Lip position in the smile aesthetic: Literature review

Objective: Determine the lip position influence on dental aesthetics in adults older than 19 years according to academic publications in the last 5 years.
Material and methods: A systematic research was carried out in the medical literature (UNAM, Cochrane, BVS, Scielo, PubMed), using the following search strategy: (lip line) OR (smile line) AND (parameters) AND (analysis) AND (evaluation) to identify articles that reported data on lip position parameters that influence dental aesthetics. The results of each study were extracted and classified as follows: smile line or lip line, length of the lip with the smile line, gingival display, smile arc, smile type and upper lip curvature.
Results: From the 4497 articles analyzed, 17 studies were selected for the final review process. Considering the studies in this literature review, the most frequent criteria are: a midline smile, a low gummy smile line, a consonant smile arc, a static smile, a commissural type of smile, and an upward curvature of the upper lip.
Conclusions: An aesthetically attractive smile includes different parameters, among those that have a positive influence are a high or medium anterior smile line, a parallel smile arc, straight or upward upper lip curvature, type of commissural smile and a gingival exposure less than 2 mm.