Re-cementation of a Lithium Disilicate Restoration

There are instances when an e.max lithium disilicate restoration comes off a prepared tooth. It is important to evaluate why this has occurred, and determine the next steps to recement the restoration.

If there is cement on the tooth and no residual cement is bonded to the intaglio surface of the restoration, I would assume the surface of the ceramic was contaminated before the initial ​cementation. Cleaning of the ceramic surface is essential. First, I would use alcohol or acetone in an ultrasonic cleaner for 10 minutes. Then, apply Ivoclar's Ivoclean for 20 seconds, spray rinse and dry. 

The protocol I use for cleaning the prepared tooth is to first remove as much of the residual cement with a scaler as possible. I then use micro air particle abrasion with 50-micron aluminum oxide at 40 psi to remove any remaining debris and create a freshly prepared tooth surface. This establishes the best tooth surface for bonding. 

If the cement is bonded to the intaglio surface of the restoration it must be removed, ideally without weakening the ceramic. Ivoclar recommends using a cement burn-out cycle. The cycle to use is as follows:

• Low temperature: 403° C
• Entry time: 4 minutes
• Rate of temp climb: 60° C/min
• High temperature: 500° C
• Hold time at high temp: 2 minutes
• No vacuum

After cement burn-out, there might be a black residue on the intaglio surface because of the carbon in the cement. Steam clean to remove this residue.

Two other options to remove the cement are:

1. Grinding with a fine diamond bur in a slow speed handpiece at a maximum of 10,000 rpm.
2. Air-abrading with 50-micron aluminum oxide at 1 bar (15 psi) pressure.

Ivoclar has always recommended you not air-abrade the intaglio surface of e.max lithium disilicate. With either of these techniques, the biaxial strength, even with gentle air-abrasion, can decrease to approximately 300 MPa.

Complete the preparation of the intaglio surface of the restoration by following this protocol:

1. Ultrasonic in water for 5 minutes.
2. Apply Ivoclar's Ivoclean for 20 seconds, spray rinse, and dry.
3. Apply Monobond Etch and Prime and agitate for 20 seconds, then allow it to react for an additional 40 seconds.
4. Follow the manufacturer recommendation for adhesive cementation.

It is strongly recommended that you adhesively bond the restoration, especially if the ceramic has been weakened due to grinding or using air particle abrasion. Monobond Etch and Prime is recommended because it etches the crystal structure of the ceramic instead of the glass phase, so it minimizes the chance of over-etching the ceramic if it was etched with 5 percent HF during the initial cementation protocol.

Following these recommendations is the most conservative approach to patient care if the restoration has not fractured. If it comes off a second time, I recommend altering the preparation design to increase resistance and retention form, and then fabricate a new restoration.

(Click this link to read more dentistry articles by Dr. Bob Winter.)

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