Autotransplantation of mature impacted tooth to a fresh molar socket using a 3D replica and guided bone regeneration: a one year retrospective study

Objective The aim of this study was to evaluate the performance of autotransplantation of a mature third molar to a fresh molar extraction socket using a 3D replica. Materials and Methods Ten patients underwent autotransplantation of teeth. We observed the mobility, percussion, radiography examination, the probing depth and the masticatory function of the transplanted teeth during one year following up, which were transplanted into fresh molar sockets by using a 3D replica, and GBR when it is necessary. Results The average extra-oral time of donor tooth had been shortened to 1.65 min. The clinical examination of the autotransplantation teeth during one year follow-up showed no sign of failure. Expect one patient feel slight sensitive when chewing with soft food at 4 weeks, and 3 points of probing depth deeper at different patients than 3mm and 1 points of probing depth deeper than 4mm at 4 weeks among them, and 1 points of probing depth deeper than 3mm at 5 weeks at the same patient. Conclusions The autotransplantation of teeth using 3D replica is an effective method which can reduce the extra-oral time of the donor teeth and the demand for the experience of a surgeon, and had a high success rate. Clinical Relevance The new 3D replica of donor tooth can make the surgery of tooth autotransplantation much easier, and improve it success rate.


Introduction
The autotransplantation of a tooth is a predictable method to reconstruct a missing tooth or replace a tooth that needs to be extracted due to caries, trauma, or tooth fracture. Since it was rst introduced by Fauchard in his book, Le Chirurgien Dentiste, in 1728, the treatment strategy had been developed for hundreds of years [1][2][3]. Its brief process involves donor tooth (mostly an impact tooth or a supernumerary tooth) that is extracted for the insertion of a prepared recipient socket [4]. Compared to implants, the autotransplantation of teeth is a better way to restore a missing teeth for its proprioception, the vital periodontium, preservation of alveolar bone volume and the papilla [5], and also better than a xed bridge.
Many previous studies have demonstrated that third molars, premolars, impacted teeth and supernumerary teeth can be donor tooth in the clinical practice [6][7][8]. The incidence of the compromised molars which need to be extracted due to caries is much higher than in other teeth, especially in young Chinese range from 25-30 years old. The transplantation of a third molar to replace compromised rst or second molar has more practical value. The survival rates of autotransplantation teeth with incomplete root formation after 1, 5 and 10 years were 97.4%, 97.8% and 96.3% respectively [9]. However, some studies showed that the estimated 10-years success rate of a transplanted premolar with mature root was 81.6% which is much higher than that of a molar, with a 33.8% 10-years success rate [10]. Many factors affect the success of tooth transplantation, such as root development stage, surgical trauma, the recipient site (local in ammation, alveolar bone volume and quality), the surgery procedure (stabilization method, use of intraoperative drugs and storage) and so on [9]. The lower success and survival rates of the molar can be related to more complex root anatomy, more tissue trauma during extraction, and the requirement of high individual surgical skill [11]. The most important factor that affect a successful tooth transplantation is the preservation of the healthy periodontal tissue [12]. The duration of the extra-oral time and the try-ins into the recipient socket will damage the periodontal tissues of the donor teeth.
Researchers still need to discover how to shorten the extraoral time of donor tooth, reduce the damage of the periodontal tissue, and improve the surgeon's skill. Many attempts tried to reduce the extraoral time of donor tooth [13]. With the development of radiological and 3D printing technology, a precisely replica of donor teeth can be fabricated by a 3D printer, according to the data of cone beam computed tomography.
Many case reports have indicated that the use of a 3D replica of donor tooth can decrease the extraoral time and increase the ease of surgery [14]. Lee et al have used computer-aided rapid prototyping for tooth transplantation and shorten the extraoral time [15]. The bone defect between the prepared socket and the donor tooth is inevitable when transplantation was done in a fresh extraction socket. And the bone graft materials will need to ll the bone defect. Yu et al have autotransplanted canine combined with guided bone regeneration, which show an acceptable result during 7.1 years following up [16]. The technique of guided bone regeneration had been widely used in the implantation, where the bone graft materials create a space for bone regeneration. Yu. et al also eported that the survival rate of the autotransplantation of third molars with completely formed roots in both surgically created and fresh extraction sockets were 93.1% and 95.2% during 10 years following up [17]. However, investigations of the clinical advantages and the success rate of this autotransplantation technique associationg with GBR are still lacking.
Therefore, the purpose of this study is to evaluate the e cacy of the transplantation of third molar to a fresh rst or second molar extraction socket by using a 3D replica of donor teeth and grafting with autogenous bone to ll the gap between the tooth and the prepared socket.

Study population and design
This was a retrospective observational study of 10 autotransplantation of third molars into fresh rst or second molar extraction socket positions simultaneously using a 3D replica and grafting with autogenous bone mixed with concentrated growth factor (CGF) in 10 patients (8 males and 2 females) The patients included in this study reach the following criteria: 1. First or second molar need to be extracted.
2. Third molar with mature root need to be extracted.
3. Recipient site without local acute in ammatory. 4. The rest bone height of the recipient site is enough for the donor tooth (the height from alveolar ridge crest to inferior alveolar nerve). 5. Systemic diseases such as diabetes mellitus and hypertension, which is not suit for oral surgery, were absent.

Preoperative work-up
All patients received a cone-beam computed tomography (CBCT) examination to analysis the compromised teeth and the donor teeth (the stage of the root development and the shape of the root), and the bone height / bone width in the recipient site were adequate for the donor teeth. All patients underwent an overall dental hygiene assessment, teeth washing or scaling, and root planning one week before surgery, if necessary. The 3D replica of the donor teeth, made of resin material, was fabricated by a 3D printer (Vida, Envision TEC) according to the data from the CBCT.

Surgical proceduce
All the surgical proceduces were performed by the same surgeon, who had more than 20 years of experience in oral surgery. Block anesthesia of the inferior alveolar nerve was used when the donor teeth and the recipient site were in the mandibular; local anesthesia was used when the donor teeth or the recipient site were in the maxillary. Local anesthesia was achieved with articaine chlorhydrate 4% and adrenaline 1:100 000. A crevicular incision was made from second premolar to third molar, and the vertical releasing incision in distal side was made if necessary. The compromised molar was extracted by minimally invasive maneuver, using high-speed ssure bur (SINOL) and a dental elevator or forceps (Stoma). The preparation of recipient site was done by piezosurgery according the root shape of the 3D replica of the donor teeth, which was sterilized by ethylene oxide before surgery. Meanwhile, the bone fragment was collected during the preparation of the recipient site if the recipient site had any bone defect. The impacted tooth was extracted by minimally invasive technique, using a dental elevator or forceps (Stoma) after the 3D replica of the donor teeth try-ins into the recipient socket. We put the donor teeth into the recipient socket immediately after the extraction of the donor teeth and then achieve an optimal t. If there were bone defect around the neck of the donor tooth after inserted into the recipient site, we performed a bone graft by using the autogenous bone, which was collected during the socket preparation process, mixed with CGF (Medifuge, Silfradenstsr, S. So a, Italy) which was done immediately before surgery. Blood from the patient was centrifuged using a tabletop centrifuge and the topmost layer consisting of CGF. Then the bone graft area was covered by CGF membrane which was also done before surgery. Finally, the ap was repositioned and sutured. We used ber band to xed the autotransplantation teeth with the adjacent teeth. The brief surgical procedure of the tooth autotransplantation was showed in Fig 1. Postoperative treatment After surgery, all the patients received mouth rinsing for 1 week. After 1 week, the sutures were removed and the wound was cleaned by normal saline. The preparation of the root canal was performed 2 weeks after surgery and the lling of the root canal was done 5 weeks after surgery. The ber band was removed 5 weeks after surgery.

Postoperative examination
Follow-up recalls were scheduled for1, 2, 4 weeks and for 3, 6,12 months. At each time of the follow-up the mobility and percussion were checked, while the probing depth of the mesial-buccal, buccal, distalbuccal, mesial lingual, lingual, and distal-lingual of the autotransplantation teeth and the masticatory function were checked 1, 3, 6, and 12 months after surgery. The radiography examination was taken before surgery and immediate, 1, 3, 12 months after surgery. We de ned the masticatory function as the patient' ability to chew normal food without pain or discomfort. The primary success criteria of the transplanted tooth were followed according to the book of Tsukiboshi[18]. In terms of the radiography (1)

Results
Retrospective, we evaluated 10 patients (8 male and 2 females, mean age 31.6+8.75, range from 19 to 42 years) who underwent transplantation of their third molar to their fresh rst or second molar extraction socket, using a 3D replica. The basic information of the patients about the gender, age, site of the donor tooth, recipient site, reason for extraction, the extraoral time, as well aa whether guided bone regeneration (GBR) was performed, are recorded in table 1. All the patients met the criteria of the success as we enumerated the points previously, and no periodontal pocket, mobility, in ammation and absorption of the root were found. The average extraoral time of the donor teeth spent was 1.35 min, and three donor teeth were transplanted in the recipient socket less than 1min after extraction. But there were two cases cost 3.5 and 4 minutes respectively due to the error range of the 3D replica.
No mobility was found in any cases during the follow-up period and only one patient felt slight pain from percussion of the transplanted tooth at 4 weeks. In addition, only one patient feel slight sensitivity when chewing soft food at 4 weeks. In terms of probing depth, three patients' probing depth was deeper than 3 mm, and one patient's probing depth was deeper than 4 mm at 4 weeks, all the probing sites were distalbuccal/lingual. Meanwhile, the probing depth at the distal-buccal/lingual site was deeper than 3 mm in one patient at 3-months follow-up whose probing depth was deeper than 4 mm at 4 weeks. The probing depths in other transplanted teeth were normal at all follow-ups. The speci c data about the related clinical symptoms appear in Table 2. In terms of the X-rays, no sign of bone loss of more than one third of the root length, ankyloses, or root resorption occurred during the 1-year follow-up, as shown in Figure 2.

Discussion
In our retrospective study, the autotransplantation teeth, using 3D replica, was an e cient method with a 100% success rate during one-year follow-up, according the success criteria previously mentional. Verweij et al [14] reported that high success rates were reported when using donor tooth replicas, success and survival rates of 80.0 -91.1 % and 95.5 -100 %, respectively. Healthy periodontal ligament and the good tissue adaptation are considered the most important factors in successful tooth transplantation [12].
Meanwhile, the extraoral time, number of tting attempts of the donor teeth, skill of surgeon, and the trauma of the recipient socket may in uence the periodontal ligament.
We used a 3D replica of donor tooth to preserve the periodontal ligament of the donor tooth. Firstly, the 3D replica of donor tooth can replace the real one to determine whether the recipient socket is ideally suited for the donor tooth; the process will damage the periodontal ligament seriously. Second, the use of In our cases, there are two cases cost 3.5 and 4 minutes due to the error range of the 3D replica, that is the inaccuracy of the model. So the accuracy of the 3D replica model is important to the produce of the surgery. The accuracy of the 3D replica model also effected the tness of the donor teeth to the recipient socket. Many factors may affect the accuracy of the replica model, such as the data from the CBCT, the material shrinkage during the building or postcuring and the minimal thickness of the layers [20]. So far there is no standard de nition of the clinically acceptable differences between the replica model and the donor teeth, although several studies reported that the differences of less than 0.25 mm are clinically acceptable [21]. And Lee et al reported that the mean deviations of the replica model manufactured by 3D printer were 0.038-0.047 mm [22], which is much less than the clinically acceptable value. Also Lee and Kim reported that the 3D replica models were, on an average, 0.149 mm smaller in size than the real teeth [23]. And Khalil et al proved that the dimensional differences between the 3D replica models made by 3D printing technologies and the real teeth were below 0.25 mm, which is accepted by the clinical demand [24]. Therefore, the 3D printing technologies, used for 3D replica models of the donor teeth, is accuracy enough for the autotransplantation of the teeth. The tness of the donor teeth to the recipient socket was well in our clinical operation, expect the two cases due to the date of the CBCT was incomplete during the date transmission. Many other factors affect the success of the autotransplantation tooth. Yoshino et al analyzed the in uence of age on the tooth autotransplantation and found that the younger the patient is, the higher success rate of the tooth autotransplantation, the success rate was lower in the 55-69 years old group [27]. Sugai et al and Yoshino et al also reported that patients under 40 years old showed a higher success rate than the older one group [28,29] Yoshino et al also analyzed the in uence of gender on the tooth autotransplantation and found that compared with female the survival rate of the tooth autotransplantation of males was low at 5-years, 10-years and 15-years follow-ups and need more attention during the autotransplantation process [30]. Therefore, the use of donor tooth replicas are more needed in male patients so that the surgery process can be handle well.
The third molars slated for autotransplantation in all cases in the present study is mature teeth with developed roots, so the revascularization of the pulp is not likely to happen after transplantation and needed root canal therapy [28,31]. Some cases in the present study use the GBR to regeneration the bone defect. Yu. HJ et al reported that using GBR during autotransplantation in recipient site where buccolingual alveolar bone atrophy had occurred could also result in a good long-term outcome [17].
Other studies also proved that the usefulness of GBR in the autotransplantation at recipient sites with bone defects [16]. The autogenous bone that was collected from extraction socket was used for the GBR in the present study. Compared with xenogenic bone, autogenous bone has the capable of osteogenesis, osteoinduction, and osteoconduction, and may reduce the forgein-body reaction. The success rate of using GBR in autotransplantation is consistent with the non GBR one.
The success rate of the autotransplantation, using 3D replica, is high, but the long-term survival rate still need to be observed, and the precise of the autotransplantation need not only a 3D replica as a guide but also a preparation guide of the recipient site and a guide for occlusion, all of which still need more research.

Declarations
Acknowledgements Thank the help of Pro. Chen who give the suggestion about the design of the study and the writing assistance of the article.

Compliance with Ethical Standards
Con ict of Interest: The authors declare that they have no con ict of interest. Funding: The work was supported by the project of "Training Project for Young Backbone Talents in Fujian Health System" (2015-ZQN-ZD-27) Ethical approval: The study protocol was evaluated and approved by the Institutional Ethics Committee of the School of Stomatology, Fujian Medical University (Ref. [2016] NO.10). All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards." Informed consent: All patients provided written informed consent. The X-ray photograph before surgery (a) and immediate (b), 1 (c), 3 (d), 12 (e) months after surgery.

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