# Prototype of Augmented Reality Technology for Orthodontic Bracket Positioning: An In Vivo Study
## 4 Discussion  
The ideal bracket position is vital for efficient orthodontic treatment. Many studies have discussed ideal positioning since 1976. [PERSON] introduced the bracketing technique of the straight wire concept, which involved placing the bracket up or down until the middle of the bracket slot base is at the same height as the mid-point of the clinical crown. [7; 8; 9]  
In the current study, we used initial digital modelling to predict the final setup to define each volunteer's bracket position and measure the bracket height before transferring to the AR-assisted bracket navigation system. Various methods have been proposed for ideal bracket positioning [2; 12; 13; 18; 19; 20]. They can be divided into direct and indirect bonding techniques. The direct bonding technique uses a gauge to directly measure the ideal bracket positions in oral cavity. This technique has the advantages of no interference with the guiding tray, more acceptable for crowded teeth, and immediately adjustable bracket position. However, the direct bonding technique is influenced by the measure scale of gauge, tooth morphology, and operator's experience. The indirect bonding technique uses a transfer tray to transfer the brackets into the intra-oral teeth. They are divided into 2 stages: The lab stage, which involves locating the bracket position on the stone model and fabricating a transfer tray to duplicate the bracket position, and the clinical stage, which involves setting the tray with brackets into the patient's mouth. Therefore, the indirect bonding technique overcomes the limitation of the limited view in the oral cavity. Nevertheless, placement errors may occur depending on the transfer tray material, operator's finger pressure, and technician skills. Several researchers have designed many types of transfer trays, including polyvinyl siloxane trays, vacuum-formed trays, 3-dimensional-printed stent, and transfer jigs [11; 13; 18; 21; 22; 23]. AR-assisted bracket navigation system combines the advantage of both bonding techniques and overcomes the disadvantage. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multirow{2}{*}{**Direction**} & \multirow{2}{*}{**Sample Size**} & \multirow{2}{*}{**Medium \(\pm\) IQR (mm)**} & \multirow{2}{*}{**Sample Size**} & \multicolumn{2}{c}{**Novice**} & \multicolumn{2}{c}{**Expert**} \\ \cline{5-8}  & & & & & **Medium \(\pm\) IQR (mm)** & & **Medium \(\pm\) IQR (mm)** & \\ \hline Boone & X & 62 & 0.32 \(\pm\) 0.18 & 31 & 0.28 \(\pm\) 0.09 & 0.36 \(\pm\) 0.21 & 0.495 \\ AR & X & 62 & 0.26 \(\pm\) 0.11 & 31 & 0.27 \(\pm\) 0.16 & 0.25 \(\pm\) 0.10 & 0.942 \\  & & **_p_ + value_** & 0.414 & & 0.92 & 0.21 & \\ \hline Boone & Y & 62 & 0.64 \(\pm\) 0.37 & 31 & 0.90 \(\pm\) 0.06 & 0.40 \(\pm\) 0.29 & \textless{}0.001 \\ AR & Y & 62 & 0.35 \(\pm\) 0.15 & 31 & 0.51 \(\pm\) 0.24 & 0.29 \(\pm\) 0.08 & \textless{}0.001 \\  & **_p_ + value_** & \textless{}0.001 & & \textless{}0.001 & & \textless{}0.05 & \\ \hline \hline \end{tabular}  
*: Mann-Whitney U test; + Wilcoxon Signed-Rank Test; augmented reality (AR), AR-assisted bracket navigation system; X: Mesiodistal direction (mm); Y: Incisoginiyi direction (mm); IQR: Interquartile range.  
\end{table} 
Table 1: Differences in the distance between the simulated and actual post-operative bracket positions. [PERSON] et al. (2012) used digital volume tomography of a computed tomography scan to overlay the orthodontist bonded procedure video image by using an AR system in vitro, and the average error with their technique was 2.1 mm [24]. By contrast, the average error in our study with novice and expert orthodontists was 0.51 mm and 0.29 mm, respectively, indicating significantly high accuracy. Our study has clinical significance because the clinically acceptable placement error is 0.5 mm. Furthermore, we used digital modeling with an intra-oral scanner to determine the bracket position, thus avoiding any radiation exposure due to computed tomography, unlike [PERSON] et al. 's study.