When the advantages of dental gold and or porcelain do not suggest the best approach as ONE or the OTHER – we can use BOTH! The ceramometal, or porcelain-fused-to-metal crown may the way to go. It is possible in many instances that the advantages of BOTH the metal and the porcelain can be realized.
Not a lot of dentists these days get this – especially when abrasion possibilities are concerned. If a patient is grinding their teeth, placing any kind of a ceramic crown will abrade the opposing teeth. When these crowns are highly polished, this abrasion is less, but once the surface roughens again, the abrasion starts.
I will note here that the term “porcelain” may well refer to other ceramics as well, including zirconia and lithium disilicate ceramics that are similarly used in dentistry, and also significantly abrasive. But for the crowns that include both ceramic and metal (the PFM), it is actually feldspathic porcelain.
For a PFM – porcelain-fused-to-metal crown – the metal part can be made to cover the contacts with the opposing teeth – protecting them! AND – the margins can be made mostly of metal, hence being more accurately fit to the prepared tooth – lowering recurrent decay.
Organization of Chapter
You May Skip to Whatever Subject Interests You Now
Basics: Crowns with Only Porcelain or Only Gold
Is there another possibility?
Reduction of Tooth for Porcelain-fused-to-metal Crowns
The Esthetics of PFM Crowns
Disadvantages of Metal?
The Invention of the PFM
Bottom Line for Gold versus Porcelain versus Both
Basics: Crowns with Only Porcelain or Only Gold
We’ve discussed in several places so far the advantages and disadvantages of gold versus porcelain, so you might have a pretty good idea of where we are going with this chapter.
I was in the dentist’s office the other day as a patient, seeing about the need to have one of my wisdom teeth extracted, and heard the son of an older, not to say elderly, patient asking for clarification about what kind of crown his mother should get. He was asking about gold and porcelain and was getting into some questions about expansion and other surprisingly technical things. The dentist was trying to field these while making sure the mother was comfortable to go home. The dentist was getting a little annoyed about subtle questions at a time that would not normally be used for casual conversation. Well – I couldn’t resist leaning into the topic and told the patient’s son that I always tell my students that if gold were tooth colored, nobody would ever use anything else – because it has ALL of the other advantages. That seemed to solidify the situation for the son, and the dentist’s response was pleasant.
But there are times where porcelain just has to be used – certainly the anterior teeth, but also, sometimes for the posteriors. When my 17 year old female high-school patient came in needing a lower molar crown, even though she obviously ground her teeth, I never considered doing a gold crown for her. Why not? If you have ever been a girl in high-school, maybe the answer is obvious – the PEER PRESSURE is immense – and when one of her friends would comment to say that she has an uncle with a crown like that, that’s the end of her membership in the popular girls group!
So, what are the choices if a gold crown just won’t work socially even if conversationally unapparent, and a porcelain crown would accelerate the grinding on the opposing teeth? Sounds like neither would be a good idea.
You can explore in more depth the subjects of all gold and all ceramic restorations by reading these other chapters: Gold: Ch 5 and Ch 6; Porcelain: Ch 7.
Is there another possibility? Yes.
We can do a crown that has porcelain over a substructure, called a coping, of noble metal – not gold but a silver color more like “white gold” in jewelry. Now, the cool thing is that the metal and porcelain can be distributed over the surface of the crown however we want.
In the case of the 17 year old, I was able to make a porcelain-fused-to-metal crown (PFM) where most of the visible surfaces of the crown were porcelain, but the areas that were actively in contact with the opposing tooth were in metal. I studied how her jaw moved and how her cusps on that tooth moved in relation to the opposing tooth, and had the laboratory make a PFM where the metal protected the vulnerable contacts and sliding surfaces of the opposing tooth. The final result looked like a natural tooth with a few really well-done and shiny silver fillings done in it. That was very acceptable to her, and her friends!
So, can we make a PFM, also known as a ceramometal crown, that has the advantages of the porcelain with none of the disadvantages? Mostly.
The abrasion issue is more challenging, but in the posterior case described above, there was a successful solution. If the dentist is doing an upper front crown, metal can be brought to the surface on the lingual side, so that the lower teeth don’t touch porcelain in the centric bite. BUT – when the patient slides forward, protruding their chin, the edges of the opposing teeth may touch, and there is porcelain on the upper one which will still have an abrasive effect, perhaps a devastating one, on the lower incisors. IF the canines are positioned well and naturally shaped, then possibly the incisors DO NOT touch when the teeth are moved forward, and this would be the ideal situation – because no abrasion could happen.
Reduction of the Tooth for Porcelain fused to Metal Crowns
The amount of reduction required for a PFM crown, can be less than for an all porcelain crown, as much of the substance of the crown is metal, which can be much thinner. On the facial surface, however, there still has to be enough reduction to place adequate porcelain for the desired esthetics, but for the rest of the preparation it can be more conservatively reduced.
For the marginal adaptation, many if not all of the margins can be made from metal – and these cast metal margins are far more accurate than for hand-stacked or CAD/CAM porcelain margins. The question as to the facial margin is important to consider, however. If the facial margin of the crown, under the gingiva, were made of metal, there would be a thin band of metal, called a collar, that would be visible if the gums recede enough to expose it to sight, or even might be seen THROUGH the gingival tissue if it is unusually thin. The compromise here is that we generally make the facial margin with the metal JUST disappearing at the margin, but it provides some support to the porcelain in that area – resulting in a better adapted margin than for full ceramic crowns.
For the cementation of a PFM, since the substructure is metal, the walls are less tapered and made tall with sharp features to give good mechanical retention, which would not be wise for an all porcelain crown as discussed earlier. Now, we do NOT need to use an adhesive cement, we can use typical cements in a dental office – so the cementation process is no where near as TECHNIQUE SENSITIVE and susceptible to failure. In other words, we are not relying on adhesive cementation.
The Esthetics of a Porcelain-fused-to-Metal Crown
The esthetic REQUIREMENTS are always dependent on the individual patient. As we’ve discussed, for older patients the need for attention in this area, particularly for anterior teeth, is paramount.
In fact, many dentists will NOT do a crown on ONE central incisor of the upper arch, especially for an older person. The problem is that it is REALLY difficult to achieve a good match to the other tooth, when they have lots of subtle characteristics and are SO visible with every expression that the patient makes. When I was in dental school my father had one central incisor crowned by a dentist in Palm Springs – where there is a very high percentage of retired people. This dentist really knew what he was doing, because I would bet that very few people could tell the difference between the natural tooth and the PFM, and I had to look hard to see the difference!
In any event – it is certainly possible to do a very natural looking crown, even if there is a thin layer of metal under the porcelain. The laboratory technician will first fire a thin opaque layer of porcelain over the metal, to hide its color, and create a little of a yellow hue that is natural for dentin.
In the case where the patient’s teeth are thin and seem to be more transparent throughout the tooth, the PFM may be more challenging, but this is probably 5% of the total patient population.
I mentioned before that when the PFM is made with a metal collar, when the gums recede and the color shows, it is not a good thing. When the PFM is made with the metal going to zero at the facial margin, when THAT margin shows it just appears a little gray or dark in the area – far better than the metal collar. But – if the esthetics in the facial area is critical were there to be recession, we can even keep metal away from the margin entirely and make a full porcelain margin. This can be made to look natural even if seen in the mouth.
Disadvantages of Metal?
Most full-porcelain crowns are done because the dentist has a CAD/CAM machine and must use it! Call me cynical, but it IS a fact that if you have this machine you must market the product from that machine: “Horray, we now have a metal-free practice”! That kind of statement is not unusual, and it puts metal restorations in a deliberately poor light.
We know by now that there is nothing inherently bad about either silver amalgam restorations or gold restorations or PFM restorations that utilize another metal alloy. In fact the only thing wrong with metals for some people is the occasional sensitivity or allergy. Some people are allergic to amalgam. Some people are allergic to nickel, or at least sensitive to it, and we know this because of cheap jewelry. Nickel is not used in the mouth, and the rare person allergic to amalgam won’t be able to enjoy its benefits.
Quite the contrary – silver amalgam is the most versatile and longest lasting direct restoration we can do in the mouth, other than direct gold. Cast gold crowns are by far the longest lasting crowns because of their excellent margination, and for the posterior teeth can often be made so they are not even visible. The dental materials are there, and the expertise is decades old, but the acceptance in today’s “marketplace” depends on how the options are presented to the patient.
The Invention of the Porcelain-fused-to-Metal Crown
In the 1940s it was possible to do full-porcelain crowns – they were called porcelain jacket crowns. They were not very successful. You may be able to figure out why – the cement that was available at the time was not adhesive, so the porcelain crowns tended to fracture, as they were not intimately supported by the tooth structure in the way they are today. So, in 1952 the PFM was patented.
Now, this was no mean feat. Someone had to do some Edisonian research to find the right combination of porcelain formulation and metal alloy, so that they would stay together under all of the temperature changes that exist in the mouth! But it got done.
Now an anterior porcelain crown could be made that would not fracture, because it was bonded to a metal coping, and stayed on the tooth well with the cement available at the time through mechanical retention.
The PFM reigned supreme for many decades, until adhesive cements were invented, and then all porcelain crowns, and most particularly, CAD/CAM crowns were possible. The incredible technology of the CAD/CAM systems would be totally useless without the advent of the adhesive cement!
But from the mid 50s to the late 80s, the only choice for anterior crowns was the PFM, and patients were quite satisfied with that in most circumstances. It was commonplace for much of that time to make the facial margin with a metal collar, which showed after a decade of use. By the time the mid 80s came around it was more common to compromise somewhat on the adaptation of the facial margin to preserve the esthetics in this area.
Sad to say but the genius of laboratory technicians in making perfectly natural PFM restorations will decline when dentists request more and more full porcelain and full ceramic crowns.
Bottom Line for Porcelain and Metal Crowns
The bottom line is that each individual dentist, in collaboration with his laboratory, can provide what will be the best benefit to you – both in terms of longevity and appearance. Of course, the willingness of the dentist to have in place such an individualized and customized offering for each patient is variable.
But, wouldn’t you want to go to a dentist who offers the greatest range of restorative techniques and methods?
No one approach is appropriate for everyone nor every situation. Thankfully, dentists have many tools in their toolbox, with which they can fabricate many possible variations of direct and indirect restorations. And this is ALL for the benefit of the patient.