What is the difference bwt. cementing and bonding a dental crown?

I am concerned if the permanent dental crown I get causes a reaction of some sort with other metals in my mouth that it will be 'bonded' in and difficult to cut out without damaging or fracturing the tooth underneath. I was planning on getting a IPS Empress CAD made in the dental office which he etches and then uses luting cement (Rely-X). Are there other choices of bonding an Empress that would allow easier removal if I need to change it in the future for whatever reason?