Yes, mercury vapour from dental amalgam alone is, on a group level, a bigger source than all the other sources together. Breast milk from fish-eating mothers can be quiet high in mercury. The WHO report based their data on intake alone. 7.2.2 Excretion of mercury. The major part of absorbed mercury is excreted in urine and feces.
Conclusion is that dental amalgam is by far the biggest source to excreted mercury.
7.2.3 Accumulation of mercury in humans. The presence of raised mercury levels, in it self, does not necessarily cause pathologic reactions - the levels will have to exceed a persons threshold level. Some levels in some children were above those of adults without amalgam, but the mercury levels in both foetuses and children did not, on a group level, exceed the levels of deceased amalgam-bearing adults have. However, some of the children in Drasch's report had mercury levels in their kidneys as high as those of amalgam-bearing adults or children. These subtle effects are defects in psychomotor performance, objectively detectable tremor, and evidence of impair nerve conduction velocity, which are present only in particularly sensitive individuals.