If your not using MySQL you should create another text file called badwords.txt
Have a new badword on each line.
From there do a loop, to check the string from the text file that has the reviews in it.
and in the loop do this
//Assuming $string is the string that has the review text
$string = eregi_replace($word[$i],"*****",$string);
$i would be to get the new line.