Chulalongkorn University Dental Journal

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Smile is a complicated system to express emotions. It was formed by both skeletal tissue and soft tissue. In the investigations of hard tissue, sella-nasion to mandibular plane (SN-MP) and sellanasion to palatal plane to upper incisal edge are the comprehensive factors. For soft tissue studies, nasolabial fold acts as the keystone of the smiling mechanism. The circumoral muscles play and important roll in 2 stages to raise upper lip first and then lip and fold are raise as well as contracted later. As smile was formed, it represented high, average, and low smile line. Upper lip that touches gingival margin of anterior teeth and lower lip that pointed at incisal edge of the sixth maxillary teeth when smile were concerned to be the ideal smile. Criteria for perfect smile was set and to accomplish this goal, multidisciplinary treatment are required.



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