Objective:To investigate characteristics of masticatory movement path in young adults with AngleⅡ1 malocclusion.Meth-ods:1 5 youths with normal occlusion(group Ⅰ)and 1 5 with AngleⅡ1 malocclusion(group Ⅱ)were included.Mandibular movement paths of the incisal point of the incisor during unilateral-sided gum-chewing were recorded by the BioEGN mandibular kinesiography an-alyzer.Both maximal distances and directions (FH-opening/closing angles)in sagittal plane were analyzed.The statistic analyses were performed with SPSS 1 3.0 software.Results:Lateral distances of left masticatory movement path in Group I and Group II were (8.24 ±1 .48)mm and (6.58 ±2.49)mm,those of right(8.05 ±1 .05)mm and (6.42 ±2.47)mm,respectively(P <0.05).The aver-age of FH-opening/closing angle of masticatory movement path in Group I was higher than that in Group II at each level(P <0.05)ex-cept 0.5 mm point in the left masticatory movement path.Conclusion:Maximal lateral distance and FH-opening/closing angle of mas-ticatory path in young adults with AngleⅡ1 malocclusion are less than those with normal occlusion.

Objective: To explore the cause and preventive measures of floor-of-mouth hematoma after dental implant placement. Methods: The prevention of hematoma of the floor of the mouth in a case of lower anterior teeth implant placement was analyzed, and the literature was reviewed. Results: Four mandibular vascular canals were found on the lingual side of the anterior mandible before dental surgery in the reported case. Two of them were quite thick (1.4 mm and 1.0 mm, respectively) and were located adjacent to the crest of the alveolar bone and superior to the mental spine. These two thick endosseous branches from the sublingual artery were dissected and ligated , and there was no obvious hematoma in the patients immediately after the operation and at the postoperative 3 d review. The results of the literature review show that the incidence of endosseous branches from the lingual vascular canal of the mandible is 90%-100%. The distribution of the vessels on the lingual side of the mandible is highly variable and adjacent to the lingual cortical plate. Accidental injury of the lingual cortical plate during implant surgery would probably lead to bleeding or hematoma on the floor of the mouth. Conclusion Mastering the anatomy of blood vessels on the floor of the mouth, elaboratively examining preoperative three-dimensional radiographic imaging, and cautiously exploring the lower jaw bone morphology after flap elevation are preventive measures to avoid damage to the arterial supply on the lingual side of the anterior lower jaw and to prevent complications of hematoma in the floor of the mouth.