Comparative Testing and Evaluation of Metal Ceramics, Zirconia, Modified Zirconia, E.max and Composite Materials

Hello. My name is Estevam Bonfante. I’m a prosthodontist and professor at UNIGRANRIO University in Rio de Janeiro, Brazil. In this presentation, we shall discuss relevant topics that will hopefully help you choose an appropriate material for your implant supported restorations. So the literature shows that the most common technical complication in implant prosthodontics is abutment screw fracture and or loosening, which happens in 12.5% of the cases in the five year follow-up range. Since the locking taper implant abutment connection does not involve screws, we will focus on the mechanical performance of materials for prosthetic reconstructions and more specifically to the mechanical behavior of the integrated abutment crowns and bridges. When we look back in time, we must acknowledge that metal ceramic restorations are the gold standard. And for this reason, we will look at published data addressing its mechanical behavior so we can compare it to other materials. This graph shows that under fatigue loading that simulates mastication, metal ceramic crowns will fail under loads above one thousand newtons, which is way beyond the physiological chewing forces. Therefore, any new material to be used for an implant supported reconstruction is expected to fail in the same load range or higher than metal ceramic. The current knowledge on zirconia for fixed implant prosthodontics, as we may see from this recent publication and many others, is that there’s a major concern on the high rate of porcelain veneer fracture observed in single crowns and fixed dental prostheses, which happens from 7% to 53% in a six to fifteen month period. So when comparing metal ceramic with zirconia single crowns, we have observed that whereas metal ceramic fails under fatigue loads above one thousand newtons as we have previously shown, zirconia veneered crowns will fail at significantly lower loads, here shown by the non overlap between the contours and around three hundred newtons. It has been suggested in the past that framework design modification, here seen as the addition of a lingual collar that extends to both proximal areas, would help improve porcelain support. So we have looked into that in a subsequent fatigue study. And the results have shown that the modified zirconia framework crown was significantly stronger as we can see by the positioning of the orange contour towards the right hand side compared to the conventionally designed framework zirconia crown. But still significantly lower than the metal ceramic. The next comparison involved full contour or monolithic lithium disilicate e.max crowns. The results show that either two millimeters or one millimeter thickness e.max crowns should behave like metal ceramics in terms of reliability, as you can see by the overlap between these contours on the right hand side of the graphic. Although the reliability of materials for prosthetic reconstructions under fatigue loading has been described in several papers, their specific behavior when used for implant supported restorations and their effect on bone response have been explored to a very limited extent and somewhat anecdotally. For implant supported single crowns, for example, it has been shown that forces transmitted to the peri implant bone are significantly higher for ceramic than for composite. These authors concluded that composite crowns are better able to absorb shock from occlusal forces than those made of ceramics. Similar findings have been observed for fixed dental prostheses in a recent investigation where these authors have concluded that implant supported fiber reinforced composite fixed partial dentures could eliminate the stresses in the bone implant interface and maintain normal physiological loading of the surrounding bone, therefore minimizing the risk of peri implant bone loss. While these findings are relevant and they definitely need to be validated from a laboratory and clinical perspective, they have motivated us to further look at the mechanical behavior of composites when used for implant supported reconstructions. So when a technique involving bonding of an indirect composite onto the abutment in a screwless and cementless restoration comes to question, such as the integrated abutment crown or the IAC concept, we should ask the following questions. Firstly, how well the composites bond to titanium? Secondly, what is the mechanical performance especially under fatigue? Thirdly, what do we know about staining? To address the first question, does the study have done bond testing of several composites after bonded and aged in water? The results showed that strong bonds could be achieved and maintained with composites, making them suitable materials for aesthetic fixed restorations. Subsequently, the load to failure behavior of IACs made of several different composites was compared to metal ceramic. The results showed that the average load to failure was not significantly different between composite IACs and metal ceramics. Under fatigue loading, IACs made of two different composites showed that the average load in which they failed was around eight hundred newtons and as you see from the contours overlapping they were not statistically different. Interestingly failures occurring even at high loads comprise chippings that could be either polished or repaired depending on their extent. And as you may see from these scanning electron micrographs. This is exactly how they have shown to fail in a clinical study where out of fifty nine IACs only one chipping was observed, which could be repolished and the crown returned to clinical function. As we may change the IAC abutment design due to either occlusal constraints where we may need a shorter post for composite retention or a narrower abutment base due to limited proximal space, let’s see how these different challenging scenarios behaved when we fatigued them. This is a cross section showing how they looked in terms of composite support after veneered for the anatomy of a molar crown. We have called them large base, small base with 4.0mm post, and small base with a two millimeter post in the center for composite retention. Just like the graphic we have seen in the previous investigation, the positioning of the contours showed that the large base abutment was significantly stronger than the small base with the 2.0mm post. However, the reduced base on a 4.0mm post resulted in similar strength of the large base, as we may see from the overlapping between these two contours. An interesting aspect that we have observed in our fractographic analysis was that voids were incorporated from packing with indirect composite. This motivated us to further test IACs made from CAD/CAM composites. This is the finished CAD/CAM IAC molar crown, and the results showed an improved mechanical performance of CAD/CAM produced composites compared to indirect composites used as IACs. When it comes to more complex geometries such as fixed dental prostheses, we propose to compare metal ceramic to zirconia in addition to composites used either as a full contour material or as a veneered onto a CAD/CAM produced fiber reinforced framework. This is how the composite groups looked like in a cross section. A full contour block of indirect composite in one group and the other was the same composite supported by a fiber reinforced CAD/CAM framework. The results show that composites with or even without the support of a fiber reinforced composite framework presented the same characteristic strength under fatigue as a metal ceramic bridge. When the probability of survival, here given as percentage values, are compared, these three groups comprised by fiber reinforced composite framework, the solid composite and the metal ceramic were not statistically different from each other, whereas the zirconia bridges were significantly lower. As we move on to even more complex scenarios, such as full arch zirconia reconstructions, it is important to bear in mind that chipping scenarios are also a concern and have shown to be somewhat frequent as in the study that showed thirty four percent of fracture within the veneering porcelain in a three year follow-up clinical study. For the last question regarding staining, there’s a recent study where several composites were aged and subjected to staining coffee and wine. The authors have found that staining is as superficial as twenty micron and that repolishing can reestablish the composite’s original color. So as we could conclude, the first question, bonding to composites does not seem to be an issue. The reliability of IACs and bridges seem to match those of metal ceramics. And third, should staining be an issue, the possibility of reestablishing composite color by repolishing has shown to be effective. In addition, composites in general are very user friendly as they can always be added chairside. The information presented here is the result of years of productive collaboration. I’m Estevam Bonfante. Thank you for watching.