Another interesting group of studies popped out of my AI search of PubMed literature. As a statistician, I see that the articles that says it was ok are old ones and from the literature it seems that different results were obtained according to sample methods. Recent studies indicate that mercury does influence the microbiome and there is an absence of contemporary studies (using modern measurement techniques) on dental amalgams to clarify the matter.
In a survey of 640 human subjects, a subgroup of 356 persons without recent exposure to antibiotics demonstrated that those with a high prevalence of Hg resistance in their intestinal floras were significantly more likely to also have resistance to two or more antibiotics….Mercury released from dental “silver” fillings provokes an increase in mercury- and antibiotic-resistant bacteria in oral and intestinal floras of primates. 1993
Representative mercury-resistant isolates of three selected bacterial families (oral streptococci, members of the family Enterobacteriaceae, and enterococci) were also resistant to one or more antibiotics, including ampicillin, tetracycline, streptomycin, kanamycin, and chloramphenicol.
The aim of this review is to point out the health hazards of the uncontrolled global use of implanted mercury-leaking dental amalgam fillings. In spite of the pandemic use of amalgam, most dentists and doctors are still ignorant about the levels of mercury exposure and its health implications. This review discusses the following chronically neglected aspects in clinical practice: The use of materials science in calculating the mercury exposure levels, which may exceed the TLVs by an order of magnitude; Microbial dissolution and methylation of mercury from amalgam by oral and intestinal bacteria; Diagnostic problems and effects of chronic mercury exposure with emphasis on intestinal, cardiovascular, mental and neurologic symptoms and disorders; Diagnostic value of faeces–instead of urine examination–as the main indicator of Hg exposure; Lack of control groups unexposed to Hg (amalgam free) for epidemiologic investigations of health problems; Contribution of dental mercury to environmental pollution. In conclusion, a lack of interdisciplinary research and of a critical approach to established clinical routine appears to be the reason for the failure of the dental profession to protect the patient from Hg exposure when saving the tooth.Dental mercury–a public health hazard. 
The group exposed to dental amalgam (n = 92) had 13 times more mercury in feces than the group that had never been exposed to amalgam (n = 43) and the group whose amalgam fillings had been removed (n = 56). No significant differences in either mercury resistance or antibiotic resistance in the fecal aerobic gram-negative flora of these subject groups were seen.Antimicrobial and mercury resistance in aerobic gram-negative bacilli in fecal flora among persons with and without dental amalgam fillings. 1995
The results of this study show that there was no significant difference between children with amalgam fillings and those without such fillings with regard to the prevalence, or the proportion, of Hg-resistant bacteria in their oral microflora.Prevalence and antibiotic resistance profile of mercury-resistant oral bacteria from children with and without mercury amalgam fillings. 2002
A significant correlation between the prevalence of mercury resistance and multiple antimicrobial resistance in intestinal bacterial strains was observed.Resistance of the normal human microflora to mercury and antimicrobials after exposure to mercury from dental amalgam fillings. 1996
According to the conclusions of independent evaluations from different state health agencies, the release of mercury from dental amalgam does not present any non-acceptable risk to the general population.Resistance of the normal human microflora to mercury and antimicrobials after exposure to mercury from dental amalgam filling 1998
the Cu group (CCu group), the Hg group (CHg group), and the Cu + Hg group (CCH group). …Furthermore, compared to the control group, the abundance of bacteria genera Rikenella, Jeotgailcoccus, and Staphylococcus were significantly decreased, whereas the bacteria genus Corynebacterium was significantly increased in the CCu group. The abundance of bacteria genera of Sporosarcina, Jeotgailcoccus, and Staphylococcus were significantly decreased in the CHg group and CCH group. The bacteria genus Anaeroplasma was significantly increased in the CCH group. The results indicated that high doses of Cu and Hg caused histopathological lesions and changed the diversity of microbiota in the cecum of female mice, which provide a theoretical basis for more accurate assessment of the risk in intestinal diseases caused by Cu and Hg.High Doses of Copper and Mercury Changed Cecal Microbiota in Female Mice. 2018
“Redundancy analysis showed that arsenic and mercury were significantly associated with Parabacteroides and Oscillospira in the gut. ” 2019