Effect of Different Software Programs on the Accuracy of Dental Scanner Using Three-Dimensional Analysis

Do intraoral scanning technologies affect the trueness of dental arches with crowding, diastema, and edentulous spaces? A clinical perspective

OBJECTIVES

To evaluate the trueness of dental arches digitised by two intraoral scanning (IOS) technologies from patients presenting crowding, diastema, and bilateral posterior edentulous space with tilted molar.

METHODS

Conventional impressions and dental stone models were generated from three patients presenting the aforementioned dental arch conditions. These models were digitised on a desktop scanner, and the resulting mesh was used as reference. Subsequently, the patients were scanned using confocal based (CF; iTero Element 2) and blue laser-multiscan (BLM; Virtuo Vivo) imaging IOS technology, totalling thirty scans. The meshes from the scans were exported in Standard Tessellation Language format and analysed using Geomagic Control X software. Root mean square (RMS) indicated deviation magnitude. Differences in IOS technologies were evaluated with paired t-tests, and dental arch conditions compared using ANOVA and post-hoc Tukey tests (α=0.05).

RESULTS

Digital dental arch from blue laser-multiscan technology showed lower trueness compared to confocal based technology for crowding (p = 0.0084) and edentulous spaces (p = 0.0025) conditions. When the types of oral condition were compared, discrepancies were significantly different for both IOS technologies, featuring the arch with diastema showing the lowest trueness, followed by edentulous spaces and crowding.

CONCLUSION

Dental arches presenting crowding and edentulous spaces digitised by blue laser-multiscan technology exhibited greater discrepancies compared to confocal based imaging technology. Furthermore, trueness varied among the dental arch conditions.

CLINICAL SIGNIFICANCE

The IOS technology and patient's dental arch condition can influence the trueness of dental arch digitisation. Being aware of these effects allows clinicians to take them into account during scanning procedures, digital planning and manufacturing.

Comparison of the reverse scan technique with an intraoral scanner and the traditional impression technique

STATEMENT OF PROBLEM

Intraoral scanners have many advantages but have limited applicability for extensive tooth-supported or implant-supported prostheses because of merging errors.

PURPOSE

The purpose of this study was to compare the reverse scan technique (RST) with an intraoral scanner using the traditional impression technique both in vitro and in vivo.

MATERIAL AND METHODS

A participant was scanned 10 times with an intraoral scanner. Then, the RST was performed 3 times in the oral cavity. One of the intraoral scans was chosen to make a 3-dimensionally (3D) printed cast. The printed cast was scanned 10 times with a laboratory scanner (Control cast) and 10 times with an intraoral scanner (IOS cast). The RST was performed 10 times (RST cast), and 10 dental impressions were made using the traditional splinted technique on the same cast (Impression cast). A laboratory scanner was used to obtain standard tessellation language (STL) files of the tested methods. A newly developed pyramid replacement method was used to evaluate accuracy. This method uses modified virtual abutments with integrated pyramids that determine the exact measurement points. The obtained data were processed using Procrustes analysis and statistically analyzed (α=.05).

RESULTS

The Procrustes distances were Control cast 0 to 0.4 µm (median 0.3 µm), RST cast 5.6 to 6.9 µm (median 6.2 µm), Impression cast 5.4 to 7.1 µm (median 6.5 µm), and IOS cast group 4.5 to 41.2 µm (median 5.8 µm). In the participant, the Procrustes distance values were RST intraoral 9.5 to 9.6 µm (median 9.5 µm) and IOS intraoral 5.7 to 18.3 µm (median 10.9 µm).

CONCLUSIONS

The reverse scan technique is an acceptable fully digital replacement for traditional impression making. Using an IOS to obtain a 3D cast of an implant-supported interim prosthesis with scannable implant analogs is not recommended. It is more beneficial to use laboratory scanners rather than intraoral scanners for the digitization of precision improvement devices such as bonded interim implant-supported prostheses with a scannable implant analog or solid index.

Comparison of 1- and 3-piece directly 3-dimensional printed indirect bonding trays: An in vitro study

INTRODUCTION

This study aimed to compare the transfer accuracy of indirect bonding trays of different thicknesses and numbers of pieces.

METHODS

Digital indirect bonding was performed on 56 printed resin models, divided into 4 groups with 14 models in each: 1-mm 1-piece tray (OPT), 2-mm OPT, 1-mm 3-piece tray (TPT), and 2-mm TPT. The trays were designed using Appliance Designer (3Shape A/S, Copenhagen, Denmark). Angular (torque, tip, or angulation) and linear (mesiodistal, buccolingual, occlusogingival, or vertical) differences were compared by using open-source GOM Inspect software (GOM GmbH, Braunschweig, Germany).

RESULTS

In the buccolingual direction, the 1-mm TPT (0.180 ± 0.041 mm) was significantly more accurate than the 1-mm OPT (0.240 ± 0.032 mm). In the vertical direction, significant differences were seen between the 1-mm and 2-mm OPTs (1-mm OPT: 0.220 ± 0.043 mm; 2-mm OPT: 0.428 ± 0.143 mm; P = 0.003) and between the 1-mm and 2-mm TPTs (1-mm TPT: 0.210 ± 0.072 mm; 2-mm TPT: 0.340 ± 0.062 mm; P = 0.004) in the total region. In the tip angle, significant differences were seen between the 1-mm and 2-mm OPTs and between the 1-mm OPT and TPT. In the torque angle, a significant difference was seen between the 1-mm TPT (2.815°±0.350°)and 2-mmTPT (2.368° ± 0.245°; P = 0.017).

CONCLUSIONS

Both the thickness and the splitting of the trays impacted the bracket bonding accuracy. The 1-mm trays were more accurate than the 2-mm trays. Despite a few statistically significant differences between the 1-mm OPT and TPT, the 1-mm OPT was recommended for clinical use, considering the designing and placing of the trays.

Impact of the superimposition methods on accuracy analyses in complete-arch digital implant investigation

OBJECTIVES

To measure the impact of the superimposition methods on accuracy analyses in digital implant research using an ISO-recommended 3-dimensional (3D) metrology-grade inspection software.

MATERIALS AND METHODS

A six-implant edentulous maxillary model was scanned using a desktop scanner (7Series; DentalWings; Montreal, Canada) and an intraoral scanner (TRIOS 4; 3Shape; Copenhagen, Denmark) to generate a reference and an experimental mesh, respectively. Thirty experimental standard tesselletion language (STL) files were superimposed onto the reference model's STL using the core features of six superimposition methods, creating the following groups: initial automated pre-alignment (GI), landmark-based alignment (G1), partial area-based alignment (G2), entire area-based alignment (G3), and double alignment combining landmark-based alignment with entire model area-based alignment (G4 ) or the scan bodies' surface (G5). The groups underwent various alignment variations, resulting in sixteen subgroups (n = 30). The alignment accuracy between experimental and reference meshes was quantified by using the root mean square (RMS) error as trueness and its fluctuation as precision. The Kruskal-Wallis test with a subsequent adjusted post-hoc Dunn's pairwise comparison test was used to analyze the data (α = 0.05). The reliability of the measurements was assessed using the intraclass correlation coefficient (ICC).

RESULTS

A total of 480 superimpositions were performed. No significant differences were found in trueness and precision among the groups (p > 0.05), except for partial area-based alignment (p < 0.001). Subgroup analysis showed significant differences for partial area-based alignment considering only one scan body (p < 0.001). Initial automated alignment was as accurate as landmark-based, partial, or entire area-based alignments (p > 0.05). Double alignments did not improve alignment accuracy (p > 0.05). The entire area-based alignment of the scan bodies' surface had the least effect on accuracy analyses.

CONCLUSIONS

Digital oral implant investigation remains unaffected by the superimposition method when ISO-recommended 3D metrology-grade inspection software is used. At least two scan bodies are needed when considering partial area-based alignments.

CLINICAL SIGNIFICANCE

The superimposition method choice within the tested ISO-recommended 3D inspection software did not impact accuracy analyses in digital implant investigation.

Effect of analysis software program on measured deviations in complete arch, implant-supported framework scans

STATEMENT OF PROBLEM

Implementation of fabrication trueness analysis by using a recently introduced nonmetrology-grade freeware program may help clinicians and dental laboratory technicians in their routine practice. However, knowledge of the performance of this freeware program when compared with the International Organization for Standardization recommended metrology-grade analysis software program is limited.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of an analysis software program on measured deviations in the complete arch, implant-supported framework scans.

MATERIAL AND METHODS

A total of 20 complete arch, implant-supported frameworks were fabricated from a master standard tessellation language (STL) file from either polyetheretherketone (PEEK) or titanium (Ti) (n=10). All frameworks were then digitized by using different scanners to generate test STLs. All STL files were imported into a nonmetrology-grade freeware program (Medit Link) and a metrology-grade software program (Geomagic Control X) to measure the overall and marginal deviations of frameworks from the master STL file by using the root mean square (RMS) method. Data were analyzed by using the two 1-sided paired t test procedure, in which 50 µm was considered as the minimal clinically meaningful difference (α=.05).

RESULTS

When overall RMS values were considered, the nonmetrology-grade freeware program was not inferior to the metrology-grade software program (P<.05). When marginal RMS values were considered, the nonmetrology-grade freeware program was inferior to the metrology-grade software program only when PEEK frameworks were scanned with an E4 laboratory scanner (P>.05).

CONCLUSIONS

The use of the tested nonmetrology-grade freeware program resulted in overall deviation measurements similar to those when a metrology-grade software program was used. The freeware program was inferior when marginal deviations were analyzed on E4 scans of a PEEK framework, which was the only scanner-material pair that led to a significant difference, among the 15 pairs tested.

Impact of the superimposition reference area on intraoral scanning accuracy in a partially dentate maxilla

STATEMENT OF PROBLEM

The alignment of 3-dimensional (3D) files involves selecting a reference area before performing a local best fit alignment during the digital scan superimposition and is essential for comparing digital scans. Scan alignment relies on both reference area location and the alignment algorithm. However, a consensus on the impact of different reference areas on intraoral scanning accuracy is lacking.

PURPOSE

The purpose of this in vitro study was to assess the impact of 3 superimposition reference areas on the accuracy of 3 intraoral scanners for a partially dentate maxilla.

MATERIAL AND METHODS

A Kennedy class II resin cast was scanned using 3 intraoral scanners (Primescan, TRIOS 3, and Emerald) outputting 30 digital scans (10 per scanner). Test scans from intraoral scanners were subsequently compared with a reference digital standard tessellation language file generated by a laboratory scanner with validated accuracy. The files were superimposed using best fit alignment for each intraoral scanner using 3 different superimposition reference areas (whole region of interest, palate, and all teeth). Accuracy was assessed by using a 3D analysis program (Geomagic Control X; 3D systems) for each scanner at 4 preselected areas. Test and reference scan differences were depicted on color maps and quantified via root mean square deviations. Differences were analyzed using regression analysis with the post hoc student t test and Bonferroni correction (α=.05).

RESULTS

The TRIOS 3 and Emerald produced positive deviations in the palatal color maps, whereas Primescan produced more uniform color maps, regardless of the superimposition strategy used. Primescan exhibited the best accuracy (trueness and precision) in both palatal and bounded edentulous areas, regardless of the superimposition reference area. The TRIOS 3 recorded the highest distal extension trueness (ranging from 42.9±7.7 µm to 65 ±19.5 µm), and Primescan achieved the highest precision (ranging from 28.5 ±9.8 µm to 48.9 ±16.9 µm), regardless of the superimposition area. Emerald demonstrated the highest teeth trueness (ranging from 31.6 ±6.8 µm to 69.6 ±11.5 µm), while Primescan produced the highest precision (ranging from 17.9 ±6.1 µm to 30.7 ±9.2 µm), regardless of the reference area used.

CONCLUSIONS

The chosen reference area for best fit alignment significantly influenced digital scan accuracy (P<.001). Primescan displayed the highest palatal and bounded edentulous area accuracy, with TRIOS 3 recording the highest distal extension trueness. Emerald recorded the highest teeth trueness and Primescan recorded the highest distal extension and tooth precision. All conclusions were independent of the superimposition strategy used.

Effect of implant scan body geometric modifications on the trueness and scanning time of complete arch intraoral implant digital scans: An in vitro study

STATEMENT OF PROBLEM

The effect of the surface geometry of implant scan bodies (ISBs) on the accuracy and scanning time of complete arch implant digital scans remains uncertain.

PURPOSE

The purpose of this in vitro study was to evaluate whether geometric modifications on implant scan bodies (nonmodified, subtractively modified, and additively modified ISBs) affect the trueness and scanning time of complete arch intraoral implant digital scans.

MATERIAL AND METHODS

A completely edentulous maxillary cast with 2 anterior parallel and two 17-degree posteriorly tilted implant abutment analogs was prepared. A digitized reference was created from this cast with polyetheretherketone (PEEK) (CARES Mono Scanbody for screw-retained abutment) ISBs by using a desktop scanner (E3). Three different groups were created: nonmodified (NM group), subtractively modified (SM group), and additively modified (AM group). For the NM group, no modifications were made to the ISBs. For the SM group, 4 round-shaped grooves were created on the buccal, lingual, mesial, and distal sides. For the AM group, PEEK beads were printed and cemented on the same areas of the ISB of the SM group. Fifteen consecutive scans were captured with an intraoral scanner (TRIOS 3) for each group, and the scanning time was recorded. By using a metrology software program, scans of each group were superimposed on the reference file to determine the 3D surface, linear, and angular position discrepancies of each ISB. Repeated-measures analyses of variance followed by univariate analysis and Bonferroni multiple comparison tests were performed to analyze the data (α=.05). To compare the mean time among groups, 1-way analysis of variance was performed followed by the Tukey post hoc tests.

RESULTS

Significant 3D surface, linear, and angular position discrepancies were found when measuring trueness among the NM, SM, and AM groups (P<.001). Discrepancies in 3D surface deviation were highest for the AM group (0.266 ±0.030 mm), and the lowest mean angular deviation values were for the SM group (0.993 ±0.062 degrees). However, the mean scanning time was not significantly different among the groups tested (P=.237).

CONCLUSIONS

For complete arch intraoral implant digital scans, subtractive modifications on ISBs enhanced scanning trueness, while additive modifications on ISBs decreased scanning trueness. However, implant scan body geometric modifications did not affect scanning time.

Scan accuracy and time efficiency of different implant-supported fixed partial denture situations depending on the intraoral scanner and scanned area: An in vitro study

STATEMENT OF PROBLEM

The type of intraoral scanner (IOS), region of the implant, and extent of the scanned area have been reported to affect scan accuracy. However, knowledge of the accuracy of IOSs is scarce when digitizing different partially edentulous situations either with complete or partial arch scans.

PURPOSE

The purpose of this in vitro study was to investigate the scan accuracy and time efficiency of complete and partial arch scans of different partially edentulous situations with 2 implants and 2 different IOSs.

MATERIAL AND METHODS

Three maxillary models with implant spaces at the lateral incisor sites (anterior 4-unit), right first premolar and right first molar sites (posterior 3-unit), or right canine and right first molar sites (posterior 4-unit) were fabricated. After placing implants (Straumann S RN) and scan bodies (CARES Mono Scanbody), models were digitized by using an optical scanner (ATOS Capsule 200MV120) to generate reference standard tessellation language (STL) files. Complete or partial arch scans (test scans) of each model were then performed by using 2 IOSs (Primescan [PS] and TRIOS 3 [T3]) (n=14). The duration of the scans and the time needed to postprocess the STL file until the design could be started were also recorded. A metrology-grade analysis software program (GOM Inspect 2018) was used to superimpose test scan STLs over the reference STL to calculate 3D distance, interimplant distance, and angular (mesiodistal and buccopalatal) deviations. Nonparametric 2-way analysis of variance followed by Mann-Whitney tests with Holm correction were used for trueness, precision, and time efficiency analyses (α=.05).

RESULTS

The interaction between IOSs and scanned area only affected the precision of the scans when angular deviation data were considered (P≤.002). Trueness of the scans was affected by IOSs when 3D distance, interimplant distance, and mesiodistal angular deviations were considered. The scanned area affected only 3D distance deviations (P≤.006). IOSs and scanned area significantly affected the precision of scans when 3D distance, interimplant distance, and mesiodistal angular deviations were considered, while only IOSs significantly affected buccopalatal angular deviations (P≤.040). Scans from PS had higher accuracy when 3D distance deviations were considered for the anterior 4-unit and posterior 3-unit models (P≤.030), when interimplant distance deviations were considered for complete arch scans of the posterior 3-unit model (P≤.048), and when mesiodistal angular deviations were considered in the posterior 3-unit model (P≤.050). Partial arch scans had higher accuracy when 3D distance deviations of the posterior 3-unit model were considered (P≤.002). PS had higher time efficiency regardless of the model and scanned area (P≤.010), while partial arch scans had higher time efficiency when scanning the posterior 3-unit and posterior 4-unit models with PS and the posterior 3-unit model with T3 (P≤.050).

CONCLUSIONS

Partial arch scans with PS had similar or better accuracy and time efficiency than other tested scanned area-scanner pairs in tested partial edentulism situations.

Impact of the superimposition methods and the designated comparison area on accuracy analyses in dentate models

OBJECTIVES

To measure the impact of superimposition methods and the designated comparison area on accuracy analyses of dentate models using an ISO-recommended 3-dimensional (3D) metrology-grade inspection software (Geomagic Control X; 3D Systems; Rock Hill, South Carolina; USA).

MATERIALS AND METHODS

A dentate maxillary typodont scanned with a desktop scanner (E4; 3 Shape; Copenhagen; Denmark) and an intraoral scanner (Trios 4; 3 Shape; Copenhagen; Denmark) was used as reference. Eight groups were created based on the core features of each superimposition method: landmark-based alignment (G1); partial area-based alignment (G2); entire tooth area-based alignment (G3); double alignment combining landmark-based alignment with entire tooth area-based alignment (G4); double alignment combining partial area-based alignment with entire tooth area-based alignment (G5); initial automated quick pre-alignment (G6); initial automated precise pre-alignment (G7); and entire model area-based alignment (G8). Diverse variations of each alignment and two regions for accuracy analyses (teeth surface or full model surface) were tested, resulting in a total of thirty-two subgroups (n = 18). The alignment accuracy between experimental and reference meshes was quantified using root mean square (RMS) error as trueness and its repeatability as precision. The descriptive statistics, a factorial repeated measures analysis of variance (ANOVA) and a post hoc Tuckey multiple comparison tests were used to analyze the trueness, and precision (α = 0.05).

RESULTS

A total of 576 superimpositions were performed. The unique partial area-based superimposition method demonstrated the least precise alignment and was the sole group to exhibit a significant difference (p<.001). Automated initial pre-alignments demonstrated similar accuracy to other superimposition methods (p>.05). Double alignments did not result in accuracy improvement (p>.05). The designated comparison area displayed differences in both trueness (p<.001) and precision (p<.001), leading to an overall discrepancy of 8 ± 4 μm between selecting the teeth surface or full model surface.

CONCLUSIONS

The superimposition method choice within the tested software did not impact accuracy analyses, except when the alignment relies on a unique and reduced area, such as the palatal rugae, a single tooth, or three adjacent teeth on one side.

CLINICAL SIGNIFICANCE

The superimposition method choice within the tested ISO-recommended 3D inspection software did not impact accuracy analyses.

Feasibility of images acquired using smartphone camera for marginal and internal fit of fixed dental prosthesis: comparison and correlation study

This study aimed to measure marginal and internal fit using images captured with both an optical microscope and a smartphone camera, comparing the fit measurement performance of these devices and analyzing their correlation. Working casts (with 10 posterior and 10 anterior teeth) created to fabricate fixed dental prostheses were used. These working casts were scanned using a desktop scanner (E1) to design an interim crown, and the designed interim crown was fabricated using a three-dimensional (3D) printer. Utilizing the silicone replica technique, the fabricated interim crown replicated the fit, which was then captured using both an optical microscope and a smartphone camera. The captured images were used to measure the marginal and internal fit according to the imaging device. Intraclass correlation coefficients (ICC) were used for reliability analysis according to the imaging device. Furthermore, the Wilcoxon signed-rank test was adopted for the comparative evaluation of the marginal and internal fit between the imaging devices (α = 0.05). The measurement results of the marginal and internal fit according to the optical microscope and smartphone camera did exhibit a significant difference (P < 0.05). The ICC between the two devices showed an "excellent" agreement of over 0.9 at all measurement points (P < 0.001). A smartphone camera could be used to obtain images for evaluating the marginal and internal fit.

Trueness and precision of mandibular complete-arch implant scans when different data acquisition methods are used

OBJECTIVES

To evaluate the effect of different data acquisition methods on the trueness and precision of mandibular complete-arch implant scans.

METHODS

An edentulous polyurethane master mandibular model with 6 implants was digitized by using an industrial-grade blue light scanner (ATOS Core 80 5MP) to obtain a master standard tessellation language (MSTL) file. The master model was also digitized by using either direct digital workflow with a stereoscopic camera (iCam 4D (IM)) or intraoral scanners (CEREC Primescan (PS) and Trios 4 (T4)) or indirect digital workflow with laboratory scanners (inEos X5 (X5) and CARES 7 (S7)) to obtain test-scan STLs (n = 10). All STL files were imported into a metrology-grade analysis software (Geomagic Control X 2020.1) and test-scan STLs were superimposed over MSTL. The root mean square method was used to calculate surface deviations, while angular deviations were also calculated. Kruskal-Wallis and Dunn's tests were used to evaluate measured deviations (surface and angular) for trueness and precision (α = 0.05).

RESULTS

X5 and S7 had the lowest, and IM had the highest surface deviations (P ≤ .036). The angular deviations of PS were lower than those of X5, S7, and IM (P ≤ .008). When surface deviations were considered, T4 had the lowest precision among tested scanners (P ≤ .002), and the scans of IM had higher precision than those of PS (P = .003). Scanner type did not affect the precision of the scans when angular deviations were considered (P = .084).

CONCLUSIONS

The data acquisition method affected the trueness (surface and angular deviations) and precision (surface deviations) of mandibular complete-arch implant scans.

CLINICAL SIGNIFICANCE

Tested data acquisition methods may be feasible to digitize mandibular complete-arch implants considering the deviations of the scans, which were in the range of previously reported thresholds, and the high precision of scans. However, the frameworks fabricated with the direct digital workflow that involves the scans of the stereoscopic camera might require more adjustments than those fabricated by using the scans of other tested scanners.

Effect of scan powder and scanning technology on measured deviations of complete-arch implant supported frameworks digitized with industrial and intraoral scanners

OBJECTIVES

To evaluate the suitability of intraoral scanners (IOSs) to analyze the fabrication trueness of titanium complete-arch implant-supported frameworks by comparing with an industrial-grade scanner and investigate how anti-reflective scan powder affects measured deviations.

METHODS

Ten titanium complete-arch implant-supported frameworks were milled from a reference standard tessellation language (STL) file. An industrial-grade blue light scanner (ATOS Core 80 (AT)) and three IOSs (Primescan (PS), TRIOS T3 (T3), and TRIOS T4 (T4)) with (PS-P, T3-P, and T4-P) or without (PS, T3, and T4) anti-reflective scan powder application were used to generate test STL (TSTL) files of the frameworks. Reference STL and TSTLs were imported into a metrology-grade analysis software (Geomagic Control X) and whole surface root mean square (RMS) values were calculated. Another software (Medit Link v 2.4.4) was used to virtually isolate marginal surfaces of all STL files and marginal RMS values were calculated by using the same metrology-grade analysis software. A linear mixed effects model was used to compare the transformed deviations of the scans performed by using each IOS (with or without powder) with the deviations of those performed by using the reference AT scanner within each surface, where a Box-Cox type transformation was used for variance stability. Bonferroni corrected post-hoc tests were used to compare conditions within each IOS (α=0.05).

RESULTS

All IOSs had significantly higher whole surface and marginal RMS values than AT, regardless of the condition (P≤.002). However, scan powder application did not affect the whole surface and marginal RMS values in scans of tested IOSs (P≥.054).

CONCLUSION

Measured whole surface and marginal deviations in all IOS scans performed with or without the use of scan powder were higher than those in AT scans. The application of anti-reflective scan powder did not affect the deviations in scans of tested IOSs.

CLINICAL SIGNIFICANCE

Even though deviations measured in the scans of tested scanners were significantly different than those in the reference scanner, the maximum raw mean difference was 37.33 µm and the maximum raw confidence interval value of estimated differences was 47.88 µm, which can be considered clinically small taking into account the size of the frameworks tested. Therefore, tested intraoral scanners may be feasible to scan prostheses similar to or smaller than tested frameworks for fabrication trueness analysis, which may facilitate potential clinical adjustments.

Comparison of intraoral and laboratory scanners to an industrial-grade scanner while analyzing the fabrication trueness of polymer and titanium complete-arch implant-supported frameworks

OBJECTIVES

To compare the scans of different intraoral scanners (IOSs) and laboratory scanners (LBSs) to those of an industrial-grade optical scanner by measuring deviations of complete-arch implant-supported frameworks from their virtual design file.

MATERIAL AND METHODS

Ten polyetheretherketone (PEEK) and 10 titanium (Ti) complete-arch implant-supported frameworks were milled from a master standard tessellation language (STL) file. An industrial-grade blue light scanner (AT), 2 LBSs (MT and E4), and 3 IOSs (PS, T3, and T4) were used to generate STL files of these frameworks. All STLs were imported into an analysis software (Geomagic Control X) and overall root mean square (RMS) values were calculated. Marginal surfaces of all STL files were then virtually isolated (Medit Link v 2.4.4) and marginal RMS values were calculated. Deviations in scans of tested scanners were compared with those in scans of AT by using a linear mixed effects model (α = 0.05).

RESULTS

When the scans of PEEK frameworks were considered, PS and T3 had similar overall RMS to those of AT (p ≥ .076). However, E4 and T4 had higher and MT had lower overall RMS than AT (p ≤ .002) with a maximum estimated mean difference of 13.41 µm. When the scans of Ti frameworks were considered, AT had significantly lower overall RMS than tested scanners (p ≤ .010) with a maximum estimated mean difference of 31.35 µm. Scans of tested scanners led to significantly higher marginal RMS than scans of AT (p ≤ .006) with a maximum estimated mean difference of 53.90 µm for PEEK and 40.50 µm for Ti frameworks.

CONCLUSION

Only the PEEK framework scans of PS and T3 led to similar overall deviations to those of AT. However, scans of all tested scanners resulted in higher marginal deviations than those of AT scans.

CLINICAL SIGNIFICANCE

Scans performed by using PS and T3 may be alternatives to those of tested reference industrial scanner AT, for the overall fabrication trueness analysis of complete-arch implant-supported PEEK frameworks.

Quantitative analysis of zirconia and titanium implant artefacts in three-dimensional virtual models of multi-slice CT and cone beam CT: does scan protocol matter?

OBJECTIVES

Artefacts from dental implants in three-dimensional (3D) imaging may lead to incorrect representation of anatomical dimensions and impede virtual planning in navigated implantology. The aim of this study was quantitative assessment of artefacts in 3D STL models from cone beam CT (CBCT) and multislice CT (MSCT) using different scanning protocols and titanium-zirconium (Ti-Zr) and zirconium (ZrO2) implant materials.

METHODS

Three ZrO2 and three Ti-Zr implants were respectively placed in the mandibles of two fresh human specimens. Before (baseline) and after implant placement, 3D digital imaging scans were performed (10 repetitions per timepoint: voxel size 0.2 mm³ and 0.3 mm³ for CBCT; 80 and 140 kV in MSCT). DICOM data were converted into 3D STL models and evaluated in computer-aided design software. After precise merging of the baseline and post-op models, the surface deviation was calculated, representing the extent of artefacts in the 3D models.

RESULTS

Compared with baseline, ZrO2 emitted 36.5-37.3% (±0.6-0.8) artefacts in the CBCT and 39.2-50.2% (±0.5-1.2) in the MSCT models. Ti-Zr implants produced 4.1-7.1% (±0.3-3.0) artefacts in CBCT and 5.4-15.7% (±0.5-1.3) in MSCT. Significantly more artefacts were found in the MSCT vs CBCT models for both implant materials (p < 0.05). Significantly fewer artefacts were visible in the 3D models from scans with higher kilovolts in MSCT and smaller voxel size in CBCT.

CONCLUSIONS

Among the four applied protocols, the lowest artefact proportion of ZrO2 and Ti-Zr implants in STL models was observed with CBCT and the 0.3 mm³ voxel size.

Evaluation of the accuracy of intraoral scanners for complete-arch scanning: A systematic review and network meta-analysis

OBJECTIVES

This network meta-analysis (NMA) aimed to compare the complete-arch scanning accuracy of different intraoral scanners (IOSs) to that of reference standard tessellation language (STL) files.

DATA

Studies comparing the trueness and precision of IOS STL files with those of reference STL scans for different arch types (dentate, edentulous, completely edentulous with implants, and partially edentulous with implants) were included in this study.

SOURCES

An electronic search of five databases restricted to the English Language was conducted in October 2021.

STUDY SELECTION

A total of 3,815 studies were identified, of which 114 were eligible for inclusion. After study selection and data extraction, pair-wise comparison and NMA were performed to define the accuracy of scanning for four arch subgroups using four outcomes (trueness and precision expressed as mean absolute deviation and root mean square values). Cochrane guidelines and the QUADAS-2 tool were used to assess the risk of bias. GRADE was used for certainty assessment.

RESULTS

Fifty-three articles were included in this NMA. Altogether, 26 IOSs were compared directly and indirectly in 10 network systems. The accuracy of IOSs scans were not significantly different from the reference scans for dentate arches (three IOSs), edentulous arches (three IOSs), and completely edentulous arches with implants (one IOS). The accuracy of the IOSs was significantly different from the reference scans for partially edentulous arches with implants. Significant accuracy differences were found between the IOSs, regardless of clinical scenarios.

CONCLUSIONS

The accuracy of complete-arch scanning by IOSs differs based on clinical scenarios.

CLINICAL SIGNIFICANCE

Different IOSs should be used according to the complete arch type.

Comparative Analysis of Three Facial Scanners for Creating Digital Twins by Focusing on the Difference in Scanning Method

BACKGROUND

Multi-dimensional facial imaging is increasingly used in hospital clinics. A digital twin of the face can be created by reconstructing three-dimensional (3D) facial images using facial scanners. Therefore, the reliability, strengths, and weaknesses of scanners should be investigated and approved; Methods: Images obtained from three facial scanners (RayFace, MegaGen, and Artec Eva) were compared with cone-beam computed tomography images as the standard. Surface discrepancies were measured and analyzed at 14 specific reference points; Results: All scanners used in this study achieved acceptable results, although only scanner 3 obtained preferable results. Each scanner exhibited weak and strong points because of differences in the scanning methods. Scanner 2 exhibited the best result on the left endocanthion; scanner 1 achieved the best result on the left exocanthion and left alare; and scanner 3 achieved the best result on the left exocanthion (both cheeks); Conclusions: These comparative analysis data can be used when creating digital twins through segmentation, selecting and merging data, or developing a new scanner to overcome all shortcomings.

Effect of measurement techniques and operators on measured deviations in digital implant scans

OBJECTIVES

To evaluate the effect of different measurement techniques and operators on measured deviations in vitro implant scans.

METHODS

A 2-piece system that comprises a healing abutment (HA) and a scan body (SB) was mounted onto an implant at right first molar site of a polymethylmethacrylate mandibular dentate model. Model was digitized by using an industrial scanner (reference model scan, n = 1) and an intraoral scanner (test scan, n = 20). All standard tessellation language files were imported into a 3-dimensional analysis software and superimposed. Three operators with similar experience performed circle-based and point-based deviation analyses (n = 20). Deviations measured with different techniques were compared with paired samples t-test within each operator, while the reliability of the operators was assessed by using F-tests for both technqiues (α = 0.05).

RESULTS

Point-based technique resulted in lower deviations than circle-based technique for all operators (P = .001) with to higher reliability among operators (ICC = 0.438, P = .001). The correlation among the operators was nonsignificant when circle-based technique was used (ICC = 0.114, P = .189).

CONCLUSION

Lower deviations were detected with the point-based technique. In addition, different operators' measurements had higher correlation when point-based technique was used compared with circle-based technique.

CLINICAL SIGNIFICANCE

Point-based technique may be preferred over circle-based technique for research studies on scan accuracy of implants, given its higher reliability. The accuracy of measured deviations may increase if the number of planes are increased, which can facilitate point generation at different surfaces of the scan body.

Effect of intraoral scanner and fixed partial denture situation on the scan accuracy of multiple implants: An in vitro study

BACKGROUND

Accuracy of intraoral implant scans may be affected by the region of the implant and the type of the intraoral scanner (IOSs). However, there is limited knowledge on the scan accuracy of multiple implants placed for an implant-supported fixed partial denture (FPD) in different partially edentulous situations when digitized by using different IOSs.

PURPOSE

To investigate the effect of IOS and FPD situation on the scan accuracy of two implants when partial-arch scans were performed.

MATERIALS AND METHODS

Tissue level implants were placed in 3 maxillary models with implant spaces either at right first premolar and right first molar sites (Model 1, 3-unit FPD), at right canine and right first molar sites (Model 2, 4-unit FPD), or at lateral incisor sites (Model 3, 4-unit FPD). Reference standard tessellation language (STL) files of the models were generated by using an optical scanner (ATOS Capsule 200MV120). Two IOSs (CEREC Primescan [CP] and TRIOS 3 [TR]) were used to perform partial-arch scans (test-scans) of each model (n = 14), which were exported in STL format. A metrology-grade analysis software (GOM Inspect 2018) was used to superimpose test-scan STLs over the reference STL to calculate 3D distance, inter-implant distance, and angular (mesiodistal and buccopalatal) deviations. Trueness and precision analyses were performed by using bootstrap analysis of variance followed by Welch tests with Holm correction (α = 0.05).

RESULTS

Trueness of the scans was affected by IOS and FPD situation when 3D distance deviations were considered, while inter-implant distance, mesiodistal angular, and buccopalatal angular deviations were only affected by the FPD situation (p < 0.001). Scan precision was affected by the interaction between the IOSs and the FPD situation when 3D distance and buccopalatal angular deviations were concerned, while IOSs and FPD situation were effective when all deviations were concerned (p≤ 0.001). When 3D distance deviations were considered, CP scans had higher accuracy TR scans in Models 1 and 3 (p ≤ 0.002), and the Model 1 scans had the highest accuracy (p < 0.001). When inter-implant distance deviations were considered, Model 1 scans had the highest accuracy with CP and higher accuracy than Model 2 when TR was used (p ≤ 0.030). When mesiodistal angular deviations were considered, Model 1 scans had the highest accuracy (p ≤ 0.040). When buccopalatal angular deviations were considered, Model 1 scans had the highest accuracy among models when CP was used (p ≤ 0.020).

CONCLUSIONS

Posterior 3-unit fixed partial denture implant scans, CP scans, and combination of these two factors had accuracy either similar to or better than their tested counterparts.

Additive or subtractive manufacturing of crown patterns used for pressing or casting: A trueness analysis

OBJECTIVES

To investigate the effect of subtractive and additive manufacturing techniques on the trueness of crown patterns used for pressing or casting.

MATERIAL AND METHODS

A complete-coverage mandibular right first molar crown was designed in standard tessellation language (STL) format. This STL served as the control (C-STL) and was used to fabricate 30 crown patterns in 3D-printed resin (PR, ProArt Print Wax), millable wax suitable for casting (BW, ProArt CAD Wax Blue), and millable wax suitable for pressing (YW, ProArt CAD Wax Yellow) (n = 10). Subtractively manufactured patterns were fabricated by using a 5-axis milling unit (PrograMill PM7), while 3D-printed patterns were fabricated by using a digital light processing-based 3D printer (PrograPrint PR5; Ivoclar Vivadent, Schaan, Liechtenstein). All fabricated patterns were digitized by using an intraoral scanner (CEREC Primescan SW 5.2) to generate test-STLs. C-STL and test-STLs were transferred into a 3D analysis software (Medit Link v 2.4.4). Trueness evaluation was performed at 4 different surfaces (external, intaglio with margin, marginal, and intaglio without margin) and for complete scan meshes (overall) by using the root mean square (RMS) method. Data were analyzed with Kruskal-Wallis and Mann-Whitney U tests (α = .05).

RESULTS

RMS values varied significantly at all surfaces (P < .001), except for marginal surface (P = .151). PR had the highest RMS values at external surface (P ≤ .007), intaglio surfaces (with (P ≤ .003) and without margin (P ≤ .005)), and overall (P ≤ .01). No significant differences were observed between YW and BW (P ≥ .223).

CONCLUSION

Patterns fabricated by using subtractive manufacturing exhibited high trueness. The deviation values, in general, were small, particularly at intaglio and marginal surfaces; thus, clinical difference in crown-fit may be negligible using additive or subtractive technique.

CLINICAL SIGNIFICANCE

The fit of definitive crowns may be similar when tested crown patterns are additively or subtractively manufactured. However, crowns fabricated by using tested 3D-printed resin patterns may require more chairside adjustments compared with those fabricated by using subtractively manufactured wax patterns.

Effect of Different CAD/CAM Milling and 3D Printing Digital Fabrication Techniques on the Accuracy of PMMA Working Models and Vertical Marginal Fit of PMMA Provisional Dental Prosthesis: An In Vitro Study

Background: Minimal evidence exists on the efficacy of different digital manufacturing techniques in the fabrication of precise dental working models and provisional prosthesis. Aim of study: The objective was to evaluate the effect of two digital fabrication techniques (CAD/CAM milling and 3D printing) on the accuracy of PMMA working models and marginal fit of PMMA provisional prosthesis. Materials and methods: Two abutment teeth of modified typodont were prepared. A reference stone model was fabricated, and an optical impression was performed to obtain a CAD reference model. Four CAM milled working models and four printed working models were fabricated. CAD software was used to design the provisional prostheses. Group A tested four milled provisional prosthesis, and group B tested four 3D printed prosthesis. The 3D accuracy of working models was assessed by superimposition of the control reference working model on the CAD test working model. A stereo-optical microscope was used to assess vertical marginal fit of the provisional dental prosthesis. Student’s t and Mann–Whitney U tests were utilized to compare the two groups. Results: Results showed no statistically significant difference between the two tested groups. Conclusion: The two digital working model fabrication techniques recorded comparable accuracy. Similarly, 3D printed provisional prosthesis showed comparable marginal fit to the CAD/CAM milled ones.

Congruence between the meshes of a combined healing abutment-scan body system acquired with four different intraoral scanners and the corresponding library file: an in vitro analysis

OBJECTIVES

To investigate the congruence between the meshes of a combined healing abutment-scan body (CHA-SB) system acquired with four different intraoral scanners and the corresponding library file.

MATERIAL AND METHODS

A CHA-SB was fixed to an implant at the right first molar position in a dentate mandibular model and digitized by using 4 different intraoral scanners (IOSs) [TRIOS 3 (T3), Omnicam (OC), Primescan (PS), and Virtuo Vivo (VV)] (n=8) and an industrial grade optical scanner (ATOS Core 80) (n=1) to generate standard tessellation language (STL) files of the test scans (CHA-SB-STLs) and the master reference model scan (MRM-STL). A reverse engineering software (Studio Geomagic X) was used to superimpose the proprietary library file of the CHASB over the generated STL files. Root mean square (RMS) values representing the deviations between the library file and the superimposed STL files were statistically analyzed by using 1-way ANOVA (α=.05). Qualitative analysis of the deviations was performed by visual inspection.

RESULTS

Differences between the congruence of the library file and the CHA-SB scans among different IOSs were nonsignificant (F=1.619, df= 3, P = .207). The single best result was 29 ±28.9 µm for OC, 30.8 ±29.6 µm for VV, 35.6 ±35.5 µm for T3, and 39.5 ±39.2 µm for PS, which were all above the deviation value of the scan performed by using the industrial-grade scanner (23.2 ±23.2 µm).

CONCLUSION

The dimensional congruence between the library file and the standard tessellation language file of the combined healing abutment-scan body system scans was similar when intraoral scanners with different acquisition technologies were used to scan a model with an implant.

CLINICAL SIGNIFICANCE

Scans of the tested intraoral scanners may result in crowns with similar positional accuracy, given the similarities in congruence of their scans with the library file.

Influence of 3D analysis software on measured deviations of CAD-CAM resin crowns from virtual design file: an in-vitro study

OBJECTIVES

To evaluate a nonmetrology-grade and a metrology-grade 3D analysis software when measuring the deviations of CAD-CAM fabricated crowns from the virtual design file.

MATERIALS AND METHODS

A right first molar on a mandibular dentate model was prepared and scanned by using an intraoral scanner, i500 (Medit). A complete coverage crown was designed in standard tessellation language format and 20 resin crowns were fabricated by using computer aided design-computer aided manufacturing (CAD-CAM). The crowns were then digitized by using the same intraoral scanner (test-scans). Root mean square (RMS) method was used to evaluate the deviations between the test-scans and the design file of the crowns on 3 surfaces (overall, external, and internal) by using a metrology-grade, Geomagic Control X (3D Systems) and a nonmetrology-grade, Medit Link (Medit) software. The data were analyzed with Welch two-sample t-tests to compare two software for the non-inferiority of the nonmetrology-grade software with a 50 µm threshold and the potential superiority of the metrology-grade software (α = 0.05).

RESULTS

The Welch two-sample t-tests for the non-inferiority analysis showed that the differences between the nonmetrology-grade and the metrology-grade software were below the threshold of 50 µm for each surface tested (p <.001). The differences between the two-tested software were nonsignificant for each surface analyzed when superiority was considered (p ≥.194).

CONCLUSION

The nonmetrology-grade software performed similar to the metrology-grade software when analyzing the deviations of CAD-CAM crowns. Therefore, the nonmetrology-grade 3D analysis software may be considered for the deviation measurements of similar restorations.

CLINICAL SIGNIFICANCE

The trueness of crowns after fabrication may affect their fit, and 3D analysis of trueness prior to the delivery appointment with the tested nonmetrology-grade software after fabrication may facilitate potential clinical adjustments and delivery of the crowns.

Effect of Printing Layer Thickness on the Trueness and Margin Quality of 3D-Printed Interim Dental Crowns

The information in the literature on the effect of printing layer thickness on interim 3D-printed crowns is limited. In the present study, the effect of layer thickness on the trueness and margin quality of 3D-printed composite resin crowns was investigated and compared with milled crowns. The crowns were printed in 3 different layer thicknesses (20, 50, and 100 μm) by using a hybrid resin based on acrylic esters with inorganic microfillers or milled from polymethylmethacrylate (PMMA) discs and digitized with an intraoral scanner (test scans). The compare tool of the 3D analysis software was used to superimpose the test scans and the computer-aided design file by using the manual alignment tool and to virtually separate the surfaces. Deviations at different surfaces on crowns were calculated by using root mean square (RMS). Margin quality of crowns was examined under a stereomicroscope and graded. The data were evaluated with one-way ANOVA and Tukey HSD tests. The layer thickness affected the trueness and margin quality of 3D-printed interim crowns. Milled crowns had higher trueness on intaglio and intaglio occlusal surfaces than 100 μm-layer thickness crowns. Milled crowns had the highest margin quality, while 20 μm and 100 μm layer thickness printed crowns had the lowest. The quality varied depending on the location of the margin.