Three-dimensional CBCT analysis of cranial base symmetry
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Background: Craniofacial skeletal asymmetry is a common finding in the general population that often goes undetected. Interest in this topic has led to many studies aimed at describing this type of asymmetry, its distribution and etioIogy. The cranial base, being cIosely related to the face and brain, is a key component in craniofacial growth and may also display varying amounts of asymmetry contributing to this anomaly. Though many studies have explored underlying skeletal asymmetry, most of them were limited by their two-dimensional method of investigation. With the advent of three-dimensional technology, more recent studies have had the advantage of studying the cranial base in its true anatomic form, resulting in greater accuracy of analysis. Despite access to this technoIogy, there is still a lack of literature regarding the cranial base in a normal population. Determining average skull base dimensions will provide a set of normative data that can be used as a reference for future studies. Material and Methods: Pre-treatment Cone Beam Computed Tomography (CBCT) films of 160 esthetic human subjects previously used by another investigator were screened for use in our current research. These DICOM files were imported into InVivoDental5.3 software (Anatomage[TM]; San Jose, Calif.) for screening and 70 CBCT scans were selected for analysis. All patients were classified as cervical vertebral stage 4 and above. The images were oriented in all three planes of space for uniformity and 14 bilateral anatomic landmarks were identified on each scan. A mid-sagittal reference plane was created using crista galli as the origin, and extending a perpendicular passing through the middle of the right and left clinoid points connected by a line, and through posterior points basion and opisthion. Each landmark was given an x-, y- and z- coordinate representing its three dimensional position and bilateral linear measurements to the reference plane were recorded using the software system. Statistical Analysis: InVivoDental5.3 software was used to calculate linear distances between each landmark and the mid-sagittal plane. This data was exported into Microsoft excel for analysis. Descriptive statistics of our sample and paired t-tests with a 5% significance level, or p value of 0.05, were performed. Results: The means of the right and left measurements of each bilateral landmark were calculated along with their standard deviations. A comparison between right and left means was accomplished with the use of paired t-tests. 12 1andmarks did not show a statistical difference in their locations on either side of the mid-sagittal plane. However, the means of 2 landmarks were found to be statistically significant. These were euryon (p = 0.01) and the jugular foramen (p = 0.00) Conclusion: The overall trend of our data indicated that the cranial base in a normal population, without craniofacial anomaly, displays symmetry, with the exception of the location of euryon and the jugular foramen. These findings are in accordance with those of similar three-dimensional studies. It is likely that the significant findings were due to tracing error, given the indiscrete location of euryon and the large, relatively asymmetric shape of the jugular foramen. However, if these structures are truly asymmetric, we can infer from our sample of symmetric patients, that there is no clinical relevance. Further studies with an increased sample size, additional landmarks or a more discrete sample can be performed to continue describing the skull base. The results of this study offer valuable reference data that can be used as a baseline for future studies.
Thesis (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Orthodontics and Dentofacial Orthopedics).Includes bibliographic references: leaves 37-42.
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