International Journal of Computerized Dentistry, 04/2022

Purpose: Creating wax-ups of missing teeth for backward planning in implant surgery is a complex and time-consuming process. To facilitate implant-planning procedures, the automatic generation of a virtual wax-up would be useful. In the present study, the reconstruction of missing teeth in partially edentulous patients was performed automatically using newly developed software. The accuracy was investigated in order to test its clinical applicability. Materials and methods: This study presents a new method for creating an automatic virtual wax-up, which could serve as a basic tool in modern implant-planning procedures. First, a statistical shape model (SSM) based on 76 maxillary and mandibular arch scans from dentally healthy individuals was generated. Then, artificially generated tooth gaps were reconstructed. The accuracy of the workflow was evaluated on a separate testing sample of 10 individuals with artificially created tooth gaps given as a median deviation, in millimeters. Scans of three clinical cases with partial edentulism were equally reconstructed using the SSM and compared with the final prosthodontic work. Results: The reconstruction of the artificial tooth gaps could be performed with the following median reconstruction accuracy: gap 21 with 0.15 mm; gap 27 with 0.20 mm; gap 34 with 0.22 mm: gap 36 with 0.22 mm; gaps 12 to 22 with 0.22 mm; gaps 34 to 36 with 0.22 mm. A scenario for an almost edentulous mandible with all teeth missing except teeth 33 and 43 could be reconstructed with a median reconstruction accuracy of 0.37 mm. The median tooth gap deviation of the SSM-based reconstruction in clinical cases differed from the final inserted prosthodontic teeth by 0.49 to 0.86 mm in median. Conclusion: A first feasibility of creating virtual wax-ups using an SSM could be shown. Artificially generated tooth gaps could be reconstructed close to the original with the proposed workflow. In the clinical cases, the SSM proposes an anatomical reconstruction, which does not yet consider prosthodontic aspects. To obtain clinical use, contact with antagonist teeth must be considered and more training data must be implemented. However, the presented method offers a fast and viable way for the approximate placement of missing crowns. This could be used in a digital planning workflow when implant position must be determined. (Int J Comput Dent 2022;25(4):349–0; doi: 10.3290/j.ijcd.b2599407) Keywords: statistical shape model, virtual wax-up, partial edentulism, accuracy, implant planning

Aim: There is controversy in the literature regarding clinical outcomes of CAD/CAM laminate veneers. The aim of the present study was to assess the impact of different levels of CAD expertise and different software programs on the reliability and reproducibility of digital wax patterns of laminate veneers and single crowns. Materials and methods: The present preliminary in vitro study was performed on 10 prepared maxillary central incisors available in dental study models. Of the total, five central incisors were prepared with shoulder finish lines for single crowns, whereas the other five underwent incisal shoulder preparation for laminate veneers. The models were scanned using an intraoral scanner. Four dentists (group DENT) and four CAD dental technicians (group CAD) with expertise in different software programs performed digital diagnostic waxing on all prepared teeth. The resulting digital wax patterns (n = 80) were exported as standard tessellation language (STL) files and superimposed on gold standard digital wax patterns (obtained from the original shape of the teeth before preparations). 3D mesh deviations at the cervical margins as well as distal, mesial, and incisal/palatal surfaces between each STL and the gold standard digital wax patterns were calculated in millimeters using a CAD software program. The mean time required by each operator to perform digital waxing was also recorded. Paired comparisons between groups DENT and CAD as well as between nondental and dental software programs were performed for the crowns and laminate veneers using the Wilcoxon signed-rank and paired t tests (α = 0.05). Results: For group DENT, median deviations for single crowns were 0.15 mm (range: 0.08 to 1.05 mm) and for laminate veneers they were 0.15 mm (range: 0.08 to 0.76 mm). For group CAD, median deviations for single crowns were 0.16 mm (range: 0.09 to 0.73 mm) and for laminate veneers they were 0.10 mm (range: 0.06 to 0.53 mm). The Wilcoxon signed-rank test revealed a statistically significant difference between groups DENT and CAD (P = 0.041) and between the software programs (P = 0.029) for laminate veneers, but not for single crowns (P > 0.05). Furthermore, mean times required for group CAD and for dental software programs were significantly shorter than those for group DENT (P = 0.001) and for nondental software programs (P = 0.001), respectively. Conclusion: Within the limitations of the present study, the findings suggest that CAD expertise and the software program significantly affect digital wax patterns for laminate veneers, but not for single crowns. (Int J Comput Dent 2022;25(4):361–0; doi: 10.3290/j.ijcd.b3555819) Keywords: computer-aided design, intraoral scanning, digital waxing, diagnostic wax-up, software, standard tessellation language (STL)

Aim: A prospective study was conducted to evaluate the accuracy and complications of 3D-printed patient-specific surgical guides and plates that were designed and finished in-house. Materials and methods: Eighteen patients who required advancement genioplasty, with or without concomitant orthognathic surgery, were enrolled in the study. Virtual surgical movements were simulated using the patient’s CBCT scans, and the computer-aided designing of patient-specific surgical guides and fixation plates was performed in the authors’ department. CBCT scans were taken at 1-month postoperatively, and stereolithographic models of the preoperative virtual plan and the postoperative CBCT scan were registered. Part comparisons were performed to assess the accuracy of the movements. The median, minimum, and maximum differences were measured. Two landmarks, the Menton (Me) and Pogonion (Pog), were also used to compare the differences locally. Results: The median deviation for the 18 cases was 0.19 mm. The median deviation at the Me and Pog were 0.67 and 0.41 mm, respectively. There was no significant correlation between the surgical movement of < 7 mm advancement and the transfer accuracy (P = 0.77). No adverse events or complications were reported within the postoperative 6-month period. Conclusion: The protocol of self-designed 3D-printed patient-specific surgical guides and plates provided an accurate method to transfer the virtual surgical plan to the operating theater. (Int J Comput Dent 2022;25(4):369–0; doi: 10.3290/j.ijcd.b2599791) Keywords: genioplasty, patient-specific implants, chin, patient-specific plates, computer planning, 3D printing

Aim: The main objective was to evaluate the accuracy of dynamic navigation-guided surgery (DNGS) for implant positioning performed by a novice operator. The secondary objectives were to analyze the operator’s learning curve and identify possible complications deriving from the technique. Materials and methods: Twenty-five implants were placed in eight partially edentulous human heads. Preoperative CBCT scans were imported to planning software to determine the implant positions. Implants were placed using a dynamic navigation system. Postoperative CBCTs were superimposed onto the implant planning images. Discrepancies between the virtually planned implant positions and the postoperative positions were evaluated by measuring horizontal platform deviation, apex deviation, apicocoronal (vertical) deviation, and angular deviation. Results: Mean platform, apex, vertical, and angle deviations were 1.55 ± 0.81 mm, 2.45 ± 0.84 mm, 1.59 ± 0.70 mm, and 5.56 ± 4.03 degrees, respectively. No significant differences were found between the maxilla and mandible or between anterior and posterior sites. A flat learning curve was observed, with the exception of the implant platform, where a tendency toward improvement in accuracy was observed between the 8th and the 17th implant placed. No complications were reported. Conclusions: Based on the results of a study performed by a novice operator on a cadaveric model, DNGS allows accurate implant placement within a 2-mm safety margin in terms of implant platform and vertical positions, and a 3-mm margin in apical vicinities. The technique requires practice to learn the required eye–hand coordination. (Int J Comput Dent 2022;25(4):377–0; doi: 10.3290/j.ijcd.b2588207) Keywords: computer-assisted surgery, computer-guided surgery, dynamic navigation, accuracy, dental implant, dental navigation

Aim: To evaluate the accuracy of tridimensional (3D)-printed guide-assisted flapless cortical bone micro-osteoperforations (MOPs) in the anterior mandible on a cadaver model. Materials and methods: Five human cadaver heads with complete dentition in the anterior mandible were used in the present study. Preplanning CBCT and intraoral surface scans were obtained. After alignment, drilling sites in the interradicular areas were planned from canine to canine, and a surgical guide was printed. The drilling was performed and a postprocedure CBCT scan was obtained to assess the accuracy of the procedure in relation to the virtual planning. Results: The mean ± standard deviation (SD) mesiodistal interradicular space was 2.67 ± 0.84 mm. The mean ± SD error of the actual drilled hole compared with the planned position of the mesial drill site was 0.66 ± 0.33 mm, and to the distal drill site it was 0.56 ± 0.33 mm. There was a statistically significant difference between the number of times the teeth were hit mesially (10 out of 64 holes) and distally (none). Conclusions: The proposed technique, limited to an ex vivo scenario, provides a valid and reliable method for mandibular MOPs using a 3D-generated surgical guide. However, the risk of damaging adjacent radicular surfaces, particularly in areas with limited mesiodistal interradicular bone, needs to be considered. Further studies should focus on using thinner drills and adding other methods to stabilize the guide. Additionally, by selecting individuals and perforation sites with more mesiodistal interradicular bone, less damage is likely. (Int J Comput Dent 2022;25(4):387–0; doi: 10.3290/j.ijcd.b2599841) Keywords: corticotomy, guided surgery, 3D printing, micro-osteoperforations, accuracy, preorthodontic surgery

Aim: The aim of the present prospective proof-of-concept study was to evaluate the accuracy of 3D orthognathic surgical planning and CAD/CAM splints by comparing planned with actual postoperative outcomes. Materials and methods: Ten patients scheduled for bimaxillary orthognathic surgery to correct a skeletal Class III dentofacial deformity were recruited. All subjects had CBCT scans taken not more than 2 months preoperatively and within the 1-week postoperative period. The distance between six dental landmarks (midpoint of the maxillary and mandibular incisors, mesiobuccal cusps of the maxillary and mandibular first molars) and three intersecting symmetry planes (Frankfort horizontal plane [FHP], midsagittal plane [MSP], and coronal plane [CP]) were measured, and the differences between the virtually simulated and actual postoperative models were computed. The threshold for accuracy was set at 2 mm. Results: Differences between the planned and actual outcomes were analyzed via chi-square tests and two-tailed paired student t tests. The overall mean linear difference for all six landmarks was 0.98 mm. The overall mean linear differences for both maxillary and mandibular landmarks relative to the FHP, MSP, and CP were 1.3, 0.7, and 0.9 mm, respectively. Four cases showed all linear differences of the six landmarks to be < 2.0 mm, while the other six cases had at least one linear difference of > 2.0 mm, the majority of which were in the superior-inferior direction. There were statistically significantly greater inaccuracies in the FHP compared with the MSP and CP (P < 0.05). Conclusion: Most of the linear differences between the simulated and actual outcomes were clinically acceptable. However, greater linear differences were seen in the superior-inferior direction, indicating a greater surgical error in achieving the desired vertical position of the maxillomandibular complex. (Int J Comput Dent 2022;25(4):397–0; doi: 10.3290/j.ijcd.b2599749) Keywords: orthognathic surgery, virtual surgical planning, CAD/CAM, 3D planning, 3D printing, accuracy

Digital tools now enable an effective and efficient workflow even for complex implant-prosthetic restorations such as the immediate restoration of the edentulous maxilla. Planning predictability due to high process reliability, time saving, cost reduction due to shortened therapy sequences, high patient satisfaction due to predictable results, and high patient comfort are the advantages of the digitally supported therapy phases – from digital volume tomography of the bony structures to planning software to CAD/CAM-generated temporaries and prototypes to all-ceramic restorations. However, the use of digital procedures and techniques alone is no guarantee for a successful, indication-appropriate, and patient-specific restoration. In addition to having digital knowledge, the conditio sine qua non for the dental technician team is still analog competence coupled with corresponding experience to be able to interpret the various influencing factors. Using an immediately loaded maxillary restoration as an example, an analog–digital workflow is presented that is geared to surgical, prosthetic, and patient-specific requirements. (Int J Comput Dent 2022;25(4):407–0; doi: 10.3290/j.ijcd.b3555715) Keywords: CBCT, planning software, additive drilling template, PlaneSystem, Comfour system, digital fabrication, digitally supported workflow