# Digital Design of Minimally Invasive Endodontic Access Cavity
## 2 Materials and Methods  
A total of 40 artificial resin upper right first molars (TrueTooth(tm) Replica # 3-001 (DELabs, Santa Barbara, CA, USA)) were randomly divided into 4 identical groups (n = 10), placed in specific silicon material bases acting as an artificial jaw and scanned by using cone beam computed tomography (CBCT) (OP-Maxio 300, Instrumentarium--Kavo, Finland). The initial sample size (n = 40) was calculated by power analysis (\(p\) = 0.05% and 80% interval of confidence).  
A unique code was assigned to each group (X1, X2, Y1, Y2). By using dedicated software for implant planning of the Navident dynamic navigation system (DNS) (ClaroNav, Toronto, Ontario, Canada) the DICOM images of dental replicas were acquired and the planning of the access cavity was virtually performed [19]. For each tooth, a different PEAC was designed to get endodontic access to the MB1 canal, with different locations on the occlusal surface of the tooth (Figures 1 and 2)  
X1: ultra-conservative access cavity planning, on MB1 canal. Performed on the buccal-palatal plane (buccal view) by planning the opening axis coinciding with the coronal third orifice of the canal (green);  
X2: ultra-conservative access cavity planning, on MB1 canal. Performed on the buccal-palatal plane (buccal view) by planning a straight-line access following the axis of the median-apical part of the canal (yellow);  
Y1: ultra-conservative access cavity planning, on MB1 canal. Performed on the mesio-distal plane (mesial view) by planning the opening axis coinciding with the coronal third orifice of the canal. (purple);  
Y2: ultra-conservative access cavity planning, on MB1 canal. Performed on the mesio-distal plane (mesial view) by planning a straight-line access following the axis of the median-apical part of the canal (blue);After the first step (planning), PEACs of each group (Figure 3) were prepared using DNS: the second step was to match the CBCT images with the artificial jaws where replicas were placed, using the Navident \"trace registration\" system. An optical tracer was glued on the artificial jaw; the teeth surfaces were touched in six different points with a tracer instrument that was also tracked by an optical positioning sensor. During this procedure, the DNS software continuously acquired and recorded points on the traced teeth, and then matched with the CBCT data. A final accuracy check was performed to ensure the precision of such a critical match. Last step was handpiece and burs calibration: this allowed DNS to continuously keep tracing and showing in real time on the computer screen the bur's position. Finally, each planned PEAC was then performed by the same skilled operator, using a precision micro endodontic burr (EndoGuide EG1a--SSWhite) and all canals were located with a size 08 manual instrument (Edge Endo, Albuquerque, New Mexico). Then all 3D replicas were scanned again with CBCT to evaluate and compare if inclination of each PEAC corresponded with the planned one (Figures 4 and 5). A virtual line was traced between the central part of occlusal entry point and the center of the cavity reaching the canal orifice. The angulation of this line was compared to the planned one, which was precisely ending in the central part of the orifice, using a virtual goniometer (Figure 4c). Ideally no differences should be present in terms of angulation; the smaller the difference (in degrees) of the inclinations, the more precise the procedure was. Data were recorded and statistically analyzed using ANOVA and Tukey's post hoc tests (SPSS, Inc., Chicago, IL, USA) and statistical significance was set at \(p<0.05\).