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Episode 7 - Exploring Full Arch Materials

Full-Arch Restoration - Mission Possible (Mini-Series)

Selecting the appropriate prosthetic materials for full arch restorations requires a specific understanding of the patient's functional and esthetic needs. In episode 7 of “Full Arch Restoration…Mission Possible,” Dr. Frank LaMar discusses how to evaluate a patient’s prosthetic requirements and then select the most appropriate materials to achieve the patient’s goals.

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Episode 7 - Exploring Full Arch Prosthetic Materials 

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Watch the Hybridge Podcast Video: Episode 7 - Exploring Full Arch Prosthetic Materials


TRANSCRIPT

Randal: Joining me this morning is Dr. Frank LaMar, and we're going to talk a little about the prosthetic materials that are used in restorations. Today Zirconia is a very popular medium for restorations, especially in the full arch area. 

Dr. LaMar: Thanks Randal. This is is a question that, a common question in the industry, that doctors that are looking to get into the full arch space want to know, they see all of these ads in options out there. First of all, let's start with what we think the criteria might be for materials for a full art restoration.  Because it's a little bit different than what you might use if you were to do a conventional implant-supported bridge maybe three or four tooth implant supported bridge. With full arch, because you're splinting 5, 6 implants together and it's the full arch of teeth, the percussive feel of material should have some have some bit of a dampening effect. It shouldn't be too hard. The materials that we choose ideally should be adjustable so patients who, post-treatment, decide that something feels too thick or they're biting your cheek, we want to be able to adjust those materials. So adjustability to me is a big criteria.  The ability to add as well, you know especially in the maxilla, there are times we want to add to the undersurface of the restoration.  Slo the ease of adding is also there. So there are a lot of things that we decide on pre-treatment. Now, you mentioned zirconia as a restorative material. Zirconia, by the way, is probably one of the best restorative materials to come on the market in a really long time. We use zirconia for a lot of our implant restorations. To be clear, our non-full arch restorations. Any anterior implant restorations or posterior, we do it all with zirconia, and the reason is zirconia is so hard. I always joke around that you could get run over by a truck, and your zirconia restorations would be intact.

Randal: Everything else would be flat.

Dr. LaMar: Everything else would be flat and your zirconia would still be sitting there just fine.  So as far as incisal strength, if you were to do a full arch restoration with full contour zirconia, we call it monolithic, the likelihood of having any sort of incisal chip or break or tooth cracked pretty much really doesn't exist. So if the reason for picking a material is strictly about the durability of incisal edges, and most important by the way most of the prosthetic failure on the incisal edge is usually in the maxillary anterior. So from 6 to 11, then zirconia is the choice. Patients who are bruxer's (grind their teeth) where anything that you put in their mouth they're going to ruin, you might want to consider zirconia as the material of choice for maybe that 5% of the population that you really worried about. But understand that if you're making a materials decision based on durability then you're giving up some other advantages to some other materials.

Randal: Such as?

Dr. LaMar: Acrylic's, or polymethyl methacrylate acrylics, we refer to them as the PMMA materials, they've come a long way over the last five years. Today the PMMA that we use is milled out of a puck. It's all CAD-CAM designed, and these 12 tooth pieces are fused onto a metal framework. So as we look at different materials, being able to use a polymethyl methacrylate tooth insert on these restorations has a lot of advantages. Number one, they have a very normal percussive feel to them. Zirconia tends to be really very harsh. Especially if you go zirconia to zirconia restoration, you could really hear that across the room if somebody were to tap their teeth together. Actually, I've had patients complain of that.  That's not the worst part of zirconia. But when you're using acrylics you have the ability to adjust for them, the ease of adjustability, and full arch restorations, you're talking about hitting the target and the target on a full arch restoration of success is much smaller than on any other kind of restoration we're going to do as restorative doctors. One of the disadvantages to zirconia to me, and I think this is a big thing, you know again, the advantage being the strength of incisal edge, but what's the weak link to a zirconia restoration? Because there's always a weak link to something. The thing with zirconia is the underside, the surface that fits to the implant platform, that can't be zirconia. So what that is is a titanium abutment that is cemented within the zirconia restoration.  That's the only way you can connect. So you have this really strong restoration, but it's being attached to the implants and the cement bond of that abutment within the little shoe, we call them shoes, the little shoes being cemented within the restoration, that cement bond is going to be the weak link. And so what we've found is that the potential for these abutments or these shoes from debonding is actually very high, and it's not being talked about.

Randal: That's because of the bonding capabilities of titanium?

Dr. LaMar: Well actually, we can chemically bond to sandblasted titanium really well, it's actually the cement to zirconia bond that is really really low compared to metal. And so doctors who are doing these restorations, I think as they accumulate in their practices, I think what they're going to find, over years, is that they're going to have a very high level of complication that nobody is talking about, which is these cement bonds breaking down. And if you think about five or six implants being splinted together and screwing them on, the passivity...first of all, there's no such thing as totally passive. None of these restorations really, if you looked under a microscope would be 100% passive. They have to be within a certain range, and when you're screwing on zirconia restorations and you're putting pressure on those screws, on those metal shoes, there's immediately a tension that's created between the screw, and it's a pull onto that metal shoe.  And so that's I think why over time, under load, these cement seals fatigue.  And so that's a big deal that nobody seems to be talking about.  One of the other disadvantages I see is that when we go and we're creating the zirconia framework, and we're creating enough strength of thick wall thickness to be able to cement one of these shoes into it, there needs to be a bulk of material there.  And so what happens is, my zirconia full arch restorations, on the palatal surface of an upper, they tend to be much bulkier. 

Randal: So does that add weight?

Dr. LaMar: It creates what I think is one of the biggest complications in maxillary hybrid restorations, is phenetic issues for a patient. If you put the implants a little too palatal and now you're putting this mass of material around these abutments, you have no way to adjust for that, and you have what looks like a shelf where the tongue is usually hitting. At that juncture of where the cingulum of those anterior teeth is now, there's this over contoured mass, it could be 4, 5 or 6 millimeters thick, where something isn't' normally there.  Now the patient complains that they don't sound right because there's this obstruction.  I call it, there's a turbulence as the air comes off the palate, the air gets messed up. So phenetic issues, over time maintenance issues with these shoes, these are big deals.  Of course, I could go on, but the assumption is zirconia is so strong, therefore monolithic, or full contoured zirconia is when it's at it's strongest, but most zirconia doesn't look as good as the PMMA materials that we have. Actually, PMMA is much more esthetic than full contoured zirconia. So what happens is, is when doctors like myself want to use zirconia and we have a patient that has a reasonable to a high level of expectation that it's going to look like real teeth, we then ask our technicians to veneer the zirconia.  And so now we're putting feldspathic porcelain and we're fusing it to the outer surface, facially veneered zirconia, which basically brings us back to what a PFM was, which is two different materials and we're depending on the bond of those two materials onto that surface and now you're actually creating a much weaker surface.  The incisal strength goes far below what a milled PMMA is. So that's the irony. People say, I'm doing zirconia because it's so strong. But if they're facially veneering it with feldspathic porcelain it's actually not stronger, it's actually weaker.

Randal: So the advantage as you describe them in terms of reducing chair time or the ability to make modifications chair side are much more capable with the PMMA.

Dr. LaMar: So a PMMA CAD-CAM designed PMMA restoration, not what we think about ten years ago which was denture teeth fused to a titanium frame. These are CAD-CAM designed restorations milled and fused to a metal frame, and that bond, by the way, is very strong, but yet we have all the advantages of CAD-CAM but all the advantages of a softer material to work.  And at the end of the day, it is about when you're all done, is this patient going to be happy?  I can make a patient happier with PMMA predictably than I can with zirconia.

Randal: Well that's great insight and great depth of understanding of how those materials interact and the advantages and disadvantages. I thank you for your time this morning.

Dr. LaMar: Thank's a lot Randal.

Randal: And thank you, ladies and gentlemen, for joining us today, on Full Arch Restoration Mission Possible.

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