Analysis of Normal Anatomy of Oral Cavity in Open-mouth View with CT and MRI: Comparison with Closed-mouth View

PURPOSE: When MRI and CT of the oral cavity utilize the traditional closed-mouth approach, direct contact between the tongue and surrounding structures may give rise to difficulty in recognizing the anatomy involved and demonstrating the possible presence of pathologic features. we describe a more appropriate scan technique, involving open-mouthed imaging, which may be used to demonstrate the anatomy of the oral cavity in detail. MATERIALS AND METHODS: Axial and coronal MR imaging and axial CT scanning were performed in 14 healthy volunteers, using both the closed and open-mouth approach. For the latter, a mouth-piece was put in place prior to examination. In all volunteers, open-mouth MR and CT examinations involved the same parameters as the corresponding closed-mouth procedures. The CT and MR images obtained by each method were compared, particular attention being paid to the presence and symmetry of motion artifact of the tongue and the extent of air space in the oral cavity. Comparative imaging analysis was based on the recognition of 13 structures around the boundaries of the mouth. For statistical analysis, Student 's t test was used and a p value < 0.05 was considered significant. RESULTS: Due to symmetry of the tongue, a less severe motion artifact, and increased air space in the oral cavity, the open-mouth method produced excellent images. The axial and coronal MR images thus obtained were superior in terms of demarcation of the inferior surface and dorsum of the tongue, gingiva, buccal surface and buccal vestibule to those obtained with the mouth closed (p<0.05). In addition, axial MR images obtained with the mouth open showed better demarcation of structures at the lingual margin and anterior belly of the digastric muscle (p<0.05), while coronal MR images of the base of the tongue, surface of the hard palate, soft palate, and uvula, were also superior (p<0.05). Open-mouth CT provided better images at the lingual margin, dorsum of the tongue and buccal surface than the closed-mouth approach (p<0.05). CONCLUSION: Open-mouth MRI and CT are both practical and useful for evaluation of the structures of the oral cavity. The images thus obtained are superior to those acqhired with the month closed.