Basics of Indirect Restorations Part 1 – Decision Making – PS006

Jaz’s Introduction:
So, to spare you my sweat patches, I am recording in my living room, and I’ve got about three minutes before my wife and kids come home, so let’s crack on.

Look, crowns and bridges, anything indirect is a big steep learning curve when you’re a student. But what I’m hoping to cover today will not only help guide students, but also is like a basic revision of indirect restorative. I remember being taught PFM, porcelain fused to metal crowns, and speaking to Emma, our Protrusive student, she’s also learning porcelain fused to metal.

Let me tell you, in the real world, many of our restorations are all ceramic. So Emma really was interested in learning more about this. So remember, Emma’s our protrusive student, follow her journey through all these episodes. And really, I’m getting Emma to ask all the relevant questions because sometimes you lose touch in the struggles of when you were a beginner.

And that’s why Emma’s really gonna make things tangible for us, break things down. And ask me the right questions so I can cover things that can actually help young dentist students and those who just want some revision of the basics. We cover key themes like direct vs indirect, on lays vs full crowns.

I know we did a full episode on that recently by the way, PDP189, you should totally check that one out. But we kind of talk about it more in the basics foundational student friendly version. Hope you enjoy this episode, and yes, there are Emma’s famous student notes available to download in the student forum and Protrusive Vault section of Protrusive Guidance, our app.

The website for that is protrusive. app or download it on iOS and Android. Remember, if you email student at protrusive. co. uk with proof that you’re a student, you get full access to this area. Enjoy the main episode, I’ll catch you in the outro, and of course, do come back for part two.

Emma Hutchison, the Protrusive Student, and all the students listening and watching, and Dentist, who sometimes like to join us here. Welcome back to another edition for Dentist students. This is June. This is June’s edition. We’re focusing on onlays and crowns and that kind of stuff, which is the theme of the month. But particularly, we’re going to have an opportunity to catch up with you, Emma, and also answer your questions from a student’s perspective.

Main Episode:
So firstly, Emma, How you been? How’s the last week or so? How’s the last month been? Anything new that you’ve learned last time with dentures? Any new experiences that you’ve had?

[Emma]
Yeah, so the last time that we’ve recorded, it’s actually been a quiet one actually. I had a patient in last Friday with a fractured fill in, had to take all that out and patch that back up. Other than that, I’ve not seen any more frost patients or anything like that. So it’s actually been quite quiet. I’ve only seen one patient, but not as-

[Jaz]
Academically? What are all the kind of themes that you’ve been covering academically?

[Emma]
So, recently, I think in Glasgow, towards the end of the semester, because we’ve only got a month or two left. It’s February right now that we’re recording this. They start to pile in more and more of the theory stuff. I don’t know if that’s just how it works out in Glasgow. But you sort of wince down on the clinical time and ramp up a bit more on the theory stuff. So it’s been a lot of consent, ethics, all that sort of thing that we’ve been covering, which would be good to do on here at some point as well. But yeah, just whole range of things, but it’s good just trying to keep on top of it, I suppose.

[Jaz]
I think that our next chat has now been decided on the consent ethics of communication. So there we are. Easy as that. Right. Great. Well, today let’s talk about crowns, right? So I remember being a dental student and you learn all these different types of preps on the phantom head.

And initially you still feel like you’ve got two left hand in five years out of it. And you’re trying really hard not to hit the adjacent tooth and you end up tapering too much. And I found crowns at a very, deep learning curve in terms of getting my hand coordination right. Being able to use the mirror and focus on the reflection and not trying to use a direct vision, trying to switch to indirect vision. Are these the challenges that you’re living and breathing right now?

[Emma]
Yeah, definitely. I mean, I’ve not had any crown or bridge patients so far. Nothing like that. I’ve only had complete crowns down on phantom heads at the moment. And even that without a tongue in the way, cheeks and all the rest of it, it’s really, really challenging.

The only thing that I can think of at the moment, we have been taught sort of two different ways. It might be different in lots of universities about the process you go through and metal ceramic crowns versus all ceramic crowns. And that’s been a lot of my teaching so far, is the differences between those two. Nothing quite like-

[Jaz]
Well, they’ve told you the differences, but I mean, fair enough, but have they given you any indications of what we’re actually doing in the real world? What you should be focusing a bit more on, or when you actually come to treating your patients, what’s the more likely type of crown that you may be doing? Have they sort of covered that?

[Emma]
No, actually, I’m not really sure what type of crowns that we do provide in Glasgow Dental Hospital. I actually don’t know. I really don’t know.

[Jaz]
I mean, I’d be fascinated because back when I was in Sheffield, it was very traditional metal based and PFM, so porcelain infused to metal. I don’t think I did a all ceramic crown as a dental student, to be honest with you. I’m struggling to remember if I did. Maybe one anterior tooth. But things have shifted a long way in the world of ceramics. So I’m hoping, because really PFM is getting phased out. Like there are still a big place of PFM.

We’ll talk about that when I would use PFM, but it’s all the buzz materials are lithium disilicate, which is Emax is a brand name, if you like, by either part of lithium disilicate. Have you covered that ceramic name, lithium disilicate?

[Emma]
Yes. Yeah. Yeah. And that’ll definitely be included in the notes for this month as well.

[Jaz]
Brilliant. Excellent. So yeah, this is a type of glass ceramic. It’s an etchable ceramic. So one of the things I remember learning as a student is etchable and non etchable ceramics. And then zirconia is the other one. Okay. So, it’s being used a lot for it’s a different properties like strength and whatnot, but we always have to balance it out with how abrasive it is to natural tooth, how much tooth height you have and how much reduction you can do. So many different things you consider in the matrix. So where do you want to start, Emma? What’s your top question?

[Emma]
Yeah. So my first top question, I’ve been thinking about this, so as I’ve been saying, what I’ve been taught so far in university is to prep the teeth depending on the material that’s going to be used for, let’s just say, a crown.

Again, quite a broad question that I’ll start off with, does this align with real life dentistry? I don’t know if you’ve seen many of the bits and bobs that I’ve put, that I’ve sent to you for my teaching on this already, but yeah, does that align with real life dentistry? Like, how much does your prep rely on the material that you’re going to use? Does that influence it a huge amount?

[Jaz]
Okay, great question. And really, at the beginning, when you’re new to crown preps, you’re kind of, so much visual stimulus. You’re trying to keep your hands steady. You’re trying not to taper too much. And so, as a newbie dentist, as a dental student, you’re just trying to get the basics right.

And really, your hand skills aren’t there. And so you’re trying to just about get a margin that the technician could read. And so you’re doing all that. And then you kind of just pray that it’s enough and you send it to the technician and hopefully they can make a crown out of it.

And the most common one is you didn’t give enough occlusal clearance. So actually what you’re being taught is a really good way that you should begin with the end in mind. That’s a really, really good thing. So I’m not one to say that. I will look at a tooth and I’ll say for definitely, for sure, it’s going to be this material.

Sometimes it is clear, but a lot of time I will do the following, Emma. So let’s take a tooth that’s carious. It’s an old MOD amalgam. It’s carious. We know that by the time we remove all the amalgam and the caries, there’s not going to be a lot of tooth structure left and it’ll be too ambitious for a composite. Okay. So does that make sense so far? You’ve decided already that you think you’re going to be going indirect. You’re going to do your gold standard caries removal. You’re going to build up a core or a foundation restoration, typically, a bulk kill, dual kill composite, that kind of stuff.

I use something called Paracore. Some people use GIC, which is a bit weak. I tend to stress composite to be honest with you. So we’ve got a core in, but now you need to prep it. Now, when we’re prepping it, before we prep it, we kind of now decide, right? What material am I aiming for? So, aesthetics will come into play here.

Functional demands will come into play here. For example, for an anterior tooth, you’re going to get better aesthetics from, let’s say, a lithium disilicate crown than you would from a PFM, generally speaking. To get the same level of aesthetics from PFM, you’d have to be very aggressive, give a nice meaty shoulder, which is more invasive.

So let’s say you decided that you’re going to do an Emax crown. And so Emax is like the brand name of Ivoclar. So it’s a lithium disilicate and they produce these guidelines, right? So they say, okay, for example, a one millimeter a rounded shoulder, for example, all the way around and a 1. 5 millimeters occlusal clearance.

Okay. Let’s say, okay. And so you have that in your mind and you know that you want to give your technician enough space for aesthetics and also to respect the integrity of the material. So yes, you are going to then prep according to what’s gold standard for that. It all depends on that initial decision you make.

Okay. And once you’ve decided that I’m picking this material for this reason, then yes. Aesthetics and material integrity. So for PFM, like I think I was reading your notes. You said 2. 5 millimeters occlusal reduction, right?

[Emma]
Yeah. Yeah.

[Jaz]
That’s a lot.

[Emma]
Okay. Okay.

[Jaz]
That is a lot. So, and okay. In the real world, we are moving more to this dentistry. I doubt you’ve been taught this yet, and maybe you won’t get taught this, I don’t know, but onlays and overlays made out of ceramic. Is that something that’s been covered yet?

[Emma]
I don’t think so. I’m not sure.

[Jaz]
Do you know what an onlay, overlay is? Do you know what these terms are?

[Emma]
Yeah, I know what inlays onlays are. I think I’ve maybe prepped one onlay in Phantom Head, and that was it, really. That was it.

[Jaz]
Was that a metal one, by any chance?

[Emma]
I couldn’t even tell you, Jaz. I couldn’t even tell you.

[Jaz]
Okay, well, put it this way. Let’s just, for the students, just break it down. Onlay is you’re replacing at least one custom. So you’re replacing one at the one cusp. Overlay is you’re covering all the cusps. For example. Now, you could do an onlay in metal. So let’s say you can use your non-precious metal or gold. Okay. Right. And the way that preparation will differ to a ceramic one is the metal one is allowed to have sharp internal line angles, right?

Because the metal can tolerate it. It’s very well defined and it’s very minimally aggressive. It’s like, 0. 7, sometimes 0. 5 millimeters. of axial reduction and occlusally, it could be a millimeter thin, which is great. So very minimally invasive. If you compare that to a lithium disilicate, it’s much more rounded and slowing.

There is no sharp internal corners allowed because sharp internal corners, it starts to crack glass, glass ceramic, you’re cracking the glass base. So the prep, when you look at a tooth and the prep looks different, it’s more rounded. I’ve actually got good photos to add to this. So while I’m saying this for those who are watching and not listening, I remember the scenario where I was prepping a lower second molar and a lower first molar, right?

On the same patient, same quadrant. And one was for a metal onlay because I wanted to reduce less occlusally. I had limited crown height and I didn’t want to drill so much in the occlusal clearance. So I went for metal and the tooth in front, I had a good amount of enamel. But I had more to play with in terms of occlusal clearance, so I went for ceramic.

And the distinctive features was one was way more well defined than the other one. So the top theme so far is, yes, begin with the end in mind. And the type of material you choose will influence what your prep looks like. And there is a difference whether you’re going for it onlay, or for a full crown. What questions have you got based on that? Cause I know I’m saying 50 million things here, but that’s going to lead to a hundred million different questions.

[Emma]
Yeah, definitely. So I even wondered this when I was working full time as a dental nurse and it’s just, okay, so let’s take a tooth which hasn’t been root canal treated just for easy, I suppose. What criteria do you consider when you’re selecting the most appropriate type of restoration? Like what are the deciding factors between direct and indirect or an onlay versus a whole crown? And I know that’s a huge question but that’s something I just, I don’t think I would be able to judge very well where I am clinically at the moment. I find that very hard to sort of comprehend put that into practice.

[Jaz]
Emma, even qualified dentists mess with me all the time. Even I’m the same. Like I often ponder a lot less now, but as a young dentist, even I used to, I needed more clarity on this. And so I think it’s a great question. And always remember Emma, throughout as we develop our podcasting relationship, you have to remember that you are the advocate for students, right?

So if I’ve said anything that you’re thinking, it doesn’t 100 percent make sense. There’s tons of students out there thinking, well, what the hell did I just say? So remember, you’re the advocate for students, right? So there’s no such thing as a silly question and you must challenge me and you must stop me because the whole reason we’re meeting together is to benefit those damn students, right?

And some dentists who want to just go back to basics, right? So let’s start with direct versus indirect. We did our very first episode about when is potentially a direct restoration of large composite too large and the larger the composite, the less successful was the number one reason the composite to fail if it was too ambitious.

So if you feel like you’re using more than two compules and probably you’re being a bit too ambitious with your composite, right? If you’re trying to get these perfect contact areas, so the tooth in front and behind, and you’re trying to, you’re faffing around, you’re spending an hour and a half to do a big filling.

That’s too long. Okay. You’re better off doing something indirect. You’re going to, the patient will be better serviced and it will last longer to get something stronger and better made from the lab. So there’s a point where the restoration gets too big. The other times you may consider that, hmm, should I go for direct composite or indirect crown onlay is you’ve got loads of cracks in a tooth.

You’ve got loads of cracks in the tooth. You kind of want to hug the tooth. You want to prevent the flex. Composite flexes more than an indirect material. So these are some of the things that you consider and for longevity, like that indirect would be good. Direct can be less invasive, can be less invasive.

So there’s a point where actually it’s a small MO or a small DO, fine, composite. A large MO, large DO, fine. MOD, maybe fine, composite. But then if you look at the patient and the patient’s got broken cusps everywhere, large muscles, high forces, then maybe you’re going to get better longevity by going for the indirect. So there’s no hard and fast rules. You’ve got to really base it on that individual. But if I was to say one thing, the larger the composite, the more you’re going to tend towards indirect.

[Emma]
Okay, that makes sense. And then, so I suppose again, I suppose again, it is one of those things where a common theme is as we’re going through this Jaz and just you get better at it as you go along judging these types of things. Because I could look at it and someone will ask me, would you put a composite on that? Would you do a crown? And I would believe whatever you say. Because I just don’t know. I just don’t know.

[Jaz]
Emma, this stuff still split room. You can have dentists a room who are all 40 years qualified, right? And we show them an MOD cavity with a small crack inside. Half of them will go for a large composite and half of them will go for some sort of crack. You’d be amazed. There really is very few like true indications. Especially nowadays where we’re really pushing the boundaries of our large composites.

We’ve got some nicer matrices, we’ve got some higher quality composites. So really people are pushing the boundaries of composites. So yeah, I wouldn’t expect anyone to be to say definitively, but the more of the factors you have, for example, the crack, the root filled tooth, for sure, if it’s a root filled tooth, it’s weaker, it flexes more, it’s potentially more brittle, quote unquote, and therefore you’re tending more towards an indirect.

But there’s no very few definite cases where it’s like, hmm, you can’t do indirect. Now, when you look at tooth and to actually reconstruct this with a large composite, it’s going to be so technically demanding to actually get a good contact and a good result. Then again, that’s another reason to go indirect.

Now, there are some rules, like if the isthmus is at least a third of the width of the entire buccal to lingual, those again, little guidelines that we use, but they’re not a hundred percent definitive. Once you make that decision that, okay, I feel as though this tooth needs indirect. And you know what? A lot of young dentists are doing large, they have composite day in, day out, where they should be doing indirect because A, they’re not confident with indirect and no. So clinician experience comes into play. I did that for, for a long time. B, the patients don’t wanna pay for it. And that depends a lot on your communication. So this is maybe really farfetched too.

Like you can’t even imagine, like then again, actually you’ve been nursing, so you’ve seen these live conversations and so the conversation goes like this, right? You know in your heart that this tooth would benefit from an indirect, but what you say to the patient is, okay, we can do a big filling, it’s going to be X amount, or we can do a crown, it’s going to be 3X.

And then you let the patient choose, and they’re going to go for X, they’re going to go for the large filling. But if you’ve seen their facial profile and all the cracks and stuff, that’s actually a disservice to the patient. So, what our young dentists will do, really push the boundaries of those large composites.

When you get that confidence and once you can see your dentistry come back and see that actually those large composites start chipping or staining or the contacts aren’t so good and you really come to terms with the fact that, okay, there are certain teeth which need indirect restoration. The next question you then ask is, how do you decide whether to do?

Something like an onlay or something like a full crown. So I think this is the last thing we’ll discuss for today because this is a big topic in itself. Okay. At dental School, I didn’t prep a single onlay, I don’t think. And it really was full crown, full crown, full crown, a lot of PFM stuff, heavy margin and stuff, right?

So a lot of the stuff I had to learn in the real world. What my current philosophy is now is if I can do an onlay, Okay. I will. Because onlay is more conservative of tooth tissue. There will be studies, when you do a full crown, you remove up to 70 percent of the volume of a tooth. But when you’re doing an onlay, you’re removing like something like 40 percent or 35 percent of the volume of a tooth.

So why not? Right. And so the type of onlay I’m doing more often than not, Emma, is a lithium disilicate onlay. We’re trying to bond basically by bonding. We’re again, we’re not having to control extra bits to get retention grooves and stuff. Then last bit here is why would you bond and why would you not bond?

Well, if you’ve got nice enamel all the way around. You got peripheral enamel, then totally, believe in the bond. It’s going to be predictable. Use lithium disilicate. But if you’ve got your dentine everywhere, the quality of your enamel is poor, it’s hyper mineralized, it’s flaky, it’s thin, then really in that case, we’re probably better off going more traditional and doing our crown.

But even then, Emma, what you’re being taught, 1. 5 millimetre buccal margin, right? I will be doing something like, 0. 7 millimetre or, 1 millimetre margin in zirconia. Again, that’s so much more conservative, right? So that’s a quick fire on, onlays versus crown. Please tell me as a student, does that make sense?

[Emma]
It does make sense. I think the best thing for me, even just this short chat that we’ve had is just, there’s not always a solid answer. And sometimes you don’t know until you go in. And you explore further, and I think that sort of ties in with one of the huge challenges I’ve found as a dental student is sort of having your own opinion and build, being able to have your own opinion because you see different clinicians for the same treatment plan every week and sometimes you do have to stick to your guns and they’re asking you, why are you doing this?

Why would you not do this? But they like it when you fight your own corner, and you have a reason as to why you are choosing this treatment plan. So, no, it is good to know there’s just you give ten different dentists one patient and they’ll come up with ten different treatment plans, so. No, that’s, yeah.

[Jaz]
It’s not only is a frustration point in dentistry, it’s also the beauty of dentistry. I used to only see this as the most frustrating thing of dentistry, whereby, oh my goodness, why can’t dentists just agree? Why can’t dentistry be black and white? Why can’t we just all, if this tooth comes in, then we do this. But that will take away the fun and the artistic element of dentistry. So if we start to flip it and see the beauty of it, right, and no one’s dictating you, and you can justify it in either way that you want.

The most important thing, just like you said, when you come into an exam scenario and you’ve made a decision, then you want to be like in a school debate. You want to say, well, this house believes in this. Now, some may argue that you can do this, but the reason I have rationalized it is because A, B, and C.

And this is my clinical reasoning. This is my clinical philosophy and I would encourage everyone to over their years, develop a clinical philosophy and refine that philosophy and be open minded to learn from new evidence based and new people that you encounter that teaches something that really resonates with you.

As long as you do no harm. There are some things that, unfortunately, Emma, I’ve seen before I’ve worked these clinics whereby I’m seeing these small MO restorations, which just need a small MO replacement and they’re being prepped for full crown. I’ve seen that. And I used to work in Singapore.

I saw a lot with one clinician in Singapore and we could talk about the whole ethics and stuff that becomes very difficult thing to discuss. But most dentists, I truly believe have got the patient’s best interest at heart and they will always try to look at the patient as a whole.

Because, Emma, one thing we haven’t mentioned is that tooth, that you look at anything, this tooth needs a crown, but you don’t know how the nerve’s going to go. So you do that large composite and you wait and you see, and you do like a posh core, you do a large foundation because truly you don’t want to put a crown the next week, come back and they need a root canal treatment through the crown for a biting tooth.

So, this is why the tooth is attached to a patient who has their values, who has their individual anatomical considerations, individual budgets, right, and their own baggage. So, we need to take it as a beautiful thing that dentistry is a variable and not be hindered by that.

[Emma]
Yeah, that’s such a different take because that is, something that I do actually worry about in dentistry is having my own opinions and being able to stick to them. So no, that’s a nice way to look at it. I suppose the beauty of it. Yeah.

[Jaz]
I think if you, I used to do this a to focus on the negative point and why are there second and third opinions, but the more clinicians I meet and the more letters I read, the letters start with in my clinical opinion, it is a clinical opinion and the practice of dentistry is the practice of dentistry.

We are practicing. No one’s perfect. And as long as you can really follow some key guidelines, doing no harm, having the patient’s best interest at heart, working within your expertise. I don’t think you can go wrong Emma, you’ll be fine.

[Emma]
Everyone will be fine. No, that’s good to know though, that’s good to know.

[Jaz]
Excellent, brilliant. Well, Emma, enjoy the chat. Next time, let’s talk about, was it consent and ethics and communication, that kind of stuff, right?

[Emma]
Yeah, a big one, yeah.

[Jaz]
What are the notes that you’ll be dropping in the student space for this month?

[Emma]
So, we might pop, and we’ll, everyone’s favorite, DMS. Very important for crowns.

[Jaz]
That’s dental material science for someone who’s tuning in for the first time.

[Emma]
Very heavy on the examinable stuff there, but also my teaching in Glasgow and just the guidelines that I’ve been given forcrown preps and different types of materials that are used. Again, all very examinable stuff, so.

[Jaz]
Amazing, and I’ll try and collate some freely available PDFs that are online and just bring them all in one place. That are like helpful guides, some good videos. I’ve got loads of videos of me doing preps and stuff. So my only worry is, Emma, by uploading these videos is, if in dental school you don’t get taught a lithium disilicate overlay, and all I’ve got is a lot of those videos, and also a different type of crown, which I do as a vertical preparation, but I don’t even want to go into that, right?

And so, the thing to appreciate here, Emma, is the way I’m practicing now, only about five, 10 percent of it, is what I learned in dental school, which is scary, right? You’re there, you’re in the heat, you’re in the cold face. You’re like, okay, I’ve got to learn this, got to learn it really well.

But this guy’s telling you that actually you’re only going to do 5, 10 percent of those things because things evolve, things change, you go on courses and some of the stuff in the real world actually is more current and relevant than what, no offense to dental schools, but they might be teaching.

[Emma]
Yeah, absolutely. I mean, I think we also covered, gold crowns and things like that. And it was practiced, like, you’ll probably never do this, but it’s all still included in there anyway.

[Jaz]
It’s a good skill to have. It’s a good thing to know. Sometimes, on second molars, I will operate in the right patient. I think, it’s good to train your hand eye coordination. So all these preps. Practice them, learn the rationale, always, always think why, what’s the end result, and base it on that. So always begin with the end in mind. And with that, Emma, thank you so much for another student segment, and we’ll catch you next month.

[Emma]
See you later, bye.

Jaz’s Outro:
There we have it guys, nice and sweet one today, but do check out part two. In part two, we actually talk about the actual fitting of the crown. When do you reject lab work? How do you even quality control the crown when it comes back from the lab for example? And the exact stages of fitting the crown.

And I think this will help anyone who’s got their first few crown preps coming up, or maybe even a qualified dentist who’s thinking, hmm, how do others do it? So do check out Indirect Restorations Part 2, coming soon. Thanks so much for listening all the way to the end, and do check out the Protrusive Student Notes, available only on Protrusive Guidance.

Thanks for joining us, and I’ll catch you next time.