Coincidence of the Cranial Base Facial and Upper Cervical Midlines and Soft Tissue Markers of the Face and their Correlation with Cranial Base and Facial Asymmetry

Introduction and Purpose: This longitudinal study uses cone beam computerized tomography (CBCT) to investigate midline, facial, cranial base, cervical, and rotational asymmetry to the cranial base midline (CBML) in 120 patients in a general dental population in Australia. Many dental patients require alterations to the habitual midline mandibular position during treatment. Little is known about facial midline asymmetry in the general population.;Materials and Methods: A 0.4voxel, 20 second CBCT scan was taken with soft tissue midline points marked. The CBML was drawn from foramen cecum to basion, and extended onto the coronal scan. Measurements were made from soft tissue, skeletal midline points, and various cranial base, cervical, and facial skeletal points to the CBML. Midline coincidence was accepted if points fell within 0.5mm of the left or right of the cranial base midline. Correlations were made using the Pearson correlation coefficient (r) between midline, facial, cervical, cranial base, and rotational asymmetry.;Results: The frontonasal suture (0.22mm) was the most reliable skeletal indicator of the CBML. There were no soft tissue facial points that were reliable midline markers of the CBML. The maxillary midline frenum (0.87mm) was not coincident with the CBML, but was coincident with the buccal maxillary midline suture (0.49mm). The mandibular midline frenum was not a reliable midline marker of the mandible at the genial foramen (0.84mm). The spinous process of C2 was angled an average of 4.44% from the CBML in 91.7% of cases. There was generally positive correlation between midline facial structures. The cervical midline points, tip of dens and tip of the spinous process of C2 showed no correlation with any midline facial structures.;Conclusions: Frontonasal suture and Posterior nasal spine are reliable skeletal midline markers. There are no clinically reliable soft tissue markers of the cranial base midline. The maxillary frenum is a reliable midline marker of the maxilla, but the mandibular midline frenum is not a reliable midline marker of the mandible. Rotational asymmetry is common in C2, and is not correlated to any other midline structure. The cervical midline points had no correlations with any facial skeletal or soft tissue midline point. There was no correlation between the medial or lateral pterygoid plates and GF or any soft tissue midline points. The distance from the medial surface of the condyle to the CBML had mild correlation with the distal pterygoid plate, and moderate correlation with the medial pteryrgoid plate distance to the CBML.