• Polyethylene fibers showed no short-term clinical advantage. • Long-term trials are needed to assess if fibers prevent late fractures. • Fiber reinforcement not routinely justified based on current evidence. Purpose: To synthesize evidence from randomized controlled trials (RCTs) on the clinical performance of ultra-high-molecular-weight polyethylene (UHMWPE) fiber-reinforced direct composite restorations compared to conventional composites in posterior teeth and non-carious cervical lesions. Methods: A systematic review was conducted following PRISMA guidelines (PROSPERO: CRD420251178877). Databases were searched up to November 2025 for RCTs evaluating fiber-reinforced versus non-reinforced direct composite restorations in Class I, II, or V cavities. Grey literature and trial registries were not searched, framing this as a restricted-source systematic review of peer-reviewed published evidence. The primary outcome was restoration failure/survival; secondary outcomes included marginal adaptation, discoloration, and postoperative sensitivity. Risk of bias was assessed using RoB 2, and certainty of evidence was evaluated with GRADE. Results: Four RCTs (404 patients, 494 restorations) with 12-24 month follow-up were included. All trials reported 100% restoration survival in both fiber-reinforced and control groups. No statistically significant differences were found in any clinical performance parameter. The evidence was of moderate certainty for primary outcomes in adults but low to very low for secondary outcomes and pediatric/NCCL indications, limited by short follow-up, imprecision, and risk of bias. Conclusions: Within the limited observation period of up to 24 months, UHMWPE fiber reinforcement did not demonstrate a measurable clinical advantage over contemporary non-reinforced composite protocols for posterior teeth. The uniformly high survival rates and comparable performance indicate excellent short-term outcomes for both approaches under controlled conditions. Absence of observed benefit should not be interpreted as equivalence; long-term RCTs are required to determine if fiber reinforcement mitigates late complications such as fracture in structurally compromised teeth.
Bourgi et al. (Fri,) studied this question.