Can implant crown be used an abutment for mandibular removable denture?

I am not sure you would want to use a fixed implant crown which is immobile on a partial since partials are great for slowly extracting natural teeth. I have seen well balanced locators under partials which work well. I would ask a prosthodontist on this one since they are the experts on thus treatment plan and I respect that.

Removable partial dentures undergo various movements with different vectors. You are best to remove the crown and use an "O-Ring" or locator abutment on top of the implant. This will minimize any cantilever force on the implant and probable enhance the esthetics of the RPD. You need to consider the health of the implant.

One word, Locator....

It has been my experience that the Locator option will provide retention superior to any clasp. I have attached 3 partial dentures to implant crowns with no apparent negative impact (longest is 5 years). That is not hundreds, so my results are of no interest to science, and likely of no interest to you. If you prefer to keep the crown and you are concerned about excessive forces, then I would fabricate a metal framework/valplast base partial with no metal touching 19.

I'm a prosthodontist. Yes, by all means use the crown as retention. I've been doing it for years. treat it just like a natural tooth. I would suggest not replacing #18 and placing a distal rest on #19 with a mesiobuccal undercut. There aren't any cantilever forces on the crown since, without replacing the second molars, it is a tooth borne partial. Don't use valplast in a partial. By all means have metal against the crown, it is mandatory for a properly designed RPD. A partial must have a rest, reciprocal arm, retentive clasp and guide plate to be successful, only the retentive arm is on a valplast partial. Therefore the valplast clasp drives the partial tissue ward and strips tissue. Have you thought about a fixed bridge or implant to replace #29 and not replace the second molars? That way you eliminate the bulk on an RPD framework

If only 18, 29, and 31 are missing, why not place an implant in #29 area, forget about 18 and 31, and eliminate the partial completely? If a RPD is wanted instead, use the implant crown as you would a crown on a natural tooth. Locator attachments are great, but may not be worth the sacrifice of the crown on a partial this size.