Setting characteristics and mechanical properties of self-adhesive resin luting agents

To evaluate the degree of conversion (DC%), salt yield and mechanical properties of self-adhesive luting agents (SAA) set under dual-cure (E) and self-cure (NE) modes.

Three SAA (GC LinkAce/GCLA, MaxCem Elite/MXEL, Rely-X Unicem 2/RXUN) and an adhesive resin luting agent (Rely-X Ultimate/RXUL-control) were used. The properties tested under E and NE modes were a) DC% and phosphate salt yield after 10min, 1h (h) and 3 weeks (w) storage, by infrared spectroscopy; and b) the mechanical properties of 3w-stored specimens by instrumented indentation testing (Martens hardness/HM, Elastic modulus/EIT, Elastic index/ηIT) and microscopic Vickers hardness/VH. Statistical analysis was performed by 3-way ANOVA (DC%), 2-way ANOVA (salt yield) and 1-way ANOVA (mechanical properties) at an a=0.05.

Significantly higher DC% was found in E, except from the 3w groups of GCLA and MXEL. Within E, no significant differences were found, but within NE, there were differences in the 3 w groups of GCLA (vs 10 min) and MXEL (vs 1h). All materials demonstrated increased salt yield in NE, with the highest values found in RXUL and RXUN. GCLA, RXUL showed the lowest HM in E and MXEL the highest in NE. The rankings of the significant differences in EIT were MXEL>GCLA,RXUN,RXUL (E) and RXUL,MXEL>GCLA,RXUN (NE), whereas for ηIT RXUL,RXUN>GCLA,MXEL (E) and GCLA>RXUL>MXEL,RXUN (NE). The results of VH measurements showed an overestimation ranging from 13% up to 38% in comparison with HM.

There are significant differences in the properties tested, which may anticipate variations in the chemical, mechanical and biological performance of the products.