Comparison of Skull Dimension and Geometric Formulas Method to Solve Projection Errors in 2D Cephalometric Radiographs
Journal Title: Biomedical Journal of Scientific & Technical Research (BJSTR) - Year 2018, Vol 12, Issue 1
Abstract
Background: Two dimensional (2D) cephalometry showed projection errors of mandibular curved structures which led to inaccuracies in landmark measurements. Objective: To create geometric formulas for ramal height and mandibular corpus length and test the validity of these hypothetical geometric formulas in comparison to the actual skull measurements to solve the problems of projection errors. Material and Methods: Twenty-two skulls were included in the study. Two-dimensional(2D) cephalometric films which include Lateral (1), Postero-anterior (2) and Submento vertex (3) were taken for each skull. The actual measurements of ramal height (Co-Go), mandibular corpus lengths (Go-Me) and total mandibular lengths were obtained directly from the skull. 2D measurements were obtained from 3 views of 2D cephalometric films. Based on 3-dimensional co-ordinate axis (X, Y, Z), geometric formulas were constructed using variables from multiple 2D films to calculate ramal height (R) and mandibular corpus length (M). Validity of these formulas were tested with matched pair T-test statistics by comparing with the direct skull measurements. Results: All 2D cephalometric mandibular measurements were significantly shorter than direct skull measurements. The average ramal height and mandibular corpus lengths measured from Lateral cephalometry was 1.27mm. (SD 0.97) and 17.64mm. (SD 2.12) shorter than actual skull measurements. Geometric formulas significantly reduced mean difference between values from 2D cephalometrics and skull measurements. Most valid formulas for ramal height and mandibular corpus length were √YR12+ ZR32+ XR22 and √M12+XM22 respectively. Cephalometry is one of the indispensable diagnostic tools in orthodontics for diagnosis of dentofacial problems, growth evaluation, treatment planning and outcome evaluation [1,2]. However, the most highlighted drawback still remains the representation of three-dimensional (3D) structures in twodimensional (2D) axis, leading to projection distortion, positional distortion, image magnification, landmark identification error, superimposition of structures which has partly frustrated clinicians particularly in the aspect of treatment evaluation [2- 4]. To overcome the drawbacks of 2D projection, Adams invented a correction formula for image enlargement and distortion [5]. Similarly, a compensator for lateral films was developed by Wylie and Elsasser which was later modified by Vogel to include PosteroAnterior (PA) cephalograms [6,7]. Savara also introduced a method to measure landmarks in three-dimension using lateral and PA cephalograms [8]. Additionally, in an attempt to combine the use of lateral and PA films together, Broadbent and Bolton introduced “Broadbent Orientator” which was an acetate overlay of lateral and PA film registered at Frankfort horizontal plane [1]. Additionally, Buamrind, et al.[9]. attempted to combine the use of two coplanar films based on the principle of photo-stereometry.
Authors and Affiliations
Ugyen Phuntsho, Julalak Komoltri, Nita Viwattanatipa
Keywords
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- EP ID EP586019
- DOI 10.26717/BJSTR.2018.12.002201
- Views 136
- Downloads 0
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