###### Abstract  
The aim of this study was to compare the alveolar bone crest (ABC) level of root canal filled (RCF) teeth without apical periodontitis with corresponding non-filled teeth in the same individual using three-dimensionally cone-beam computed tomography (CBCT) data. Two hundred and thirty-five matching pairs of RCF teeth and corresponding teeth without RCF were selected from a pool of 580 random CBCT-images (voxel size 160-200 \(\upmu\)m). Teeth with apical periodontitis, perio-endodontic lesions or surgical endodontic treatment were excluded. The distance between the cemento-enamel-junction (CEJ) and the ABC was assessed centrally mesial, distal, palatal/lingual and buccal at each tooth (\(\sum\)1880 measuring points) in a standardized manner. Topographic, gender, and age-related relationships were also noted. Data were analyzed using the Kruskal-Wallis-test. The ABC-level between RCF teeth (2.64 \(\pm\) 1.25 mm) and teeth without RCF (2.61 \(\pm\) 1.16 mm) did not differ significantly (\(p>\) 0.05). No differences concerning localization (maximila/mandible, tooth type) and gender (\(p>\) 0.05) occurred. Overall, ABC-level in the maxilla (2.74 \(\pm\) 1.48 mm) was significantly lower (\(p<\) 0.001) compared to mandibular teeth (2.50 \(\pm\) 1.41 mm). Patients > 41 years had significantly lower ABC-levels than younger patients (\(p<\) 0.05). Men showed a reduced bone level compared to women (\(p<\) 0.05). In conclusion, RCF teeth are identical to their non-RCF counterparts, at least in terms of crestal bone level, regardless of the location or type of tooth and the gender of the patient. Thus, root canal treatment is an essential pillar for long-term tooth preservation.  
al; 21 August 2021  
13 September 2021  
15 September 2021  
[[http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci)]([http://www.mdpi.com/journal/applsci](http://www.mdpi.com/journal/applsci))  
[[http://www.mdpi.com/](http://www.mdpi.com/)]([http://www.mdpi.com/](http://www.mdpi.com/))of apical and marginal periodontitis has been described--independent of patient-related factors such as age, number of remaining teeth, relative frequency of root-filled teeth and smoking habits [11].  
According to the common radiographic projections (periapical, bite-wing and panoramic radiographs) for the analysis of periodontal tissues, all existing studies concerning alveolar bone loss/periodantal attachment loss in root canal treated teeth rely on two-dimensional radiographs evaluating only the interproximal bone level by measuring one mesial and one distal measuring point per tooth. Hence, no information concerning the oral and buccal aspect of bone level are available up to now.  
Cone-beam computed tomography (CBCT) allows a three-dimensional analysis of the teeth and the surrounding, especially bony structures free from superimposition [12; 13]. The diagnosis of periodontal diseases and bony defects offers a sensitivity between 80-100% [14; 15; 16; 17]. Therefore, CBCT data allow a more precise assessment of the marginal bone level than two-dimensional radiographs.  
Thus, the present cross-sectional observational comparative study in a German population solely aimed to compare the alveolar bone crest (ABC) level of root canal filled teeth without apical periodontitis and the corresponding non-filled teeth in the same individual, irrespective their periodontal status, using 3D radiographs (CBCT) based on four measuring points at each tooth--centrally mesial, distal, buccal and palatal/lingual, respectively.  
The null-hypothesis was that bone levels around root canal filled teeth do not differ from those of untreated teeth.