Titanium dental implants are rough: the rougher, the better. It helps them to osseointegrate (bond with bone).

Because the majority of titanium implants are two-piece (a screw and an abutment), bacteria can enter through micro-gaps between the components, and thrive within the actual implant. This often leads to peri-implantitis.

Single-piece implants don't have this problem (but usually have many others).

Disclaimer: I'm working with a 'maverick' doctor who invented a (revolutionary) non-surgical dental implant.