I believe that we are fortunate to have such wonderfully esthetic dental materials at our fingertips these days – from composite to lithium disilicate to zirconia, tooth colored restorative materials have universal acceptance in the dental marketplace. As the demand for natural looking dentistry has increased, our manufacturers have answered this call.
While we have these great esthetic materials available today, not so long ago we were routinely restoring anterior teeth with metal post and cores, and porcelain-fused-to-metal crowns.
Certainly master ceramists and highly skilled dentists could, and still can, create relatively esthetic results with metal based materials. Esthetic success for the average clinician and dental laboratory technician are however, limited. Dentistry, professionals and patients alike, became immune and complacent to this cosmetic compromise until recently. It used to be ok for crowns to look artificial and not resemble natural teeth. But now the stakes are higher.
Given our patients’ demands, we are often pressed into finding ways to create esthetic restorations in highly challenging areas. One case in point, and the one that we will review today, is when we have an existing metal post-and-core on an anterior tooth that needs crown replacement – which is especially valuable on a patient with high esthetic demands.
Ideally the metal post and core is removed and replaced with a tooth colored post and core material, either direct or indirect. There are circumstances, however, where it may be difficult or impossible to safely remove the existing post and core without damaging the root structure.
The two crown material options commonly considered today are either using metal (with an opaquer over the surface), or a dense, highly opaque zirconia based restoration. In my experience, the dental technicians that I routinely work with no longer use metal based restorations for esthetic situations due to the inherent challenges in the laboratory technique.
For highly esthetic cases, my technicians will typically utilize zirconia based restorations where blockout is required. As great of a material that zirconia is, we often find the final restorations is not ideal. The crowns can turn out low in value, or just not bright enough.
There remains a ‘shine-thru’ effect even though the ceramist is using an opaquing zirconia material for the basis of the crown. In an effort to completely block out the dark post and core, the restoration is overly opaque, again not ideally esthetic in the final result. In either case the shade can be corrected, but the final esthetic result is limited due to the inappropriate value, or brightness of the restoration. It is because of this shine-thru, and the challenges for the ceramist, that I prefer to block out the metal at the tooth preparation.
In the case that I am sharing with you today, the existing failing crowns on teeth #8 and #9 were removed exposing two very dark tooth abutments. I felt it was too risky to remove the existing cast post and core on the right central incisor, as the post was quite large with thin remaining root structure walls. Our treatment plan was to restore the central incisors with all-ceramic crowns and use prototype bonding to enhance the esthetics of the other teeth in the esthetic zone. You’ll note in this case that Fran has a very ‘gummy’ smile. I was able to create a more pleasing smile by performing a ‘gum lift’.
Read my blog post on predictable esthetic crown lengthening to learn more.
With the crowns removed, the dark post and core of #8 and the dark tooth of #9 are realized. The post and core on #8 was stable and intact, and outside the esthetic nature of the metal post, the post and core was quite serviceable. Again, due to the diameter of the post, I opted to leave the post and core in place and block out the metal prior to impressions for the final crowns.
The technique that I use for blocking out metal is a little different than when I block out a natural tooth (
read my ‘Masking the Dark Tooth with Direct Resin’ blog). When I am blocking out metal, especially grey metal, I need to block out the darkness entirely. Pink Opaque (Cosmedent) is used as the first layer in masking the metal because of how the pink neutralizes the dark grey of the metal.
The reason that pink neutralizes the grey is based on the Munsell color system, but quite frankly, it’s a little above my head. I just know that it works. If you’ve used white opaque in the past to block out metal, then you probably had the same experience that I did; if I used a little, then the white turned grey but if I used a lot, the block out was too white and opaque, and impossible for me to block out in the final restoration.
After removing the PFM crowns, I slightly overprep on the facial to give me a little more restorative space. If there is enamel, I’ll use phosphoric acid as the first step in the adhesion technique. More often than not though, I’ll be entirely in dentin in these cases so I can use a self-etch adhesive, like Clearfil SE from Kurrary. Here is the first part of the technique:
