Never etch glass ceramic with hydrofluoric acid (5% HF), more than once! This will cause the ceramic surface to be degraded and decreases the bond strength. Ivoclar's Etch and Prime can be used once after etching with HF or twice if HF acid was not previously used.
Never temporarily cement all-ceramic restorations. This sounds simple, but I hear about it all too often.
If a ceramic restoration or even a ceramic fused-to-metal restoration with ceramic margins is temporarily cemented, any movement of the restoration while it is cemented may cause the ceramic to chip or even fracture, causing a catastrophic failure. Ceramic margins may fracture with removal of the restoration if an explorer or scaler is used to dislodge it.
This is the first step during the restoration try-in. Once the provisional is removed, remove the provisional cement as quickly as possible to avoid tooth dehydration.
Try the all-ceramic restoration on the tooth with clear/colorless try-in paste or glycerin. This connects the tooth to the ceramic by filling in and eliminating the air space between the two. If the tooth is going to influence the ceramic, it will be apparent at this time. If there is an air space between the ceramic and the tooth, you will not be able to visualize the true appearance of the final outcome.
Changing tooth color or opacity of the try-in paste may be necessary to idealize the final shade. If the incisal edge of the preparation is seen through the ceramic restoration, use a fine diamond bur to reduce the facial aspect of the tooth in the incisal one-third. Reduce the tooth approximately 0.2 mm in depth, beveling 2.0 mm from the incisal edge and rounding the edge toward the lingual.
Shade change/adjust requests
If an alteration in the shade is required to achieve the best esthetic outcome and the restoration needs to be sent back to the laboratory technician, a photograph of the restoration tried on the prepared tooth with try-in paste is strongly recommended. In fact, it’s essential!
Photograph the restoration at multiple angles and include the closest shade tabs which match the shade of the desired outcome. Include a tab from each of the Vita Classical and 3D Master shade guides. This allows the ceramist to determine the tooth’s influence on the color and value of the restoration. The photographs along with the returned restoration allows the ceramist to make the appropriate adjustments.
Never adjust all-ceramic restorations intraorally before final cementation. The risk of the ceramic fracturing is too high!
I check the occlusion carefully before I cement the restoration but do not adjust it. First, visually check the occlusal contacts on the teeth adjacent to the restoration to be inserted before trying the restoration on the preparation.
Mentally note how the teeth contact each other. Place the restoration on the preparation and have the patient carefully close. Never allow the patient to bite with any force on all-ceramic restorations. This may cause the restoration to fracture, or the ceramic margins to chip.
Visually inspect to determine if the occlusal contacts on the adjacent teeth are the same as without the restoration. This is an indication the occlusion on the restoration is close to what is desired, realizing it may be moving slightly because it is not cemented. The actual occlusal adjustment is completed after cementation.
If the occlusion seems excessively open on the adjacent teeth, the restoration was made too high or the provisional restoration was not ideal, and the teeth have moved. In this case, occlusal adjustment should be done extraorally with a slow-speed handpiece.
Marking the occlusal contacts is best accomplished by placing a very small amount of Vaseline on the Accufilm articulating paper. This will leave more precise marks on glazed ceramic.
Intraoral occlusal adjustment should be accomplished with an extra fine diamond in a slow speed friction grip handpiece (preferably electric), operating at a maximum of 20,000 rpms using light pressure. This will reduce vibration and heat, minimizing trauma to the ceramic which may cause chipping or fracturing of the ceramic at the time of adjustment or in the future.
Robert Winter, D.D.S., is a member of Spear Resident Faculty.