcommittees under the Dental Committee. And subcommittee two pertains to all aspects of prosthodontic materials. And even within prosthodontic materials, there's a wide variety of tests and standards. And so we have a lot of work groups under subcommittee two. And work group number one is for dental ceramics. We handle the standard ISO 6872, which covers testing. fracture toughness, strength, solubility, radioactivity, all those aspects of ceramics for dental prostheses. And we used to publish and edit a standard 9693 on metal ceramic materials intended for use in PFM, crowns and bridges, porcelain fused to metal. And we also have standards telling how laboratory furnaces should be calibrated under our work group. When these companies that manufacture these products, or the dentists buy, They reach out to ISO. They look at these standards. They either purchase the information, the research, whatever the PDF is, and then they make sure that they're compliant to the best of their ability to this standardization, which is testing their materials and which will ultimately affect the claims they make on the packaging and their advertising. Is that right? That's correct. And in addition, many of the manufacturers send representatives, some of their employees, to serve on the ISO Dental Committee, and they help the academic scientists with understanding the way that the materials are changing and developing new test methods for new materials that are coming to the market. So we work together on that. Yeah. So what should a dentist look for when they're purchasing a product, a ceramic dental material, that would give them the confidence that it's the gold standard? And give us an example of a gold standard in ceramic dental materials. There are a lot of aspects depending on what location the ceramic crown or bridge is going to be placed in the mouth. And so obviously color hue, translucency, properties like that are important. But as I mentioned earlier, the Achilles heel of ceramics is that they have less predictable strength and lifetime compared to other materials. So for confidence, the dentist definitely wants to take a look at the strength or the fracture toughness of the... the ceramic material. As far as a material with, we could call a gold standard, I would go for one with a long track record of proven reliability and one that also is fairly, you know, translucent for the aesthetics as well. If I needed to have a crown or bridge placed in the anterior of my mouth personally, I would ask the dentist to use Emax CAD or Emax Press, the lithium disilicate glass ceramic product. The Emax CAD has been used for 15 years now. And before it, the same manufacturer was producing IPS Impress 2, which is very similar in composition and performance. And so there's even more than a 15-year successful history. I think they have 10 years now of... ongoing clinical trial data showing that the failure rate is a little bit less than 3% after 10 years. And so if I had to choose a gold standard, I would hold that material up as a point of comparison for other dental ceramics. I want to ask you about flexural strength versus fracture toughness. We always hear this as dentists. We see it in advertisements. We see it in webinars. some research article that talks about flexural strength. Tell us the difference between flexural strength and fracture toughness, and why is it important to the clinician? Well, the flexural strength is the amount of stress that a crown or bridge can take before it fractures. And I think that's a pretty intuitive concept for a lot of people, and so it's great for that reason. But the problem... with flexural strength you don't want that to be the only material property you look at because it's quite variable from one restoration to the next or from one test specimen to the next and the strength of a particular specimen will depend on the the size or severity of the flaws that are present like a scratch or a bubble or a place where The crown had to be adjusted for better fit by grinding it. And the strength also can be changed a lot by differences in test method. Even within the ISO standard test method, there could be a variation in how that test is properly performed from one lab to the next. And both labs can be performing the test within the standard and can get... different strength values. So the fracture toughness is important for three reasons to dentists. One is that it's more of a material constant. It's almost constant for a given material independent of the way that the material was tested. There's less variation in strength. It's also important because the fracture toughness determines how sensitive the strength is to the presence of flaws. So for example, a material with a very high fracture toughness would have almost the same strength. after a scratch was introduced into it as it did before the scratch was introduced. And then the last reason fracture toughness is important is because we had a study by Dr. Bob Kelly previously that showed a good correlation between fracture toughness and clinical data, the actual annual failure rates of prostheses in the clinic. And so if we measure the fracture toughness of a material, we can use Dr. Kelly's regression model to predict what percent of crowns made from that material will fail per year. Now, of course, it also has to do with the preparation design, the laboratory technique, the occlusion. I mean, there's all these other factors involved as well. But putting everything on an even playing field, it sounds like to me the fracture toughness is something that's more of a universal. measurement or metric that doctors should pay attention to because that's less of a variable, as you explained, in the testing technique and how they actually test it. Whereas the flexural strength, there's variabilities that even happen within the ISO recommendations and that criteria. Yeah, that makes a lot of sense. So if I was a practicing dentist, I would certainly pay attention to the fracture toughness. I would make sure the ISO recommendations were followed and are being taken seriously by the manufacturer. And then, of course, look at the track record because it is difficult sometimes for dentists to make decisions to use certain materials. But I agree. Emacs has been around a long time. And I think that's a pretty solid recommendation made by a company that is very, very strong and stringent with R&D. and working with people like you, Dr. Griggs from the ISO. Thanks very much for your time. I appreciate it. I think there's been a lot to listen to here and it's a little bit detailed more than our typical podcast, but I think if people rewind it and listen to it three times, they'll get it all straightened out in their head. Thanks so much and have a great evening, Dr. Griggs. Thank you so much for your help. Phil, thank you for having me on.