Table 4. Previous published works comparing the outcomes, particularly the incidence rate of PD between amalgam filling patients (AF) and non-amalgam filling patients (non-AF).

Authors	Published year	Incidence rate (AF vs. non-AF)	Study Settings
Ngim CH et al.	1989	There was a clear monotonic dose-response association between PD and blood mercury levels.	A case-control study among the multiethnic population of Singapore to test the hypothesis that a high level of body burden mercury is associated with an increased risk of PD.
Seidler A et al.	1996	PD cases reported a higher number of amalgam fillings (n = 7.8) than both neighborhood controls (n = 6.5, p = 0.0008) and regional controls (n = 6.1, p<0.00005).	A case-control study comparing 380 German PD patients with 379 neighborhood controls and 376 regional controls
Bates MN et al.	2004	There were insufficient cases for investigation of the association between amalgam filling and PD.	A retrospective cohort study restricted to people who were at New Zealand Defense Force entry, were aged <26 years and had all their posterior teeth
Hsu YC et al.	Current study	Patients with dental amalgam filling(s) have a higher incidence of PD compared to those without dental amalgam filling(s) (adjusted HR: 1.583, p<0.01).	A population-based cross-sectional study in Taiwan enrolling 1,000,000 beneficiaries from the Longitudinal Health Insurance Database