Metal Ion Release and Hypersensitivity Reactions Associated with Base Metal Alloys in Fixed and Removable Prosthodontics: A Narrative Review

Abstract

Introduction: Base metal alloys, especially cobalt–chromium (Co–Cr) and nickel–chromium (Ni–Cr), remain widely used in fixed and removable prosthodontics because of favorable mechanical strength, rigidity, wear resistance, and low cost. Despite these advantages, corrosion-mediated release of metallic ions in the oral cavity may pose chemical and biological health risks.

Objectives: This narrative review critically evaluates available evidence regarding metal ion release, toxicological implications, hypersensitivity reactions, clinical manifestations, diagnostic methods, and preventive strategies associated with base metal alloys used in prosthodontic treatment.

Methods: Relevant peer-reviewed literature including systematic reviews, in vitro investigations, clinical studies, and toxicological reports concerning dental base metal alloys was analyzed. Evidence relating to cobalt, chromium, nickel, corrosion behavior, oral exposure pathways, and immunologic responses was synthesized

Results: Ion release is influenced by alloy composition, manufacturing technique, surface roughness, salivary pH, fluoride exposure, galvanic interactions, thermal cycling, and biofilm activity. Nickel remains the most frequent sensitizer, whereas cobalt and chromium may contribute to oxidative stress, inflammatory responses, mucosal irritation, and delayed hypersensitivity. Clinical manifestations include burning mouth, lichenoid reactions, gingival inflammation, stomatitis, dermatitis, and prosthesis intolerance. Although most patients tolerate restorations satisfactorily, susceptible individuals may experience adverse reactions.

Conclusions: Base metal alloys continue to be valuable restorative materials; however, measurable chemical health risks exist in selected patients. Careful history taking, risk-based material selection, optimized finishing and polishing, regular maintenance, and use of alternative biomaterials when indicated are recommended.