The facial alveolar bone (FAB) width has a crucial impact on the soft and hard tissue response to extraction, implant placement, periodontal surgery, and orthodontic treatment. The inevitable changes including bone remodeling and resorption observed in the facial alveolar bone affect the results of the treatments involving the esthetic zone (Caiazzo et al., 2013). When the thickness of the FAB is less than 2 mm, significant changes in bone volume are observed due to the resorption (Tomasi et al., 2010). Furthermore, when the thickness of FAB is less than 1 mm, a mean bone loss was 7.5 mm after extraction, while in the case of more than 1 mm, it has been observed to be only 1.1 mm (Chappuis et al., 2013). Besides, the thickness of FAB may contribute to the risk factor of fenestration (Coşkun and Kaya, 2019, Tomasi et al., 2010).

Fenestration is a circumscribed type of alveolar defect that results in exposure of the root surface characterized by the absence of cortical bone, and generally occurs as bilateral defects and can be seen as a window-like aperture (Lindhe & Lang, 2015). Fenestration is also defined as a physiological anatomical variation concerning the health of pulp, periodontium, and oral mucosa as it provides communication pathways to these regions (Boucher et al., 2000). American Association of Endodontists defines fenestration as a window-like aperture exposing a portion of the root and generally located on the buccal aspect of the root (AAE, 2003). In fenestration, the denuded root area does not involve bone margin and is covered only by gingiva and underlying periosteum (Newman et al., 2018). Numerous potential etiological factors for fenestration have been identified, including periodontal or endodontic pathology, bruxism, root position and curvature, thin bone plate, an orthodontic force beyond a normal limit, and occlusal trauma (Jhaveri et al., 2010, Nimigean et al., 2009, Zachrisson and Alnaes, 1973). Owing to the low alveolar support of the tooth, periodontal diseases that already create bone loss induce devastating effects on these teeth and their periodontium (Årtun and Urbye, 1988, Zachrisson and Alnaes, 1973). The alveolar bone should be well examined in terms of the thickness of FAB and the presence of bone defects like fenestration to predict the esthetic results of dental treatments such as periodontal surgery or implant treatment.

Cone-beam computed tomography (CBCT) enables three-dimensional examination of dentoalveolar structures and determination of alveolar bone thickness via multiplanar visualization (Kumar et al., 2015). Numerous studies have used CBCT to investigate the quantity of alveolar bone (Castro et al., 2016, Vera et al., 2012, Wang et al., 2014). Depending on its low radiation dose and compact size equipment, CBCT is routinely used in dentistry and provides high-quality and detailed images of the bone structure (Rojo-Sanchis et al., 2017; Zekry et al., 2014). Therefore, the authors have investigated bone thickness and the presence of fenestration using CBCT.

Previous studies have generally focused on examining the FAB widths and the fenestrations of maxilla incisors and canines (Botticelli et al., 2004, Ghassemian et al., 2012, Nowzari et al., 2012). However, maxillary premolars are displayed in an average smile line and they are considered the esthetic zone variables (Wang et al., 2018). In the literature, there are few studies analyzing the FAB thickness and the fenestration in first and second premolars (Enhos et al., 2012, Nimigean et al., 2009, Vera et al., 2012, Wang et al., 2014). The FAB thickness has been reported 0.60–2.42 mm in maxillary premolars (Braut et al., 2011, Ganji et al., 2019, Rojo-Sanchis et al., 2017, Temple et al., 2016, Vera et al., 2012; Zekry et al., 2014). In addition to this, there are contradictory results in the literature regarding the coronal to apical thickening of the FAB in the maxillary anterior region (Ghassemian et al., 2012, Nowzari et al., 2012, Zekry et al., 2014). The pattern of FAB thickness throughout the root of the tooth is important for the immediate implant placement, or for the movement of the tooth in orthodontic treatment. Nonetheless, no clear data has been stated in the literature regarding the pattern of FAB thickness along the root (Zekry et al., 2014). On the other hand, there is limited data on fenestration rates of maxillary premolars examined with CBCT (Rojo-Sanchis et al., 2021). Most of the studies are focused on the dry skull to examine bone topography. However, there are critical concerns about the investigations using dry skulls, which is the misdirection of the damage or abrasion (Nimigean et al., 2009, Rupprecht et al., 2001). The present retrospective study aimed to investigate the facial bone thickness of maxillary first and second premolars using CBCT and to examine the frequency of fenestration in the maxillary premolar teeth in the Turkish subpopulation. The null hypotheses of this study were that [1] there is no difference between the facial alveolar bone thicknesses of the first and second maxillary premolar and [2] there is no difference between the presence of fenestration among these teeth.