Does long-term water-storage affect retentive strength of self adhesive cements?

Objectives: The retentive strength of seven self adhesive cements (RelyX Unicem Aplicap, RelyX Unicem Clicker, RelyX Unicem2 Automix/3M ESPE, iCEM/Heraeus, Maxcem Elite/sds Kerr, Bifix SE/VOCO, SpeedCEM/Ivoclar), two self adhesive cements with self etch primers (Panavia 21/Kuraray, Secure/Sun Medical) one glass ionomer-cement (Ketac Cem Aplicap/3M ESPE), one resin modified glass ionomer-cement (Meron Plus/VOCO), and a zinc-phosphate cement (Harvard) were examined for luting zircon-oxide ceramic crowns (LAVA, 3M ESPE) on extracted human teeth after thermocycling and after one year of water storage. Method: 240 extracted teeth (n=10) were prepared in a standardized manner (10°, h=3mm). The resin cements and the adhesive system were used according to manufacturers' recommendations; in dual-curing systems, only the self-curing approach was conducted. The crowns' inner surfaces were sandblasted. After thermocycling (5000x, 5-55°C) and one year of water storage, the cemented ceramic crowns (Rocatec-pretreatment at the outer surface; connected over a low shrinkage epoxy resin to a resin block, made of Paladur denture base material) were removed along the path of insertion using a Zwick universal testing device. Statistical analysis was made using the two-sample Kolmogorov-Smirnov test. Results: The median retentive strength values [N/mm2] for samples thermocycled only (1st number) and samples thermocycled + 1 a of water storage (2nd number) were: Panavia21: 1.7/2.5, Secure: 3.0/3.0, RelyX Unicem Aplicap: 3.1/3.4, RelyX Unicem Clicker: 4.1/4.2, RelyX Unicem2 Automix: 3.0/3.1, iCEM: 2.3/2.7, Maxcem Elite: 3.0/3.2, BiFix SE: 1.7/1.7, Quickcem 1.3/1.6, Meron Plus AC: 3.1/2.7, Ketac Cem Aplicap: 1.4/1.4, Zinc phosphate cement: 1.1/1.6. No significant difference was found between the samples thermocycled only and those who underwent an additional one year of water storage (p>0.2) in any single comparison. Conclusion: Long term water storage did not affect the retentive strength of self adhesive cements significantly. This study was supported by 3M ESPE, Heraeus, Ivoclar Vivadent, VOCO, and Sun Medical.