###### Abstract  
The present umbrella review aimed to assess the prevalence of cases diagnosed with lesions potentially due to Titanium (alloy) and other metal nanoparticles released from dental implants and implant-supported restorations, characterizing lesions' macroscopic, imaging, and microscopic features. Secondary aims were to categorize the reported lesions as resembling or ascribable to peri-implant mucositis and peri-implantitis, reactive lesions of the peri-implant mucosa, or hypersensitivity reactions, and to evaluate their relationship with cases', dental implants, and implant-supported restorations' characteristics, and with the evidence of Titanium allergy. The study protocol, developed in advance and compliant with the PRISMA statement, was registered on PROSPERO (CRD42022354676). Systematic reviews were searched through the Web of Science, Scopus, MEDLINE/PubMed, Cochrane library databases, and the PROSPERO register until 19 August 2022; reference lists were also screened. Data from four systematic reviews of critically low /low quality (AMSTAR 2), one including a meta-analysis, were analyzed qualitatively. An overall prevalence of 16.9% of cases was estimated. Reported lesions resembled or were ascribable to peri-implant mucositis and peri-implantitis (55.17%), reactive lesions (17.22%), and hypersensitivity reactions (24.12%); no oral contact lichenoid lesions were described. Titanium allergy was hardly and heterogeneously investigated. Due to the severely incomplete data, no definitive conclusions could be drawn on the potential role of cases' and implant characteristics and Titanium allergy on lesions onset, development, and treatment responsiveness. Keywords:oral; periodontal; peri-implant; lesions; reactions; nanoparticles; dental implant; hypersensitivity; Titanium; alloy +
Footnote †: journal: Medical Imaging and  
grade IV are the most employed materials for dental implant fixtures, and a Titanium alloy (Ti6 Al4V) is the most used for the abutment and prosthetic structures, tribocorrosive processes may lead to Titanium and, to a minor extent, Aluminium and Vanadium particles release [15]. Such metal nanoparticles have been presumably implied, in conjunction with foreign bodies (i.e., cementum), chronic irritation and biofilm accumulation due to complex and improper oral hygiene maintenance, especially in case of implant exposure [16], in the onset of reactive exophytic lesions of the peri-implant mucosa [17]. Such lesions, mainly represented by pyogenic granuloma and peripheral giant cell granuloma, are characterized by high recurrence rates,ectively requiring excision and curettage and leading to dental implants explantation in about 41% of the cases [17]  
Moreover, Titanium nanoparticles released by dental implant degradation are considered a common finding in peri-implant soft and hard tissues [18] and have been detected in peri-implant submucosal biofilm [9]. In detail, larger amounts of Titanium nanoparticles were found in peri-implant mucosa [13; 19] and the submucosal biofilm [20] of peri-implantitis sites compared to healthy ones. Thus, such nanoparticles have been somehow implied in peri-implant disease pathogenesis [21], raising further concerns about dental implant degradation and inflammation [9] of the outer and inner peri-implant tissues [10; 11]. Furthermore, similar to mucocutaneous and boney hypersensitivity reactions from Titanium alloys of medical devices, including pacemakers, stents, orthopedic prostheses, and others [21; 22], also those suspected to be related to Titanium nanoparticles from dental implants were first described in 2008 [20] and recognized as putative epiphenomena of underlying immune-inflammatory allergic disorders. Indeed, T-cell-mediated delayed hypersensitivity immune reactions to Titanium alloy nanoparticles from dental implants have been proposed to be responsible, in genetically susceptible and sensitized subjects [23], for the genesis of heterogeneous lesions that constitute the spectrum of allergic contact stomatitis.