Blocking out the dark tooth

Ok, in your head, name the hardest things to do in cosmetic dentistry. Closing diastemas? Tough, but not the hardest. Prepping tooth #15 in the small mouth patient with the big cheeks and fat tongue? No fun…but not the hardest. Taking accurate final impression of crowns and veneers on an entire arch? Stressful and difficult, but not the worst.

What do I think is the most challenging treatment in cosmetic dentistry? One of three things:

1. Matching the single central incisor with an indirect restoration

2. Replacing the missing anterior tooth, especially when there are bone and soft tissue compromises.

3. Blocking out the dark anterior tooth!

In today’s blog, we are going to limit our conversation to just this one overly stressful dental procedure – blocking out the dark tooth.

The dark tooth comes in several varieties and forms: the traumatized tooth with endodontic treatment, the traumatized tooth that is vital, and the tetracycline stained teeth. When a tooth has been endodontically treated, intracoronal bleaching – i.e. walking bleach, can be utilized with varying degrees of success. However, there are times when the tooth is restored with a post and core build-up restoration and it may be dangerous to remove the post and restorative material in fear of damaging the tooth or fracturing the root. In other cases where the teeth are vital, intracoronal bleaching is not an option. Whitening techniques, such as Kor (in the US) or Enlighten (UK), can lighten tetracycline stained teeth for some individuals, but the timeframe to get to a satisfactory level is extended, and it may be difficult for patients to stay motivated to perform the home bleaching aspect of the treatment.

All three of these options have their advantages and disadvantages. Obviously, full coverage restorations are our least conservative treatment option. Properly executed full crown preparations allow the dental ceramist adequate space to block out the underlying tooth color and still have space for layering porcelain. This is especially true with the more highly opaque zirconia materials that will block out the discoloration leaving enough space for the ceramist to create natural characteristics in the veneering porcelain. Unfortunately, so many of the patients that I have seen with tetracycline staining, have otherwise incredibly healthy teeth free of dental restorations, and they are looking for a treatment option that is not so damaging to their teeth.

Recently, zirconia veneers have been introduced to dentistry. I have yet to place a zirconia veneer (though I have cemented/bonded) many full zirconia crowns and a number of anterior zirconia resin bonded bridges (think single winged Maryland bridge without the metal). The restorations have maintained well, so it is likely that given the proper adhesive protocol and techniques, zirconia veneer restorations should be equally similar in their success rate. But as of now, there is no research that I am familiar with that demonstrates long-term success bonding zirconia veneers.

The other issue, and this where things get really tough when we are dealing with dark teeth, is that the more that we prep the tooth for the restoration, the darker the tooth becomes! That’s right – the enamel is filtering the darkened dentin underneath, and as we remove the enamel to gain restorative space, we make it harder on ourselves to block out the discoloration.

 So now that we are prepping deeper to gain space for our restorative material, the more likely we are to having to rely on dentin as our bonding substrate, rather than enamel. In this case, if I am relying on my bond to dentin instead of enamel, my choice of restorative material will always be composite. Why, you ask? For two reasons. Reason #1 – porcelain, especially zirconia, is a very stiff substrate whereas the dentin of the tooth has more flex, especially under function. Composite, in my experience, is better able to ‘bend’ and flex with the tooth structure and I find that the margins maintain better than when I have bonded porcelain to teeth with reduced enamel. The second issue, and this is critical, we must realize that regardless of the material chosen, over time, there will likely be breakdown of the restorative margin interface.

 A major advantage of composite over porcelain or zirconia, is its reparability. In cases of margin breakdown, or recession, I can roughen the existing composite and tooth structure, and following proper adhesion procedures, bond new composite to the existing composite covering over the failed margin or the exposed, dark tooth structure. It is my opinion that using composite to veneer dark teeth allows me to manage the inherent challenges of maintaining the restorations long term.

The other advantage of composite is that it is inherently more opaque than porcelain. We can use this to our advantage when we are working with dark teeth. But it is important to understand the step-by-step workflow when using composite. The first key when blocking out dark teeth is to use a pink opaquer as the first layer of material, after the adhesion technique. Pink opaquer is used to neutralize the dark under color. For clinicians that have tried to use white opaquers, they probably have found that when the white opaquer is used in a thin layer, the value (brightness) is low and the white becomes grey.

 Alternatively, when the white is used in a thicker layer, the white will become too opaque in an effort to block out the underlying dark tooth structure, and masking the white with the composite becomes impossible, resulting in an opaque, unnatural restoration. The pink opaque in contrast, when placed in thin layers, raises the value of the restorative surface without over opaquing the tooth. Utilizing pink opaquer as an undersurface allows the dentist to layer traditional composites to create a natural and esthetic final restoration.

I hope that the information on pink opaquer was helpful in understanding its use in pre-opaquing to raise the value of the dark tooth.

Yours for better dentistry,