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Evaluation of the Nasolabial Angle in Orthodontic Diagnosis: A Systematic Review

Background: This study is a systematic literature review aiming at identifying the variation of the average nasolabial angle (NLA) in various orthodontic situations. The NLA is one of the key factors to be studied in an orthodontic diagnosis for the aesthetics of the nose and facial profile. Methods: Out of 3118 articles resulting from four search engines (PubMed, Cochrane Library, Turning Research Into Practice (TRIP) and SciELO), the final study allowed the analysis and comparison of only 26 studies. These included studies have considered the NLA in the following cases: teeth extraction, class II malocclusion, class III malocclusion, rapid palatal expansion (RPE), orthognathic surgery, and non-surgical rhinoplasty with a hyaluronic acid filler. Results: The results indicate that teeth extraction and the use of hyaluronic acid fillers significantly affect the NLA. Conclusions: This systematic review shows that a statistically significant change in NLA values occurs in: extractive treatments of all four of the first or second premolars in class I patients; in class II patients with upper maxillary protrusion; in patients with maxillary biprotrusion, except for cases of severe crowding; and in patients undergoing non-surgical rhinoplasty with a hyaluronic acid filler. Trial registration number: PROSPERO CRD42020185166