Showing papers by "Amirali Zandinejad published in 2021"

Additive Manufacturing of Zirconia Ceramic and Its Application in Clinical Dentistry: A Review.

Abstract: Additive manufacturing (AM) has many advantages and became a valid manufacturing technique for polymers and metals in dentistry. However, its application for dental ceramics is still in process. Among dental ceramics, zirconia is becoming popular and widely used in dentistry mainly due to its outstanding properties. Although subtractive technology or milling is the state of art for manufacturing zirconia restorations but still has shortcomings. Utilizing AM in fabricating ceramics restorations is a new topic for many researchers and companies across the globe and a good understanding of AM of zirconia is essential for dental professional. Therefore, the aim of this narrative review is to illustrate different AM technologies available for processing zirconia and discus their advantages and future potential. A comprehensive literature review was completed to summarize different AM technologies that are available to fabricate zirconia and their clinical application is reported. The results show a promising outcome for utilizing AM of zirconia in restorative, implant and regenerative dentistry. However further improvements and validation is necessary to approve its clinical application.

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

Abstract: 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.

Abstract: 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). 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.

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

Abstract: 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 277a; 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 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

Workflow of a fiber-reinforced composite fixed dental prosthesis by using a 4-piece additive manufactured silicone index: A dental technique.

Abstract: A digital workflow for fabricating a fiber-reinforced composite prosthesis is described. A facial scanner and an intraoral scanner were used to gather records, and dental and open-source software programs were used to elaborate a diagnostic waxing and design a 4-piece additively manufactured clear silicone index. Advantages of the index design included precise translation of the diagnostic waxing, optimal composite resin stratification, and minimal clinical time.

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

Abstract: 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 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.

Accuracy of a patient 3-dimensional virtual representation obtained from the superimposition of facial and intraoral scans guided by extraoral and intraoral scan body systems.

Abstract: Statement of problem A patient 3-dimensional virtual representation aims to facilitate the integration of facial references into treatment planning or prosthesis design procedures, but the accuracy of the virtual patient representation remains unclear. Purpose The purpose of the present observational clinical study was to determine and compare the accuracy (trueness and precision) of a virtual patient obtained from the superimposition procedures of facial and intraoral digital scans guided by 2 scan body systems. Material and methods Ten participants were recruited. An intraoral digital scan was completed (TRIOS 4). Four fiduciary markers were placed in the glabella (Gb), left (IOL) and right infraorbital canal (IOR), and tip of the nose (TN). Two digitizing procedures were completed: cone beam computed tomography (CBCT) (i-CAT FLX V-Series) and facial scans (Face Camera Pro Bellus) with 2 different scan body systems: AFT (ScanBodyFace) and Sat 3D (Sat 3D). For the AFT system, a reference facial scan was obtained, followed by a facial scan with the participant in the same position as when capturing the CBCT scan. For the Sat 3D system, a reference facial scan was recorded, followed by a facial scan with the patient in the same position as when capturing the CBCT scan. The patient 3-dimensional representation for each scan body system was obtained by using a computer program (Matera 2.4). A total of 14 interlandmark distances were measured in the CBCT scan and both 3-dimensional patient representations. The discrepancies between the CBCT scan (considered the standard) and each 3-dimensional representation of each patient were used to analyze the data. The Kolmogorov-Smirnov test revealed that trueness and precision values were not normally distributed (P Results The accuracy of the virtual 3-dimensional patient representations obtained by using AFT and Sat 3D systems showed a trueness ranging from 0.50 to 1.64 mm and a precision ranging from 0.04 to 0.14 mm. The Wilks lambda detected an overall significant difference in the accuracy values between the AFT and Sat 3D systems (F=3628.041, df=14, P Conclusions The accuracy of the patient 3-dimensional virtual representations obtained using AFT and Sat 3D systems showed trueness values ranging from 0.50 to 1.64 mm and precision values ranging from 0.04 to 0.14 mm. The AFT system obtained higher trueness than the Sat 3D system, but both systems showed similar precision values.

The Flexural Strength and Flexural Modulus of Stereolithography Additively Manufactured Zirconia with different Porosities.

Abstract: PURPOSE: Additive manufacturing (AM) technologies are capable of fabricating complex geometries with different porosities. However, the effect of such porosities on mechanical properties of stereolithography (SLA) AM zirconia with different porosities is unclear. The purpose of this in vitro study was to investigate the mechanical properties namely flexural strength, and flexural modulus of AM zirconia with different porosities. MATERIALS AND METHODS: A bar (25×4×3 mm) for flexural strength test (ISO standard 6872/2015) was designed by CAD software program and standard tessellation language (STL) file was obtained. STL file was used to fabricate a total of 80 bars in four groups. Three experimental groups each contained 20 samples were manufactured using SLA ceramic printer (CeraMaker 900; 3DCeram Co) and zirconia material (3DMix ZrO2 paste; 3DCeram Co) with different sintering post process to achieve different porosities including 0%-porosity (AMZ0), 20%-porosity (AMZ20), and 40%-porosity (AMZ40). The same STL file was used for subtractive manufacturing or milling of 20 zirconia bars as control group (CNCZ) with the same dimensions using a commercial zirconia. Three-point bending tests were performed for all groups following ISO standard 6872/2015 specification using a universal testing machine. Outcomes measured included load at fracture, mean flexural strength, and flexural modulus were compared across the experimental groups using a 1-way ANOVA. Post-hoc pair wise comparison between each pair of the groups were performed using Tukey test. RESULTS: There was a significant difference between the four groups, in terms of fracture load, flexural strength and flexural modulus using one-way ANOVA. AM zirconia with 0% porosity (AMZ0) showed the highest value for fracture load (1,132.7 ±220.6 N), flexural Strength (755.1 ±147.1 MPa) and flexural modulus (4,1273 ±2193 MPa) and AM zirconia with 40% porosity (AMZ40) showed the lowest fracture load (72.13 ±13.42 N), flexural strength (48.09 ±8.95 MPa) and flexural modulus (7,177 ±506 MPa). Tukey's pairwise comparisons detected a significant difference between all the possible pairs for all variables except flexural modulus between AMZ0 and CNCZ. The Weibull moduli presented the lowest value for AMZ20 (4.4) followed by AMZ40 (6.1), AMZ0 (6.1) and the highest value was for CNCZ (8.1). CONCLUSION: AM zirconia with 0% porosity shows significantly higher flexural strength and flexural modulus when compared to milled and AM zirconia with 20% and 40% porosities. This article is protected by copyright. All rights reserved.

Surface roughness and shear bond strength to composite resin of additively manufactured interim restorative material with different printing orientations.

Abstract: Statement of problem Additive manufacturing (AM) is a technology that has been recently introduced into dentistry for fabricating dental devices, including interim restorations. Printing orientation is one of the important and influential factors in AM that affects the accuracy, surface roughness, and mechanical characteristics of printed objects. However, the optimal print orientation for best bond strength to 3D-printed interim restorations remains unclear. Purpose The purpose of this in vitro study was to evaluate the effect of printing orientation on the surface roughness, topography, and shear bond strength of AM interim restorations to composite resin. Material and methods Disk-shaped specimens (O20×10 mm) were designed by a computer-aided design software program (Geomagic freeform), and a standard tessellation language (STL) file was obtained. The STL file was used for the AM of 60 disks in 3 different printing orientations (0, 45, and 90 degrees) by using E-Dent 400 C&B material. An autopolymerizing interim material (Protemp 4) was used as a control group (CNT), and specimens were fabricated by using the injecting mold technique (n=20). Surface roughness (Sa, Sz parameters) was measured by using a 3D-laser scanning confocal microscope (CLSM) at ×20 magnification. For shear bond testing, the specimens were embedded in polymethylmethacrylate autopolymerized resin (n=20). A flowable composite resin was bonded by using an adhesive system. The specimens were stored in distilled water at 37 °C for 1 day and thermocycled 5000 times. The shear bond strength (SBS) was measured at a crosshead speed of 1 mm/min. The data were analyzed by 1-way ANOVA, followed by the Tukey HSD test (α=.05). Results The 45-degree angulation printing group reported the highest Sa, followed by the CNT and the 90-degree and 0-degree angulations with significant difference between them (P Conclusions Printing orientation significantly impacted the surface roughness of 3D-printed resin for interim restorations. However, printing orientation did not significantly affect the bond strength with composite resin.

The Fracture Resistance of Additively Manufactured Monolithic Zirconia vs. Bi-Layered Alumina Toughened Zirconia Crowns When Cemented to Zirconia Abutments. Evaluating the Potential of 3D Printing of Ceramic Crowns: An In Vitro Study.

Abstract: (1) Background: This study compared the fracture resistance of additively manufactured monolithic zirconia and bi-layered alumina toughened zirconia crowns on implants. (2) Methods: Maxillary model with a dental implant replacing right second bicuspid was obtained. Custom abutments and full-contour crowns for additively manufactured monolithic zirconia and bi-layered alumina reinforced zirconia crowns (n = 10) were fabricated. The crowns were cemented to implant-supported zirconia abutments and the assembly fixed onto resin blocks. Fracture resistance was measured using a universal testing machine at a crosshead speed of 2 mm/min. A Kruskal-Wallis test was used to analyze the data. (3) Results: Although additively manufactured monolithic zirconia crowns demonstrated a higher mean fracture resistance than bi-layered alumina toughened zirconia crowns, statistical analysis revealed no significant difference in fracture resistance between the two groups. All specimens fractured at the implant-abutment interface. (4) Conclusions: Additively manufactured bi-layered alumina toughened zirconia crowns demonstrated similar fracture resistance to additively manufactured monolithic zirconia crowns when cemented to implant-supported zirconia abutments.

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

Abstract: Statement of problem Vat-polymerized casts can be designed with different bases, but the influence of the base design on the accuracy of the casts remains unclear. Purpose The 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 methods A 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). Results The 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 Conclusions The 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.

Additively Manufactured Dental Crown with Color Gradient and Graded Structure: A Technique Report

Abstract: To assess the feasibility of manufacturing a dental crown with internal color gradient and graded structure design using additive manufacturing technology, a mandibular first molar was prepared and a monolayer dental crown with 1.5 mm uniform thickness was designed in a dental software (STLC1 ). The monolayer crown design was sliced into multiple layers of 0.1 mm thickness and a design for a multilayer crown was obtained (STLC2 ). A multilayer crown was manufactured with gradient color and graded structure using a material jetting printer. Different materials with different colors and properties were used and mixed in different ratios during manufacturing to achieve the prospected design. The feasibility of manufacturing such a crown was reported. This report confirms that multilayer dental crowns with internal gradient color and graded structure are possible when using a multimaterial jetting printer.

Influence of the polymerization post-processing procedures on the accuracy of additively manufactured dental model material.

Abstract: PURPOSE To measure the influence of postpolymerization condition (dry or submerged in water) and time (2, 10, 20, and 40 minutes) on the accuracy of additively manufactured model material. MATERIALS AND METHODS A bar standard tessellation language file was used to manufacture the resin specimens (E-Model Light, EnvisionTEC) using a 3D printer (Vida HD, EnvisionTEC). Two groups were created based on the postpolymerization condition: dry (D group) or submerged in water (W group). Each group was divided into four subgroups (D1 to D4 and W1 to W4) depending on the postpolymerizing time (2, 10, 20, and 40 minutes; n = 20 each; N = 160). The specimen dimensions were measured using a low-force digital caliper (Absolute Low Force Caliper Series 573, Mitutoyo). The volume was calculated: 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 values were found among the subgroups (P < .0018). In all groups, the width dimension (x-axis) presented the worst 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; additionally, no significant differences were found between the two subgroups (P < .0018). Dry condition showed higher manufacturing accuracy compared to the water-submerged condition. In the water-submerged subgroups, the highest accuracy was obtained in the W2 and W4 subgroups (P < .0018). CONCLUSION Postpolymerization conditions and time influenced the accuracy of the material tested. Dry postpolymerization condition with a time of 10 and 40 minutes obtained the highest accuracy.

Self-perception and self-representation preference between 2-dimensional and 3-dimensional facial reconstructions among dentists, dental students, and laypersons

Abstract: Statement of problem Computer-aided design (CAD) software can merge the intraoral digital scan with patient photographs or 3-dimensional (3D) facial reconstructions for treatment planning purposes. However, whether an individual perceives a 3D facial reconstruction as a better self-representation compared with a 2-dimensional (2D) photograph is unclear. Purpose The purpose of this observational study was to compare self-perception ratings and self-representation preference of the 2D and 3D facial reconstructions among laypersons, dental students, and dentists. Material and methods Three populations participated in the study: laypersons, dental students, and dentists (n=20, N=60). Facial and intraoral features were digitized by using facial and intraoral scanners, and a complete-face smile photograph was obtained. Two simulations were performed for each participant: 2D (2D group) and 3D (3D group) reconstructions. In the 2D group, a maxillary digital veneer waxing from the left to the right second premolars was produced without altering the shape, position, or length of the involved teeth. A software program (Dental Systems; 3Shape A/S) was used to merge the maxillary digital waxing with the full-face smile photograph. One image was obtained for each participant. In the 3D group, a dental software program (Matera 2.4; Exocad GmbH) was used to merge the intraoral and facial scans. Subsequently, 1 video of a 180-degree rotation of each 3D superimposition was obtained. Participants evaluated both superimpositions on a scale from 1 (least esthetically pleasing) to 6 (most esthetically pleasing). Finally, participants were asked which superimposition they preferred for a potential treatment outcome representation. Results All the ratings were esthetically pleasing (median group rating 5 or 6). When analyzed solely for differences across occupation groups, ratings for the 2D representation varied significantly across populations (Kruskal-Wallis chi-squared=13.241, df=2, P=.001), but the ratings for the 3D representation did not exhibit statistically significant differences (Kruskal-Wallis chi-squared=4.3756, df=2, P=.112). Ordinal logistic regression revealed no significant main effects but a significant effect of the population×image-type interaction on the esthetic rating. All participants felt well-represented in both the 2D and 3D representations. Also, 40% of dentists, 55% of dental students, and 50% of laypersons preferred the 3D reconstructions. Sex and occupation in general had no effect on the ratings. However, students tended to give higher ratings to the 3D representations of themselves. Conclusions There is no evidence based on the current study that 2D and 3D representations were perceived differently, but representation preferences may depend on a person’s occupation. When individuals rated 3D visualization higher than 2D visualization, they strongly preferred the 3D visualization for representing the treatment outcome.

Digital and analog vertical dimension measurements: A clinical observational study

Abstract: PURPOSE To compare the rest vertical dimension (RVD) and occlusal vertical dimension (OVD) measurements obtained using a facial scanner with conventional methods and to evaluate the influence of the file format on the accuracy of the digital calculations. MATERIALS AND METHODS Participants (N = 30) received marks on the glabella (Gb), tip of the nose (TN), and pogonion (Pg). Interlandmark distances Gb-TN and TN-Pg in the OVD and RVD positions were recorded by two operators conventionally (manual group) and digitally (digital group). For the manual group, measurements were obtained using a caliper. For the digital group, 10 scans in each position were obtained using a facial scanner (Face Camera Pro, Bellus3D) and exported in tessellation with polygonal faces (OBJ) and standard tessellation language (STL) file formats. Digital measurements were performed using both facial scan file formats and a software (Matera 2.4, exocad). The interocclusal rest distance (IRD) and the intraclass correlation coefficient were calculated. Shapiro-Wilk test was used to determine normal distribution. An independent samples t test, one-way analysis of variance, and post hoc Tukey test were used for analyses (± = .05). RESULTS No significant differences were found between the manual and digital measurements using the OBJ files or digital measurements using the STL files (P > .05). The IRD ranged from 0.72 ± 0.48 mm to 5.00 ± 1.34 mm. The inter- and intra-operator reliability were significant (P < .001), with a Cronbach's alpha value ranging from .994 to .997. CONCLUSION No difference was found between manual and digital measurements. A high measurement consistency was encountered for each operator and between the operators. The facial scan file format did not influence the digital measurements.

Additively manufactured implant abutment screw-access guide to remove a cement-retained implant crown: A technique.

Abstract: A complete digital workflow to remove a cement-retained implant-supported crown by using an additively manufactured implant abutment screw-access guide is described. The existing cone beam computed tomography (CBCT) scan was superimposed on the digital scans of the patient, which facilitated the visualization of the implant abutment screw access and guided the design of the device. Advantages of the technique described include the precise translation of the implant abutment screw access, safe removal of the implant crown, and conservative clinical intervention.

Fabrication of a complete-arch implant-supported fixed interim prosthesis by using a cone beam computed tomography digital scan for a patient with primordial dwarfism: A dental technique

Abstract: A complete-arch implant-supported interim prosthesis was fabricated from a cone beam computed tomography digital scan of the implant abutments for a patient with primordial dwarfism. The patient presented with limited mouth opening, which hindered the use of a conventional impression technique. The described technique provided an alternative digital procedure to obtain a virtual implant definitive cast.