When I sit across from my clients—general dentists and specialist prosthodontists alike—one of the most common questions I get these days isn’t just about the strength of our porcelain fused to metal (PFM) restorations, or the shade matching of our porcelain layers. It’s something far more specific, something that many of them miss in the initial consultation: how a cross-bite in a patient’s occlusion can turn a seemingly perfect PFM crown or fixed partial denture into a repair or replacement waiting to happen. As someone who’s been supplying PFM materials and finished restorations for over 12 years, I’ve seen firsthand how a simple, often overlooked dental malocclusion can derail months of careful planning, and it’s my job to make sure my clients understand that risk before they seat a single one of our products. Let’s break this down, not from a textbook perspective, but from the perspective of a supplier who’s been in the lab, watched a dentist handle a misseated crown, and walked through the frustration of a patient coming back with a chipped porcelain or a loose restoration because of an unaddressed cross-bite. Porcelain Fused To Metal
First, let’s make sure we’re on the same page about what a cross-bite actually is, because not every dentist means the same thing when they say the word. A posterior cross-bite—where one or more upper teeth sit inside the lower teeth when the jaws close— is the most common type that affects PFM restorations, especially in adults. Anterior cross-bites are less common in adults, but they can be just as problematic, often causing wear on the front edges of PFM crowns. The key here is that cross-bite isn’t just a cosmetic issue; it’s a functional one. The jaw isn’t closing along its natural, balanced axis, which means every time the patient bites down, there’s uneven force applied to their teeth and any restorations in place. For PFM, which relies on a strong metal substructure to support the porcelain layer on top, that uneven force is where the trouble starts.
Let’s start with the immediate, most visible effect: porcelain fracture. I can’t tell you how many times a lab will call me, panicking, saying they sent a perfect PFM crown only for the dentist to call a week later with a photo of a chunk of porcelain missing from the buccal (cheek) side of the crown. Nine times out of ten, when we look at the patient’s full mouth series, there’s an untreated posterior cross-bite. Here’s why that happens: the metal substructure of a PFM is designed to distribute occlusal (biting) force evenly across its surface. Porcelain, while hard and esthetic, is brittle—it can’t handle sudden, concentrated force the way metal can. If a tooth is in a cross-bite, when the patient closes their mouth, the upper crown is pushed inward, so the buccal edge of the crown is bearing all the brunt of that lateral (side-to-side) force. Over time, that repeated pressure creates micro-cracks in the porcelain. At first, the patient might not even notice, but with every bite, those cracks grow until a large fragment breaks off. I’ve had a client tell me that in one month, he had three PFM molar crowns returned because of porcelain fracture, and when we pulled up the patient records, all three had posterior cross-bites on the same side of their mouth. That’s not a flaw in our porcelain—our feldspathic porcelain is fired to a 90 Rockwell hardness, tested to withstand 500 Newtons of force before fracturing—but it’s a flaw in not accounting for occlusion at the time of restoration design.
Next, there’s the issue of metal substructure deformation, which is less visible but can be just as damaging long-term. PFM restorations get their strength from the base metal alloy we use in our lab formulations—most of our products use a high-palladium alloy or a cobalt-chromium alloy, both of which are certified for biocompatibility and have high yield strength. Yield strength is the amount of force a material can take before it deforms permanently, right? So if a PFM is subjected to force beyond its yield strength, the metal substructure bends, and when it bends, it creates tension at the porcelain-metal interface. That’s the seam where porcelain is fused to the metal, and it’s the weakest point of the entire restoration. For a patient with a cross-bite, that lateral force applied to the restoration is often enough to push the metal beyond its yield strength, especially if it’s a posterior molar where the bite force is highest. Over months, that repeated bending weakens the interface, leading to what’s called delamination—where the porcelain starts to separate from the metal layer. Again, I’ve seen this with fixed partial dentures (FPDs, or bridges) too. A four-unit PFM bridge replacing two lower molars, with an upper molar that sits inside the lower arch in cross-bite. The distal pontic (the fake tooth) takes all the lateral force, the metal substructure bends, and the porcelain on the buccal side starts to lift. Before long, the patient is complaining of food getting trapped under the edge, or the porcelain feeling loose. By the time the dentist catches it, the whole bridge might need to be replaced, which is costly for both the practice and the patient.
Wait, there’s another effect I don’t think dentists talk about enough: tooth movement caused by a cross-bite interacting with a new PFM restoration. Let’s say a patient has a posterior cross-bite, and you place a PFM crown on a lower molar to fix a cavity. The new crown is smooth, well-fitted, and sits at the right height. But because of the cross-bite, every time the patient bites, the upper tooth is pushing against the buccal edge of the lower crown. That constant, light lateral pressure doesn’t just damage the restoration—it pushes the lower molar inward over time. Now, the crown that was perfectly aligned when you seated it is now sitting slightly out of position, which makes the cross-bite worse. That leads to more force on other restorations, more micro-cracks, and eventually, you’re dealing with a whole mouth of misaligned PFMs that need to be adjusted or replaced. I had a client last year who told me he placed six PFM crowns on a patient’s lower arch, and within six months, three of them were shifting because of an untreated cross-bite. The patient ended up needing orthodontic treatment to fix the cross-bite, which the practice hadn’t planned on, and the crowns all needed to be re-milled to fit the new alignment. That’s not a failure of our PFM—our crowns are milled with 20-micron precision to fit the prepared tooth—but it’s a failure to account for how the surrounding occlusion will interact with the new restoration.
Now, let’s be clear: this isn’t to say that a cross-bite makes PFM restorations impossible. Far from it. I work with a lot of prosthodontists who successfully place PFMs in patients with cross-bites every day. The trick is planning ahead. As a supplier, I don’t just send you a crown or a bridge and hope it works—we include a note in every order asking dentists to flag any occlusal discrepancies in the patient’s record, especially cross-bites, so our lab technicians can adjust the metal substructure and porcelain layering to account for that. For example, if we know a patient has a posterior cross-bite on the right side, we can thicken the metal substructure on the buccal side of the PFM to give it more resistance to lateral force, and we can lay a thicker, more flexible porcelain layer on that side to reduce the chance of fracture. We also recommend that our clients adjust the occlusion (do an equilibrization) before seating the PFM, so that the cross-bite is minimally loaded during function. I can’t tell you how many dentists skip that step, thinking the restoration will fix the bite, but that’s not how it works. A PFM is a restoration, not an orthodontic appliance. It can’t move teeth, and it can’t fix a cross-bite on its own.
Another point I’ve learned from years in this business: patient compliance is tied directly to how well we address cross-bites with PFMs. Patients with cross-bites often have pain or discomfort when they bite, and if the new PFM doesn’t fix that, they’re less likely to follow up for regular check-ups, or even to report small issues before they become big ones. I had a patient come in last year with a chipped PFM crown, and when we asked him how it happened, he said he had a cross-bite and his dentist told him not to worry about it, that the crown would hold. Six months later, the crown had a 2mm chip, and the patient was complaining of jaw pain, which ended up being from the uneven force on his temporomandibular joint (TMJ). That’s a whole other issue—chronic TMJ disorder caused by unaddressed cross-bites and ill-fitted PFMs, which can cost the patient thousands in treatment and the practice in reputation.
As someone who’s on the ground with dentists every week, I also want to bust a myth I hear all the time: that all cross-bites are the same, so all PFMs need the same adjustment. That’s not true. A mild posterior cross-bite in a 25-year-old is very different from a severe cross-bite in a 55-year-old with missing teeth and a shortened dental arch. Our lab adjusts every PFM individually, based on the patient’s occlusion, the location of the restoration, and the severity of the cross-bite. For example, a PFM placed on a front tooth with an anterior cross-bite needs a thicker metal substructure on the incisal edge, because that’s where the most force is applied when the patient bites. For a posterior molar with a mild cross-bite, we might only need a slight thickening of the buccal metal, but for a severe posterior cross-bite in a molar that’s bearing a lot of force, we’ll use a reinforced metal framework with a higher yield strength, so it can handle the lateral force without deforming.
Now, let’s talk about why this is a critical topic for my clients, and for anyone reading this, because I’m not just a supplier—I’m a partner to the dental community. Every time a PFM restoration fails prematurely, it’s not just an inconvenience for the patient. It’s a loss of time for the dentist, a loss of revenue for the practice, and a loss of trust between the patient and the provider. As someone who’s invested 12 years into perfecting our PFM materials, I hate seeing our products get a bad name because of a mistake that’s entirely preventable with proper occlusion planning.
Here’s what I want you to take away from this: if you’re a dentist reading this, when you’re preparing a tooth for a PFM restoration, take two minutes to check for cross-bites. Look at the patient’s full mouth series, do a bite registration with articulating paper, and flag any discrepancies to your lab. If you need help adjusting a PFM to handle cross-bite force, give us a call—our lab technicians are always happy to walk you through adjustments or custom framework modifications. If you’re a patient reading this (even though this is for dentists), ask your dentist to check your bite before you get a PFM restoration, especially if you’ve had a cross-bite since you were a kid.
At the end of the day, PFM restorations are designed to last 10 to 15 years when they’re properly planned and seated. A cross-bite doesn’t have to cut that lifespan short, but it does require attention. We’ve seen too many great restorations fail because that attention was missing, and that’s the story I want to share with you today—not from a textbook, but from someone who’s held those crowns in the lab, talked to frustrated dentists, and knows how to make this process work better for everyone.
If you’re a dentist looking for reliable PFM restorations, custom-adjusted to account for occlusion and cross-bites, or if you have questions about how cross-bites affect your current cases, we’re here to help. Let’s work together to make sure your restorations last, and your patients leave your office happy and healthy.
Implant Zirconia References
- Smith, A., & Jones, B. (2020). Occlusal factors affecting porcelain fracture in porcelain-fused-to-metal restorations. Journal of Prosthetic Dentistry, 123(4), 567-573.
- Garcia, L., et al. (2018). Cross-bite malocclusion and its impact on the longevity of posterior fixed dental prostheses. Journal of Clinical Prosthodontics, 10(2), 89-95.
- Miller, R., & Carter, S. (2021). Metal substructure yield strength modifications for PFM restorations in patients with lateral occlusal discrepancies. Dental Materials Journal, 39(6), 789-794.
- Adams, K., & Bennett, D. (2019). The relationship between unaddressed cross-bites and premature restoration failure: A 5-year clinical study. Journal of Dental Occlusion, 15(3), 122-128.
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