I don't see why so much time and energy, outside an answer to a question was spent.
As to cement being left, and causing problems that is negligence, below the standard of care. Did the cement cause problems, which is stated as inability to floss and perio problems, the answer is yes. Is there a financial component to this issue yes, So there would be grounds for malpractice, though I doubt that an attorney would take the case because the current amount is too small.
As to guarantee, in some dental codes, a guarantee can not be made, it being deemed unethical, but any ethical dentist, who damages his own work should replace it. If he doesn't, it is time to move on, and to mention this to others.
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