How do you prepare your restorations for seating after try-in? When I act as my own technician by scanning and fabricating in the office, the porcelain doesn't get etched until the restoration is ready for insertion.
When I ask the Winter Lab to fabricate the restorations I still have to try them in, but the restorations are returned to me already etched with hydrofluoric acid (for lithium disilicate that's 5 percent for 20 seconds per manufacturer's recommendations). I take that beautiful, prepared for bonding ceramic surface and contaminate it.
Try-in pastes and oral fluids need to be removed before final seating or they interfere with the ability of the bonding materials to create attachment and weaken the bond.
I was visiting with a group of clients at Winter Lab recently and one of the clients stated that he always re-etched the restoration with hydrofluoric acid. That is absolutely contra-indicated. Re-etching an etched ceramic surface with another dose of hydorfluoric acid destroys much of the ceramic matrix that was created by the intial etch and results in lower bond strengths. Most of the group was doing what I have been taught, using phosphoric acid as a cleaning agent. Some of us, myself included, then placed the phosphoric acid coated restorations in water and an ultrasonic for two minutes, others simply rinsed and dried.
One of the participants in our meeting always requested his restorations from the lab unetched so that he would now treat every restoration the same, whether he served as technician with his CEREC and completed the restoration in the office or had Winter Lab complete the restoration and return it to him. He believed this created a more consistent result.
One manufacturer has created a new cleaning agent (Ivoclean) that is claimed to eliminate contaminates from the etched ceramic. No one in this group had used it yet; I'm very interested in knowing if anyone has, and their experiences with it.
It's important to note that no one in the group was having an issue with restorations coming off—not even the doctor who was re-etching the ceramics with hydrofluoric acid.
It appears that in most cases, careful attention to technique, even when the technique is not optimal, results in adequate bonding of the materials. Knowing that, and then attempting to get in harmony with those optimal recommendations creates high confidence in the connection of my restorations to the tooth.