Evaluating the accuracy (trueness and precision) of interim crowns manufactured using digital light processing according to post-curing time: An in vitro study

PURPOSEThis study aimed to compare the accuracy (trueness and precision) of interim crowns fabricated using DLP (digital light processing) according to post-curing time.MATERIALS AND METHODSA virtual stone study die of the upper right first molar was created using a dental laboratory scanner. After designing interim crowns on the virtual study die and saving them as Standard Triangulated Language files, 30 interim crowns were fabricated using a DLP-type 3D printer. Additively manufactured interim crowns were post-cured using three different time conditions-10-minute post-curing interim crown (10-MPCI), 20-minute post-curing interim crown (20-MPCI), and 30-minute post-curing interim crown (30-MPCI) (n = 10 per group). The scan data of the external and intaglio surfaces were overlapped with reference crown data, and trueness was measured using the best-fit alignment method. In the external and intaglio surface groups (n = 45 per group), precision was measured using a combination formula exclusive to scan data (₁₀C₂). Significant differences in accuracy (trueness and precision) data were analyzed using the Kruskal-Wallis H test, and post hoc analysis was performed using the Mann-Whitney U test with Bonferroni correction (α=.05).RESULTSIn the 10-MPCI, 20-MPCI, and 30-MPCI groups, there was a statistically significant difference in the accuracy of the external and intaglio surfaces (P <.05). On the external and intaglio surfaces, the root mean square (RMS) values of trueness and precision were the lowest in the 10-MPCI group.CONCLUSIONInterim crowns with 10-minute post-curing showed high accuracy.     

Evaluation of the adaptation of complete denture metal bases fabricated with dental CAD-CAM systems: An in vitro study

Statement of problemConventional fabrication of complete denture metal bases is being replaced by the computer-aided design and computer-aided manufacturing (CAD-CAM) systems. However, a comparative analysis of subtractive and additive CAD-CAM manufacturing techniques is lacking.PurposeThe purpose of this in vitro study was to compare the adaptation of complete denture metal bases fabricated by milling (subtractive manufacturing) and stereolithography apparatus (SLA) and digital light processing (DLP) (additive manufacturing).Material and methodsThirty metal bases were manufactured by using the milling (MIL group), SLA (SLA group), and DLP (DLP group) techniques. The silicone replica technique was used to evaluate the adaptation of the complete denture metal bases, and 30 silicone blocks were fabricated. The silicone block was cut equally in the canine, first molar, and second molar areas. The gap between the model and the metal base was measured by using a digital microscope at the 3 locations, and the measured data were statistically analyzed by using a statistical software program (α=.05).ResultsThe gaps measured at the 3 areas showed significant differences in all 3 groups (P<.05). At the anterior, middle, and posterior areas, the SLA group showed the narrowest gap (302 ±31 μm, 241 ±39 μm, 201 ±43 μm, respectively). The SLA group also had the narrowest total gap of the metal bases (218 ±33 μm).ConclusionsThe adaptation of the fabricated metal bases varied significantly across the techniques used but fell within a clinically allowable range. The SLA group was the most precise in the fabrication of complete denture metal bases. Further studies are required to analyze the effects of the layer thickness setting, wax elimination, and casting temperature on the adaptation of metal bases manufactured by using SLA.     

Evaluation of dimensional accuracy and degree of polymerization of stereolithography photopolymer resin under different postpolymerization conditions: An in vitro study

Statement of problemThe appropriate postpolymerization of stereolithography (SLA) resins with the least effect on dimensional accuracy and with optimal polymerization is unclear.PurposeThe purpose of this in vitro study was to investigate the dimensional accuracy and degree of polymerization of a photopolymer resin for SLA with different postpolymerizing times and temperatures.Material and methodsSixty 1.5-mm-thick specimens were made from clear photopolymer resin with a 3D printer to simulate a maxillary complete denture. They were postpolymerized for different periods (15 and 30 minutes) at 3 different temperatures (40 °C, 60 °C, and 80 °C). Both prepolymerization and postpolymerization gap sizes for each specimen were measured at 5 different locations under a stereomicroscope. The tissue surface was scanned before and after polymerization, and the images were superimposed. The deviation was analyzed by using computer-aided design (CAD) software; root mean square estimates (RMSE) and color map data were obtained. Fourier transform infrared spectrometry was used to determine the degree of conversion (DC) of all specimens. The Kruskal-Wallis and Mann-Whitney tests were used to calculate the difference value of the gap sizes (α=.05). One-way ANOVA and the Tukey test were used for RMSE and DC (α=.05).ResultsThe smallest average change in gap sizes was found at 15 minutes and 40 °C, and the largest change at 30 minutes and 80 °C. The lowest RMSE was obtained at 30 minutes and 40 °C (P<.05). On the color map, a uniform deposited layer was created at 15 minutes and 40 °C and 30 minutes and 40 °C. The highest DC was found at 30 minutes and 60 °C, which differed significantly from 15 minutes and 40 °C (P<.05). The lowest degree of polymerization was found at 30 minutes and 40 °C.ConclusionsThe polymerizing temperature exerted a greater effect than polymerizing time, with lower temperatures leading to improved fit and tissue surface accuracy. The recommended parameters for SLA polymerization are 15 minutes and 40 °C. These conditions offered high dimensional accuracy, favorable surface tissue adaptation, and satisfactory DC.     

Influence of base design on the manufacturing accuracy of vat-polymerized diagnostic casts: An in vitro study

Statement of problemVat-polymerized casts can be designed with different bases, but the influence of the base design on the accuracy of the casts remains unclear.PurposeThe purpose of the present in vitro study was to evaluate the influence of various base designs (solid, honeycombed, and hollow) with 2 different wall thicknesses (1 mm and 2 mm) on the accuracy of vat-polymerized diagnostic casts.Material and methodsA virtual maxillary cast was obtained and used to create 3 different base designs: solid (S group), honeycombed (HC group), and hollow (H group). The HC and H groups were further divided into 2 subgroups based on the wall thickness of the cast designed: 1 mm (HC-1 and H-1) and 2 mm (HC-2 and H-2) (N=50, n=10). All the specimens were manufactured with a vat-polymerized printer (Nexdent 5100) and a resin material (Nexdent Model Ortho). The linear and 3D discrepancies between the virtual cast and each specimen were measured with a coordinate measuring machine. Trueness was defined as the mean of the average absolute dimensional discrepancy between the virtual cast and the AM specimens and precision as the standard deviation of the dimensional discrepancies between the virtual cast and the AM specimens. The Kolmogorov-Smirnov and Shapiro-Wilk tests revealed that the data were not normally distributed. The data were analyzed with Kruskal-Wallis and Mann-Whitney U pairwise comparison tests (α=.05).ResultsThe trueness ranged from 63.73 μm to 77.17 μm, and the precision ranged from 44.00 μm to 54.24 μm. The Kruskal-Wallis test revealed significant differences on the x- (P<.001), y- (P=.006), and z-axes (P<.001) and on the 3D discrepancy (P<.001). On the x-axis, the Mann-Whitney test revealed significant differences between the S and H-1 groups (P<.001), S and H-2 groups (P<.001), HC-1 and H-1 groups (P<.001), HC-1 and H-2 groups (P<.001), HC-2 and H-1 groups (P<.001), and HC-2 and H-2 groups (P<.001); on the y-axis, between the S and H-1 groups (P<.001), HC-1 and H-1 groups (P=.001), HC-1 and H-2 groups (P=.02), HC-2 and H-1 groups (P<.001), HC-2 and H-2 groups (P=.003); and on the z-axis, between the S and H-1 groups (P=.003). For the 3D discrepancy analysis, significant differences were found between the S and H-1 groups (P<.001), S and H-2 groups (P=.004), HC-1 and H-1 groups (P=.04), and HC-2 and H-1 groups (P=.002).ConclusionsThe base designs tested influenced the manufacturing accuracy of the diagnostic casts fabricated with a vat-polymerization printer, with the solid and honeycombed bases providing the greatest accuracy. However, all the specimens were clinically acceptable.     

Comparing the accuracy (trueness and precision) of models of fixed dental prostheses fabricated by digital and conventional workflows

Purpose

This study aimed to evaluate and compare the accuracy.

Evaluation of implant abutment screw tightening protocols on reverse tightening values: An in vitro study

Statement of problemImplant abutment screw loosening is a common prosthetic complication of implant-supported crowns. However, reports that have objectively evaluated the effectiveness of different tightening protocols on reverse tightening values are sparse.PurposeThe purpose of this in vitro study was to determine the optimal tightening protocol for implant abutment screws.Material and methodsFifty Neoss implants were randomly distributed to 5 groups (n=10). The implants received a cover screw and mounted, and the impression coping was tightened. Tightening was measured by using a digital measuring device. Then, the implant abutments were placed and tightened to 32 Ncm by using a Crystaloc screw. In Group 2T10I, the screws were tightened twice with an interval of 10 minutes between the first and second tightening. In Group 2T0I, the screws were tightened twice with no interval time. In Group 1T, the screws were tightened 1 time only. In Group TCT, the screws were tightened, counter-tightened, and then tightened again. In Group TCTCT, the abutment screws were tightened, counter-tightened, tightened, counter-tightened, and then tightened again. All the mounted implants were left in the same environment for 3 hours, and the reverse tightening values were then measured.ResultsThe mean reverse tightening values of the first 4 groups ranged from 21.49 Ncm to 22.57 Ncm, whereas the reverse tightening value for the fifth group was 25.51 Ncm. A significant difference was found among the groups (P<.05) with reverse tightening data.ConclusionsNo significant difference was found in tightening the abutment screw 2 times with a 10-minute interval time, no interval time, or tightening it 1 time only. However, a significant difference was found in reverse tightening in the 3-time tightening and counter-tightening group.     

Evaluation of the trueness and precision of eight extraoral laboratory scanners with a complete-arch model: a three-dimensional analysis

PurposeThe purpose of this study was to evaluate the trueness and precision of eight different extraoral laboratory scanners using three-dimensional (3D) analysis method.MethodAn arch-shaped master model was designed with a computer software (Rapidform XOR2) and manufactured with a 3D printer (Projet 3510 MP). Then the master model was digitized with an industrial 3D scanner (ATOS Core 200). With each scanner master model was scanned ten times and stereolithography (.stl) data were imported into 3D analysis software (Geomagic Control). Accuracy was determined with evaluating trueness and precision.ResultsTrueness of the scanners were 27.5 μm for 7 series; 30.9 μm for D640; 26.8 μm for D710; 33.3 μm for Activity 102; 32.4 μm for Tizian Smart-Scan; 21.6 μm for NeWay; 26.1 μm for inEOS X5 and 17,47 μm for D2000. 28.2 μm for laser; 32.9 μm for white light and 21.7 μm for blue light scanners. Significant differences were found between scanners (p < .001), (p < .001). Precision of the scanners were 30.1 μm for 7 series; 31.7 μm for D640; 26.3 μm for D710; 22.7 μm for Activity 102; 25.1 μm for Tizian Smart-Scan; 15.7 μm for NeWay; 26.1 μm for inEOS X5; 16.6 μm for D2000. 29.2 μm for laser; 24.4 μm for white light and 19.2 μm for blue light scanners. Significant differences were found between scanners (p < .001), (p = .027).ConclusionsThe systems that had the best combination of trueness and precision for complete-arch scanning were D2000 and NeWay. Scanners using blue-light showed more accurate results than the white-light and laser scanners.     

Assessment of the trueness and tissue surface adaptation of CAD-CAM maxillary denture bases manufactured using digital light processing

Statement of problem

Limited information is available evaluating the trueness and tissue surface adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) maxillary denture bases fabricated using digital light processing (DLP).

Comparison of the accuracy of implants placed with CAD-CAM surgical templates manufactured with various 3D printers: An in vitro study

Statement of problemThe fit of a 3D printed surgical template will directly influence the accuracy of guided implant surgery. Various 3D printing technologies are currently available with different levels of resolution and printing accuracy; however, how the different systems affect accuracy is unclear.PurposeThe purpose of this in vitro study was to assess the effect of using various 3D printers for the fabrication of implant surgical templates and its effect on the definitive implant position compared with the planned implant position.Material and methodsA cone beam computed tomography scan from a partially edentulous patient and an extraoral digital scan of a dental cast obtained from the same patient were used. The digital imaging and communications in medicine and standard tessellation language (STL) files were imported to an implant planning software program and merged, and an implant was digitally positioned in the mandibular right first molar region. A surgical template was designed and exported as an STL file. Ten surgical templates were printed for each of the following groups: stereolithography (SLA) printing, PolyJet, and MultiJet. The region where the implant was planned was cut away from the cast onto which the surgical templates were seated, allowing a passive positioning of the implant through the template, which was held in place with polyvinyl siloxane material. A scan body was inserted in the implant, and the cast was scanned with a laboratory scanner. The STL files obtained from the definitive implant position were imported into an implant planning software program and registered with the planned implant position, allowing for a comparison between the planned and actual implant position. Mean deviations were measured for angle deviation, entry point offset, and apex offset. Data normality was tested by using the Shapiro-Wilk test. The Kruskal-Wallis test was used to determine whether the outcomes of angle deviation, apex offset, and entry offset were statistically different between groups (α=.05).ResultsThe median and interquartile range for the angle deviation (degrees) were 1.30 (0.62) for SLA; 1.15 (1.23) for Polyjet; and 1.10 (0.65) for Multijet. No statistically significant differences were found in the angular deviation among groups (χ2(2)=3.08, P=.21). The median and interquartile range for the entry offset and apex offset (mm) were 0.19 (0.16) and 0.36 (0.16) for SLA, respectively; 0.20 (0.13) and 0.34 (0.26) for Polyjet, respectively; and 0.23 (0.10) and 0.32 (0.08) for Multijet, respectively. Similarly, nonsignificant differences were found for entry point offset (χ2(2)=0.13, P=.94) and apex offset (χ2(2)=1.08, P=.58).ConclusionsThe different types of 3D printing technology used in this study did not appear to have a significant effect on the accuracy of guided implant surgery.     

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

Background

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

Purpose

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

Materials and Methods

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

Results

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

Conclusions

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