Raj Vishnu, Heymann Harald O, Hershey H Garland, Ritter Andre V, Casko John S
Department of Orthodontics, School of Dentistry, University of Texas Health Sciences Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
J Esthet Restor Dent. 2009;21(2):96-111. doi: 10.1111/j.1708-8240.2009.00240.x.
The apparent contact dimension (ACD), a determinant of dental esthetics, has been purported to exhibit an esthetic relationship termed the "50:40:30" rule, implying that in an esthetic smile, the ACD between the central incisors, central and lateral incisors, and lateral incisor and canine would be 50, 40, and 30% of the height of a central incisor, respectively. This study assessed the existence of this proportion using casts of orthodontically treated (N = 40) and nontreated (N = 27) subjects deemed to possess excellent occlusion. Covariates studied included tooth size, tooth shape, tip, and torque. The average ACD proportions in this study, relative to the height of an ipsilateral central incisor, were found to be 49, 38, and 27% between the central incisors, central and lateral incisors, and the lateral incisor and canine, respectively. The ACD exhibited a positive correlation (p < 0.05) with the height of the clinical crown and a negative correlation (p < 0.05) with the width/height ratios of the corresponding teeth. No statistically significant correlations were evident between the ACD with the shape of the clinical crown, tip, and torque. However, the tip and torque did exhibit a statistically significant (p < 0.05) correlation with the height of the clinical crown. This study is the first to validate the existence and proportions of the ACD.
This study validates the existence of the ACD and quantifies the relationship of the ACD with tooth size, tooth shape, mesiodistal crown angulation (tip), and labiolingual crown inclination (torque) among subjects deemed to possess excellent occlusion and alignment. This quantifiable "ideal" and its correlation with the other determinants of dental esthetics may be used in conjunction with various evidence-based paradigms in the esthetic appraisal of the maxillary anterior teeth.
表观接触尺寸（ACD）是牙齿美学的一个决定因素，据称呈现出一种被称为“50:40:30”规则的美学关系，这意味着在一个美观的微笑中，中切牙之间、中切牙与侧切牙之间以及侧切牙与尖牙之间的ACD分别为中切牙高度的50%、40%和30%。本研究使用正畸治疗（N = 40）和未治疗（N = 27）且咬合良好的受试者模型评估了该比例的存在情况。研究的协变量包括牙齿大小、牙齿形状、倾斜度和转矩。本研究中，相对于同侧中切牙的高度，中切牙之间、中切牙与侧切牙之间以及侧切牙与尖牙之间的平均ACD比例分别为49%、38%和27%。ACD与临床冠高度呈正相关（p < 0.05），与相应牙齿的宽高比呈负相关（p < 0.05）。ACD与临床冠形状、倾斜度和转矩之间未显示出统计学上的显著相关性。然而，倾斜度和转矩与临床冠高度确实呈现出统计学上的显著相关性（p < 0.05）。本研究首次验证了ACD的存在及其比例。
本研究验证了ACD的存在，并量化了在被认为咬合和排列良好的受试者中，ACD与牙齿大小、牙齿形状、近远中冠角（倾斜度）和唇舌向冠倾斜度（转矩）之间的关系。这种可量化的“理想”情况及其与牙齿美学其他决定因素的相关性可与各种基于证据的范式一起用于上颌前牙的美学评估。
