import re


def replace_square_brackets(sent):
    """Converts sentences where missing characters are indicated by full stops enclosed by square brackets to sentences where the missing characaters are indicated by hash symbols."""
    masked_sent = list(sent)
    matches = re.finditer(r"\[\.+\]", sent)
    for m in matches:
        # replace the dots
        for i in range(m.start() + 1, m.end() - 1):  # just replace the dots
            masked_sent[i] = "#"
        # remove the brackets
        masked_sent[m.start()] = ""
        masked_sent[m.end() - 1] = ""
    return "".join(masked_sent)