Accuracy of 3D Printed and Digital Casts Produced From Intraoral and Extraoral Scanners With Different Scanning Technologies: In Vitro Study

Influence of CAD-CAM manufacturing methods on the accuracy and mechanical properties of implant-supported prostheses: A systematic review

PURPOSE

This systematic review aimed to provide comprehensive insights on the accuracy, fit, and mechanical characteristics of implant-supported computer-aided design and computer-aided manufacturing (CAD-CAM) prostheses, with a focus on milled and 3D-printed approaches.

METHODS

The research question focused on implant-supported dental prostheses, comparing different manufacturing techniques (conventional, milled, and 3D-printed) to determine the different factors affecting the mechanical properties and fit of the CAD-CAM implant-supported prosthesis. The eligibility criteria encompassed studies involving implant-supported restorations, clear reporting of manufacturing techniques, and English-language publications from the last decade. The search was conducted across three main databases, MEDLINE, Scopus, and Web of Science in September 2023. Publication details, study characteristics, and methodological details of each included study were described.

RESULTS

Of the initial 1964 articles, 581 met the inclusion criteria, and 104 studies were included in the final qualitative analysis. The majority of studies were conducted in the United States, Turkey, and Brazil. Fourteen studies evaluated accuracy parameters, while four studies focused on mechanical characteristics. The studies revealed variability in mechanical properties and marginal and internal fit, with fabrication methods impacting the structural integrity and stress distribution of the prostheses.

CONCLUSIONS

The findings suggest that digital manufacturing workflows, both milling and 3D printing, yield acceptable properties for implant-supported restorations with minimal variations in fit and accuracy. Notably, 3D printing and hybrid techniques demonstrate advantages in specific aspects like marginal fit and stress distribution. However, the milled prosthesis provided superior results in flexural strength and fracture resistance compared to conventional methods. Further research is needed to confirm these findings in clinical settings.

Digital impression perception among dental students in Saudi Arabia: A cross-sectional study

INTRODUCTION

The use of digital dentistry is rapidly increasing in prosthodontics. However, most dental students are not familiar with applying digital technologies in dental clinics. Thus, the aim of the current study was to assess the perception of dental students at different educational years towards digital impressions in comparison to conventional impressions.

MATERIALS AND METHODS

A cross-sectional questionnaire-based study was conducted on various educational years of dental students in the College of Dentistry, Imam Abdulrahman Bin Faisal University, between February and April 2023. The students had performed at least one intraoral scan (Trios 3shape) and another conventional polyether impression for phantom casts/patients. The questionnaire assessed students' perceptions of digital impressions using a 5-point scale ranging from strongly agree to strongly disagree. Mann-Whitney U and Kruskal-Wallis tests were used to compare students' perceptions of digital impressions according to gender and educational year, respectively.

RESULTS

The study included 122 students. About 55% were females with a mean (SD) age = 22.51 (3.36). Most students thought that digital impressions are faster and more user-friendly compared to conventional impressions. Significantly more female students thought that the handpiece was too big for intraoral use (p = 0.04) and that the process of the software was time-consuming and complicated. In general, higher educational year students were more satisfied with the digital impressions than lower educational year students.

CONCLUSIONS

Digital impressions were perceived by most students as being faster and easier than conventional ones. However, male students and those with higher educational years showed better perception of digital impression.

Finite Element Analysis: Connector Designs and Pontic Stress Distribution of Fixed Partial Denture Implant-Supported Metal Framework

This virtual study was designed to evaluate the stress-deformation of a metal fixed partial dentures (FPDs) pontic under different loads using two different connectors. The STL file was generated for a RPD of two implant-supported restorations. The Co-Cr metal substructure was designed with two types of connector design. The pontic is connected to implant-supported crowns with square and round shape connectors. This study was designed for a cementless-retained implant-supported FPD. Finite element modeling (FEM) is used to assess the stress and deformation of the pontic within a metal substructure as the FEM might provide virtual values that could have laboratory and clinical relevance. The Co-Cr alloy mechanical properties like the Poisson ratio and modulus of elasticity were based on the parameters of the three-dimensional structure additive method. Nonparametric analyses (Mann-Whitney U test) was used. The use of square or round connectors often resulted in non-significant changes in stress, and deformation under either three or each loaded point on the occlusal surface of a pontic (P > 0.05). However, the deformation revealed distinct variations between loads of the three points compared to each loaded point (P ≤ 0.05). According to this study data, the pontic occlusal surface appears to be the same in stress and deformation under different loads depending on whether square or round connectors are used. While at the same connector designs, the pontic occlusal surface deformed significantly at three loaded points than it did at each point.

Prediction of learning curves of wired and wireless intraoral scanners

This clinical study aimed to predict the learning curve of wireless and wired intraoral scanners (IOSs) and to compare the reduction patterns of working time. Overall, 14 participants were enrolled in the study. The intraoral scanning procedure was repeated four times, each using wireless and wired IOSs (i700; MEDIT). The work time from the first to the 600th iterations was predicted using the Wright model. Regarding statistical analysis, the Mann-Whitney U-test was performed for comparison between wireless and wired IOSs and between groups with and without an IOS usage experience, and the Friedman test was performed to evaluate the time reduction (α = 0.05). There was a significant difference between wireless and wired IOSs in the first (P = 0.008) and the third (P = 0.035) iterations. Moreover, the time for 600 iterations was statistically significantly different between wireless and wired IOSs (P < 0.05); however, there was no significant difference after the sixth iteration (e.g., seventh iteration: P = 0.062). In wireless IOS, no significant difference was found between participants with and without an IOS usage experience after the 34th iteration (P = 0.053). The difference in the learning effect between wireless and wired IOSs can be overcome by initial learning; however, an IOS usage experience can affect the learning time of wireless IOSs.

Marginal and internal fit of five-unit zirconia-based fixed dental prostheses fabricated with digital scans and conventional impressions: A comparative in vitro study

PURPOSE

This study aimed to compare the marginal and internal fit of five-unit zirconia-based fixed dental prostheses (FDPs) fabricated using digital scans and conventional impressions.

MATERIALS AND METHODS

Nine master models with three zirconia abutments were scanned with an intraoral scanner (test group), and nine conventional impressions (control group) of these same models were also made. The stone casts from these impressions were scanned with a laboratory extraoral scanner (D700, 3Shape, Copenhagen, Denmark). A total of 18 five-unit zirconia-based FDP frameworks (test group, n = 9; control group, n = 9) were manufactured. Marginal and internal fit (in μm) were evaluated using the replica method under micro-computed tomography. Analysis of variance (one-way ANOVA) and Kruskal-Wallis tests were used to compare continuous variables across two groups. A level of p < 0.05 was accepted as statistically significant.

RESULTS

The mean ± standard deviation of the marginal fit was 95.03 ± 12.74 μm in the test group and 106.02 ± 14.51 μm in the control group. The lowest marginal mean value was observed in the test group, with a statistically significant difference compared to the control group (F = 14.56, p < 0.05). The mean ± standard deviation of the internal fit was 103.61 ± 9.32 and 106.38 ± 7.64 μm, respectively, in the test and control groups, with no statistically significant difference (F = 1.56, p > 0.05). The mean values of both groups were clinically acceptable.

CONCLUSIONS

The five-unit zirconia-based FDPs fabricated with digital scans showed better fit than those in the conventional impression group. Within the limitations of this study, these results are encouraging, and continued progress in the digital field should allow for more accurate long-span restorations.

Intraoral scanners in children: evaluation of the patient perception, reliability and reproducibility, and chairside time-A systematic review

Purpose

The aim of this systematic review is to evaluate the perception of the patient, the chairside time, and the reliability and/or reproducibility of intraoral scanners for full arch in pediatric patients.

Methods

A data search was performed in four databases (Medline-Pubmed, Scopus, ProQuest and Web of Science) in accordance with the PRISMA 2020 statements. Studies were classified in three categories (patient perception, scanning or impression time and reliability and/or reproducibility). The resources, the data extraction and the quality assessment were carried out independently by two operators. The variables recorded were population characteristics, material and methods aspects and included country, study design and main conclusion. A quality assessment of the selected studies was performed with QUADAS-2 tool, and Kappa-Cohen Index was calculated to analyze examiner agreement.

Results

The initial search obtained 681 publications, and finally four studies matching inclusion criteria were selected. The distribution of the studies in the categories was three for the analysis of the patient's perception and scanning or impression time; and two items to assess the reliability and/or reproducibility of intraoral scans. All included studies have a repeated measures-transversal design. The sample size ranged between 26 and 59 children with a mean age. The intraoral scanners evaluated were Lava C.O.S, Cerec Omnicam, TRIOS Classic, TRIOS 3-Cart and TRIOS Ortho. The quality assessment of the studies using QUADAS-2 tool revealed a low risk of bias while evaluating patient perception, but an unclear risk of bias in the analysis of accuracy or chairside time. In relation to the applicability concerns, the patient selection was of high risk of bias. All studies agreed that the patient perception and comfort is better with intraoral scanners in comparison with the conventional method. The accuracy or reliability of the digital procedure is not clear, being clinically acceptable. In relation with the chairside time, it depends on the intraoral scanner, with contradictory data in the different analyzed studies.

Conclusion

The use of intraoral scanners in children is a favorable option, finding a significantly higher patient perception and comfort with intraoral scanners compared to the conventional impression method. The evidence for reliability or reproducibility is not strong to date, however, the differences between the intraoral measurements and the digital models would be clinically acceptable.

Effect of Different Scaling Methods on the Surface Topography of Different CAD/CAM Ceramic Compositions

This study evaluated the effect of ultrasonic and manual scaling using different scaler materials on the surface topography of computer-aided designing and computer-aided manufacturing (CAD/CAM) ceramic compositions. After scaling with manual and ultrasonic scalers, the surface properties of four classes of CAD/CAM ceramic discs: lithium disilicate (IPE), leucite-reinforced (IPS), advanced lithium disilicate (CT), and zirconia-reinforced lithium silicate (CD) of 1.5 mm thickness were evaluated. Surface roughness was measured before and after treatment, and scanning electron microscopy was used to evaluate the surface topography following the performed scaling procedures. Two-way ANOVA was conducted to assess the association of the ceramic material and scaling method with the surface roughness. There was a significant difference in the surface roughness between the ceramic materials subjected to different scaling methods (p < 0.001). Post-hoc analyses revealed significant differences between all groups except for IPE and IPS where no significant differences were detected between them. CD showed the highest surface roughness values, while CT showed the lowest surface roughness values for the control specimens and after exposure to different scaling methods. Moreover, the specimens subjected to ultrasonic scaling displayed the highest roughness values, while the least surface roughness was noted with the plastic scaling method.

Comparison of the color stability and surface roughness of 3-unit provisional fixed partial dentures fabricated by milling, conventional and different 3D printing fabrication techniques

OBJECTIVES

To compare the color stability and surface roughness of 3-unit provisional fixed partial dentures (FPDs) fabricated by milling, conventional, and different 3D printing fabrication techniques.

METHODS

A total sample of 160, 3-unit FPDs were subdivided into four groups; subtractive milled resin (SM), two 3D printed resins (Stereolithography; SLA and Digital Light Processing; DLP) and conventional self-cured polymethyl methacrylate resin (CM). Surface roughness (Ra) was assessed twice; at baseline (Ra1) and after artificial tooth brushing (Ra2). Color of the samples was measured after immersion in four different solutions (cola, coffee, black tea and distilled water) at three time intervals (1, 7 and 30 days). Comparisons of the Ra and the color change (∆E₀₀) were done using one-way ANOVA followed by multiple pairwise comparisons using Bonferroni adjusted significance level. Comparisons of the Ra at two stages (Ra1 and Ra2) were done using paired t-test. Univariate linear regression was performed followed by multivariable regression to assess the association between ∆E₀₀ and different factors (materials, solution, and time). Significance was set at P value <0.05.

RESULTS

The highest change in Ra following artificial tooth brushing was reported in the CM group, while the lowest change was reported in the SM group, with a significant difference between both groups (P<0.001). SM group had significantly lower ∆E₀₀ than the CM group followed by 3D printed SLA and DLP groups (P<0.001). Storage in coffee for 30 days showed the highest ∆E₀₀ values (P<0.001).

CONCLUSIONS

SM resin showed the least surface roughness and color change followed by 3D printed SLA resin. The difference in printing technology affected the tested properties with improved readings of 3D printed SLA resin.

CLINICAL SIGNIFICANCE

Milled provisional FPDs showed higher surface smoothness and color stability than those fabricated by SLA printing technology, but with no significant difference between both groups. Therefore, SLA printed resins can be an adequate substitute to milled resins in the fabrication of provisional FPDs to overcome the high expenses of milled provisional FPDs.

In vitro comparison of five desktop scanners and an industrial scanner in the evaluation of an intraoral scanner accuracy

OBJECTIVES

The study aimed to compare the precision of ATOS industrial, 3ShapeE4, MeditT710, CeramillMap400, CSNeo, PlanScanLab desktop, and Mediti700 intraoral scanners. The second aim was to compare the trueness of Mediti700 assessed by ATOS and desktop scanners.

METHODS

Four plastic dentate models with 7-12 abutments prepared for complete arch fixed dentures were scanned by all scanners three times. Scans were segmented to retain only the abutments. The precision and trueness were calculated by superimposing scans with the best-fit algorithm. The mean absolute distance was calculated between the scan surfaces. The precision was calculated based on the 12 repeats. Trueness was evaluated by superimposing the desktop and IOS scans to the industrial scans. IOS was also aligned with the two most accurate desktop scanners.

RESULTS

The precision of 3ShapeE4 and MeditT710 (3-4μm) was only slightly lower than that of ATOS (1.7μm, p<0.001) and significantly higher than CeramillMap400, CSNeo, and PlanScanLab (6-10 μm, p<0.001). The trueness was the highest for the 3Shape E4 (12-13 μm) and Medit T710 (13-16 μm) without significant difference. They were significantly better than CeramillMap400, CSNeo, and PlanScanLab (22-31μm, p<0.001). Accordingly, the Mediti700 trueness was evaluated by ATOS, 3ShapeE4, and MeditT710. The three trueness was not significantly different; ATOS (23-26 μm), 3Shape E4 (22-25 μm), and Medit T710 (20-23 μm).

CONCLUSIONS

All desktop scanners had the acceptable accuracy required for a complete arch-fixed prosthesis. The 3Shape E4 and the Medit T710 might be used as reference scanners for studying IOS accuracy.

CLINICAL SIGNIFICANCE

3ShapeE4, MeditT710, CeramillMap400, CSNeo, PlanScanLab laboratory, and Mediti700 intraoral scanners can be used for the prosthetic workflow in a complete arch. 3ShapeE4 and the MeditT710 could be used to test the accuracy of various phases of a laboratory workflow, replacing the industrial scanners.

Implementation of CAD/CAM program in a nonface-to-face classroom environment due to the COVID-19 pandemic

PURPOSE/OBJECTIVES

This study aimed to evaluate a nonface-to-face crown designing module in a preclinical dental course.

METHODS

Free dental planning software (Blue Sky Plan) was installed on the personal computers of dental college students, and a #46 full veneer crown designing practice was performed individually. An online survey was conducted on the computers' specification and main usage of the students, the practice process, and results. Statistical analysis was conducted to analyze the association between variables, such as "operating system," "central processing unit ," "number of cores," "random-access memory (RAM)," "graphic card," and task performance.

RESULTS

Of the D2 students, 75.4% (52 of 69) responded to the survey. Overall, 96% of the respondents used their computers, and all respondents had no problem running the program. Most of the students marked their level of computer literacy as intermediate and had purchased the computers for the purpose of performing light work. The most common specifications of the computer were Intel i5, quad core, 8 GB RAM, and Windows 10. Students had little experience with computer-aided design/computer-aided manufacturing before the class. The relationship between computer specifications and task performance was not statistically significant.

CONCLUSIONS

Overall, students with intermediate-level computer literacy used computers with less than the recommended specifications of the program; however, they were able to run the program and individually proceed with modules to submit results. Using an individually available crown designing program can provide an opportunity to diversify curricula and broaden students' perspectives even under circumstances like the COVID-19 pandemic that limits intimate face-to face classes.

Influences of Different CAD/CAM Ceramic Compositions and Thicknesses on the Mechanical Properties of Ceramic Restorations: An In Vitro Study

The aim of this study was to assess the influences of different CAD/CAM ceramic compositions and thicknesses on the surface roughness and hardness of ceramic restorations. Four different ceramics were used in the current study: lithium disilicate (LD), leucite reinforced (LE), advanced lithium disilicate (ALD), and zirconia-reinforced lithium silicate (ZLS). Each group included 30 specimens subdivided into three different ceramic thicknesses (0.5, 1 and 1.5 mm thicknesses). The microhardness was measured for all the specimens using a microhardness testing machine, while the surface roughness was measured using a non-contact optical profilometer at three intervals (before toothbrushing and after toothbrushing, with and without toothpaste). Three-way and two-way ANOVA were used to determine the factors influencing the surface roughness and microhardness. There was a significant difference in the surface roughness between the studied groups for all the thicknesses. The findings showed that ALD had the lowest surface roughness, while ZLS showed the highest surface roughness. Moreover, ALD, followed by ZLS, had the highest hardness, while LD and LE had the lowest hardness values. Regarding the thicknesses, both the 0.5 and 1 mm ceramic thicknesses showed a significantly lower surface roughness than the 1.5 mm thickness, while the 1.5 mm thickness showed a significantly higher microhardness than the 0.5 mm thickness. The surface roughness and hardness were significantly affected by the ceramic composition and type of filler. It is recommended to use 1.5 mm-thick ceramic materials for the fabrication of definitive full-coverage ceramic restorations, while veneers require 0.5 mm-thick materials. ALD is a promising CAD/CAM material that can be used for the fabrication of restorations with a proper strength in both anterior and posterior regions.

Influence of CAD/CAM Milling and 3D-Printing Fabrication Methods on the Mechanical Properties of 3-Unit Interim Fixed Dental Prosthesis after Thermo-Mechanical Aging Process

This study assessed the influence of CAD/CAM milling and 3D-printing fabrication methods on mechanical properties of 3-unit interim fixed dental prosthesis (IFDPs) after thermo-mechanical aging. Forty 3-unit IFDPs were fabricated on a mandibular right second premolar and second molar of a typodont cast. Samples were fabricated from the following materials; auto-polymerized polymethyl methacrylate (conventional resin), CAD/CAM PMMA (milled resin) and two different CAD/CAM 3D-printed composite resins; digital light processing Asiga (DLP AS) and stereolithography NextDent (SLA ND). Mechanical properties were compared between the studied materials using Kruskal−Wallis test, followed by multiple pairwise comparisons using Bonferroni adjusted significance. There was a significant difference in flexural strength and microhardness between the studied materials (p < 0.001), with the highest mean ± SD reported in the milled IFDPs (174.42 ± 3.39, 27.13 ± 0.52), and the lowest in the conventional IFDPs (98.02 ± 6.1, 15.77 ± 0.32). Flexural strengths differed significantly between the conventional IFDPs and all materials except DLP AS. The highest elastic modulus was recorded in the milled group, and the lowest in the SLA ND group (p = 0.02). In conclusion, superior flexural strength, elastic modulus, and hardness were reported for milled IFDPs. SLA ND printed IFDPs showed comparable mechanical properties to milled ones except for the elastic modulus.

Development of Dental Poly(methyl methacrylate)-Based Resin for Stereolithography Additive Manufacturing

Poly(methyl methacrylate) (PMMA) is widely used in dental applications. However, PMMA specialized for stereolithography (SLA) additive manufacturing (3D-printing) has not been developed yet. This study aims to develop a novel PMMA-based resin for SLA 3D-printing by mixing methyl methacrylate (MMA), ethylene glycol dimethacrylate (EGDMA), and PMMA powder in various mixing ratios. The printability and the viscosity of the PMMA-based resins were examined to determine their suitability for 3D-printing. The mechanical properties (flexural strength and Vickers hardness), shear bond strength, degree of conversion, physicochemical properties (water sorption and solubility), and cytotoxicity for L929 cells of the resulting resins were compared with those of three commercial resins: one self-cured resin and two 3D-print resins. EGDMA and PMMA were found to be essential components for SLA 3D-printing. The viscosity increased with PMMA content, while the mechanical properties improved as EGDMA content increased. The shear bond strength tended to decrease as EGDMA increased. Based on these characteristics, the optimal composition was determined to be 30% PMMA, 56% EGDMA, 14% MMA with flexural strength (84.6 ± 7.1 MPa), Vickers hardness (21.6 ± 1.9), and shear bond strength (10.5 ± 1.8 MPa) which were comparable to or higher than those of commercial resins. The resin’s degree of conversion (71.5 ± 0.7%), water sorption (19.7 ± 0.6 μg/mm³), solubility (below detection limit), and cell viability (80.7 ± 6.2% at day 10) were all acceptable for use in an oral environment. The printable PMMA-based resin is a potential candidate material for dental applications.