It is important to seek medical attention as soon as possible if you suspect that a thread has broken during the procedure.
When a PDO thread snaps, patients can feel a sudden sharp pain, which is often accompanied by a popping or cracking sound. This occurs due to the sudden release of tension in the thread.
The threads may break due to excess facial movement, rubbing the skin, or exposure to moisture. When it does happen, breakage tends to be near the ends near the incision point. The broken thread poses no threat to you. The piece may migrate up until it extrudes from the skin.
If the thread has become extruded it may be possible to simply remove it, otherwise you may have to have it surgically removed, possibly through a facelift incision.