## 2 Case Report
There is no issue regarding where to place the sleeve for the pin because the presurgical scan is taken immediately prior to surgery and the postoperative scan is taken just after surgery thus allowing one to place the pin in the exact same hole performed during the presurgical scan. There is no need to place in a particular place in the preoperative scan since the latter represents the reference for the second one, the only issue is to have the pin positioned in the same spot in both scans as explained above. Regarding the distal support points as one may notice in Figure 4D it is possible to improve precision by relying the occlusal rests of the resin index with some Duralay (Reliance Dental, Worth, IL) to improve the fitting between the digital index and the occlusal rest seats of supporting posterior teeth. Figure 3: Preliminary digital impression. (**A**) Maximillary preliminary digital impression. (**B**) Mandibular preliminary digital impression. Figure 4: Design of the lower acrylic resin jig. (**A**) The digital lower scan is imported into Autodesk Meshmixer (Autodesk Inc., San Rafael, CA, USA) to design the digital index which will later serve to superimpose mandibular preoperative and postoperative scans. (**B**) The inferior digital index is designed in order to obtain stability thus proving occlusal clearance on all teeth but the lower second molars and providing the space for a frontal median stabilization pin. (**C**) Cubic and tetrahedral reference points are positioned to ease the match between the preoperative and the postoperative scan. (**D**) The digital index was printed using a monochromatic LCD 3D printer (Liquid Crystal Precision 1.5, Photometric, Phoenix, AZ, USA) with XY resolution equal to 47 \(\upmu\)m and Anycubic Dental Non-Castable UV Resin (Anycubic Shenzhen, Guangdong, China). In the picture it can be seen on the lower 3D printed model (Form 3B, Somerville, MA, USA) that was printed using Gray Model Resin (Form 3B, Somerville, MA, USA) with the same printing resolution. The guided anchor pin sleeve (Nobel Biocare AB, Gothenburg, Sweden) was secondarily fixed with the dental composite in the anterior hole left for this purpose in Mesh Mixer computer aided design (see Figure **C**). Figure 5: The lower preoperative impression taken immediately before surgery with the resin jig. If the existing dentition lacks one or more distal teeth that can be maintained even after surgery (second and third lower molars) to be used as support points, one or more anchor pins should be used instead to provide sufficient stability for the digital index. A median anterior anchor pin is always needed to provide anterior stability. Geometrical patterns are to be included in the digital index in order to provide sufficient reference points to superimpose preoperative and postoperative impressions. In this patient only the anterior pin was needed. In the second appointment, immediately prior to surgical intervention and right after the local anesthesia, the digital index was placed in the lower jaw. Lower impression was taken (Figure 5) and it was superimposed over the prior lower scan to keep the information regarding vertical dimension of occlusion in centric occlusion recorded on the existing dentition during the first appointment using an occlusal wax (Miltex beauty pink xhard, York, USA) to stabilize the maxilla-mandibular relationship (Figure 6). Extraction of all teeth was performed apart from the lower second molars that did not impair implant placement and served as distal support points for the digital index. Implants were inserted and scan abutments and the lower digital index was placed to take the postoperative digital impressions (Figure 7). Figure 6: Frontal view of the three-dimensional relationship (**A**) between the maxillary and the mandibular digital impressions recorded during the first visit and (**B**) the lower presurgical scan superimposed over the lower impression. Figure 7: Scan abutments and the lower digital index placement. (**A**) Scan abutment placement after implants insertion.