# Digital Design of Minimally Invasive Endodontic Access Cavity
## 4 Discussion
\begin{table}
\begin{tabular}{c c} \hline
**Group** & **Mean Values and Standard Deviations** \\ \hline X1 & 3.6\({}^{\circ}\) (\(\pm\)0.4) \({}^{\text{a}}\) \\ \hline X2 & 3.4\({}^{\circ}\) (\(\pm\)0.3) \({}^{\text{a}}\) \\ \hline Y1 & 7.1\({}^{\circ}\) (\(\pm\)0.8) \({}^{\text{b}}\) \\ \hline Y2 & 7.2\({}^{\circ}\) (\(\pm\)0.7) \({}^{\text{b}}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Deviation from planned view: different superscript letters indicate statistical significance. Table 1 showed that DNS allowed a significantly higher accuracy (\(p<0.05\)) when compared to X2 and Y2, but no significant difference with Y1. Even if X1 and X2 PEACs were found to be more accurate, these differences may not be so clinically relevant due to the low recorded angles. On the contrary, the X2 and Y2 planning seemed to be almost coincident, and the two groups showed similar results in terms of accuracy; theoretically they could be considered as best options providing both a minimally invasive and an efficient approach. They allowed the preparation of a small \"straight line\" cavity with a valid access to the MB1 canal, by designing a straight insertion of the rotating instrument. In terms of risk of weakening of tooth structure, X2 is probably the less invasive PEAC, but these assumptions should be validated by further experimental studies. Overall, DNS was found to be very helpful in following the planned trajectory, with very small deviations recorded: it is not easy to do the same with free-hand instrumentation, especially when the access cavity is angulated. The differences among PEACs in the present study may be related to the fact that endodontists usually visualize and execute access cavity with a bucco-lingual image of the canal trajectory (the one used for X1 and Y1), while the disto-lingual image of canal trajectory has never been taught and it is commonly not used by clinicians. Therefore, their experience is limited to most common periapical views, which may preclude the visualization of peculiar angulation or position of the coronal orifices. In the present study artificial 3D replicas were used, instead of extracted teeth. Since the aim was to evaluate cavities with different pathways, the use of identical models allowed to standardize the internal and external anatomy and avoid all possible bias related to unusual anatomy or location of canals, width of the occlusal surfaces and the thickness from occlusal surface to canal orifices. Studies on natural teeth, could give indications on the possibility of get this conservative type of access to all canals in most molar cases. When comparing these results with those provided by a study on guided implantology [22; 23], we found a slight increase in the percentage variations of the angles: this could be a result that both burs and access cavities are much smaller in endodontics. However, 2% variation in a 1.50 mm wide implant cavity leads to a 0.03 mm clinical error, while a 4% variation in a 0.50 wide endodontic cavity leads to a smaller 0.01 mm error. In both cases, such variations can be considered very small and allow very precise performance of the planned cavities, both in implantology and endodontics. A future prospect is the creation of customized access cavities for each tooth, by digitally planning the best strategy for each canal, previewing it through a graphic interface, and deciding--depending on the case--which cavity is best, according to above-mentioned concepts of \"biologic savings\" and \"straight line access\" [24; 25; 26]. The present preliminary study will lead to a series of studies analyzing in vitro, the influence of each cavity in determining instrumentation stress and tooth weakening, if any. The Navident system will not only allow to plan such treatments, but also to execute them precisely and predictably.