Accuracy of Digital Impressions and Fitness of Single Crowns Based on Digital Impressions

In vitro assessment of the accuracy of two intra-oral scanners for post space scanning in a fully digital workflow

BACKGROUND

With the rapid advancements in computer-aided imaging, the potential for chairside fabrication of custom-made posts utilizing intraoral scanners may offer a reliable alternative to traditional physical impressions. Accordingly, this study aimed to evaluate the accuracy (trueness and precision) of two intra-oral scanners when different post space diameters were employed. Additionally, the scan depth of each intra-oral scanner (IOS) was assessed.

METHODS

An endodontically treated mandibular canine was inserted in a printed typodont model and prepared with two post-space diameters; a small one (1.5 mm) and a large one (2 mm). Polyvinyl siloxane impressions for the two post-space diameters were taken and then scanned with an extra-oral scanner to serve as reference scans. Each post-space diameter was scanned using CEREC Primescan (n = 8) and Medit i700 (n = 8) intra-oral scanners. Standard tessellation language (STL) files of all intra-oral and extra-oral scans were uploaded to a 3D matching program to evaluate trueness, precision, and post-space length difference. Statistical analysis was performed using different tests for parametric and non-parametric data. The significance level was set at P < 0.05.

RESULTS

Regarding the effect of the IOS and the effect of the post-space diameter, both Medit i700 and the small diameter groups using both scanners showed significantly higher root mean square (RMS) values when evaluating trueness. For precision, Medit i700 showed a significantly higher RMS value in the large diameter group. Medit i700 showed a significantly higher difference in post-space length than Primescan in both diameters. Primescan recorded a zero difference in the large diameter group compared to the reference scan.

CONCLUSIONS

The IOS type and the post-space diameter influenced the scan accuracy and the depth of the scan. Accuracy results were superior when Primescan was implemented for scanning the large diameter post-space subgroup.

The Comparison of Accuracy of Post Space Digital Impressions Made by Three Different Intraoral Scanners: An In Vitro Study

BACKGROUND AND OBJECTIVES

The present study aims to assess and compare the accuracy of post-space impressions captured by three different intraoral scanners (IOS) using various canal diameters.

METHODS

Three extracted natural maxillary central incisors were selected and prepared for a 1 mm wide margin and a 3 mm ferrule. All steps required for the endodontic procedure were performed, and the post space was prepared using post drills. The post length was kept constant at 12 mm, whereas the width was varied (Group 1: 1.4 mm, Group 2: 1.6 mm, and Group 3: 1.8 mm). Three IOSs (Trios3, iTero2, and Medit i700) were used to acquire a digital impression of the prepared post space. Each tooth was scanned 10 times by each scanner. So, in the end, 90 digital images were recorded, and the STL files were stored. GC Pattern resin was used to fabricate resin post and core patterns, which were scanned using an extraoral scanner (EOS). The STL file obtained was used as the reference file. To evaluate the trueness of the tested IOSs, each three-dimensional scan from an IOS was superimposed on the reference scan with the help of the Medit Design software 2.1.4. The software generates color plots and gives numerical values as deviations in the Root mean square (RMS) for the variance between the two superimposed scans. The data collected was tabulated for statistical analysis. One Way ANOVA was used to test the significance difference between three different IOSs, followed by Bonferroni Post-hoc test pairwise test to identify the differences between every two different IOS. Statistical significance was set at p < 0.05.

RESULTS

The mean deviation for trueness in post space impression values recorded by the Medit i700 was highest among groups 1, 2, and 3 [0.825 (±0.071), 0.673 (±0.042) and 0.516 (±0.039), respectively], followed by iTero2 [0.738 (±0.081), 0.569 (±0.043) and 0.470 (±0.037), respectively] and Trios3 [0.714 (±0.062), 0.530 (±0.040) and 0.418 (±0.024), respectively]. Significant differences were found between the groups for all three IOSs (Trios3: p-value < 0.0001; iTero2: p-value < 0.0001; Medit i700: p-value < 0.0001).

CONCLUSIONS

Within the limitations of this study, it can be concluded that Trios3 IOS has higher accuracy (as it exhibited minimal deviation for trueness) in recording post space, followed by iTero2 and Mediti700 IOS. As the diameter of the post space is increased, the accuracy of recording by IOS increases. For all the tested IOSs (except for Trios3 and iTero2, when used to record post space with 1.8 mm canal diameter), the deviations in trueness were higher than the clinically acceptable limits. Thus, IOSs should be used cautiously when recording impressions of post spaces.

Complete-arch accuracy of seven intraoral scanners measured by the virtual-fit method

OBJECTIVES

This study compared the accuracy of seven intraoral scanners (IOS) by the virtual-fit method.

METHODS

Four maxillary arches with tooth abutments were scanned with an industrial reference scanner (n=1) and by Aoralscan3, EmeraldS, Helios600, Lumina, Mediti700, Primescan, and Trios5 IOSs (each n=12). Two complete-arch fixed frameworks were designed on each IOS scan with a 70 µm (group 70) and a 90 µm internal cement space (group 70+20, additional 20 µm at the margin). The virtual-fit method was comprised of superimposing the framework designs onto the reference scan using a non-penetrating algorithm simulating the clinical try-in. Internal and marginal gaps were measured. Precision was estimated by the mean absolute errors (MAE).

RESULTS

In group 70, Mediti700 (43 µm), Primescan (42 µm), and EmeraldS were in the best homogenous subset for the marginal gap, followed by the Lumina (67 µm), Aoralscan3 (70 µm), and Trios5 (70 µm), whereas Helios600 (118 µm) was in the third subset. Based on the MAE at the margin, Mediti700, Trios5, and EmeraldS were in the first-best homogenous subset, followed by Primescan. Lumina and Helios600 were in the third subset, and Aoralscan3 was in the fourth subset. In group 70+20, the marginal gap was significantly decreased for Lumina and Aoralscan3, whereas MAE significantly decreased for EmeraldS and Aoralscan3. The rank of IOSs was similar for the internal gap.

CONCLUSION

EmeraldS, Mediti700, Primescan, and Trios5 meet the marginal and internal fit criteria for fixed tooth-borne complete arch restorations. Increasing the cement space during design could enhance restoration fit.

CLINICAL SIGNIFICANCE

The virtual-fit alignment method can effectively evaluate the accuracy of different intraoral scanners, offering valuable clinical guidance for distinguishing among them. Recent software and hardware versions of long-standing IOS manufacturers are suitable for fabricating complete arch restoration.

Fabrication trueness and marginal quality of additively manufactured resin-based definitive laminate veneers with different restoration thicknesses

OBJECTIVES

To evaluate how restoration thickness (0.5 mm and 0.7 mm) affects the fabrication trueness of additively manufactured definitive resin-based laminate veneers, and to analyze the effect of restoration thickness and margin location on margin quality.

METHODS

Two maxillary central incisors were prepared either for a 0.5 mm- or 0.7 mm-thick laminate veneer. After acquiring the partial-arch scans of each preparation, laminate veneers were designed and stored as reference data. By using these reference data, a total of 30 resin-based laminate veneers were additively manufactured (n = 15 per thickness). All veneers were digitized and stored as test data. The reference and test data were superimposed to calculate the root mean square values at overall, external, intaglio, and marginal surfaces. The margin quality at labial, incisal, mesial, and distal surfaces was evaluated. Fabrication trueness at each surface was analyzed with independent t-tests, while 2-way analysis of variance was used to analyze the effect of thickness and margin location on margin quality (α = 0.05).

RESULTS

Regardless of the evaluated surface, 0.7 mm-thick veneers had lower deviations (P < 0.001). Only the margin location (P < 0.001) affected the margin quality as labial margins had the lowest quality (P < 0.001).

CONCLUSION

Restoration thickness affected the fabrication trueness of resin-based laminate veneers as 0.7 mm-thick veneers had significantly higher trueness. However, restoration thickness did not affect the margin quality and labial margins had the lowest quality.

CLINICAL SIGNIFICANCE

Laminate veneers fabricated by using tested urethane-based acrylic resin may require less adjustment when fabricated in 0.7 mm thickness. However, marginal integrity issues may be encountered at the labial surface.

Influence of intraoral scanner and finish line location on the fabrication trueness and margin quality of additively manufactured laminate veneers fabricated with a completely digital workflow

STATEMENT OF PROBLEM

Knowledge of the fabrication trueness and margin quality of additively manufactured (AM) laminate veneers (LVs) when different intraoral scanners (IOSs) and finish line locations are used is limited.

PURPOSE

The purpose of this in vitro study was to evaluate the fabrication trueness and margin quality of AM LVs with different finish line locations digitized by using different IOSs.

MATERIAL AND METHODS

An LV preparation with a subgingival (sub), equigingival (equi), or supragingival (supra) finish line was performed on 3 identical maxillary right central incisor typodont teeth. Each preparation was digitized by using 2 IOSs, (CEREC Primescan [PS] and TRIOS 3 [TS]), and a reference LV for each finish line-IOS pair (n=6) was designed. A total of 90 LVs were fabricated by using these files and urethane acrylate-based definitive resin (Tera Harz TC-80DP) (n=15). Each LV was then digitized by using PS to evaluate fabrication trueness (overall, external, intaglio, and marginal surfaces). Each LV was also qualitatively evaluated under a stereomicroscope (×60), and the cervical and incisal margin quality was graded. Fabrication trueness and cervical margin quality were evaluated by using 2-way analysis of variance, while Kruskal-Wallis and Mann Whitney-U tests were used to evaluate incisal margin quality (α=.05).

RESULTS

The interaction between the IOS type and the finish line location affected measured deviations at each surface (P≤.020). PS-sub and TS-supra had higher overall trueness than their counterparts. and the subgingival finish line resulted in the lowest trueness (P≤.005). PS and the subgingival finish line led to the lowest trueness of the external surface (P≤.001). TS-sub had the lowest intaglio surface trueness among the TS subgroups, and PS-sub had higher trueness than TS-sub (P<.001). PS-sub and PS-supra had higher marginal surface trueness than their TS counterparts (P<.001). TS resulted in higher cervical margin quality (P=.001).

CONCLUSIONS

Regardless of the IOS tested, subgingival finish lines resulted in the lowest trueness. The effect of IOS on the measured deviations varied according to the surface evaluated and finish line location. The cervical margin quality of AM LVs was higher when TS was used.

Impact of different CAD software programs on marginal and internal fit of provisional crowns: An in vitro study

Statement of the problem

Different CAD software programs used for designing crowns show variations in marginal and internal fit. Marginal and internal discrepancies may cause poorly fitting crowns.

Purpose

The aim of this study was to compare the marginal and internal fit of single crown temporary restorations designed using three different CAD software programs.

Materials and methods

Dentbird, Exocad and Inlab 20 were used to design temporary single crowns using the same cement gap. Three experimental groups (n = 10/group) were formed based on the CAD software used. Geomagic Control X three-dimensional analysis software was used to compare the marginal and internal fit among the groups. Measurements were obtained at nine different thickness points. IBM SPSS Statistics, version 22 was used for all statistical analyses.

Results

Among the CAD software programs tested, Dentbird produced the best internal fit on the buccal surface and the best marginal fit on both buccal and mesial surfaces. Exocad achieved the best values on the distal surface for both internal and marginal fit, while Inlab showed the best values on the mesial surface for internal fit and on the palatal surface for marginal fit.

Conclusions

The Dentbird CAD software program provided the most accurate fit values that closely matched the design. The marginal and internal fit oftemporary crowns may vary depending on the CAD software used.

Digitization accuracy and scannability of different prosthodontic materials: An in vitro trial

STATEMENT OF PROBLEM

Digital scanning of different prosthodontic materials is commonplace in contemporary practice. However, the scannability of prosthodontic materials has not been thoroughly investigated.

PURPOSE

The purpose of this in vitro study was to evaluate the scanning accuracy and measure the unscanned area in a preset time limit of commonly used framework materials.

MATERIAL AND METHODS

A mandibular acrylic resin reference dental typodont with 3 teeth, with the central one prepared for a complete coverage crown, was digitized by using a desktop scanner. A complete coverage crown was generated in standard tessellation language (STL) format. Three groups were created from the digital design according to the crown material: milled polyetheretherketone (PEEK), milled airborne-particle abraded titanium, and milled polymethylmethacrylate (PMMA). They were scanned with the desktop scanner to be used as reference files for each group. The intraoral scanner Medit i700 was used to digitize each specimen 10 times (n=10). Using a nonmetrology grade software program, the deviations between the test STL file of the intraoral scanner and the reference STL file of the desktop scanner were assessed by using the RMS values. The unscanned surface area in a preset time limit of 6 seconds (scannability) was assessed. Groups were compared by using 1-way ANOVA followed by the Tukey post hoc test with Bonferroni correction when the results were significant. All tests were 2-tailed (α=0.05).

RESULTS

Regarding deviation analysis, RMS discrepancies were computed, and significant differences in trueness were found (P<.001) among the 3 studied groups. The titanium group had the highest trueness followed by the PEEK and PMMA groups, which were statistically similar (P>.05). Precision differed significantly among the 3 studied groups (P<.001). PEEK was the most precisely scanned material followed by titanium, and the PMMA group had the least precision. Regarding scannability, there were overall significant differences (P<.001). Titanium was the most scannable, followed by PEEK and then PMMA.

CONCLUSIONS

Airborne-particle abraded titanium had better trueness and scannability than PEEK and PMMA. However, PEEK was the most precisely scanned material.

Comparing the accuracy of distinct scanning systems and their impact on marginal/internal adaptation of tooth-supported indirect restorations. A scoping review

OBJECTIVE

To summarize the existing scientific evidence on the effect of distinct intraoral (IOS) and extraoral (EOS) scanners in terms of their accuracy for image acquisition and the marginal/internal adaptation of indirect restorations.

METHODS

The protocol of this scoping review is available online (https://osf.io/cwua7/). A structured search, with no date restriction, was performed in LILACS, MEDLINE via Pubmed, EMBASE, Web of Science, and Scopus, for articles written in English. The inclusion criteria were studies that considered at least two scanners, regardless of method (intra or extraoral), for the production of tooth-supported restorations. Two independent and blinded researchers screened the studies, collected and analyzed the data descriptively.

RESULTS

103 studies were included (55 on marginal/internal adaptation, 33 on accuracy, 5 on both outcomes, and 10 reviews). Most of them, shown clinically acceptable adaptation (<120 μm). Factors commonly related to the performance of scanners are: use of anti-reflection powders, method of image acquisition, and restoration/tooth characteristics. The need of anti-reflection powders was controversial. Different scanning principles seems to result on similar performance; IOS that combine them could be promising. The most explored systems were Omnicam - IOS, and inEos X5 - EOS, which showed similar performance on marginal/internal adaptation. Scarce studies explored the performance of EOS systems, especially in terms of accuracy. Different restoration designs as single-unit seemed not to modify the performance of scanners. Limited information is available regarding the planned cement space, restorative material and design (multi-unit restorations), as also techniques to measure adaptation.

CONCLUSIONS

Digital scanners are valid approaches to obtain accurate impressions resulting in clinically acceptable restorations. Systems that uses combined principles of image acquisition seems promising for optimal performance. Based on high discrepancy, the quality of evaluated evidence is low, and well-designed studies are still encouraged, especially considering validated IOS/EOS as a control comparison condition.

The trueness of an intraoral scanner in scanning different post space depths

OBJECTIVES

The purpose of this in vitro study was to evaluate the trueness of scanning the post space up to 20 mm with an intraoral scanner (IOS).

METHODS

We captured 20-, 18-, 16-, 14-, 12-, and 10-mm length post space scans using an IOS (Primescan) eight times each by shortening the apical 2 mm end of the same mandibular canine tooth. The reference impressions of each length group were taken using a light-body polyvinyl siloxane impression material and were scanned with an extraoral scanner. The recorded standard tessellation language (STL) data of all impressions were uploaded to a 3D matching program for the trueness evaluation via the root mean square (RMS) calculation. For the statistical analysis, the Kruskal-Wallis and post-hoc Mann-Whitney U nonparametric tests were performed to compare the differences among the groups (α=0.05).

RESULTS

The median RMS values increased in direct proportion to the length of the post space from 10 mm (357.1 µm) to 20 mm (897.5 µm). We noted a significant difference among groups (p< 0.001). In the pairwise comparisons, there were no significant differences between the 14 mm and 16 mm groups (p=0.431) or between the 18 mm and 20 mm groups (p=0.036), while other paired groups showed significant differences (p=0.001).

CONCLUSIONS

The scanned space depth affected the trueness of the IOS (Primescan). If the post depth was below 14 mm, and the minimum diameter was 2.2 mm, Primescan could be used for impressions of the post-core structure, simplifying the impression procedure.

CLINICAL SIGNIFICANCE

IOS seems to be a promising technology for taking digital impressions of post spaces, but cannot be recommended as a routine procedure at its present stage, as final results are highly dependent on the clinical situation. Further studies with different IOS systems are needed to gain sound evidence.

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crowns: A case series

OBJECTIVES

The aim of this study is to evaluate surgical and prosthetic outcomes of immediate functional loading of implants with glass-ceramic screw-retained single crowns.

METHODS

A total of 22 implants were placed. Within 24 hours, functional full-contour glass ceramic crowns were delivered to patients. The amount of attached gingiva, Simplified Oral Hygiene Index Score, bleeding on probing, time after extraction, bone type, implant size, soft tissue thickness, primary stability, a general fit of the restoration, occlusal and proximal contacts were recorded. Restorations were followed-up at 1, 3, and 6 months tracking marginal bone loss (MBL), noting changes in occlusal and interproximal contacts, checking other possible complications.

RESULTS

One implant failed and was removed after 4 weeks (95.5 % survival rate). The rest of the implants and crowns functioned with no complications during the follow-up period of 6 months. Factors such as time after extraction, bone type, implant size, soft tissue thickness, and primary stability recorded in Ncm and implant stability quotient (ISQ) values, were not associated with MBL (p<0.05). Mean MBL was found to be 0.3 mm (standard deviation = 0.42) mesially and 0.4 mm (standard deviation = 0.66) distally. One distal and one mesial proximal contact were found to be missing at the 6-month check-up appointment.

CONCLUSIONS

Within the limits of this study, fully digital workflow without a 3D printed model could be successfully employed for immediate functional loading with single-unit implant-supported crowns. Further studies are needed to obtain long-term results with a larger sample of patients.

CLINICAL SIGNIFICANCE

Model-free digital workflow and immediate functional loading of implant-supported monolithic glass-ceramic crown might be viable option to restore a single tooth defect.

Comparison of accuracy between digital and conventional implant impressions: two and three dimensional evaluations

PURPOSE

The present study compared the accuracy between digital and conventional implant impressions.

MATERIALS AND METHODS

The experimental models were divided into six groups depending on the implant location and the scanning span. Digital impressions were captured using the intraoral optical scanner TRIOS (3Shape, Copenhagen, Denmark). Conventional impressions were taken with the monophase impression material based on addition-cured silicones, Honigum-Mono (DMG, Hamburg, Germany). A high-precision laboratory scanner D900 (3Shape, Copenhagen, Denmark) was used to obtain digital data of resin models and stone casts. Surface tessellation language (STL) datasets from scanner were imported into the analysis software Geomagic Qualify 14 (3D Systems, Rock Hill, SC, USA), and scan body deviations were determined through two-dimensional and three-dimensional analyses. Each scan body was measured five times. The Sidak t test was used to analyze the experimental data.

RESULTS

Implant position and scanning distance affected the impression accuracy. For a unilateral arch implant and the mandible models with two implants, no significant difference was observed in the accuracy between the digital and conventional implant impressions on scan bodies; however, the corresponding differences for trans-arch implants and mandible with six implants were extremely significant (P<.001).

CONCLUSION

For short-span scanning, the accuracy of digital and conventional implant impressions did not differ significantly. For long-span scanning, the precision of digital impressions was significantly inferior to that of the traditional impressions.

Effect of Die Materials on Marginal and Internal Adaptation of Zirconia Copings: An In Vitro Study

Aim:

Close adaptation of cemented CAD/CAM restorations to their abutments is highly dependent on precise impressions and accurate replicas of teeth and adjacent oral tissues. This in-vitro study compared the effect of two die materials, as physical replicas of prepared teeth, on internal and marginal adaptations of zirconia copings to their corresponding abutments.

Materials and Methods:

A virtual model simulating a prepared premolar was designed and used for the milling of thirty identical metal models. Impression was taken of all models by Polyvinyl siloxane material. Fifteen impressions were poured in with Type IV stone and the other fifteen with polyurethane resin to make dies. All dies were scanned, and for each of them, zirconia coping was designed and milled. The copings were cemented to their corresponding metal models. Marginal gap between each coping and its metal model was measured at 20 points with a stereomicroscope (×60). Then the specimens were sectioned into two halves, and the internal gap was measured at seven points, including right and left cervico-axial, mid-axial, occluso-axial, and mid-occlusal. The data were analyzed with an independent T-test and repeated measure ANOVA at a 95% confidence level (p<0.05).

Results:

Mean value of marginal gap for Type IV stone and Exakto-Form groups were 54.31 ± 4.11 μm and 56.25 ± 4.24 μm, respectively. Mean values of the internal gaps for both groups ranged from 48 μm to 120 μm.

Conclusion:

Based on the results of this study, an internal and marginal adaptation of zirconia copings designed on digitized polyurethane and Type IV stone dies are clinically acceptable.

A Comparative Study of the Accuracy of Dental CAD Programs in Designing a Fixed Partial Denture

PURPOSE

Error testing at each stage of prosthetic manufacturing remains relatively underdeveloped for computer-aided design/computer-aided manufacturing methods, and no experimental studies have validated the computer-aided design programs. This study aimed to test the accuracy and trueness of the computer-aided design of a three-unit fixed prosthesis.

MATERIALS AND METHODS

Three computer-aided design programs (Exocad, Dental System™, and inLab 16) were tested on the designs of a three-unit fixed partial denture, and a three-dimensional analysis program was used to calculate the internal clearance error for the computer-aided design prostheses. The Kruskal-Wallis and Dunn's post hoc tests were used to reveal significant differences in trueness between the three computer-aided design programs (α < 0.05).

RESULTS

Dental System™ showed the lowest mean error values for #24 and #26 at the mesial margin (both 0 µm), mesial wall (0.10, 0.12 µm, respectively), occlusal surface (-0.05, 0.10 µm), distal wall (0.23, -0.02 µm), and distal margin (both 0 µm). In sum, except for the mesial margin and distal margin site of tooth #26, the mean error value of Dental System™ was statistically the lowest, followed by those of Exocad and inLab 16 (p < 0.003).

CONCLUSIONS

The accuracy of computer-aided design differed according to the type of computer-aided design program. Dental System™ achieved the best trueness at the margins, axial walls, and occlusal surface, followed by Exocad and inLab 16.

Influence of Liquid on the Tooth Surface on the Accuracy of Intraoral Scanners: An In Vitro Study

PURPOSE

To assess the influence of liquid attached on the tooth surfaces on the accuracy (trueness and precision) of intraoral scanners and the effectiveness of the drying method (using compression air) to exclude the influence of liquid on the scanning results.

MATERIALS AND METHODS

A mandibular jaw model was scanned using an industrial computed tomography scanner to obtain a reference model. A scanning platform was designed to simulate three specific tooth surface states (dry, wet, blow-dry). Two kinds of liquids (ultra-pure water and artificial saliva) were used for the test. Two intraoral scanners (Trios 3 and Primescan) were used to scan the mandibular jaw model 10 times under each condition. All scanning data were processed and analyzed using dedicated software (Geomagic Control 2015). Trueness and precision comparison were conducted within the 12 groups of 3D models divided based on different intraoral scanners and liquids used under each condition. The root mean square (RMS) value was used to indicate the difference between the aligned virtual models. The color maps were used to evaluate and observe the deviation distribution patterns. The 3-way ANOVA (condition, intraoral scanner, liquid) followed by the Tukey test were used to assess precision and trueness. The level of significance was set at 0.05.

RESULTS

The mean RMS values obtained from wet condition were significantly higher than those of the dry and blow-dry condition (p < 0.001, F = 64.033 for trueness and F = 54.866 for precision), which indicates less accurate trueness and precision for wet condition. For two different types of liquids, the mean RMS value was not significantly different on trueness and precision. The deviations caused by liquid were positive and mainly distributed in the pits and fissures of the occlusal surface of posterior teeth, the interproximal area of the teeth, and the margin of the abutments.

CONCLUSIONS

Liquid on the tooth surface could affect intraoral scanning accuracy. Blow-drying with a three-way syringe can reduce scanning errors.

Accuracy of impression-making methods in edentulous arches: An in vitro study encompassing conventional and digital methods

STATEMENT OF PROBLEM

Studies evaluating the accuracy of edentulous arch impressions encompassing conventional and digital methods are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate 8 impression-making methods for edentulous arches and to determine the effects of using a 3-dimensionally printed polyetheretherketone (PEEK) scanning aid on the accuracy of intraoral scanners.

MATERIAL AND METHODS

Three sets of edentulous arch typodonts were scanned with an industrial scanner as a reference. Subsequently, a scanning aid for the edentulous arch was individually designed on each reference scan dataset by using a 3-dimensional modeling software program and fabricated in PEEK with a 3-dimensional printer. Each typodont was scanned with 2 intraoral scanners 12 times, with and without the assistance of a scanning aid for the edentulous arch. Impressions were made with 4 different conventional impression materials (irreversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane)-12 times for each typodont-the casts were poured and digitized with a tabletop scanner. Each scan data set was superimposed over the corresponding scan data set, and the original and absolute distance values from the paired surface points were obtained to measure the trueness and precision. These were expressed by using the mean, median, root mean square, and (90 percentile-10 percentile)/2 of the absolute distance value (NMT) concepts, based on the raw data extraction protocol. A repeated-measures ANOVA followed by a post hoc Bonferroni test was conducted (α=.05).

RESULTS

The impression-making methods did not show statistically significant differences (P>.05) for either trueness or precision, particularly when the median values of the original and absolute distance values from the paired surface points were chosen as the standard values. One of the intraoral scanners used exhibited significantly superior outcomes to conventional impression materials when scanned with the scanning aid for the edentulous arch for both trueness and precision when the mean, root mean square, and NMT concepts were applied (P<.05).

CONCLUSIONS

Intraoral scanners demonstrated accuracy comparable with that of conventional impression materials for making edentulous arch impressions, regardless of the concepts used to express the trueness and precision. The PEEK-based scanning aid for the edentulous arch did not improve the accuracy of the intraoral scanners; however, its application resulted in higher accuracy compared with that of conventional impression materials.

Comparison between Occlusal Errors of Single Posterior Crowns Adjusted Using Patient Specific Motion or Conventional Methods

Recently, digital technology has been used in dentistry to enhance accuracy and to reduce operative time. Due to advances in digital technology, the integration of individual mandibular motion into the mapping of the occlusal surface is being attempted. The Patient Specific Motion (PSM) is one such method. However, it is not clear whether the occlusal design that is adjusted using PSM could clinically show reduced occlusal error compared to conventional methods based on static occlusion. In this clinical comparative study including fifteen patients with a single posterior zirconia crown treatment, the occlusal surface after a clinical adjustment was compared to no adjustment (NA; design based on static occlusion), PSM (adjusted using PSM), and adjustment using a semi-adjustable articulator (SA) for the assessment of occlusal error. The root mean square (RMS; μm), average deviation value (±AVG; μm), and proportion inside the tolerance (in Tol; %) were calculated using the entire, subdivided occlusal surface and the out of tolerance area. Using a one-way ANOVA, the RMS and +AVG from the out of tolerance area showed a statistical difference between PSM (202.3 ± 39.8 for RMS, 173.1 ± 31.3 for +AVG) and NA (257.0 ± 73.9 for RMS, 210.9 ± 48.6 for +AVG). For the entire and subdivided occlusal surfaces, there were no significant differences. In the color-coded map analysis, PSM demonstrated a reduced occlusal error compared to NA. In conclusion, adjustment occlusal design using PSM is a simple and effective method for reducing occlusal errors that are difficult to identify in a current computer-aided design (CAD) workflow with static occlusion.

A comparison of the marginal gaps of lithium disilicate crowns fabricated by two different intraoral scanners

BACKGROUND

The purpose of this study was to assess marginal gaps of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations.

METHODS

Twenty four Columbia model lower left molars were prepared for lithium disilicate crowns in a simulated environment by undergraduate students. The crown preparations were scanned by E4D and Trios 3 intraoral scanners and CAD/CAM lithium disilicate crowns designed and manufactured. The crowns were seated onto the original crown preparations and three vertical marginal gap measurements taken at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface.

RESULTS

The MMG was not statistically significantly different for the Trios 3 and E4D scanners (P = 0.111). There was no statistically significant effect of measurement location on the tooth on the marginal gap (P = 0.1134).

CONCLUSIONS

There was no difference in the MMGs of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations. Within the limitations of this study, the advances in scanning technology have produced small and insignificant improvements in the accuracy of crown margins.

Accuracy of Five Intraoral Scanners and Two Laboratory Scanners for a Complete Arch: A Comparative In Vitro Study

This study aims to evaluate the accuracy of five different intraoral scanners and two different laboratory scanners for a complete arch. A computer-aided design (CAD) reference model (CRM) was obtained using industrial scanners. A CAD test model (CTM) was obtained using five types of intraoral scanners (CS3500, CS3600, Trios2, Trios3, and i500) and two types of laboratory scanners (3shape E1 and DOF) (N = 20). In addition, the CRM and CTM were superimposed using a 3D inspection software (Geomagic control X; 3D Systems) and 3D analysis was performed. In the 3D analysis, the accuracy was measured by the type of tooth, the anterior and posterior region, and the overall region. As for the statistical analysis of the accuracy, the differences were confirmed using the Kruskal–Wallis H test (α = 0.05). Also, the differences between the groups were analyzed by post-hoc tests including Mann–Whitney U-test and Bonferroni correction method (α = 0.0017). There was a significant difference in the scanning accuracy of the complete arch according to the type of scanner (P < 0.001). The i500 Group showed the lowest accuracy (143 ± 69.6 µm), while the 3Shape E1 Group was the most accurate (14.3 ± 0.3 µm). Also, the accuracy was lower in the posterior region than in the anterior region in all types of scanners (P < 0.001). Scanning accuracy of the complete arch differed depending on the type of scanner. While three types of intraoral scanners (CS3500, CS3600, Trios3) can be recommended for scanning of a complete arch, the two remaining types of intraoral scanners (Trios2 and i500) cannot be recommended.

Trueness of cone beam computed tomography versus intra-oral scanner derived three-dimensional digital models: An ex vivo study

OBJECTIVES

To compare the trueness of 3D digital models derived from CBCT and IOS and to evaluate their accuracy for implementation in oral implant rehabilitation.

MATERIALS AND METHODS

A dry human mandible with a full set of intact teeth was included in the study. The mandible was scanned using Trios IOS and four different CBCT machines with various protocols for generation of 3D digital models. A µCT was utilized to scan each tooth individually. Following registration and segmentation, the trueness evaluation of 3D digital models was carried out by part comparison analysis and color-coded mapping of the superimposed teeth surfaces.

RESULTS

The four CBCT-derived 3D digital models with different protocols had better trueness than Trios IOS. NewTom VGi evo (110 KV), ProMax 3D (90 kV), 3D Accuitomo 170 (90 kV), Green 21 (110 kV), and Green 21 (90 kV) showed significantly better trueness than IOS. However, 3D Accuitomo 170 and ProMax 3D CBCT devices with 70 kV protocol showed better trueness without any significant difference with IOS.

CONCLUSION

CBCT-derived 3D digital models showed better trueness when compared with IOS. When CBCT data are available for preoperative planning for oral implant rehabilitation, it may preclude the need for IOS for obtaining 3D study models.

Accuracy of marginal fit and axial wall contour for lithium disilicate crowns fabricated using three digital workflows

STATEMENT OF PROBLEM

Comparative assessment of the effectiveness of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies used to fabricate complete-coverage restorations is needed. A quantitative assessment requires precise documentation of the marginal adaptation and external surface contour of fabricated restorations. Limited information is currently available regarding the effects of milling mode on marginal adaptation and reproduction of the external surface contour for CAD-CAM-fabricated restorations.

PURPOSE

The purpose of this in vitro study was to evaluate the outcomes for 3 different digital workflows on the marginal gap and the external surface contour reproducibility of CAD-CAM-fabricated lithium disilicate complete-coverage restorations.

MATERIAL AND METHODS

Twelve Ivorine molars were prepared to receive lithium disilicate crowns. The preparations were digitally recorded using 2 intraoral scanners (TRIOS 3; 3Shape A/S and Planmeca PlanScan; E4D Technologies), and the restorations were designed using their associated design software with reference to the anatomy of an unprepared tooth. The designed restorations were then manufactured from lithium disilicate blocks using a 3-axis milling machine. Twelve restorations were manufactured using the detailed mode (Planmeca PlanScan detailed mode [PPD-D]), and 12 using the standard mode for the Planmeca system (Planmeca PlanScan standard mode [PPD-S]). Restorations from the 3Shape system were fabricated using the detailed mode (TRIOS 3Shape detailed mode [T3S-D]). The restorations were secured on their associated preparation with an elastomeric material. The marginal gap of each restoration was then measured in the ImageJ software using images captured by a stereo microscope at ×20 magnification. External surface reproducibility was evaluated by measuring undercut at 4-line angles using a dental surveyor. Differences in the marginal gaps of restorations fabricated using the 3 different workflows were compared by Brown-Forsythe robust ANOVA, followed by a post hoc test (α=.05). Chi-square analysis (α=.05) was used to evaluate differences in the contours of the external surface of the restorations, resistance form, and marginal integrity produced using the 3 workflows.

RESULTS

The mean marginal gap for restorations fabricated using the T3S-D workflow was 60 μm, a distance significantly lower (P<.05) than that of PPD-D and PPD-S workflows, which yielded a marginal gap of 95 μm for the detailed mode and 124 μm for the standard mode of milling. Restorations fabricated using PPD-D and PPD-S workflows produced a significantly more reproducible external surface contour than those fabricated using the T3S-D workflow.

CONCLUSIONS

Restorations fabricated using the T3S-D workflow produced the smallest marginal gap. However, reproducibility of the external surface contour for this workflow was the worst of the three workflows analyzed.

A New Approach to Accuracy Evaluation of Single-Tooth Abutment Using Two-Dimensional Analysis in Two Intraoral Scanners

The aim of this study was to two-dimensionally evaluate deviation errors at five digital cross-sections of single-tooth abutment in regards to data obtained from two intraoral scanners, and to evaluate accuracy of individual scanners. Two intraoral scanners, the Trios 3^® (3 Shape, Copenhagen, Denmark) and EzScan^® (Vatech, Hwaseong, Korea), were evaluated by utilizing 13 stone models. The superimposed 3D data files were sectioned into five different planes: buccal-lingual section (BL), mesial-distal section (MD), transverse high section (TH), transverse middle section (TM), and transverse low section (TL). Accuracy comparison between the two scanners in 5 groups was performed. BL vs. MD of each scanner, and three transverse groups (TH, TM, TL) of each scanner were analyzed for accuracy comparison. In comparison of 2-D analyses for two intraoral scanners, Trios 3^® showed statistically significant higher accuracy in root mean square (RMS) at BL, TH, and TL (p < 0.05). For each scanner, RMS value showed that mesial-distal sections were more prone to error than buccal-lingual section, which exhibited statistically significant errors (p < 0.05) while the transverse groups did not. Two-dimensional analysis is more insightful than three-dimensional analysis on single-tooth abutment. In mesiodistal areas, rough prepped areas, and sharp edges where scanner accessibility is difficult, high deviation errors are shown.

Impact of Occlusal Intercuspal Angulation on the Quality of CAD/CAM Lithium Disilicate Crowns

PURPOSE

Modification of intercuspal angulation (ICA) influences the amount of tooth structure removal, which may impact the retention and resistance form of the preparation. This study evaluated the impact of ICA on the marginal gap of CAD/CAM crowns and the influence that tooth structure removal, caused by variation of ICA, has on the resistance and retention form of the preparation.

MATERIALS AND METHODS

Sixty ivorine molars were manufactured with various ICAs (100°, 110°, 120°, 140°, 160°, and 180°; 10 per group). The preparations were digitized using an intraoral scanner, and the crowns were designed using a design software. The designed crowns were then manufactured from lithium disilicate using a 3-axis milling machine, with the "detailed mode" selected for the manufacturing. The marginal gap of each crown was evaluated using a stereomicroscope at 20× magnification. Then, the marginal integrity and the resistance form of the preparation were assessed by tactile-visual evaluation, and they were given a categorical score. Crowns were then secured on their associated preparations using a temporary luting agent, and retention force was measured on a universal testing machine under tension with a 0.5 mm/min crosshead speed. Wilcoxon test followed by post-hoc tests (α = 0.05) were used to evaluate the impact of the ICA on the marginal gap and the retention form of the preparation. Fisher's exact test followed by post-hoc tests (α = 0.05) were used to assess the impact of the occlusal preparation design on the marginal integrity and the resistance form of the preparation.

RESULTS

The marginal gap was significantly larger for ICA-180 preparations (72 μm), compared to the other groups (ICA-180 vs ICA-100, ICA-110, ICA-120, and ICA-160 p = 0.0001; ICA-180 vs. ICA-140 p = 0.0017). None of the crowns for ICA-180 preparations had clinically acceptable resistance form. Preparations with ICAs of 100°, 110°, and 120° had a significantly higher value of retention than the other groups (ICA-100 vs. ICA-120 p = 0.0119; ICA-100 vs. ICA-140, ICA-160, and ICA-180 p < 0.0001; ICA-110 vs. ICA-140, ICA-160, and ICA-180 p = 0.0001; ICA-120 vs. ICA-180 p = 0.0017).

CONCLUSIONS

Crowns fabricated for preparations with various ICAs had clinically acceptable marginal adaptation. Variation in ICA impacts the loss of tooth structure. This loss of tooth structure may influence the resistance and retention form of the preparation.

Digital Implant Impression Technique Accuracy: A Systematic Review

PURPOSE

The objective was to provide a comprehensive systematic review about the accuracy of digital implant impression in comparison with the conventional implant impression approach.

MATERIALS AND METHODS

PubMed, Google Scholar and Cochrane databases were used to classify the related articles with no year limitation in 3 stages by 2 reviewers. Finally, 10 articles were included based on inclusion and exclusion criteria.

RESULTS

Five articles supported the use of intraoral scanners in implant dentistry. The two in vivo pilot studies showed that digital scanning is not reliable and could not be used in clinical routine.

CONCLUSION

Because each study included in this review has its unique methodology and design, it is therefore early to conclude whether to use digital scanners for clinical practice or not. More well-conducted in vitro and clinical trials studies are recommended to investigate the accuracy of intraoral scanners.

Method to evaluate the noise of 3D intra-oral scanner

In dentistry, 3D intra-oral scanners are gaining increasing popularity essentially for the production of dental prostheses. However, there is no normalized procedure to evaluate their basic performance and enable comparisons among intra-oral scanners. The noise value highlights the trueness of a 3D intra-oral scanner and its capacity to plan prosthesis with efficient clinical precision. The aim of the present study is to develop a reproducible methodology for determining the noise of an intra-oral scanner. To this aim, and as a reference, an ultra-flat and ultra-smooth alumina wafer is used as a blank test. The roughness is calculated using an AFM (atomic force microscope) and interferometric microscope measurements to validate this ultra-flat characteristic. Then, two intra-oral scanners (Carestream CS3500 and Trios 3Shape) are used. The wafer is imaged by the two intra-oral scanners with three different angles and two different directions, 10 times for each parameter, given a total of 50 3D-meshes per intra-oral scanner. RMS (root mean square), representing the noise, is evaluated and compared for each angle/direction and each intra-oral scanner, for the whole mesh, and then in a central ROI (region of interest). In this study, we obtained RMS values ranging between 5.29 and 12.58 micrometers. No statistically significant differences were found between the mean RMS of the two intra-oral scanners, but significant differences in angulation and orientations were found between different 3D intra-oral scanners. This study shows that the evaluation of RMS can be an indicator of the value of the noise, which can be easily assessed by applying the present methodology.

In vivo evaluation of inter-operator reproducibility of digital dental and conventional impression techniques

PURPOSE

The aim of this study was to evaluate and compare the inter-operator reproducibility of three-dimensional (3D) images of teeth captured by a digital impression technique to a conventional impression technique in vivo.

MATERIALS AND METHODS

Twelve participants with complete natural dentition were included in this study. A digital impression of the mandibular molars of these participants was made by two operators with different levels of clinical experience, 3 or 16 years, using an intra-oral scanner (Lava COS, 3M ESPE). A silicone impression also was made by the same operators using the double mix impression technique (Imprint3, 3M ESPE). Stereolithography (STL) data were directly exported from the Lava COS system, while STL data of a plaster model made from silicone impression were captured by a three-dimensional (3D) laboratory scanner (D810, 3shape). The STL datasets recorded by two different operators were compared using 3D evaluation software and superimposed using the best-fit-algorithm method (least-squares method, PolyWorks, InnovMetric Software) for each impression technique. Inter-operator reproducibility as evaluated by average discrepancies of corresponding 3D data was compared between the two techniques (Wilcoxon signed-rank test).

RESULTS

The visual inspection of superimposed datasets revealed that discrepancies between repeated digital impression were smaller than observed with silicone impression. Confirmation was forthcoming from statistical analysis revealing significantly smaller average inter-operator reproducibility using a digital impression technique (0.014± 0.02 mm) than when using a conventional impression technique (0.023 ± 0.01 mm).

CONCLUSION

The results of this in vivo study suggest that inter-operator reproducibility with a digital impression technique may be better than that of a conventional impression technique and is independent of the clinical experience of the operator.

Comparison of digital intraoral scanners by single-image capture system and full-color movie system

BACKGROUND

The use of dental computer-aided design/computer-aided manufacturing (CAD/CAM) restoration is rapidly increasing.

OBJECTIVE

This study was performed to evaluate the marginal and internal cement thickness and the adhesive gap of internal cavities comprising CAD/CAM materials using two digital impression acquisition methods and micro-computed tomography.

METHODS

Images obtained by a single-image acquisition system (Bluecam Ver. 4.0) and a full-color video acquisition system (Omnicam Ver. 4.2) were divided into the BL and OM groups, respectively. Silicone impressions were prepared from an ISO-standard metal mold, and CEREC Stone BC and New Fuji Rock IMP were used to create working models (n=20) in the BL and OM groups (n=10 per group), respectively. Individual inlays were designed in a conventional manner using designated software, and all restorations were prepared using CEREC inLab MC XL. These were assembled with the corresponding working models used for measurement, and the level of fit was examined by three-dimensional analysis based on micro-computed tomography.

RESULTS

Significant differences in the marginal and internal cement thickness and adhesive gap spacing were found between the OM and BL groups.

CONCLUSIONS

The full-color movie capture system appears to be a more optimal restoration system than the single-image capture system.

Evaluation of the accuracy and precision of four intraoral scanners with 70% reduced inlay and four-unit bridge models of international standard

The aims of this study were to evaluate the feasibility of 70% reduced inlay and 4-unit bridge models of International Standard (ISO 12836) assessing the accuracy of laboratory scanners to measure the accuracy of intraoral scanner. Four intraoral scanners (CS3500, Trios, Omnicam, and Bluecam) and one laboratory scanner (Ceramill MAP400) were used in this study. The height, depth, length, and angle of the models were measured from thirty scanned stereolithography (STL) images. There were no statistically significant mean deviations in distance accuracy and precision values of scanned images, except the angulation values of the inlay and 4-unit bridge models. The relative errors of inlay model and 4-unit bridge models quantifying the accuracy and precision of obtained mean deviations were less than 0.023 and 0.021, respectively. Thus, inlay and 4-unit bridge models suggested by this study is expected to be feasible tools for testing intraoral scanners.