What is the best cement to use for porcelain or zirconia crowns?
G. Franklin Shull, DMD
Every restorative dentist has asked this question at some point in their career. We all want to know the strongest and easiest way to use material to adhere our crown to the tooth structure. Unfortunately, the answer is not always a simple one.
Many factors can be considered to best answer this question, including how we design our preparation. If we prep the tooth with traditional retention and resistance form, paying close attention to adequate reduction in all planes, we can choose from multiple delivery modes. Preparing the tooth in a more conservative onlay style leaves healthy tooth structure unprepared and may compromise retention and resistance, necessitating high strength adhesion to dentin, enamel, and crown substrate.
In years past, when our crowns were mainly gold and metal alloys, a cement that would harden between the metal and tooth structure worked nicely when the tooth was properly prepared. With the advent of all-ceramic veneers, onlays, and crowns, the need for mechanical and chemical adhesion was necessary. Resin-based cements accomplished this with a primer on the ceramic and an etch-and-rinse–based adhesive system on the tooth. As use of high-strength ceramics in the anterior and posterior regions of the mouth became more popular, we saw the need to simplify the protocol for resin cements.
High-strength bonds to dentin, enamel, and porcelains can be achieved with fourth- or fifth-generation adhesives and dual-cure or light-cure–only resin cements. Many clinicians have found this technique to be very difficult and the cleanup is tricky, but it is popular when high-strength bonds are needed. A similar technique uses a self-etch adhesive on enamel and dentin instead of an etch-and-rinse adhesive to obtain high bond numbers.
Self-etch resin cements combine the dentin and enamel adhesive with the resin cement to omit the need for the separate steps. This greatly simplifies the delivery, but results in lower bond strengths. If this category of cements is used, it is advisable to prep for retention and resistance.
Conventional cements can also be used for a simplified technique with high-strength ceramics if a traditional prep is used. This technique may be the most advisable for zirconia. We have to consider the possible need to be able to retrieve a restoration without destroying the tooth. High-strength bonding to zirconia should only be considered when the retention of the prep is compromised.
The introduction of universal adhesives may add more versatility to the process by allowing the clinician to choose self-etch, total-etch, or selective-etch modes. Improvements in handling and cleanup will also allow clinicians to feel more comfortable.
Making a decision about cement for high-strength and esthetic restorations should be made before the patient is in the chair for delivery. It should be made the day of prep, evaluating factors like prep design, ability to isolate, and strength required. Thankfully, we have many good choices.
About the Author
G. Franklin Shull, DMD, is in private practice in Lexington, South Carolina.
