Influence of Polymerization Postprocessing Procedures on the Accuracy of Additively Manufactured Dental Model Material.

PURPOSE: To measure the influence of postpolymerization condition (dry and water-submerged) and time (2, 10, 20, and 40 minutes) on the accuracy of additively manufactured model material. MATERIALS AND METHODS: A bar standard tessellation language (STL) file was used to manufacture all the resin specimens using a 3D printer. Two groups (n = 80 each) were created based on postpolymerization condition: dry (D group) and water-submerged (W group). Each group was then divided into four subgroups (D1 to D4 and W1 to W4; n = 20 each), which were each assigned a postpolymerizing time (2, 10, 20, and 40 minutes). The specimens' dimensions were measured using a low-force digital caliper. The volume was calculated as follows: V = l × w × h. Shapiro-Wilk test revealed that the data were not normally distributed. Data were analyzed using Kruskal-Wallis and pairwise Mann-Whitney U tests (α = .05). RESULTS: Significant differences in length, width, height, and volume were found among the subgroups (P < .0018). In all groups, the width dimension (x-axis) presented less accuracy compared to height (z-axis) and length (y-axis) (P < .0018). The D2 and D4 subgroups obtained the closest dimensions to the virtual design, and there were no significant differences between these subgroups (P < .0018). The dry condition showed higher manufacturing accuracy than the water-submerged condition. In the water-submerged subgroups, the highest accuracy was obtained in the W2 and W4 subgroups (P < .0018). CONCLUSIONS: Postpolymerization condition and time influenced the accuracy of the material tested. The dry postpolymerization condition with times of 10 and 40 minutes obtained the highest accuracy.

Trueness and precision of complete-arch photogrammetry implant scanning assessed with a coordinate-measuring machine.

STATEMENT OF PROBLEM: Photogrammetry technology has been used for the digitalization of multiple dental implants, but its trueness and precision remain uncertain. PURPOSE: The purpose of this in vitro investigation was to compare the accuracy (trueness and precision) of multisite implant recordings between the conventional method and a photogrammetry dental system. MATERIAL AND METHODS: A definitive cast of an edentulous maxilla with 6 implant abutment replicas was tested. Two different recording methods were compared, the conventional technique and a photogrammetry digital scan (n=10). For the conventional group, the impression copings were splinted to an additively manufactured cobalt-chromium metal with autopolymerizing acrylic resin, followed by recording the maxillary edentulous arch with an elastomeric impression using an additively manufactured open custom tray. For the photogrammetry group, a scan body was placed on each implant abutment replica, followed by the photogrammetry digital scan. A coordinate-measuring machine was selected to assess the linear, angular, and 3-dimensional discrepancies between the implant abutment replica positions of the reference cast and the specimens by using a computer-aided design program. The Shapiro-Wilk test showed that the data were not normally distributed. The Mann-Whitney U test was used to analyze the data (α=.05). RESULTS: The conventional group obtained an overall accuracy (trueness ±precision) value of 18.40 ±6.81 µm, whereas the photogrammetry group showed an overall scanning accuracy value of 20.15 ±25.41 µm. Significant differences on the discrepancies on the x axis (U=1380.00, P=.027), z axis (U=601.00, P<.001), XZ angle (U=869.00, P<.001), and YZ angle (U=788.00, P<.001) were observed when the measurements of the 2 groups were compared. Furthermore, significant 3-dimensional discrepancy for implant 1 (U=0.00, P<.001), implant 2 (U=0.00, P<.001), implant 3 (U=6.00, P<.001), and implant 6 (U=9.00, P<.001) were computed between the groups. CONCLUSIONS: The conventional method obtained statistically significant higher overall accuracy values compared with the photogrammetry system tested, with a trueness difference of 1.8 µm and a precision difference of 18.6 µm between the systems. The conventional method transferred the implant abutment positions with a uniform 3-dimensional discrepancy, but the photogrammetry system obtained an uneven overall discrepancy among the implant abutment positions.

Manufacturing accuracy and volumetric changes of stereolithography additively manufactured zirconia with different porosities.

STATEMENT OF PROBLEM: When compared with subtractive fabricating methods, additive manufacturing (AM) technologies are capable of fabricating complex geometries with different material porosities. However, the manufacturing accuracy and shrinkage of the stereolithography (SLA) AM zirconia with different porosities are unclear. PURPOSE: The purpose of this in vitro study was to measure the manufacturing accuracy and volumetric changes of AM zirconia specimens with porosities of 0%, 20%, and 40%. MATERIAL AND METHODS: A digital design of a bar (25×4×3 mm) was obtained by using an open-source software program (Blender, version 2.77a; The Blender Foundation). The standard tessellation language (STL) file was exported. Three groups were created based on the material porosity: 0% porosity (0% group), 20% porosity (20% group), and 40% porosity (40% group). The STL was used to manufacture all the specimens by using an SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO2 paste; 3DCeram Co) (n=20). After manufacturing, the specimens were cleaned of the green parts by using a semiautomated cleaning station. Subsequently, debinding procedures was completed in a furnace at 600 °C. The sintering procedures varied among the groups to achieve different porosities. For the 0% group, the ZrO2 was sintered in a furnace at 1450 °C, and for the 20% and 40% groups, the sintering temperature varied between 1450 °C and 1225 °C. The specimen dimensions (length, width, and height) were measured 3 times with digital calipers, and the mean value was determined. The manufacturing volume shrinkage (%) was calculated by using the digital design of the bar and the achieved AM dimensions of the specimens. The Shapiro-Wilk test revealed that the data were not normally distributed. Therefore, the data were analyzed by using the Kruskal-Wallis followed by pairwise Mann-Whitney U tests (α=.05). RESULTS: The Kruskal-Wallis test demonstrated significant differences among the groups in length, width, and height (P<.001). The Mann-Whitney U test indicated significant differences in pairwise comparisons of length, width, and height among the 3 groups (P<.001). The 0% group obtained a median ±interquartile range values of 20.92 ±0.14 mm in length, 3.43 ±0.07 mm in width, and 2.39 ±0.03 mm in height; the 20% group obtained 22.81 ±0.29 mm in length, 3.74 ±0.07 mm in width, and 2.62 ±0.05 mm in height; and the 40% group presented 25.11 ±0.13 mm in length, 4.14 ±0.08 mm in width, and 2.96 ±0.02 mm in height. Significant differences in manufacturing volumetric changes were encountered among the 3 groups (P<.001). In all groups, volumetric changes in the length, width, and height were not uniform, being higher in the z-axis direction compared with the x- and y-axis. The manufacturing volumetric changes varied from -20.33 ±1.00% to +3.5 ±2.00%. CONCLUSIONS: The 40%-porosity group obtained the highest manufacturing accuracy and the lowest manufacturing volume change, followed by the 20%-porosity and the 0%-porosity groups. An uneven manufacturing volume change in the x-, y-, and z-axis was observed. However, none of the groups tested were able to perfectly match the virtual design of the specimens.

Influence of the base design on the accuracy of additive manufactured casts measured using a coordinate measuring machine.

PURPOSE: To measure the accuracy of the additively manufactured casts with 3 base designs: solid, honeycomb-structure, and hollowed bases. METHODS: A virtual cast was used to create different base designs: solid (S Group), honeycomb-structure (HC group), and hollowed (H group). Three standard tessellation language files were used to fabricate the specimens using a material jetting printer (J720 Dental; Stratasys) and a resin (VeroDent MED670; Stratasys) (n=15). A coordinate measuring machine was selected to measure the linear and 3D discrepancies between the virtual cast and each specimen. Shapiro-Wilk test revealed that all the data was not normally distributed (P<.05). Kruskal Wallis and Mann Whitney U tests were used (α=.05). RESULTS: The S group obtained a median ±interquartile range 3D discrepancy of 53.00 ±73.25 µm, the HC group of 58.00 ±67.25 µm, and the H group of 34.00 ±45.00 µm. Significant differences were found in the x- (P<.001), y- (P<.001), and z-axes (P<.001), and 3D discrepancies among the groups (P<.001). Significant differences were found between the S and H groups (P=.002) and HC and H groups (P<.001) on the x-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the y-axis; S and H groups (P<.001) and HC and H groups (P<.001) on the z-axis; and S and H groups (P<.001) and HC and H groups (P<.001) on the 3D discrepancy. CONCLUSION: The base designs influenced on the accuracy of the casts but all the specimens obtained a clinically acceptable manufacturing range. The H group obtained the highest accuracy.

Influence of rescanning mesh holes and stitching procedures on the complete-arch scanning accuracy of an intraoral scanner: An in vitro study.

PURPOSE: To measure the impact of different scanning patches on the accuracy (trueness and precision) of an intraoral scanner (IOS). MATERIAL AND METHODS: A typodont was digitized using an industrial optical scanner (GOM Atos Q 3D 12 M) to obtain a reference mesh. The typodont was scanned using an IOS (TRIOS 3). Three groups were generated based on the rescan areas created: no mesh holes (G0 group), 3 mesh holes distributed on the digital scan (G1 group), and 3 mesh holes located on the left quadrant of the digital scan (G2 group). In the G0 group, a digital scan was completed following the manufacturer's scanning protocol. In the G1 group, a digital scan was obtained following the same protocol as G0 group. Three 12-mm diameter holes were created in the occlusal surfaces of the left second first molar, incisal edges of the central incisors, and right first molar of the digital scan using the IOS software. In the G2 group, a digital scan was obtained following the same protocol as G0 group. Three 12-mm diameter holes in the digital scan were created in the occlusal surface of the left first molar and left second and first premolars using the IOS software program. The discrepancy between the control and the experimental digital scans was measured using the root mean square calculation. The Kolmogorov-Smirnov test demonstrated that data were normally distributed. One-way ANOVA followed by post hoc multiple comparison Bonferroni test were used to analyze the data (α = .05). RESULTS: Trueness values ranged from 15 to 26 µm and the precision ranged from 21 to 150 µm. Significant differences in trueness mean values were found among the groups tested (F(2, 42) = 6.622, P = .003); the Bonferroni test indicated significant mean differences between the G0 and G2 groups (mean difference=0.11, SE=0.003, and P = .002). For precision evaluation, significant precision differences were found between the groups tested (F(2, 39)=9.479, P < .001); the Bonferroni test revealed significant precision differences between G0 and G2 groups (mean difference=-0.12, SE=0.030, and P = .001). CONCLUSIONS: Rescanning mesh holes and stitching procedures decreased the trueness and precision of the IOS tested; furthermore, the number and dimensions of mesh holes rescanned represented an important factor that influenced the scanning accuracy of IOS tested. CLINICAL SIGNIFICANCE: It is a fundamental procedure obtaining intraoral digital scans without leaving mesh holes, so the rescanning techniques are minimized and, therefore, the scanning accuracy of the intraoral scanner tested is maximized.

Influence of scan body design on accuracy of the implant position as transferred to a virtual definitive implant cast.

STATEMENT OF PROBLEM: Previous studies have analyzed factors influencing intraoral scanner accuracy; however, how the intraoral scan body design affects the implant position on the virtual definitive cast is unclear. PURPOSE: The purpose of this in vitro study was to measure the discrepancies of the implant replica positions of the virtual definitive implant cast obtained by using 3 different scan body designs when performing a digital scan. MATERIAL AND METHODS: A partially edentulous typodont with 3 implant replicas (Implant Replica RP Branemark system; Nobel Biocare Services AG) was prepared. Three groups were determined based on the scan body system evaluated: SB-1 (Elos Accurate Nobel Biocare), SB-2 (NT Digital Implant Technology), and SB-3 (Dynamic Abutment). Each scan body was positioned on each implant replica of the typodont, and was digitized by using an intraoral scanner (iTero Element; Cadent) as per the manufacturer's scanning protocol at 1000 lux illuminance. A standard tessellation language (STL) file was obtained. Before the scan bodies were removed from the typodont, a coordinate measuring machine (CMM Contura G2 10/16/06 RDS; Carl Zeiss Industrielle Messtechnik GmbH) was used to measure the scan body positions on the x-, y-, and z-axis. The linear and angular discrepancies between the position of the scan bodies on the typodont and STL file were calculated by using the best fit technique with a specific program (Calypso; Carl Zeiss Industrielle Messtechnik GmbH). The procedure was repeated until 10 STL files were obtained per group. The Shapiro-Wilk test revealed that the data were not normally distributed. The data were analyzed by using the Mann-Whitney U test (α=.05). RESULTS: The coordinate measuring machine was unable to measure the scan body positions of the magnetically retained SB-3 group because of its mobility when palpating at the smallest pressure possible. Therefore, this group was excluded. No significant differences were found in the linear discrepancies between the SB-1 and SB-2 groups (P>.05). The most accurate scan body position was obtained on the z-axis. However, the SB-1 group revealed a significantly higher XZ angular discrepancy than the SB-2 group (P<.001). CONCLUSIONS: The scan body systems tested (SB-1 and SB-2 groups) accurately transferred the linear implant positions to the virtual definitive implant cast. However, significant differences were observed in the XZ angular implant positions between the scan body systems analyzed.

Influence of printing angulation on the surface roughness of additive manufactured clear silicone indices: An in vitro study.

STATEMENT OF PROBLEM: Vat-polymerization additive manufacturing (AM) technologies can be used to fabricate clear silicone indices for diagnostic trial restorations, interim restorations, and direct composite resin restorations. Different support parameters, including print orientation of the virtual design of the silicone index, need to be determined when a dental device is fabricated with AM. However, the optimal printing angulation for minimal surface texture remains unclear. PURPOSE: The purpose of this in vitro study was to measure the surface roughness of the AM clear silicone indices manufactured by using a vat-polymerization 3D printer with different print orientations. MATERIAL AND METHODS: A virtual design of a facial silicone index was obtained, and the standard tessellation language file was exported and used to manufacture all the specimens using a vat-polymerization 3D printer. All the specimens were placed on the build platform with the same parameters, except for the print orientation which was selected as the only manufacturing variable. Therefore, the 5 different groups were 0, 25, 45, 75, and 90 degrees. To minimize variation in the procedure, all the specimens (N=50) were manufactured at the same time in the selected printer at a constant room temperature of 23°C. The printer had been previously calibrated following the manufacturer's recommendations. Surface roughness was measured in the intaglio of the left central maxillary incisor using an optical profilometer with a magnification of ×20 and an array size of 640×480. Three measurements per specimen were recorded. The Shapiro-Wilk test revealed that the data were normally distributed, and the data were analyzed by using 1-way ANOVA, followed by the post hoc Sidak test (α=.05). RESULTS: The 0-degree angulation printing group reported the least mean ±standard deviation surface roughness (0.9 ±0.3 µm), followed by the 90-degree group (3.0 ±0.6 µm), the 75-degree group (12.4 ±1.0 µm), the 25-degree group (13.1 ±0.9 µm), and the 45-degree group (13.5 ±1.0 µm). However, no statistically significant difference was found in the surface roughness between the 25-degree and 45-degree print orientation groups (P=.296). CONCLUSIONS: Print orientation significantly influenced the surface roughness measured on the intaglio of the facial AM silicone indices tested.

Influence of the Rinsing Postprocessing Procedures on the Manufacturing Accuracy of Vat-Polymerized Dental Model Material.

PURPOSE: To evaluate the influence of rinsing solvents, namely isopropyl alcohol (IPA) and tripropylene glycol monomethyl ether (TPM), and rinsing times (5-, 7-, 9-, and 11-minutes) for the postprocessing procedures on the manufacturing accuracy of an additively manufactured dental model resin material. MATERIAL AND METHODS: The standard tessellation language (STL file) of the digital design of a bar (15 mm × 4 mm × 3 mm) was obtained. A resin dental material (E-Model Light; Envisiontec, Dearborn, MI) and a 3D printer (VIDA HD; Envisiontec) was selected to manufacture all the specimens using the STL file following the recommended printing parameters at a room temperature of 23 °C. Two groups were generated based on the rinsing solvent used on the postprocessing procedures, namely isopropyl alcohol (IPA-group) and tripropylene glycol monomethyl ether (TPM-group). Each group was further divided into 4 subgroups (IPA-1 to IPA-4 and TPM-1 to TPM-4) depending on the rinsing time performed (5-, 7-, 9-, and 11-minutes). Twenty specimens per subgroup were fabricated. The dimensions (length, width, and height) of all the specimens were measured using a low force digital caliper (Absolute Low Force Caliper Series 573; Mitutoyo, Takatsu-ku, Kawasaki, Kanagawa). Each measurement was performed 3 times and the mean value determined. The volume of each specimen was calculated using the formula V = l × w × h. Shapiro-Wilk test revealed that the data were not normally distributed. Data were analyzed using Kruskal-Wallis (α = 0.05), followed by pairwise Mann-Whitney U tests (α = 0.0018). RESULTS: The IPA groups obtained significantly lower trueness and precision values compared with TPM groups (p < 0.0018). Among the IPA groups, IPA-1 subgroup obtained the highest trueness and precision values compared to the rest of the IPA subgroups. The TPM-1 and TPM-2 subgroups obtained the highest trueness and prevision values among the TPM group and among all the groups tested. No significant difference was found between the TMP-1 and TPM-2 subgroups (p > 0.0018). CONCLUSIONS: None of the manufacturing workflows tested were able to manufacture a perfect match of the bar virtual design dimensions. TPM solvent group obtained higher trueness and precision values compared to the IPA solvent group. The IPA-1 subgroup that replicated the manufacturer´s recommendations obtained the highest manufacturing accuracy among the IPA subgroup. TPM solvent used in a rinsing ultrasonic bath between 3 and 4 minutes followed by a second ultrasonic clean bath between 2 and 3 minutes of the just printed vat polymerized dental model specimens obtained the highest manufacturing accuracy values.

Scanning accuracy of nondental structured light extraoral scanners compared with that of a dental-specific scanner.

STATEMENT OF PROBLEM: Diagnostic stone casts can be digitized by using dental optical scanners based on structured light scanning technology. Nondental structured light scanning scanners could also be used; however, the accuracy of these nondental scanners remains unclear. PURPOSE: The purpose of this in vitro study was to measure the scanning accuracy (trueness and precision) of 3 nondental extraoral structured light scanners. MATERIAL AND METHODS: A representative maxillary diagnostic cast was obtained and digitized by using an extraoral dental scanner (Advaa Lab Scan; GC Europe), and a reference or control standard tessellation language file was obtained. Three nondental extraoral scanners were evaluated: groups ND-1 (Space Spider; Artec), ND-2 (Capture Mini; Geomagic), and ND-3 (DAVID SLS3; David). Ten digital scans per group were recorded at a constant room temperature (23 °C) by an experienced geodetic engineer following the manufacturer's recommendations. The control or reference file was used as a reference to measure the discrepancy between the digitized diagnostic cast and 3 different nondental scans by using an open-source software (CloudCompare v.2.6.1; CloudCompare) and the iterative closest point technique. The Shapiro-Wilk test revealed that the data were normally distributed. The data were analyzed by using 1-way ANOVA, followed by post hoc Bonferroni tests (α=.05). RESULTS: Significant differences between the 3 experimental nondental scanners and the control or reference scan (P<.001) were found. The ND-2 group had the lowest absolute mean error (trueness) and standard deviation (precision) (39 ±139 µm), followed by the ND-3 group (125 ±113 µm) and the ND1 group (-397 ±25 µm). No statistically significant differences were found in the mean error between the ND-2 and ND-3 groups (P=.228). CONCLUSIONS: Only 1 nondental extraoral scanner tested obtained trueness mean values similar to those of the reference dental scanner. In all groups, the precision mean values were higher than their trueness values, indicating low relative precision.

Accuracy of the Implant Replica Positions on the Complete Edentulous Additive Manufactured Cast.

PURPOSE: To compare the implant replica position accuracy on a duplicated complete edentulous maxillary implant definitive cast made either using conventional procedures or material jetting additive manufacturing (AM) technology using a coordinate measuring machine (CMM). MATERIAL AND METHODS: A complete edentulous maxillary cast with 6 implant replicas was prepared. The definitive cast was duplicated using two manufacturing procedures namely conventional (CNV group) and additive manufacturing procedures (AM group). On the CNV, an AM Co-Cr framework and a custom AM custom tray with a polyether impression material were used to obtain an impression of the definitive cast at room temperature (23°C). On the AM group, the definitive cast was digitized using a laboratory scanner. The standard tessellation language (STL) file was exported and used to manufacture the polymeric AM specimens using a multijet printer following manufacturer´s recommendations. A new digital implant replica was located on each corresponding housing of each AM specimen. A total of 10 specimens per group was obtained. A CMM was selected to measure the position of each implant replica on the definitive cast, CNV, and AM specimens. Linear and angular discrepancies were computed for each specimen. Thus, the Mann Whitney U test was used to analyze the data (p = 0.05). RESULTS: There was no significant difference in x-, y-, and z- linear and XZ angular discrepancy between both groups. However, the AM group revealed a significantly higher median YZ angular discrepancy than the CNV group (p = 0.007). CONCLUSIONS: Material jetting AM technology demonstrated no significant difference in trueness and precision values of the linear and angular implant replica positions when compared to the conventional technique.