By Lee Ann Brady, DMD 

When a crown comes off and we are going to put it back in the mouth, we need to remove the old resin cement that is inside the crown. What is the best way to go about this? 

First, we need to know if the crown is made of zirconia or lithium disilicate. If you have a radiograph of that restoration, you can tell immediately which one of those two things it is. If you don’t, you can always attempt to X-ray it. (That’s what I do.) Alternatively, you can assume the crown is made of lithium disilicate, which is the more technique-sensitive material when it comes to removing cement. 

For crowns confirmed to be zirconia, employing 30-micron aluminum oxide air abrasion effectively clears out the old resin cement. Subsequently, re-etching the inside of the zirconia prepares it for reseating. For crowns presumed to be lithium disilicate, this approach should be avoided to prevent crack propagation. 

In the case of lithium disilicate crowns, two alternative methods can be employed: 

1. The crown can be placed in a porcelain oven to liquefy and evaporate the old resin. However, caution must be exercised to avoid rapid heating of the hydrated ceramic that has been in the oral environment. Rapid dehydration will introduce cracks and lead to crown fracturing. 

1. An alternative method involves using a brown silicone point in a high-speed handpiece, adjusted to lowest speed. A brown silicone point at slow speed effectively removes resin without damaging ceramic. 

How will you know when all the resin has been removed? When etching lithium disilicate, whether using red 5% hydrofluoric acid or Monobond Etch & Prime from Ivoclar Vivadent, any remaining resin will be evident because the dye sticks to it after the etching solution is rinsed off.  

Seating dental restorations with resin-based cement can be daunting. The process is extremely technique sensitive and requires multiple steps. One of the things I learned years ago is to keep a small cup of acetone or ethanol on the tray table when I am seating restorations using resin-based cement.

All our resin materials have a solvent in them. That solvent is often ethanol or acetone. The solvent disrupts the chemistry, spreads out particles, and stops the resin from polymerizing. So, we can use a solvent to prevent the resin from setting and turn it completely into a liquid then wipe it away. Now we can go back to our steps to clean the ceramic, selenate the ceramic, etch the tooth, apply the dental adhesive, and freshly seat the restoration in the same appointment.

Recently, I was in the process of seating veneers. I prepped #6 and loaded the resin. As I raised the veneer, I realized it was for #11 instead of #6. So, I dropped the veneer in the little cup of acetone on my tray. I soaked a 2×2 in the solvent and completely wiped the resin off tooth #6 and completely wiped the resin off the back of veneer #11. Then, I took a deep breath and was ready for a do-over.

This was the first time I had to use that little cup of solvent in over 15 years, but I was delighted it was on my tray table. Time and again we have thrown that little cup away—for years and years, and now I have experienced firsthand why that cup of solvent is always “at the ready” when I seat restorations using resin-based cement.

Here at Pankey, we are committed to helping you through any of the questions you might have while practicing dentistry. I recommend starting your advanced dental education journey with our Essentials 1 course. You will gain essential knowledge and skills, enabling you to build a solid understanding of fundamental concepts in dentistry. From fundamental principles to essential clinical techniques, The Essentials Series will lay down the groundwork for a successful dental practice and further specialization.