I also believe that the sample above is actually hippo ivory. Not much evidence to form a basis of my belief apart from the dotted line present on hippo ivory matches with the one on these hilts and the following observations.
I noticed that there are 3 main types of ivory normally used to make keris hilts. Elephant (with cross hatch), "hippo" (mainly refered to as "gigi ikan" with the dots) and another one with no dots or cross hatch. The third type is normally smaller in size. Probably this is the real "gigi ikan"?
The thing about "gigi ikan" versus elephant ivory and hippo's tooth is that, some people here consider "gigi ikan" as clean while elephant ivory and hippo (if that is the material) as unclean according to teachings in Islam. Probably this is the reason why the material is being presented as gigi ikan in the first place.
Currently, "hippo" ivory fetches a bit higher price here as opposed to elephant ivory (probably for the above reason) However when we look to old Malay saying "Sudah dapat gading betuah, tanduk tidak berguna lagi". Meaning a person had something much more valuable (elephant ivory) compared to horn.
If "gigi ikan" is being regarded highly in the old days, probably the saying will say "sudah dapat gigi ikan bertuah...." but this is not the case. (Notice that the cleanliness issue does not seem to play any role here) Probably people the really old times are not aware or does not subscribe to the belief that elephant ivory are unclean hence the above old saying. Therefore, my speculation that this "gigi ikan" thing is actually market driven due to the cleanliness issue that arose not very long ago.
But, it's just my speculation that is built on a very brittle foundation..
