In contemporary orthodontic practice, achieving consistent bond strength between brackets and tooth surfaces is crucial for optimal therapeutic outcomes [1]. Bond strength directly influences treatment efficacy, duration, and patient satisfaction [2], [3], with failures extending treatment time, increasing costs, and compromising outcomes [4]. While conventional bonding methods using adhesive resins and acid etching achieve resin penetration depths of approximately 15.1 μm [2], bracket debonding remains prevalent with failure rates of 1.8–20.1% [3], [4]. This necessitates exploring alternative techniques to enhance the enamel-adhesive bond strength.

Laser pre-irradiation of bonding resins before photopolymerization has demonstrated potential in the field of restorative dentistry [5], [6]. Research utilizing Nd: YAG and 970 nm diode lasers (DL) has shown improved bond strength and increased resin tag formation when applied to dentin adhesives before curing [6], [7]. The underlying mechanism involves synergistic photothermal and photochemical effects: DL elevates the adhesive temperature, thereby reducing viscosity to enhance substrate penetration, while simultaneously accelerating the monomer-to-polymer conversion through increased molecular mobility [7], [8], [9]. Furthermore, DL may pre-activate photoinitiators, augmenting free radical generation prior to LED curing and promoting cross-linking density [10], [11], [12]. Nonetheless, the effects of DL pre-irradiation on orthodontic adhesive penetration into enamel, microtensile bond strength (μTBS), and the degree of conversion (DC) remain unexplored, highlighting a significant gap in knowledge for clinical application.

Nanoparticles (NPs), particularly cerium oxide nanoparticles (CeO₂NPs), present significant potential for enhancing orthodontic bonding. These particles, ranging from 1 to 100 nm, exhibit increased surface area-to-volume ratios, thereby enhancing their reactivity and interaction with substrates [13], [14]. CeO₂NPs are characterized by their antioxidant properties, antimicrobial activity, biocompatibility, remineralization potential, and anti-inflammatory effects [14], [15], [16]. Although Alnazeh et al. reported that the incorporation of 1% CeO₂ enhances bracket bond strength [17], further investigation is required to elucidate their role in improving adhesive penetration and bonding mechanisms.

Despite the existing body of evidence, no research has systematically explored the synergistic effects of combining diode laser (DL) pre-irradiation with cerium oxide (CeO₂)-modified orthodontic adhesives. This study distinctively investigates: (1) the application of 940 nm DL pre-irradiation to CeO₂-modified adhesives before LED photopolymerization, representing a novel combination; (2) a comprehensive analysis of the impact of this dual modification on μTBS, RTL, and DC concurrently; and (3) whether the integration of these modifications yields additive or synergistic effects on the properties of the enamel-adhesive interface. Understanding this interaction could lead to the development of an optimized bonding protocol that reduces bracket failure rates through a mechanistically distinct approach, thereby potentially enhancing treatment efficiency and patient outcomes.

Therefore, the present study evaluated the impact of 940 nm DL pre-irradiation on conventional and CeO₂-modified orthodontic adhesives before LED photopolymerization, examining μTBS, RTL via enamel-adhesive interface, and DC. Two null hypotheses were tested: (1) DL pre-irradiation of unmodified and CeO₂-modified adhesives, and CeO₂-modified adhesive with LED alone, would show no significant difference in RTL and μTBS compared to conventional bonding; and (2) DC of modified adhesives would not differ significantly from unmodified adhesive polymerization.