# Surgical Repositioning of an Inverted Developing Incisor Assisted by 3D Technology
## 3 Discussion  
The permanent central incisor can be impacted during the mixed dentition period. Calcification of the central incisor occurs at age 3 to 4 months and erupts at 6 to 9 years. Treatment of the impacted central incisor is important for facial esthetics [12]. Treatment options for impacted teeth with ectopic eruption pathways include surgical exposure and orthodontic traction, surgical repositioning, or extraction [13]. Determination of the treatment method is based on the position of the impacted tooth, its angulation, stage of root development, and presence of root dilaceration [14]. Forced eruptions have several issues such as long-term treatment, lack of attachment gingiva, and need for additional root canal therapy in dilacerated roots. Occasionally, forced eruption cannot be applied to cases of teeth that are too deeply impacted or exhibit complete vertical inversion. In that case, extraction may be considered but surgical repositioning can be selected as an alternative treatment option. The advantage of surgical repositioning is that the tooth position can be corrected by a single surgical procedure. The mobilization of teeth in the intra-alveolar bone is easy in developing tooth germs. It has been reported that relocated tooth germs exhibit root development and normal eruption [4]. Treatment at the beginning of root growth redirects the Hertwig's epithelial root sheath, inducing the root to grow in the proper direction against the long axis of the crown, leading to normal root development [15]. Since the impacted tooth has growth potential even after early treatment, its root can continue to grow in a normal position [16]. However, damage to the tooth or adjacent surrounding tissues is unavoidable. For example, damage to the dental pulp, periodontal ligament, and Hertwig's epithelial root sheath can cause pulp necrosis, inflammatory or replacement resorption of the dental root, interruption of root development, and ankylosis [17]. In this respect, repositioning of the inversely impacted teeth to the forward direction at the early stage of root growth has the advantage of facilitating revascularization and inducing root \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Pre-op** & **Post-op** \\ \hline Location of tooth & Inverted (malpositioned) & Forward (normal position) \\ Expectation for self eruption & Impossible & Possible \\ Related pathology & Possible & Expected not to occur during \\ Root development & May be disturbed & Showed normal development \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Postoperative results compared to preoperative condition. Figure 4: (**A**) Immediate postoperative panoramic view; (**B**) Postoperative 3 months panoramic view, arrow: repositioned central incisor, arrowhead: developing root. growth in the correct direction. In this case report, we attempted to solve the issue of an inversely impacted central incisor at the same time as extraction of the supernumerary tooth. It was expected that root growth would be limited due to insufficient space for growth if only the supernumerary tooth was removed. We evaluated the positional interference relationship with the adjacent permanent developing teeth and obtained sufficient space for replantation by moving the tooth on the 3D virtual image obtained from the CBCT data before surgery. The tooth can be placed into the ideal position through the virtual surgery. In the actual surgery, the tooth was repositioned by removing the palatal bone so that the developing root could remain in the bony socket as much as possible. The actual tooth was wrapped in saline-soaked gauze to prevent drying. The tooth replica was used to remove bony interference on behalf of the real tooth. We made efforts to reduce the actual operation time by evaluating the amount and location of bone to be removed in advance. When replanting a tooth, the possibility of tooth damage may increase as the repetitive fitting and the time outside the socket increases.