Reliable studies comparing the accuracy of complete-arch casts from 3D printers are scarce.
The purpose of this in vitro study was to investigate the accuracy of casts printed by using various ...extrusion- and photopolymerization-based printers.
A master file was sent to 5 printer manufacturers and distributors to print 37 identical casts. This file consisted of a standardized data set of a maxillary cast in standard tessellation language (STL) format comprising 5 reference points for the measurement of 3 distances that served as reference for all measurements: intermolar width (IMW), intercanine width (ICW), and dental arch length (AL). The digital measurement of the master file obtained by using a surveying software program (Convince Premium 2012) was used as the control. Two extrusion-based (M2 and Ultimaker 2+) and 3 photopolymerization-based printers (Form 2, Asiga MAX UV, and myrev140) were compared. The casts were measured by using a multisensory coordinate measuring machine (O-Inspect 422). The values were then compared with those of the master file. The Mann-Whitney U test and Levene tests were used to determine significant differences in the trueness and precision (accuracy) of the measured distances.
The deviations from the master file at all 3 distances for the included printers ranged between 12 μm and 240 μm (trueness), with an interquartile range (IQR) between 17 μm and 388 μm (precision). Asiga MAX UV displayed the highest accuracy, considering all the distances, and Ultimaker 2+ demonstrated comparable accuracy for shorter distances (IMW and ICW). Although myrev140 operated with high precision, it displayed high deviations from the master file. Similarly, although Form 2 exhibited high IQR, it did not deviate significantly from the master file in the longest range (AL). M2 performed consistently.
Both extrusion-based and photopolymerization-based printers were accurate. In general, inexpensive printers were no less accurate than more expensive ones.
To investigate the influence of additive manufacturing method and build angle on surface characteristics and Candida albicans (C. albicans) adhesion to 3D printed denture base polymers.
Specimens of ...3D printing denture base polymers were prepared by two printers, namely, stereolithography (SLA, Form 3B) and digital light processing technology (DLP, Solflex 350 plus). Three build angles were used: 0°, 45°, and 90°. Surface topography was examined by scanning electron microscopy. Also, arithmetical mean height (Sa) values were calculated. An adhesion test was performed to observe initial C. albicans adhesion to the specimens. The data were statistically analyzed using the two-way analysis of variance and Tukey's multiple comparison test.
The data of Sa values had statistically significant differences, which were mainly determined by the main factor of build angle (p < 0.05). Moreover, the quantitative results of C. albicans adhesion exhibited no significant differences: printing techniques (p = 0.7794) and build angle (p = 0.0589), respectively.
Surface roughness was significantly influenced by the build angle rather than by the AM method. Whereas, AM method (SLA and DLP) and build angle (0°, 45°, and 90º) had no impacts on the C. albicans adhesion to the 3D printed denture bases.
Build angle dominates the surface roughness and topography of the 3D printed denture polymers. Our results indicate that C. albicans' adhesion might not be influenced by AM method and build angle.
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Objectives
With direct and indirect digitalisation, two access points to CAD/CAM-generated restorations are available. The aim of this study was to compare the accuracy of the single steps of both ...approaches by comparing construction datasets using a new methodology.
Material and method
Twelve test datasets were generated in vitro (1) with the Lava Chairside Oral Scanner (COS) (2) by digitizing polyether impressions (IMP) and (3) by scanning the referring gypsum cast by the Lava Scan ST laboratory scanner (ST) at a time. Using an inspection software, these datasets were superimposed by a best fit algorithm with the reference dataset (REF), gained from industrial computed tomography, and divergences were analysed.
Results
On the basis of average positive and negative deviations between test- and REF datasets, it could be shown that direct digitalisation accomplished the most accurate results (COS, 17 μm/−13 μm; SD ± 19 μm), followed by digitized polyether impression (IMP, 23 μm/−22 μm; SD ± 31 μm) and indirect digitalisation (ST, 36 μm/−35 μm; SD ± 52 μm). The mean absolute values of Euclidean distances showed the least values for COS (15 μm; SD ± 6 μm), followed by IMP (23 μm; SD ± 9 μm) and ST (36 μm; SD ± 7 μm). The mean negative and mean absolute values of all groups were significantly different. Comparing the mean positive values of the groups, IMP and COS (
p
= 0.082) showed no significant difference, whereas ST and COS, and ST and IMP exhibited statistically significant differences.
Conclusions
Within the limitations of this in vitro study, the direct digitalisation with Lava C.O.S. showed statistically significantly higher accuracy compared to the conventional procedure of impression taking and indirect digitalisation.
Clinical relevance
Within the limitations of this study, the method of direct digitalisation seems to have the potential to improve the accuracy of impressions for four-unit FDPs.
All-ceramic abutments are employed increasingly often in implant dentistry for esthetic reasons. In vitro stress testing is required to evaluate the suitability of these constructions, especially in ...load-bearing posterior regions. The purpose of the study was to assess and compare the fatigue and fracture resistance of one- and two-piece computer-aided design/computer-assisted manufacture (CAD/CAM) zirconia implant abutments with an internal-hex connection and prefabricated commercially available zirconia stock abutments.
Twenty-one abutment-crown specimens were prepared for three test groups. Control group 1 (SZ) included specimens with unprepared stock zirconia abutments, test group 2 (OP) included one-piece CAD/CAM zirconia abutments, and test group 3 (TP) included two-piece CAD/CAM zirconia abutments. All 21 specimens underwent thermocycling and fatigue testing. Finally, all specimens were tested for fracture resistance with a universal testing machine. The maximum load was applied to the tapered occlusal area of each crown at a 30-degree angle and a crosshead speed of 0.5 mm/min until the implant-abutment connection failed. Kolmogorov-Smirnov, Shapiro-Wilk, and post-hoc Scheffé tests were used for statistical analysis.
All abutments in groups SZ and OP fractured into two or more pieces after fracture resistance testing. None of the TP abutments displayed apparent disintegration, but failure was evidenced by bending of the retention screw. OP abutments (232.1 ± 29.8 N) and SZ abutments (251.8 ± 23.2 N) showed lower fracture loads than the TP abutments (291.4 ± 27.8 N). However, only the difference between the OP and TP groups was statistically significant. Further load-displacement analyses corroborated the higher mechanical stability of the TP abutments.
Superior resistance was achieved for two-piece hybrid CAD/CAM zirconia abutments. These abutments might be clinically beneficial in high-load areas, such as premolar and molar regions.
Objectives
To evaluate the esthetic and functional rehabilitation of single implants delivering the final crown during second-stage surgery.
Materials and methods
In 26 single-tooth implants, the ...impressions were taken immediately after implant placement to fabricate the final crowns. During the second-stage surgery, the screw-retained hybrid crowns were delivered. Six months to 3 years after placement of the crown, a modified pink esthetic score (PES) was measured. Additionally, the number of treatment sessions was recorded. The mesial and distal contact points and the static and dynamic occlusion were examined. Patients’ satisfaction was measured using a questionnaire.
Results
In this retrospective study, 21 posterior and 5 anterior implants were included. The average pink esthetic score was 11.3 out of 14. The most frequent limitations were incomplete papillae and deficits of the alveolar ridge. The average number of appointments was three, consisting of impression taking and surgery consent, implant placement, and crown delivery. Average patients’ satisfaction was 46.7 out of 50 and thus, extremely high.
Conclusions
The presented approach allows the second-stage surgery and delivery of the final restoration for single-tooth implants in the same session. As the peri-implant mucosa is adapted to the final restoration in the first place, a more natural emergence profile is achieved. However, there is an increasing risk for reduced or missing papillae. Patients’ satisfaction is generally very high.
Clinical relevance
A method for direct definitive prosthetic restoration during the exposure of single-tooth implants is examined, advantages and disadvantages will be described, and patient acceptance is validated.
Objectives
Direct and indirect digitalization offer two options for computer-aided design (CAD)/ computer-aided manufacturing (CAM)-generated restorations. The aim of this study was to evaluate the ...accuracy of different intraoral scanners and compare them to the process of indirect digitalization.
Material and method
A titanium testing model was directly digitized 12 times with each intraoral scanner: (1) CS 3500 (CS), (2) Zfx Intrascan (ZFX), (3) CEREC AC Bluecam (BLU), (4) CEREC AC Omnicam (OC) and (5) True Definition (TD). As control, 12 polyether impressions were taken and the referring plaster casts were digitized indirectly with the D-810 laboratory scanner (CON). The accuracy (trueness/precision) of the datasets was evaluated by an analysing software (Geomagic Qualify 12.1) using a “best fit alignment” of the datasets with a highly accurate reference dataset of the testing model, received from industrial computed tomography.
Results
Direct digitalization using the TD showed the significant highest overall “trueness”, followed by CS. Both performed better than CON. BLU, ZFX and OC showed higher differences from the reference dataset than CON. Regarding the overall “precision”, the CS 3500 intraoral scanner and the True Definition showed the best performance. CON, BLU and OC resulted in significantly higher precision than ZFX did.
Conclusions
Within the limitations of this in vitro study, the accuracy of the ascertained datasets was dependent on the scanning system. The direct digitalization was not superior to indirect digitalization for all tested systems.
Clinical relevance
Regarding the accuracy, all tested intraoral scanning technologies seem to be able to reproduce a single quadrant within clinical acceptable accuracy. However, differences were detected between the tested systems.
Abstract Objectives Zirconia based restorations exhibited high failure rates due to veneering–porcelain fractures. Milling to full-contour might be an alternative approach for zirconia restorations. ...The aim of this study was to evaluate full-contour zirconia crowns in terms of light-transmission, contact wear (restoration and antagonist) and load-bearing capacity. Powder build-up veneered zirconia substructures and CAD/CAM-veneered zirconia substructures served as controls. Methods Four different kinds of crowns were fabricated on 12 metal dies: zirconia substructure with powder build-up porcelain (veneering technique), zirconia substructure with CAD/CAM generated veneering (sintering technique), full-contour zirconia glazed (glazed full-contour) and full-contour zirconia polished (polished full-contour). All crowns had the same dimensions. After light-transmission was measured the crowns were cemented on the corresponding metal dies. The specimens were loaded according to a special wear method in the chewing simulator (120,000 mechanical cycles, 5 kg load, 0.7 mm sliding movement, 320 thermocycles). Wear of the restoration and the antagonist were measured. All specimens were loaded until failure. One-way ANOVA and a LSD post-hoc test were used to compare data at a level of 5%. Results Polished full-contour showed significantly higher light transmission than the other groups ( p = 0.003; ANOVA). Polished full-contour exhibited significantly less contact wear at the restoration ( p = 0.01; ANOVA) and higher contact wear at the antagonist ( p = 0.016; ANOVA) compared to the other groups. Glazed full-contour zirconia showed similar contact wear at the antagonist compared to veneering technique ( p = 0.513, post-hoc LSD). Crowns with conventional veneering showed significantly lower load-bearing capacity ( p < 0.001; ANOVA). Significance Milling zirconia to full-contour with glazed surface might be an alternative to traditionally veneered restorations.
Abstract Introduction Glass-fiber–reinforced endodontic posts (GFRPs), in combination with composite resin core materials, are commonly used to build up damaged endodontically treated teeth. However, ...long-term clinical data are scarce. Thus, the aim of this investigation was to evaluate the survival of 3 different GFRP systems, taking into account several other relevant factors. Methods One-hundred forty-nine GFRPs in 122 patients were followed for up to 120 months. GFRPs were adhesively luted using the etch-and-rinse technique. The core was built with a chemically curing composite resin and restored according to the specific prosthetic treatment plan. Cox proportional hazards models were used to evaluate the association between clinical variables and the time until failure. Results Within 10 years, 55 failures could be observed (annual failure rate = 4.6%) with the most frequent ones being post fracture, loss of post retention (both n = 17), endodontic problems (n = 7), and those resulting in tooth extraction (n = 10). Sixty posts could be followed up for 105 to 120 months (34 posts lost to follow-up, mean (standard deviation) survival time: 74 (43) months). In crude analyses, only the tooth type in favor of posterior teeth compared with anterior teeth and the number of remaining cavity walls (in favor of ≥1compared with no wall) were significantly associated with the failure rate. Cox regression analysis revealed a significant hazard ratio of 2.0 (95% confidence interval, 1.1–3.5; P = .021) for tooth type in favor of posterior teeth. Conclusions The relatively high annual failure rate of GFRPs highlights that the treatment decision should take into account the most relevant factors as tooth type and the number of remaining cavity walls.
Purpose: The accuracy of intraoral and model scanners has been widely investigated with heterogeneous results, but the impact of the applied diversity of measurement methods on the outcomes remains ...unknown. This study aimed to evaluate the influence of methodological factors on the measurement result when comparing full-arch scans.Methods: The evaluation referred to a 5M model to analyze whether accuracy measurements are affected by (1) the reference geometry, (2) mesh density of the standard tessellation language (STL) datasets, (3) operator, (4) inspection software, and (5) alignment procedure. STL datasets of full-arch reference models were measured with 29 different combinations of these factors. For each combination, 10 repeated measurements of the intermolar width were performed. Trueness was statistically analyzed with one-way ANOVA and T-tests, repeatability with Levene tests, and reproducibility with interclass correlation coefficients.Results: Measurement method variations affected the intermolar width by up to 186 µm. The alignment algorithm had a significant effect on the measurement outcome (p = 0.001). Likewise, reference geometry influenced trueness and repeatability significantly (p = 0.001), whereas mesh density affected the repeatability only in some cases. The operator had no impact on the measurement result. The inspection software affected the repeatability but not the trueness.Conclusion: The factors reference geometry and alignment algorithm highly affected the measurement outcome, while the operator, inspection software, and mesh density showed no impact on the trueness of the outcome. Cylindrical reference geometries showed fewer differences than bar-shaped ones and best-fit alignments fewer variations than alignments based on boundary parameters.
Extrusion-based printing enables simplified and economic manufacturing of surgical guides for oral implant placement. Therefore, the cytotoxicity of a biocopolyester (BE) and a polypropylene (PP), ...intended for the fused filament fabrication of surgical guides was evaluated. For comparison, a medically certified resin based on methacrylic esters (ME) was printed by stereolithography (n = 18 each group). Human gingival keratinocytes (HGK) were exposed to eluates of the tested materials and an impedance measurement and a tetrazolium assay (MTT) were performed. Modulations in gene expression were analyzed by quantitative PCR. One-way ANOVA with post-hoc Tukey tests were applied. None of the materials exceeded the threshold for cytotoxicity (< 70% viability in MTT) according to ISO 10993-5:2009. The impedance-based cell indices for PP and BE, reflecting cell proliferation, showed little deviations from the control, while ME caused a reduction of up to 45% after 72 h. PCR analysis after 72 h revealed only marginal modulations caused by BE while PP induced a down-regulation of genes encoding for inflammation and apoptosis (p < 0.05). In contrast, the 72 h ME eluate caused an up-regulation of these genes (p < 0.01). All evaluated materials can be considered biocompatible in vitro for short-term application. However, long-term contact to ME might induce (pro-)apoptotic/(pro-)inflammatory responses in HGK.
