Adhesive dentistry has undergone a remarkable progress in the past two decades, with significant advancements in a bonding technology playing a pivotal role [1]. To meet clinicians’ demand for a faster, less technique-sensitive, and more user-friendly bonding techniques, universal adhesives (UAs) have been developed. [2,3] These UAs can be adapt to various adhesive strategies, such as etch-and-rinse (E&R) or self-etch (SE) [4,5] or selective enamel etching (SEE), with SEE combining ER on enamel and SE on dentin [6,7]. Additionally, they are suitable for different indirect substrates. [8]

Their versatility is significantly attributed to the incorporation of acidic functional monomers in the methacrylate formulations [6,9]. These monomers interact with dental substrates promote chemical adhesion [10,11]. Particularly, the inclusion of functional monomers, especially 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), enhances the self-etching potential on enamel [12,13] and improves the long-term durability of dentin and enamel bonding [11] by facilitating stable ionic bonding withcalcium, forming structured nano-layers of MDPCa salts at the interface with hydroxyapatite. [14]

Although UAs have demonstrated adequate in vitro performance [8,15] and clinical success [16], [17], [18], ongoing efforts to reduce application time and enhance technique sensitivity have led to the development of new technologies. One example is a “no-waiting” technique, which advocates for reduced of adhesive application time. [19], [20], [21] Clearfil Universal Bond Quick adhesive (CBUq) employs this concept, featuring. multifunctional hydrophilic acrylamide amide monomer (rapid bond technology) [22] that enhances subsurface dentine wetting, thereby decreasing application time. [23,24]

A review of the reveals conflicting results from in vitro studies using the "no-waiting" technique with CBUq. [24], [25], [26], [27] Despite several recent randomized clinical trials assessing the performance of CBUq in non-carious cervical lesions (NCCLs), [28], [29], [30] to extent of authors’ knowledge, no previous clinical studies have compared CUBq applied in “no waiting” vs “waiting” technique.

Therefore, this double-blind randomized clinical trial aims to evaluate the clinical performance of the CBUq universal adhesive in different application times (no waiting and waiting) compared to a 2-step SE adhesive in NCCLs after 18 months. The study's null hypotheses are 1) CBUq applied with the the "no waiting/waiting" technique will demonstrate comparable clinical performance (with retention/fracture as the primary outcome) in NCCLS between them and when compared to the 2-step SE adhesive after 18 months of clinical evaluation and 2) CBUq using the "no waiting/waiting" technique will show similar clinical performance in the marginal staining, marginal adaptation, spontaneous post-operative sensitivity, and recurrence of caries as secondary outcomes in NCCLS between them and when compared to 2-step SE adhesive after 18 months of clinical evaluation.