Intentional Replantation of Single-Rooted and Multi-Rooted Teeth: A Systematic Review

The technique of intentional replantation can provide a second chance to save teeth that would be destined for extraction. Therefore, the present systematic review aimed primarily to estimate tooth survival after intentional replantation and secondarily to compare treatment outcomes in single-rooted and multi-rooted teeth. The study protocol was developed before the analysis according to the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines. Articles were electronically searched in PubMed/MEDLINE, the COCHRANE library and Google Scholar by two independent reviewers, and those that met the eligibility criteria were included. A statistical analysis using the chi-square test with a p-value of <0.05 was performed on the reported outcomes of intentional replantation. A total of 44 single-rooted replanted teeth with five failures (11.36%) and 42 multi-rooted replanted teeth with six failures (14.28%) were reported in the literature, corresponding to a survival rate of 88.64% and 85.57%, respectively. The overall survival rate for the replantation procedure was 86.7%, indicating that intentional replantation can be considered a safe therapeutic choice, with no statistically significant difference between the survival rates of single-rooted and multi-rooted replanted teeth.


Introduction
Intentional replantation (IR) is a multistage surgical procedure based on the controlled extraction of a tooth and its subsequent repositioning in the original socket to perform root surface revision and subsequent endodontic treatment in the extra-oral environment [1].
Since surgical phase IR is considered the most technically delicate phase of the procedure [2], it must be performed with extreme precision and care to improve treatment outcomes and survival rates. Tooth extraction must be as atraumatic as possible to avoid both fractures of the tooth and, most importantly, damage to the periodontal ligament (PDL), which may play a critical role in healing and, consequently, treatment success [3].
Subsequently, the extracted tooth is carefully examined to assess possible fractures or anatomical features that require special attention, such as the presence of additional or accessory canals or multiple foramina [4], and accordingly decide whether to proceed with extra-oral endodontic treatment [5]. At this stage, PDL preservation as well as proper management of the tooth under extra-alveolar environmental conditions, which affect the overall treatment success, are crucial [6,7]. Since it has been found that extra-alveolar remaining in a dry environment longer than 15 min may affect the PDL conditions and consequently increase the risk of dental ankylosis after IR [8], it is recommended to keep the extra-alveolar time as short as possible and to preserve the tooth in a moist environment to improve the predictability of the procedure [9,10].
After extra-oral endodontic treatment, the original tooth socket must be prepared. Complete resection of cystic or granulomatous tissue from the dental alveolus (alveolar

Materials and Methods
The study protocol was developed, according to PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analyses) guidelines [24,25], before the analysis.
The research question was formulated according to the PICO (Population, Intervention, Comparison, Outcome) strategy and the clinical question in the "PICO" format was "What is the survival rate of IR in single and multi-rooted permanent teeth?", focusing on:

Search Strategy and Study Selection
A literature search was independently conducted by three reviewers (MP, AI, FDS), across PubMed/MEDLINE, Google Scholar, and the COCHRANE library databases and the gray literature, using the following keywords combined by Boolean operators: intentional replantation OR replanted teeth OR replanted tooth AND procedure OR technique.
Citations obtained through the literature search were recorded, duplicates were eliminated using EndNote, and titles and abstracts were independently screened by three reviewers (MP, FDS, GS). Available full-texts, compliant with inclusion and exclusion crite-ria, detailed below, were also independently reviewed for potentially eligible studies. Any disagreement between the reviewers was solved by discussion and consensus.
The inclusion criteria were: • Source: studies published in the English language from January 1996 to 1 July 2022; • Study design: case reports, case series, analytical observational studies, trials; • Study population: subjects undergone IR (no age nor gender restrictions); • Study intervention: IR of single-rooted and/or multi-rooted permanent teeth; and • Study outcomes: IR reported clinical and/or patient-related outcomes.
The exclusion criteria were: Source: studies published before 1996; Study intervention: indication to treatment not specified; and Study outcomes: IR clinical and/or patient-related outcomes not available.
No attempt to contact the authors was performed for missing information or full-text unavailability and, in case of disagreement, the evaluation of the majority was considered (two reviewers out of three).
Search and study selection was conducted for grey literature, as already described.

Data Extraction
A ten-question data extraction form was currently employed, by three independent reviewers (AI, GS, FDS), to record for each of the included study: source and design; participants' age and gender; treated teeth; extra-alveolar time stay and environmental conditions management; IR indications, follow-up and reported outcomes, classified as IR success and failure, as reported by the authors in the included studies.

Data Synthesis and Statistical Analysis
Extracted data were synthesized according to the number of roots of replanted teeth, categorized as single-or multi-rooted.
Frequencies and percentages for categorical data were computed. A chi-square test with Yates correction was used to assess the association between teeth (single-rooted vs. multi-rooted) and dental arch (upper vs. lower). A standard statistical software package (SPSS, version 28.0; SPSS IBM, Armonk, New York, NY, USA) was used. The level of significance was set at p < 0.05.

Quality Assessment
Included studies were assessed for quality through the JBI (Joanna Briggs Institute) Critical Appraisal Tool, evaluating the risk of bias of the case reports and case series included [26].

Study Selection
A total of 1556 records were retrieved from PubMed/MEDLINE (720 articles), Google Scholar (776 articles) and the COCHRANE library (60 articles). Of these, 904 were excluded because duplicates or the full text were not available. Of the remaining 652 articles, 130 were considered appropriate, but 70 were excluded because the full-text review did not reveal clinical cases treated with the technique IR. Finally, 60 articles were included in the qualitative analysis [27].
The flowchart for study selection is shown in Figure 1.

Studies Characteristics and Synthesis of the Reported Results
Sixty case reports and case series , compliant with the eligibility criteria, were included in the present systematic review, and detailed in Table 1; no observational studies or clinical trials were presently retrieved. The results of the risk of bias assessments of the included studies are reported in Table 2.
not reveal clinical cases treated with the technique IR. Finally, 60 articles were included in the qualitative analysis [27].
The flowchart for study selection is shown in Figure 1.

Studies Characteristics and Synthesis of the Reported Results
Sixty case reports and case series , compliant with the eligibility criteria, were included in the present systematic review, and detailed in Table 1; no observational studies or clinical trials were presently retrieved. The results of the risk of bias assessments of the included studies are reported in Table 2.

Discussion
The present systematic review aimed, primarily, at the teeth survival rate following intentional replantation and, secondarily, to compare treatment outcomes in single-vs. multi-rooted teeth.
Despite the various IR indications reported in the literature, such as persistent apical periodontitis [16][17][18], incongruous endodontic therapy [17], inaccessible external root resorption [20], root perforations [21], complex root/coronal root fractures [21][22][23], and teeth with developmental anomalies, such as fused teeth, the procedure is considered a "last resort" to preserve natural teeth [1]. This consideration may be mainly due to the high risk of technical errors resulting from the numerous operative phases, which make the procedure highly operator-dependent and may explain the IR heterogeneous survival rates, which range from 80% to 100% in the literature [87]. However, a recent systematic review [88] described a survival rate of 88% IR, which is consistent with the current estimated survival rate of 86.7% IR. It is suggested that these results are closely related to the extra-alveolar time stay of the replanted teeth, which is considered to be a crucial factor as it is directly involved in the preservation of the PDL cells [18,19]. Indeed, the analysis of IR clinical cases included in the present systematic review revealed that the extra-alveolar time ranged from a minimum of 4 min [66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] to a maximum of 30 min . In particular, Jang et al. [89] reported higher survival rates for teeth replanted within 15 min compared with teeth replanted after an extra-alveolar time of more than 15 min. Nevertheless, high survival rates were also reported in cases with an extra-alveolar time > 15 min. Remarkably, however, the teeth in these cases were stored in a moist environment to preserve the viability of the PDL cells [3,7,8,[11][12][13]18,19,90], suggesting that extra-alveolar stay time should be considered in the context of tooth conservation approaches. In this context, it has been previously suggested [8,10,91] that preservation of the tooth in an extra-oral humid environment, such as water, saline, and saliva, may positively influence the results of IR, making the procedure more predictable and thus supporting the hypothesis that the periodic submersion of the tooth in a bath of Hank's balanced salt solution during the root resection phase may be the best approach to avoid root desiccation [91].
Moreover, high variability in root resection methods, filling materials, and socket manipulation were also noted. Although the length of root resection was rarely reported in the studies analyzed, most authors described a mean resection length of 1 to 3 mm [6]. Several restorative materials were listed in the reports, including mainly dental amalgam, followed by recently proposed intermediate restorative materials such as SuperEBA, MTA, and Endocem, and finally eugenol cement based on zinc oxide and glass ionomer [47]. Various approaches have also been found to manipulate the alveolus prior to tooth reinsertion. These include simple blood clot aspiration using suction instruments and/or irrigation with saline solution, as well as curettage of the alveolus with surgical instruments [22], which, however, may damage the fibers of the periodontal ligament still adhering to the alveolar walls, and affect, in turn, the success of IR, as mentioned above. Therefore, the recorded results show how the manipulation of the alveolus can have a crucial impact on the results of IR, which remains highly controversial [7,87]. According to Wu et al., if the reimplanted teeth are diagnosed with an acute or chronic apical abscess on preoperative examination, the risk of failure is 2.7 times higher than for teeth diagnosed with other conditions. This is because the presence of infection combined with chronic inflammation would lead to the destruction of the periodontal bone and PDL cells damage [92].
When the survival rates of IR were compared between single-rooted and multirooted teeth, no statistically significant differences were found. Therefore, it can be concluded that the number of roots of the replanted teeth has no significant influence on the results of the IR procedure. Nevertheless, special attention must be paid to the possible anatomical variations of the treated tooth root, especially pronounced curvatures. Therefore, Cone Beam Computed Tomography (CBCT) can be an essential tool in the diagnosis of anatomical variants, fractures, or discontinuities, which were previously based on a conventional, less sensitive 2D examination. However, because CBCT has only recently been introduced to support IR surgical planning, there are few case reports to date describing an IR planning phase using 3D reconstructions [93]. In addition, other recently introduced technologies, including ultrasonic devices and microscopy, may also both minimize the extra-alveolar time stay and improve treatment outcomes by reducing the duration of the IR procedure, invasiveness, and failure rates [94].
The main limitations of the study may be the exclusion of some databases (i.e., Scopus, LILACS, and EMBASE) from the electronic search and the inclusion of only case reports or case series, which are intrinsically characterized by low evidence and positive findings, that, along with the lack of data on the methods used to preserve the teeth in an extra-oral environment during the procedure, the heterogeneous approaches used to manipulate the alveolar socket, and the follow-up periods recorded, may make the interpretation of the results challenging. However, to the authors' knowledge, this is the first study to investigate the possible role of the number of roots of the replanted teeth on treatment outcomes and to compare the survival rates of IR between single-rooted and multi-rooted teeth, even though the exact number of roots of multi-rooted teeth is not considered.
The results presented make it clear that IR can be considered a safe and predictable treatment for both single-rooted and multi-rooted teeth as long as all procedural phases are performed correctly [95]. Moreover, it seems evident that the success of IR also depends on the appropriateness of the treatment indications, suggesting the need for a comprehensive and multidisciplinary approach in complex cases [96,97] and supporting, once again that the choice of therapeutic strategy, even considering alternative procedures such as surgical extrusion and dental autotransplantation [98][99][100][101], should be based on the specific characteristics of each clinical case.

Conclusions
From the retrieved data, a survival rate of 86.7% was currently estimated for intentional replantation, and no statistically significant difference was found between single-rooted and multi-rooted replanted teeth, the survival rate of single-root implanted teeth was 89.3% while for multi-rooted reimplanted teeth it was 84%.
The reported results suggest that intentional replantation can be considered a safe therapeutic choice for both single-rooted and multi-rooted teeth, with a high survival rate and predictability, provided it is performed correctly and in accordance with basic biological principles, especially with regard to extra-oral environmental time.

Conflicts of Interest:
The authors declare no conflict of interest.