With regards to deciding what is safest , best or the least harmfull material to use you can get a test called the Melisa Test which indicates allergy & hypersensitivity to metals. Their website is http://www.melisa.org/why-melisa.php . This is a test for allergy NOT toxicity. For Lab locations see http://www.melisa.org/melisa-laboratories.php. This test only recently became available in Australia. I was one of the first to have them done and have had all the available tests done. So you could test to see if Titanium is an issue for instance before making a decision to use it for a retainer .