Pilot study on the early shear strength of porcelain-dentin bonding using dual-cure cements

Statement of problem. One of the most critical steps of the porcelain restoration technique is cementation. Mechanical stress before the resin cement reaches a certain degree of polymerization can displace or even fracture the restoration. Dual-cure materials are intended to be more effective at early stages of polymerization because they contain both photoinitiator and components for chemically activated reaction. Purpose. This study evaluated the early shear strength of bonding between porcelain and dentin, using dual-cure cements. Material and methods. Sixty nonrestored human molars and premolars were randomly divided in 12 groups. The dual-cure cements tested were Porcelite and Dual. A chemically activated cement was also tested (C&B luting composite). Ceramic pieces, 3 mm high, were etched with hydrofluoric acid, silane-coated, and then bended to flat dentin surfaces with each of the cements, associated with Optibond adhesive system. Photoactivation was made by using a light unit with 450 mW/cm(2). The specimens were stored in water at 37 degrees C. Testing times were 10, 30, 90 minutes, and 7 days (referred to as maximum strength). Results. Both Porcelite and Dual dual-cure cements show statistically similar shear strength for the same time interval. The chemically activated material showed statistically lower values when compared with both dual-cure cements, regardless of the time interval. Results at 7 days were much higher than those obtained at 90 minutes for the 3 cements tested. Conclusions. Both dual-cure cements tested presented similar results. The bond strength of dual-cure cements to dentin was higher at ail time intervals than that obtained for chemically activated material. The high values for the coefficient of variation confirmed the technique-sensitive nature of the porcelain/dentin bonding procedure. Although dual-cure cements reach higher bonding strength values faster than the chemically activated material, it is not recommended to stress the bonding until 90 minutes after cementation, because the strength at that time is much lower than the maximum.