Clinical Performance of Bulk-Fill Versus Incremental Composite Restorations in Primary Teeth: A Systematic Review of In Vivo Evidence.

: This is the first systematic review to focus exclusively on in vivo randomized controlled trials that compare bulk-fill and conventional incremental composite restorations in primary teeth. Our aim was to synthesize current evidence on their clinical performance, including retention, two-year survival rates, marginal integrity, and procedural efficiency. : A comprehensive literature search was conducted in PubMed, Scopus, and the Elicit AI platform up to March 2025. Eligible studies were in vivo randomized controlled trials involving children aged 3-12 years with carious primary teeth, directly comparing bulk-fill and incremental composite restorations. Primary outcomes included retention rates, two-year survival, and marginal integrity, while secondary outcomes were postoperative sensitivity, secondary caries, and aesthetic outcomes. Two reviewers independently performed study selection, data extraction, and risk-of-bias assessments using the Cochrane RoB 2.0 tool. A narrative synthesis was undertaken due to substantial heterogeneity in study design and outcome reporting. The review protocol was registered in PROSPERO (CRD420251021433). : Thirteen randomized controlled trials met the inclusion criteria. Both restoration techniques demonstrated high short-term retention rates (>90%) and comparable two-year survival (85-90%). Marginal integrity was generally equivalent, though incremental techniques showed modest advantages in complex cavities. Secondary outcomes were inconsistently reported, with no significant group differences. Bulk-fill restorations consistently reduced the procedural time by 2-4 min per restoration, representing a meaningful advantage in pediatric clinical settings. : Bulk-fill composites offer a clinically effective and time-efficient alternative to incremental layering in the restoration of primary teeth. This focused synthesis addresses a gap in existing reviews by concentrating solely on primary dentition and in vivo evidence. Despite similar clinical outcomes, the time savings associated with bulk-fill techniques may enhance their utility in pediatric dentistry. Further standardized and long-term trials are warranted to confirm these findings and inform clinical guidelines.