Comparison of Skull Dimension and Geometric Formulas Method to Solve Projection Errors in 2D Cephalometric Radiographs

Ugyen Phuntsho¹, Julalak Komoltri² and Nita Viwattanatipa*³

Received: December 06, 2018;   Published: December 13, 2018

DOI: 10.26717/BJSTR.2018.12.002201

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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.

Conclusion: 2D cephalometric measurements were found to be imprecise. Geometric formulas could be a tool to overcome the problems of projection errors.

Keywords :Cephalometry; Geometric Formulas; Mandibular Corpus Length; Projection Error; Ramal Height

Abbreviations : Co: Condylion; Go: Gonion; Me: Menton; Gn: Gnathion; ANS: Anterior Nasal Spine; MBC: Mandibular Body Curvature; L: Lateral Cephalogram; PA: Postero-anterior cephalogram; SMV: Submento-vertex cephalogram; 2D: Two-dimensional; 3D: Three-dimensional; CBCT: Cone Beam Computed Tomography; CT: Computed Tomography; RH: Ramal Height; MCL: Mandibular Corpus Length; Ave: Average