Considerations for Facial Margin Placement: Part IVBy Frank Spear on May 9, 2016 | comments
(Click the links for earlier articles in this series: Part I, Part II and Part III.)
In this article, I am going to focus on a 40-year-old male patient with Tetracycline stained teeth and an extremely high smile line. He wants a more esthetic smile. He has bleached daily for nine months following Haywood and Heymann's protocol for patients with Tetracycline discoloration. The incisal 2/3 of his teeth have lightened significantly, but the cervical 1/3 remains quite dark.
The challenge when restoring any teeth that are discolored in the cervical 1/3 for any reason, and visible in the patient's smile, is the need for subgingival margin placement. The use of supragingival or equigingival margins can be acceptable to some patients, but not most who are seeking treatment to eliminate the discoloration.
The key areas I look at in a patient like this are:
1. How dark are the teeth, and how light does the patient want them? The variation between the existing shade and the desired shade will have a significant impact on the restorative material chosen, as well as the amount of tooth reduction necessary. In some instances, it may dictate the need for full coverage restorations instead of more conservative partial coverage bonded restorations.
2. What restorative material is my lab most comfortable with when masking discolored tooth structure? This becomes important in determining the amount of tooth reduction. Some materials, such as feldspathic porcelain, are very easy to alter the translucency and opacity across the restoration by choosing to use different opacities and shades as the restorations are stacked. Other materials, such as products like Empress, or Lithium Disilicate, e.max, are usually monolithic and then either stained or cut back and layered to alter their appearance. The challenge in these products is that if you use an opaque material to cover the cervical 1/3, you have an entire restoration that is opaque. Instead, if you use a less opaque material, it will require more thickness to cover the cervical 1/3, but will leave the incisal 2/3 more pleasing. All these materials can work, but you need to know from your technician the specifics on reduction.
3. What is the sulcus depth? Any time we place a subgingival margin for esthetic reasons, we have to know the sulcus depth for several reasons. One, because we don’t want to prep too far below tissue and violate the biologic width, and two, because the sulcus depth gives us some idea of the risk of future recession. For a patient with facial sulcus depths of 1 to 1.5 mm, recession is unlikely unless the gingiva is very thin. When the facial sulcus depth is 2 mm or more, the risk of recession increases the deeper the sulcus. The reason is simple: The deeper the sulcus, the more unsupported tissue above the attachment to recede.
For this patient, the discoloration in the cervical 1/3 was around an A-4 on a Vita original shade tab. His desired final shade was slightly brighter than D-2 – something in the A-1 to A-2 range. This dictated cervical tooth reduction of around .6-.7 mm for the feldspathic veneers chosen. In addition, his facial sulcus depths were all 1-1.5 mm, with healthy gingiva on all teeth. I chose to place all the facial margins .5-.7 mm below tissue. In addition, since color was an issue, I chose to carry the restorations through the interproximal so there was no chance of him seeing the junction of the tooth to restoration junction.
Finally, the restorations were bonded with a light cured dentin adhesive and light cured resin cement. The shade of the cement is usually translucent; however, after try-in with water, if the restorations appear low in value, I will experiment with various try-in shades of cements with some opacity.