The Comparative Analysis Of The Panoramic Photography And CBCT With The Anatomical Relationships Of MITM And MC

Mandibular impacted third molar(MITM) extraction is one of common proceduresperformed in oral and maxillofacial surgery department. Partial MITMs are difficult toextract, and occur easily various complications after extraction,because anatomicalposition of the MITM and adjacent tissue is particular.Inferior alveolar nerve(IAN) injuryis one of the most serious complications, it can lead to sensory disfunction, mucous cyst,fibroma, scar and so on. Some literatures report that the rate of IAN injury is about0.4﹪-8.4﹪. most researches think that intimate anatomical relationship of the MITM roots andMC is the main reason of the IAN injury, external force can also lead to the IAN injurydirectly or indirectly during extracting. Therefore, Preventing IAN injury depends onpreoperative image analysis and evaluation, extracting methods during operating,prophylaxis of postoperative complications. the panoramic photograghy(PP) examination(X-ray plain film) only reflect the two-dimension anatomical relationships of the MITM roots and MC, can not reflect the bucco-lingual relationships. when there are overlappingimages between MITM roots and MC, it leads to misdiagnose easily,however, its radiationdose is low and the cost is cheap. It is more suitable to develop for the primary hospital.CBCT imaging can really reflect tissue and structure. CBCT can provide smaller voxeland higher spatial resolution, and observe slight change clearly such as bone, teeth,periodontium and so on. CBCT can observe precisely three-dimension anatomicalrelationships of the MITM roots and MC, however, its radiation dose is higher and thecost is more expensive than PP. It is not suitable to develop for the primary hospital.Therefore, we make a choice according to the specific situation in clinic practice.The aim of our study makes the comparative analysis of PP and CBCT beforeoperaton:1) finding out the constituent ratios with various classifications of PP. And testwhether or not MC touch the roots by CBCT.2) analyzing the touching rates with fourcoronal classifications of the CBCT. Finally, extracting the MITMs by MITE(defining thatstripping bone, increasing space, cutting teeth and extracting piecemeal by high-speed andpneumatic hand piece), and immediately check up the exposing situation during MITEoperating. however, at present comparative analysis of the anatomical relationships of theMITM roots and MC before operation,and TE operating methods to prevent the IANinjury are very scarce.This provides the instructions for clinical operation by ourcomparative study.In the retrospective study, we choose7751patients(15174MITMs)who ask forpartially erupted or completely unerupted MITM extraction at the fourth military medicaluniversity from April2010to April2012. after every patient takes the PP or periapicalradiograph, and Sift patients according to our inclusive principles:1)(20-60)years old;2)clinical examination: there are no pathological changes such as bone fracture, tumor,cyst, etc;3)on the PP or periapical radiograph there are superimposed images between theMITM roots and the MC, and no pathological changes, sift1213patients (1554middleand lower MITMs)by clinical examination before operation and PP examination,finallychoose out401patients(518middle and lower MITMs) and be ready to do CBCTexamination by informed consent, then test whether or not MC touch the roots by CBCT, and analyse the difference of every index by X2test. Finally, extract the MITMs by MITE.and immediately check up the MC exposing situation during MITE operating.results show as follow:1, when there are overlapping images of MCs and MITMs on the PP, touching ratebetween the MITM roots and MC is shown by the CBCT:①bifid apices on canal﹥reflexion of apex﹥interruption of canal white line﹥deviation of canal﹥narrowing ofcanal﹥darkening of apex(P﹤0.05);②roots bellow MC inferior margin﹥roots on theinferior1/2of MC﹥roots on the superior1/2of MC (P﹤0.05).2.87MCs expose during MITM operating, the exposing rate is consistent withtouchiong rate by CBCT test.3. there is only1patient(1tooth) who suffer the lower lip numbness, the occurringrate of IAN injury is about0.19﹪(1/518).Conclusion: analyzing the anatomical relationships of MITMs and MC by comparasionbetween PP and CBCT.(1) The touching and exposing rates of bifid apices on canal, reflexion of apex andinterruption of canal white line are higher, the risk is greater. In addition, the touching andexposing rates of roots bellow MC inferior margin and on the inferior1/2of MC are alsohigher, the risk of IAN injury is also greater, therefore, the PP can precisely predict therisk of TE;(2) the rate of IAN injury is about0.19﹪in our experiment, analysing thereasons:①accurate images analyse before operation;②choosing TE method is suitable,there is no direct and indirect injury force to IAN during operating by extracting theMITMs with MITE.