Luting Agents for Definitive Restorations
Contemporary cements for definitive restorations can broadly be categorised as resin-modified glass ionomers (RMGI) and resins. The latter can be further subdivided into conventional resins (CR) and adhesive resins (AR).
Resin-Modified Glass Ionomers
RMGIs exploit the benefits of both glass ionomers and resins. The glass ionomers bond to dentine, have a thin film thickness, release fluoride and are less prone to ageing degradation, while the resin part confers improved physical, mechanical and aesthetic properties. RMGIs are the most popular luting agents used in clinical practice due to ease of use, and are less technique-sensitive than resins. The indications include cast metal and high-strength ceramic core restorations such as alumina and zirconia for tooth abutments and implant-supported titanium and zirconia abutments.
Resin cements have a similar chemistry to resin-based composite filling materials. An organic resin matrix (e.g. Bis-GMA) is infiltrated with inorganic filler (e.g. silica) particles, which are coated with silane to bind with the surrounding polymer (matrix). The type and amount of filler particles determine the physical, mechanical and optical properties of the cement. The major advantage of resins is superior mechanical and optical properties, and they are particularly indicated for bonding aesthetic ceramic restorations such as inlays, porcelain laminate veneers and all-ceramic crowns and fixed partial dentures (FPD).
The adhesion mechanism at the cement–tooth interface of resins is micromechanical in conjunction with a dentine bonding agent (DBA) by forming a hybrid layer. Some DBAs offer chemical adhesion by bonding with calcium ions from the hydroxyapatite of the tooth substrate. In order to resist the polymerisation stresses of the overlying resin cement, the bond strength of the DBA should be greater than 25 MPa. The DBA can either be separately applied beforehand, or incorporated within the cement. Caution is neces/>