There are several indications for the extraction of impacted third molars, depending on the position and soft tissue envelope.

• Root resorption, caries, and demineralization of the 2nd molar.
• The presence of impacted 3rd molars during a bilateral sagittal split osteotomy may increase the likelihood of an unfavorable split and therefore may be removed six months prior to planned osteotomy.
• If uprighting or distalization of the 2nd molar is required, the 3rd molar should be removed to prevent caries and root resorption.
• No evidence exists that shows removal of impacted 3rd molars will prevent incisor crowding.

While a variety of radiologic signs have been suggested to be associated with an increase in the risk of injury to the alveolar nerve during third molar removal, only three have been positively associated with an increased incidence of neurosensory deficit

• Darkening or notching of the root
• Interruption of white lines of inferior alveolar canal border
• Diversion of inferior alveolar canal

Studies document an increase in the incidence and severity of complications associated with third molar extractions include:

• Increasing patient age
• Degree and position of the impaction
• Experience of the operating surgeon

While recent studies suggest that in certain sub groups, prophylactic antibiotics may improve quality of life related measures during recovery, there is no evidence they decrease the rate of infection.

• Pericoronal infections that are localized to the immediate enveloping tissues and give no evidence of spread to adjacent tissue planes require local debridement and definitive treatment consisting of removal of the erupting tooth and pericoronal tissue.

• The lingual nerve has been found to be superior to the lingual alveolar crest in the third molar region 14.07% of the time.
  • Belinia, H. et al. “An Anatomic Study of the Lingual Nerve in the Third Molar Region” JOMS 58 (2000) pp 649-651
• The mandibular ramus flares laterally and the lingual nerve extends above the lingual crest 10% of the time.
  • Miloro M, Halkias LE, Slone HW, Chakeres DW. Assessment of the lingual nerve in the third molar region using magnetic resonance imaging. J Oral Maxillofac Surg 1997;52:134-7.

Distance or width between the vertical ascending mandibular ramus and the distal surface of the second molar

• Class I: situated anterior to the anterior border of the ramus
• Class II: crown half covered by the anterior border of the ramus
• Class III: crown fully covered by the anterior border of the ramus

The depth of impacted third molar in relation to occlusal plane

• Class A: not buried in bone, or the occlusal plane of the impacted tooth is at the same level as the adjacent tooth
• Class B: partially buried in bone, or the occlusal plane of the impacted tooth is between the occlusal plane and the cervical line of the adjacent tooth (if any part of the cemento-enamel junction was lower than the bone level),
• Class C: completely buried in bone, or the occlusal plane of the impacted tooth is apical to the cervical line of the adjacent tooth

The angulation of impacted third molar was documented based on Winter’s classification with reference to the angle formed between the intersected longitudinal axes of the second and third molars

• Vertical impaction (10° to -10°)
• Mesioangular impaction (11° to 79°)
• Horizontal impaction (80° to 100°)
• Distoangular impaction (-11° to -79°)
• Buccolingual impaction (Any tooth oriented in a buccolingual direction with crown overlapping the roots)
• Others (111° to -80°)