Pressure Differences from Clear Aligner Movements Assessed by Pressure Sensors.

OBJECTIVES: In this study, a clear aligner was moved at intervals of 0.25 mm and pressure variations were assessed using a sensor. METHODS: The model used for producing the clear aligner was created using a 3-dimensional printer. A clear, circular thermoplastic of 0.75 mm thickness was used for making the clear aligner using the vacuum forming method. A pressure sensor was used to assess the pressure in the device, and the variation in the sheet pressure was statistically analyzed tooth movement using the clear aligner, moving at an interval of 0.25 mm, is recommended. RESULTS: The results of pressure sensor assessment showed that the pressure of the devices with 0.25 mm and 1.00 mm movements was identical to that of the device with 0 mm movement. In other words, the pressure sensor could not distinguish the pressure of devices that moved 0.25 mm and 1.00 mm. CONCLUSIONS: This experiment demonstrated that a movement of more than 0.50 mm is needed to apply the appropriate pressures needed for orthodontics in a clear polymer sheet.

Accuracy of 3-unit fixed dental prostheses fabricated on 3D-printed casts.

STATEMENT OF PROBLEM: Three-dimensional (3D)-printed casts are used successfully as diagnostic casts in orthodontics. However, whether 3D-printed casts are sufficiently accurate to be used as definitive casts for fixed dental prostheses (FDPs) is unclear. PURPOSE: The purpose of this in vitro study was to evaluate the fit of 3-unit FDPs fabricated on 3D-printed casts made by digital light processing and to investigate the clinical applicability of 3D printing. MATERIAL AND METHODS: A master model was fabricated from epoxy resin. Stone casts were made from dual viscosity impressions (conventional stone cast [CS] group, n=10). The 3D-printed casts were fabricated using a 3D printer after obtaining digital virtual casts by digital scans (3D-printed cast [3DP] group, n=10). All FDPs were fabricated with a 5-axis milling machine. The master model and intaglio surface of the milled FDPs was superimposed using 3D analysis software to measure the accuracy. Two-way ANOVA was performed to identify a significant difference between the groups (3DP and CS) and sides (pontic side, nonpontic side) and their interactive effects (α=.05). The Tukey honestly significant difference test was used for post hoc analysis. RESULTS: Two-way ANOVA showed significant differences between the 2 groups (3DP and CS) in the marginal and internal root mean square (RMS) values (P<.001). However, no significant difference was found in the marginal RMS values (P=.762) between the pontic and nonpontic sides. The 3DP showed significantly higher RMS values than the CS (P<.001). CONCLUSIONS: The fit of FDPs produced from 3D-printed casts was inferior to that of conventional stone casts; however, all FDPs showed clinically acceptable accuracy. These results suggest that 3D-printed casts have clinical applicability but that further improvement of the 3D printer is necessary for their application in prosthodontics.

Three-dimensional trueness analysis of ceramic crowns fabricated using a chairside computer-aided design/manufacturing system: An in vitro study.

PURPOSE: This study analyzed the trueness of polymer-infiltrated ceramic and glass ceramic crowns manufactured using the chairside computer-aided design/manufacturing (CAD/CAM) system. METHODS: The master model designs crowns using a CAD program after acquiring a digital impression with an intraoral scanner. Vita Enamic (VE), Vita Suprinity (VS), and IPS e.max CAD (IPS) were used to manufacture 10 crowns each (total: 30 crowns), using the chairside CAD/CAM system (inLab MC XL). Trueness was evaluated by superimposing the CAD data on the scan data using a three-dimensional program. The Kruskal-Wallis H test, a nonparametric test, and the Mann-Whitney U test were performed by applying the significance level (0.05/3=0.016), which was adjusted by post-analysis Bonferroni testing. RESULTS: There was a significant difference in the trueness between the samples (p<0.05). However, there was no statistically significant difference in the outer surface trueness between the samples (p>0.05). CONCLUSIONS: These findings show that the milling accuracy of VE is better than that of VS and IPS.

Effects of Different Thickness Combinations of Core and Veneer Ceramics on Optical Properties of CAD-CAM Glass-Ceramics.

The goal of this study was to evaluate the effects of different core and veneer thicknesses on the translucency (T%), average light transmittance (T), translucency parameter (TP), contrast ratio (CR), and spectral reflectance (R) of glass-ceramics using a computer-aided design/computer-aided manufacturing (CAD-CAM) process. In all, 42 specimens (11mm × 11mm) were prepared and divided into six groups (n = 7 for each group). Core materials (IPS e.max CAD; IPS Empress CAD, LT A2 shade) of different thicknesses (0.8, 1.0, and 1.2mm) were fabricated. Each veneer material (thicknesses of 0.7, 0.5, and 0.3mm) was combined with its compatible core ceramic. Each core material was overlapped with its corresponding veneer material to obtain a 1.5-mm thickness by using three different combinations: (0.8+0.7), (1.0+0.5), and (1.2+0.3) mm. A spectrophotometer and color data software were used to measure the T%, T, TP, CR, and R values of each ceramic. The results were statistically analyzed using two-way analysis of variables (ANOVA) and regression analysis (p<0.05). Two-way ANOVA revealed that T%, T, TP, and CR were significantly influenced by the different thicknesses of the core-veneer combinations (p<0.001). At a certain thickness, as the veneer thickness increased and core thickness decreased, T and T% all increased. Regression analysis of the ceramic materials indicated a reduction in T and T% for certain core-veneer combinations. Analysis also revealed that T% and T were all affected by different core-veneer combinations. The T% value was 74.31 for the EM group and 72.81 for the EP group when the thickness of the core was 1.2 mm and the veneer was 0.3 mm. The R value of EM2 was lower than EM1 and EM3. In conclusion, the optical properties were influenced by different core-veneer combinations.

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. METHODS: A reference model was prepared with three prepared teeth for three types of restorations: single crown, 3-unit bridge, and inlay. Stone models were fabricated from conventional impressions. Digital impressions of the reference model were created using an intraoral scanner (digital models). Physical models were fabricated using a three-dimensional (3D) printer. Reference, stone, and 3D printed models were subsequently scanned using an industrial optical scanner; files were exported in a stereolithography file format. All datasets were superimposed using 3D analysis software to evaluate the accuracy of the complete arch and trueness of the preparations. One-way and two-way analyses of variance (ANOVA) were performed to compare the accuracy among the three model groups and evaluate the trueness among the three types of preparation. RESULTS: For the complete arch, significant intergroup differences in precision were observed for the three groups (p<.001). However, no significant difference in trueness was found between the stone and digital models (p>.05). 3D printed models had the poorest accuracy. A two-way ANOVA revealed significant differences in trueness among the model groups (p<.001) and types of preparation (p<.001). CONCLUSIONS: Digital models had smaller root mean square values of trueness of the complete arch and preparations than stone models. However, the accuracy of the complete arch and trueness of the preparations of 3D printed models were inferior to those of the other groups.

Accuracy of Dental Replica Models Using Photopolymer Materials in Additive Manufacturing: In Vitro Three-Dimensional Evaluation.

PURPOSE: To evaluate the accuracy (trueness and precision) of dental replica models produced by using photopolymer materials in additive manufacturing. MATERIALS AND METHODS: A complete arch model was scanned using an extraoral scanner (Identica Blue) and established as reference. For the control group, 10 stone models were acquired through the conventional method from the reference model. For the experimental groups, digital data were acquired using an intraoral scanner (CEREC Omnicam), and 10 stereolithographic apparatus (SLA) models and 10 PolyJet models were made. All models were scanned with an extraoral scanner. Three-dimensional analysis software was used to measure differences between the 3D scanned images in root mean square values. The ISO-5725-1 specification was followed to measure trueness and precision between two 3D scanned data. Trueness was calculated by overlapping scanned data with the reference model and precision by performing pairwise intragroup comparisons. Also the ratio of region out of tolerance (> ±50 µm) was measured. One-way ANOVA and Tukey's post hoc analysis were applied. RESULTS: There was no statistically significant difference in trueness between the stone and the SLA models (p > 0.05). Dental replica models using photopolymer materials showed statistically significantly better precision than that of the stone model (p < 0.05). Regarding tolerance, no statistically significant difference was observed between the stone and the SLA models (p > 0.05). CONCLUSIONS: Although the dental replica models using photopolymer materials did not show better trueness than the conventional stone models, there was no significant difference between the SLA and the stone models. Concerning precision, dental replica models using photopolymer materials presented better results than that of the conventional stone models. In sum, dental replica models using photopolymer materials showed sufficient accuracy for clinical use.

Trueness and precision of scanning abutment impressions and stone models according to dental CAD/CAM evaluation standards.

PURPOSE: The purpose of the present study was to compare scanning trueness and precision between an abutment impression and a stone model according to dental computer-aided design/computer-aided manufacturing (CAD/CAM) evaluation standards. MATERIALS AND METHODS: To evaluate trueness, the abutment impression and stone model were scanned to obtain the first 3-dimensional (3-D) stereolithography (STL) file. Next, the abutment impression or stone model was removed from the scanner and re-fixed on the table; scanning was then repeated so that 11 files were obtained for each scan type. To evaluate precision, the abutment impression or stone model was scanned to obtain the first 3-D STL file. Without moving it, scanning was performed 10 more times, so that 11 files were obtained for each scan type. By superimposing the first scanned STL file onto the other STL files one by one, 10 color-difference maps and reports were obtained; i.e., 10 experimental scans per type. The independent t-test was used to compare root mean square (RMS) data between the groups (α=.05). RESULTS: The RMS±SD values of scanning trueness of the abutment impression and stone model were 22.4±4.4 and 17.4±3.5 µm, respectively (P<.012). The RMS±SD values of scanning precision of the abutment impression and stone model were 16.4±2.9 and 14.6±1.6 µm, respectively (P=.108). CONCLUSION: There was a significant difference in scanning trueness between the abutment impression and stone model, as evaluated according to dental CAD/CAM standards. However, all scans showed high trueness and precision.

Evaluation of marginal discrepancy of pressable ceramic veneer fabricated using CAD/CAM system: Additive and subtractive manufacturing.

PURPOSE: The purpose of this study was to evaluate the marginal discrepancy of heat-pressed ceramic veneers manufactured using a CAD/CAM system. MATERIALS AND METHODS: The ceramic veneers for the abutment of a maxillary left central incisor were designed using a CAD/CAM software program. Ten veneers using a micro-stereolithography apparatus (AM group), ten veneers using a five-axis milling machine (SM group), and ten veneers using a traditional free-hand wax technique (TW group) were prepared according to the respective manufacturing method. The ceramic veneers were also fabricated using a heat-press technique, and a silicone replica was used to measure their marginal discrepancy. The marginal discrepancies were measured using a digital microscope (×160 magnification). The data were analyzed using a nonparametric Kruskal-Wallis H test. Finally, post-hoc comparisons were conducted using Bonferroni-corrected Mann-Whitney U tests (α=.05). RESULTS: The mean±SD of the total marginal discrepancy was 99.68±28.01 µm for the AM group, 76.60±28.76 µm for the SM group, and 83.08±39.74 µm for the TW group. There were significant differences in the total marginal discrepancies of the ceramic veneers (P<.05). CONCLUSION: The SM group showed a better fit than the AM and TW groups. However, all values were within the clinical tolerance. Therefore, CAD/CAM manufacturing methods can replace the traditional free-hand wax technique.

Accuracy of provisional crowns made using stereolithography apparatus and subtractive technique.

PURPOSE: To compare and analyze trueness and precision of provisional crowns made using stereolithography apparatus and subtractive technology. MATERIALS AND METHODS: Digital impressions were made using a master model and an intraoral scanner and the crowns were designed with CAD software; in total, 22 crowns were produced. After superimposing CAD design data and scan data using a 3D program, quantitative and qualitative data were obtained for analysis of trueness and precision. Statistical analysis was performed using normality test combined with Levene test for equal variance analysis and independent sample t-test. Type 1 error was set at 0.05. RESULTS: Trueness for the outer and inner surfaces of the SLA crown (SLAC) were 49.6±9.3 µm and 22.5±5.1 µm, respectively, and those of the subtractive crown (SUBC) were 31.8±7.5 µm and 14.6±1.2 µm, respectively. Precision values for the outer and inner surfaces of the SLAC were 18.7±6.2 µm and 26.9±8.5 µm, and those of the SUBC were 25.4±3.1 µm and 13.8±0.6 µm, respectively. Trueness values for the outer and inner surfaces of the SLAC and SUBC showed statistically significant differences (P<.001). Precision for the inner surface showed significance (P<.03), whereas that for the outer surface showed no significance (P<.58). CONCLUSION: The study demonstrates that provisional crowns produced by subtractive technology are superior to crowns fabricated by stereolithography in terms of accuracy.

Evaluation of the marginal and internal fit of a single crown fabricated based on a three-dimensional printed model.

PURPOSE: To evaluate the fit of a crown produced based on a 3D printed model and to investigate its clinical applicability. MATERIALS AND METHODS: A master die was fabricated with epoxy. Stone dies were fabricated from conventional impressions (Conventional stone die group: CS, n=10). Digital virtual dies were fabricated by making digital impressions (Digital Virtual die group: VD, n=10). 3D data obtained from the digital impression was used to fabricate 3D printed models (DLP die group: DD, n=10, PolyJet die group: PD, n=10). A total of 40 crowns were fabricated with a milling machine, based on CS, VD, DD and PD. The inner surface of all crowns was superimposed with the master die files by the "Best-fit alignment" method using the analysis software. One-way and 2-way ANOVA were performed to identify significant differences among the groups and areas and their interactive effects (α=.05). Tukey's HSD was used for post-hoc analysis. RESULTS: One-way ANOVA results revealed a significantly higher RMS value in the 3D printed models (DD and PD) than in the CS and DV. The RMS values of PD were the largest among the four groups. Statistically significant differences among groups (P<.001) and between areas (P<.001) were further revealed by 2-way ANOVA. CONCLUSION: Although the fit of crowns fabricated based on the 3D printed models (DD and PD) was inferior to that of crowns prepared with CS and DV, the values of all four groups were within the clinically acceptable range (<120 µm).

A study on the machining accuracy of dental digital method focusing on dental inlay.

PURPOSE: The purpose of this study was to compare the cutting method and the lamination method to investigate whether the CAD data of the proposed inlay shape are machined correctly. MATERIALS AND METHODS: The Mesial-Occlusal shape of the inlay was modeled by changing the stereolithography (STL). Each group used SLS (metal powder) or SLA (photocurable resin) in the additive method, and wax or zirconia in the subtractive method (n=10 per group, total n=40). Three-dimensional (3D) analysis program (Geomagic Control X inspection software; 3D systems) was used for the alignment and analysis. The root mean square (RMS) in the 2D plane state was measured within 50 µm radius of eight comparison measuring points (CMP). Differences were analyzed using one-way analysis of variance and post-hoc Tukey's test were used (α=.05). RESULTS: There was a significant difference in RMS only in SLA and SLS of 2D section (P<.05). In CMP mean, CMP 4 (-5.3±46.7 µm) had a value closest to 0, while CMP 6 (20.1±42.4 µm) and CMP 1 (-89.2±61.4 µm) had the greatest positive value and the greatest negative value, respectively. CONCLUSION: Since the errors obtained from the study do not exceed the clinically acceptable values, the lamination method and the cutting method can be used clinically.

Evaluation of the reproducibility of various abutments using a blue light model scanner.

PURPOSE: To evaluate the reproducibility of scan-based abutments using a blue light model scanner. MATERIALS AND METHODS: A wax cast abutment die was fabricated, and a silicone impression was prepared using a silicone material. Nine study dies were constructed using the prepared duplicable silicone, and the first was used as a reference. These dies were classified into three groups and scanned using a blue light model scanner. The first three-dimensional (3D) data set was obtained by scanning eight dies separately in the first group. The second 3D data set was acquired when four dies were placed together in the scanner and scanned twice in the second group. Finally, the third 3D data set was obtained when eight dies were placed together in the scanner and scanned once. These data were then used to define the data value using third-dimension software. All the data were then analyzed using the non-parametric Kruskal-Wallis H test (α=.05) and the post-hoc Mann-Whitney U-test with Bonferroni's correction (α=.017). RESULTS: The means and standard deviations of the eight dies together were larger than those of the four dies together and of the individual die. Moreover, significant differences were observed among the three groups (P<.05). CONCLUSION: With larger numbers of abutments scanned together, the scan becomes more inaccurate and loses reproducibility. Therefore, scans of smaller numbers of abutments are recommended to ensure better results.

A comparison of different thicknesses of mouthguards according to the groove shape of sheets.

BACKGROUND/AIMS: Previous studies have compared the thickness of the device with and without grooves. The result was a difference in thickness of the device along the groove. The aim of this study was to assess the differences in thickness of mouthguards that result from different groove shapes of ethylene vinyl acetate sheets used to make these appliances. MATERIALS AND METHOD: Mouthguards were made using a 3-dimensional printer, and produced by softening 4 mm transparent circular sheets. Four different shapes of sheets were evaluated: normal sheets, sheets with anterior V-shaped grooves, sheets with anterior A-shaped grooves, and sheets with posterior A-shaped grooves. The groove was 3 mm deep and 5 mm wide. The thickness of the appliance was assessed with respect to the anterior incisal edge, labial surface, palatal surface, posterior cusp, buccal surface, and palatal surface. The Kruskal-Wallis test was used to analyze differences in thickness among the different groove shapes. RESULTS: No significant difference was detected between the thickness of mouthguards made using sheets with grooves and that of mouthguards made using sheets without grooves (P > .05). CONCLUSION: The presence of grooves on the sheets did not influence mouthguard thickness.

Reproducibility of different coping arrangements fabricated by dental micro-stereolithography: Evaluation of marginal and internal gaps in metal copings.

BACKGROUND/PURPOSE: To evaluate the reproducibility of the marginal and internal gaps of metal copings fabricated using dental micro-stereolithography (µ-SLA), which is an additive manufacturing system. MATERIALS AND METHODS: A study cast of abutment tooth 46 was made from type-IV dental stone and was scanned to create a standard triangulation language file. Arrays of one (ORM), three (TRM), and six (SRM) resin copings were then fabricated on the µ-SLA build platform using investment, burnout, and casting (n = 12). The marginal and internal gaps of these metal copings were measured using a silicone-replica technique with a digital microscope (×160). The data obtained were analyzed using a non-parametric Kruskal-Wallis H test, a post-hoc Mann-Whitney U test, and a Bonferroni correction. RESULTS: The mean and standard deviation of the marginal gap for each group were measured and found to be 81.1 and 53.2 µm, 68.3 and 44.8 µm, and 90.3 and 57.7 µm for ORM, TRM, and SRM, respectively. There were no statistical differences in the marginal gaps of the three groups (p > 0.05). CONCLUSION: The marginal and internal gap of ORM, TRM and SRM groups were considered clinically acceptable.

Effects of core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics.

STATEMENT OF PROBLEM: The color of dental ceramics is important for achieving successful esthetic restorations. However, insufficient studies are available of the color of recently introduced computer-aided design-computer-aided manufacturing (CAD-CAM) lithium disilicate ceramics as functions of the core and veneer thicknesses. PURPOSE: The purpose of this in vitro study was to evaluate the effects of the thickness of different core and veneer thicknesses on the color of CAD-CAM lithium disilicate ceramics. MATERIAL AND METHODS: A total of 42 specimens from 2 groups of 7 ceramic cores at 3 thicknesses (0.8, 1.0, and 1.2 mm) were fabricated. The veneer was fabricated at 3 thicknesses (0.3, 0.5, and 0.7 mm). The group name was based on the name of the ceramic core (IPS e.max CAD; lithium disilicate [LD], IPS Empress CAD; leucite-reinforced glass-ceramic [LR]), and the associated number was determined by the combined thicknesses of the core and the veneer: 1=0.8+0.7; 2=1.0+0.5; and 3=1.2+0.3. The color coordinates and the color differences were calculated using a spectrophotometer. The color difference was analyzed using the CIEDE2000 chrominance and the acceptability threshold. Two-way ANOVA was used to identify the color difference based on the core/veneer thicknesses, and the Tukey honest significant differences and Games-Howell tests were conducted to verify the ΔE00 differences of the group (α=.05). In addition, regression analysis was carried out to estimate the causal relationship between the independent variables and the chrominance. RESULTS: At a certain thickness, the color differences of LD1, LR1, and LR2 were not clinically acceptable based on the thicknesses of the core and the veneer. Results of 2-way ANOVA demonstrated that the different thicknesses of core/veneer combination significantly affected the color difference (P<.05). A significant interaction was present between the thickness and the material (P<.05). The results of multiple regression analyses showed that the average color difference of LR increased by 0.019 as the thickness of the core decreased by 0.2 mm. CONCLUSIONS: The color is influenced by the thicknesses of the core and the veneer. With a certain thickness, the color differences increased as the thickness of the core decreased, and lithium disilicate ceramics were less vulnerable to standard deviation of color difference compared with the leucite-reinforced ceramics.

Comparison and evaluation of marginal and internal gaps in cobalt-chromium alloy copings fabricated using subtractive and additive manufacturing.

PURPOSE: To evaluate the marginal and internal gaps of cobalt-chromium (Co-Cr) alloy copings fabricated using subtractive and additive manufacturing. METHODS: A study model of an abutment tooth 46 was prepared by a 2-step silicone impression with dental stone. Fifteen stereolithography files for Co-Cr alloy copings were compiled using a model scanner and dental CAD software. Using the lost wax (LW), wax block (WB), soft metal block (SMB), microstereolithography (µ-SLA), and selected laser melting (SLM) techniques, 15 Co-Cr alloy copings were fabricated per group. The marginal and internal gaps of these Co-Cr alloy copings were measured using a digital microscope (160×), and the data obtained were analyzed using the non-parametric Kruskal-Wallis H-test and post-hoc Mann-Whitney U-test with Bonferroni correction. RESULTS: The mean values of the marginal, axial wall, and occlusal gaps were 91.8, 83.4, and 163µm in the LW group; 94.2, 77.5, and 122µm in the WB group; 60.0, 79.4, and 90.8µm in the SMB group; 154, 72.4, and 258µm in the µ-SLA group; and 239, 73.6, and 384µm in the SLM group, respectively. The differences in the marginal and occlusal gaps between the 5 groups were statistically significant (P<.05). CONCLUSIONS: The marginal gaps of the LW, WB, and SMB groups were within the clinically acceptable limit, but further improvements in the µ-SLA and SLM approaches may be required prior to clinical implementation.

Evaluation of marginal and internal gap of three-unit metal framework according to subtractive manufacturing and additive manufacturing of CAD/CAM systems.

PURPOSE: To evaluate the fit of a three-unit metal framework of fixed dental prostheses made by subtractive and additive manufacturing. MATERIALS AND METHODS: One master model of metal was fabricated. Twenty silicone impressions were made on the master die, working die of 10 poured with Type 4 stone, and working die of 10 made of scannable stone. Ten three-unit wax frameworks were fabricated by wax-up from Type IV working die. Stereolithography files of 10 three-unit frameworks were obtained using a model scanner and three-dimensional design software on a scannable working die. The three-unit wax framework was fabricated using subtractive manufacturing (SM) by applying the prepared stereolithography file, and the resin framework was fabricated by additive manufacturing (AM); both used metal alloy castings for metal frameworks. Marginal and internal gap were measured using silicone replica technique and digital microscope. Measurement data were analyzed by Kruskal-Wallis H test and Mann-Whitney U-test (α=.05). RESULTS: The lowest and highest gaps between premolar and molar margins were in the SM group and the AM group, respectively. There was a statistically significant difference in the marginal gap among the 3 groups (P<.001). In the marginal area where pontic was present, the largest gap was 149.39 ± 42.30 µm in the AM group, and the lowest gap was 24.40 ± 11.92 µm in the SM group. CONCLUSION: Three-unit metal frameworks made by subtractive manufacturing are clinically applicable. However, additive manufacturing requires more research to be applied clinically.

Evaluation of marginal and internal gaps in single and three-unit metal frameworks made by micro-stereolithography.

PURPOSE: The purpose of this study is to compare single and three-unit metal frameworks that are produced by micro-stereolithography. MATERIALS AND METHODS: Silicone impressions of a selected molar and a premolar were used to make master abutments that were scanned into a stereolithography file. The file was processed with computer aided design software to create single and three-unit designs from which resin frameworks were created using micro-stereolithography. These resin frameworks were subjected to investment, burnout, and casting to fabricate single and three-unit metal ones that were measured under a digital microscope by using the silicone replica technique. The measurements were verified by means of the Mann-Whitney U test (α=.05). RESULTS: The marginal gap was 101.9 ± 53.4 µm for SM group and 104.3 ± 62.9 µm for TUM group. The measurement of non-pontics in a single metal framework was 93.6 ± 43.9 µm, and that of non-pontics in a three-unit metal framework was 64.9 ± 46.5 µm. The dimension of pontics in a single metal framework was 110.2 ± 61.4 µm, and that of pontics in a three-unit metal framework was 143.7 ± 51.8 µm. CONCLUSION: The marginal gap was smaller for the single metal framework than for the three-unit one, which requires further improvement before it can be used for clinical purposes.

Ceramic molar crown reproducibility by digital workflow manufacturing: An in vitro study.

PURPOSE: This in vitro study aimed to analyze and compare the reproducibility of zirconia and lithium disilicate crowns manufactured by digital workflow. MATERIALS AND METHODS: A typodont model with a prepped upper first molar was set in a phantom head, and a digital impression was obtained with a video intraoral scanner (CEREC Omnicam; Sirona GmbH), from which a single crown was designed and manufactured with CAD/CAM into a zirconia crown and lithium disilicate crown (n=12). Reproducibility of each crown was quantitatively retrieved by superimposing the digitized data of the crown in 3D inspection software, and differences were graphically mapped in color. Areas with large differences were analyzed with digital microscopy. Mean quadratic deviations (RMS) quantitatively obtained from each ceramic group were statistically analyzed with Student's t-test (α=.05). RESULTS: The RMS value of lithium disilicate crown was 29.2 (4.1) µm and 17.6 (5.5) µm on the outer and inner surfaces, respectively, whereas these values were 18.6 (2.0) µm and 20.6 (5.1) µm for the zirconia crown. Reproducibility of zirconia and lithium disilicate crowns had a statistically significant difference only on the outer surface (P<.001). The outer surface of lithium disilicate crown showed over-contouring on the buccal surface and under-contouring on the inner occlusal surface. The outer surface of zirconia crown showed both over- and under-contouring on the buccal surface, and the inner surface showed under-contouring in the marginal areas. CONCLUSION: Restoration manufacturing by digital workflow will enhance the reproducibility of zirconia single crowns more than that of lithium disilicate single crowns.

Evaluation of the marginal and internal gaps of three different dental prostheses: comparison of the silicone replica technique and three-dimensional superimposition analysis.

PURPOSE: The purposes of this study were to evaluate the marginal and internal gaps, and the potential clinical applications of three different methods of dental prostheses fabrication, and to compare the prostheses prepared using the silicone replica technique (SRT) and those prepared using the three-dimensional superimposition analysis (3DSA). MATERIALS AND METHODS: Five Pekkton, lithium disilicate, and zirconia crowns were each manufactured and tested using both the SRT and the two-dimensional section of the 3DSA. The data were analyzed with the nonparametric version of a two-way analysis of variance using rank-transformed values and the Tukey's post-hoc test (α = .05). RESULTS: Significant differences were observed between the fabrication methods in the marginal gap (P < .010), deep chamfer (P < .001), axial wall (P < .001), and occlusal area (P < .001). A significant difference in the occlusal area was found between the two measurement methods (P < .030), whereas no significant differences were found in the marginal gap (P > .350), deep chamfer (P > .719), and axial wall (P > .150). As the 3DSA method is three-dimensional, it allows for the measurement of arbitrary points. CONCLUSION: All of the three fabrication methods are valid for measuring clinical objectives because they produced prostheses within the clinically acceptable range. Furthermore, a three-dimensional superimposition analysis verification method such as the silicone replica technique is also applicable in clinical settings.