## 1 Introduction  
Gingivitis develops more frequently in patients undergoing orthodontic treatment mainly due to an inflammatory reaction following the accumulation of bacterial plaque [1; 2; 3].  
Many authors have shown that gingival recessions can develop during or after orthodontic treatment [4; 5]. Indeed, at the end of orthodontic therapy, the reported prevalence of gingival recessions ranges from 5% to 12% and in long-term follow-up (5 years) has been observed an increase to 47% [4; 5; 6].  
A recent systematic review has established that the direction of dental movements and the buccal-lingual thickness of the gingiva can play an important role in altering soft tissues during orthodontic treatment. There is a high probability of recession during tooth movement in areas with less than 2 mm of gingival thickness [7]. This could affect the integrity of periodontal tissues and represent a risk factor when orthodontic treatments [8], implants [9], and restorative treatments are performed [10]. Gingival biotype is defined as the thickness of the gingiva in the labiolingual direction [9]. Studies have reported that gingival biotype is an important parameter that must be evaluated to reduce the risk of gingival recession [11].  
Hence, the assessment of periodontal biotype is considered one of the most important parameters for outcomes focused on dental planning according to the classification of periodontal and peri-implant diseases and conditions [12].  
Many features of the gingival phenotype are genetically determined; others seem to be influenced by age, sex, growth, tooth shape, and tooth position [13]. Moreover, it has been shown that among individuals and intra-individual there is variation in the width [14] and thickness of the vestibular gingiva [15].  
Facial typology is classified as dolichofacial, mesofacial, or brachyfacial. A dolichofacial typology has excessive vertical facial growth and is usually associated with an increased SellaNasion'GonionGnathion (SN'GoGN) angle and increased vertical jaw relation (AnsPns'GoGn) [16; 17]. A brachyfacial typology has reduced vertical growth and is usually accompanied by reduced SN'GoGn, reduced AnsPns'GoGn, and a decreased lower facial height (SNMe) total facial height (NMe) ratio [18].  
The cephalometric evaluation of facial type is essential for orthodontic diagnosis because the amount and direction of jaw growth will significantly alter the need for orthodontic biomechanics [19].  
Craniofacial morphology may also affect the gingival phenotype [13; 20]. Some studies have evaluated the relationship of bone morphology to facial typology [21; 22; 23] and a correlation between facial and alveolar bone has already been demonstrated [24]. Indeed, in dolichofacial patients, the mandibular symphysis is high and thin, while in brachyfacial patients, the symphysis is low and thick [25]. As a consequence, before starting orthodontic treatment, it is important to evaluate and to diagnose both the gingival biotype and facial typology with the objective of decreasing the risk of periodontal destruction [26]. Only a few studies have instead evaluated the association between gingival thickness and craniofacial morphology [26].  
Facial soft tissue is evaluated using several methodologies; two of the most representative methods, used to obtain three-dimensional (3D) scans, are laser scanners and 3D stereophotogrammetry [27; 28; 29; 30]. The analysis of the face using 3D stereophotogrammetry is consistent and valid [31; 32; 33; 34]. Hence, this is a reliable method with which to analyze facial soft tissues and avoid any X-ray exposure to the patient [34; 35].  
Including only patients seeking orthodontic treatment, the aim of this study was to investigate the association between gingival biotype and facial typology evaluated by means of a cephalometric and 3D facial analysis.  
The null hypothesis was that there is no association between gingival biotype and facial typology.