LONG-TERM PERFORMANCE OF METAL-FREE ALTERNATIVES IN IMPLANT DENTISTRY: A CRITICAL REVIEW OF ZIRCONIA AND MODIFIED POLYETHERETHERKETONE (PEEK) IMPLANTS COMPARED WITH GRADE 4/5 TITANIUM

Titanium (grade 4 commercially pure and grade 5 Ti-6Al-4V) alloys remain the benchmark fixture materials in implant dentistry on the strength of several decades of cohort and randomised evidence. Growing esthetic demand, concern over thin soft-tissue biotypes, and interest in metal-free rehabilitation have driven adoption of yttria-stabilised tetragonal zirconia polycrystal (Y-TZP) implants and, more recently, modified polyetheretherketone (PEEK) as alternative fixture and abutment materials. This review critically appraises the published evidence on the long-term (>10 year) clinical performance, fatigue strength and survival of zirconia and PEEK implants relative to grade 4/5 titanium. A narrative synthesis of systematic reviews, meta-analyses, randomised controlled trials (RCTs) and mechanical fatigue studies indexed in MEDLINE, Cochrane CENTRAL and Embase was undertaken. Zirconia implants demonstrate cumulative survival rates approaching those of titanium at 5-7 years (94-98%) and a pooled 10-year cumulative survival rate near 95%, together with consistently favourable pink-esthetic and soft-tissue outcomes, but fracture-driven failure, particularly of narrow-diameter one-piece designs, remains a distinguishing mechanical weakness. Direct RCT evidence comparing zirconia with titanium is limited to two to four trials with follow-up rarely exceeding 5-7 years. PEEK implants and PEEK-based abutments offer a low elastic modulus that reduces stress-shielding but show fatigue limits and fracture toughness inferior to titanium under ISO 14801 testing, and clinical fixture-level survival data beyond the short term are essentially absent. No RCT was identified that directly compares fatigue strength and long-term survival of zirconia or PEEK against grade 4/5 titanium implants over a 10-year horizon. Titanium therefore remains the material of choice for load-bearing and long-span indications, while zirconia is a reasonable metal-free option in esthetically demanding, lower-load sites pending longer-term randomised data; PEEK's clinical role remains provisional and adjunctive rather than as a definitive fixture material.