פירוש על ברכות 10:9

By "bone" the commentators understand a tooth. Ten children of R. Johanan died, and he preserved a tooth of the last to show to people who had suffered bereavement, for the purpose of inducing them to evidence the same spirit of resignation as himself. Consequently it would seem that R Johanan regarded the loss of children, but not sterility, as "chastenings of love."