When registering intraoral features and implant position, an intraoral scanner (IOS) is a popular substitute for traditional impression materials, increasing patient comfort, accuracy, and predictability1. For an effective implant scanning comparison, understanding both technologies is crucial. The traditional splinted impression technique has been reported to provide an accurate definitive cast,2–5 but, for the precise and distortion free capture of the implant positions, a stiff and dimensionally stable splinting material is essential.6,7
A high degree of trueness, generally within a range of ≤50 µm, has been reported with IOSs when used to capture single implant and short span implant-supported prostheses.8,9 Scanning for complete arch implant-supported prostheses is more challenging because of the lack of fixed landmarks, and unacceptable passivity has been reported, particularly in mandibular prostheses.8–12 A discrepancy of <150 µm has been recognized as the clinically acceptable level of misfit for complete arch implant-supported prostheses.13–15 Photogrammetry has been used, without stitching, to scan implant coordinates while omitting the dental and gingival anatomy.16 The exclusion of unstable mucosa during scanning and the avoidance of stitching make the passive seating of implant prostheses a more predictable procedure.17–19 Although a promising technique, clinical studies of photogrammetry are scarce.10,20
Current commercially available photogrammetry systems have been considered extraoral systems that require an additional recording of the soft tissue whether with a conventional impression or a digital scan. Recently an intraoral photogrammetry scanner (IPS) has been introduced that can scan
This research did not receive any specific grant from the funding agencies in the public, commercial, or non-profit sectors. The authors declare no conflict of interest and this research did not receive any specific grant from any funding agencies.
- Lecturer, Oral Medicine, Periodontology and Diagnosis, Faculty of Dentistry, Assiut University, Assiut, Egypt.
- Associate Professor, Oral Medicine, Periodontology and
Diagnosis, Faculty of Dentistry, Ain Shams University, Cairo, Egypt. - Demonstrator, Oral Medicine, Periodontology and Diagnosis,
Faculty of Dentistry, Assiut University, Assiut, Egypt
Abstract
Statement of problem. Intraoral scanning of complete arch implant-supported prosthesis is still not predictable in all scenarios. Photogrammetry was introduced to overcome physical and anatomic limitations. The use of a new intraoral scanner combined with photogrammetry technology in a simplified workflow may improve the ease of fabrication and accuracy of complete arch implant-supported prostheses.
Purpose. The purpose of this clinical study was to evaluate the degree of trueness of a conventional intraoral scanner (IOS) and an intraoral photogrammetry scanner (IPS) for complete arch implant-supported prostheses
Material and methods.
Participants who had received 4 implants in an edentulous arch for an implant-supported complete arch fixed dental prosthesis were recruited. Three recordings were obtained for each participant: IOS, IPS (tests), and a conventional splinted open-tray impression (reference). Three-dimensional (ΔEUC), and angular deviations (ΔANGLE) for both groups (IOS and IPS) were evaluated and compared with the reference scan. Potential effects (correlation) of the impression device (IOS and SPG) and type of arch (maxilla and mandible) were evaluated. A paired t test was used to evaluate both the angular and 3-dimensional deviation for each implant position. A point-biserial correlation was conducted to assess the relationship between jaw type and angular and ΔEUC deviations in the 2 groups
Results.
Thirteen edentulous arches (9 maxillae, 4 mandibles) in 11 individuals were rehabilitated with a monolithic zirconia screw-retained prosthesis supported by 4 implants, totaling 52 implants. Conventional intraoral scanners (IOS) and intraoral photogrammetry scanners (IPS) were used to scan 104 implant positions, which were then compared with the corresponding reference scans. (mean ΔEUC IOS 59.8 µm, IPS 30.7 µm; mean ΔANGLE IOS 1.4 degrees, IPS 0.78 degrees). A paired t test revealed statistical significance in favor of IPS in terms of both Euclidian and angular deviation (P<.001). In the IOS group, angular deviation had a positive statistically significant correlation with the type of arch (rpb=0.34, n=52, P=.013)
Conclusions.
The IPS significantly improved the ease and accuracy of recording complete arch implant-supported prostheses.
Clinical Implications.
Regardless of the type of arch, intraoral photogrammetry appears promising for scanning implants for complete arch implant-supported prostheses.
Tissue and that has built-in photogrammetry technology so that it can capture implant locations through special intraoral scan flags. The IPS can accomplish both soft tissue and scan flag scanning and can also merge them in the included software program without the need for a thirdparty software program, as required with extraoral photogrammetry scanners. The authors are unaware of a previous prospective clinical trial aimed primarily at investigating and comparing the accuracy (degree of trueness) of IOS and IPS for complete arch implant recording. Trueness refers to how close the scanned fixture positions are to reality. The secondary outcome was to examine the potential association between the type of arch (maxilla versus mandible) and the degree of trueness. The chair-side scanning duration of the approaches was also evaluated. The null hypotheses were that no variations would exist between intraoral scanning and intraoral photogrammetry capturing systems for complete arch implant-supported prostheses and that neither capturing system would be affected by the type of arch (maxilla versus mandible).
Material And Methods.
All participants were recruited from the periodontology clinic of the Faculty of Dentistry Ain Shams University and Assiut University. Approval for the study had been provided by the ethical committee (FDASU-Rec IR032422). The inclusion criteria consisted of participants who had received 4 implants in a single edentulous arch (Fig. 1), were to receive a 1-piece complete arch implant-supported prosthesis, were available for follow-up visits, and were medically healthy (American Society of Anesthesiology [ASA] classification I or II). Implants were placed fully guided with an approximate location in the canine and first molar areas, respecting the anteriorposterior implant spread,21,22 with an inter- implant angulation not exceeding 15 degrees. Otherwise, angled multiunit abutments (MUA) would be used instead of straight MUA. MUAs with suitable cuffs (1 to 3 mm) (IS- II Active Fixture; Neobiotech) were fixed during the implant insertion procedure so that the finish line would be slightly subgingival. All participants had healthy peri-implant soft tissue, except 1 participant with redness around 2 implants associated with slight mobility of the healing abutments
Figure 1. Intraoral scanner group. A, B, Representative participant in second stage ready for prosthetic phase. C, Custom 3-dimensionally printed open tray with to-be-splinted open-tray impression copings for reference cast fabrication. D, E, Multiunit abutment scan bodies for digital scan capturing.
The healing abutments were retightened, and the tissues appeared healthy within a week. The implant stability quotient was assessed by a damping capacity device (Any check; Neobiotech), yielding a minimum ISQ mean value of 70 on the day of recording. All participants signed an informed consent.
The sample size had been calculated based on the primary outcome measure, which was the Euclidean deviation (ΔEUC) for each implant location. According to a previous study10 reporting a standard deviation of 115.5 µm and a mean difference of 49.6 µm, calculations were based on a dependent t test with a power=95%, and α=.05 yielded a total sample size of 57. The number was increased to 60 to account for dropouts. The sample size adequacy was assessed using a software program (PS Power and Sample Size version 3.1.2; PS). In this study, 11 participants with 52 implants were recruited, resulting in 104 recorded virtual implant locations, constituting the entire sample size for comparison with the relative reference scan. For a verified conventional splinted impression, an open-tray impression technique was made by attaching the open-tray impression copings (Multiunit transfer impression copings; Neobiotech) unsplinted to the multiunit abutments on the implant fixtures with the copings being picked up directly using a polyvinyl siloxane (PVS) impression material (Affinis Precious; Coltène).5 Type IV dental stone (Marmoplast N; Siladent) was poured into the impression after being mixed with a vacuum mixer (Twister Vacuum mixing unit; Renfert).
A light-polymerizing tray material (Megatray; Megsdenta Dentalprodukte GmbH) was used for splinting the impression copings extraorally on the primary cast. The resin devices were then sectioned and numbered. The 2-step approach saved chairside time, with minimal mess.23 A custom impression tray was designed digitally using a software program (Zirkon zahn.tray; Zirkohnzahn GmbH) and 3-dimensionally (3D) printed with a digital light processing (DLP) 3D printer (AccuafabD1s; Shining3D) (Fig. 1C).
In the second visit, the sectioned (to be splinted) open-tray impression copings were seated in the patient´s mouth. A radiograph was made to ensure that they were completely seated. They were then splinted with a low-shrinkage flowable composite resin (Gradia Direct LoFlo; GC Corp). A single operator (A.K.E.) made all impressions. The definitive cast was poured using Type IV dental stone (Marmoplast N; Siladent) in accordance with the manufacturer’s guidelines.
Titanium frameworks were milled from conventional definitive casts to verify the conventional impressions. The mucosal surfaces of the frameworks were designed to minimize contact with the gingiva, thereby reducing resistance from soft tissues during clinical evaluation. The accuracy of the conventional casts as a control was evaluated by assessing the fit of the frameworks intraorally during the subsequent visit. The Sheffield 1 screw test was used to assess any inaccuracy.10,18 Following the tightening of screws, the fit was evaluated radiographically using a paralleling technique. Conventional impressions and the following steps were repeated when an improper fit was identified to obtain verified casts as the control. Then, 2 digital scans were recorded, one with a conventional intraoral scanner (AoralScan 3; Shining3D) (Fig. 1D, E) and another with an intraoral photogrammetry scanner (Elite; Shining3D) by a single operator (A.K.E.) (Fig. 2). Both scanners had been calibrated immediately before the recordings. The scanning strategy adhered to the manufacturer’s recommendations throughout all procedures.
For each technique, the chairside time to accomplish the recording (conventional impression or digital scan) was calculated. For the conventional impression, the total time of the 2 visits was calculated. Regarding the digital scan either by IOS or IPS, the whole time of the scanning visit was calculated, including adjustments of the scan flags or scan bodies, tightening, and capturing. A monolithic screw-retained zirconia dental prosthesis was digitally constructed using definitive cast STL files (reference files) and subsequently delivered to the patient. (Figs. 3, 4). The authenticated definitive cast of the traditional impression was digitized using a high-resolution la- boratory scanner (DS MIX; Shining3D), achieving an accuracy of <7 µm according to the International Organization for Standardization (ISO) 12836 standard24 to produce a digital definitive cast (STL) file to be used as a reference. Three digital files were acquired for each participant: 1 reference scan (derived from the validated definitive cast), 1 IOS scan, and 1 IPS scan. All STL files were imported into the dental CAD software program (exocad Dental CAD; exocad GmbH), and scan bodies were used to generate multiunit Ti bases from a corresponding digital library. Subsequently, the generated STL files were imported into a software program (Mimics version 2.4; Materialise Mimics) for accuracy evaluations. The 2 STL files were superimposed with the STL file of the reference cast using the “N-point registration” and “global registration” algorithms. All the alignment processes were executed by a single investigator (K.H.B.) and verified by a second investigator (A.K.E.) to exclude errors. The Mimics software program performed multiple iterations automatically using an iterative closest point (ICP) algorithm to refine alignment. The number of iterations was set to 20 so that the probability of error was negligible.
The 3D variation between the 2 STL files was assessed regarding linear and angular deviation. The Euclidean distance is used to measure the differences between 2 points in 3D space. A central point and central axis of the virtual MUA Ti base were used for deviation measurements. The outcome measurements were defined by numbering the implants in the arch sequentially from implant 1 to implant n (n=number of implants), moving from the patient’s right to left (Fig. 5). All statistical analyses were conducted using a statistical software program (SAS version 9.4; SAS Institute). The linear and angular deviations were subjected to descriptive analysis. The 3D deviation for each implant position was calculated using the Euclidean distance, and significance was evaluated through a paired t test. The distance deviations and the clinically acceptable misfit threshold (100 µm),15,25–27 regarded as the hypothetical mean, were analyzed using a 1-sample t test. A pointbiserial correlation was conducted to assess the relationship between jaw type and both angular and ΔEUC deviations in the IOS and IPS groups. One-way ANOVA was used to compare the mean scanning time for conventional and scanning techniques (α=.05).
Figure 2. Intraoral photogrammetry group. A, B, C, D; Scan codes (scan flags) with special dot orientation tightened according to manufacturer instructions (8 to 15 Ncm). Orientation of scan flags toward center, thus facilitating capture of fixture locations in single imaging.
Figure 3. A, B, Designing maxillary and mandibular implant screw-retained monolithic prosthesis after aligning intraoral data with facial scans. C, D, E, F; 3-dimensionally printed polymethyl methacrylate (PMMA) prosthesis acts as rigid prototype to evaluate passivity, intaglio adaptation, smile line, canting, occlusion, and patient satisfaction (esthetic and functional parameters).
Figure 4. A, Evaluating prosthesis on 3-dimensionally printed cast with multiunit abutment (MUA) digital laboratory analogs in place. B, C, D, Screw- retained monolithic zirconia prostheses restoring esthetics and function.
Results.
Thirteen edentulous arches, comprising 9 maxillae and 4 mandibles, were rehabilitated in 11 patients using monolithic zirconia screw-retained implant prostheses supported by 4 implants, resulting in a total of 52 implants. Implant positions were recorded using both a conventional intraoral scanner (IOS) and an intraoral photogrammetry scanner (IPS), resulting in a total of 104 implant positions for comparison with the relative reference scans. Normality was checked with QQ plots, histograms, and the Kolmogorov–Smirnov and Shapiro–Wilk test, indicating that the data did not significantly deviate from normality (Fig. 6). The ΔEUC deviation of the IPS group had lower values (M=30.7, SD=18) than those of the IOS group (M=59.8, SD=30). A t test for paired samples indicated that the difference was statistically significant (P<.001), with a 95% confidence interval (−40.33, −17.88). The angular deviation of the IPS group had lower values (M=0.78, SD=0.27 degree) than those of the IOS group (M=1.4, SD=0.44 degree) (P<.001), 95% Confidence interval (−0.8, −0.53) (Fig. 7). Tables 1 and 2 shows Euclidian and angular deviation for each arch in both the IPS and IOS groups, respectively. Table 3 shows the differences from the reference scans of both the IOS and IPS groups. A 1- sample t test revealed that the overall mean of the 3D linear deviations of the IPS group (M=30.7, SD=18 µm) was significantly lower than 100 µm (P<.001). Also, the conventional IOS group had an overall mean (M=59.8, SD=30 µm) which was also significantly lower than 100 µm (P<.001). The angular deviation of IPS (M=0.78, SD=0.27) was lower than the hypothetical mean (P<.001). However, the angular deviation of the conventional IOS (M=1.4, SD=0.44 degree) was significantly higher than the accepted degree of angular deviation (P<.001). A point-biserial test assessed the correlation between jaw type and angular and ΔEUC deviations in both groups (IPS and IOS). In the IPS group, the relationships between angular deviation and arch type (rpb=0.15, n=52, P=.281) and between EUC and the type of arch (rpb=−0.11, n=52, P=.428) were statistically similar, indicating that intraoral photogrammetry trueness was not affected by the jaw type. In the IOS group, a statistically significant positive relationship existed between angular deviation and arch type. (rpb=0.34, n=52, P=.013). The correlation between EUC and the arch type (rpb=0.1, n=52, P=.463) was statistically similar. The chair side time for obtaining the conventional and the digital scans was statistically sig- nificantly different (P<.001) (Tables 4, 5).
Figure 5.
A, B, Alignment of STL files of both groups (IOS and IPS) to STL file of reference scan to determine both
Euclidian and angular deviations for trueness assessment in Mimics software program. IOS, intraoral
scanner; IPS, intraoral photogrammetry; STL, standard tessellation language.
Figure 6.
A, B, C, D, QQ plots and histograms show that data did not significantly deviate from normality.
Figure 7.
A, B, Box plots showing Euclidian and angular deviations of both groups.
Table 1.
Euclidian and angular deviation for each arch in intraoral photogrammetry (IPS) group
Table 2.
Euclidian and angular deviation for each arch in intraoral scanner (IOS) group
Table 3.
Mean, and standard deviation of linear, Euclidian, and angular deviations of both intraoral scanner (IOS) and intraoral photogrammetry (IPS) groups
Table 4.
Mean and standard deviation of chairside time for three recording techniques (conventional splinted open tray, IPS, IOS). IOS, intraoral scanner; IPS, intraoral photogrammetry; SD, standard deviation.
Table 5.
Chairside time of three recording techniques
Discussion
The primary outcome of this single cohort clinical trial was to compare the accuracy of intraoral scanning (IOS) and an intraoral photogrammetry capturing system (IPS) in patients with complete arch prostheses supported by 4 implants. Based on the results of this study, the null hypothesis that no variations would be found between intraoral scanning and intraoral photogrammetry capturing systems for complete arch implant-supported prostheses was rejected, as both the Euclidian (ΔEUC) and angular deviations were statistically higher in the IOS group than in the IPS group. The null hypothesis that both capturing systems would not be affected by the arch type was partially rejected, as the means of deviations were higher in the mandible than in the maxilla in the IOS group; however, no difference between the maxillary and mandibular arches was found when using the IPS capturing system.
The splinted open-tray impression technique is still the standard for capturing complete arch implant supported prostheses. Papaspyridakos et al6 reported the superiority of the splinted technique for delivering a passive complete arch, 1-piece fixed prosthesis. Recently, Revilla-León et al16 compared the splinted conventional impression technique with photogrammetry, revealing the higher trueness (3 µm difference) and precision (18 µm difference) of the splinted technique.16 The present study used the splinted technique to produce a reference cast, which was digitalized using a high-resolution laboratory scanner (DS MIX; Shining3D) with an accuracy of <7 µm (ISO 12836) to generate a digital definitive cast (STL) file.
Several approaches have been used to quantify the deviations of implant positions: some report data in 3 dimensions (X, Y, Z), others evaluate lengths and angles with a single point that is considered a fixed landmark, and a completely different approach has been used to compare the scanned scan bodies using the best-fit technique.19 Passive fit for screw-retained definitive prostheses requires precise abutment platform data. To make the results more clinically relevant, only information from the abutment platforms was extracted and used to compute the 3D deviation. The present study design focused on calculating 3D deviations for each implant position through a best-fit alignment algorithm applied to the reference and test scans. The variations of each implant can be analyzed from linear (ΔY, ΔX, ΔZ), 3D (ΔEUC) and angular (ΔANGLE) perspectives.10,28
The authors are unaware of a previous clinical trial that assessed the accuracy of complete arch digital scans executed with intraoral photogrammetry and intraoral scanning. Previous studies have assessed IOSs in complete arch implant scanning, but its use in daily practice for this purpose remains controversial.17,29,30 This debate arises from a lack of agreement regarding the permissible misfit range of a single implant in a complete arch supported by 4 and 6 implants, as well as the suitable clinical measurement method.13,14 To prevent long-term complications, a threshold value of 150 µm has been recommended.25 Moreover, manufacturing and its tolerance, which may create deviations ranging from 20 to 100 µm, should be considered,31,32 as should the implant number per arch, as the increase in the number of implants inversely affects the tolerable deviations.10,33 Recently, interimplant distance, interimplant angulation, scan body type, intraoral scanner type, and operator experience have been reported to significantly affect the accuracy of scanning.34,35
Yan et al 28 compared the accuracy of an extraoral photogrammetry system and intraoral scanning in patients with complete arch implant-supported prostheses. In all participants, photogrammetry yielded less deviation, and the results were statistically significant compared with those of intraoral scanning (range 2.70–92.80 µm, median 17.00 versus 21.30 to 815.60 µm, and median of 48.95 µm). Also, the accuracy of photogrammetry was not affected by the position or number of implants, unlike IOS. The authors did not recommend IOS for complete arch implant scanning, as the results did not pass the accepted threshold level.28 In the present study, although the IOS 3D deviation was statistically significantly different (P<.05) compared with IPS (IOS M 59.8 µm, SD=30 versus IPS M=30.7 µm, SD=18),the results were still below the accepted threshold of the misfit. This might be attributed to only 4 implants per arch for all participants. Similarly, a statistically significant correlation was found between IOS angular deviation and the mandibular arch (P<.05). However, no correlation was found between the arch type and IPS deviation, whether Euclidian or angular (P>.05).
In the present study, both IOS and IPS showed a lower Euclidian deviation mean (M 59.8 µm, 30.7 µm respectively) when compared with the hypothetical mean when considering 100 µm as the upper limit of acceptable fit. However, the angular deviation means of the IOS (1.4 degree) exceeded the acceptable theoretical limit of 1-degree angular deviation, while IPS had a 0.78-degree deviation, lower than the accepted deviation. Manzella et al15 investigated the degree of tolerable misfit by utilizing a gypsum indicating device as a brittle material that would fracture with any degree of intolerable misfit. The indicating device did fracture with a 150-µm horizontal misfit, 50-µm vertical misfit, and 1 degree of angular deviation when considering these values as the threshold of acceptable misfit.15 The clinical meaning of this deviation difference between IPS and IOS has to be further interpreted considering the overall number of implants for each arch. For complete arch digital implant scans, these variations might suggest that IPS is a more dependable option than IOS, although it is still advised to attempt a rigid prototype before making a definitive screw-retained complete arch implant-supported prosthesis. Similar outcomes have been reported in a recent in vivo study17 comparing IOS and extraoral stereophotogrammetry systems (SPG), whose clinical performance was analyzed and compared in the same participant. SPG was reported to be more accurate than IOS (mean EUC SPG 87.6 µm; mean SPG angle 0.38 degree versus mean EUC IOS 137.2 µm; mean IOS angle 0.79 degree) and was not affected by the position or number of implants.17
In the present study, the use of IPS affected not only the accuracy of capturing but also the ease of the process itself, demonstrated by the statistically significant difference in scanning times when IPS (mean 14.1 min SD 1.5) and IOS (mean 18.2 min SD 3.6) were used (P<.001). Unlike conventional intraoral scanners, photogrammetry was not affected by soft tissue or by blood or saliva making it better at scanning complete arches immediately after surgery. Limitations of the present study included that, because of the clinical design, no repetitions were conducted; therefore, precision was not evaluated, and only trueness could be calculated. The study was only on prostheses supported by 4 implants; other implant numbers per arch should be further investigated. No standardization of the type of arch (maxilla or mandible) added to the study limitations. Also, as the results of this study were based on only 1 intraoral scanning system, IPS should be compared with different intraoral scanning technologies and with extraoral photogrammetry systems.
Conclusions
Based on the findings of this clinical study, the following conclusions were drawn: 1. Intraoral scanning can be used for complete arch implants in some patients. 2. Intraoral photogrammetry system (IPS) significantly improved the ease of fabrication and accuracy of complete arch prostheses supported by 4 implants. 3. Unlike IOS, the trueness of intraoral photogrammetry (IPS) was not affected by the type of jaw.
Ethical Approval Statement
All the performed procedures were conducted according to the ethical principles and standards of the institutional and national research committee and with the Declaration of Helsinki and its later amendments (revised in October 2018). The study protocol was independently reviewed and approved by the Institutional Ethical Committee, Faculty of Dentistry, Ain Shams University (FDASU-Rec IR032422). Informed written consent was obtained from all individual participants included in the study.
Data Availability Statement
The data sets used and analyzed during the current study are available from the corresponding author on reasonable request.
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Corresponding author:
Assoc Prof Doaa Adel-Khattab Oral Medicine, Periodontology and Oral Diagnosis Faculty of Dentistry Ain Shams University Cairo EGYPT Email: dr.doaa.adel-khattab@dent.asu.edu.eg
Credit authorship contribution statement
All authors have made substantial contributions to the conception and design of the study A.K.E., and K.H.B., conceptualized and designed the study, D.A., and A.K.E., have been involved in data collection and data analysis. A.K.E., K.H.B., and D.A., have been involved in data interpretation, and drafting of the manuscript, A.K.E., and D.A., revised it critically and have given final approval of the version to be published. Copyright © 2025 by the Editorial Council of The Journal of Prosthetic Dentistry. All rights are reserved, including those for text and data mining, AI training, and similar technologies. https://doi.org/10.1016/j.prosdent.2025.03.041