Ⅰ.INTRODUCTION

Injuries to the anterior maxillary teeth are very common among children aged 8 – 12 years¹⁾. About 7 – 8% of teeth affected by injuries such as displacement cannot be replanted, and even when they are replanted, tooth loss due to progressive root resorption, or crown-root or root fracture, can result²⁾.

Autotransplantation is one of the treatment methods used to replace damaged or ankylosed teeth³⁾. In particular, autotransplantation using premolars may replace damaged anterior teeth in growing patients. This technique also has osteoinductive potential, in that it may promote the regeneration of a normal alveolar process⁴⁾. Previous studies have shown that sites in which maxillary incisors have been replaced using premolars, as well as the hard and soft tissues around these sites, biologically resemble the natural environment around incisors⁵⁾. Moreover, Andreasen et al.¹⁾ reported that tooth autotransplantation is a good treatment option in growing patients. The osteogenetic ability of the implanted tooth promotes labial bone regeneration, allowing the implanted tooth to grow at the same pace as adjacent teeth as its bone process grows, ultimately promoting orthodontic tooth movement. In addition, treatment cannot be considered successful if its aesthetic results are unsatisfactory, even if the biological results are good. For this reason, autotransplantation of premolars is mainly indicated in young patients, for whom dental appearance and esthetic results are of great importance⁶⁾.

The present report describes the case of a 10-year-old girl who underwent the autotransplantation of a mandibular first premolar that was extracted for orthodontic treatment at the site of the maxillary central incisor that had been ankylosed as a result of an injury. The transplantation was followed by orthodontic treatment to achieve biological and functional recovery of the anterior tooth, as well as aesthetic improvement. These procedures produced satisfactory results.

II.CASE REPORT

A 10-year-old girl visited a pediatric dental clinic at Wonkwang University Dental Hospital seeking the aesthetic recovery of an injured maxillary central incisor. The patient’s maxillary left incisor had been avulsed four years previously, and she had undergone delayed replantation followed by root canal filling with calcium hydroxide. She had visited the clinic for regular checkups for the first year, but had not made any further visits in the intervening three years. When she visited the clinic again, the maxillary left central incisors had black discoloration and infraocclusion, and percussion had a metallic sound and no mobility. The periapical radiographs revealed that most of the calcium hydroxide in the root canal had been lost and some of the root surface had been resorbed. This tooth was therefore diagnosed as an anklyosed tooth (Fig. 1). A clinical oral examination showed maxillary and mandibular anterior crowding, an overjet that measured 5.5 mm, and infraocclusion of the injured tooth (Fig. 2). Lateral cephalograms and an orthodontic examination showed a convex midface profile, as well as parted lips at rest (Fig. 3). The patient was diagnosed with skeletal and dental class Ⅱ malocclusion. An extraction was planned for her four first premolars to correct her prognathism, reduce her large overjet, and form a class I occlusal relationship in the posterior area (Table 1).

To replace the ankylosed maxillary central incisor, we planned an autotransplantation using a mandibular first molar that had initially been scheduled for orthodontic extraction. First, the space for the autotransplantation was secured using the ankylosed left maxillary central incisor as the anchorage (Fig. 4). Apex formation was almost complete in the left mandibular first premolar, which was chosen to be the donor tooth, and a root canal treatment was performed one week before the scheduled autotransplantation (Fig. 5).

To form the recipient site before autotransplantation, a replica of the donor tooth was produced in advance using resins. The replica was made using a wax-up method after confirming the tooth morphology on computed tomography. The wax replica was then impressed and filled with self-curing resin to reproduce the shape of the premolar. On the day of autotransplantation, the ankylosed left maxillary central incisor was extracted, and the recipient site was formed using a low-speed hand piece and an oral irrigator, with the donor tooth replica serving as a guide. A closed technique was performed. Because the computed tomography showed that the alveolar bone was thick enough to accommodate the donor teeth. The alveolar bone was removed to create a space of 1 - 2 mm between the replica and the alveolar bone. During the formation of alveolar bone, saline irrigation was used to prevent any damage (Fig. 6). After bone formation was complete at the recipient site, the first premolar, that had been selected as the donor tooth, was extracted; a tooth fracture was prevented using physics forceps (Physics Forceps^®, Goldendent, USA). To prevent PDL tissue necrosis, the roots of the extracted donor tooth were wrapped in saline-soaked gauze pads and a foil wrap. After a retrograde cavity had been formed, retro-filling was carried out using mineral trioxide aggregate (ProRoot MTA^®, Dentsply, USA). Next, the donor tooth was placed in the recipient site, and resin wire splinting to the adjacent teeth was performed using a multistranded wire (Dentaflex^®, 0.45-mm-diameter twist flex wire, DENTAURUM, Germany) (Fig. 7).

The resin wire splint was removed 3 weeks after surgery. At the time of removal, the autotransplanted tooth had grade 1 mobility. Six weeks after surgery, as an additional orthodontic treatment, indirect bracket bonding was performed using fixed appliances. The autotransplanted tooth showed satisfactory alveolar bone recovery on apical radiographs, and no unusual complications occurred during the treatment period (Fig. 8). Orthodontic treatment using fixed appliances was applied to the entire jaw, including the mandible, and satisfactory orthodontic tooth movement and alveolar bone recovery were observed in regular checkups over the period of the following two years. The difference in gingival height in the affected area due to malocclusion was also significantly reduced and the extraction space closed well (Fig. 9).

Ⅲ.DISCUSSION

The goal in the present case was to recover a maxillary anterior tooth that was undergoing ankylosis due to an injury; to this end, autotransplantation of a premolar was carried out.

Numerous studies have been conducted to increase the success rate of tooth autotransplantation. For instance, Andreasen et al.⁷⁾ reviewed autotransplantation procedures performed on 33 teeth, and reported a success rate of 88% and a survival rate of 98%. Krissterson et al.⁸⁾ reviewed autotransplantation procedures carried out on 23 teeth and reported a success rate of 87% and a survival rate of 98%. However, since problems such as ankylosis and root resorption can follow tooth autotransplantation, it may be highly challenging to achieve orthodontic tooth movement after autotransplantation, and prevention of ankylosis is essential to the success of treatment⁹⁾. The patient in the present report developed malocclusion caused by ankylosis after the replantation of an avulsed tooth. As a result, she required tooth autotransplantation and orthodontic tooth movement. While planning the procedure, however, it was necessary to consider multiple factors; for example, the patient’s age, the shape and developmental progress of the dental roots, and the condition of the alveolar bone of the donor and recipient teeth.

In general, mandibular first and second premolars are most highly recommended for maxillary central incisor loss, due to the anatomical shape of their roots¹⁰⁾. The survival rate of single rooted teeth is higher than that of multi-rooted teeth1⁷⁾. Changing the direction of the donor tooth by rotating it 90° helps ensure a better fit if the initial orientation is not possible to achieve¹⁰⁾. However, in the present case, there was no problem in setting the initial direction of the donor tooth, so the procedure was conducted without rotation.

In addition, clinical factors such as patient characteristics, donor teeth, and recipient teeth must also be considered to ensure successful tooth autotransplantation. The younger the patient undergoing the procedure, the higher the success rate; the highest success rates are in patients under 40 years old^10,17). Furthermore, the patient must not have any systemic disorders or harmful habits (e.g. smoking). Patients must have good oral hygiene, and be co-operative during treatment to ensure success in tooth autotransplantation ¹⁰⁾. Since living periodontal ligament (PDL) cells are an important factor in alveolar bone formation, donor teeth must be preserved in a physiological saline solution once outside of the oral cavity. The greater the number of living PDL cells, the better the outcome of autotransplantation. Moreover, the recipient site must be sufficiently deep and wide to accommodate the donor tooth to ensure optimal healing of PDL and pulp tissue, and the more PDL tissue remaining at the recipient site, the better the recovery. To increase the success rate of the procedure, it is recommended that the recipient tooth be extracted on the day of tooth autotransplantation, that tooth autotransplantation be performed within 1 month of the extraction, and that the procedure be conducted by a clinically experienced surgeon^7,9,10).

The developmental progress of the roots of the donor tooth prior to surgery is an important determinant of success in tooth autotransplantation. The best time to perform tooth autotransplantation is when root development is threefourths complete. Tooth autotransplantation performed at this time produces the best results in terms of tooth size and periodontal ligament recovery¹⁾. However, in the present case, root development was near completion in a pre-operative assessment; accordingly, a root canal treatment was performed before the tooth autotransplantation. In this way, the extra-alveolar period of the donor tooth after its extraction on the day of surgery was shortened.

Deep placement in a position below the occlusal level of adjacent teeth should be avoided, if possible, so that orthodontic treatment will not be needed at a later stage⁴⁾. However, in this case, the gingival level and deviation of the adjacent tooth had already occurred and the gingival level could only be recovered through orthodontic extrusion.

Preservation of healthy PDL cells during surgery, as well as good histocompatibility, are important factors in successful tooth autotransplantation¹¹⁾. Several reports have suggested that pre-applying a jiggling force on donor teeth may ease their extraction and reduce root resorption after replantation^12,18,19). This serves to minimize damage to the PDL of the donor tooth. In the present case, extraction was performed one week after a separation ring (DENTURUM, Germany) had been applied between the donor tooth and the adjacent teeth. Physics forceps was used to prevent tooth fracture during extraction. Specifically, these forceps acted as a lever during the extraction of a tooth from its dental socket. Unlike more conventional forceps, physics forceps only require a single point of contact on a tooth, and use a small, uniform rotational force—applied using wrist movement—rather than a twisting force to extract a tooth. Therefore, tooth fracture can be prevented and periodontal ligaments well-maintained by their use physics forceps^17,19). In addition, the extra-alveolar time of the donor tooth was reduced through the production of a replica, and PDL damage was minimized by securing an ideal amount of space between the donor tooth and the recipient site. Due to the development of computed tomography, the shape of the donor tooth can be copied through CAD/CAM or by creating a wax-up. In this case, the replica was made using the wax-up method, and the extra-alveolar time of the donor tooth was minimized^3,14).

There have been conflicting reports regarding the splinting period and the timing in which the orthodontic force should be applied. These are both post-operative factors. Splinting lengths reported in the literature have varied widely from one week to two months, and Hamamoto et al.¹⁶⁾ recommend avoiding orthodontic treatment in the first three to six months after surgery. However, a rigid splint that is maintained for a long period of time can increase the risk of ankylosis. For this reason, the patient in the present case report only wore a splint for three weeks, starting in the sixth post-operative week; an orthodontic force was applied to the transplanted tooth using a nickel-titanium wire.

Application of a stable, biological load immediately after the early recovery period can promote the regeneration of PDL and prevent ankylosis^4,9,12). Transplanted teeth level the alveolar bone, remove vertical defects, and improve the gingival appearance of incisors. The success of orthodontic treatment following tooth autotransplantation depends on the success of periodontal recovery after the procedure, and the survival of PDL on root surfaces may play a pivotal role in this regard. The present patient required vertical adjustment and retraction of the transplanted tooth. For this reason, efforts to prevent PDL damage were made before, during, and after tooth autotransplantation. Through a series of careful procedures, the number of teeth requiring extraction was reduced, and the ankylosed incisor was replaced with a healthy, good-looking, and functional tooth.