Off hand , I can think of several instances to use non-absorbable sutures in the mouth.
1. Through and through lip lacerations require the use of a synthetic non-absorbable (ex. nylon) for the Vermillion border/outer skin portion. to prevent unnecessary scarring.
2. When suturing over a sinus exposure or large osseous defect, a stronger/longer lasting suture is used because the healing time may be in the 12-21 day time frame. Sometimes we need the sutures to hold for longer than the 7 day standard. This is especially true in mouth as the saliva/enzymes combined with the constant manipulation by the tongue/chewing ,etc will cause an absorbable suture to come out earlier than listed in the literature.
3. Anytime I am doing a surgery in the anterior esthetic zone (1st premolar to 1st premolar), I don't use an absorbable sutures because the process of resorption is an inflammatory one by nature. Therefore, the sutures tend to cause more scarring than if a I used a synthetic like a nylon or even silk.
4. Tying gut, chromic gut,etc are difficult in blood and spit environments. Sometimes, I find it much easier to get tight knots and good closure using silk verses fighting to get a gut suture to slip off the hemostat when tying.
5. Some of the perio surgeries I perform require careful technique to minimize inflammation of the wound for the graft to “take” and succeed. WE use non-absorbable sutures (Gore-tex/ptfe) in those areas to help this problem.
6. If you don't have absorbable sutures , there is never really a contraindication to using non-absorbable ones unless you are suturing a deep wound involving layers. In that case, you have to use degradable sutures in the deep layers for instance. Of course, you know that... I forget I am writing to a Trauma surgeon.
FWIW, There are other good reasons but I am drawing a blank at the moment. Will drink a coke and wake up a little.
For you Doc T, I agree that vicryl should be used 99.9% of the time. Most of the times that I use non-absorbable sutures it involves either lip lacerations or one of the above special circumstances. Otherwise, I use chromic gut which is very similar to vicryl in its strength and durability.