###### Abstract  
The aim of this study was to evaluate the effect of different priming agents on the shear bond strength (SBS) of conventional and bioactive self-adhesive resin cements to zirconia. One hundred and twenty zirconia discs were randomly divided into four main groups according to the priming agents used (\(n=30\)): no priming agent (control), zirconia primer (Z-PRIME Plus), universal adhesive (All-Bond Universal), and universal ceramic primer (Monobond N). Then, each group was subdivided into three subgroups according to the type of self-adhesive resin cement used: ThereAem, Activa BioActive, and RelyX U200 Automix (\(n=10\)). All specimens were subjected to thermocycling. The mean SBS data were analyzed using One-Way ANOVA, followed by multiple comparison Bonferroni test. Without the application of priming agents (control), most of the specimens failed during thermocycling. The priming agent, cement type, and their interaction had a significant effect on the SBS to zirconia (\(p<0.001\)). Only the type of priming agent showed a significant effect on the mode of failure (\(p<0.001\)), resulting in mainly mixed failure with Monobond N and adhesive failure with other primers. Regardless of the type of primer, Bioactive resin cements did not improve the SBS to zirconia compared to conventional cements. d editsr; prosthodotics; zirconia; bonding; bioactive cement; shear bond strength; functional monomer; bonding; ceramic; durability; adhesion; resin cement +
Footnote †: journal: Applied Sciences
group, which bond to the zirconia and resin cement, respectively. The chemical bond of the 10-MDP primer to the zirconia surface is formed through ionic and hydrogen bonds [9]. Several reports have shown that higher bond strength was achieved with MDP-primed zirconia when compared to other priming agents or non-treated zirconia [10; 11; 12; 13; 14]. To simplify the bonding process, some bonding agents were modified with the addition of 10-MDP to their composition in a single bottle to promote bonding to zirconia and different indirect restorations [15; 16; 17; 18; 19; 20]. In a systematic review, 169 surface treatment methods performed on zirconia were investigated [21]. The authors found that 10-MDP-based resin cement provided higher bond strength to zirconia, and they concluded that the surface treatment, cement type, testing methods, and aging condition influenced the bond strength. The interface between the tooth structure and restoration is a crucial factor for the longevity of the restoration [22; 23]. One of the most common reasons for indirect restoration is secondary caries [24]. Although available self-adhesive resin cements have shown good mechanical, esthetic, and bond strength properties [5; 25], a new generation of cements given the description \"bioactive\" were introduced. The main objective of bioactive resin cement is to minimize the chance of caries with different mechanisms and chemical compositions [26]. TheraCam (BISCO Inc., Schaumburg, IL, USA) is promoted as a calcium-fluoride-releasing self-adhesive bioactive resin cement that contains 10-MDP monomer which may allow bonding to zirconia and metal substrates without the use of an additional primer [27; 28; 29; 30]. Activa BioActive (Pulpdett, Watertown, MA, USA) cement is promoted as a hybrid self-adhesive resin cement, chemically bonds to the tooth structure, provides a tight marginal seal against bacteria, reduces secondary caries, and aids in the remineralization of tooth structure [31; 32; 33]. It showed significantly higher flexural strength and calcium ion release compared to resin-modified glass ionomer [34]. Also, the manufacturer of this bioactive cement claims that this cement can bond to zirconia without the application of a ceramic primer [35]. With the frequent introduction of self-adhesive resin cement and priming agents, it is difficult for clinicians to choose the best combination to achieve a good bond strength. In addition, the recently introduced bioactive cements remain not fully investigated.