Indications of Non Hex abutments?

Nonhexed abutments are designed when antirotation of the restoration isnt a concern and thats when units are splinted together. But if doing a cemented restoration on abutments you can use hex abutments but not advised if the restoration is screw retained as it may not seat fully.

Totally agree.....sometimes, in splinters cases can use one hexed and one non engaging abutment..non hex

I think the above comment might be misleading. Non hex abutments are used when prosthetic units are splinted together (eg a bridge or bar). The main reason is because of placement difficulties (due to line of insertion) if a hex is used (and of course rotation is not an issue because of multiple units being joined). Hex abutments are used as an anti-rotational mechanism for any abutment that might rotate (eg single unit crowns). However usually ball retainers and locator retainers do not use a hex because of the direction of forces applied (ie they tend to be vertical forces rather than rotational). As such retainers are usually screwed directly into the implant and usually do not come loose (but unfortunately some do). So... it is not correct to say that hex abutments are not advised if screw retained restorations are used. Most screw retained restorations will likely be single unit crowns which will be subjected to rotational forces. Therefore in these cases, you must use a hex abutment. However if the restoration is multi-unit which will not rotate once in position, then it is true that hex abutments are not required (and indeed might make placement more difficult or impossible due to path of insertion undercuts - either with internal fixtures or external). I hope this helps your understanding.