Encyclopedia of Oral and Maxillofacial Surgery presents a broad variety of diseases and injuries of the skull, neckline, face and mouth cavity
Surgery for removal of impacted third molar surgeries may be associated with several postoperative complications; these complications are more common in the mandible than in the maxilla; they may include bleeding, dry socket, nerve injury, delayed healing, periodontal pocketing, and infection. Many are preventable. All third molars need not be removed independent of disease findings and patients need not unnecessarily have to accept adverse consequences associated with the surgery risks and discomforts in the absence of pain, radiographic findings of pathology, and or marked clinical evidence of disease. However, when surgery is indicated several new concepts and techniques presented in this chapter can prevent and or manage some of the common postoperative sequel of impacted third molar surgery.
Assessments for removal of impacted third molars
2.1. Arch-space tooth-size discrepancy
The most significant variable associated with eruption seems to be the retromolar space available for the tooth.  The accuracy of prediction has improved remarkably, with the highest values being 97%. Thus, when there is no space available for eruption the tooth should be removed (Fig.1).
2.2. Other factors for preventive removal
The Finnish Current Care guideline indicates three distinct groups of teeth for preventive removal: horizontal teeth, root ends growing close to the nerve, and partially erupted vertical teeth. On average, this preventive group comprises 25% of lower 3rd molars. Thus, instead of removing all third molars preventively, actually, it is necessary to remove only one fourth of third molars. The remaining may be treated later according to signs and symptoms.  Dental caries, tooth displacement and pathology are obvious indications for removal of third molars.
2.3. Presurgical assessment
Surgical procedures should be planned and executed according to scientific evidence. Esti‐ mating possible difficulty in the removal of third molars is a constant challenge for surgeons.  There is a highly significant correlation between the level of difficulty for surgical removal of lower third molars (predicted by the anatomic variables) and postoperative inflammatory complications.
Surgical difficulty in overweight patients is attributed to the herniation of the cheek intraorally making retraction difficult. 
2.3.2. Depth of impaction
The results of Tong Lim et al showed that the depth of impaction of the maxillary wisdom tooth serves as a factor for greater possibility of an oroantral perforation.; a deeper impaction requires a larger amount of bone removal to deliver the third molar and, hence, is more likely to cause damage to the sinus lining during the operative procedure.