الفهرس 
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Abstract
Two dry human skulls were used in this study. Fifteen different anatomical landmarks of which nine were bilateral were selected on each skull. The landmarks were identified using small pieces of gutta percha. Direct linear measurements were performed on the dry skulls using a digital calliper with accuracy 0.01 mm. These direct measured distances provided 16 linear measurements that are commonly used in cephalometric orthodontic analysis. The direct measured distances represent the gold standard.Each skull was secured in a plastic box and secured with rigid fasteners. The skull was scanned using Scanora 3D XL (Soredex, Finland) scanner. Each skull was scanned nine scans. The 1st scan was performed with the Frankfurt plane parallel to the floor and midsagittal plane and aligned with respect to the midsagittal- positioning laser of the CBCT unit.
Skulls were scanned again but with different vertical angulations, so that the Frankfurt plane made an angle +10, +20, +30,+40,-10,-20,-30,-40 with the floor respectively with each scan. These angles were adjusted using a custom adapted wooden support inclined at the desired angle.
The same linear measurement distances performed on the skull were repeated on the CBCT images in different scans. All the previous obtained measurements including physical measurements and CBCT linear measurements were tabulated in spread sheets, and statistically analyzed. The values of the physical and CBCT measurements represent the mean of six readings of three different observers.The results showed that there was no significant difference between the ideal skull position and the physical skull measurements.
The different skull positions also showed no statistically significant difference when compared to the physical skull measurements.
Conclusions -1. The accuracy and reliability of linear maxillofacial measurements obtained with CBCT.
2. The accuracy and reliability of CBCT linear measurements are not influenced by the patient position within the scanner.-3. CBCT measurements are reproducible and not operator dependent.