A Geeky Discussion on Adhesive Onlays – PDP161

I have a quadrant isolated. Classic FM is playing in the background. The teeth are bone dry. I pick up the air abrasion unit and begin my adhesive protocol. I am well and truly in my happy place!

This week we’re joined by Dr Ash Lifts – a wonderful, reflective practitioner from The States. We had a great time discussing cusp preservation to material choices for onlays.

Protrusive Dental Pearl: Build in some ‘indexing’, ‘location’ and resistance form in to your onlay preps – don’t just make it flat because you saw it on the ‘gram!

Watch PDP161 on Youtube

Need to Read it? Check out the Full Episode Transcript below!

Highlights of the episode:

00:00 Introduction
02:21 Protrusive Dental Pearl
05:14 Introduction of Dr. Ashley Chung
08:54 Learning in Biomimetic Dentistry and Ccclusion.
12:13 Direct composite vs Indirect onlays
16:51 Indications for ceramic onlays
17:30 Ceramic vs. Composite
20:49 Zirconia for overlays and onlays
24:14 Dr. Chung’s experience with EMAX and composite.
26:12 8 different ways to prepare for an onlay.
32:01 Minimum Thickness
36:01 Factors influencing cusp preservation
38:18 Panavia vs. Heated composite
43:02 Finish lines and margins for Onlays
47:13 Cusp inclines and adapting prep design

Check out Dr Ashley’s website and courses: https://drashlifts.com/contact

Courses: https://getbondedstaybonded.co.uk/

Waitlist: https://forms.gle/HBAJbK7P66dj68Vx6

If you enjoyed this episode, you will love delving deeper in to the full protocol in Ceramic Onlays from Preps, Temporisation and Bonding Protocols – PDP059

Did you know? You can get CPD from the Web App or Phone App and watch premium clinical videos, for less than a tax deductible Nando’s per month? Just head over to https://protrusive.app

Click below for full episode transcript:

Episode Teaser: When I'm prepping for a ceramic onlay or an overlay, I'm in my happy place. I've got my rubber dam isolation and I just enter this flow state. It really is a fun procedure for me because I feel that every prep and something I'll guess today, Dr. Ashley Chung, aka @dr.ashlifts, also says later in this episode that she feels like no two of her preps ever look the same.

Jaz’s Introduction:
And there is a beauty in that. You really have to think before you prep. It’s not like making a one millimeter shoulder all day round. There’s decisions to make which cusps are in compression, which cusps are in tension, which cusps can you preserve? And that’s why all of our onlay preps look different for different teeth, for different scenarios.

And it’s a big part of why I’ve been doing this for about six years now. And I just love it. I still love it. I still tell my nurse, Zoe. We have an onlay prep today. I’m going to be in the zone. We’ll put on some classical music. I’ll have rubber dam on and I just enjoy it. It’s usually either classical music or like rock music.

So those are my two-treatment music. I used to do hip hop, but then the swear words and curse words, I didn’t think that was a good vibe in my patients. So think like, Red Hot Chili Peppers, Foo Fighters, that kind of stuff. Always classic FM, right? It’s one of the two. Now in this episode with Ash, who by the way, is just the most humble dentist ever.

She’s so sweet, she’s so humble, she’s so caring, so giving. All those good things that we need in dentistry, right? There’s too much fake stuff in dentistry. There’s too much showing off. There’s too much, look at me, I’m awesome. I’ve got millions of followers and I’ve got a Ferrari and this kind of watch.

Where she is just as far away from that as you can go. And this is why she’s attracted such a large audience on Instagram, and I think she deserves all the followers and all the applause that goes with it for all her work that she does. So we need more people like Ash in dentistry, so it was great to have her on the podcast.

Whilst a good chunk of this episode was partial coverage, like how can you preserve certain cusps, and what does Ash look for on the tooth when she’s doing that? So some guidelines on thicknesses of the ceramic as well, when to use which cement, find out when I use Panavia and when I use heated composite and also what Ash’s protocols are.

Find out if you use IvoClean or not. And our thoughts on zirconia overlays and zirconia onlays, like I can tell you now I’m like what the hell, why is this even a thing, but I’m happy to prove wrong. So if in the comments later, please do let us know if you practice, if you do the zirconia partial coverage restoration, why? Let us know.

So all these are all the geeky discussions that we have around adhesive dentistry and onlay prep. So I know there’s good niche of dentists out there who will just absolutely love and geeking out to this. And this is really for you, you restorative geeks, this one’s right for you.

Protrusive Dental Pearls
Before we join the main episode, I’ve got the Protrusive Dental Pearls. So if you’re new to the podcast, welcome to Protrusive. My name is Jaz Gulati. I’m your host. And every episode I give you a gem, a pearl, a tip to try. And this one’s very relevant to onlay preps and overlay preps. One trend you might have seen if you follow me on Instagram is when you have like an onlay or multiple onlays, like a quadrant.

You then have it on your quadrant model, maybe it’s a resin dye, for example, and you have your onlays on the models, and then you tip them over, and you try and shake it, right? And loads of dentists have been doing this, and tagging me, it’s good fun, and we’re checking for how much resistance form you have.

And we’re checking for retention, because technically something that’s going to come off. Actually is retention, right? But really what it’s also checking for is like resistance. If you’re trying to shake it, it checks how much resistance you have. So if you’ve got like these really flat preps and you try this, the onlay is just going to fall off.

So the movement is basically trying to encourage you not to prep really, really flat to try and follow the natural curves of the teeth and have a degree of resistance form built in, which will help and preserve the cement lute or the composite bond. If you’re using composite to bond your onlays.

So the lesson here really is to try and build in some resistance form in your onlay preps. Quite often, if you’re involving the mesial and distal box, the fact that the ceramic will go in those areas will build some innate resistance in your preps. Another thing is that if you actually have a core of composite in the middle, then try and get your big round bur, I call that round bur, big bertha, and sink that round big bertha into the composite and make like a big hole, right?

This may not give you like resistance form so much, but one beautiful thing it does, it gives you indexing, i. e. when your technician is checking the occlusion and trying the crown on, like there’s no slippage, right? The onlay is not going to slip away from the prep. It’s a clear location of the onlay on to the prep.

And so the real gem and the real pearl here is when you try the onlay in the mouth. And one thing that me and Ash discussed is that me and her both try it in the mouth. Whereas lots of dentists will only check it on the models and not try it in the mouth. They will go straight to rubber dam, get everything clean and then try it in and then bond it.

Whereas I like to try my onlays in. And then clean them, and then put the rubber down, and then bond them. So one thing I do is when I try it in, I just check how much resistance form do I have. So once I’ve removed the temp, cleaned away the temp cement, and I’ve got the onlay on, I will push with my finger, like, from the palatal direction, pushing towards the buccal, or from the buccal to the palatal, and I’m basically testing for resistance.

I’m checking for any dislodging. With these lateral forces, is the onlay coming off easily? And I get very sad if it does, and thankfully, most times it that doesn’t happen because I’ve got enough resistance form, retention form. Technically on lays don’t have amazing retention form. The retention for on lays and overlays usually comes from the cement or your composite.

So that’s what gives us retention. But resistance form, the resistance, the lateral movements, that’s a good feature to build in. So for those of you who are watching, I had a few visuals there for those of you who are listening. I hope that made sense. Try and build some resistance form into your onlay preps. Now let’s have a geeky conversation with Dr. Ash Chung.

Main Episode:
Dr. Ashley Chung, as we know you, Dr. Ash lifts. Welcome to the Protrusive Dental podcast. How are you?

Thank you for having me. It’s an honor. I’m doing really great here from sunny Arizona in the United States.

Lovely. I just asked you in the pre recording about how close you are to Frank Spear and [unclear] and stuff. And then you told me that you’ve been to some Kois courses and done some neuromuscular and then. Obviously, we all know, everyone on Instagram and Dentistry knows about you and your love for biomimetics. But for those of my followers and listeners who don’t know much about you, haven’t seen your work, just tell us about you. And I always like to home in on each individual dentist’s journey. Just tell me about your journey to where you are today.

Well, thank you for the opportunity. I like telling this story because I first start off saying that there is nothing special about who I am. I’m just a normal person that really started this journey because I graduated dental school and I started having a lot of failures about two years out.

I was hit with this realization that I had no idea what I was actually doing. And I had a lot of failures, specifically adhesive failures. I would have debonds of my indirects. And the thing that was really hurtful for me was I was restoring D1 lesions with slot preparations and they all started to go bad kind of in a span of a few months.

And these patients were returning with D3 lesions. And I felt awful because I was just trying to restore conservatively this small lesion. And it resulted in them being sent to the endodontist for a root canal. And it was a very dark time. I considered quitting. But, the cost of education for dental school is very high here in the States. And I couldn’t leave. I had to figure out how to make it work.

You were pot committed.

Exactly. I call it our golden handcuffs. We’re handcuffed to the debt. So I had to figure out how to make it work. Like, I didn’t have the choice to pursue another career. The interesting thing is, when I left dental school, I thought to myself, I spent all this money on education.

I don’t need to take CE. I know what I’m doing. I was mainly doing just restorative dentistry, even after graduation, because that was what the office that I was working at would have me do. So I was like, I’m doing preps and fillings, like how hard could this be? And then two years later, I had this rude awakening when I realized I didn’t know what I was doing.

And I was causing harm to my patients. I had to change my mindset. And that’s when I started taking a lot of CE. I was lucky that my brother is also a dentist. He’s 13 years older than me, so he’s a bit ahead. So he actually took biomedic courses, and he’s the one who guided me to take these classes and started me down this path.

I graduated 2015. End of 2019 is when I started to take CE and then I just got hooked. Because what happened is I started to understand what I was doing wrong. And once I realized what I was doing wrong, I really wanted to learn how to do it right and the best way possible. And that really is what biomimetic dentistry is to me, is that it’s a community of dentists who are obsessed with trying to do the best that we can.

And I know that from the outside looking in, we look like a very tight knit, almost cultish like group, but really it’s just a group of very neurotic individuals who obsess about every step that we do because we understand that if we do something wrong, it could cause a lot of harm. And we really want to do the best that we can for our patients.

I went down the occlusion role because my brother was the one who also pointed me to neuromuscular dentistry. So now I did biomedic dentistry and then I’m starting to do more occlusion. Did Kois, the first two courses. I’m here in Arizona now, so the sphere is right here. So. yeah, I call it a disease.

You must, you must.

It’s a disease. Once you get started down the path of realizing how little you actually know and how much there is to learn, you just want to obsessively keep learning more to do better, ultimately for the patient care that we can provide. So that’s a short version of my story.

Congratulations on your hunger and your zest for learning and also for your humility, right? Humility and actually having that insight and reflection in yourself and having the courage to say, okay, you know what? I need to change. Like there are so many colleagues that I know of who since qualifying dental school, like I don’t see them in courses, they never go on courses at all.

And like, you always see the same people on the courses all the time. And so I think there’s something to be said about being that individual who says, you know what? No, dental school didn’t prepare me enough and I need to do, need to know more. I need to do more. I can be way better. And that’s exactly what your journey described there.

The two jokes about biomimetic dentists, just real quick. One, I always say about biomimetic dentists, like vegans, right? You always know they’ll tell you, right? So that was an old one, but it’s a joke, but it’s also not a joke. It’s not a joke at all. It’s actually a compliment. I do think, just like you said, biomimetic dentists as a community are the happiest dentists.

There was a reel we made recently. And they are the happiest dentists because they really do fall in love with the minutiae. And I really do think the joy in dentistry and joy in your career really comes from falling in love with those little details, taking photos step by step. That’s how it becomes an art. And that’s why I see a thriving community.

So I’m going to elaborate on that last statement. I think we’re very happy because we sleep well at night. But also being obsessive about the minutiae is also a bit of a disease, because sometimes I ask myself, like, do I have to be this way? Do I have to think about it this way?

Today we’re going to talk about onlay preparations, but this is a great example. There are times, especially when I first started learning how to prep onlays, where I would sit and be like, do I let go of this cusp or do I leave it? Like, and there are times where I think like, who will judge me and who will care if I reduce this one cusp?

But I sit there and I’ll think like, what is the right choice? And sometimes I do think that well, I sleep well and I know I do good work and having the confidence to do good work really helps me be happy in my career. There are times where I have to tell myself, Ashley, it’s okay. No one cares except you. And you have to let yourself be kind to yourself and let yourself chill a little bit too.

[Jaz] Be kind to yourself. Well said. That’s a great way to start off this podcast. So thanks for sharing your journey. And like I said, it’s about onlays today. Now let’s talk very basic fundamentals, maybe something for the students, indications for onlays.

Now let’s, when I say onlay, obviously we can do a direct onlay, we can just use composite and cover the cusp of the stuff. But let’s specifically talk about indirect onlays. On one end, you have the direct composite, right, as an onlay option, and on the other end, you’re just going to prep a loads more and go for a conventional crown.

Where do you see the indications, the ideal indications for a let’s say a lithium disilicate, for example. A classic ceramic onlay. What are the ideal features that will lend you towards that decision as that as a restoration of choice for you?

First, let’s talk really quick about when we would do a direct onlay versus when we would do an indirect because I want to kind of get that over the humps that way we could hone in on more of when we would do an Emax onlay.

I would do a direct onlay if my patient, let’s say, just financially could not afford the ceramic. I would do it direct for them. The issue with going direct is, biomimetic dentists, we are not bulk filling our onlays. We are layering, little bit at a time, the direct composite to be able to do the onlay in the mouth.

I actually, with the biomimetic strategy, doing a large direct is so much more technique sensitive, so much more back breaking. I call it a labor of love. You have to love the tooth and the patient to be able to do a large restoration with composite with the direct method. Because there’s just so many nuances we understand.

High quality one with good context and good occlusion. Like you can just do it. You can slap on some content.

Exactly. With the anatomy.

Of course.


So yeah, it’s a tough gig.

Exactly. So if I have to do a full cost replacement, I do not like to take the direct approach. Mainly because of the time, I always try to think about my restorations like this. What can I do to give my patient the best result? And I mean from the beginning of when I could bond the tooth, from the prep, the bond, to all the way the anatomy of the restoration itself. And I understand my limits of going direct, and I will only do it if I know my patient can financially afford it.

If they’re literally at the point of, I gotta pull this. Or, I can’t afford what you believe to be the ideal, then I’ll say, hey, I’ll break my back for you and do this direct. I’ll do large inlays direct, but I just believe cusp reconstruction is just a lot harder. Especially when you take in occlusion into mind and other factors like that. So let’s say a patient can afford the ceramic only for me, I don’t really do full cover.

Actually before you talk about the, just wanna stop you there and just wanna talk. Okay. So you mentioned direct composite and you mentioned the reason to do it, and I love how you say it’s a labor of love.

I totally agree. I see a lot of my colleagues, Herman, for example, he’s posting a lot about doing these composites outside the mouth, so they’re semi indirect, right? Is that something that you’ve employed in your protocols as well, to try and be less backbreaking?

I’ve done it for my one patient who couldn’t afford the onlay. I’ve done it once, until before I had CEREC. So what I would do is, with CEREC dentistry, I would negotiate with the patient. Hey, let’s find a way to make this work for you. But I knew I could always use like a composite material versus a ceramic material because I had the CEREC machine there to do it for me.

I think Irman, who’s also a good friend of mine, he’s better than the CEREC machine if you look at his restorations. I’m currently in an office that’s doing lab, sending our restorations to the lab. And I’ve had one case where I did do a semi direct, which, it is also a learning curve. It could have gone better.

But, you know, I was able to still offer that for my patients. Now, I do think, okay, I’m in a situation where I can do more of these and that’s something that if my patient ever has resistance, I will always want to work with them because I never want money to be the reason that they can’t get good work.

Luckily, in my short time at this office, I’ve only had to do it once and I haven’t had to make the decision of do I go for a large onlay? Or do I do the semi direct? And ask me again in like six months and I’ll see if I have an answer for you. And some of the listeners may think, oh, well, money should have no part in how we make these decisions.

But I actually think that it makes a huge part. Because no matter what, we still have to value our own time. I have to still provide the best care that I can do to my patients. And ultimately, I tell every patient, I never want you to get bankrupt because of the dental work that you need to have done. So I do think it’s finding a compromise between these factors that allows us to give good treatment to our patients.

Agreed. And I think in the real world, money always plays a part in any healthcare system. And I think it’s one factor that is, truly has its place in the scheme of decision making.

Yeah. So back to the original question. Okay. When are we doing a ceramic onlay? We always have that situation where a patient comes to our office with lower mandibular molar, distolingual or mesolingual cusps chewed off, broken off.

They have a large class one. For me, that’s the perfect indication for an onlay. Because there’s certain cusps under the amalgam, which there’s going to be more cracks. They be weak. But there’s going to be other cusps that are still going to look really good. As someone that really believes in conservative dentistry, I want to try to save as much of the tooth that is good and only have to remove the part that is bad.

And for me, that is why onlay prepping is such an awesome treatment to have because no onlay really looks the same. So it really makes you think, which I like. I don’t like the repetitive motion of just prepping the crown. It makes me feel a little bit too robotic. So I love the decision making and the thinking process of knowing, okay, what cusp am I going to save, which ones am I going to remove?

In terms of actual material, my lab that I’m currently working with mainly does ceramic. I haven’t done a composite onlay with them. But with my CEREC, I did composite all the time. And what I would do is if I could save one cusp, at least in the mouth, to make sure it had good occlusion on that cusp, I would have no issue doing composite.

It was a time factor. I worked in a high volume CEREC office, so sometimes there’s just no time for me to sit for the 20 extra minutes for it to fire. I would do composite because I know the stability of the cusp that’s left will help hold that occlusion in place. I know even though the composite may wear a little bit more than the ceramic, but the bond that I achieve is just as good, and so I know it’s a really good material.

So picking between ceramic, and composite has always been kind of more about time and situation. If I have to do an overlay, I do stick, and an overlay is when we have to reduce all four cusps. I do pick to stay to ceramic, mainly because I do worry about the long term occlusion. I’ve had mixed experience and discussions with mentors.

Some think that the composites will wear over time. Others say that it doesn’t. I personally think it matters to the patient and their chewing cycle and occlusion. So that’s why when I do all four cusps, I do like to stick to the ceramic.

It’s almost 2024, so it’ll be interesting to know 2023, 2024. Is there a place for gold in your material selection?

I love gold. I believe you can bond it. My always issue is this. When it’s expensive, it’s an extra two, three hundred dollars on the patient for the extra lab bill. And so if I have a patient who wants gold, I’ll tell them, it’s an extra cost. Do you still want it? And the patient, most of the time will say no. There’s been a few.

I’ll have the white one please.

Yeah, exactly. Exactly. I’ve had one patient though, they were getting an implant on their first premolar and they wanted it to be gold. So when they smiled, they could have the grill and they pay the extra for it.


Like you’ll have one off. My big thing with gold is always starting there. Patient, are you willing? And I actually think gold is such a great material. If anything, I see gold in some of my patients mouths older than me, and they still look pristine. The other thing I do worry about gold, though, is I was never trained to prep gold. Like, if I were to do a gold onlay, I would still prep it the way that I would, for a ceramic, which is not the way you should prep for a gold, right?

The most expensive way you could ever do it.

Exactly. There’s such a minimal art to do gold restorations. And I believe to be successful, you have to first understand how to prep them well and how to manage the material well, which for me, I’m not that confident in. Luckily, I do work with Patrick Calalang, who is a great dentist, who’s also been around for much longer than me.

So I would refer the patient to them and be like, hey, I think Patrick has more experience with the gold restorations and do it for you. But that’s the situation with gold here, at least in the States.

And then the new material nowadays, not new, but zirconia being used for overlays and onlays. I never got this, right? Because I know we can bond, but when you have such a reliable and predictable bond in lithium. Why are collisions- And maybe you’ll tell me that you’re part of this trend and and maybe I’m I’m missing out but using zirconia as your overlay material above and beyond lithium disilicate, do you find, do you see there is a reason?

I don’t use zirconia at all. The only time I ever bond zirconia to the mouth is if a patient comes in with a debonded zirconia crown and they really want the zirconia to put back on. It’s a biomimetic philosophy. We try to use materials that are similar in the physical properties of the natural tooth.

And so ceramic is very similar in properties to the enamel, composite to the dentine. It’s a very brief way to describe it. With zirconia, it’s a lot stiffer, a lot harder material. And that is why we shy away from it. Personally, for me, I don’t like using zirconia because it takes away my ability to cement with a composite.

And that is a pure technical issue. And the reason for that is, especially when you do CAD CAM dentistry, it is really hard to get perfect margins on that EMAX, and my hands are not the best. My hands shake a little bit. I know I, as a dentist, I don’t know if I should admit that on public, but so I love biomimetic dentistry because learning how to cement with restorative composite, it allows me to overcompensate for some of these errors that I may have in my margin.

But with zirconia, I wouldn’t be able to do that because light doesn’t pass through the restoration. I have seen other clinicians use it as overlays and onlays, and I do think part of it is, as humans, we love trying new things, right? They’re probably like, well, let’s try it and see. Like, I’m bored of doing it this way for so long.

Let’s see if the Zirconia will work. And then I wonder also if there’s a cost issue. I know, at least with the lab, it’s a lot cheaper to get zirconia restoration back than it is a ceramic. And so that might also be a reason why a dentist wants to be conservative, but also wants to have a smaller lab bill. And that’s just a theory. There’s no proof of data for that statement.

If there’s anyone listening or watching right now, be it on YouTube or app, just comment, if you’re one of those dentists using zirconia for partial coverage and onlays and stuff, tell us, let’s just debate, what’s your rationale?

We’d love to understand, seek to understand where you’re coming from. I just don’t see it as a place that I do zirconia crowns because I do vertical preparations. For when I don’t have enough enamel, I’m going to do a conventional crown, then I’ll use zirconia, and I’m going to preserve as much pericervical dentine as possible, and then the whole highly polished and unglazed zirconia and how much the tissues love it, that’s a whole another debate, but for back on track, for an onlay or an overlay, I just don’t see the point of it, but if someone can enlighten me, I’m more than happy to learn and listen to that point of view.

So we’ve discussed yet which materials you’re using. Before we get to the main thing about the different ways, which I’m very excited to learn about, what are the angles you’re going to approach this from, the different ways to prepare for an onlay or an overlay, any other points on materials before we move to this next bit?

Those are the two main things. It’s either don’t be afraid to use composite for your onlays. Yeah, quick story. Since starting biomimetic dentistry, I have not had an EMAX break on me except for one. I did an onlay on the second lower molar. Make sure not to use tooth numbers here.

Yes, exactly.

Distal lingual cusp chip for the patient it broke off. So I did an Emax onlay and it broke. Suspecting there was an occlusal shift some occlusal problems right there, but it was still kind of early on I didn’t recognize it. I redid it and it broke again. So on this patient, Emax’d it twice and at that point I didn’t know what to do, and in my head, I’m like, I’m not going to prep this for a full overlay just because this one corner of this cusp is breaking, and I actually changed the patient’s material to composite, and it actually held up, and it didn’t break, so.

There’s this kind of connotation, and I do think this is one small issue, like when we try to be so biomedic, we’re like, the enamel has to be ceramic, but I actually believe the real core of biomimetic dentistry is really learning the materials and knowing the strengths and weaknesses of each material and understanding where each can be applicable for us to have success. So that’s just the last thing I want to say when it comes to materials.

And I just want to add to that and say I’ve been in place hundreds of EMAX and now [lithium disilicate] units, onlays, I love doing onlays and overlays. I’ve only ever had one fracture in the last six years, and that was a lower first molar, but it was because the occlusal clearance was not enough, and the part where the occlusal clearance wasn’t enough, it was also bonded to dentine, not enamel at that point.

So that was my bad and then just prepped a little bit more and also the opposing plunger cusp reduced that a bit and got the right amount of space or thickness for my lithium disilicate. And that’s been fine for the last two and a half years now. So that’s just my anecdote from that. So, Ashley, tell us what are the eight different ways to prepare for an onlay?

Oh, it’s interesting. We’re discussing on Instagram about the title and stuff. So I really love this. Yeah, the mic is yours. I wanna, I’m hearing about. Which is the angle you’re going to approach this?

I think you’re thinking that I have some like mind blowing thought. All I thought is, and just to give a little background, this is something I hear all the time, whenever I ask on my Instagram, what are some topic ideas that you want to learn about, everyone says prep design.

For some reason, prep design is something that we can talk about so much, but people still have confusion with. And I think part of it too is we may be overcomplicating it. So when I say eight ways to prepare for an onlay, I’m thinking. The upper molar and the lower molar. And learning there’s specific prep designs that you can do if you are going to save one cusp, two cusps, three cusps, or let go of all four.

And it’s that simple. And I believe it should be that simple. When we’re prepping for an onlay, especially with ceramic, we just have a few rules that we need to follow. Like you just mentioned, we need to have thickness of the ceramic. So making sure we have proper reduction. Making sure we have sharp exit angles.

And the other thing that I see often is whenever a cusp is saved, there isn’t a clear margin line around the cusp, and we always have to think about it. Also, from the technician’s point of view, if the technician is trying to do an onlay, they have to see a definitive line of where to put the margin against the cusp.

And so following those rules and then just knowing in your mind what the prep should look like if you are going to save each of the cusps and there you have eight different ways to prep an onlay. It’s just that simple. I hope I didn’t let you down by that explanation.

No, no, no, no, no. It’s good when you think of it like that. That’s innovative. Just because you mentioned it. So let’s just extract that out of you. Guidelines for thickness, for actual material thickness of lithium disilicate or LiSi I’ve heard clinicians say that if you’re bonding to enamel, let’s say you’ve got a wear case and you’re opening the vertical dimension and you have the opportunity to bond purely to enamel, that you can actually go really thin on your Emax, 0. 8 millimeters.

Someone even says 0. 3 millimeters. I was like, well, I would never do that in a molar, but I don’t know, maybe I’m missing out. What kind of thicknesses would you recommend as a guideline?

If we have dentine involved, so not just enamel. I still believe you could go really thin. I believe the strength of the Emax actually comes from how well you bonded it to the tooth. And if there’s any discrepancies in the bond itself, it’s then when things fit, you need a little bit more thickness. If you think back to when Emax first hit the market, a lot of people are still using Fugi or Unicem or RMGI to cement it. And that’s where this whole notion of you can’t put Emax on the second molar because one, it wasn’t bonded, it wasn’t reduced enough probably on the second molar, and so that’s why all the Emax was breaking.

But if we understand, hey, if we bond this properly, and we still have to give it proper reduction, it’s not going to break. I still teach, whenever I teach prep design, we still want to shoot for two millimeters of reduction, which my conservative dentist friends freak out. Two millimeters is so much.

But what I recognize, and this is something I see myself, I never bury my two millimeter depth cut all the way. And if you use one of those depth cut burs with the little top hats, it stops you in the central groove before you even go all the way. And so I had under reduced Emax issues for so long.

And if anyone’s done CEREC dentistry, it’s even worse. They show you in red everywhere, right? Oh, you’re under reduced here. I struggled with that for so much. And so what I had to do is I had to reverse psychology myself and tell myself, you have to bury this thing two milimeters. I’ll take my depth cut bur. I’ll go in through the groove.

I’ll go across the cusp. And once everything is reduced, I actually take off just a little bit more. And the other reason we want at least two is if you follow our principles of using immediate dental sealing and resin coating, which I do for all of my indirects. We add about 0. 5 mm of composite of a liner back onto the prep.

So if I do a perfect 2 mm reduction, that’s going to give me 1. 5 mm of actual material thickness. I still think that’s a lot. You don’t need that much. But like I said, I still under reduce even though I tell myself I need to take off two millimeters. So I always tell conservative docs you need to shoot for 2 and knowing you’re probably going to end up at like 1. 2, 1 millimeter on the actual thickness.

And that’s what I tell them, you need to at least shoot for that. In my head, I know you could probably go thinner, but it all comes down to the clinician and their hand skills and how much they’re going to do. I teach them don’t go beyond two because we don’t want to be that aggressive. So it’s trying to hit that sweet spot when I’m talking to different clinicians.

I totally agree. Jason Smithson taught me 1. 5 to 2 and try and go for 2. So I do that as well. So I’m glad, I really didn’t know what you’re going to say there. I think maybe you’re going to say, oh, you can’t go more than one.

I was worried. So I’m glad you’re going for 2 as well. Just a point on that actually, for our friends who worry about 2 millimeters being an aggressive amount, we have to always remember that it’s 2 millimeters from the, as far away from the pulp as you can get. And from the weakest part of the tooth, right?

The bit that’s connecting. It’s something, a structure that is tall and thin rather than we want short and flat right to get the rigidity and the strength so those really coronal two millimeters are not as important as the gingival third of a tooth hence why again if you can prep to 1. 5 millimeters knowing just like you said that it’s probably going to end up being less is a good thing is that the same because you mentioned earlier actually composite.

You say composite. Composite. I say composite. But with composite, you were suggesting that perhaps you can go even, even lower. How does that work?

[Ashley] So there was actually a paper, I could never say the author’s name, but I believe Magne was part of the paper, Pascal, Dr. Pascal Magne, but they actually looked at ultra thin occlusal veneer type preps and the thickness of the restoration.

So they were going like 0. 6 in the central groove. They did actually [unclear] IDS, they cemented with composite. And what they found is that the composite could go even thinner. The composite survived even better than the ceramic. So whenever I actually have very little clearance, I actually will go towards composite than to do ceramic.

Luckily, I haven’t had that kind of issue, but if you have like a tooth that’s erupted or there’s not enough space from the pulp or wear case, if you don’t have a lot of clearance, trust the composite. It actually works. So that’s actually really cool. And if you don’t mind, I actually want to backtrack and just mention what you were saying about the actual biomechanics of the tooth.

That is such a big part of biomimetic dentistry as well. And understanding that the top half of the tooth above the height of contour, a lot of the tooth takes a lot of compressive forces, which if we know anything about ceramic, it does well in compression but not good in tension. And then the gingival third of the tooth is where a lot of the tensile forces will go in and be absorbed into the tooth during function.

And because of that, a lot of us, we don’t want to put a conventional crown prep when the gingival portion of the tooth has not been prepped, because we want the tooth to handle the tensile stresses, because we believe the tooth will take care of it better than any of our restorations. So I just wanted to add that bit in there for you.

That’s good. And what was the last time, just out of random interest, when was the last time you prepared for a conventional crown? Like de novo, like not even replacing an old conventional crown with a shoulder, like just, I’m going to do a shoulder crown here.

So probably would have been 2019, like early. So I started my biomimetic journey end of 2019, and once I started, I stopped. And it’s easier. I do think part of it is I haven’t dedicated myself to improve my skills. But when you actually go to prep an onlay, once you understand the rules of how the margin line should be, I believe that it’s much easier to prep an overlay or onlay than it is to do a crown where you have to be careful of the taper, have proper resistance form.

Make sure your margin is smooth and even all the way around. My hand skill definitely was not great for the full coverage crowds. And I still sometimes struggle when I have to do a replacement. And I take it off and I’m like, oh, they didn’t prep this properly. So I got to smooth everything out. I struggle definitely a lot more in those cases.

I totally agree. And it’s just an enjoyable prep to do actually onlays in general. Back on track of the different ways. How do you want to disseminate the information about preserving one cusp, two cusps? What structure should we follow to lead this conversation?

So, this is where it could get tricky, because there’s actually different schools of thought. So, when I was trained with the Six Lessons approach with Dr. David Alleman, he has a very simple rule. When you’re in the tension cusp, is what he calls it, which is the non functional cusp. So, it’s the buccals of the uppers and the lowers of the lingals.

The lingals of the lowers.

Oh, the lingals of the lowers. Thanks for correcting me. Don’t say that wrong. We want at least three millimeters of cusp width from the base of the cusp to the cable surface. We take those calipers and measure in the mouth. And if it was a functional cusp, then we could go two millimeters. It doesn’t have to be as thick. And the idea is that when the tooth on your jaw is going into lateral movements, the tension cusp has greater risk of getting caught in a lateral excursive movement.

So there’s more tension forces on it. Hence why a lot of times we see those lingual cusps on those lower molders break in our patients. So that was the idea. Since taking his course, I’ve taken Mimetika with their group in Europe, and for them, they go even more conservative.

They don’t actually believe, oh, it has to be as thick as three. It could be even thinner. And I think what’s hard is, if you want to go thinner, everything is case by case. So what I actually look for now, is I actually look for wear on the tooth. So if I notice a cusp has a lot of wear, then I play safer rather than sorry.

And I may reduce it, even though it’s a little thicker. But if I see a cusp and it’s pristine, like virgin anatomy is still on the cusp. Then even, let’s say there’s carries under there, so I have to remove a lot of it, I’ll still try to save as much of it as possible. So, I love the conservative philosophy.

It’s a philosophy that doesn’t necessarily mean it’s right or wrong, so I really try to follow it. And there are times where I just, it’s like an enamel shell. But in my mind, I’m like, you know those cases where the decay takes out all the dentine, but the enamel is pristine?

Completely unsupported.

Exactly. But occlusally it looked good. There was no wear on it. Didn’t break. So I’ll reinforce it with fibers and I’ll fill it up. And then I’ll put my margin line right against it. And sometimes that takes time, but it makes me super happy to know that I could save a thin tuft like that and feel good about it.

And this is where the happiness part comes in, right? To the fact that we are happy dentists. Yeah, this is it.

For those of you listening and watching, like, the smile was so organic that you did. Like, that was, that was genuine. That was so, that was so real from you. Like, you were just, yeah, you were in the zone there. I like that very much.

Thank you.

When you were trying to be more conservative and you’re trying to preserve these cusps, sometimes I found that when the overlay comes back, the overlay comes back and I try it in, the marginal gap in that area where you preserve the cusp is much more. Is that to be expected?

Is that something that I have done wrong in my prep, or is that something that the technician’s been too wary of? Is that something that you found as well?

Let me answer this in two parts. So, first, with CEREC dentistry, the software is actually built to have a bit more of a gap against the cusp, so that the actual cement could extrude in that area better.

I agree that a lot of it is prep design. If you do not give a really good marginal finish line, or if you have an undercut, or worse, if you have like a short bevel against the cusp, then it’s not going to sit well. This is why cement is so important to me to have immediate dental sealing and resin coating on my preps so that I could cement with heated composite.

Because I also get that discrepancy a lot. If I was just using resin cement, I would be worried that it would wash out in the future because the gap is big, but when I’m able to use restorative composite, then I feel like, oh, it’s still sealed. It looks good. And it’s going to hold up over time with the function. And so no Jaz, it’s not just you. It happens to everybody. It happens to everyone.

And I’m glad you mentioned how that influences some cement choice. So in my current protocols, if it’s a single overlay, single overlay, I’m a Panavia fan boy. I love Panavia so much. And I’ve been using it for years. It works in my hands, but when I’m doing multiple overlays, a quadrant, I will then use heated composite.

It just gives me that time and control is less stressful procedure, right? I can do them all together and floss and check. But when I had the single unit, where I’ve preserved cusps and I have any of those discrepancies, then yes, I will choose a heated composite actually. So that’s a really good point made there about how that can influence which cement a dentist may choose to use because it fills up those voids so well.

I also use Panavia a lot. If I ever feel like I didn’t do my immediate distance sealing and resin coating well, or if something was a little exposed, and if God forbid, I know my occlusion is a little off, like it’s going to come back a little high, I’ll use Panavia. It has its place, too. For me, I think the hardest thing of using resin cement now is I’ve lost my touch for the tack cure.

When you have to tack that perfect amount, you have to clean it off. It’s like, I cure and I’m like, oh, it’s still runny. And so I go to tack again, now it’s rock hard. And then I’m like having to bur everything off. It goes to show that if you stop using something regularly, you lose the touch.

And then suddenly you’re not as confident anymore in doing it. And so I believe Resin Cement is still very good. It’s been used for so long, everyone has such good results with it. It’s just, the composite for me is just a way for me to compensate for some of my shortcomings.

Very good. And is IvoClean as part of your protocol? Like in terms of you learn from two different schools of thoughts, Mimetika, you said, and also Alleman’s. Are they big on IvoClean, the product?

So we do use it in my office, but in the protocol, you technically shouldn’t need it.

No way. Okay. You shouldn’t need it or you shouldn’t use it.

You shouldn’t. It’s because that idea of doing the protocol the best we can is we hydrofluoric acid etch and this is emax. So we’re hydrofluoric acid etching the emax. We clean off precipitates either with phosphoric acid or putting it into an ultrasonic. And then we do silane, and then what we do is we go straight into we rubber dam. Right? So there’s no point of contamination that could happen. I do try-

Okay, the reason I’m using it, Ashley, is I think you’re just going to make the same point. I try it in before the rubber dam, hence why I use Ivoclean.

Okay. Yes. So, in our office, we do try it on before. I know biomimetic dentists who will try it on, and then they will hydrofluoric acid etch. Then they start their treatment process. So they never have to Ivoclean. So for us, because we have it etched before, and then, we’re trying it on and it’s getting contaminated, we’re doing IvoClean. I know it’s actually a bit controversial because I know some people who believe that silane, because it’s hydrophobic, even though saliva may get on it, it doesn’t decrease the efficacy of the silane. But I have not done that yet. So for now I just play safe than sorry.

Yeah. And for me, I take control of the etching myself because yeah, just having that control basically. So I have my restoration back, not etch with HF acid. And then when I tried it and I then use IvoClean, then I will go to HF etching.

And then I will do phosphoric acid because, I bought this ultrasonic bath. Someone told me they want to buy from Amazon and I just, it’s just there. I need to actually pick it up and start using it. Do I have to use ethanol or can I use something else?

I’ve always used distilled water. Ethanol is what we’ve used in a lot of the studies that, I used distilled water. The interesting other thing is I always did cat cam. And I’ve been told by someone that when you do it with ceric blocks, you don’t get the precipitates when you do hydrofluoric acid etch, but with pressed do you do. So it’s very interesting because when I was in my old office and doing the CEREC, I was much more of a control freak and I had to do every single step.

And I would notice that it’s very matte on the intaglio. There’s no white speckles. But when now that I’m at the lab, I do notice it. And sometimes I ask myself, oh, like, we should come back and clean this again. But, hey, we haven’t had a debond yet. The girls, they’re very good. They do everything.

I’m trying to learn to trust and let go a little bit more for my own mental health. And so far, it’s been working out.

Okay, very good. Well, my final question, just looking at the time now, is finish lines. Unless you had anything more to add about prep designs, I’m so sorry.

The one last thing I do want to say is, I started off the talk saying, sometimes I sit and ponder, should I save a cusp or not? And sometimes I love that thinking process, but other times, especially when you’re running behind, there’s patients waiting, sometimes it’s also harmful. I always like to say, when in doubt, just reduce it. There is no dental god in this universe who will punish you because you decided to reduce the cusps.

Make your life easier. Don’t try to make complicated prep designs. Make it easy. There’s eight ways. Depending on which cusps you save, just follow those guidelines and then you’re well on your way. And as you get more used to doing online preps, you can start doing the more interesting prep designs where you’re saving marginal ridges. And doing, cross cusp saving and things like that. But keep it simple to start. It’s just what I want to end with.

Brilliant. And when we’re choosing our margin, our finishing margin, so for example, you can have a butt joint. So if those dental students are listing butt joints like flat, then we have the bevels, then we have chamfer.

What guidelines have you been taught or do you employ or have you been teaching as well? To use in which scenarios, because this is itself, I’m sure there’s so many different opinions and a little bit of an art form to it?

I agree. And so this is what I teach. It comes down to your hand skill. Theoretically, beveling is what we’re taught to be the best for the enamel. We want to bevel. But if you don’t bevel right, then you’re going to have thin ceramic at the margin. Especially when you have like a really steep bevel, or like a really short bevel. It could cause your restoration more harm at the end.

So, in everything we do as clinicians, we need to be able to analyze what is my limitation, what is my skill to provide the best result. I did butt joint for a long time, and I never had issues, but that’s because I would try to bevel and I could see it on my CEREC that I didn’t bevel right, and all of a sudden I had a thin area.

Right on that margin. Lately though, I’ve been trying to bevel more. And it’s because I realized I wasn’t beveling properly. What I was doing is I would go in and I would try to just bevel the enamel, which is actually really hard to do. What you really want to do is a long bevel that starts from the dentine.

You’re actually creating the shape. That’s coming off the margin that’s more sloped, not so flat. And by that you naturally will have a bevel in the enamel as well. So I’ve been looking at some awesome preps. I think It was Raphael, Dr. Raphael Wymann, who had this amazing post where he did, it was a lower molar, and he took a photo of it, kind of from the side, and it showed that long bevel down.

And it was beautiful, and that’s when it kind of clicked to me. That’s how you do the bevel, not just right at the enamel, because that’s when you get the thin ceramic. So I always tell my clinicians, you need, that’s why you need to take photos of your work. If you don’t have a scanner, you need feedback from your lab on your quality of your prep, and that’s how you know where to improve and how to do be better. And that should be what determines which finish line you do. Not necessarily which one is right or wrong in the theoretical science sense, but which one is right for you.

I mean, I tend to bevel if it’s like a first molar or a premolar, and I made that decision with the patient. That we’re going to be conservative, we’re not going to go right up to the sort of gingiva to try and sort of hide that transition and I want to try and blend my restoration to the tooth, I’d go for a bevel, whereas politely I might finish with a butt because it’s just easier to prep. Is that similar guidelines that you follow or any deviations from that?

Because I wasn’t confident in my bevel for a long time, I wasn’t even offering it for aesthetic reasons. Right? I would do my best to match my butt joint on my premolars to make it match. And I always had good success if I used It is really tough.

So it’s a lot of patient selection as well. At the same time, if you do the right material and if it’s, the patient has the right shade, it blends really well, especially if you use like a heated composite, the tube, it just looks seamless. And now that I am getting better, I actually try to bevel everything.

So I also try to think about the anatomical reductions. So like the palate of the uppers, we’re going to need a little bit more reduction ’cause of the palatal cusps coming out. Not reduction, but we have to follow the incline. So there I would do a longer bevel like on the palatal versus on the lower.

I’ll do that longer bevel on the buccal because that’s where a lot of the times the upper cusp is coming inclined down. I hope that made sense. But those are the things that I see when I do and that’s the benefit to me of scanning because you can see that so clearly and I’ll always see oh I’m a little under reduced possibly if I just do a butt joint on the like the buckle of the lower molar So instead let’s do that long bevel so that it follows the incline of the upper cusp. So those are the things that I think about now.

I will put a visual on to, for people to visualize. Cause if that would be supportive of a visual, but I have a visual in mind. I’ve got a case where I prepped and that shows that, yeah, very well. How you’re doing a bevel at that point, just give you the extra space where you need it the most.

And that can really help. Amazing. Ash, you’ve answered all my questions so brilliantly. It’s been an absolute joy to speak with you. Finally, please tell us how we can follow you, learn more from you. Whereabouts are you teaching nowadays? What kind of stuff do you get up to?

So, everyone knows me from my Instagram, @dr.ashlifts. I have a website, drashlifts.com. If you actually email me straight from the contact page there, it goes to my email and that’s actually the best way to get a hold of me these days, Instagram. I have to go through like a certain day where I go through all my messages because it could get a little overwhelming.

And I do try to, if everyone, and I ask everyone, if you have a question, just ask the question. Don’t start off with a hi, because I don’t respond back. But I do try to respond every dental question that comes my way and at least point people in the right direction for them to learn. Patrick and I are starting a course for new graduate dentists called Synergy.

We’re actually having our first lecture this coming Saturday. Really excited about that and so that’s the online platform that we’re on in teaching and I’m actually going to be in the UK December 1st through the 3rd at teaching with Sammy and Irman there as well.

Oh, lovely.

That’s where I’ll be.

What I’ll do is I’ll put the links to your course that you’re doing starting this Saturday Just send me that link. I’ll put that in the show notes. And also the event for December for all the UK, who want to learn some biomimetic dentistry, that’d be great. So, to support you guys and Sammy as well. So that’s amazing. And of course, definitely to follow Dr. Ashlifts on Instagram guys. Ash, thanks so much for giving your time today. We appreciate it.

Thank you for having me. You made this easy and I really enjoyed my time chatting with you.

Jaz’s Outro:
Well, there we have it guys. Thank you so much for listening. All the way to the end wasn’t Ash brilliant, right? She’s so sweet. She’s so humble. I love her journey. I love her story I love everything that she shares so do follow her on instagram. And if you check out the show notes I put the link to her online course and also her visit to England for the course in biomimetic dentistry as well. So if you’d like to check that out, that’s in the show notes If you’ve listened all the way here, you want to claim some CPD or CE, just download the app on the app store or iOS.

The best way to do it is actually to head to protrusive.app website. You make an account there. It’s very inexpensive. I may say so myself, cause it’s all tax deductible. It costs, it costs less than a Nando’s per month, basically to get access to all the episodes, CPD and the premium content uploaded once a month.

Which goes a long way to support this channel and allow it to grow. Once you sign up and make a login online on your laptop, you can then use that login on Android and on iOS. The best way is to usually make it by your browser on your laptop, and then use that premium login on your devices. You can also download content offline.

Like no other membership site allows you to do that, right? When you go on these big CE websites, they don’t allow you to download the videos to your device. But the app allows you to do that on your phone. So that’s a cool feature. If you’re catching a plane or a train and you have a choppy signal. So that’s another reason to become a Premium Protruserati.

If you found this video useful, please do give it a thumbs up on YouTube and leave a comment. I love reading the comments or Apple or Spotify or the rating. So I would really much appreciate that and catch you in the next episode. Same time, same place.

Hosted by
Jaz Gulati

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Episode 219