Managing Sensitive Crowns - Keeping Dentine Bonding Simple

Welcome back to the Correct Dentistry Podcast and it's our first podcast for 2026. I know if I recall back to university, you did a lot of fillings before you were allowed to move on into the next big exciting part, which was cutting a tooth for a crown. That's what we all wanted to do and you had a quota and fillings were boring in comparison. And now I look at the way my appointment book is structured and if I have a single crown prep, I, my blood pressure is low. I feel pretty calm about that procedure if I have a large composite booked in my blood pressure is high. I start to stress about contacts, postoperative sensitivity, making a long term functional restoration. It's interesting how the more you go on in the career, some of the simple things actually become the hard things and I do know from fieldings some of the questions that you get at your programs or via email that a lot of the problems that people have is bonding related, postoperative pain and sensitivity or things breaking. What are we getting wrong with bonding? We've got all of these amazing bonds on the market, you spend a lot of time going through the generations of bonds in your course, which helps us to understand that there's been a lot of research into how do we get the best bond. But technically it's still a very challenging thing to nail every time, what are we doing wrong? Yeah, you can't really do very much data stream without doing some bonding. There is many years ago that wasn't the case, but now it is, so you really have to be able to do bonding well and it's really not that difficult a topic to understand. I think where it goes wrong before we get into some of the detail is that today there are a lot of different dentine bonding agents and if you're the company making it, you want to sell it, so there's marketing and so the marketing sometimes is where things go wrong. The marketing just simplifies the process, you know, just buy our product, apply our product and it will just work. And many times it just does too, but it doesn't help you to understand what you're doing. So if you don't do it perfectly or if from that day something doesn't quite go as per normal, you don't understand what's happened. There's no recourse and so sometimes you know bad bonding is misdiagnosed and we can probably talk about that later. But you know at the end of the day, good bonding to enamel is fundamental and simple. Everybody knows you put phosphoric acid on enamel. You rinse it off, you dry the enamel, the enamel is gone from glossy to frosty. You've got a micro etch pattern and all you have to do is put your hydrophobic bond over that and you will glue to it and that's it and it's, you know, the most durable bond we've got. But dentine is also an equally simple concept to grab and that is you've got to etch dentine to expose the dentine tubules, to open up those tubules so you can flow some resin into them and to de-mineralize the dentine around the tubules so that you remove the mineral content and leave the collagen backbone behind and then you flow a primer into that surface. So if you were to think that through just for a second we all know that enamel is essentially mostly mineral whereas dentine has a much lower mineral content and has a lot of organum and a component to it and it's got a lot of water there, it's a moist live substrate. So when we bond to enamel we can think of a dry environment and it works but when we bond to dentine we've got a bond to wet environment. So moist bonding is this term that's used all the time and I think that's where people go wrong too often is that they etch dentine and then they over dry the dentine and you know I have a lovely slide, well I think it's a lovely slide, that graphically tries to illustrate that and I can put that up now so that you can have a look at it. But when you look at that slide you'll sort of see there's two, the first one is the idea once you've etched the dentine that you see these collagen fibers all exposed and the collagen fibers standing upright, they're suspended in a water surface like there's enough moisture on the surface that the collagen fibers stand up in the water. If you over dry the collagen fibers then collapse. If they collapse they kind of congeal, they stick to each other, they create gaps between each other and on that first slide you could fly a primer through that collagen surface, the primer will displace the water, it'll wrap itself around the collagen fibers and now you've got this resin bonded to the collagen fibers and I think of it like getting chewing up stuck in here, you know will blue tack stuck in here, you know kids do that and you can't get that out of the hair, you've got to cut it out and the same happens when you bond to the collagen fibers correctly. If you over dry and the collagen fibers collapse now you can't get that primer to flow around them and so you don't get a good bond and you leave these little gaps behind and ultimately those gaps contribute to postoperative sensitivity issues and in the bonding lectures that we go through we try to explain that process and explain how you then end up with postoperative sensitivity, a decreased bond and how you get discomfort under crowns even when you've gone through a bonding process by doing that. So you know that the mechanism is so simple, it's a matter of how moist is moist, you know what's too dry, what's too wet, different types of adhesives probably have better leeway or technique sensitivity. If you work with a self etching system it's still opening up collagen fibers, you know and exposing them but you've got a lot more leeway to say that you're not over drying things. If you work with an etch and rinse system, you know you can over dry things and if it's a solvent based system you might over dry too easily. If it's a water based solvent then you know the fourth generation systems are a little bit more forgiving but that's you know the benefit of going through that bit of education versus me saying here's a new bond, here's the three steps you need, just use it, it works and probably eight or nine out of time, ten times it'll work well without complication but the one time it doesn't, it didn't have to be like that, it was just that you've abused the process without understanding it. Yeah that's a mouthful. It reminds me very clearly of a moment in my career after I wasn't working in the practice with you where I was experiencing a lot of post-op sensitivity with my patients, I didn't seem to have that problem when I was in the practice with you and you won't remember this but I called you and I said what's going on? You asked me what bond I was using and you knew straight away what I was doing wrong because you understood the chemistry of the bonding system I was using and you also understood the chemistry of the bonding system I was using in your practice and I think you touched on it you know some systems are more forgiving and so clearly I was a technique problem, not a bond problem and I think often when you have people at your courses the questions they ask myself and Gabby is what bond is he, so I'll buy that bond because it's the best or what bird is he is and I feel maybe what I'm understanding is it's not what you use, it's understanding the technique in intricate detail, understanding the chemistry of what you use so you can understand what the problem is when it occurs, am I reading that correctly? Yeah that's exactly it, the protocol you know I think overall how it works is pretty simple but if you don't understand what you're doing along that path of events to achieve a bond if you don't understand what's happening when you're etching, when you're rinsing, when you're applying the adhesive, what the adhesive is doing on the surface of the tooth, how it's encapsulating the collagen fibers, how it's penetrating into tubules, how long that takes, why you need to dry, what's happening when you're drying, if you don't understand all of those steps then at the end of the day you're cooked by the process, you're not cooked by the adhesive, you've got it wrong because you've got the process wrong and often the materials are good enough that you get away with it and otherwise every single time you're bonded you'd have a problem but when it goes wrong it's a matter of why, which step did I do wrong today and which one can I fix and you know that's another one of the little themes as we go through our courses you know we talk about always having the same protocol, always trying to do things exactly right, where something is a certain number of seconds you time it, you know when a material needs to be handled a certain way if it has to be in the fridge it's always in the fridge, it's meant to be in the drawer it's always in the drawer so you make every step of what you do the same, so something goes wrong and you don't get the outcome you're expecting you try to work out what didn't we do according to normal, yeah, on that I remember been a dental assistant for a long time and seen a lot of dentists work but when I worked with you that was one thing that I noticed set you apart you would write exactly what bonding system you'd used for every restoration precisely for that reason, a lot of dentists would you know write that I placed a composite it's like very well what did you do so you could actually understand the problem and you touched on before a misdiagnosis of the problem, how often when we don't have an understanding of the fundamentals is it incredibly challenging to actually understand what went wrong and what to do next, I suppose an example is if you've got a patient coming back with the tooth it's very sensitive for a long time after a filling, it might be that they need an endo, how do we work it out, how do we know or if we just dive into an endo it'll fix the problem right but it doesn't fix the technique problem, and I suppose that's what you're trying to get at in talking about understanding the technique so you can actually understand the failure and then understand what to do about the failure, yeah that's I think you've summarized it perfectly, if you understand the technique then you know what you should be doing you know what the outcome should be and if you don't get that outcome your first nexus of that situation is everything was fine until I did the procedure, so it's very likely that this bad outcome has come from the procedure it's not a coincidence okay let's take a step back let's look at the procedure what can go wrong with the procedure and I think you know we're scurrying around the topic but a couple of times a year a patient will be referred in with a crown, a beautiful brand new crown that that looks great appears to have really nice margins and the dentist says crown saw, the patient keeps complaining they can't chew on it you know it can be temperature sensitive you know what's what's wrong what has to happen here you know and they're one step away from referring to the endodontist or jumping in and doing the endo themselves, so you look at the crown the crown's perfect I mean superficially it looks great you take out your sharpest explorer go around the margins the margins look good you've seen a radiograph that they've sent through the radiograph looks good so what's wrong as you go to buy it or you put some pressurants or and it's not I mean it can of course be that they were just dead unlucky and the pulp died as a result of the procedure you know it just was on the way out but 9 out of 10 times it's in complete bonding and you know and you know within complete bonding that the prognosis can be very good I have to use the word can be very good there's the standard case and then there's the unusual case if the patient's waited you know a month or two to come and see me and they've got some discomfort in the tooth they're going to continue to get better if the patient doesn't get to me it's because it it ramped up to a bad situation but what I'm trying to say maybe put it in a better a better explanation if you have incomplete bonding and you have some nanogaps where you didn't seal the collagen properly then you load the restorations that patient choose on the tooth that load goes through the bond and it goes into these spaces where things weren't bonded correctly well they're not air spaces they're fluid filled spaces dentine tube your fluid comes up fills it so you're pressing on this liquid which then presses on the adiodoblastic process which causes pain it's the hydrodynamic theory of pain so the patient gets pain on biting and so they tend not to chew on that side and the reality is if it's not too severe and they don't keep trying to chew on it and really irritate the pulp it'll just settle down the pulp will lay down secondary dentine or tertiary dentine and sort of wall off that area I guess the euro pathways get sensitized to the point that they're being you know constantly hit and they sort of the brain almost starts to switch off a little bit to the sensitivity and essentially with time that sensitivity just gets less and less and less till it disappears and the best thing that you can do is support the patient psychologically as well as you know physically and that's by just you know reassuring them as to what's happened writing down the details of what's happened to them at the present time and they might say to you you know I cannot put anything in my mouth on that side without it hurting I'm fine but as soon as I put some pressure on their hurts I say you write that down in a couple of weeks time you sort of review them and you say how's things going and they say it's just you know I don't think it's getting any better and you say well what's the specifics and they say well you know every time I have any meal you know as I'm chewing there I suddenly I get this pain that occurs and you're like well okay that's good because when I first saw you didn't matter what you put there it hurt now it's you can have a meal and any couple of times during the meal it hurts you know can we check you again another four or six weeks and the patient comes back and four to six weeks and you ask how it's going and they say yeah you know I might be getting better you know I noticed it a couple of times a week and you say yeah but when you came in last time it was every day every meal now it's only a couple of times and so you can track it getting better and I think you can you can do that as a service to the patient and it takes a few minutes to see them you don't have to charge the patient for that review and it shows that you're on their side and you want the best outcome for them and you've averted something they didn't need like a root canal it you just be very unlucky if from day one the incomplete bonding was so severe and you traumatized the tooth that much that it's just an ache and it gets worse and it's going to peak immediately and they're going to need endo in that situation. So how long would be reasonable to for the patient to expect as the absolute out-of-limit of how long that would take to get better spontaneous. Oh I think maybe it could be as much as four to six months but I mean often often just within a couple of months the pain is so much less that maybe they're not as aware of it like they probably do notice it but they're not paying attention to it as much. So you know they might sort of think they notice it a couple of times a week in reality maybe they're noticing it once a day but it's low grade it's less often psychologically they're reassured that they're fine and they're no longer worried about it. So understanding how to bond in the first instance is important. Understanding what the sensitivity is due to and the value that you've had is important. But can you share how you actually describe that to the patient because I feel there's a lot of chat about collagen fibrils and a patient is just not going to understand that. How would you word that discussion to the patient to not a throw a referring dentist under the bus or if it was your own patient and they were experiencing those concerns. How would you say you know it's essentially an error in bonding and if a patient hears an error they might want a solution and the solution here is to wait. How do you actually discuss that with the patient? This is pretty much word for word what I would say. I would explain to the patient that when we're gluing something to a tooth we're glowing to the deeper part of the tooth that's the bit that's alive and that's the reason we have to numb you up. When we touch that part of the tooth it hurts and if you ever had a little bit of recession you know the gum shrinks down and the enamel stops and you are seeing a bit of the root surface and that's the bit that's a bit sore when you drink some cold water or put a toothbrush on it. But you probably notice that eventually that goes away and unless you keep getting more recession. So when we're gluing to the deeper parts of the tooth everybody would like to think we've perfectly glued to this tooth you know we cover it 100% everything's great but the reality is we probably glue 96, 97, 98, 99 percent effectively it's probably a case that we don't perfectly glue to the entire surface of the tooth and it makes no difference. And that one or two or three percent of imperfect bonding gluing to the tooth could be just touches here and there all over the surface of the tooth and they're just little freckles, little speckles that mean nothing and everything works nicely. It would be a problem if we didn't glue well near the margin because things could leak underneath but you know that doesn't seem to happen. But sometimes we're just unlucky when we do that imperfect bonding that that couple of percent is concentrated more in one area and that is enough then to give us the symptoms that you've got and when that happens as long as that area is not at the margin where things can leak in as long as it's up underneath the tooth the tooth is going to get better with time you know and then I might sort of explain how we'll do a review what we're expecting what we see for a review but I kind of use it in that context that despite our best efforts we're never 100 percent but it's just tiny spread areas of imperfectness that are somewhat inconsequential because they're spread out but if they're together then we get the problem and then I suppose the last part of that is to reassure them you know if I could see it was at the margin then I'd tell you and say that's where it's gone wrong and that's something we've got to fix you know but when it's not at the margin it could be anywhere on that tooth. Now the question is what if the patient says well you know what are my alternatives so well you know your alternative is if you don't want to wait the alternative is for us to remove it. There is another alternative which is pretty quick and that's a root canal treatment no one wants that right so then if they lean towards or ask more about removing the crown I sometimes it'll be a bit theatrical than what I say but you don't have to be but you could just sort of explain to the patient look we can remove it and redo it if you're really worried we can do that I think it would be the wrong thing to do but if you want to we can do that but just so that you're aware this is what's involved I've got to bring you back again there's probably going to be a two-hour appointment to cut that off because most of it use the word cut sounds bad. Cut that off you know most of it is so well glued because it's a brand new adhesive it's going to take forever to grind all that away so we'll need to numb you up maybe top it up if the anesthetic wears off part way through left to make another one of those impressions or try really hard you don't gag during the impression we'll make your temporary crown again and it'll be a few weeks while you have to wear that temporary crown as a chance that temporary crown could come off but don't worry if it does we'll get you back in and we'll numb you again as we put that temporary crown back on so that you can go about your life until the final one's ready when the final one comes like last time it should fit okay but you know sometimes the lab isn't does just something doesn't go quite wrong and if that happens don't worry because we'll just remake it again we'll put the temporary crown back on we'll bring it back for another appointment and just tell them in every conceivable step how difficult this would be to redo and how it's just not something that they want now if someone still calls you bluff and wants it I mean at the end of the day I do it yeah but it's still telling me I think it's the wrong thing to do yeah anyway I think most people that want to do it when you sort of go into some of that detail but that's the truth you just you're just colouring it your way rather than their way and so in in really having an intimate understanding of bonding you speak in a really eloquent way about the generations of bonding and you make that really clear but if you're a graduate and you start in a practice and you find the you know orange bottle in the drawer how do they find out what generation that is so they can look back at your slide and say okay I know I know what's happening is it a matter of talking to the rep asking the dentist in the room next door or the dental assistant how do I use this or is there some you know is the information on the printout in the box exactly what they need to make sure that they're using that product perfectly yeah I mean you have to say that you always have to follow the instructions right because the instructions are written so that you know you use the product well so that it works in your hands correctly and that's fine and if you could find the PDF for it because the instructions are probably thrown away because using your analogy there's just the orange bottle in the drawer but I would like to think that the dentist understands what that material is and how it's meant to be used so I would like to think that they look at the orange bottle and the brand and the name hasn't rubbed off and they look up the product online and they find its proper instructions and with the instructions it says you know apply this to the tooth don't use any phosphoric acid first just apply it it's a self-etching material and then dry it and light cure it and so then they might be able to say well that equates to a seventh-generation system and yes if they went back to our lecture and our notes and went through it said okay now I understand how a seventh-generation system works in reality if I'm going to use it you know I really do need to be etching enamel and rinsing off the enamel but ideally not etching the dentine and then I can apply it to the enamel and the dentine in a moist state you know and have the right amount of contact time according to the instructions and I can proceed to bond from there alternative they look up the bottle it's the orange bottle and it's actually when they look up the name it's one of two bottles the other one's disappeared you know well obviously don't go forward using that product because it's designed as a two-step adhesive you can't use it as it is so the instructions might be floating around but it'd be really great if they could categorize it to know conceptually how that product should work so when they follow steps they do those steps with purpose and do those steps accurately and you are a big fan of the fourth generation bonding systems for a lot of the things that you do obviously you don't use it for everything but do you feel like if a graduate goes into a practice and there's a bonding system that they've been using a long time irrespective of what generation it is as long as they're using the instructions the way the material away the instructions describe that's the right thing to do it's not a matter of we need to do what Michael Mandercost is doing and get the fourth generation and panic about needing new products are there any you know bad bonding systems on the market we've we've moved up the generation ladder is that because obviously it's not because the fourth is not worse than the universal is any bonding system good as long as you handle it well yes I think I think really any bonding system is going to create clinically acceptable clinically favorable outcomes if it's handled correctly you know that begs the question well if fourth is good wise there are fifth or a sixth or a seventh etc but at the time when there's only a fourth you don't know that it's potentially the best system you know until the fifth has come and it's been around long enough to be able to compare them and then until the sixth has come etc so there's always reasons why new ones will come along and they come along to address clinical issues techniques sensitivity speed efficiency the ability to bond multiple surfaces etc but at the end of the day yeah if you go into a practice and this is a system that they've got it's it's your goal if that's the system that you've got to work with your goal and your responsibilities to understand what that product is how it works and then use it so you get the best results from it and you'll get clinically acceptable results I don't really think there's anything that's bad on the market now though we've got great examples in years gone past where quick quick to the market or rushed products came that that weren't so good I'm spending a lot of time speaking about sensitivity after a restoration is done there's been a lot of talk over many years about adding additional things into the regime like products like glooma or scrubbing the dentine with chlorhexidine and all sorts of different things and I've noticed in the time I've been a dentist they kind of come in and go out and come in and go out depending on who's teaching who's CBD is happening at the moment and who likes it but can you comment on are they necessary why have they been brought into the market and do you use them yeah like an answer the last one first no I don't use any additional step so additional steps have sort of come into technique often to address a problem and so then you have to ask the question well why is there the problem and sometimes the problem is there because a bad technique so it's sort of like throwing a product at a problem that is only there because the technique's not good enough and if you upskill the technique you don't need that problem so yeah two big ones that come to mind would be using glooma as a desensitizing step before applying the adhesive well glooma is essentially the second and third generation bonding concepts so that was chemical bonding to tooth structure so you splash that on the dentine and you in effect are sort of sealing up the dentine as you chemically bonding to the dentine but those generations don't exist because of their own they weren't sufficiently strong bond strengths compared to the micro-mechanical bonding that we have from the fourth generation up so to put it on first seems like an unnecessary step unless you just can't get mechanical bonding right without leaving gaps without incomplete bonding but that doesn't seem like a problem either because when we move into the self-etching systems which is the sixth and seventh generation and the universals those materials eliminate a big part of the risk of post-operative sensitivity because they're self-etching which then means you don't need glooma as an additional step so I think once again rather than somebody having an ad hoc discussion and sort of saying oh look you know I I get some sensitivity issues that I'm doing bonding and then someone's trying out a solution saying well you know maybe what you need to do is put glooma down first and then proceed with your bonding process like what that's doing is covering up the failed process rather than understanding the failed process fixing it and having less products and just doing things well the other one corexidine has been advocated for inhibiting the MMP enzymes that come out of dentine in response to to acid stimulation or acid etching and so the theory there just in a nutshell goes that when you expose those enzymes they break down the collagen so let's say you etch a tooth as part of a etch and rinse bonding protocol you've just exposed collagen fireballs with acid and so now the MMPs are released and now you bond to the surface and then at the end of the day you've bonded to that surface but as the next six to 12 months go by in clinical service the bond strength breaks down as the collagen fireballs are hydrolyzed by these enzymes so that process is true that does happen but only happens to exposed collagen fireballs so if we go backwards again and we say well what if we use a self-etching system or when you have a self-etching system if you understand how that works it doesn't leave collagen fireballs exposed so you don't get MMP problems or what if you use an etch and rinse system a fourth or fifth generation well again if you apply the adhesive and you wrap up all the collagen fireballs and you don't leave nanogaps and you don't get post-operative sensitivity you're not going to see the MMP effects in any clinically tangible way so you don't need that and chlorhexanine and you inhibit some of the MMPs not all of them so even then it's a step that's being kind of thrown at a problem that can be fixed with just better application of the adhesive. Thank you Michael that was a really great chat. Yeah thanks Jill always a pleasure. Till next time. See you.