## 1 Introduction  
The reconstruction of alveolar crest deficiencies for creating a sufficient implant site is one of the main challenges in oral implantology. Although there are a variety of alloplastic, allosteric, and xenogenic bone substitute materials available for this purpose, grafting procedures using autogenous bone are still considered to be the \"gold standard\" due to the bone's excellent osteoconductive, osteoinductive, and osteogenic properties [1]. However, a substantial disadvantage is the need for an additional surgical site for graft harvesting, with an increased risk of complications and postoperative comorbidities [2, 3]. In recent years, the use of autogenous dentin as a possible alternative autogenous grafting material has become a focus of scientific research [4, 5, 6]. Dentin is very similar to the bone in its organic and inorganic composition in terms of percentage and in its individual components. The organic matrix of dentin and bone, for example, consists of \(\sim\)90% type I collagen and \(\sim\)9% of non-collagenous proteins such as osteocalcin, osteonectin, phosphoproteins, proteoglycans, and sialoprotein, as well as growth factors such as bone morphogenetic proteins, tissue growth factor-8 or insulin-like growth factor-2 [4, 5, 6, 7]. Histological analyses have shown that dentin has osteoconductive and osteoinductive properties [6, 7, 8, 9, 10, 11, 12, 13] and is involved in the bone remodeling process [14, 15, 16, 17]. In addition, autogenous dentin appears to have lower resorption rates than autogenous bone [18, 19]. For these reasons, autogenous dentin can be considered as a viable alternative to autogenous bone. Meanwhile, the use of dentin has been investigated in numerous implantological measures. These include socket preservation, immediate implant placement, sinus floor elevation, and block transplants [4; 11; 13; 17; 20; 21; 22]. Since only in very few cases will impacted or retained teeth be available, non-retainable teeth, especially in the area of prospective implant placement, represent the main source of autogenous dentin. While most studies only use uncompromised healthy teeth such as retained or impacted teeth for these indications to minimize the risk of bacterial infection, there is a lack of clinical evidence regarding the use of compromised teeth. Animal studies yielded results that indicate that grafts derived from endodontically treated or periodondually compromised teeth did not show increased signs of inflammation histologically. However, increased graft exposures could be observed compared to grafts obtained from uncompromised teeth [14; 23]. Teeth that have undergone endodontic treatment, for example, may host residual bacteria in the dentin that were not eliminated by the endodontic procedure. Dentinal tubules represent a niche in which bacteria can persist, even in clinically or radiologically inconspicuous teeth [24]. Residual bacteria in endodontically treated teeth are dominated by anaerobic and Gram-positive microbiota. Recurrent infection after endodontic treatment is mostly characterized by an infection with only one or a few species, while primary endodontic infection is predominantly polymicrobial [25]. One of the most frequently found pathogens in teeth with endodontic failure is _Enterococcus faecalis_, which is characterized by specific virulence factors, e.g., adhesins [26] and is able to penetrate deeply into the dental tubules [27], where they may resist sufficient removal by disinfection procedures during graft preparation. This could be problematic, especially in grafting procedures where sufficient wound closure is desired, such as block grafts. In the present study, the tooth shell technique (TST) [22] was applied using processed autogenous dentin obtained from endodontically and non-endodontically treated teeth. The tooth shell technique is a modification of the shell technique according to [PERSON], in which autogenous bone is used [28; 29]. The present retrospective study is a proof-of-concept study.