We’ll start the discussion by walking through how I would prep a tooth that is in an ideal position and is an ideal size. This will take some of the nuances out of the picture so we can talk about the general philosophy. Once we have the general form and style, we will look at the variations that can be made to the preparation that are necessary to deal with the different circumstance.
To wrap or not to wrap, that is the question. This question is where the most disagreement occurs between cosmetic dentists. Wrapping is where the preparation extends through the interproximal contact, and it is utilized quite often and has merits. Some respected cosmetic dentists still use this method, the main reason being that it makes seating the veneers very simple. While there is nothing wrong with wrapping, and has its uses as we will discuss, I do not use in unless needed because it takes away too much tooth structure. It is important to clarify that “too much”, is our own opinion and philosophy. I say this because the research shows that wrapping your preparations does not weaken the tooth or the veneer in any way and is structurally and biologically sound. That being said, we would rather save as much tooth structure as possible. If I were to have veneers, even though they are permanently bonded, I wouldn’t want small teeth underneath. I make a point to show my patients their prepped teeth since they have anxiety about this, and they always sigh relief when they see that their teeth are the same side and still look like their teeth. It is comforting to know that your natural teeth are still preserved underneath so that is what we prioritize with our prep design.
The preparation process commences after finalizing the smile and teeth’s shape and size. Rather than prepping teeth based on their current size, it’s crucial to work from the final desired outcome. Porcelain typically requires 0.4mm to 0.6mm facial reduction and 0mm to 1.5mm incisal reduction. These reductions must be taken from the veneers’ final position because it is more conservative and often means that you don’t need to take away tooth structure at all. Maintaining thin facial reduction allows the tooth’s natural color to shine through, giving the veneers vitality and a life-like look. Enough incisal reduction is important for incisal translucency. If no translucency is desired then no incisal reduction is required, and no more than 1.5mm of reduction should be left because it will weaken the final veneers.
After facial and incisal reduction, a light chamfer margin should be place circumferentially. Gingivally, we place the margin half a millimeter into the sulcus, except for at the papilla where I will leave it at the level of the gingiva. We prefer to not place the margin more subgingival to reduce inflammation. Interproximally, we push the margin to the contact point. If the teeth have a narrow contact point, pushing the margin here will break the contact just enough for light to pass through, which is ideal for the impression or scan as well as for the ceramist. If the teeth have a broad contact point, we leave the margin at the most facial part of the contact point and break the contact with a sanding strip. It is important to keep the
insertion point for the prep from the facial so that it can remain as conservative as possible. If you are reducing incisally, create a sharp 90 degree angle on the incisal palatal junction, and smooth all of the facial angles.
That is the design for an ideal tooth. But often we don’t have the right gingival contour, or there is a rotation in a tooth, or there are spaces that we are closing. With each of these variations, we need to alter our preparations accordingly:
- Gingival Contour: If the gingival contour is off, place the margin more subgingival where needed so the gums can heal around the new margin. The main place we see this are on the maxillary incisors when the zenith is too far mesial. If this is the case, place the mesial margin 0.5mm – like normal – and place the distal margin proportionally to that, which will make it more subgingival on the distal.
- Black Triangles: Black triangles usually result from gingival recession and can be a large source of insecurity for many people. When black triangles exist, extend the margin interproximally to make a wing. Wrap the wing fully interproximally, keeping the wing cervical to the contact point of the tooth. The interproximal margins should also be placed 1mm to 1.5 mm into the sulcus to allow for a better emergence profile.
- Diastema: When diastemas are present and there is a full space between two teeth the interproximal preparation is extended interproximally on that side. This is the one time that we do wrap the prep, but it is not necessary to remove tooth structure, a margin just needs to be created on the interproximal and the tooth needs to be shaped so that there is a clean path for insertion. The margins should be placed subgingival in the papilla, like with black triangles, to allow for a more natural emergence.
- Short or Fractured Teeth: If you are adding more than 1.5mm of length to the
tooth, we don’t add the extra with porcelain. If extra length is needed for cosmetics and function, we add the length with composite, and then reduce to 1.5mm or less and add the porcelain from there. This will give the desired length without compromising the strength of final veneer and tooth.
There are more nuances to the process and many more scenarios that need specific adjustments. However, this is a general approach to veneer tooth preparation and the philosophies that we use to create beautiful long-lasting veneers while saving as much tooth structure as possible. This isn’t a comprehensive step-by-step guide to take you to cosmetic expertise, but hopefully it has clarified some of the obscurities and is at the very least a good start.
Photo citation Fava, Joseph. “Porcelain Therapy: Veneers vs Jacket Crowns, the ALARA Principle for Prosthodontics.” Oral Health Group, 15 Nov. 2015, www.oralhealthgroup.com/features/1003918624/attachment/fava-fig-1d/.
