Determining shapes and dimensions of dental arches for the use of straight-wire arches in lingual technique

INTRODUCTION: This study aims to determine the shape and dimension of dental arches from a lingual perspective, and determine shape and size of a straight archwire used for lingual Orthodontics. METHODS: The study sample comprised 70 Caucasian Brazilian individuals with normal occlusion and at least four of Andrew's six keys. Maxillary and mandibular dental casts were digitized (3D) and the images were analyzed by Delcam Power SHAPET 2010 software. Landmarks on the lingual surface of teeth were selected and 14 measurements were calculated to determine the shape and size of dental arches. RESULTS: Shapiro-Wilk test determined small arch shape by means of 25th percentile (P25%) - an average percentile for the medium arch; and a large one determined by means of 75th percentile (P75%). T-test revealed differences between males and females in the size of 12 dental arches. CONCLUSION: The straight-wire arch shape used in the lingual straight wire technique is a parabolic-shaped arch, slightly flattened on its anterior portion. Due to similarity among dental arch sizes shown by males and females, a more simplified diagram chart was designed.INTRODUCTION: 本研究旨在从舌侧视角明确牙弓的形态与尺寸，并确定用于舌侧正畸（lingual Orthodontics）的直型弓丝的形状与尺寸。 METHODS: 本研究样本共纳入70名咬合正常且满足Andrews六项咬合标准中至少四项的巴西高加索裔个体。对上、下颌牙颌模型进行三维数字化扫描，并采用Delcam Power SHAPET 2010软件对扫描图像进行分析。选取牙齿舌面的解剖标志点，计算14项测量指标以确定牙弓的形态与尺寸。 RESULTS: 采用夏皮罗-威尔克检验（Shapiro-Wilk test），以25th百分位（P25%）界定小型牙弓形态——该值为中型牙弓的平均百分位；以75th百分位（P75%）界定大型牙弓形态。t检验结果显示，12项牙弓尺寸指标在男性与女性群体间存在统计学差异。 CONCLUSION: 本研究所用舌侧直丝技术的直型弓丝形态为抛物线形，其前牙段略呈扁平状。鉴于男女牙弓尺寸具有较高相似性，本研究设计了更为简化的参考图表。