A person’s tooth bears an imprint of all the experiences that he has undergone–that he broke his hand at a certain age, the various diseases from which he has suffered, and so forth.
An impression of all of these is left on each tooth.
Similarly, whatever happens to any Jew (physically or spiritually) affects every other Jew wherever he may be, even if that effect is not consciously perceived.
–Rabbi Adin Steinsaltz