Options Expanding for Restorative Materials
SACRAMENTO - Digital impressions have many advantages over traditional methods as they eliminate distortions and inefficiencies seen in earlier techniques. However, the selection of the restorative material along with the method of cementation is critical to long-term success. The goal is to choose the strongest material available that meets the cosmetic needs of the patient, according to a speaker at the Advances in Digital Restorative Dentistry Meeting held here recently.
Jack D. Griffin, Jr., DMD, in a lecture titled ?Let?s Stick Together,? discussed restorative and cementation materials for predictable long-term success. Dr. Griffin said that of all the advances in the digital-CAD/CAM world, the changes in materials are perhaps the most significant. ?Monolithic? restorations, particularly lithium disilicate (e.max, Ivoclar) and zirconia (Bruxzir, Glidewell), have brought clinicians an unsurpassed ?combination of strength and beauty. Their clinical performance surpasses any materials ever used in dentistry if preparations are good and correct cementation protocols are followed. ?
Materials and Preparation
Dr. Griffin emphasized that regardless of the restorative materials chosen, the preparation is key, noting, ?Great bonding cannot overcome a poor preparation.? The amount of reduction for either lithium disilicate or zirconia is between that required for a PFM and gold restoration, with a 1 mm definite round shoulder or chamfer finish lines, 1 mm of axial reduction, and occlusal clearance of 1-2 mm. If zirconia will be used, preparations can be slightly more conservative. For maximum retention, walls should taper between 4 and 8 degrees with at least 4 mm of height. When these parameters are met, either adhesive or non-adhesive cementation would be effective. One advantage of always performing adhesive cementation is the ability to provide a seal and reduce the propagation of iatrogenic fractures in the materials; one disadvantage is the need for isolation and another the harder clean-up. Dr. Griffin stressed that both materials exceed overall performance and strengths of PFM and other all-porcelain restorations because of their ability to be used without layering the porcelain. He showed many cases of delamination of porcelain-to-metal or all-ceramic substructures and stressed the choosing of a material that is both esthetically acceptable and offers a much higher overall strength. The problem with layering porcelain is the flexural strength of somewhere near 100 MPa compared to flexural strengths of about 400 MPa for lithium disilicate and about 1000 MPa for zirconia.
He stressed that lithium disilicate (e.max) without layering porcelain is acceptable in all but the most esthetically-demanding situations. In that case, a material with customized layering porcelain can be chosen. Monolithic zirconia is primarily used for patients where parafunctional habits are present and in situations where maximum strength and non-adhesive cementation is desired. He noted that the esthetics of zirconia have improved greatly with time, and stressed the accuracy of digital impressions, particularly CEREC (Sirona), because of its high speed and long-term success. Perhaps what he stressed the most is that for those offices opposed to purchasing the entire CAD/CAM system, that they consider the CEREC Connect digital impression system. He described a ?24-hour-tooth-in-a-bag,? which he said is his concept of taking a digital impression, e-mailing it to the lab, and cementing the restoration the next day.
Dr. Griffin said that the combination of digital impressions and newer materials have given clinicians new levels of predictability in esthetic restorations. Cementation is key. He covered in detail ?adhesive cementation? versus ?non-adhesive cementation."
When preparations are good and isolation is achievable, non-adhesive cementation with resin-modified glass ionomers such as RelyX Luting (3M ESPE) is acceptable and particularly with zirconia. Dr. Griffin noted that Ceramir (Doxa Dental) is a new material that ?bioactively? bonds to dentin while also bonding to zirconia, metal, and ceramics,and offers super easy clean-up. When more retention is warranted, Dr. Griffin encourages the use of adhesive cementation with a seperate bonding agent and dual-cure resin cement.
The luting systems offering maximum retention feature a universal dentin bonding agent followed by use of the resin cement. All Bond Universal and DuoLink (Bisco), along with Scotchbond Universal with RelyX Unicem (3M ESPE), offer maximum long-term bond strengths without acid etching.
Discussing other restorative materials, Dr. Griffin noted that he really likes Shofu?s BEAUTIFIL Flow Plus, which he said combines the convenience of a flowable delivery system with strength and functionality that rivals leading hybrid composites, and offers a rechargeable high fluoride release. ?Now you have a flowable you can put into a class 2,? he said. He also talked about the need for bulk fill materials to increase efficiency in class 2 composites and really likes materials such as Tetric EvoCeram (Ivoclar), Venus Bulk Fill (Heraeus), and Sonicfill (Kerr).
Summarizing his presentation, Dr. Griffin noted, ?all of these advancements are leading us to unsurpassed clinical performance and predictability never before seen in the esthetic dentistry world.?