Scotchbond universal

The primary materials used in this study are listed in Table 1. Power analysis was conducted using G-power software (version 3.1; Heinrich-Heine-Universität, Düsseldorf, Germany) to determine the sample size. Three dual-cured resin cements with their corresponding ceramic primers were used as the experimental groups for the µSBS test: PANAVIA V5/Clearfil Ceramic Primer Plus (V5/CCP; Kuraray Noritake Dental, Tokyo, Japan), PANAVIA F2.0/ Clearfil Ceramic Primer Plus (F2.0/ CCP; Kuraray Noritake Dental), and Rely X Unicem 200/Scotchbond Universal (Un/SBU; 3M ESPE, St. Paul, MN, USA). One light-cured resin cement with its corresponding ceramic primer was used as the control group: Variolink Esthetic/Monobond N (Es/MN; Ivoclar Vivadent, Schaan, Liechtenstein). However, these primers seemed different in translucency and color when applying to the ceramic surface, especially universal primer (Scotchbond Universal 3M ESPE) is a translucent yellow liquid. Therefore, we chose the other ceramic primer (Porcelain Etch and Silane, Ultradent, South Jordan, UT, USA) which was transparent and monofunctional to avoid the possible influence on the color stability measurements. Lithium disilicate ceramic (IPS e.max Press HT A1, Ivoclar Vivadent) was used to fabricate the thin ceramic disk and mimic veneer restoration in the clinical situation.

The present study was set up as a controlled experimental design with four groups. Group 1 consisted of CoCr (N = 4) implants (Maxx Orthopedics Inc., US), which served as a control for the other three groups because of its present clinical applications ( Fig. 1 A). Group 2 was a regular PEEK implant (N = 5) with the exact same geometry as the CoCr component and identical cement pockets, yet lacking the surface roughness of CoCr ( Fig. 1 B). They were machined from a block of annealed PEEK-OPTIMA® (Invibio Ltd, Thornton-Cleveleys, UK). Group 3 was the injection molded PEEK-OPTIMA® (N = 5) with enhanced cement-bonding features (ribs and laser-etching, Fig. 1 C). Group 4 was added which were the same implants as group 3 but included a primer on the PEEK surface prior to implantation (N = 4). This primer (Scotchbond Universal, 3M ESPE, Neuss, Germany) is commonly used in dental applications with positive results when tested with PEEK [25] .

2.1. Experimental two-step UA and commercial reference adhesives. The experimental two-step UA, further being referred to as 'Exp_2UA', combines an experimental primer based on technology of the commercial UA G-Premio Bond ('G-PrBp', GC), used as primer without being separately light-cured, with an experimental particle-filled adhesive resin synthesized by GC under the code name 'BZF-21' (Tokyo, Japan). The basic composition is detailed in Table S1. Noteworthy is that both the primer and adhesive resin do not contain the highly hydrophilic monomer 2-hydroxyethyl methacrylate (HEMA), while the adhesive resin contains zinc-calcium-fluoride bioglass and fumed silica filler.
Representing the adhesive generation of UAs, the commercial products G-Premio Bond ('G-PrB', GC), Prime&Bond Active ('P&Ba'; Dentsply Sirona, Konstanz, Germany) and Scotchbond Universal ('SBU'; 3M Oral Care, Seefeld, Germany), and the gold-standard two-step self-etch adhesive Clearfil SE Bond 2 ('CSE2'; Kuraray Noritake) served as reference (control) adhesives.

Three universal adhesives used were Scotchbond Universal (SU, 3M, St. Paul, MN, USA), G-Premio Bond (GB, GC, Tokyo, Japan), and All-Bond Universal (AU, BISCO, Schaumburg, IL, USA). Adhesives are listed in Table 1 along with these associated lot numbers and components are shown. Ultra-Etch (Ultradent, South Jordan, UT, USA) was used as a 35% phosphoric acid pre-etching agent.

Dentin specimens were divided randomly by using Microsoft Excel (Windows) randomization into two principal groups (n=12) based on the bonding technique used: SE and ER. Universal adhesive employed was Scotchbond Universal (3M-ESPE, St. Paul, USA). The composition and application procedures are listed in Table 1. Resin composite build-ups were constructed in 3 horizontal layers (2-mm thick) up to 6 mm with Spectrum ® TPH® resin composite (Dentsply, Denver, USA). Photoactivation of the resin-based materials was performed using LED curing unit DB85 (Dabi Atlante, Ribeirao Preto, Brazil).
The output intensity was monitored with a Demetron Radiometer (Model 100, Demetron Research, Danbury, USA) to maintain a minimal light output intensity of 1000 mW/cm 2 throughout all experiments. All materials were used following the manufacturers' recommendations. During to the bonding procedures, the samples from each main group were divided into subgroups (n=6), regarding the use or not of Zol-primer before adhesive application. Specimens of each principal group were divided into another sub-groups (n=3), based on the challenge test: Control: water immersion for 24h and MCL: mechanical-cycling load regimen. Spreading of specimens division is presented in Figure 1.