We all have our own idea of what the perfect smile should look like, whether we show a mouthful of pearly whites or keep our lips closed and turned up at the corners just so. New research suggests that there really is a proper way to smile, and it has everything to do with facial expression.

When we think of the perfect smile, we often envision①envision 英 [ɪnˈvɪʒn] 美 [ɪn'vɪʒn] vt. 想象；预想a wide, beaming②beaming 英 ['biːmɪŋ] 美 ['bimɪŋ] adj. 喜气洋洋的；愉快的；光亮的；耀眼的v. 照耀（beam的ing形式）grin, with all of our teeth showing. However, Nathaniel Helwig and his colleagues at the University of Minnesota discovered that a genuine smile actually rests less on showing teeth and more on facial balance and symmetry .

Researchers looked at 3D computer-animated facial models of more than 800 participants. Thecomputer-animated facial models underwent a series of facial transformations, with researchers changing the mouth angle, amount of teeth shown,the extent of the smile, and how symmetrical③symmetrical 英 [sɪ'metrɪk(ə)l] 美 [sɪ'mɛtrɪkl]adj. 匀称的，对称的the smile was. Participants were then asked to rate④rate 英 [reɪt] 美 [ret] n. 比率，率；速度；价格；等级vt. 认为；估价；责骂vi. 责骂；被评价the models' smiles based on effectiveness, genuineness,pleasantness, and perceived emotional intent.

The results of the study found that the most successful smile—one that was rated most pleasant,genuine, and effective—had a perfect balance of teeth, an ideal mouth angle, and as mile length that extended to what was dubbed⑤dub 英 [dʌb] 美 [dʌb] vt. 配音；轻点；打击；授予称号n. 笨蛋；鼓声the "sweet spot⑥sweet spot 甜蜜点；最有效点；最佳击球位置."

完美的微笑应该是什么样子的呢？是露出一口大白牙，还是抿起双唇并使嘴角上扬？对此我们都有自己的想法。一项新研究指出，确实是有正确的微笑方式的，而且这与面部表情密切相关。

当我们想起完美的微笑的时候，我们往往想象的是喜气洋洋且露出所有牙齿的微笑。然而，明尼苏达大学的纳撒尼尔·赫尔维希和他的同事们发现，真正的微笑实际上并不在于露出几颗牙齿，而更多地在于面部表情的均衡和对称。

研究人员着眼于800多位参与者的3D电脑动画面部模型。他们为这些模型做了一系列的面部转换，改变了这些模型嘴角的弧度、露出的牙齿的数量、微笑的程度以及微笑的对称度。然后参与者被要求基于有效性、真诚度、愉悦感以及所领会到的情感意图来为这些模型的微笑评分。

研究发现，最成功的微笑，也就是那个被评为最令人愉快、最真诚、最有效的微笑，它所展现的牙齿非常匀称，嘴角的弧度十分完美，而且微笑的时间也被认为是“最合适的”。