Define the Principles of Periapical Surgery (PAS)  

1. Avoid horizontal, sever angled vertical incision Because the collagen fibers of the mucoperiosteum are parallel to the tooth.

2. Avoid incisions over boney eminence Because of the thin mucoperiosteum at this area "such as canine eminence", if I do suture it will cause tearing.

3. Incision and flap reposition over solid bone

4. Avoid incisions across major muscles

Because it will heal with a fibrous tissue

5. Tissue retractor should rest on solid bone "to prevent tearing of soft tissues".

6. Extension of the horizontal incision should be adequate

7. The junction between horizontal and vertical incisions should exclude or include dental papillae "i.e. it shouldn't be cut, it should be kept entirely"

8. The flap should include the entire mucoperiosteum.