Efficiency and limitations of polywave light-curing units in restorative dentistry: a systematic review.

Objectives: This systematic review aimed to evaluate the efficiency and limitations of polywave light-curing units (LCUs) compared to monowave LCUs for the polymerization of resin-based composites in restorative dentistry. The primary outcomes assessed included the degree of conversion (DC), microhardness, and depth of cure (DoC).

Materials and methods: A systematic literature search was conducted following PRISMA 2020 guidelines across five electronic databases: PubMed, Scopus, Web of Science, Cochrane Library, and EMBASE. In vitro studies comparing polywave and monowave LCUs in terms of polymerization outcomes were included. Two reviewers independently performed study selection, data extraction, and risk of bias assessment using the RoBDEMAT tool. Due to substantial methodological heterogeneity (I² >75%), a narrative synthesis was conducted in place of a meta-analysis.

Results: Twenty-six in vitro studies were included. Polywave LCUs achieved significantly higher degree of conversion (83.7-92%) than monowave LCUs (70-81%), particularly with TPO-containing composites (p < 0.05). Microhardness was greater in 15 studies, with bottom/top ratios often exceeding 0.85. Depth of cure reached 4.3 mm with polywave LCUs versus 3.6 mm with monowave devices (p < 0.001). Temperature rise was higher with polywave units (up to 12 °C), and color stability outcomes (ΔEab = 2.1-4.97) varied widely across materials, with no consistent advantage for polywave LCUs; differences were mainly attributed to composite formulation.

Conclusions: Polywave LCUs enhance polymerization efficiency compared to monowave LCUs, especially for bulk-fill and photoinitiator-diverse composites. Nevertheless, their clinical use requires protocol optimization to manage irradiance variability and mitigate thermal risks.

Clinical relevance: This review highlights the importance of matching the spectral output of light-curing units (LCUs) with the photoinitiators used in composite resins. Polywave LCUs showed superior outcomes in degree of conversion, microhardness, and depth of cure especially in composites containing TPO or Ivocerin. However, their higher thermal emission and beam non-uniformity may pose clinical challenges. Selecting an appropriate LCU should consider the composite's photoinitiator system and cavity depth to avoid under-curing and ensure restoration longevity. These findings support a more tailored, evidence-based approach to light-curing in contemporary restorative dentistry.