Intracoronal retainer placed in the abutment teeth has the following disadvantage
It is unaesthetic
They cannot provide support and stability
Difficult laboratory procedure
Difficult to repair and replace
Internal or precision attachments
Advantages:

Improved aesthetics, by elimination of a visible retentive component and vertical support.

Disadvantages:

Difficulty in repair and replacing.
Greater cost to the patient.
Inability to use in teeth having short clinical crowns and tissue-supported distal extension denture bases.