Clinical Investigations Into The Risk Assessment And Prevention Of Impacted Mandibular Third Molar Extraction

Surgical removal of the impacted mandibular third molars is one of the most frequent procedures performed by dentists and oral surgeons.It has various types of postoperative complications including bleeding,swelling,pain,limited mouth opening,dry socket,adjacent tooth damage,inferior alveolar nerve(IAN)injury,lingual nerve injury,lingual plate fracture,root displace into adjacent space and mandibular fracture.Temporary or permanent damage of the IAN is regarded as the most serious complication.The affected patients suffered from paresthesia or numbness of the lower lip and chin,leading to morbidity and psychological distress.Fracture of lingual plate and displacement of roots or root fragments into adjacent fascial spaces is rare but serious,which might result in bleeding,infection of submandibular and pterygomandibular spaces and lingual nerve injury.The retrieval was complex due to the adequate access and limited space,a secondly extra-oral approach was needed sometimes.Therefore,how to prevent the occurrence of these unwanted complications and to identify the relevant risk factors remains largely underexplored yet.The anatomical relationship between the inferior alveolar canal(IAC)and the third molar roots may be the risk factor for injury of IAN.Previous studies have proposed that the risk factors for lingual plate fracture,root fragment displacement as well as lingual nerve damage are associated with thin lingual cortical plate or its fenestration.Currently,identifying the relevant risk factors associated with complications during and after the impacted third molar surgery primarily depends on pre-surgical radiographic examinations.CBCT is widely used in oral and maxillofacial region due to its advantages such as high spatial resolution,low radiation dosage.Objective:The present study was aimed 1)to identify the radiographic signs between the tooth root and IAC on CBCT images as risk factors and prognostic predictors associated with IAN damage following tooth removal,2)to determine the topographic relationship between root apex of the mesially and horizontally impacted mandibular third molar and lingual plate of mandible.Materials and methods:1)A retrospective clinical study was performed involving 136 patients with 257 impacted lower third molars from January 2013 to December 2014.The relationship between the root and the IAC,the cortication status of IAC,IAC position and shape were analyzed on the CBCT images.The neurosensory function of the lower lip and chin was evaluated.The preoperative CBCT data were retrieved and analyzed to identify the radiographic signs associated with postoperative IAN injury.2)The original CBCT data of 364 teeth from 223 patients were retrospectively collected and analyzed.The topographic relationship between root apex and lingual plate and morphology of lingual plate were determined,the bone thickness of lingual cortex and the distance between root apex and the outer surface of lingual plate on cross-sectional CBCT images were measured.Results:1)The overall incidence of IAN injury in our patient cohort was 13.2%.Multiple radiographic features on CBCT images including contact between IAC and root,IAC position relative to root,IAC shape and cortication status were found to be significantly associated with IAN damage(p<0.05,χ2 test).Furthermore,bucco-lingual position,teardrop/dumbbell shape and cortication status of IAC were identified as independent prognostic predictors for IAN damage.2)The topographic relationship between root apex and lingual plate on cross-sectional CBCT images was classified as non-contact(99),contact(145)and perforation(120).The cross-sectional morphology of lingual plate at the level of root apex was defined as parallel(59),undercut(175),slanted(114)and round(16).The distribution of topographic relationship between root apex and lingual plate significantly associated with gender,impaction depth,root number and lingual plate morphology.Moreover,the average bone thickness of lingual cortex and distance between root apex and the outer surface of lingual plate were 1.02 and 1.39 mm,respectively.Furthermore,multivariate regression analyses identified impaction depth and lingual plate morphology as the risk factors for the contact and perforation subtypes between root apex and lingual plate.Conclusion:Our findings indicate that the relationship between the root and the IAC and proximity of root to the lingual plate might be associated with intraoperative and postoperative complications during tooth extraction.