# Influencing Factors in Autotransplantation of Teeth with Open Apex: A Review of the Literature
## 4 Review  
Both studies assessing children and young adolescents were considered in this review, since the age range for the presentation of teeth with a physiological open apex may extend to 21 years of age. According to the literature consulted, numerous factors influence the success of dental autotransplantation in incompletely developed teeth. They are detailed below and categorized according to the donated tooth, the recipient socket or the treatment technique. When selecting the donated tooth to be transplanted into another socket, the following should be considered:  
* **Stage of tooth root formation:** It is most optimal when between two-thirds and three-quarters of the root have formed [22]. Some authors did not find significant differences if the tooth presented a minor root formation [23]. Some authors indicated that the diameter of the root canal in a tooth with a wide open apex (1-2 mm) decreases the risk of pulp necrosis, since the revascularization of the pulp is greater and implies a new supply of blood and nervous fibers that achieve the vitality of the tooth [17; 24]. If the formation of the tooth root is not completed, it will do so in its new location [25]. In addition, the preservation of the alveolar bone and revascularization of the pulp may be achieved [25], avoiding root canal treatment and its possible complications due to its difficulty in this kind of tooth [26]. * **Type of tooth [17]:** According to the literature, the premolar is the tooth most used as a donor in cases of open apex [27; 28]. It has been described that this may be because pre- molars are the teeth most commonly extracted in orthodontic treatments [22; 27; 29; 30]. Others report that transplants of third molars, impacted canines and supernumerary teeth are also common, and that there is no significant difference if the donor's tooth comes from the maxilla or the mandible [29; 31; 32; 33]. In his study, [PERSON] considered an optimal root as one that is morphologically conical, smooth and simple, considering teeth with multiple roots and a rough surface to be more complicated [29]. * **Eruption state [17]:** Teeth can be categorized as not erupted, partially erupted or fully erupted [17]. [PERSON], in his study, included erupted or embedded teeth that were not previously functional [29], with those that had erupted being easier to remove without damaging the periodontal ligament. * **The state of the periodontal ligament [17]:** [PERSON] et al. [17] described how the state of the periodontal ligament is key to the success of dental transplantation and that excessive trauma has a negative influence on the treatment's prognosis [17]. It of vital importance that the soft tissue surrounding the periodontal ligament--that is, the cells that make up Hertwig's root sheath--is not injured during the extraction of the donor's tooth [26], as well as the apical papilla stem cells (SCAPs), which are fundamental for the root development of immature teeth [34]. The extraction must be atraumatic and prevent damage to the tissues surrounding the tooth [25; 27; 29], in order to increase the success and survival rate of the autotransplant [23]. Additionally, [PERSON] et al. [35] assured us that an intact periodontal ligament around the tooth facilitates its growth and adaptation to the alveolar bone, and also explained that to avoid damage to this tissue, the size of the new alveolus must be greater than that of the donor tooth. This guarantees the preservation of the tissue and thus reduces the risk of ankylosis and external root resorption [35]. However, he also described how teeth transplanted into the socket without any modification have a higher survival rate [35]. [PERSON] qualified this factor as the most important for successful transplantation [36].