One of the toughest challenges in restorative dentistry is to mimic the translucency of natural teeth. In the esthetic zone, the most common type of indirect restoration is fabricated out of a translucent, all-ceramic material.

The approach is highly predictable, as technicians using these materials can replicate the translucency of natural teeth. The appearance of the restoration is most ideal when it is bilayered, but nice outcomes can be produced when surface characteristics are applied to a monolithic restoration. 

When masking a severely discolored tooth, you must use a material that is opaque to   completely mask the tooth. The discoloration may be isolated to a small area on the preparation or involve the whole tooth. If the tooth has not been treated endodontically and the discoloration is isolated to a small area of the preparation, a treatment option is to remove 0.2 to 0.3 mm of dentin and mask the discoloration with an opaque resin.

The masking resin I currently use is Estolite Color Low Chroma Opaque (Tokuyama Dental).  This material looks like A1 dentin. If the tooth is endodontically treated, extreme caution must be used to prevent removing tooth structure, which could result in a structurally compromised tooth. Preparing the tooth deeper in isolated areas may significantly weaken the tooth. A minimum of 1.5 mm ferrule must be maintained on the labial and lingual aspect of the preparation. The remaining tooth structure should be a minimum of 1.0 mm in thickness. If the discoloration is in the gingival one-third of a tooth with a crown preparation, it is difficult at times to achieve the 1.0 mm shoulder preparation which is required to achieve adequate strength for most materials.  

If most of the tooth to be prepared is severely discolored, the material for the crown restoration must have a base or substructure that is totally opaque to mask the discoloration. A metal ceramic crown has traditionally been used in this situation. When an opaque substructure is used to fabricate the restoration, it requires a more skilled technician to manage the layering of the ceramic to mimic the depth of translucency of a natural tooth. 

The recommended preparation design is an extensive crown preparation with facial reduction depths of 1.2 mm for the shoulder and 1.7 mm in the incisal one-third. If the tooth is endodontically treated, this gingival depth may not be achieved without structurally compromising the tooth, and should not be done in order to preserve adequate tooth structure. The esthetic outcome in the gingival one-third will be compromised, generally appearing too opaque and high value. The alternatives to metal to mask discolored preparations are e.max Press HO (high opacity) or e.max Press MO (medium opacity), depending on the severity of the discoloration, the depth of the preparation, and the thickness of the material. 

These materials have a 500 mpa flexural strength. The base layer (e.max Press MO or HO) must comprise at least 50 percent of the total thickness of the restoration. If they are thinned to less than 0.8 mm, the veneer glass ceramic overlay will be thicker than the base layer. This may cause fracturing of the restoration. Both materials require application of a layer of e.max Ceram (flexural strength of 80 mpa) to develop the translucency required to mimic nature. If a monolithic technique is used with the e.max Press MO and HO, it is extremely challenging to simulate the depth of translucency of natural teeth. The opaque substrate is at the surface and stains are applied on the surface to simulate translucency. 

Another material option is high strength zirconia (approximately 1000 mpa), which is used for crown and bridge substructures. If the zirconia is thick enough it is opaque. In the anterior region of the mouth, it is often thinned, which makes it more translucent and therefore will not mask effectively. All high strength zirconia materials should be layered with a glass ceramic for esthetic reasons (80 mpa). 

(Note: article continues after photo set)

severely discolored teeth treatment
1. In this case, the canine was prepared as an extensive veneer and the restoration was fabricated with a slightly opacified core (e.max LT – low translucency) and layered with e.max Ceram.
discolored teeth restoration
2. The original metal ceramic crown was removed. Decay was removed on the distal aspect of the tooth. The tooth was previously endodontically treated, and now retreated. An opaque resin was bonded to the tooth. The new translucent all-ceramic crown was tried in using try-in paste.
restoring discolored teeth
3. This tooth was previously restored with a metal post and core. The tooth required endodontic retreatment due to a periapical radiolucency. A glass ceramic, Cosmo ingot (Ivoclar) was pressed to a zirconia post. Changing the post and core to an esthetic option allows for a translucent crown to be fabricated.
anterior crown restoration
4. Conventional crown preparation reduction recommendation.
restoration of discolored teeth
5. Extensive crown preparation reduction recommended for severely discolored teeth.
anterior crown extensive restoration
6. A metal-ceramic crown can be the most predictable restoration for masking severely discolored teeth.
restoring discolored teeth
7. When restoring two maxillary central incisors, one of which is a veneer and the other is a crown masking a severely discolored tooth, I recommend making both restorations using e.max. The veneer substrate could be LT or MO, and the crown HO. Both would be layered with e.max Ceram.

Clear collaboration with the dental technician is required before beginning treatment. The technician must determine which materials he/she believes can use to predictably mask the underlying discolored tooth. Remember, as the tooth is prepared, and the enamel is either thinned or removed, the discoloration generally appears more intense. 

(Click the link for more articles by Dr. Bob Winter.)  

Bob Winter, D.D.S., Spear Faculty and Contributing Author

 

Comments

Commenter's Profile Image Logan C.
August 16th, 2018
So this is kind of out of left field but what is your experience using zirconia And then stacking porcelain on top of that in the esthetic zone? Especially when I’m dealing with a anterior bridge. It will cover dark teeth well...I’m just worried about that junction between the proc and the zirconia failing. Any input? Thanks for your time and great article just brought up some other thoughts and questions I was seeking insight.
Commenter's Profile Image Robert W.
August 20th, 2018
Thanks for your comment. The high strength zirconia substrate that I mentioned in the article is what you are inquiring about. If the zirconia is thick enough it can mask discolored tooth structure. When high strength zirconia was introduced almost 20 years ago there was a significant chipping problem with the veneer ceramic for some manufactures material. Some manufacturers changed the coefficient of thermal expansion of the veneer ceramic to solve the problem in addition to the instructions for firing and cooling cycles of the ceramic. These 2 changes have essentially solved the chipping problems. Most of the chipping problems were isolated to posterior restorations not anteriorly.