Influence of scanning pattern on accuracy, time, and number of photograms of complete-arch implant scans: A clinical study Miguel Gómez-Polo a,*, Rocío Cascos b, Rocío Ortega c, Abdul B. Barmak d, John C. Kois e, Jorge Alonso Pérez-Barquero f, Marta Revilla-León g a Associate Professor Department of Conservative Dentistry and Prosthodontics, Complutense University of Madrid, Madrid, Spain, Director of Postgraduate Program of Advanced in Implant-Prosthodontics, School of Dentistry, Complutense University of Madrid, Madrid, Spain b Student Postgraduate Program of Advanced in Implant-Prosthodontics, School of Dentistry, Complutense University of Madrid, Madrid, Spain c Adjunct Professor Department of Prosthetic Dentistry, School of Dentistry, European University of Madrid, Madrid, Spain d Assistant Professor Clinical Research and Biostatistics, Eastman Institute of Oral Health, University of Rochester Medical Center, Rochester, NY, USA e Kois Center, Private Practice, Seattle, Wash and Assistant Professor, Graduate Prosthodontics, School of Dentistry, University of Washington, Seattle, Wash, USA f Adjunct Professor, Department of Dental Medicine, Faculty of Medicine and Dentistry, University of Valencia, Valencia, Spain g Affiliate Assistant Professor, Graduate Prosthodontics, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, WA; Faculty and Director of Research and Digital Dentistry, Kois Center, Seattle, WA; and Adjunct Professor, Department of Prosthodontics, School of Dental Medicine, Tufts University, Boston, MA, USA A R T I C L E I N F O Keywords: Accuracy Digital impression Intraoral scanner Implant scan Scanning pattern A B S T R A C T Objectives: To measure the influence of scanning pattern on the accuracy, time, and number of photograms of complete-arch intraoral implant scans. Methods: A maxillary edentulous patient with 7 implants was selected. The reference implant cast was obtained using conventional methods (7Series Scanner). Four groups were created based on the scanning pattern used to acquire the complete-arch implant scans by using an intraoral scanner (IOS) (Trios4): manufacturer’s recom mended (Occlusal-Buccal-Lingual (OBL)), zig-zag (Zig-zag), circumferential (Circumf), and novel pattern that included locking an initial occlusal scan (O-Lock group) (n = 15). Scanning time and number of photograms were recorded. The linear and angular measurements were used to assess scanning accuracy. One-way ANOVA and Tukey tests were used to analyze trueness, scanning time, and number of photograms. The Levene test was selected to assess precision (α=0.05). Results: Statistically significant differences in trueness were detected among OBL, Zig-zag, Circumf, and O-Lock regarding linear discrepancy (P < 0.01), angular discrepancy (P < 0.01), scanning time (P < 0.01), and number of photograms (P < 0.01). The O-Lock (63 ± 20 µm) showed the best linear trueness with statistically significant differences (P < 0.01) with Circumferential (86 ± 16 µm) and OBL (87 ± 19 µm) groups. The O-Lock (93.5 ± 13.4 s, 1080 ± 104 photograms) and Circumf groups (102.9 ± 15.1 s, 1112 ± 179 photograms) obtained lower scanning times (P < 0.01) and number of photograms (P < 0.01) than OBL (130.3 ± 19.4 s, 1293 ± 161 pho tograms) and Zig-zag (125.7 ± 22.1 s, 1316 ± 160 photograms) groups. Conclusions: The scanning patterns tested influenced scanning accuracy, time, and number of photograms of the complete-arch scans obtained by using the IOS tested. The zig-zag and O-Lock scanning patterns are recom mended to obtain complete-arch implant scans when using the selected IOS. 1. Introduction The accuracy of definitive implant casts is fundamental for fabri cating complete-arch implant-supported prostheses [1,2]. Dental liter ature has identified different factors that can impact the accuracy of definitive implant casts obtained by using conventional impression methods, namely impression technique [3], implant angulation [4,5], impression material type [6] and its polymerization shrinkage [7-9], and pouring of the dental impression [7-9]. Digital data acquisition technologies such as intraoral scanners * Corresponding author at: Pza. Ramón y Cajal s/n. School of Dentistry, Complutense University of Madrid. Zip Code: 28033, Madrid, Spain. E-mail address: mgomezpo@ucm.es (M. Gómez-Polo). Contents lists available at ScienceDirect Journal of Dentistry journal homepage: www.elsevier.com/locate/jdent https://doi.org/10.1016/j.jdent.2024.105310 Received 9 February 2024; Received in revised form 1 August 2024; Accepted 12 August 2024 Journal of Dentistry 150 (2024) 105310 Available online 15 August 2024 0300-5712/© 2024 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC license ( http://creativecommons.org/licenses/by- nc/4.0/ ). mailto:mgomezpo@ucm.es www.sciencedirect.com/science/journal/03005712 https://www.elsevier.com/locate/jdent https://doi.org/10.1016/j.jdent.2024.105310 https://doi.org/10.1016/j.jdent.2024.105310 http://crossmark.crossref.org/dialog/?doi=10.1016/j.jdent.2024.105310&domain=pdf http://creativecommons.org/licenses/by-nc/4.0/ http://creativecommons.org/licenses/by-nc/4.0/ (IOSs) and photogrammetry systems [10,11] have enabled the obtention of virtual definitive implant casts [12-17]. Similarly, as in conventional methods, it is important to understand the operator- and patient-related factors [18,19] that can reduce the scanning accuracy of intraoral implant scans [20]. Among these factors, scanning pattern or the sequence at which the intraoral scan is acquired is an operator-related factor that can reduce the accuracy of the intraoral implant scans [20]. Limited dental literature has analyzed the impact of different scan ning patterns on the accuracy of complete-arch intraoral implant scans [21,22]. These laboratory investigations demonstrated that if the scan ning pattern is changed, the accuracy of the complete-arch intraoral implant scans would vary [21-25]. However, the optimal scanning pattern for complete-arch intraoral implant digital scans remains un clear, due to heterogeneity among the studies. Additionally, only in vitro investigations are available. Therefore, it is unclear if the scanning pattern would impact in the same manner when complete-arch intraoral implant scans are acquired in the patient’s mouth. Previous studies have analyzed the impact of rescanning and locking an existing scan when performing rescanning techniques on the scan ning accuracy of IOSs [26-29]. The results of these studies demonstrated that rescanning procedures reduce scanning accuracy of IOSs [26-29]. Additionally, locking the existing scan prior to rescanning improves the accuracy of the intraoral scan [26-29]. However, the impact of this locking procedure on the accuracy of complete-arch implant scans is unknown. The purpose of this in vitro study was to evaluate the influence of four different scanning patterns (manufacturer’s recommended (Occlusal-Buccal-Lingual (OBL)), zig-zag, circumferential, and a novel scanning pattern) on the accuracy (trueness and precision), scanning time, and number of photograms of complete-arch implant scans ac quired by using an IOS (Trios 4; 3Shape A/S, Copenhagen, Denmark). The present study analyzed the accuracy of a novel scanning pattern that included locking an initial occlusal scan for acquiring the complete-arch implant scan. This scanning strategy aims to improve implant digital scańs accuracy by avoiding the stitching procedure across the complete arch. It will be further described in the Material and Methods section. The null hypotheses were: 1, that there would be no trueness discrep ancies between the complete-arch intraoral implant digital scans ac quired with different scanning patterns; 2, that there would be no precision discrepancies between the complete-arch intraoral implant digital scans acquired with different scanning patterns; 3, that there would be no difference in the scanning time between the complete-arch intraoral implant digital scans acquired with different scanning patterns; and 4, that there would be no difference in the number of photograms between the complete-arch intraoral implant digital scans acquired with different scanning patterns. 2. Materials and methods The protocol of the present investigation was reviewed and approved by an ethical committee (22/645-E). The clinical study involved the collection of complete-arch intraoral implant scans with different scanning strategies. The inclusive criteria included an individual older than 18-years in good medical conditions or with mild systemic disease (ASA Type I or II). Additionally, the individual should have between 4 and 8 implants in the edentulous maxillary or mandibular arch in healthy conditions. Patients with limited opening or with peri‑im plantitis were considered as not eligible for the present investigation. Screening procedures were completed by an experienced restorative dentist. The selected individual volunteered to participate on the present study and a signed informed consent was obtained. A patient with 7 dental implants placed in the maxillary arch was selected. The dental implants were located in the left second molar, right and left first premolar, left canine, right and left lateral incisor, and right first molar positions. Each implant had an implant abutment (Trans epithelial Abutment IC 3.5/4.1 GH3; Avinent Implant System, Barcelona, Spain). The patient had a maxillary screw-retained interim implant-supported prosthesis. A conventional maxillary complete-arch implant impression was obtained. First, the implant-supported interim prosthesis was removed, and a brand new implant impression abutment was hand-torqued on each implant abutment (Impression Coping Open Tray Transepithelial 4.8 Non-Eng; Avinent Implant System, Barcelona, Spain) (Fig. 1A). The preliminary conventional impression was poured following conven tional methods. Then, an implant abutment analog (Transepithelial implant analog model; Avinent Implant System) was positioned on each implant impression abutment. Tissue moulage (Gi-Mask; Coltene, Altstätten, Switzerland) and Type IV dental stone (GC Fujirock EP; GC, Lucerne, Switzerland) with a setting expansion of 0,09 % were used to pour the impression. The dental stone was mixed with water (22 mL of water per each 100 g of dental stone) under vacuum for 30 s, as per manufacturer recommendations. A splinting framework was milled in a polymethyl methacrylate material (CAD/CAD Idodentine disk; Unidesa, Madrid, Spain) by using an additive manufacturing technology (Micro lay Versus 385; Microlay, Madrid, Spain) (Fig. 1B) [30,31]. Addition ally, a custom tray was manufactured using light photopolymerizing material (Kiero Planchas Tray; Kuss dental, Madrid, Spain). A brand new implant impression abutment was then hand torqued on each implant abutment (Impression Coping Open Tray Transepithelial 4.8 Non-Eng; Avinent Implant System) following the manufacturer’s recommendations, for acquiring the definitive implant impression. The printed framework was connected to the implant impression abutments by using photopolymerizing resin (Conlight; Kuss dental) (Fig. 1C). After the complete polymerization of the resin, the custom open tray was used to obtain the polyether impression (Impregum; 3 M ESPE, Bayern, Germany) with an elastic recovery of 98,7 %. Lastly, after the poly merization of the polyether material, the impression was removed from the patient’s mouth. The definitive impression was poured following the same methodology as the preliminary impression. The definitive implant stone cast was kept at 23 ◦C for 48 h (Fig. 1D). The definitive implant stone cast was digitized by using a laboratory scanner (E4 Desktop Scanner; 3Shape A/S) (accuracy: 4 µm) [32]. The scanner was previously calibrated as per manufacturer’s instructions. A brand-new implant scan body (ISB) (transepithelial scan body 2800; Avinent Implant System) was positioned and tightened to 10 Ncm by using a torque wrench following the manufacturer’s recommendations on each implant abutment of the definitive implant cast. The implant scan body geometry bevel feature was oriented towards the lingual surface [33]. Then, the laboratory scan was acquired. The standard tessellation language (STL) file was exported. A dental computer-aided design (CAD) software program (Dental CAD 3.1, Rijeka; Exocad GmbH, Darmstadt Germany) was used to design an implant-supported bar. First, the STL file of the digitized definitive implant stone cast was imported. The virtual definitive implant cast was obtained by aligning the CAD object of the ISB with each ISB of the STL file. Subsequently, the CAD tools were used to design an implant- supported bar (Fig. 2A). The bar designed was used to fabricate a mil led (PrograMill PM7; Ivoclar Vivadent, Zurich, Switzerland) titanium grade 5 (Colado CAD Ti5 Disc; Ivoclar Vivadent) implant-supported bar (Fig. 2B). The fit of the implant-supported bar was checked in the definitive implant stone cast and patient’s mouth by using the Shef field’s test (Fig. 3). Periapical radiographs were obtained. Four groups were created based on the scanning pattern used to acquire the complete-arch intraoral implant scan by using an IOS (Trios 4, v.22.2 3Shape A/S): scanning pattern recommended by the IOS manufacturer for scanning completely dentate patients (OBL group), zig-zag scanning pattern (Zig-zag group), circumferential scanning pattern (Circumf group), and a novel scanning pattern that included locking the initial occlusal scan (O-Lock group) (n = 15). The IOS selected was previously calibrated by using the manufacturer’s recom mended protocol [34]. A brand-new ISB (transepithelial scan body 2800; Avinent Implant System) was placed on each implant abutment of M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 2 the patient by following the manufacturer’s recommendations [35]. The ISBs were not splinted. Additionally, the ISBs were maintained in the same position until all the data acquisition procedures of the same group were completed. Sample size was determined based on previous studies with similar methodology [21,36-38]. All the intraoral digital implant scans were recorded by a restorative dentist with more than 10 years of previous experience handling IOSs (M.G-P) [38,39]. Intraoral implant scans were captured in a room without windows and a dental chair [40,41]. Ambient lighting illumi nation at the patient’s mouth was 1000-lux [42,43] measured by using a luxmeter (LX1330B Light Meter; Dr. Meter Digital Illuminance, Union City, USA). The complete-arch intraoral implant scans always started on the implant positioned in the right second molar of the patient for all subgroups. Additionally, the palate was not included in the scans, as its inclusion does not significantly impact the accuracy of complete-arch intraoral images [44]. Rescanning procedures were avoided [24,28, Fig. 1. Conventional maxillary complete-arch implant impression procedures. A, Implant impression abutments placed. B, Splinting framework. C, Implant impression abutments joined to the splinting framework. D, Definitive implant cast. Fig. 2. A, Design of implant-supported bar on the virtual definitive implant cast. B, Milled implant-supported bar. Fig. 3. Clinical evaluation of the milled titanium implant-supported bar. A, Maxillary right quadrant. B, Maxillary left quadrant. M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 3 29]. The scanning time and number of photograms for each specimen were registered, as provided by the software program of the IOS selected. In the Circumf group, the scan stared on the occlusal surface of the ISB positioned on the right first molar, which was then completely scanned by moving the IOS in a circular motion around the circumfer ence of the ISB. Next, in an anterior movement towards the contralateral ISB, the remaining ISB were digitized in a similar circular circumfer ential motion [45] (Fig. 4A). In the O-Lock group, the intraoral scan started on the occlusal surface of the ISB positioned on the right first molar. Then, the occluso-lingual surfaces of the ISBs were scanned towards the contralateral ISB. The objective is to record as much ISBs surface as possible including the smaller number of photograms. This is the reason to perform the first movement by the inner part of the arch, trying to the reduce the accu mulation of inaccuracies due to the stitching. [46,47] Subsequently, the scanning process was stopped, and the ISB surfaces registered were locked by using the “lock” tool of the IOS software program [29]. It aims to avoid the modification of the ISBśpositions during the remaining scanning procedure, The second step started in the registered surface of the ISB positioned in the right first molar. From this point, the IOS was moved by the interproximal and vestibular surfaces until the complete record of the ISB (Fig. 4B). Then, the scanner advanced, recording the soft tissues and the entire surfaces of all the ISBs. In the OBL group, the scanning pattern started on the occlusal surface of the ISB positioned on the right first molar and moved towards the occlusal surface of the ISB positioned on the left second molar. Then, the IOS was rotated towards the buccal surface, and the buccal surfaces from the ISB positioned on the left second molar towards the right first molar were digitized. Afterwards, the IOS was rotated towards the lingual surface, and the lingual surfaces from the ISB located on the left second molar to the right first molar were scanned (Fig. 4C). This procedure was repeated until specimens were captured. In the Zig-zag group, the scan started on the occlusal surface of the ISB positioned on the right first molar, then moving the IOS in a zig-zag motion towards the contralateral ISB, the occlusal, buccal, and lingual surfaces were digitized [48-50] (Fig. 4D). The digitized definitive implant cast (reference STL file) was used as a reference to measure the discrepancy with the experimental scans obtained among the different groups tested. The reference STL file was imported into a reverse engineering software program (Geomagic Con trol X; 3D Systems, Rock Hill, USA). A CAD cylinder geometry was aligned with each ISB of the reference file using the best fit technique [51]. The longitudinal axis of each ISB was located, followed by marking the z-plane positioned on the most apical surface of each ISB. The intersection between the longitudinal axis and z-plane of each ISB was determined as the measurement point. Linear and angular measure ments among the seven ISBs were calculated (Fig 5A and B). The same procedures were completed on each experimental scan. The linear and angular measurements obtained on the reference file was used to calculate the discrepancies with each experimental scan. The 6 ISB linear and angular discrepancies were averaged per scan before aver aging the 15 scans for each group. Trueness was defined as the linear and angular discrepancies between the reference and experimental scans [52,53]. Precision was described as the linear and angular variations per each group. It was determined by the standard deviation (SD) [52,53]. The Kolmogorov-Smirnov test was employed to evaluate the normality of the sample for each variable. These tests revealed that the linear and angular discrepancies, scanning time, and number of photo grams data were normally distributed (P > 0.05). (Table 1) One-way ANOVA, followed by the pairwise comparison Tukey tests were used to analyze the linear and angular trueness, scanning time, and number of photograms data. The Levene test was used to analyze the linear and angular precision. The statistical analysis was performed by using a statistical software program (IBM SPSS Statistics for Windows, v26; IBM Corp) (α = 0.05). 3. Results The trueness and precision values, scanning time, and number of photograms obtained among the groups tested are presented in Table 2. Regarding linear trueness, one-way ANOVA showed significant linear trueness differences among the groups tested (df = 3, MS=0.00183673, F = 6.79, P < 0.01) (Table 3). Tukey test revealed significant linear trueness discrepancies among the groups tested, being the Circumf and O-Lock groups (P < 0.01) and OBL and Zig-zag groups (P < 0.01) significantly different from each other (Fig. 6A) (Table 4). Hence, the zig-zag and O-Lock groups had the best linear trueness among the groups Fig. 4. Scanning patterns tested. A, Circumferential. B, O-Lock. C, OBL. D, Zig-zag. M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 4 tested. However, Levene test revealed no difference on the linear pre cision values among the groups tested (P = 0.34) (Table 5). Regarding angular trueness, one-way ANOVA showed significant angular trueness differences among the groups tested (df = 3, MS = 0.42383855, F = 14.59, P < 0.01) (Table 6). Tukey test revealed sig nificant angular trueness discrepancies among the groups tested, being the Circumf and OBL groups (P < 0.01), Circumf and Zig-zag groups (P < 0.05), O-Lock and OBL groups (P < 0.01), O-Lock and Zig-zag groups (P < 0.01), OBL and Zig-zag groups (P < 0.001) significantly different from each other (Fig. 6B) (Table 7). Thus, the zig-zag group obtained the best angular trueness among the groups tested. However, Levene test revealed no difference on the precision values among the groups tested (P = 0.25). (Table 8) Regarding scanning time, one-way ANOVA demonstrated significant scanning time differences among the groups tested (df=3, MS=4694.15556, F = 14.74, P < 0.01) (Table 9). The Tukey test showed significant scanning time differences among the groups tested, being the Circumf and OBL groups (P < 0.01), Circumf and Zig-zag groups (P < 0.01), O-Lock and OBL groups (P < 0.01), O-Lock and Zig-zag groups (P < 0.01) significantly different from each other (Fig. 6C) (Table 10). Therefore, the O-Lock group obtained the lowest scanning time among the groups tested. Regarding the number of photograms, one-way ANOVA revealed significant differences in the number of photograms across the sub groups tested (df = 1, MS = 221,512.222, F = 9.40, P < 0.01) (Table 11) Tukey test showed significant differences in the number of photograms between the groups tested, being the Circumf and OBL groups (P < 0.05), Circumf and Zig-zag groups (P < 0.01), O-Lock and OBL groups (P < 0.01), O-Lock and Zig-zag groups (P < 0.01) significantly different from each other (Fig. 6D) (Table 12). Therefore, the O-Lock group ob tained the smallest number of photograms among the groups tested. 4. Discussion Based on the results obtained, the scanning patterns tested signifi cantly impacted the scanning trueness, scanning time, and number of photograms of the complete-arch implant scans acquired by using the IOS selected. Therefore, the second null hypothesis was accepted, while the remaining three null hypotheses were rejected. Based on the results of the present clinical study, the linear trueness ±precision ranged from 63 ± 20 to 87 ± 16 µm, while the angular trueness ±precision ranged from 0.43 ± 0.05 to 0.84 ± 0.29 degrees. Dental literature has reported that the clinically acceptable discrepancy of the implant-prosthodontic gap is 150 µm [54,55]. Nevertheless, the results obtained in this study should be interpretated with caution, as the linear distance between platforms was determined instead for the linear deviation in the platform [46]. The fit of the implant framework is the result of the distortion obtained during the fabrication of the conven tional or virtual definitive implant cast and the manufacturing tech niques of the implant-supported prostheses. The clinically acceptable discrepancy threshold for complete-arch implant impressions or defin itive implants casts is uncertain [54,55]. However, the scanning distortion should be below the acceptable discrepancy of the implant-prosthodontic gap [56]. In the present study, the scanning distortion measured in all groups was significantly lower than the clin ically acceptable discrepancy of the implant-prosthodontic gap. In the present study, the zig-zag and O-Lock scanning patterns tested demonstrated the best linear trueness values when compared with the OBL and circumferential scanning patterns. However, the zig-zag scan ning pattern obtained significantly better angular trueness when compared with the O-Lock scanning pattern; nonetheless, only a 0.12 degrees mean discrepancy was observed between both scanning pat terns. Additionally, although the zig-zag technique reported lower values (8 µm) than the other techniques (16–20 µm), the scanning pat terns tested did not significantly impact the precision values of the IOS Fig. 5. Representative figures of linear and angular measurements among ISBs. A, Linear measurements. B, Angular measurements. Table 1 Normality tests conducted for the studied variables. Normality Tests statistic p Linear Distance Kolmogorov-Smirnov 0.102 0.559 Angular Distance Kolmogorov-Smirnov 0.133 0.238 Scanning Time Kolmogorov-Smirnov 0.0746 0.892 No. of Photograms Kolmogorov-Smirnov 0.0855 0.773 Table 2 Trueness and precision values, scanning time, and number of photograms measured among the subgroups tested. Group Mean ±SD linear discrepancies (µm) Mean ±SD angular discrepancies (degrees) Mean ±SD scanning time (seconds) Mean ±SD number of photograms Circumf 86 ± 16B 0.60 ± 0.15B 102.9 ± 15.1 A 1112 ± 179 A O-Lock 63 ± 20A 0.62 ± 0.08B 93.5 ± 13.4 A 1080 ± 104 A OBL 87 ± 19 B 0.84 ± 0.29 C 130.3 ± 19.4 B 1293 ± 161 B Zig-zag 78 ± 8 AB 0.43 ± 0.05A 125.7 ± 22.1 B 1316 ± 160 B B, buccal; Circumf, circumferential; L, lingual; O, occlusal; SD, standard devia tion. Groups with same superscript letter (within column) indicate not signifi cantly different (P > 0.05). Table 3 ANOVA table for linear distance discrepancies. Source DF Sum of Squares Mean Square F Value Pr > F Model 3 0.00551018 0.00183673 6.79 0.0006 Error 56 0.01514680 0.00027048 Corrected Total 59 0.02065698 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; DF, degrees of freedom. M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 5 tested. Therefore, the zig-zag and O-Lock scanning patterns may be recommended to obtain complete-arch implant scans when using the selected IOS (Trios 4; 3Shape A/S), aiming to maximize the accuracy of the virtual definitive implant cast. A previous in vitro and clinical studies have shown that rescanning techniques reduce the accuracy of IOSs, but locking the existing scan before rescanning maximizes the accuracy of the procedure [26-29]. In the present investigation, the novel scanning pattern that includes locking an initial occlusal scan for capturing complete-arch implant scans has been tested. This novel scanning pattern obtained similar linear and angular trueness and precision values than the zig-zag Fig. 6. A, Boxplot of linear discrepancies measured among the groups tested. B, Boxplot of angular discrepancies measured among the groups tested. C, Boxplot of scanning time measured among the groups tested. D, Boxplot of number of photograms measured among the groups tested. Table 4 Tukey test for linear distance discrepancies. Significant differences highlighted in bold. Least Squares Means for effect Group LSMean(i)=LSMean(j) i/j Circumf O-Lock OBL Zig-zag Circumf 0.0018 0.9989 0.4986 O-Lock 0.0018 0.0011 0.0849 OBL 0.9989 0.0011 0.4128 Zig-zag 0.4986 0.0849 0.4128 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; LS, Least Squares. Table 5 Levene test for linear distance discrepancies. Levene’s Test for Homogeneity of Angular Distance Variance ANOVA of Squared Deviations from Group Means Source DF Sum of Squares Mean Square F Value Pr > F Group 3 0.0532 0.0177 1.41 0.2494 Error 56 0.7046 0.0126 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; DF, degrees of freedom. Table 6 ANOVA table for angular discrepancies. Source DF Sum of Squares Mean Square F Value Pr > F Model 3 1.27151565 0.42383855 14.59 <0.0001 Error 56 1.62723320 0.02905774 Corrected Total 59 2.89874885 DF, degrees of freedom. Table 7 Tukey test for angular discrepancies. Significant differences highlighted in bold. Least Squares Means for effect Group LSMean(i)=LSMean(j) i/j Circumf O-Lock OBL Zig-zag Circumf 0.9819 0.0017 0.0404 O-Lock 0.9819 0.0054 0.0151 OBL 0.0017 0.0054 <0.0001 Zig-zag 0.0404 0.0151 <0.0001 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; LS, Least Squares. M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 6 scanning pattern. Additionally, the novel scanning pattern assessed obtained the lowest scanning time and number of photograms, which may represent an advantage when compared with the zig-zag scanning pattern. Two previous in vitro studies have analyzed the influence of the scanning pattern on the accuracy of complete-arch implant scans [21, 22]. Due to the heterogeneity on the research methodology among these in vitro studies (reference cast, digitizing method to obtain the control file, IOS system and generation, and measurement method), direct comparisons with the results obtained in the present study is difficult. Additionally, in the best authors’ knowledge, this is the first clinical investigation that assessed the impact of four scanning patterns on the accuracy of complete-arch intraoral implant scans. A previous in vitro study evaluated the influence of different scanning patterns on the accuracy and scanning time of complete-arch maxillary implant scans obtained by using 2 IOSs: Trios 3 from 3Shape A/S and CS 3600 from Carestream [22]. The reference cast had 6 parallel implant abutment analogs that were digitized by using a labo ratory scanner (D2000; 3Shape A/S) for capturing the reference or control scan. This study did not include the O-Lock scanning pattern. The results revealed scanning accuracy and scanning time differences among the implant scans acquired with different scanning patterns. Three of the six scanning patterns tested corresponded to the OBL, circumferential, and zig-zag scanning patterns tested in the present study; however, research methodology discrepancies with the present study make difficult the result comparisons between both studies. Gómez-Polo et al. evaluated the influence of six scanning patterns on the accuracy of maxillary and mandibular complete-arch implant scans obtained by using an IOS (Trios 4, v.21.3; 3Shape A/S) [21]. The six scanning patterns tested included the OBL, circumferential, and zig-zag patterns when scanning a maxillary and mandibular model, having each cast 6 dental implants placed. This study did not consider the O-Lock scanning pattern. Authors reported that the circumferential and OBL scanning patterns obtained the highest accuracy values, while the zig-zag pattern obtained the worse accuracy values among all the groups tested. In the present investigation, the zig-zag scanning pattern ob tained higher linear and angular trueness than the OBL and circumfer ential scanning patterns. This may be explained by the clinical conditions of the present study, IOS software version, different implant position (location in the dental arch, depth, angulation, and inter-implant distance) [57,58], amount of available attached mucosa or mobile tissue [59], arch width [60], and humidity [61]. Further studies are needed to evaluate the influence of the scanning pattern on the scanning accuracy of complete-arch intraoral implant scans. Dental literature is unclear regarding the efficacy of splinting ISB techniques when acquiring intraoral digital implant scans [62,14]. This may be explained as additional variables must be considered such as implant position or ISB design selection [20,35]. In the present study, the experimental intraoral digital scans were obtained without splinting the ISBs. The implants of the patient selected were relatively parallel, and the inter-implant distance was favorable. The results of this study revealed a mean linear discrepancy ranging from 63 to 87 µm and a mean angular discrepancy ranging from 0.43 to 0.84 degrees. These values can be considered within the clinically acceptable discrepancy [54-57]. Dental literature has shown varying scanning trueness and precision values among the different IOSs [3,20,35,44]. Therefore, it is important to understand that if a different IOS is selected, the results of the present clinical study may vary. Additional studies are needed to further eval uate the impact of the scanning patterns on the accuracy of complete-arch implant scans. Similarly, additional operator- and patient-related factors can decrease the scanning accuracy of IOSs [18-20], not only the scanning pattern used to acquire the intraoral implant scan. It is critical to understand these influencing factors for maximizing the accuracy of the IOSs [40-43]. In the present study, these ambient environmental conditions were standardized, aiming to minimize the effect of these variables on the scanning accuracy measured. Additionally, implant scan body design [63,64], the geometry bevel feature position of the implant scan body [33], and implant scan body wear [65] can influence intraoral scanning accuracy. In this study, new implant scan bodies were used and main tained in the same position during all the data acquisition procedures. Additionally, the geometry bevel feature of the implant scan body was oriented towards the lingual surface to maximize the accuracy of the digitizing procedure [33]. A previous in vitro study has analyzed the influence of the scanning pattern on the accuracy of complete-arch implant scans obtained by using an IOS (Trios 4, v.21.3; 3Shape A/S) [21]. This study did not consider the O-Lock scanning pattern. The results revealed that the circumferential scanning pattern obtained the lowest scanning time and Table 8 Levene test for angular discrepancies. Levene’s Test for Homogeneity of Angular Discrepancies Variance ANOVA of Squared Deviations from Group Means Source DF Sum of Squares Mean Square F Value Pr > F Group 3 0.0532 0.0177 1.41 0.2494 Error 56 0.7046 0.0126 DF, degrees of freedom. Table 9 ANOVA table for scanning time. Source DF Sum of Squares Mean Square F Value Pr > F Model 3 14,082.46667 4694.15556 14.74 <0.0001 Error 56 17,836.93333 318.51667 Corrected Total 59 31,919.40000 DF, degrees of freedom. Table 10 Tukey test for scanning time. Least Squares Means for effect Group: LSMean(i)=LSMean(j) i/j Circumf O-Lock OBL Zig-zag Circumf 0.4788 0.0006 0.0051 O-Lock 0.4788 <0.0001 <0.0001 OBL 0.0006 <0.0001 0.8944 Zig-zag 0.0051 <0.0001 0.8944 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; LS, Least Squares. Table 11 ANOVA table for number of photograms. Source DF Sum of Squares Mean Square F Value Pr > F Model 3 664,536.667 221,512.222 9.40 <0.0001 Error 56 1,319,462.667 23,561.833 Corrected Total 59 1,983,999.333 DF, degrees of freedom. Table 12 Tukey test for number of photograms. Significant differences highlighted in bold. Least Squares Means for effect Group: LSMean(i)=LSMean(j) i/j Circumf O-Lock OBL Zig-zag Circumf 0.9379 0.0109 0.0033 O-Lock 0.9379 0.0019 0.0005 OBL 0.0109 0.0019 0.9768 Zig-zag 0.0033 0.0005 0.9768 B, buccal; Circumf, circumferential; L, lingual; O, occlusal; LS, Least Squares. M. Gómez-Polo et al. Journal of Dentistry 150 (2024) 105310 7 number of photograms [21]. Based on the results of the present study, the O-Lock scanning pattern obtained the lowest scanning time and number of photograms. However, the circumferential group obtained lower scanning time and number of photograms than the OBL and zig-zag scanning patterns. Therefore, similar results were obtained. The present clinical study presents several limitations, including the single patient tested. Additionally, a unique ISB and implant abutment design were considered. The implants’ maxillary location must also be considered, as the scanning procedure may vary in complete-arch intraoral implant scans. Only one operator and IOS system were involved in the digital data acquisition procedures, so the obtained re sults can not be extrapolated to other IOS systems. Finally, the obtained results should be extrapolated with caution, considering that the linear distances between platforms was considered.[46] Additionally, the overall discrepancies of the 6 linear and angular Euclidean distances were considered. The analysis of each independent linear and angular measurement was not evaluated. Further studies are needed to evaluate the influence of the scanning pattern on the scanning accuracy of complete-arch implant scans recorded by using different IOSs. 5. Conclusions Based on the results obtained in the present clinical study, the following conclusions were drawn: - The scanning patterns tested influenced the trueness and precision, time, and number of photograms of complete-arch implant scans acquired by using the intraoral scanner assessed. - The O-Lock and zig-zag scanning patterns obtained the best linear trueness values. The zig-zag scanning pattern obtained significantly better angular trueness than the O-Lock scanning pattern; however, only a 0.12 degrees mean discrepancy was observed between both scanning patterns. Therefore, the zig-zag and O-Lock scanning pat terns are recommended to obtain complete-arch implant scans when using the selected IOS. - The O-Lock scanning pattern demonstrated the lowest scanning time and number of photograms among all the scanning patterns tested. All authors discussed the evolution and commented on the manu script at all stages. Clinical significance The O-Lock or Zigzag scanning patterns are recommended to maxi mize scanning accuracy and reduce scanning time and number of pho tograms in complete-arch implant digital scans. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. 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