Light-curing units in restorative dentistry: a clinically oriented narrative review of performance, selection, and emerging optical functions

OBJECTIVE: To synthesize current evidence on dental light-curing units (LCUs), focusing on their radiometric performance, clinical selection criteria, and emerging optical functionalities. METHODS: This narrative review was conducted in accordance with the SANRA recommendations. A structured search of PubMed/MEDLINE was performed to identify publications addressing the technological evolution of light-curing units, the parameters guiding device selection, clinical optimization and safety considerations, as well as the integration of fluorescence, transillumination and beam-shaping adjunctive features within contemporary systems. RESULTS: LED LCUs have become the clinical standard, evolving from monowave to polywave devices to better match both Norrish type II and type I photoinitiators. Across technologies, the effectiveness of curing depends on the delivered radiant exposure, spectral compatibility, beam homogeneity and effective tip diameter rather than the manufacturer-reported irradiance. Clinical determinants (distance, angulation, maintenance, battery state and training) strongly modulate the delivered energy. Thermal and ocular hazards must be addressed through controlled protocols and protective measures. Multifunctional LCUs integrating fluorescence-aided identification and transillumination functions and interchangeable tips may support diagnosis and workflow optimization, but independent evidence remains limited. CONCLUSIONS: Curing should be approached as controlled energy delivery. Reliability depends on the radiant exposure, spectral compatibility and beam geometry rather than the nominal irradiance. Third-generation polywave LED LCUs appear to be the most versatile reference option for routine practice, particularly when the photoinitiator system of the material is unknown or includes Norrish type I initiators. The clinical value of integrated diagnostic and beam-shaping functions remains to be independently validated.