In recent years, implant denture have been widely developed. It is of importance knowing the width of the mandible and the location, diameter, path of the mandibular canal prior to operation to improve the rate of success and prevent complications in dental implantation. Former study information was acquired mainly through cephalometric analysis and viviperception
[4-8]; X-ray imaging had some magnification, the error may give rise to relevant complications such as nerve injury. In our study, we meter the thickness of each wall of madibular canal on extracorporeal mandibles. So it is more direct and accurate. Distance from the alveolar ridge crest to superior border of mandibular canal showed that distance from the second, the first molar and the second premolar to madibular canal were gradually increased, so shorter implants should be chosen in molar region than that in premolar region. The present results demonstrated that there was no marked difference between left and right sides. Distance from inferior border of mandibular canal to lingual bone plate was significantly shorter than that from exterior border of mandibular canal to buccal bone plate. Distance from superior border of dentulous mandibular canal to alveolar ridge crest was significantly longer than that form inferior border of mandibular canal to inferior border of mandible. These results demonstrated that the path of mandibular canal appeared regular, that mandibular canal ran towards the lingual side and was close to the inferior border of mandible in the mandibular bone, these results were consistent with literature
[1-4] . The difference between the transverse and the longitudinal diameters of the mandibular body was statistical significant; furthermore, the longitudinal diameter was longer than the transverse diameter. That is, the cross section of the mandibular canal was an ellipse with a longer longitudinal diameter. There was no significant difference between the transverse and longitudinal diameters in the premolar and molar region of the mandible. This means the dimension of mandibular canal is constant in mandible. Vernier caliper with an accuracy of 0.02 mm was used by the same conner, who greatly enhances measurement accuracy, and consumedly decreases system error rate, therefore, the data acquired by this method are more reliable and the values in normal range could provide references for clinical operations. As the chosen specimens are mandible with teeth, there is no absorption of alveolar ridge, and the results have general guidance significance to immediate implantation.
An injury to the inferior alveolar nerve and side wall piercing often happens in mandible operation. It is important to know the precise location and the diameter of the mandibular canal in the posterior segment of the mandible to prevent the inferior alveolar nerve from injuring during implantation. An injury to the inferior alveolar nerve is often due to ignorance of the course of the mandibular canal, excess enlargement of X-ray photograph[9-12], excessively long implant, or the wrong drilling direction. The mandibular canal travels near the lingual bone wall and is close to the inferior border of the mandible. Therefore, there is enough bone to hold the implant with proper length if the drilling direction is correct. Although the mandibular canal travels near the lingual plate, however, it just lie under the first molar root tip, which can be seen in Figure 2, it is also consistent with document[13]. Doctor must know this characteristic very well, so as not to injury nerve.
Few reports describe the realationship between the blood vessels and nerve. The study shows that the blood vessels travel above the nerve in the inferior alveolar neurovascular bundle. Implant patients may be elderly or lose tooth for long time, Their alveolar ridges are completely or seriously atrophied; therefore implanting posterior teeth may provide increased risk of injury such as underlip numb and bleeding since it is easier to penetrate the mandibular canal
[14-20]. As a result, when the mandibular canal is penetrated during the implanting operation, the blood vessels will be hurt firstly with resulting hemorrhage, which is not easy to stop bleeding. At this time, the nerve may not yet be damaged, and then operation should be stopped. Accordingly, the hemorrhage of mandibular canal can predict nerve injury if surgery continues.
