Effect of a new support design on the marginal and internal gap of additively manufactured interim crowns using direct light deposition technology.

PURPOSE: To investigate the design and location of supporting structures on the marginal and internal gap of interim restorations. MATERIALS AND METHODS: A mandibular right first molar resin tooth was prepared for a full coverage crown and scanned using a laboratory scanner (3Shape D900). The scanned data were converted into standard tessellation language (STL) format and an indirect prosthesis was designed using computer-aided design (CAD) software (exocad DentalCAD). The STL file was used to fabricate a total of 60 crowns with a 3D printer (EnvisionTEC Vida HD). The crowns were printed using E-Dent C&B MH resin and divided into 4 groups based on four different support structure designs, including supports on the occlusal (0° group), buccal and occlusal (45° group), buccal (90° group), and a new design consisting of horizontal bars placed on all surfaces and line angles (Bar) (n = 15). The silicone replica technique was used to determine the gap discrepancy. Fifty measurements were obtained for each specimen to examine the marginal and internal gaps by using a digital microscope (Olympus SZX16) at ×70 magnification. Additionally, the marginal discrepancy at different locations of the tested crowns, including buccal (B), lingual (L), mesial (M), and distal (D), as well as the maximum and minimum marginal gap intervals among groups, were analyzed. The collected data were analyzed using factorial ANOVA, followed by the Tukey HSD test for multiple comparisons (a = 0.05). RESULTS: There was a significant difference in marginal and internal gaps among the groups (p < 0.001). The buccal placement supports (90° group) had the least marginal and internal discrepancies (p < 0.001). The new design group showed the highest marginal and internal gap. The marginal discrepancy in different locations of the tested crowns (B, L, M, D) was found to be significantly different among the groups (p < 0.001). The mesial margin of the Bar group had the largest marginal gap, whereas the buccal margin of the 90° group had the lowest marginal gap. The new design had a significantly smaller difference between the maximum and minimum marginal gap intervals than other groups (p < 0.001). CONCLUSION: The location and design of the supporting structures affected the marginal and internal gaps of an interim crown. The buccal placement of supporting bars (90° printing orientation) showed the smallest mean internal and marginal discrepancies.

An In Vitro Comparison of Zirconia and Hybrid Ceramic Crowns With Heavy Chamfer and Shoulder Finish Lines.

Purpose This in vitro study aimed to compare the marginal fit and internal adaptation of computer-aided designed and computer-aided manufactured (CAD-CAM) zirconia and hybrid ceramic crowns on heavy chamfer and shoulder finish line designs using silicon replica method. Materials and methods Forty die samples were divided into four groups of 10 dies each. Out of 40 diecasts scanned, zirconia crowns were milled on 20 casts (10 prepared with shoulder and 10 prepared with heavy chamfer finish line design), while hybrid ceramic crowns were milled on the rest of the 20 casts. After milling crowns, the silicone replica technique measured the marginal fit and internal adaptation. Results The heavy chamfer finish line design provided a better marginal fit than the shoulder finish line design for zirconia and hybrid ceramic crowns. Hybrid ceramic crowns had a better marginal fit and internal adaptation than zirconia crowns, both at heavy chamfer and shoulder finish line design. The gap at the margin was less than the axial and occlusal walls, and the maximum gap was observed in the occlusal area. In addition, the marginal gap was less than the internal gap, which showed a positive correlation with each other. Conclusion The study concluded that the difference in CAD-CAM materials and finish line designs influences marginal fit and crown restoration's internal adaptation. A heavy chamfer finish line design provides a better marginal fit for zirconia and hybrid ceramic crowns than a shoulder finish line design. Hybrid ceramic crowns have a better marginal fit and internal adaptation than zirconia crowns in heavy chamfer and shoulder finish lines.

Evaluating the Marginal and Internal Discrepancy of Nickel-Chrome Copings Made on Fixed Partial Denture Implants with Conventional and 3D Printing Techniques.

AIM: This study aimed to evaluate the marginal and internal discrepancy of nickel-chrome (Ni-Cr) copings made on implant bridges with conventional and 3D printing techniques. MATERIALS AND METHODS: 30 three-unit Ni-Cr FDPs (60 copings) were made by 3D-printing technique (PolyJet group), lost-wax method with die spacer technique (die spacer group), and lost-wax method with burn-out the cap (burn-out cap group). Then, the frames obtained from the three methods were checked to examine the marginal discrepancy by stereomicroscope after preparation and polishing. The silicon replica method was used to investigate the internal discrepancy at 6 points (buccal portion of occlusal surface, lingual portion of occlusal surface, middle area of the axial surface in the lingual, middle area of the axial surface in the buccal, cervico-buccal area, and cervico-lingual area). Kolmogorov-Smirnov test was performed first to estimate the normality of data distribution. A one-way ANOVA and post hoc Tukey test were done for comparing marginal and internal discrepancies between groups. The significant level was considered p < 0.05. RESULTS: The mean ± standard deviation of marginal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 37.9 ± 15, 68.8 ± 31.8 and 42.7 ± 3.6 µm for buccal margins and 40.4 ± 12.3, 64 ± 21.7, and 42.4 ± 2.1 µm for lingual margins, respectively. The means of buccal and lingual marginal discrepancy in the burn-out cap group and PolyJet group were significantly lower than the die spacer group (p < 0.001). Marginal discrepancy was not statistically different between the burn-out cap group and the PolyJet group. The mean ± standard deviation of overall internal discrepancy in the PolyJet group, die spacer group, and burn-out cap group was 64.6 ± 3.7, 72 ± 22.2, and 58.7 ± 2 µm, respectively. There was a significant difference between the mean of internal discrepancy between three groups (p = 0.001). The mean of internal discrepancy of the burn-out cap group was significantly lower than the die spacer group (p = 0.001) and PolyJet group (p = 0.005). Internal discrepancy was not significantly different between the PolyJet group and the die spacer group (p = 0.168). CONCLUSION: The marginal and internal gap rates of the three groups were within clinically acceptable limits. The 3D printing technique and lost-wax method with burn-out the cap had the lowest buccal and lingual marginal discrepancies. The burn-out cap method had better fitness and less internal discrepancy than 3D printing and die spacer groups. CLINICAL SIGNIFICANCE: Lower marginal discrepancy of copings fabricated by using 3D printed patterns may improve clinical success of implant restoration. How to cite this article: Ziaei M, Bajoghli F, Sabouhi M, et al. Evaluating the Marginal and Internal Discrepancy of Nickel-Chrome Copings Made on Fixed Partial Denture Implants with Conventional and 3D Printing Techniques. J Contemp Dent Pract 2023;24(11):826-833.

Effect of full arch two scanning techniques on the accuracy of overdenture conventional and CAD/CAM Co-Cr bars.

This work evaluates the internal and marginal adaptation of implant-assisted overdenture cobalt-chromium (Co-Cr) bars manufactured using conventional as well as CAD/CAM subtractive and selective laser melting (SLM) utilizing two scanning techniques. METHODS: An edentulous study model containing four dental implants placed at teeth sites 36, 33, 43, and 46 was used. The study cast was scanned and compared to the virtual casts developed from two scanning techniques, straight and zigzag motion, using the in silico superimposition process. Then, conventional techniques were used to produce full-arch bars that were compared to the bars fabricated using the two scanning techniques and CAD/CAM subtractive and additive techniques. RESULTS: The conventional impression and casting techniques had the smallest marginal gap among the groups (P-value < 0.05). The CAD/CAM subtractive milling techniques in groups II and III had significantly smaller marginal gaps than SLM technique used in groups IV and V (P-value < 0.05). The analysis of the internal gap within each group showed statistically significant differences between different implant sites in all groups (P-value < 0.001), except when using the conventional impression and casting techniques in group I (P-value = 0.20). CONCLUSION: The conventional impression and fabrication techniques were better than the digital impression and CAD/CAM subtractive and additive techniques for the fabrication of full-arch bars. However, both straight and zigzag scanning techniques and the CAD/CAM subtractive technique had marginal and internal gaps that were within clinically accepted ranges, and the SLM was found to be unsuitable for long-span framework fabrication with either scanning technique used.

Marginal and Internal Gap of Metal Copings Fabricated Using Three Types of Resin Patterns with Subtractive and Additive Technology: An In Vitro Comparison.

This study analyzes the evidence of the marginal discrepancy and internal adaptation of copings fabricated using three types of resin patterns with subtractive (milling) and additive technology (3D printing), as it is not widely reported. Working casts (n = 15) were scanned and patterns were completed using computer-aided designing (CAD). Resin patterns were fabricated using the designed data and divided into three groups according to the method of fabrication of patterns: subtractive technology-CAD milled polymethyl methacrylate resin (Group-PMMA), additive technology [digital light processing (DLP) technique]-acrylonitrile-butadiene-styrene (ABS) patterns (Group-ABS), and polylactic acid (PLA) patterns (Group-PLA). Resin patterns were casted with Cobalt-Chromium (Co-Cr) alloy (lost wax technique). Internal and marginal gaps of the metal copings were analyzed with the replica technique under optical microscope. The Kruskal-Wallis test was used to compare values among the groups, and post hoc multiple tests confirmed the specific differences within the groups. The median marginal gap was least for CAD milled resin patterns, followed by PLA printed resin patterns and ABS printed resin patterns. There were significant differences between Group-PMMA and Group-PLA and Group-ABS (p = 0.0001). There was no significant difference between Group-PLA and Group-ABS (p = 0.899). The median internal gap was least for metal copings fabricated from Group-PLA, followed by Group-ABS and Group-PMMA. The differences were not statistically significant (p = 0.638) for the internal gap. Full metal Co-Cr copings fabricated from the milled PMMA group had a better marginal fit, followed by the PLA and ABS printed groups. Copings fabricated with the PLA printed group had the best internal fit, though the values were statistically insignificant between the groups.

Three-dimensional fit of self-glazed zirconia monolithic crowns fabricated by wet deposition.

This study evaluated the 3-dimensional (3D) fit of self-glazed zirconia monolithic crowns fabricated by wet deposition, in comparison with milled zirconia and lithium disilicate monolithic crowns. Dual-scan protocol was used to assess the fit of crowns. Root mean squares (RMS) and uniformity index (UI) were calculated to describe the gap size and uniformity. The self-glazed zirconia crowns had significantly lower RMS values for the gaps at axial wall and transition regions than the milled zirconia crowns, and for the gaps at occlusal region than both milled crowns. All 3 types of crowns had comparable RMS values for the gaps at marginal and chamfer regions and comparable UI values for both marginal and internal gaps. The 3D fit of the self-glazed zirconia monolithic crowns was clinically acceptable and they exhibited better fit at occlusal region than the milled crowns.

Effect of Finish Line Design on the Fit Accuracy of CAD/CAM Monolithic Polymer-Infiltrated Ceramic-Network Fixed Dental Prostheses: An In Vitro Study.

A polymer-infiltrated ceramic network (PICN) material has recently been introduced for dental use and evidence is developing regarding the fit accuracy of such crowns with different preparation designs. The aim of this in vitro study was to evaluate the precision of fit of machined monolithic PICN single crowns in comparison to lithium disilicate crowns in terms of marginal gap, internal gap, and absolute marginal discrepancies. A secondary aim was to assess the effect of finish line configuration on the fit accuracy of crowns made from the two materials. Two master metal dies were used to create forty stone dies, with twenty each for the two finish lines, shoulder and chamfer. The stone dies were scanned to produce virtual models, on which ceramic crowns were designed and milled, with ten each for the four material-finish line combinations (n = 10). Marginal gaps and absolute marginal discrepancies were evaluated at six pre-determined margin locations, and the internal gap was measured at 60 designated points using a stereomicroscope-based digital image analysis system. The influence of the material and finish line on the marginal and internal adaptation of crowns was assessed by analyzing the data using two-way analysis of variance (ANOVA), non-parametric, and Bonferroni multiple comparison post-hoc tests (α = 0.05). ANOVA revealed that the differences in the marginal gaps and the absolute marginal discrepancies between the two materials were significant (p < 0.05), but that those the finish line effect and the interaction were not significant (p > 0.05). Using the Mann-Whitney U test, the differences in IG for 'material' and 'finish line' were not found to be significant (p > 0.05). In conclusion, the finish line configuration did not seem to affect the marginal and internal adaptation of PICN and lithium disilicate crowns. The marginal gap of PICN crowns was below the clinically acceptable threshold of 120 µm.

Evaluation of Marginal/Internal Fit and Fracture Load of Monolithic Zirconia and Zirconia Lithium Silicate (ZLS) CAD/CAM Crown Systems.

Fit accuracy and fracture strength of milled monolithic zirconia (Zi) and zirconia-reinforced lithium silicate (ZLS) crowns are important parameters determining the success of these restorations. This study aimed to evaluate and compare the marginal and internal fit of monolithic Zi and ZLS crowns, along with the fracture load, with and without mechanical aging. Thirty-two stone dies acquired from a customized master metal molar die were scanned, and ceramic crowns (16 Zi Ceramill Zolid HT+ and 16 ZLS Vita Suprinity) were designed and milled. Absolute marginal discrepancies (AMD), marginal gaps (MG), and internal gaps (IG) of the crowns, in relation to the master metal die, were evaluated using x-ray nanotomography (n = 16). Next, thirty-two metal dies were fabricated based on the master metal die, and crowns (16 Zi; 16 ZLS) cemented and divided into four groups of eight each; eight Zi with mechanical aging (MA), eight Zi without mechanical aging (WMA), eight ZLS (MA), and eight ZLS (WMA). Two groups of crowns (Zi-MA; ZLS-MA) were subjected to 500,000 mechanical cycles (200 ± 50 N, 10 Hz) followed by axial compressive strength testing of all crowns, until failure, and the values were recorded. Independent sample t tests (α = 0.05) revealed no significant differences between Zi and ZLS crowns (p > 0.05); for both internal and marginal gaps, however, there were significant differences in AMD (p < 0.005). Independent samples Mann-Whitney U and Kruskal-Wallis tests revealed significant differences between the two materials, Zi and ZLS, regardless of fatigue loading, and for the individual material groups based on aging (α = 0.05). Multiple comparisons using Bonferroni post-hoc analysis showed significant differences between Zi and ZLS material groups, with or without aging. Within the limitations of this study, the ZLS crown fit was found to be on par with Zi, except for the AMD parameter. As regards fracture resistance, both materials survived the normal range of masticatory forces, but the Zi crowns demonstrated greater resistance to fracture. The monolithic Zi and ZLS crowns seem suitable for clinical application, based on the fit and fracture strength values obtained.

Evaluation of internal adaptation of flowable and bulk-fill resin-based composites

@#This study aimed to evaluate and compare the internal adaptation of bulk-fill resin-based composite restorative materials with flowable composites as lining materials using self-etch adhesive system. Class I cavities (2mmx4mm) were prepared on flattened occlusal surfaces of fifty extracted human premolars and randomly assigned into five groups (n=10) according to the materials used: Beautifil Bulk-fill Restorative (BR); Beautifil Bulk-fill Flowable (BF); Beautifil Flow Flowable F10 (BF10); and Self-etch adhesive (SEA). Group A: SEA+BR; Group B: SEA+BF10+BR; Group C: SEA+BF+BR; Group D: SEA+BF10+SEA+BR and Group E: SEA+BF+SEA+BR. The samples were thermocycled for 500 cycles, then sectioned mesiodistally, polished and pre-treated prior to scanning electron microscopy (SEM) evaluation. From SEM images, measurement of adhesive and cohesive adaptation failures was recorded at multiple sites of the pulpal floor and in between materials. Data were analysed using one-way ANOVA and post-hoc Tukey tests (p<0.05). Cohesive failure in SEA was observed at the pulpal floor with the lowest percentage in Group A (5.14%), and highest in Group C and E (>16%). However, there were no significant difference among all groups. Adhesive failure was seen at the pulpal floor between SEA+BF/BF10/BR and between SEA+dentine with the highest percentage of gaps formed in Group A between SEA+dentine (6.62%) and SEA+BR (5.30%). Nonetheless, no significant differences were observed among all groups with p=0.89 and p=0.70, respectively. With the use of BF/BF10 at the pulpal floor, adhesive failure was reduced but resulted in increased of cohesive failure. However, both adaptation failures were absent between materials (BF/BF10 and BR) regardless with or without application of SEA.

Evaluating the effect of different combination of impression and pouring materials on marginal and internal adaptation of zirconia crowns / Evaluación del efecto de diferentes combinaciones de materiales de impresión y vertido en la adaptación marginal e interna de las coronas de circonio

Purpose: Two important factors in dental prosthesis are making an accurate impression and producing a suitable cast which represents the exact relationship between prepared tooth and oral structures. This study, aimed to investigate the effects of different combinations of impression and pouring materials on marginal and internal adaptation of premolar zirconia crowns. Material and Methods: Forty maxillary premolars were prepared considering round shoulder finish line. The impressions were made either by additional (Panasil) or condensation (Speedex) silicon, and poured by two different types of gypsum materials (Siladent or GC gypsum) (N=10). Zirconia crowns were fabricated using a CAD-CAM system. The crowns were cemented, and the samples were cut in bucco-lingual direction. Marginal and internal gaps were measured by stereomicroscope (×25). Results: The mean marginal gaps for Pansil-Siladent, Panasil-GC, Speedex-Siladent, and Speedex-GC were 141 µm, 143 µm, 131 µm, and 137 µm respectively. The internal gaps were 334 µm, 292 µm, 278 µm, and 257 µm respectively. The independent T-Student test showed no significant differences in average marginal or internal gap among various impression and gypsum materials or their interactions (p>0.05). Two-way ANOVA test showed no significant differences in maximum marginal or internal gap among various impression and gypsum materials and their interactions (p>0.05). Conclusion: The present study revealed no statistically significant difference in marginal/internal gap among crowns prepared using different combinations of impression-pouring materials evaluated.

Introducción: Dos factores importantes en la prótesis dental son hacer una impresión precisa y la producción de un modelo adecuado que represente la relación exacta entre el diente preparado y las estructuras orales. Este estudio, tuvo como objetivo investigar los efectos de diferentes combinaciones de materiales de impresión y vertido sobre la adaptación marginal e interna de coronas de zirconio premolar. Material y Métodos: Se prepararon cuarenta premolares maxilares considerando la línea de meta del hombro redondo. Las impresiones se realizaron con silicio adicional (Panasil) o de condensación (Speedex) y se vertieron con dos tipos diferentes de materiales de yeso (yeso Siladent o GC) (N = 10). Las coronas de zirconio se fabricaron utilizando el sistema CAD-CAM. Las coronas se cementaron y las muestras se cortaron en dirección buco-lingual. La brecha marginal e interna se midió con estereomicroscopio (×25). Resultados: Las brechas marginales medias para Pansil-Siladent, Panasil-GC, Speedex-Siladent y Speedex-GC fueron de 141µm, 143µm, 131µm y 137µm, respectivamente. Las brechas internas fueron 334µm, 292µm, 278µm y 257µm, respectivamente. La prueba de T-Student independiente no mostró diferencias significativas en la brecha marginal o interna promedio entre varios materiales de impresión y yeso o sus interacciones (p>0.05). La prueba ANOVA bidireccional no mostró diferencias significativas en el espacio marginal o interno máximo entre varios materiales de yeso y de impresión y sus interacciones (p>0.05). Conclusión: El presente estudio no reveló diferencias estadísticamente significativas en la brecha marginal/interna entre las coronas preparadas con diferentes combinaciones de materiales de impresión y vertido evaluados.

A Validation Study of the Impression Replica Technique.

PURPOSE: To validate the well-known and often-used impression replica technique for measuring fit between a preparation and a crown in vitro. MATERIALS AND METHODS: The validation consisted of three steps. First, a measuring instrument was validated to elucidate its accuracy. Second, a specimen consisting of male and female counterparts was created and validated by the measuring instrument. Calculations were made for the exact values of three gaps between the male and female. Finally, impression replicas were produced of the specimen gaps and sectioned into four pieces. The replicas were then measured with the use of a light microscope. The values received from measuring the specimen were then compared with the values received from the impression replicas, and the technique was thereby validated. RESULTS: The impression replica technique overvalued all measured gaps. Depending on location of the three measuring sites, the difference between the specimen and the impression replicas varied from 47 to 130 µm. CONCLUSION: The impression replica technique overestimates gaps within the range of 2% to 11%. The validation of the replica technique enables the method to be used as a reference when testing other methods for evaluating fit in dentistry.

Comparison between direct chairside and digitally fabricated temporary crowns.

The mechanical properties of temporary crowns are considered to be crucial in order to achieve successful definite restorations. This study compared marginal fit, internal fit, fracture strength and mode of fracture of CAD/CAM temporary crowns to direct chairside counterparts. An upper left first premolar Frasaco tooth was prepared for all-ceramic crown. The materials used for comparison were VITA CAD-Temp®, ArtBloc®Temp, PMMA DISK and Acrytemp (control group). The crowns were divided into four groups (n=10). Each crown was investigated for the above parameters. Statistical analysis was performed using SPSS v.20. The average marginal gap, internal gap and fracture strength showed statistically significant difference between groups (p<0.01). The fracture mode showed statistically non-significant difference (p>0.05) among experimental groups. The CAD/CAM temporary crowns demonstrated superior mechanical properties compared to direct handmade counterparts.

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.

Marginal and internal fit of cobalt-chromium copings fabricated using the conventional and the direct metal laser sintering techniques: A comparative in vitro study.

BACKGROUND AND OBJECTIVES: This in vitro study seeks to evaluate and compare the marginal and internal fit of cobalt-chromium copings fabricated using the conventional and direct metal laser sintering (DMLS) techniques. METHODS: A master model of a prepared molar tooth was made using cobalt-chromium alloy. Silicone impression of the master model was made and thirty standardized working models were then produced; twenty working models for conventional lost-wax technique and ten working models for DMLS technique. A total of twenty metal copings were fabricated using two different production techniques: conventional lost-wax method and DMLS; ten samples in each group. The conventional and DMLS copings were cemented to the working models using glass ionomer cement. Marginal gap of the copings were measured at predetermined four points. The die with the cemented copings are standardized-sectioned with a heavy duty lathe. Then, each sectioned samples were analyzed for the internal gap between the die and the metal coping using a metallurgical microscope. Digital photographs were taken at ×50 magnification and analyzed using measurement software. Statistical analysis was done by unpaired t-test and analysis of variance (ANOVA). RESULTS: The results of this study reveal that no significant difference was present in the marginal gap of conventional and DMLS copings (P > 0.05) by means of ANOVA. The mean values of internal gap of DMLS copings were significantly greater than that of conventional copings (P < 0.05). CONCLUSIONS: Within the limitations of this in vitro study, it was concluded that the internal fit of conventional copings was superior to that of the DMLS copings. Marginal fit of the copings fabricated by two different techniques had no significant difference.

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.

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.

Evaluation of marginal and internal gaps of Ni-Cr and Co-Cr alloy copings manufactured by microstereolithography.

PURPOSE: The purpose of this study was to evaluate the marginal and internal gaps of Ni-Cr and Co-Cr copings, fabricated using the dental µ-SLA system. MATERIALS AND METHODS: Ten study dies were made using a two-step silicone impression with a dental stone (type IV) from the master die of a tooth. Ni-Cr (NC group) and Co-Cr (CC group) alloy copings were designed using a dental scanner, CAD software, resin coping, and casting process. In addition, 10 Ni-Cr alloy copings were manufactured using the lost-wax technique (LW group). The marginal and internal gaps in the 3 groups were measured using a digital microscope (160 ×) with the silicone replica technique, and the obtained data were analyzed using the non-parametric Kruskal-Wallis H test. Post-hoc comparisons were performed using Bonferroni-corrected Mann-Whitney U tests (α=.05). RESULTS: The mean (±standard deviation) values of the marginal, chamfer, axial wall, and occlusal gaps in the 3 groups were as follows: 81.5±73.8, 98.1±76.1, 87.1±44.8, and 146.8±78.7 µm in the LW group; 76.8±48.0, 141.7±57.1, 80.7±47.5, and 194.69±63.8 µm in the NC group; and 124.2±52.0, 199.5±71.0, 67.1±37.6, and 244.5±58.9 µm in the CC group. CONCLUSION: The marginal gap in the LW and NC groups were clinically acceptable. Further improvement is needed for CC group to be used clinical practice.

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.