Mandibular asymmetry: A proposal of radiographic analysis with public domain software

OBJECTIVE: This preliminary study aimed to propose a new analysis of digital panoramic radiographs for a differential diagnosis between functional and morphological mandibular asymmetry in children with and without unilateral posterior crossbite. METHODS: Analysis is based on linear and angular measurements taken from nine anatomic points, demarcated in sequence directly on digital images. A specific plug-in was developed as part of a larger public domain image processing software (ImageJ) to automate and facilitate measurements. Since panoramic radiographs are typically subject to magnification differences between the right and left sides, horizontal linear measurements were adjusted for greater accuracy in both sides by means of a Distortion Factor (DF). In order to provide a preliminary assessment of proposed analysis and the developed plug-in, radiographs of ten patients (5 with unilateral posterior crossbite and 5 with normal occlusion) were analyzed. RESULTS: Considerable divergence was found between the right and left sides in the measurements of mandibular length and position of condyles in patients with unilateral posterior crossbite in comparison to individuals with normal occlusion. CONCLUSION: Although there are more effective and accurate diagnostic methods, panoramic radiography is still widespread, especially in emerging countries. This study presented initial evidence that the proposed analysis can be an important resource for planning early orthodontic intervention and, thus, avoid progression of asymmetries and their consequences.

研究目的：本初步研究旨在针对伴或不伴单侧后牙反（牙合）（unilateral posterior crossbite）的儿童，提出一种全新的数字化全景X线片（digital panoramic radiographs）分析方法，用于鉴别功能性与形态性下颌不对称（mandibular asymmetry）。研究方法：本分析基于从9个解剖点位获取的线性与角度测量值，上述点位可直接在数字化影像上依次标记。本研究针对公共领域图像处理软件（ImageJ）开发了专属插件，以实现测量流程的自动化与便捷化。由于全景X线片通常存在左右两侧放大倍率差异，本研究通过畸变因子（Distortion Factor, DF）对双侧的水平线性测量值进行校正，以提升测量精度。为初步评估所提出的分析方法与开发的插件，本研究对10例患者的全景X线片进行了分析，其中5例为单侧后牙反（牙合）患者，5例为咬合正常者。研究结果：与咬合正常的个体相比，单侧后牙反（牙合）患者的下颌长度测量值及髁突位置存在显著的左右侧差异。研究结论：尽管目前已有更高效、精准的诊断方法，但全景X线检查仍被广泛应用，尤其在新兴经济体国家。本研究提供了初步证据，证实所提出的分析方法可作为早期正畸干预规划的重要参考资源，从而避免不对称畸形的进展及其后续不良后果。