Is the Treatment of the Tear Trough Deformity with Hyaluronic Acid Injections a Safe Procedure? A Systematic Review  
[PERSON]  
1 Oral and Maxillofacial Surgery Unit, Multidisciplinary Department of Medical-Surgical and Dental Specialities, University of Campania \"[PERSON]\", Via [PERSON], 6, 80138 Naples, Italy; [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (R.F. ); [EMAIL_ADDRESS] (R.V.) 1  
[PERSON]  
1 Oral and Maxillofacial Surgery Unit, Multidisciplinary Department of Medical-Surgical and Dental Specialities, University of Campania \"[PERSON]\", Via [PERSON], 6, 80138 Naples, Italy; [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (R.F. ); [EMAIL_ADDRESS] (R.V.) 1  
[PERSON]  
2 Aesthetic Surgeon Private Practice, Chirurgia Della Bellezza, Via Melisurgo, 4, 80138 Naples, Italy; [EMAIL_ADDRESS] 2  
[PERSON]  
3 Department of Neurosciences, Reproductive and Odnotostomatological Sciences, Maxillofacial Surgery Unit, University of Naples \"Federico II\", Via Pansini, 5, 80131 Naples, Italy; [EMAIL_ADDRESS] 3  
[PERSON]  
4 Department of Maxillofacial Surgery, University of Siena, Strada delle Scotte, 4, 53100 Siena, Italy; [EMAIL_ADDRESS] 4  
[PERSON]  
1 Oral and Maxillofacial Surgery Unit, Multidisciplinary Department of Medical-Surgical and Dental Specialities, University of Campania \"[PERSON]\", Via [PERSON], 6, 80138 Naples, Italy; [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (R.F. ); [EMAIL_ADDRESS] (R.V.) 1  
[PERSON]  
1 Oral and Maxillofacial Surgery Unit, Multidisciplinary Department of Medical-Surgical and Dental Specialities, University of Campania \"[PERSON]\", Via [PERSON] De Crecchio, 6, 80138 Naples, Italy; [EMAIL_ADDRESS] (S.D. ); [EMAIL_ADDRESS] (R.F. ); [EMAIL_ADDRESS] (R.V.) 1  
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characterized by marked circumferential depression along the orbital rim, often associated with marked depression of the cheek and malar eminence [4]. Although our understanding of these anatomical concepts has evolved, the treatment of the lacarimal canal has still remained a challenge today. There are various techniques that can be adopted to rejuvenate this area. In the past, good results were obtained through fat grafts or through the subperiosteal placement of tear implants (Byron Medical or Implantech) [3]. However, according to the criteria described by [PERSON], patients with smooth, thick skin with well-defined lacarimal sulcus can be successfully treated with HA injections [5]. Currently, the non-invasive method of HA injections is the first-choice treatment for tear deformities, all thanks to the development of new fillers that are safer, more predictable, and more affordable [6]. In general, two main classes of fillers can be distinguished: non-absorbable and resorbable ones such as HA, which can be dissolved through the use of Hyaluronidase (HYAL) [7; 8]. Techniques such as these are gaining widespread acceptance, and this procedure has other desirable features: it is fast to perform and has a lasting but not permanent effect [9; 10]. In fact, it is known that HA injected subcutaneously is absorbed within 1-3 years, and this is closely related to the treated area [11]; however, the bulking effects can persist in the treated area thanks to in situ neo-collagenogenesis, angiogenesis, and adipocyte proliferation in the area [12]. The onset of complications related to filler injection may be mainly due to the injection technique or the implanted material [13; 14; 15]. When HA is injected near the surface of the skin, a bluish tint, known as the \"Tyndall effect\", may emerge, which in persistent cases can be treated with hyaluronidase [16]. Other possible adverse effects related to HA injections are nodules, infections, granulomatous and immune-mediated reactions, edema, erythema, and ecchymosis.