Department of Orthodontic Science, Tokyo Medical and Dental University (TMDU) Graduate School, 1-5-45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan.
Department of Oral and Maxillofacial Radiology, The University of Tokushima, Tokushima, Japan.
Prog Orthod. 2018 Feb 19;19(1):7. doi: 10.1186/s40510-018-0204-6.
Magnetic resonance imaging (MRI) has been used to study configurations of speech organs in the resting state. However, MRI is sensitive to metals, and numerous types of metallic appliances, most of which have a large magnetic susceptibility, are used in orthodontic treatment and may cause severe artifacts on MRI. We have developed techniques for obtaining MRI movies of the oral region, to evaluate articulatory changes, especially movement of the tongue, palate, and teeth, pre- and post-orthodontic/orthognathic treatment. We evaluated the influence of artifacts caused by orthodontic appliances, including fixed retainers, metal brackets, and wires, on measurements in 3-T MRI movies.
Sixteen healthy young adults (nine males, seven females; average age, 27 years) with normal occlusion were recruited. Four types of customized maxillary and mandibular plates were prepared by incorporating one of the following into the plate: (a) nothing, (b) a fixed canine-to-canine retainer, (c) metal brackets for the anterior and molar teeth, or (d) clear brackets for the anterior teeth and metal brackets for molars. A 3-T MRI movie, in segmented cine mode, was generated for each plate condition while participants pronounced a vowel-consonant-vowel syllable (/asa/). The size of the artifact due to the metallic brackets was measured. The face size and orthodontically important anatomical structures, such as the velum, the hard palate, and the laryngeal ventricle, were also measured.
A large artifact was observed over the entire oral region around orthodontic appliances, altering regional visibility. The velopharyngeal height was measured as significantly longer in the presence of metal brackets. The maximum artifact size due to a metallic bracket was > 8 cm. Our results show that even if it is possible to obtain the measurements of palate length, nasion to sella, and nasion to basion in individuals wearing metal brackets for molars, the measurements might be affected due to the presence of artifacts.
Orthodontic appliances, including metallic materials, sometimes produce significant measurement error in speech evaluation using MRI movies, which often become invisible or distorted by metallic orthodontic appliances. When the distorted image is measured, caution should be exercised, as the measurement may be affected. Based on the study, it is concluded that orthodontists should not necessarily remove all metallic appliances before MRI examination because the influence varies among the appliances and should also know that a significant measurement error in speech evaluation using MRI movie may occur by image distortion caused by metallic artifacts.
磁共振成像（MRI）已被用于研究静止状态下的言语器官结构。然而，MRI 对金属很敏感，正畸治疗中使用了许多类型的金属器具，其中大多数具有较大的磁敏感性，可能会在 MRI 上产生严重的伪影。我们已经开发了获取口腔区域 MRI 电影的技术，以评估发音变化，特别是舌、腭和牙齿的运动，在正畸/正颌治疗前后。我们评估了正畸矫治器（包括固定保持器、金属托槽和金属丝）引起的伪影对 3-T MRI 电影测量值的影响。
招募了 16 名健康的年轻成年人（9 名男性，7 名女性；平均年龄 27 岁），他们的咬合正常。通过在板上加入以下一种物质来制备四种定制的上颌和下颌板：(a) 无，(b) 固定尖牙到尖牙保持器，(c) 前牙和磨牙的金属托槽，或 (d) 前牙的透明托槽和磨牙的金属托槽。参与者发出/vasa/元音-辅音-元音音节时，为每个板条件生成分段电影模式的 3-T MRI 电影。测量由于金属托槽引起的伪影的大小。还测量了面部大小和正畸重要的解剖结构，如悬雍垂、硬腭和喉室。
在正畸矫治器周围的整个口腔区域观察到一个大的伪影，改变了区域可见度。在存在金属托槽的情况下，软腭-咽高度测量值明显更长。由于金属托槽引起的最大伪影大小>8cm。我们的结果表明，即使可以在佩戴金属托槽的磨牙患者中获得腭长、鼻根至蝶鞍和鼻根至颅底的测量值，由于伪影的存在，测量值也可能受到影响。
正畸矫治器，包括金属材料，有时会在使用 MRI 电影进行语音评估时产生显著的测量误差，这些误差通常会被金属正畸矫治器变得不可见或扭曲。当对失真的图像进行测量时，应谨慎操作，因为测量结果可能会受到影响。基于该研究，可以得出结论，正畸医生不一定在 MRI 检查前必须去除所有金属器具，因为器具之间的影响各不相同，还应知道，由于金属伪影引起的图像失真，使用 MRI 电影进行语音评估可能会产生显著的测量误差。
