1. IntroductionThe intentional replantation (IR) technique consists of tooth extraction with an intentional atraumatic method, extra-alveolar evaluation of the root surface, root canal treatment, and reinsertion of the tooth into its original position [1,2]. The advantage of IR is that it can be used to directly evaluate and treat the tooth outside the alveolar socket. Despite advancements in surgical root canal treatment, IR has been used in some challenging cases involving endodontic–periodontal lesions and lesions with difficult accessibility (maxillary sinus, perforation of root, and palatal groove) [3]. IR also has the advantage of being cost effective compared to dental implants [4]. Therefore, IR can be considered another choice for preserving teeth and may be an alternative to tooth extraction and implant placement [5].Previous studies of IR reported success rates ranging from 50% to 95% [6,7]. Wu and Chen demonstrated that survival rates were decreased in the first year, but these values were stable at 4 years with 82.8% survival rate [8]. Recent systematic studies have reported survival rates of approximately 90% for IR [4]. Surgical variables including orthodontic techniques, root-end bio-materials, tissue-regeneration agents, and anti-inflammatory medication have resulted in an increase in the survival rate associated with IR. Choi et al. suggested that a preoperative orthodontic treatment helped increase the IR success rate with inducing atraumatic tooth extraction and periodontal ligament (PDL) healing [9]. Wang et al. demonstrated the extraoral time period seems to be a critical factor to the success of the IR procedure [10]. Over 30 min of extra-alveolar time result in nonviable PDL cells due to drying. Less than fifteen minutes of extraoral time are recommended to clinicians in previous studies [11]. Mineral trioxide aggregate (MTA) is a suitable retro-filling material which has properties of biocompatibility and calcific barrier formation by reinforcing osteogenic PDL cell differentiation [12]. The 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate-tri-n-butylborane (4-META/MMA-TBB) dentin-bonded resin is also recommended as a proper sealing material to repair damaged roots of teeth [13].IR for teeth with periodontal disease is a challenging procedure for clinicians. A previous study documented that periodontally involved teeth with over 6 mm on the two sites may be negative on tooth survival [3]. Although IR is considered to be contraindicated in teeth with moderate-to-severe periodontal disease [14], one previous study reported successful results in periodontally compromised teeth [3]. Manikar et al. reported that one of the indications for IR is periodontally compromised teeth [4], and previous studies have shown favorable results for IR in teeth with periodontally poor prognosis [15,16]. In addition, guided tissue regeneration (GTR) was a proposed good choice for teeth with inadequate bony support, and it maintains space for osteoblastic cells by preventing the migration of epithelial cell into PDL space [17].Radiographic images can provide anatomical information regarding aspects such as the marginal bone level, root distortion, and the presence of impacted teeth [18]. Panoramic and intraoral periapical radiography is the most commonly used radiographic method for such assessments [19]. However, these conventional radiographic measurements with two-dimensional plane show limitations that can lead to misinterpretation, such as image magnification and distortion by projection errors [20]. Cone–beam computed tomography (CBCT) has been proposed to overcome these limitations. Lee et al. evaluated the marginal bone level after GTR and open flap procedures using CBCT [21]. Previous studies have suggested that CBCT is helpful in evaluating the anatomical structure of teeth and surrounding areas before and after IR procedures [22,23].One review article suggested that the literature on IR for periodontally involved teeth is quite limited [24]. Therefore, the present study aimed to evaluate the clinical outcomes and bone changes before and after IR in periodontally compromised teeth by using CBCT. The null hypothesis of this study was that the bone height showed no difference before and after IR for periodontally compromised teeth. 4. DiscussionThe present study showed that the clinical outcomes and bone changes determined using CBCT before and after IR for periodontally compromised teeth were different. Our findings indicated that the VAS scores for pain, tooth mobility, PD, and BOP decreased after the IR procedure (mean values: pain, 4.71 to 1.00; tooth mobility, 1.36 to 0.29; PD, 5.60 to 2.85; and BOP, 3.50 to 0.79). These parameters showed significant differences before and after IR. Bone heights of the maxilla and mandible increased (maxilla: 4.00 mm; mandible: 1.95 mm) after treatment. This finding may be explained by the findings of a previous study, in which Zhang et al. reported that PD and alveolar bone height decreased after IR of periodontally involved hopeless teeth [26]. However, the maxillary and mandibular bone heights did not differ before and after IR in this study.IR involves intentional extraction and reinsertion of a tooth into the socket after endodontic manipulation and/or obturation of the canals [36]. By performing this procedure extraorally, the root surface can be visualized and treated easily without damaging the adjacent periodontal complex. In addition, all local factors in teeth that cause periodontal inflammation, attachment loss, and alveolar bone resorption can be eliminated. IR can yield a better prognosis in patients with endodontic–periodontal lesions. Using the IR procedure, the origin of periodontal problems (such as subgingival calculus and salivary parameters, etc.) as well as endodontic problems can be easily removed [11,37]. Periodontal involvement is a major contraindication for IR. Grossman [1] suggested that IR was contraindicated in teeth with extensive mobility or alveolar bone destruction, or when the septal bone (at the bifurcation) was destroyed or missing in cases involving the posterior teeth. Bender and Rossman [35] reported that IR is not recommended for teeth with excess mobility, furcation involvement, or gingival inflammation. However, some studies have shown favorable results for IR in teeth with periodontal involvement. Lu [38] reported successful clinical results with IR in periodontally involved teeth after intentionally replanting an endodontically mistreated and periodontally involved mandibular first molar. The tooth was maintained under asymptomatic and functional conditions for 32 months. Demiralp et al. [30] performed IR for 15 periodontally involved hopeless teeth and followed the outcomes for 6 months. Thus, IR has been suggested as an alternative approach in cases showing advanced periodontal destruction with extraction as the only other treatment option.In this study, most preoperative symptoms, including pain, mobility, PD, and BOP, decreased significantly, and the patients showed no occurrence of generalized root resorption, no evidence of periapical rarefaction, and no presence of slight localized evidence of root resorption. According to one previous study, the presence of periapical lesions is correlated with the maxillary sinus mucosa thickness (MSMT) [39]. In Figure 4A,B,E,F, the MSMT decreased after the IR procedure. Although the teeth were functioning normally, the goal of the treatment is to achieve an asymptomatic status with healthy gingiva for ≥5 years, a significant reduction in pocket depth, and new bone formation for long-term success. Failure of IR presents with evidence of resorption, rarefaction, or discomfort. The key factor for the success of IR is a viable PDL [40]. In cases showing severe periodontal involvement, maintenance of the viability of PDL is challenging, and the healing process after intentional extraction and reinsertion may not be encouraging. Without a viable PDL, ankylosis is a common complication of replanted teeth that leads to gradual resorption of hard tissues and their replacement by bone. The teeth evaluated in this study met the criteria of success listed above, and showed good functioning with no patient discomfort. The patients showed no gingival recession, pathological periodontal pocket formation, evidence of additional marginal bone loss, or evidence of ankylosis and root resorption. Bone grafting was performed with IR in this study. Bone grafting seems to maintain space for osteoblasts by precluding contact between the connective tissue and PDL [41]. Zufia et al. reported that IR, including bone grafting, should be considered when the bone support is insufficient [17].This study differs from previous studies in that it compared changes before and after IR by using CBCT. Although conventional clinical measurements such as PD, BOP, and mobility are good evaluation factors, they have limited reliability [42]. Intraoral periapical and panoramic radiographs cannot easily yield accurate images because of the 2D plan images. CBCT has been used to overcome the limitations of conventional radiographic methods. With a multidimensional view, CBCT can reveal the anatomy of the tooth and its surrounding structures [43,44]. Previous studies have suggested that CBCT may be helpful for IR procedures [27,30,31]. Granichi et al. strongly recommended the use of CBCT for diagnosis and treatment in cases requiring IR [45]. The radiation in CBCT has been demonstrated to be 15 times lower than that in conventional radiography [46]. This low radiation dose may be another advantage of CBCT in such examinations.

Nevertheless, the sample size used in this study was insufficient, and a larger sample size is needed to evaluate IR of teeth affected by periodontal diseases. Future studies should aim to include long-term follow-up assessments and evaluation of various factors (anterior or posterior position) affecting IR. In addition, research on the varying degrees of periodontal destruction is required to obtain more clarity about guidelines for applying IR to more “last resort” cases.