undercut regions med.

[IuriiA]

Пожалуйста, помогите перевести.

Выражение встречается в следующем контексте:

After the initial aligner sequence is completed, in select cases it may be necessary to detail the case to correct minor anterior rotations, perform minor anterior in-out movements, tighten light interproximal contacts or enhance aligner retention in undercut regions.

Вот некоторые возможные определения (англ.), но с переводом я все равно затрудняюсь:
the part of a tooth or artificial crown that lies between the height of contour and the gingivae, only if that part has a smaller diameter than the height of the contour.

the area of an abutment tooth or soft tissue across which a unit of the removable partial denture must pass without interference and hence must be blocked out (filled with wax or clay) before the master cast is duplicated. Use of a surveyor produces a surface that is parallel to the proposed path of a placement and removal.

Буду весьма благодарен за помощь.
Заранее спасибо.
С уважением, Юрий