Improved Chemical Properties Produce Longer-Lasting Restorations in Fewer Steps
John O. Burgess, DDS, MS
As restoratives have transitioned to primarily all-ceramic materials, cements have been developed with improved properties such as increased retention strength, reduced leakage, resistance to contamination, low film thickness, caries prevention, better marginal gap-sealing ability, and reduced thermal sensitivity. Resin-modified glass-ionomer (RMGI) cements have a successful clinical track record, are economical, resist contamination, seal well, and facilitate easy removal of marginal excess. But as zirconia restorations with stronger mechanical properties have increased in popularity, preparations have become more conservative. Resin cements provide better retention than RMGI cements, but more importantly, bonding restorations with resin cements helps prevent the fracture of all-ceramic restorations. Resin cements may be classified by the curing mechanism (ie, light, chemical, or dual-cure) or the number of steps required for bonding a restoration.
Preparations with subgingival margins and poor tissue health may result in contamination during cementation. Self-etching cements (eg, Panavia™, Kuraray; RelyX™ Ultimate, 3M) are contact cements that require a primer to be applied to both the preparation and the restorative. When the cement contacts the primer, it polymerizes. Contact cements produce low film thickness, provide intermediate retention, and are easy to apply. The simplest to use of all, self-adhesive resin cements have a smaller contamination window, but the retention produced is lower than that of total-etch resin cements. The major problem associated with the use of all resin cements is the removal of excess cement at the margin. Tack curing provides easy cement cleanup, but only if the restorative margin is closed prior to cementation. If left open, then cement can be pulled from under the restorative material during cleanup, opening the margin even further. Additional research in this area is needed.
Newer ion-releasing cements (eg, Activa™, Pulpdent; Ceramir®, Doxa Dental Inc.) could reduce recurrent caries and form hydroxyapatite layers, creating a natural seal. However, bioactive cements are the weakest, and the clinical support for their ability to create a marginal seal is limited.
John O. Burgess, DDS, MS, is an adjunct professor at the University of Alabama at Birmingham, where he was previously the assistant dean for clinical research as well as the director of the biomaterials graduate program. He is also an adjunct professor at the University of Texas Health Science Center at San Antonio. In addition to serving on the American Dental Association's Council on Scientific Affairs and as a military consultant in general dentistry to the US Air Force Surgeon General, he received the Hollenbeck Award for outstanding accomplishments in operative dentistry and biomaterials from the Academy of Operative Dentistry. A prolific researcher, he lectures extensively and has presented more than 1,000 CE courses.