## 3 Results
### Study Characteristics and Qualitative Synthesis  
Of the four systematic reviews presently considered [34; 35; 36; 37], one also included meta-analysis [37], all full texts were available, and no authors declared funding. Three studies were of a critically low [34; 36; 37] and one of a low [35] quality, based on the AMSTAR 2 tool evaluation. All the systematic reviews [34; 35; 36; 37] analyzed results from clinical (cross-sectional and/or retrospective and/or prospective) studies, along with case reports and case series. Data were extracted and collected based on eligibility criteria from seven cohort, four case-control, six undefined clinical studies, one prospective and one retrospective study,  
Figure 1: PRISMA 2020 flow diagram for new systematic reviews, which included searches of databases and registers only. and from five case reports and three case series, overall involving 3277 participants. Age and gender ratio were recorded for 509 participants, specifically 149 males and 360 females, with a mean age of 52.74 (Table 1). \begin{table}
\begin{tabular}{p{12.8 pt} p{128.0 pt} p{128.0 pt} p{128.0 pt} p{128.0 pt} p{128.0 pt}} \hline \hline
**Source** & **Studies and Population** & **Cases** & **Dental Implants Implant-Supported Restorations** & **Reported Lesions and Hypersensitivity Reactions** & **Diagnosis, Therapy, and Progression Evidence of Titanium Allergy** \\ \hline \hline  & & Cases n.113 & & & All Cases \\  & & n.30 (38.45\%) with Ti & & & All Cases \\  & & allergy & & & **Definitive diagnosis:** \\  & & Mean age: 46.9 y.o. & & Number: MD & **features:** MD & MD \\
**Javed, 2013** & & 33M/71F/19 MD & Position: MD & Number: MD & **Diagnostic procedure(s):** \\
[34] & & **History of allergies:** & Characteristics: MD & Distribution: MD & MD \\ CIDR & Studies: n.7 MD & MD & Survival: MD; or & Location: MD & **Pharmacological** \\ No meta-analysis & CR (n.2) & **Other comorbidities:** & 6 months or more & **Imaging features:** & **Therapy:** MD \\ Critically Low & CS (n.1) & MD & than 6 months & MD & **Treatment:** MD \\ quality & RS (n.1) & **Ongoing** & **Restorations** & **Microscopic** & **Resolution/Progression:** \\  & PS (n.1) & **pharmacological** & Type: MD & **features:** MD & MD \\  & Clinical (n.1) & **therapies:** MD & Materials: MD & **Time to onset:** MD & **Evidence of Titanium** \\  & Experimental (n.1) & **Smoking habit:** MD & & & ** allergy:** MD \\  & Sample size: n.127 & & & & **Plaque Index:** MD & \\ \hline  & (n.32, 25.2\% with Ti allergy & Case n.1 & & **Macroscopic features:** \\  & Mean age: 46 y.o. & n.0 (0?o) with Ti & & & \"Chronic \\  & (14.3-84.1 y.o.) & allergy & & & inflammatory \\  & Gender ratio: & Mean age: 50 y.o. & **Dental Implants** & response with \\
34M/74F/19 MD & Gender ratio: 1F & Number: 2 & fibrosis” & \\
**History of allergies:** & Position: MD & Number: MD & & Number: MD \\  & MD; & Characteristics: MD & Distribution: MD \\  & **Other comorbidities:** & Survival: 2 years & Location: & Location: \\ MD & **Resorations** & & peri-implants tissues \\
**Ongoing** & Type: MD & & **Imaging features:** & \\
**pharmacological** & Materials: MD & MD & & **Treatment:** MD \\  & **therapies:** MD & & & **Microscopic** \\
**Smoking habit:** MD & & & **features:** MD & \\
**Plaque Index:** MD & & & **Time to onset:** MD & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Data extracted and collected from the studies included in the present systematic review. Source: First Author, year, reference, journal of publication, meta-analysis, assessed quality, and funding (if any). Studies of the systematic reviews included in the present umbrella review: design and number. The population of the systematic reviews included in the present umbrella review: sample size (n.), number of subjects with Titanium allergy, mean age (y.o. ), and gender ratio (M/F).