Veneer pre-treatment: Get ready for success.
To select the correct pre-treatment and cement, it is essential to know what material your lab technician uses and if any pre-treatment has already been performed by the lab. This will both guide you toward the best possible bond and help you avoid any undertreatment or unnecessary overtreatment. Using a form, such as the 3M Success Simplified Cementation Guide, can help optimize communication with the lab and ensure you have all the information you need for cementation.
Different materials require different pre-treatments, and it’s important to know which is best for the case at hand. Glass ceramics like lithium disilicate or feldspathic glass ceramics veneers should be etched with hydrofluoric acid to create micro-retentions in the material (fig 6). On the other hand, oxide ceramics that don’t have etchable glass particles, like zirconia, or resin-based materials, should be sandblasted with alumina and subsequently cleaned with alcohol.
Figure 6: Etching pre-treatment of a glass ceramic veneer with hydrofluoric acid. Image courtesy of Dr. Paulo Monteiro.
Glass ceramic veneers need to be carefully cleaned after etching to remove silica-fluoride salts precipitated on the etched surface. This can be done by rinsing with a water spray until all the white debris is removed (fig 7).
Figure 7: Cleaning of a glass ceramic veneer after etching with a strong water spray. Image courtesy of Dr. Paulo Monteiro.
But what if the lab has already completed etching or sandblasting before delivering the restorations to you? In this case, a more intense cleaning protocol is required to remove any contamination that might have occurred during try-in. For glass-ceramic restorations, this can be achieved by rubbing with phosphoric acid for one minute before rinsing with water. In contrast, phosphoric acid should not be used on zirconia, as it does impair the bond. Here sodium hypochlorite (NaOCl) or dedicated cleaning agents can be used to remove try-in contaminations from pre-sandblasted bonding surfaces.
Once washed, the glass-ceramic veneer should be dried before applying a silane.1 Many silane options are available, from stand-alone silane primers to universal primers with a silane component to all-in-one universal adhesives containing silane, such as 3M™ Scotchbond™ Universal Plus Adhesive. The latter has a proven silane formulation that enables bond strength to glass ceramics on the level of classic separate silane primers.2 In addition to the silane component, Scotchbond Universal Plus Adhesive also contains MDP for priming zirconia veneers.
Figure 8: Application of 3M™ Scotchbond™ Universal Plus Adhesive as the silane primer on the etched glass ceramic veneer bonding surface. Image courtesy of Dr. Paulo Monteiro.
After rubbing in Scotchbond Universal Plus Adhesive for 20 seconds (fig 8) air dry for 5 sec until all solvent is removed and then protect the coated surface from light until applying the cement for seating.