الفهرس 
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Abstract
The removal of third molars is one of the procedures most commonly performed by oral surgeons. Dysfunction of the inferior alveolar nerve (IAN) after mandibular third molar extraction, although uncommon, is probably one of the most undesirable consequences of this, and is acknowledge to be very distressing for the majority of patients. The panoramic radiograph is a useful screening tool for assessing the anatomical relationship between the third molars and the IAN. Several clinical studies have determined the specific radiographic signs detected in panoramic radiographs, which may suggest the presence of a close relationship between the inferior alveolar canal and mandibular third molars. These radiographic signs include superimposition of the tooth roots on the canal, narrowing of the canal, deviation of the canal, interruption of the radiopaque borders of the canal, darkening of the roots, narrowing of the tooth roots as well as deviation of the tooth roots and the bifid apex. Although panoramic radiography is one of the most effective and widely used dental radiographic tools for evaluating the risk of nerve damage, the absence of the cortical bone of the inferior alveolar canal may not be clearly evident with this method, and it is impossible to determine whether its course is buccal or lingual to the roots or between the roots.Computed tomography (CT) may be recommended to verify the close relationship between the third molar and the mandibular canal in a three-dimensional (3D) view. The higher radiation dose, increased financial cost and less accessibility, however, are the negative aspects of CT compared with conventional imaging. The value of CBCT to aid the evaluation of the anatomical relationship of the IAN and the position of third molars is beginning to be realised. These scans allow the surgeon to gain an appreciation in all dimensions of the precise relationship between the inferior alveolar canal and mandibular third molar.Forty three patients seeking surgical removal of fifty impacted mandibular third molars ranging in age from 18 to 35 years, were presented with one or more of the close relationship between the impacted mandibular third molar and the inferior alveolar canal in the preoperative panoramic radiographs. All patients were referred for further evaluation using CBCT scans, a three dimensional reconstruction screen was used to scroll through the axial, sagittal and coronal planes with a 0.2 mm slice thickness evaluate.The incidence of root contact with the canal in CBCT was found in 30% of the third molars in the present study, Interruption of white line were significantly associated with contact status (residuals > ±1.69). All other panoramic radiographic signs showed no association with contact status (residuals < ±1.69). In this study, cases showing darkening of roots in panoramic images were clearly seen in CBCT without contact of mandibular canals, who found no intimate relationship between root darkening and mandibular canals. This may be due to small sample size in patient groups in this study. It can be concluded that cone beam computed tomography (CBCT) provides useful information regarding the 3-dimensional relationship between the mandibular third molar and the mandibular canal. Thus it can be used for risk assessment and planning of the surgical procedure for removal of impacted lower third molar. Especially, with presence of interruption of white line of mandibular canal in panoramic radiographic.