Protrusive Dental Podcast podcast

Understanding Cracked Tooth Syndrome and the Dental Occlusion Triad – PS019

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You’re doing a routine exam when you spot it – a stained hairline crack snaking across the marginal ridge of a molar. Your patient hasn’t mentioned any symptoms… Yet.

Should you sound the alarm? Monitor and wait? Jump straight to treatment?

Cracked teeth are one of dentistry’s most misunderstood diagnoses. Colleagues debate whether to crown or monitor. And that crack you’re staring at? It could stay dormant for years—or spiral into an extraction by next month.

So what separates the teeth that crack catastrophically from those that quietly hold together?

In this episode, I am joined by final-year dental student Emma to crack the code (pun intended) on cracked tooth syndrome.

We break down the easy-to-remember “position, force, time” framework to help you spot risk factors before disaster strikes, and share a real-world case of a 19-year-old bruxist whose molar was saved by smart occlusal thinking.

If you’ve ever felt uncertain about diagnosing, explaining, or managing cracked teeth, this episode will change how you think about every suspicious line you see.

https://youtu.be/mU8mM8ZNIVU Watch PS019 on YouTube

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

Key Takeaways

  • Risk factors include large restorations and bruxism.
  • Occlusion plays a significant role in tooth health.
  • Diet can impact the integrity of teeth.
  • Every patient presents unique challenges in treatment.
  • Communication about dental issues is key for patient care.
  • Certain teeth are more prone to fractures due to their anatomy.
  • The weakest link theory explains why some patients experience more dental issues.
  • Patient history is crucial in predicting future dental problems.
  • The age and dental history of a patient influence treatment decisions.
  • Understanding occlusion is essential for diagnosing and treating cracked teeth.
  • The location of a tooth affects the force it experiences during chewing.
  • Bruxism increases the risk of tooth fractures.
  • Tooth contacts and forces play a critical role in diagnosing issues.
  • Opposing teeth can provide valuable insights into tooth health.
  • Effective communication is essential in managing cracked teeth.
  • Stains on teeth can indicate deeper issues with cracks.
  • Monitoring and documenting cracks over time is crucial for patient care.

Highlights of this episode:

00:00 Teaser

00:49 Intro

03:25 Emma’s Dental School Updates

07:18 What is Cracked Tooth Syndrome (CTS)?

10:02 Crack Progression and Severity

12:45 Risk Factors

14:54 Position–Force–Time Framework

21:53 Which Teeth Fracture Most Often?

25:32 Midroll

28:53 Which Teeth Fracture Most Often?

30:37 The Weakest Link Theory

34:05 Diagnostic Tools

37:56 Treatment Planning

39:42 Case Study – High Force Patient

47:27 Communication and Patient Management

51:03 Key Clinician Takeaways

53:03 Conclusion and Next Episode Preview

53:42 Outro

Check out the AAE cracked teeth and root fracture guide for excellent visuals and classification details.

Literature review on cracked teeth – examines evidence around risk factors, prevention, diagnosis, and treatment of cracked teeth.

Want to learn more about cracked teeth? Have a listen to PDP028 and PDP098 – both packed with practical tips and case-based insights.

#BreadAndButterDentistry #PDPMainEpisodes #OcclusionTMDandSplints

This episode is eligible for 0.75 CE credits via the quiz on Protrusive Guidance.

This episode contributes to the following GDC development outcomes:

  • Outcome C

AGD Subject Code: 250 – Operative (Restorative) Dentistry

Aim: To help dental professionals understand the causes, diagnosis, and management of cracked teeth through a practical, evidence-based approach. It focuses on identifying risk factors using the Position–Force–Time framework and improving patient outcomes through informed communication and tailored treatment planning.

Dentists will be able to:

  1. Explain the aetiology and progression of cracked tooth syndrome
  2. Identify high-risk teeth and patient factors—such as restoration design, occlusal contacts, and parafunctional habits—that predispose to cracks
  3. Communicate effectively with patients about the significance of cracks, prognosis, and monitoring options, improving patient understanding and consent

Click below for full episode transcript:

Teaser: Sometimes, you have a tooth position problem. Sometimes you have a tooth force problem, and sometimes you have a tooth contact time problem. So time, force, position. A crack is an end product of overload. So risk factors for cracked teeth, right?

Teaser:
So if we think, again, that is to do with overload, right? When you have a patient who’s got large amalgam restorations, MOD, I don’t remember the last time I removed an amalgam and I didn’t see a crack underneath.

Why is it that maxillary premolars are more likely to crack than mandibular premolars? This is really fascinating. If all you do is remove the crack and put a composite, the composite will also fail through overload eventually. So you must change something about the environment to reduce the crack propagation.

Jaz’s Introduction:
I’ve been involved in dental communities for many years now. I run my own community, the Protruserati, Protrusive Guidance. And one of the questions that keep propping up week by week, month by month, year by year… it’s just all seasons, all time, is about cracked teeth management, diagnosis, cracked tooth syndrome, and getting very patient specific, describing the symptoms and signs, and all the discussions are about cracked teeth.

So there’s still obviously some uncertainty about the best way to diagnose and manage cracked teeth, which is why we created this episode. I know it’s part of the PS, Protrusive Student series, but honestly, the way I ended up explaining cracks in my philosophy and the way I think about how cracks form and how the management very much depends on so many patient factors is pretty unique, I think. I don’t think I’ve ever spoken about cracks in this way, and I think it ended up being a really wholesome episode. Again, thanks to some wonderful questions from our student, Emma.

Now, alongside this episode in the show notes, we’ve put together some essential reading and some great PDF, excellent data and visuals on cracked teeth, and I mentioned a good review, literature review on cracked teeth. That’s also referenced in the show notes. If you are watching or listening on Protrusive Guidance, just scroll below and download it.

And if you haven’t yet joined the community, what are you waiting for? We’re waiting for you on protrusive.app. I really enjoyed recording this episode, Emma, and I hope you enjoy listening or watching it. Oh, and this episode is eligible for CE. There was so much substance. So whether you’re gonna collect CPD hours or CE credits, whoever you are in the world, this episode is eligible again through the Protrusive Guidance app. Let’s catch the main episode.

Main Episode:
Emma, the Protrusive Student. Welcome back to the Protrusive Dental Podcast. It’s so nice to have you. We’re talking about cracked teeth today. Look, I can talk about cracked teeth for days. It’s something when I, in the early episodes, one of the early episodes, it’s titled I Hate Cracked Teeth.

I still hate cracked teeth. We all hate cracked teeth. No one likes cracked teeth. But you know what? Over the years, I’ve learned so much about cracked teeth, and now I’ve got some things to share with you and I’m really excited to share with you that will really change how you approach cracked teeth and how you communicate cracked teeth and all that kind of good stuff.

But what I wanna start with is what’s more important to you as a student? You are connected to students and young dentists better than I am. You are right there in the trenches, okay? Like asking these questions that no one wants to ask anymore because they’re afraid to ask, right?

Because, hmm, maybe I should know this already, but you have no fear, no shame because you’re a student, it’s fine. So it’s cool. Like, you don’t have to know everything. And so you are in a position to ask, to represent everyone and ask those questions. So firstly, Emma, tell us, give us an update. How’s final year going at uni?

[Emma]
Yeah, final year’s going good. Just the same as when I caught up with you a couple weeks ago. It’s just our finals are out the way, so I’ve got a lot more time in the evening to sort of decompress and focus on the things that I know will be in my book the day after. If I’ve got a crown prep or something or something that I need to look up on, I know what I’m gonna be doing.

I can go home and I can focus on that for the next day rather than stressing about exams. But it’s good. It’s going really well. It’s going good. I’m enjoying it.

[Jaz]
Good. You made me remember something, right? Like I was just trying to remember how long does it take for you not to… like for example, I remember being a student, and you get a root canal the next day, you’d have to like revise the steps for a root canal. Did you do that?

[Emma]
There’s a lot of things that I don’t do that for anymore, where I probably would’ve in about third year or something like that. But for something like root treatment, I’ll always just remind myself, just look over, make sure that I know. ‘Cause I’m always gonna be asked questions, so just to keep on top of everything. I do still do that, yeah.

[Jaz]
I won’t forget, Emma, I was playing FIFA. That’s what we did. With that clinic, we’d come home, we’d play FIFA. That’s all we did. So maybe, I dunno if student life’s changed yet for the guys or not.

But that’s kind of how we lived life. And so I remember playing FIFA and it was like 20 minutes to go until my clinic starts, right? Okay, one more match. One more match kind of thing. And I was there, I was living in the fifth year. I was third year, and I was just revising with him, okay, I’ve gotta wax your registration for complete dentures.

Let’s go over the five things I wanna check for while I’m button-mashing and playing kind of thing. So it’s just-in-time learning, it’s revision. I was just trying to remember, as a dentist, a qualified dentist, how long did it take me before I was comfortable not even looking at my day list anymore, and whatever life’s thrown my way, I’ll be able to deal with it. And it’s a good number of years, maybe 5, 6, 7 years until I got to a stage where, you know, whatever comes through my door now, it’s okay, I got this.

I think the only caveat here is if you go down the path of comprehensive dentistry, right, and there are multiple steps involved and long appointments. You have to do your due diligence. So sometimes you’re checking the day list not to like, oh, let me revise the steps for how I’m gonna raise the OVD and do the mockup and preps, or whatever.

It’s more, has the lab delivered the lab work? Let me make a checklist to make sure that my nurse is gonna be happy supporting me on that day for that treatment. It’s other challenges that it brings. So it’s all fun and games as long as you relish it and enjoy it. And part of the enjoyment is that every patient is different.

Every patient has unique challenges. Even cracked teeth in one individual is treated completely differently to a cracked tooth in another individual. So with that, Emma, what would you like to know about cracks?

[Emma]
Yes. So this idea about cracked tooth syndrome episodes came to me because it was one of the first questions we had in our finals, and it was one of the last lectures that we ever received in fourth year. And you know, at the very end of—

[Jaz]
So what question? What’s a typical finals question look like about cracked teeth? Amuse me.

[Emma]
So I think for one of the—so the topic was cracked tooth syndrome, and one of the first questions was: give me however many modalities of diagnosing a cracked tooth, signs and symptoms, things like that.

I’m one of those people that typically forget everything that is asked as soon as you walk out of an exam. But I remember this one, and I remember it because it was one of the last lectures that was given to us. And because it was the last one, it’s not something that I really looked over. It was the first question. I’m sure it was one of the first questions in the paper, and I was like, oh no.

[Jaz]
You were kicking yourself.

[Emma]
Yeah. Yeah, I was kicking myself. So the first question I had for you was just, in your own terms, what is cracked tooth syndrome and does it differ from like a fully split tooth?

[Jaz]
Okay, great question. So cracked tooth syndrome is a set of symptoms and signs that tell you—that’s why it’s called syndrome, right?—it’s a set of symptoms and signs that lead you to a diagnosis towards, okay, this tooth is cracked, and that’s the cause of the symptoms. Symptoms could be like cold sensitivity, hot sensitivity, classically pain on biting, especially on the release.

So that’s like the classic syndrome, and then you kind of make that diagnosis. The reason why it’s difficult to diagnose sometimes is because it’s not easy for patients to pinpoint exactly where the pain’s coming from. Quite often with pulpitic pain, like, it’s somewhere around here, and as you know, it spreads.

And that’s the pulp involvement. The other one is that these cracks can sometimes be very difficult to see, and only when you start wearing more magnification, and like literally more and more magnification, you can start to see it. And just because a crack looks innocuous doesn’t mean it can’t actually be responsible for the patient’s pain.

So these can be some challenging factors. Now, how does cracked tooth syndrome differ from a split tooth? Well, split tooth is like—imagine a spectrum, right? Split tooth is like, okay, this tooth is absolutely shot. Split tooth is like vertical root fracture in a way. So it’s completely split, it’s vertical root fracture.

So on one end of the spectrum, that is like completely hopeless prognosis. Is that what you’re expecting with split tooth?

[Emma]
Yeah. So from my understanding, like cracked tooth syndrome, you know, you can have pulpal involvement, but you don’t need pulpal involvement to still get symptoms. But then if you’ve got like a fully fractured tooth, I don’t know if that would even come under like cracked tooth syndrome. I don’t really know.

[Jaz]
So split tooth and vertical root fracture… like the difference between them is kind of academic. Like what started it? The end result of both those is that the tooth is for the bin, right? It needs the forceps.

So just like what I’ll do is, in the show notes and in the student section of the app, I’m gonna put the American Association of Endodontics’ whole guide. They’ve got on cracked teeth, really good visuals, absolutely fantastic. And the way it shows visuals for a split tooth is something that starts by the cusps and the crack goes all the way down, and then the tooth is like in two pieces.

Imagine a premolar with the buccal cusp and the lingual cusp like completely split. And now that tooth’s unrestorable. Whereas a vertical root fracture, we commonly associate with like an upper central that’s got a metal post inside. The crack started at the point of where the post is, right where that stress is.

So it’s subgingival, and the crack extends upwards. So either way, when you look at the end product, they’re both shot. And they’re kind of like massive cracks. So though at one end you’ve got the split tooth and vertical root fracture, but they all have to develop into that.

There’s often the initial crack. Now ignoring the whole vertical root fractures, go with split tooth: every split tooth begins life with a more innocuous crack, higher up by the cusp. And if you are lucky, if a patient’s lucky, the direction that that crack travels… it kind of goes like, let’s say marginal ridge, but then it starts to go more buccal or more lingual.

So if it’s going more buccal or lingual, what will be sacrificed when that breakage event happens? When that force exceeding event happens? What, Emma, will be sacrificed?

[Emma]
So one of the cusps.

[Jaz]
Exactly. So that’s when you get someone coming in and the cusp is broken off. You must have seen that, right?

[Emma]
Yeah, yeah.

[Jaz]
So that’s fine. But if the patient’s unlucky and the trajectory of that crack is going straight down, straight down into the gingiva eventually, and then it’s going through the floor of the pulp chamber, if you like, and eventually the whole tooth is being split… that’s way more advanced. So there is like the very tiny crazing in enamel, then there’s a crack that goes further into dentine.

Then that crack kind of propagates and propagates and goes spread across, and it goes subgingival. And our job is to really intervene in a timely manner. So it’s a difficult one because if we all lived to age 400, right? Then every one of us, no matter how much low force you produce, or I don’t clench or whatever, every one of us would all have cracked teeth, split teeth, if you live to age 400.

Now, some people, they generate so much force or various other factors, anatomical as well, that they’re able to split a tooth in their forties, whereas someone in their eighties may do it as well. But it kind of depends on what kind of pressures.

Ultimately, a crack is an end product of overload. Overload is a process. There has to be some degree of overload that is beyond the adaptation of the enamel and dentine. That flexure. If you imagine a molar, Emma, and when every time you’re chewing, there is—believe it or not—the cusps are like moving away from each other. The tooth is flexing.

It’s hard to imagine, but when you start getting a crack, okay, then those cusps, they start to flex even more. Like because imagine microscopically, they’re waving around. And then as the crack gets bigger and bigger and longer and longer, that sort of waving around gets more and more, and then that just makes the situation worse.

[Emma]
Yeah. So I was going to ask as well about particular risk factors. So I’m guessing the number one is things like bruxism, parafunctional habits, things like that. I was also gonna ask if there’s certain teeth that are more commonly affected, like i.e. molars more than a central, like more force put on those teeth.

[Jaz]
Okay, these are great questions. Let’s do it in two parts. Okay. So risk factors for cracked teeth, right? So if we think, again, that is to do with overload, right? When you have a patient who’s got large amalgam restorations, MOD, I don’t remember the last time I removed an amalgam and I didn’t see a crack underneath.

It’s just the nature of it. You’ve got this stiff, really strong metal restoration, okay? And every time the patient’s chewing, those cusps are flexing. That metal’s not bonded to the tooth. Those cusps are flexing, and often those big MOD cavities, they render the walls very weak and flexible. Therefore, you are more prone to getting a crack.

So if you already have a large restoration inside the tooth, that’s like more than a third of the isthmus, if you like, classically, as they say, right? So the bigger the restoration in the kind of buccolingual direction, and the deeper the restoration, the more the tooth’s gonna crack.

It’s a bit like if you get a virgin tooth and you do those experiments that you see whereby they load and load and load a tooth until it cracks, okay? You know that the virgin tooth is going to survive until a very high load, whereas the tooth that has essentially got a big hole cut down the middle—because all you’re replacing that hole with is metal—metal’s not protecting that tooth.

So essentially you have this naked tooth with a giant cavity, and you’re loading it. You can imagine that at 20% of the force of what it would’ve taken to break the virgin tooth, that tooth’s gonna split completely.

So having a large restoration is absolutely a risk factor. The other risk factor—and sometimes I see cracks on virgin teeth, so teeth are completely unrestored—and this is a red flag for a high-force patient. If you see cracks on virgin teeth, then that is something to really pay attention to.

So this could be someone… and what I like to do in my occlusion stuff that I teach, this is how I like to break it down. Please, Emma, let me know because very few people have heard this spiel. I’m working on like the ultimate occlusion lecture 2025, 2026, like every year trying to make… break down the occlusion.

And this is my new way of presenting it. So let me know what you think. First person ever to hear it, right? If we—like obviously the joints are very important, and if you change anything about both joints or one joint, both TMJs or one TMJ, then you change the occlusion, okay?

But when we’re students, young dentists, it’s very difficult for us to think in that kind of plane. You wanna just… let’s think dental for a moment. Let’s think the teeth together. And sometimes you have a tooth position problem. Sometimes you have a tooth force problem. And sometimes you have a tooth contact time problem.

Time, force, position.

So stay with me now. With the position, if two teeth—let’s imagine premolars, because that kind of leads onto your second question about which teeth are at risk of fracturing. Well, premolars: classically very steep cusps, okay? And if you keep loading it, they flex and they’re very prone to vertical root fractures and split tooth.

The premolars are very prone to that. But let’s imagine upper premolar. When you bite together, the buccal cusp or the cusp tip of that lower premolar sits right in the middle of the fossa. The cusps are not bending, they’re not asked to bend in any way. However, if the lower molar is a little bit off and maybe it’s a little buccal position, can you now imagine that with the upper premolar, the force contact is not in the fossa?

It’s somewhere up the buccal wall. Do you know what we call that contact? Go on. It’s called an incline contact. Don’t worry—I had no idea when I was on stage. I had no idea it was called incline contact.

[Emma]
No, I didn’t know that. I didn’t know that.

[Jaz]
It’s an incline—but can you imagine what I mean? Like it’s not in the flat area, it’s on an incline, right? So you can imagine you’re loading the incline. And what’s that incline exacerbating? What’s it encouraging? It’s encouraging that buccal cusp to flex away from the tooth. So that is a tooth position problem.

Loads of our patients have really suboptimal occlusions. They’ve got incline contacts everywhere. In nature, we see incline contacts. So why isn’t everyone destroying their teeth? Okay, well, because position is one factor. It’s not the factor. It is one factor. So tooth position and the malocclusion can predispose someone to a crack.

Number two is tooth force. Can you guess or extrapolate where I’m going with this tooth force?

[Emma]
Bruxism habits.

[Jaz]
Bruxism, yes. But bruxism is also linked to the third one, which is tooth time contact. But yes—so essentially you’re putting… you’re overloading. So clenching, okay? So act of clenching, getting your masseter and temporalis and medial pterygoid.

So that one’s linked more to the tooth time contact as well. When the patient’s elevator muscles contract, a force goes through the teeth, and so the more force you put through a tooth, the more you are overloading that tooth. And so yes, clenching is one, but also a patient who’s got large hypertrophic muscles, square jaw… you can imagine that they’re gonna put more force through their teeth.

Now, I don’t know of any great evidence that, Emma, your tooth, your premolar, your first premolar, is way stronger naturally than my first premolar. I don’t know if that’s true. I don’t know if like you put your tooth in the machine and put my tooth in the machine that genetically—unless we have like amelogenesis imperfecta, that kind of stuff.

But let’s assume that me and you, our first premolars are very similar. Maybe 1 or 2% difference. Genetic variation. Maybe Scottish enamel is stronger than Afghani enamel. So it’s probably true. So you can imagine that there might be minor difference, but if I have got like strong muscles—which I do—in my jaw, and if I’m clenching a lot and you are not…

The lifetime of how much force is gonna go through that tooth is different. So it’s force.

And then that also ties in with diet in a way. Now I don’t buy that, oh, we should avoid eating nuts. But however, the harder the food you eat… imagine trapping some food between your premolars. Like imagine you put an almond between your premolars, and then you bite and you crush it. What happens is that the teeth overload the almond. The almond doesn’t overload our teeth. Our teeth overload the almond.

However, to be able to produce that load to crack the almond, some load had to be received into the premolars. Now if you have a very big, hard diet… I mean the worst are ice chewers. Imagine someone who just chews ice. So you have to constantly break ice, and how you’re breaking it—you’re breaking it with your cusps.

What your cusps have to do every time you clench together… they have to flex. So you are promoting cusp flexure. So diet actually plays a role as well. Someone who’s an ice chewer, eating a lot of nuts—they are more likely. Okay, it’s not the only thing, but if they’re also clenching, if they’ve also got incline contacts, you can now imagine all those factors add up to someone having more cracked teeth.

The other one that goes hand in hand back with tooth position is the fact that some people have steeper cusp angles and other people genetically have shallower cusp angles. Can you figure out why this may be significant?

[Emma]
If you’ve got deeper cusp angles, are you more likely to have that sort of incline contact?

[Jaz]
Well, well done. You’re more likely to have an incline contact, but also the following. The patient, when they chew on ice or an almond… when you’ve got steeper inclines and you chew on it, there’s more flex, there’s more pressure going in right in the middle, and there’s more flexure versus a shallow one.

And also imagine if I give you like a model of a tooth, one with steep angles and one with shallow angles, and I told you, you have to break it with your hands. The one that’s got steep— you get it, and you kind of wedge in between and you can break it way more easily. If I give you a flat tooth and I say break this flat tooth, what are you gonna grip onto to break it? It’s just physics, right? So it’s just physics.

And so the last one is tooth time contact. It goes back to if someone’s touching their teeth together for 18 minutes a day and that’s it… that’s completely different to someone who’s doing it for four hours a day, or three hours they’re touching their teeth together.

So not one of these factors is more responsible than the other, but all of these together are resulting in overload of individual teeth. And the systems, the muscles get overloaded, right? Everything is a system.

Has this helped you to maybe—and be honest, Emma—is this useful to think about it in terms of tooth position, tooth force, tooth time contact, in terms of the scope, the triad of what can happen to a tooth?

[Emma]
Yeah, I would think so. It almost reminds me of like those diagrams and you see the triangles. That’s what I’m picturing in my head, but I think that’s so interesting, especially about the almond analogy that you used there. I’ve never really thought about it like that before, and people’s diets and things. That’s really, really interesting.

[Jaz]
I’m looking forward to making like an introduction to occlusions, and there’s one way to explain it, and then I wanna bring the joints into it and the muscles and describe symptoms, talk about the importance of adaptation, the variables in occlusion. So that’s a little starter piece, so I’m glad you like it.

Now, going with that, there are certain teeth that are, just evidence-based, more likely to fracture than others. First premolars—very prone to fracture. And so these are teeth that are more prone to splitting. So first premolars. Second molars. So first three molars because of that steep angulation that they have often. Second molars. Can you guess why second molars?

[Emma]
Just a large amount of force generated on the seat?

[Jaz]
Correct. Why is there more force being perceived through a second molar?

[Emma]
Closer to the TMJ, like the Nutcracker analogy.

[Jaz]
Perfect. It’s closer to the fulcrum, the TMJ. The muscles are right there as well. Like actually, where is your muscle? It’s right there. But your muscles are right there. And then also when you’re gonna chew ice, where are you gonna stick it? Stick it between your back teeth, right? You put the ice right between your sevens and go for it. And also if there is bruxism, you’re clenching, squeezing together, then that cusp flexure and the contacts and the strain absolutely is felt on those.

Now this is all from my memory, right? It’s first premolars, second molars. I’m trying to think. And then I think it’s first molars. I’m going to now validate this. Let’s do a validation.

So we’re gonna validate this, guys. I’ve been talking now, and this is from memory. But let’s see if I’m right. I probably have made a mistake somewhere. But let’s see—cracked teeth, a review of the literature—and let’s see what it says. Lovely. Good.

Oh, you see—so those of you listening, there’s some great visuals there. Again, I’ll share this paper in the show notes. So when I share the American Association of Endodontists’ guide on cracked teeth, which is awesome, and this paper as well.

And let’s find out. I think it’s lower mandibular molars. So it talks about different prevalence of incidences. Most of the studies reporting the incidence or prevalence of incomplete tooth fractures agreed that cracked teeth were significantly associated with intracoronal restoration.

So that’s the first thing I said, right? If someone’s got a large restoration, it will crack. And were most prevalent in mandibular molars. Mandibular molars. So second molars and first molars. The highest prevalence rates appeared in patients over 40 years. So there we are, okay. So why is that significant? Why 40 years? Why not 18 years?

[Emma]
Just over time.

[Jaz]
It’s that third part, the triad, right?

[Emma]
Yes.

[Jaz]
It’s tooth time contact, right? Not only just during the day, but extrapolate it throughout life. And so women—okay, I have no idea why women—women being more affected than men. I think women are just more stressy. I dunno if I’m allowed to say that. Am I allowed to say that? Is that sexist?

[Emma]
Oh, no, that’s fine.

[Jaz]
I can’t speak for women. I’ll speak for just my wife only. My wife is more stressy than me. Therefore, she’s more likely to get cracked teeth than me. There we are. Fact, okay. I can’t generalize about any genders and that kind of stuff. Although one study showed an almost—I’m gonna get cancelled on—almost equal distribution between gender groups. Fact. They’ve got a little table in this study, right? And it looks like the study author, the tooth type, the incident rate… so mandibular molars, overwhelmingly the most likely to crack.

And then followed by maxillary molars, and followed by maxillary premolars. But look here, how rarely mandibular premolars fracture, relatively. Can you figure out why that’s the case?

[Emma]
For the mandibular?

[Jaz]
Yeah. So why is it that maxillary premolars are more likely to crack than mandibular premolars? This is really fascinating.

[Emma]
I’m just putting, I guess, forward, something to do with different bone densities down there, or you’ve got a more amount of bone on your mandible. I don’t know.

[Jaz]
That’s an interesting one, Emma. You know what? It could have something to do with that, but here—oh, here’s another. This is so good. So another thing you reminded me of is, have you seen many perio patients?

[Emma]
A few, yeah.

[Jaz]
Okay. I dunno if you are maybe too young to have made this observation. And I’m hoping some of the more experienced colleagues can be like, “Oh yeah, I’ve seen that,” is: our perio patients don’t tend to get cracked teeth.

Their teeth look beautiful. Their teeth anatomically don’t look worn and they don’t have cracks. They just look stunning. I dunno if you’ve noticed that.

[Emma]
No, I haven’t noticed that. No, not…

[Jaz]
Okay. So this is going back to something called the weakest link theory. Okay. Now we’re gonna pause that for a second. You’re saying you’ve seen the lectures on OBAB, so okay, well we’re talking about that. We’ll come back to that in a moment. So we’ll come back to the weakest link theory in a moment ’cause you made a great point there.

But the point I was gonna make is: the reason why mandibular premolars… go back to anatomy, right? If you feel your lower first premolar, look how tinchy that lingual cusp is. There’s nothing for food or a cusp to come into and split the tooth. If I had a giant version of a lower premolar in my hand and I had to crack it, I’d really struggle to crack that. Whereas a maxillary first premolar—oh yeah, I can grip on those cusps and really go for it.

Okay, it’s in the anatomy of the teeth, which is really, really interesting. Again, this is consistently reproduced in the studies that I’m seeing here. Mandibular molars—most crack. Followed by maxillary molars. Closely followed by maxillary premolars. And yeah, mandibular premolar is very rare. So isn’t that just a fascinating observation?

[Emma]
Mm-hmm. Yeah. It’s strange.

[Jaz]
So now we’ve answered your second question. Now let’s just touch on the weakest link theory. The weakest link theory says that—and it’s just a theory, but I love it because it explains our perceptions and what we see in the populations—which is that when you observe your patients, they’ve got something like: when there’s overload in the teeth, there are certain systems that are affected.

So it’s either the periodontium that’s suffering the system, or it’s the muscles and the joints, or it’s the teeth—whichever is the weakest link. And quite often you have two of the systems affected together. Very rarely you have all three systems.

So let’s break this down. How does this actually work? And I think it’s best explained by: why is it that the periodontal patients don’t often get cracks? Or can you figure out, Emma, why a perio patient is less likely to get cracks and wear?

[Emma]
So over time their teeth are gonna become more mobile and almost move out of the way. They’ve got a bit more give in the PDL.

[Jaz]
Exactly. So when there’s more give, when there’s softer bone, when there’s mobility and you are chewing on something hard… the pressure has to dissipate somewhere. Now on the opposite end of the spectrum: that big bloke with mandibular tori, hard stiff bone that you are afraid to do an extraction on because you stick a luxator in and nothing is budging.

Your luxator is gonna break, but the tooth’s not going to budge, right? That’s the patient that gets the cracks. Because when they’re chewing, the bone is not helping. The bone is not absorbing the force. The PDL is not absorbing the force, so the force is going into all the stress in the cusps.

But when you have a system or a patient whereby they’ve got a bit more give in the system, instead of the cusps flexing, it’s the PDL taking the load away. I think we’ve touched on this before, Emma, previously, but it’s worth mentioning again that someone who’s got a grade one or grade half mobile tooth—that patient, if you use that tooth as a resin-bonded bridge abutment—will be more successful than a patient who’s got no mobility and you use that tooth as a resin-bonded bridge abutment.

Because when he loads that bridge, the patient who’s got really stiff, hard teeth or hard bone, and there’s no give—when you load that pontic, all the load is absorbed by the lute, by the cement.

But when you’ve got the mobility and you’re chewing, some of the pressure is eased off—is absorbed by the PDL before it actually gets to hit the cement. It’s the same kind of concept, and that really helps to explain cracked teeth. I’m really enjoying this. I’m hoping you are.

[Emma]
Yeah, yeah. No, it’s really, really interesting. I’ve never really thought about it. I know about the weakest link theory, but I never really thought to bring that into cracked teeth and things like that, so that’s quite interesting. Another question that I did have for you, Jaz, which you might find boring, but we had in an OSCE scenario—it must have been BDS2 or BDS3.

It was about diagnosing, I think it was cracks in teeth from memory. Just like, extra points if you can answer these kinds of questions. And I know that the answers are a Tooth Slooth, a bite test, transillumination, but I’ve never seen—I don’t even know if that’s available in Glasgow Dental Hospital—transillumination. Is that something that you’ve ever, ever used before?

[Jaz]
You know what, Emma? I’ve actually never used transillumination, okay? I’ve just never had it. I’ve actually got the tip, I’ve actually got the tip that you put in your… but quite often it’s a different light source or something, and I never bought it.

I didn’t have access to it, so it’s one thing I haven’t used. But I know that the light kind of stops, it doesn’t go through, because there’s a break in the crack, and there’s a very characteristic appearance. So no, I haven’t used it, but it can be quite helpful.

I’ll tell you what’s really helpful to me: just really high magnification. At least five times, eight times better. At least five times. Dry teeth and having a really good look. Good photography as well, and you’ll be able to pick up these cracks, even virgin teeth. And sometimes it’s difficult to see if they’re not stained, but when they’re stained, they’re further along the pathophysiology.

When your probe is getting in there, that’s really bad news. You’ve left it too late. You are really now reactive and not proactive anymore. Even though the patient’s having no pain, if you can feel a crack with a probe… I think Pascal Magne said it’s something like 200 microns or something like that.

So Pascal Magne taught me that if your probe is getting in the crack, that’s like 200 microns at least resolution. Whereas when you’re using high magnification, you can actually detect cracks that are way smaller than your probe ever could. So if you’re just relying on your probe, you’re leaving it too late. You really need high magnification.

I don’t trust any dentist that doesn’t use loupes, honestly. Like you must. I wouldn’t let anyone near my mouth without magnification.

[Emma]
Fair. Okay. So is a Tooth Slooth something that you have in your surgery?

[Jaz]
Oh, of course. Yeah, yeah, yeah. I think Tooth Slooths are very common. They’re autoclavable, they’re very readable. And so I think that the good thing is you can test cusp per cusp.

And then the patient bites together. And then one cool thing that Karina taught us in that episode—I think it was episode 28, all those years ago—is that what I used to do is: you put the bit that slots onto the cusp to get the patient to bite together. But then just give it a tiny wiggle.

Give it a tiny wiggle when the patient’s biting together. That helps with your diagnosis basically. So Tooth Slooth is one aspect. Doing cold testing, see what kind of response you get. Visually taking a look. Yes, there’s transillumination, but it’s something I don’t have experience with.

But very often, it is like, you know the epidemiology. You know it’s mandibular molars, maxillary molars, maxillary premolars. You kinda know which teeth are more likely. And then you look at the patient. You look like, okay, if they’re missing teeth on the other adjacent side, find out why were they taken out.

Because quite often, it’s like someone who’s had difficult extractions in the past—that’s the best predictor of a difficult extraction in the future. Is that right? And so if you’ve lost teeth to cracks before, then you’ve got… not only do you have to be more vigilant, but you have to then consider that, okay, I’m probably dealing with a cracked tooth again. The past is the best predictor of the future.

[Emma]
Okay. And if you see a crack in a tooth and if you’ve got a radiograph and you can’t see much on the radiograph…

[Jaz]
You won’t. So with a radiograph, it is very rare. I’ve got a radiograph I took this year that shows a crack beautifully, because the crack—the plane of the crack—just happens to be exactly going down the plane of the X-ray. But very rarely does that ever happen, basically. So it’s extremely rare.

It can happen, though. But very often we are only taking a PA just to confirm what is the apical situation, okay?

But the radiograph is not gonna help us that much when it comes to crack diagnosis. It’s a clinical diagnosis.

[Emma]
Okay. And if you’re seeing no periapical pathology on the radiograph, is often treating that crack and the symptoms in the tooth going in and removing the crack and seeing where you end up? What’s sort of the treatment options for that?

[Jaz]
Really good question. Because now we’re getting into decision-making treatment planning. This is a wonderful question. And like with everything complicated, everything occlusion, that kind of stuff, it depends, unfortunately. But let’s talk about what it depends on.

Because if you just leave it as “depends,” then that’s no good. But if we talk about: okay, what does it depend on? And play different scenarios. And I’ll give you real-life scenarios.

I have a 19-year-old patient. She’s got huge masseters. Huge. She is a major clencher. I’ve confirmed on something called a brux checker, and I’ll put the image here. Her parafunctional pattern one night is just so broad, and she’s got huge muscles. Every two years she destroys her splint and she gets a new one. But before she ever started wearing splints, okay, she’s just 19. She’s just 19.

And she presented to me with a virgin… a crack in a virgin lower first molar. And so the first time it presented to me is it was symptoms. And so really had to dry the tooth to see it. It was like, oh wow. Yeah, there is a crack there. It wasn’t stained, but it was symptomatic.

For this individual, it is a completely different treatment to someone who is 56 years old and they’ve got a giant MOD amalgam and you diagnose cracked tooth syndrome. You know that the giant MOD amalgam is gonna get a crown or an onlay or something. Whereas the 19-year-old—it’s a distal crack.

Would I really want to reduce the cusp by two millimetres all day round on a 19-year-old? So what I decided to do on this 19-year-old is: okay, well if the crack is distal, let’s explore distal.

What I’m gonna do now, guys, is—those who are listening on Spotify and Apple—I’m gonna keep it very descriptive. I’m gonna show Emma some photos. If you’re watching on Protrusive Guidance on YouTube, you’ve got some visuals. But don’t worry—my numero uno are always the audio listeners who’ve been with me since day dot. I’m gonna make sure you’re not feeling alienated.

So the first image I’m showing you, Emma, is an Essix retainer—because you had context before—absolutely destroyed, right? And then what’s the next thing you wanna know when you see an Essix retainer like this? What’s the next thing you want to know?

[Emma]
When you see an Essix retainer like this—

[Jaz]
When you see a destroyed Essix retainer, like chewed up, okay?

[Emma]
Like how long they’ve had it for.

[Jaz]
There we go. Okay. Because if it’s been like seven years, I’m like, okay, that’s fine. I can deal with that. But if this is six months—which is what it was—what can that tell you? What information do you now gain from seeing this retainer after six months and it’s in this stage? A lot of chewed-up holes. Perforated.

[Emma]
Yeah. A lot of, you know, prolonged tooth time contacts.

[Jaz]
Wonderful. Beautiful tooth time contact and tooth force. It’s a combination of the two. And even position, because there’s a lot more back tooth contact than there is front tooth contact, right? So that’s kind of leading to it as well.

So anyway, she comes to me. Let’s see… yeah. So here’s the situation, though. Lower molar, we said. This crack that I’m showing you—and those listeners—it looks fairly harmless. It looks like a fairly harmless crack. Like this. We see this in teeth all the time. But she’s complaining of symptoms. And she’s just 19, but she’s a high-force patient.

Now, on the photo I’m showing Emma, there are some articulating paper marks. I’m firstly highlighting my mouse around a cusp tip contact. That’s a cusp tip contact there. And then here, it’s on the occlusal table of the cusp. But can you now describe what kind of contact this is?

[Emma]
An inclined contact.

[Jaz]
Well done. So I’m showing Emma an incline contact. The dot is not in the fossa. The dot should be here. But actually the dot or the smear, the large contact, is actually halfway up the cusp.

No wonder there’s a crack here on this high-force patient.

Now, just to confirm—I didn’t need to do this, but because you have the retainer as evidence—but we did something called a brux checker. And a brux checker is like this thing, which is like… it’s painted red and your patient just wears it for one night. Then anywhere there’s tooth rubbing going on, the ink wears away. And it’s not like every time it touches the ink is gone. It takes a fair bit of effort to rub this ink away, which is important because you don’t want a false positive, right?

So you can see how much force is going down the molars. And actually she’s bruxing onto her front teeth as well, but this just confirms that, yeah, for sure, she’s a bruxist. And we have the incline contact again. I’ve got blue ink here now.

And then there’s an aggressive cusp of the upper molar. So the other thing that you see on this molar is on the mesial half the molar—this part of the tooth, right guys?—it looks completely like a six-year-old’s tooth. Look how pristine the anatomy looks here, right? And then now when I move the angle of view to the distal half of the same molar, can you see how aged the tooth looks?

So my question, guys, for those listening is: why would that happen? Why would one half of the tooth look like pristine, no wear, and the other half is the one that’s got the crack? It’s got some wear. It looks like it’s been in the mouth far longer than it has been.

[Emma]
Is there a—

[Jaz]
It’s not a trick question, but it’s something that… it is an interesting discussion point when we look at the tooth level. Go on.

[Emma]
Is there a bit of like a rotation on the opposing tooth?

[Jaz]
Beautiful. So essentially what you’re saying, Emma—I mean, it may or may not be rotation—but what you’re thinking of is the opposing tooth, right? So imagine the best way to describe it is: imagine the mesial half of the tooth doesn’t have an opposing tooth. Imagine a missing tooth. But the distal half of the tooth has one. It is just as basic as that.

For example, I’m just making this up in this scenario just to help to explain the point. But when you see some damage on the cracked tooth, you always must—it’s a lesson I’m teaching you guys—look at the opposing tooth. Because that will give you a clue, right? Often there’ll be something sharp there. Something that’s gonna like—a dagger—something that’s gonna be damaging there.

So always look. And actually a great point to consider is: if all you do is remove the crack and put a composite, the composite will also fail through overload eventually.

If you do not change something about the upper tooth, i.e. lightening the force there, or changing it from a sharp dagger to a rounded soft cusp, or maybe changing it so that now you are converting it from an incline contact to fossa contact.

So you must change something about the environment to reduce the crack propagation.

Anyway, so what I did, guys, for those listening, is: I actually reduced the incline, the angle. Can you see? I reduced the angle. So now I’ve actually converted this tooth from a steep angle to a shallow angle. And some people may be saying, “On a 19-year-old, you removed enamel?” Well, listen: this 19-year-old—if I didn’t do this, she’d be the 40-year-old with a virgin tooth who has split her tooth because all the dentists said the cracks were harmless and then she lost her tooth.

So we have to sometimes be appropriately invasive to preserve teeth in the long run. So I’ve sacrificed some enamel. Now that’s what occlusion is all about. Practical occlusion is all about these decision-makings. Actually taking a bur to a tooth and doing that for the greater good.

And so you can see, when I explored the crack, okay, you can actually see it quite clearly now, right? And what do you often find in a crack? You find caries. So can you see there’s some caries? Guys, I’m showing Emma some caries which were not present radiographically, right?

But wherever there’s crack, there’s demineralisation. It’s the entry point of caries. So thank goodness we intervened. And we didn’t allow this to become worse or bigger and actually become radiographically evident.

I restored it with a composite. And what I didn’t do is: I didn’t just recreate the old anatomy and make it steep again. I kept it shallower. So now the opposing palatal cusp, when it now grinds on this molar, it’s doing so in a shallow way.

And what I’m showing here, guys, for the audio listeners, is an image which is just one of my favourite images in education, okay? Because that point I made about the mesial half of the tooth looking good and the distal looking battered… but now you see this across the first molar and the second molar. There’s like: this tooth is age 19 and this tooth is age 70. Like the distal half of the tooth is age 70.

Yeah. And so it really drives home the point of tooth contact time, tooth force, and tooth position. All those things that I spoke about earlier are being manifested here.

And so her pain went away and everything was good, except actually she’s having the same issue on the left side, and I ended up treating her left side as well. So you have to look at the patient as a whole.

And the main lesson here, guys, is: if you are treating a cracked tooth, your treatment modality will depend on how old the patient is, how bad the crack is. So here, for her: composites. But not just a composite—it’s composite and careful and judicious adjustment of both the existing tooth angles, where the occlusal contact will be, and being purposeful for that, and doing some opposing adjustment to remove the noxious stimulus.

[Emma]
Yeah, that’s really, really interesting, and I think it’s fun because I usually just spring these questions on you. I usually ask, “Oh, do you want me to send you over the questions that I have in advance?” And you’re usually like, “No, let’s just go for it and see what happens.” But I think it’s really interesting that you had such a good case to show there.

I thought that was really, really interesting. That was really interesting.

[Jaz]
I’ve got great images as well, guys. I’ll put them on the app, on Protrusive Guidance, but like when you air-abrade teeth, once you remove that amalgam and you air-abrade, you’ll see the cracks pop out at you.

So if you’re not able to see the cracks before, when you air-abrade, suddenly they all come out of the woodwork and you can see the cracks basically. So really important diagnostic tool.

And so the final thing—talk about running out of time here—but communication. That’s the thing that stressed me out the most because the patient’s like, “Hang on a minute…” Vast majority of patients who’ve got cracks are asymptomatic because not only do cracks come in a spectrum, but the patient’s development or progression of a crack also comes in a spectrum—at what point they present to you in life and how proactive you are.

And so if the crack has just formed and is barely in enamel and just about entered the dentine and they have no symptoms, you might even miss it. In a quick exam, you might even miss it, right?

Then they come back. The crack gets a bit deeper. A few years have passed by and the crack’s getting a little bit bigger. Maybe it’s starting to stain now. And stain is significant because—do you know why stain is significant for a crack?

[Emma]
Does it go back to possibly caries in there?

[Jaz]
Kind of, because a crack can only stain when it’s wide enough to allow the stained particles and bacteria through. So basically, if the stain’s getting through, we know the bacteria’s getting through.

So vast majority of these cracks are completely asymptomatic. But it’s up to us as the dentist to take photos, to explain to the patient that, okay, you may be low-risk caries, you may be low-risk perio, but you are high-risk for cracks.

You have four cracks, two of which I think are gonna be okay, but the other two I think I’m a bit concerned. I think let’s watch this one, but I think we need to investigate the other one.

So yeah, cracks come in all sorts of different presentations. So it’s up to us to lead the patient and really advise them and let them own their problem. And it’s like, “Listen, the crack is in your mouth. You have overloaded your tooth and caused this crack. I can help you, and this is what we take, but a cracked tooth is a really upset tooth. The nerve—even though you’re not in pain—the nerve is always, always a little bit traumatized from a crack.”

“We will try our best to do it, but I wish there was no such thing as cracked teeth because cracked teeth really, really reduce the chance of your tooth surviving throughout lifetime. So if you want to give your tooth the best chance, we can restore it now with X, Y, Z restoration. But know that the nerve may already be damaged.”

“We’ll only find out. If we do nothing though, then you are heading towards a split tooth. And these things—they don’t just appear overnight. They all start like the crack you have. I can’t predict, with your diet and with your clenching, how fast it will progress in your case.”

And very often you’re monitoring photographically. You’re monitoring symptoms. Very often with general practice, we have this beautiful relationship we get to form with patients. So very often we see these patients year on year on year. And we mention, “Okay, yeah, that decay’s doing fine. It’s not progressed.”

“The crack on this tooth, however, based on my photos and what I remember, I think this one’s got worse.” And by the time you’ve been seeing them four years, they trust you. They get it, okay?

And it’s one of those things where patients are very… unless they have a relationship with you, something that doesn’t hurt them—they won’t really do anything. Something that A: doesn’t hurt them, and B: they don’t want—no one wants to have their back teeth drilled for cracks, okay?

If it’s aesthetic dentistry, then they don’t have to trust you. It’s something they want. They’ll go for it, kind of thing, right? So it’s one of those things. Cracks that are asymptomatic can very quickly lead to tooth loss, and that’s why the communication element really comes into it.

[Emma]
Yeah, that is really interesting. And I think I was gonna ask you before what your number one piece of advice would be, but I know that you already said, like, look at the patient as a whole, and especially looking at the contralateral tooth on the other side and also the opposing—

[Jaz]
Opposing, yeah. Contralateral, opposing. Look at them. The shape of their jaw. When you get them to bite together, have they got giant golf balls that come out as masseters, or are they very gentle, okay? And these things are so, so important. What their retainers look like. What do the other teeth look like?

What does the opposing tooth look like? Does it look like a plunger cusp that’s right overlying where the crack is?

[Emma]
Yeah. Yeah. So very, very interesting. And I like all the—you just had to hand all the photos that were so, so helpful in visualizing that there. So that’s good. I like this episode.

[Jaz]
Amazing. Brilliant. Well, which notes are you gonna make available to all the Protrusive students for this time around?

[Emma]
So I can make… I know that the American Endodontic Society has really good notes on cracked tooth syndrome. And I can just release anyway. I already have. I know we were gonna do a boring episode about medical histories, but I think we decided against that. But I have some really good notes anyway, so I might just use that.

[Jaz]
I would love that. It’s such an important thing, right? Medical histories. Yeah. It’s just so boring to talk about, and it’s like where do you draw the line, right? So I think let’s make this—because students will need this for their exams and stuff—so let’s make medical histories available.

It’s not really relevant to cracks. So we’ve given you something clinical and highly actionable and relevant, and something that hopefully will stay with you for life in how you practice and how you look at cracks. Never look at a cracked tooth the same way again after these episodes.

Now you also have medical histories to keep your examining board happy as well.

So all that is available on the StuDent’s protrusive section. And of course, all our Protrusive on the app, you all have access to it, whether you’re a student, young dentist, experienced dentist. It’s always nice to listen to a different way of explaining things and connecting back with the basics. The basics can be beautiful.

[Emma]
Yeah, for sure. And it’s easy enough to answer these questions in an exam, but when it comes to actually doing dentistry and being dentists, it can just take a bit more explaining.

[Jaz]
Well, Emma, thanks so much for your time. All the best with the rest of your final year. We’ll catch you in the next episode. Have you got an idea of what you wanna talk about next episode?

[Emma]
So I think when I’ve been in outreach centres recently, I’ve been seeing a lot of failed composites—not from me, but from previous students before. So maybe even a conversation about that. Who, where, what, why, when went wrong. Failing composites.

[Jaz]
Beautiful. Again, another clinical topic. I love it. Oh, there’s so much we can talk about. Okay. Excellent. Let’s talk about failed—maybe, well, we can talk about failed composites in general because there’s a whole decent protocol. There’s the occlusion management, there’s the layering management, all that kind of stuff.

And then some things we say will be more applicable to posterior teeth, some to more anterior teeth. And we can talk all about that. Amazing. Okay. I’ll look forward to it. Thank you so much, Emma.

[Emma]
Perfect. Thank you.

Jaz’s Outro:
Well, there we have it, guys. Thank you so much for listening all the way to the end. Please do answer those questions below to claim your CE. We are a PACE-approved education provider. Hope you enjoyed my take on occlusion in terms of position, force, and time, and how the combination of these results in overload, which is the ultimate cause of cracks.

If you did enjoy this episode, please comment below. Tell me what was your biggest takeaway from this episode. If you’re watching on YouTube, hit subscribe. If you’re watching on Protrusive Guidance: A, don’t forget to answer the quiz. And B, it’s always lovely to read your comments. We hope you’re enjoying these kind of basic student-based series. But as you can see, it’s not really for students.

It’s a nice geeky chat on some of the fundamentals, and there’s beauty in the basics. I wanna thank Team Protrusive, as ever, for all their hard work, and thanking you once again, Protruserati, for sticking around. I’ll catch you same time, same place next week. Bye for now.

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