Dark Curing and Early Post-Irradiation Stress Spike in Light-Cured Composites: Overlooked Phenomena Compromising Freshly Bonded Interfaces in Large Restorations and Leading to Marginal Gaps and Cuspal Deflection

Hassan KA and Khier SE

Published on: 2025-10-11

Abstract

Objective: To highlight and critically examine the phenomena of dark curing and the associated early post-irradiation stress spike in light-cured composites, and to discuss its mechanistic basis, clinical implications, and currently available strategies for mitigation.

Methods: A focused literature review was conducted, synthesizing experimental studies on polymerization kinetics, post-irradiation shrinkage stress, and viscoelastic property evolution in light-activated resin composites. Studies examining stress development in various cavity geometries, photoactivation protocols, and adhesive systems were included to inform clinical relevance.

Results: Polymerization continues after exposure to curing light, and the transition from a resin to a glassy state (vitrification) can induce a rapid early stress spike within the first minutes post-irradiation. Laboratory evidence shows that stress accumulation in this window can exceed adhesive bond strength, promoting marginal gaps, cuspal deflection, and potential postoperative sensitivity. Currently available strategies such as modulating irradiance (soft-start/ramped curing), incremental placement, and allowing quiet time before finishing procedures can reduce the magnitude and clinical impact of the stress spike.

Clinical Relevance: Early post-irradiation stress spikes can compromise freshly bonded interfaces, leading to marginal gaps and cuspal deflection. Evidence-informed strategies such as incremental placement and controlled irradiance (soft-start/ramped curing) can mitigate these risks and enhance the long-term performance of bonded restorations.

Conclusions: Dark curing and the early post-irradiation stress spike are mechanistically and clinically significant phenomena that are often underestimated in adhesive dentistry. Awareness of this time-dependent stress evolution allows clinicians to optimize curing protocols, restorative techniques, and adhesive strategies for ultimately improving interfacial integrity and restoration longevity.