You're not supposed to chew the Ti !!! The thing to avoid in your mouth [and body] is two different metals touching or nearby [galvanic corrosion]. Stuff they use in your mouth may include - gold, platinum, amalgam [silver/mercury], nitinol [ nickel/titanium] and others. Introduced materials in your body must not cause allergic reactions,galvanic corrosion, or rejection by the body. I've heard that about 10 % of implants must be removed because of adverse reactions.