Preventive Study Of The Inferior Alveolar Nerve Injury, When Removing Mandibular Third Molars Closed To The IAN

Inferior alveolar nerve is one of terminal branches of the mandibular branch of the trigeminal nerve,through the mandibular foramen into the mandibular canal, which dominates the feeling of lips and chin side gingiva of mandibular teeth, skin and mucosa of the lower lip and the skin of chin. Once the inferior alveolar nerve is damaged, the patients will feel inconvenience on speech, chewing in their daily life. Common causes of the inferior alveolar nerve injury are tumor suppression, inflammatory infiltration, trauma and surgery and so on. The iatrogenic factors are the main reason of the inferior alveolar nerve injury, which include endodontic treatment of molars, mandibular third molar extraction surgery, implant surgery, mandibular distraction osteogenesis and mandibular cyst or tumor removal surgery. The inferior alveolar nerve injury due to the removal of mandibular third molars is accounted for 81.5%, which is the main reason of the inferior alveolar nerve injury in clinic.The roots of the mandibular third molars is close to the IAC. Extracting the mandibular third molars are easy to damage the IAN. The reasons of the inferior alveolar nerve damage contain ① separating tooth in violence; ② using teeth collar improper improperly ③using cutting handpiece improperly; ④ hematoma formation; ⑤ apical inflammation spreading; ⑥ taking root blindly; ⑦ roots are adhesion with bones; ⑧ roots are directly contact with the nerve; ⑨ scraping the tooth socket blindlyHow do we effectively prevent the inferior alveolar nerve injury? At present, common preventive measures include:①Preoperative examination. It includes intraoral examination and imaging examination, of which the imaging examination is a more effective means. It can evaluate the relationship between mandibular third molars and mandibular nerve canal. Check means include periapical film, panoramic radiograph and CBCT. Among them, CBCT is a three-dimensional image, which can evaluate the spatial relationship of the mandibular canal and root precisely. But the large radiation dose, expensive in price and whether CBCT can avoid the inferior alveolar nerve injury, which are still a lot of controversy. ②The extraction methods. The splitting crown method is a common clinical dental surgery. Because using hammer to split crown, cut bone and increase the gap. It uses longer operative time, and improper force can make the root into the mandibular canal, which can damage the inferior alveolar nerve. So Orthodontic extraction, pericoronal ostectomy and coronectomy are used to avoid to damage the IAN. However, because of their long period, patients facing a second surgery and other shortcomings, they are difficult to popularize in clinical, and only apply for special industry groups, such as musicians, singers and so on. It is currently recognized that cutting tooth can effectively avoid the inferior alveolar nerve damage, but there are only case reports, no systematic study.Once the inferior alveolar nerve injury occurrs after tooth extraction,shall and when we choose conservative treatment or surgical treatment, which is no uniform guidance.For the issues raised above, we made the following studies: ① When extracting the mandibular third molars, we made a research about the CBCT and periapical film in the prevention of the inferior alveolar nerve injury; ② We made a comparative research about the split crown method and the surgical IAH method in preventing the inferior alveolar nerve injury; ③ After mandibular third molar extraction surgery, we made a follow-up study on the patient feeling lip numbness. The final results showed that: ① A Although CBCT could provide a accurate assessment of the positional relationship between the root and the mandibular canal, but in the prevention of nerve damage, there was no absolute advantage. Compared with using periapical film alone, there was no significant difference. ② By means of cutting action to spilt the tooth, remove the bone and increase the gap, avoiding the use of violence,IAH method prevented the inferior alveolar nerve injury intraoperative. ③ We collected the clincal cases in which the IAN was injured after extraction. The circumstance of nerve damage was confirmed by CBCT examination, accroding to which the patients were treated respectively. The followed up results showed better therapeutic effect. On this basis, we concluded the function tests flowchart, which can help clinicians diagnose and treat the postoperative paresthesia.