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EVALUATION OF FITTING ACCURACY OF METAL FRAMEWORKS OF FIXED DENTURES DEPENDING ON THEIR LENGTH

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Objective: To carry out a comparative analysis of the accuracy of the adherence of tooth-supported cast and milled cobalt chrome alloy frameworks in the shoulder area depending on the length of the prostheses. Methods: For the clinical trial 314 patients who needed metal-ceramic fixed dental prostheses (FDPs) were recruited. Metal frameworks of prostheses were made with conventional lost-wax technique (CLW) and computer aided design and manufacturing (CAD/CAM). To assess the accuracy of the adhesion of the frameworks to the ledges of the prepared teeth stumps, the silicon film between the abutment teeth and inner surface of crowns was obtained, cut into 8 pieces and measured in the shoulder area. The marginal gaps were measured using ImageJ2 application from digital photos obtained with calibrated digital microscope (250×). The data obtained were analyzed using the non-parametric Kruskal-Wallis H-test and Mann- Whitney U-test. Results: The average values of the marginal gap in the CLW group ranged from 71.9±7.6 μm in single and double crowns to 117±3.7 μm in prostheses with a length of 7-8 units. With a corresponding increase in the length of the prostheses, the average values of the marginal gap in the CAD/CAM group were from 67.1±6.8 μm to 90.8±8.3 μm. Differences in marginal clearance parameters between all groups were statistically significant (p

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Methods for obtaining working and auxiliary dental impressions of patients have been revised in recent decades, which is associated with 3D scanning. At the same time, the policy of import substitution in dentistry is also developing quite actively, which is reflected in the introduction of domestic impression masses for analog prints into public health institutions. The aim of study. Reducing the number of complications of dental orthopedic treatment by optimizing the approach to choosing a method for obtaining a working anatomical impression. Methodology. Impressions of the mandible of 10 patients were obtained. 7 impressions were obtained from each patient using the most commonly used techniques, silicone impression materials and intraoral scanning. Further, jaw models of 4 types of plaster were made for each impression and scanned with an off-site dental scanner. With the help of a micrometer in the oral cavity, measurements of teeth 3.5, 4.4 and 4.2 were made according to the maximum vestibular-oral size of the clinical crown, which were taken as a standard. The reference size is compared with the dimensions obtained on digital models according to the selected parameters with an accuracy of up to thousandths of a millimeter. A statistical analysis of the data obtained was carried out. Results. The data obtained confirmed the manufacturer's claims about the accuracy of the impression masses. A slight decrease in the studied sizes was noted on the models obtained by intraoral scanning. Whereas on models obtained using silicone impressions, the dimensions, on the contrary, were slightly larger than the reference ones. A statistically significant difference was revealed when comparing models obtained using intraoral scanning and models obtained by laboratory scanning from analogues of jaws using silicone impressions. When comparing the data obtained with the standard, no critical differences were revealed. Conclusions. It is impossible to unequivocally assert the advantage of a digital or analog method of obtaining impressions in modern orthopedic dentistry. The method of obtaining an impression should be chosen depending on the indications for a particular type of treatment and clinical conditions.
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Statement of problem: Comparative assessment of the effectiveness of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies used to fabricate complete-coverage restorations is needed. A quantitative assessment requires precise documentation of the marginal adaptation and external surface contour of fabricated restorations. Limited information is currently available regarding the effects of milling mode on marginal adaptation and reproduction of the external surface contour for CAD-CAM-fabricated restorations. Purpose: The purpose of this in vitro study was to evaluate the outcomes for 3 different digital workflows on the marginal gap and the external surface contour reproducibility of CAD-CAM-fabricated lithium disilicate complete-coverage restorations. Material and methods: Twelve Ivorine molars were prepared to receive lithium disilicate crowns. The preparations were digitally recorded using 2 intraoral scanners (TRIOS 3; 3Shape A/S and Planmeca PlanScan; E4D Technologies), and the restorations were designed using their associated design software with reference to the anatomy of an unprepared tooth. The designed restorations were then manufactured from lithium disilicate blocks using a 3-axis milling machine. Twelve restorations were manufactured using the detailed mode (Planmeca PlanScan detailed mode [PPD-D]), and 12 using the standard mode for the Planmeca system (Planmeca PlanScan standard mode [PPD-S]). Restorations from the 3Shape system were fabricated using the detailed mode (TRIOS 3Shape detailed mode [T3S-D]). The restorations were secured on their associated preparation with an elastomeric material. The marginal gap of each restoration was then measured in the ImageJ software using images captured by a stereo microscope at ×20 magnification. External surface reproducibility was evaluated by measuring undercut at 4-line angles using a dental surveyor. Differences in the marginal gaps of restorations fabricated using the 3 different workflows were compared by Brown-Forsythe robust ANOVA, followed by a post hoc test (α=.05). Chi-square analysis (α=.05) was used to evaluate differences in the contours of the external surface of the restorations, resistance form, and marginal integrity produced using the 3 workflows. Results: The mean marginal gap for restorations fabricated using the T3S-D workflow was 60 μm, a distance significantly lower (P<.05) than that of PPD-D and PPD-S workflows, which yielded a marginal gap of 95 μm for the detailed mode and 124 μm for the standard mode of milling. Restorations fabricated using PPD-D and PPD-S workflows produced a significantly more reproducible external surface contour than those fabricated using the T3S-D workflow. Conclusions: Restorations fabricated using the T3S-D workflow produced the smallest marginal gap. However, reproducibility of the external surface contour for this workflow was the worst of the three workflows analyzed.
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Aim This systematic review and meta‐analysis were conducted to assess and compare the accuracy of conventional and digital implant impressions. The review was registered on the PROSPERO register (registration number: CRD42016050730). Material and Methods A systematic literature search was conducted adhering to PRISMA guidelines to identify studies on implant impressions published between 2012 and 2017. Experimental and clinical studies at all levels of evidence published in peer‐reviewed journals were included, excluding expert opinions. Data extraction was performed along defined parameters for studied specimens, digital and conventional impression specifications and outcome assessment. Results Seventy‐nine studies were included for the systematic review, thereof 77 experimental studies, one RCT and one retrospective study. The study setting was in vitro for most of the included studies (75 studies) and in vivo for four studies. Accuracy of conventional impressions was examined in 59 studies, whereas digital impressions were examined in 11 studies. Nine studies compared the accuracy of conventional and digital implant impressions. Reported measurements for the accuracy include the following: (a) linear and angular deviations between reference models and test models fabricated with each impression technique; (b) three‐dimensional deviations between impression posts and scan bodies respectively; and (c) fit of implant‐supported frameworks, assessed by measuring marginal discrepancy along implant abutments.) Meta‐analysis was performed of 62 studies. The results of conventional and digital implant impressions exhibited high values for heterogeneity. Conclusions The available data for accuracy of digital and conventional implant impressions have a low evidence level and do not include sufficient data on in vivo application to derive clinical recommendations.
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Objective: This in vitro study aimed to evaluate marginal and internal fit of single crowns produced from high-frequency ultrasound based digital impressions of teeth prepared with finish lines covered by porcine gingiva, in comparison with those obtained by optical scanners with uncovered finish lines. Methods: Ten human teeth were prepared and forty zirconia crowns were fabricated from STL-datasets obtained from four dental scanners (n=10): extraoral CS2 (Straumann), intraoral Lava COS (3M), intraoral Trios (3Shape) and extraoral ultrasound scanner. The accuracy of the crowns was compared evaluating marginal and internal fit by means of the replica technique with measurements in four areas; P1: occlusal surface; P2: transition between occlusal and axial surfaces; P3: middle of axial wall; and P4: marginal gap. Restoration margins were classified according to their mismatch as regular, underextended or overextended. Kruskal-Wallis one-way ANOVA and Mann-Whitney U test were used to evaluate the differences between groups at p<0.05. Results: The median value of marginal gap (P4) for Ultrasound (113.87μm) differed statistically from that of CS2 (39.74μm), Lava COS (41.98μm) and Trios (42.07μm). There were no statistical differences between ultrasound and Lava COS for internal misfit (P1-P3), however there were statistical differences when compared with the other two scanners (Trios and CS2) at P1 and P2. Significance: The ultrasound scanner was able to make digital impressions of prepared teeth through porcine gingiva (P4), however with less accuracy of fit than that of conventional optical scanners without coverage of the finish lines. Where no gingiva was available (P1-P3), the ultrasound accuracy of fit was similar to that of at least one optical scanner (Lava COS).
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Marginal fit is important in treatment using fixed dental prostheses. Poor marginal adaptation can result in dental caries and a periodontal disease. The objective of this study was to analyze and to compare the marginal fit of all-ceramic crowns fabricated from impressions acquired by direct digital scans intraorally and by indirect digital scans extraorally from working models. Twenty-three posterior teeth were prepared to receive all-ceramic crowns and, then, were digitally scanned intraorally (direct). Impressions were made for working model fabrication and then digitally scanned extraorally (indirect). A total of 46 all-ceramic crowns (Feldspathic ceramic, VITA Mark II; VITA Zahnfabrik) were fabricated by using a CEREC 3D computer-aided design/computer-aided machining system (Sirona). The marginal fit was evaluated by measuring a silicone replica of the gap between the intaglio of the full-veneer crown and the margin of the prepared tooth. The 46 specimens were examined by using an MM-40 Measuring Microscope (Nikon, Japan) at a magnification of 50×. Statistical differences in the marginal fit of the all-ceramic crowns were found between crowns fabricated from direct digitally scanned (70.1 μm ± 13.3) and indirect digitally scanned (82.3 μm ± 12.2) impressions (P < 0.05). The all-ceramic crowns fabricated from the direct digitally scanned impressions were significantly more accurate than those from the indirect digitally scanned impressions.
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The accuracy of fit is considered as one of the main factors in establishing the long-term functional success of the restoration, which is influenced by several factors, one of them is the impression technique. The objective of this in vitro study was to evaluate and compare the marginal and internal fitness of monolithic CAD/CAM zirconia crowns fabricated from four different conventional impression techniques and intra-oral digital impression using silicone replica technique. Two metal dies for a dentoform maxillary right first molar tooth were fabricated using lost wax technique: one for the dentoform before its preparation and the other one after preparation of the dentoform tooth to receive a monolithic zirconia crown. Impressions were then taken using vinyl polysiloxane impression material with four different conventional impression techniques (two-step putty/wash with and without spacer, one-step single and dual viscosity) and digital impression. All conventional impressions were poured with type IV gypsum product to produce thirty-two die stones, which were then scanned extra-orally using in Eos X5 extra-oral scanner. Forty crowns were then designed and fabricated (eight crowns for each technique). Marginal and internal gaps were measured using silicone replica technique. The measurements were done using a digital microscope at twenty-one different measuring points for each specimen, which represented four different areas of measurement (margin, chamfer, axial and occlusal). The data were then analyzed using One-way ANOVA test and LSD test. The digital impression yielded the least mean marginal and internal gaps as compared with all conventional impression groups with statistically significant and highly significant differences. Among the four conventional impression groups, the results showed that the two-step putty/wash impression technique without spacer yielded the least mean marginal and internal gaps followed by the two-step putty/wash impression technique with spacer with statistically significant difference between them, while the one-step dual viscosity impression technique yielded the greatest mean marginal and internal gaps, but with statistically non-significant difference with the one-step single viscosity impression technique. As a conclusion, it is recommended to use intra-oral scanner, when available, to take a digital impression for the tooth preparation as it produced crowns with better marginal and internal fitness than conventional impression. Otherwise, the two-step putty/wash impression technique could be the next choice, which is preferred over both one-step impression techniques.
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This study evaluated the marginal accuracy of CAD/CAM-fabricated crown copings from four different materials within the same processing route. Twenty stone replicas of a metallic master die (prepared upper premolar) were scanned and divided into two groups. Group 1 (n=10) was used for a pilot test to determine the design parameters for best marginal accuracy. Group 2 (n=10) was used to fabricate 10 specimens from the following materials with one identical CAD/CAM system (GAMMA 202, Wissner GmbH, Goettingen, Germany): A = commercially pure (cp) titanium, B = cobalt-chromium alloy, C = yttria-stabilized zirconia (YSZ), and D = leucite-reinforced glass-ceramics. Copings from group 2 were evaluated for the mean marginal gap size (MeanMG) and average maximum marginal gap size (AMaxMG) with a light microscope in the “as-machined” state. The effect of the material on the marginal accuracy was analyzed by multiple pairwise comparisons (Mann–Whitney, U -test, α=0.05 , adjusted by Bonferroni-Holmes method). MeanMG values were as follows: A: 46.92 ± 23.12 μ m, B: 48.37 ± 29.72 μ m, C: 68.25 ± 28.54 μ m, and D: 58.73 ± 21.15 μ m. The differences in the MeanMG values proved to be significant for groups A/C (p=0.0024) , A/D (p=0.008) , and B/C (p=0.0332) . AMaxMG values (A: 91.54 ± 23.39 μ m, B: 96.86 ± 24.19 μ m, C: 120.66 ± 32.75 μ m, and D: 100.22 ± 10.83 μ m) revealed no significant differences. The material had a significant impact on the marginal accuracy of CAD/CAM-fabricated copings.
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Objectives: This study focused on the clinical investigation of the internal and marginal fit of CAD/CAM-fabricated zirconia single crowns produced via conventional and digital impression techniques. Materials and methods: In a private practice, 20 molar teeth, one from each of 20 patients, were prepared with a circumferential 1.0-mm deep chamfer and an occlusal reduction of 1.5 mm. Conventional impression (CI) taking with a polyvinylsiloxane material (Aquasil Monophase + Aquasil XLV; Dentsply, Konstanz, Germany) and intraoral scanning (IS) (Cara TRIOS; Heraeus, Hanau, Germany) of each of the preparations was performed, and then two respective zirconia copings per tooth were produced (20 crowns per group). The marginal and internal fit of the restorations was evaluated employing a replica technique. For statistical analysis, a pairwise comparison (Wilcoxon rank test) was performed. Results: Zirconia single crowns produced with the IS technique revealed a statistically significant better precision of internal fit only in specific areas (chamfer area/occlusal area). The evaluation of marginal fit showed no significant differences between the two groups. All restorations of both groups offered internal and marginal gaps within the postulated clinical tolerance ranges. Conclusions: CAD/CAM-fabricated zirconia single crowns produced with CI and IS techniques offer adequate marginal and internal precision. However, the IS technique provides lower internal gaps in some specific areas. Clinical relevance: The clinical precision of fit of restorations produced with a CI and an IS technique appeared to be equivalent. Therefore, the IS technique can be rated as a suitable alternative for the manufacturing of single crowns.
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Objective: The aim of this study was to compare the marginal and internal fit accuracy of crowns constructed using three different wax production methods; conventional, milled, and 3D printed and utilizing three different cement gap thicknesses. Methods: 15 identical stone dies were made for each method. Wax patterns were produced and then cast into metal crowns, which were assessed for differences in accuracy of both marginal and internal fit. Measurement points were 4 points per crown; occlusal, axial, marginal gap, and marginal discrepancy points. A silicone impression technique and conventional cementation technique were employed to facilitate the measurements. Results: There was no significant difference (p > 0.05) in accuracy between the digitally and manually produced crowns, with the 3D printed crowns being slightly more accurate. Whereas, statistically significant differences were noticed between the conventional versus printed groups, in occlusal and marginal gap points (p < 0.05). Conclusion: The marginal and internal fit of 3D printed wax patterns is more accurate than the other two production methods. The milling of wax crowns is as accurate as the conventional hand carved production in terms of internal and marginal fit. The manufacturer recommended offset/die-spacer of 30 μm produced the most accurate internal and marginal fits.
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Background Different CAD/CAM machines’ generation may impact the restoration overall quality. The present study evaluated the marginal fit of CAD/CAM restorations manufactured with different generations of CEREC milling unit systems. Material and Methods Sixteen typodont teeth were divided into two groups (n=8) according to the machine’s generation assigned. These are control group (G1): Cerec AC with Bluecam/Cerec 3 milling unit and (G2): Cerec AC with Bluecam/MC XL Premium Package milling unit. Scanning of the preparation were performed and crowns were milled using the Vita Mark II blocks. Blocks were cemented using epoxy glue on the pulpal floor only and finger pressure applied for 1 min. Upon completion of the cementation step, misfits between the restoration and abutment were measured by microphotography and the silicone replica technique using light body silicon material on Mesial (M) and Distal (D) surfaces. Results Mean and SDs of marginal gaps in micrometers were: G1/M: 94.90 (±38.52), G1/D: 88.53 (±44.87), G2/M: 85.65 (±29.89), G2/D: 95.28 (±28.13). Two-way ANOVA indicated no significant differences among different groups (P>0.05); surface area (P>0.05) and the interaction (P>0.05). Overall, G2 had greater margin gaps than G1, however, without statistical difference (P>0.05). Conclusions Difference in milling unit generation did not significantly affect the marginal fit. Marginal gap means were in the range of the clinical acceptance levels for both generations of Cerec milling units, regardless the teeth site area. Key words:CAD/CAM, margin, ceramics.
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Objectives: (1) To measure the marginal and internal adaptation of different prosthetic crowns infrastructures (IS); (2) to analyze two types of methodologies (replica and weight technique) used to evaluate the adaptation of indirect restorations. Methods: Ceramic IS were fabricated using CAD/CAM technology and slip-casting technique, and metal IS were produced by casting (n=10). For each experimental group, the adaptation was evaluated with the replica (RT) and the weight technique (WT), using an impression material (low viscosity silicon) to simulate the luting agent. Cross-sectional images of the silicon replica were obtained and analyzed with Image J software to measure the low viscosity silicon layer thickness at pre-determined points. The silicon layer was also weighted. Results were statistically analyzed with ANOVA and Tukey's test (α=0.05). Pearson correlation was used to analyze the relation between the two types of evaluation methods. Results: All IS evaluated showed clinically acceptable internal and marginal adaptation. Metal IS showed the best adaptation, irrespective of the measuring technique (RT and WT). The IS produced by CAD-CAM showed greater gap values at the occlusal area than at other evaluated regions. The IS produced by the dental laboratory technician showed similar gap values at all evaluated regions. There is no correlation between RT and WT (p>0.05). Significance: Different levels of adaptation were found for the different experimental groups and for the different evaluation methods. However, all IS evaluated showed clinically acceptable values of marginal and internal adaptation.
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Alzheimer’s disease is the most widespread form of neurodegenerative disease in the world. Its clinical manifestations are explained by selective degeneration of neurons in the portions of cerebral cortex responsible for cognitive perception and memory. Amyloid peptide is accumulated beyond nerve cells at neuron contact sites into ordered strands (fibrils), forming the so-called amyloid plaques. It is found that amyloid peptide (β-amyloid or Aβ1–38–Aβ1–43), which aggregates and forms amyloid plaques in brain, is a product of successive cleavage of membrane glycoprotein-precursor of β-amyloid by β- and γ-secretases in the plasmatic membrane of neurons. The results of structural studies of this process and the main proteins involved in it are considered.
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The receptor for advanced glycation end products (RAGE) is considered to contribute to the pathogenesis of Alzheimer's disease (AD), mediating amyloid beta (Aβ) accumulation, mitochondrial damage, and neuroinflammation. Previously, we have synthesized small peptides corresponding to the fragments (60–76) (P1) and (60–62) (P2) of the RAGE extracellular domain, and have shown that administration of P1 fragment but not P2 results in restoration of the spatial memory and decreases the brain Aβ (1–40) level in olfactory bulbectomized (OBX) mice demonstrating main features of Alzheimer's type neurodegeneration. In the present study, we have investigated the supposed mechanism of the therapeutic efficacy of P1 RAGE fragment and compared it to P2 short fragment. We have found that P1 restored activities of the respiratory chain in the Complexes I and IV in both cortical and hippocampal mitochondria of the OBX mice while P2 had no effect. Besides, fluorescein-labeled analog Flu-P1 bound to Aβ (1–40) and Aβ (1–42) with high affinity (Kd in the nanomolar range) whereas Flu-P2 revealed low affinity with tenfold higher Kd value for Aβ (1–40) and did not bind to Aβ (1–42). However, neither of the peptides had a notable impact on inflammation, estimated as mRNA expression of proinflammatory cytokines in the brain tissues of OBX mice. Taken together, our results suggest that direct Aβ-P1 interaction is one of the molecular events mediating the protection of the mitochondria in OBX animals from Aβ toxic effect. The RAGE fragment P1 would be the soluble decoy for Aβs and serve as a promising therapeutic agent against neurodegeneration accompanied by mitochondrial dysfunction.
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Statement of problem: Because of their relatively small scanning area, intraoral scanners may result in less accurate fixed dental prostheses (FDPs) than do laboratory scanners. Purpose: The purpose of this in vitro study was to evaluate the accuracy of monolithic zirconia FDPs with different numbers of pontics fabricated with different impression techniques. Material and methods: The mandibular right premolars and molars of an acrylic resin model were prepared to receive 4-unit FDPs. Three master models were fabricated with epoxy resin: model NP, no pontic; model 1P, 1 pontic; and model 2P, 2 pontics. Each master model was scanned by using direct (DD) and indirect digitalization (ID). Four-unit monolithic zirconia FDPs were fabricated and divided into 3 groups (groups NP, 1P, and 2P) and then subdivided according to the digitalization technique (group DD and ID; n=10). The FDPs were also evaluated based on the presence (Po) or absence (NPo) of an adjacent pontic. The marginal, axial, and occlusal gap widths of each FDP were measured, and statistical analyses were performed to evaluate and compare the amount of gap present (α=.05). Results: For direct digitalization, group 2P had significantly greater marginal (69.4 μm versus 60.9 μm or 62.3 μm; P<.001) and axial gap widths (127.1 μm versus 108.9 μm or 110.4 μm; P<.001) than group NP or 1P. Group DD resulted in significantly smaller gaps compared with group ID at marginal (64.8 μm versus 73.6 μm), axial (114.8 μm versus 124.3 μm), and occlusal (172.6 μm versus 184.1 μm) measurement locations (P<.001). Greater marginal and axial gaps were noted in group Po than NPo (P<.001). Conclusions: The length of the edentulous area significantly influenced the extent of the marginal and internal gap with the use of direct digitalization. Direct digitalization resulted in significantly smaller gap widths in all measurement areas than indirect digitalization; however, the mean differences were less than 12 μm, which is considered clinically insignificant. The presence of an adjacent pontic had a significant effect on the adjacent marginal and axial gap widths.
Article
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.
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Objectives: The aim of this prospective clinical study was to evaluate the clinical performance of veneered anatomically designed zirconia fixed dental prostheses (FDPs) resulting from intraoral digital impressions. Methods: 24 patients requiring treatment were provided with all-ceramic FDPs. Intraoral scans (iTero) were performed and veneered anatomically designed CAD/CAM-zirconia FDPs (Zerion/VitaVM9) were fabricated. A feldspar veneering ceramic following a slow cooling firing protocol was applied. A self-curing resin based luting material was used for adhesive cementation. Clinical evaluations were performed at baseline and 6, 12, and 18 months recalls according to the modified USPHS-criteria. Intraoral digital surface scans (iTero) were performed at each recall examination and were digitally superimposed (Geomagic) to evaluate potential veneer cohesive fractures. Kaplan-Meier survival analysis comprised secondary caries, clinically unacceptable fractures, root canal treatment and debonding. Kaplan-Meier success rate included restorations with minimal crevices, tolerable color deviations and clinically acceptable fractures. Data were statistically analyzed. Results: The Kaplan-Meier survival rate and success rate of the FDPs were 100% and 91.7%, respectively. Clinically acceptable veneer cohesive fractures and crevices at the restoration margin were observed in two patients. These shallow veneer fractures were only detected by overlapping baseline and recall scans. Ceramic surface roughness increased significantly over time (p<0.0001). Conclusions: Veneered zirconia FDPs fabricated from digital intraoral scans showed a favorable clinical performance over an observation period of 18 months. Anatomical zirconia core design and slow cooling firing protocol of the veneering ceramic reduced the incidence of chip fractures to a level that could not be detected clinically. Clinical significance: The digital workflow on the basis of intraoral digital impressions resulted in clinically satisfying outcomes for veneered zirconia FDPs.
Article
The purpose of this clinical study was to compare the marginal fit of dental crowns based on three different intraoral digital and one conventional impression methods. Forty-nine teeth of altogether 24 patients were prepared to be treated with full-coverage restorations. Digital impressions were made using three intraoral scanners: Sirona CEREC AC Omnicam (OCam), Heraeus Cara TRIOS and 3M Lava True Definition (TDef). Furthermore, a gypsum model based on a conventional impression (EXA'lence, GC, Tokyo, Japan) was scanned with a standard laboratory scanner (3Shape D700). Based on the dataset obtained, four zirconia copings per tooth were produced. The marginal fit of the copings in the patient's mouth was assessed employing a replica technique. Overall, seven measurement copings did not fit and, therefore, could not be assessed. The marginal gap was 88 μm (68-136 μm) [median/interquartile range] for the TDef, 112 μm (94-149 μm) for the Cara TRIOS, 113 μm (81-157 μm) for the laboratory scanner and 149 μm (114-218 μm) for the OCam. There was a statistically significant difference between the OCam and the other groups (p < 0.05). Within the limitations of this study, it can be concluded that zirconia copings based on intraoral scans and a laboratory scans of a conventional model are comparable to one another with regard to their marginal fit. Regarding the results of this study, the digital intraoral impression can be considered as an alternative to a conventional impression with a consecutive digital workflow when the finish line is clearly visible and it is possible to keep it dry.
Article
Statement of problem: Relatively little information is available on the accuracy of the abutment-implant interface in computer-aided design and computer-aided manufacturing (CAD/CAM)-fabricated zirconia and cobalt-chromium frameworks. Purpose: The purpose of this study was to compare the fit accuracy of CAD/CAM-fabricated zirconia and cobalt-chromium frameworks and conventionally fabricated cobalt-chromium frameworks. Material and methods: Four groups of 3-unit, implant-supported, screw-retained frameworks were fabricated to fit an in vitro model with 3 implants. Eight frameworks were fabricated with the CAD/CAM system: 4 in zirconia and 4 in cobalt-chromium. Another 8 were cast in cobalt-chromium with conventional casting, including 4 with premachined abutments and 4 with castable abutments. The vertical misfit at the implant-framework interface was measured with scanning electron microscopy when only 1 screw was tightened and when all screws were tightened. Data were analyzed with the Kruskal-Wallis and Mann-Whitney tests (α=.05). Results: The mean vertical misfit values when all screws were tightened was 5.9 ±3.6 μm for CAD/CAM-fabricated zirconia, 1.2 ±2.2 μm for CAD/CAM-fabricated cobalt-chromium frameworks, 11.8 ±9.8 μm for conventionally fabricated cobalt-chromium frameworks with premachined abutments, and 12.9 ±11.0 μm for the conventionally fabricated frameworks with castable abutments; the Mann-Whitney test found significant differences (P<.05) among all frameworks, except between the conventionally fabricated frameworks (P=.619). No significant differences were found among the groups for passive fit gap measurements (P>.05). Conclusions: When all of the screws were tightened, the CAD/CAM frameworks exhibited better fit accuracy compared with the conventionally fabricated frameworks. High levels of passive fit were achieved for the evaluated techniques.
Article
Objectives To analyse the marginal fit of 4-unit fixed dental prostheses (FDPs) and the accuracy of three-dimensional cast-datasets using both approaches to Computer Aided Design (CAD)/Computer Aided Manufacturing (CAM): direct and indirect digitalization. Methods A titanium model of a 4-unit FDP was digitized by an intraoral scanning device (iTero, Align Technology, Carlstadt, US; DD, n = 12). Additionally 12 conventional impressions were taken and referring master casts were digitized by a laboratory scanner (CS2, Straumann, Basel, Switzerland; ID, n = 12). Frameworks were fabricated (CARES CADCAM GmbH, Straumann, Markkleeberg, Germany) from base metal alloy (coron, Straumann; DD-C: n = 12; ID-C: n = 12) and zirconia (zerion, Straumann; DD-Z: n = 12; ID-Z: n = 12) from the same datasets. The marginal fit of the resulting frameworks and the accuracy of the underlying datasets from DD and ID were evaluated. Data were analyzed by unpaired two sample Student's t-test with Levene-test (p < 0.05). Results Frameworks from group DD-C showed significantly better marginal fit than ID-C (DD-C: 56.90 ± 27.37 μm, ID-C: 90.64 ± 90.81 μm). For zirconia frameworks no differences between both digitalization methods (DD-Z: 127.23 ± 66.87 μm, ID-Z: 141.08 ± 193.17 μm) could be observed. Base metal alloy frameworks exhibited significantly better marginal fit than zirconia frameworks (DD: p < 0.001; ID: p = 0.022). Regarding the accuracy group DD showed significantly higher “trueness” than ID. Significance Direct and indirect digitalization lead to clinically acceptable marginal fit of 4-unit FDPs from base metal alloy and zirconia. Higher accuracy of datasets from DD leads to better marginal fit of frameworks from base metal alloy but not for ones from zirconia.
Article
Purpose: To review methods used to investigate marginal adaptation of crowns and fixed dental prostheses (FDPs), and to discuss testing variables employed and their influence on results. Methods: Online libraries including PubMed, Scopus, and Ovid were searched for articles evaluating the marginal adaptation of crowns and FDPs using a combination of the keywords: "marginal accuracy," "marginal fit," "marginal gap," "marginal discrepancy," "fitting accuracy," "crown," and "FPD." Peer-reviewed publications in English in the period 1970 to December 2011 were collected, evaluated by their abstract, and included if they met the inclusion criteria. The criteria involved studies evaluating marginal adaptation of crowns and FDPs through clear experimental protocols. Exclusion criteria involved longitudinal prospective and retrospective clinical evaluations, studies using subjective tactile sensation, and other predefined criteria. Results: A total of 277 papers were identified; only 183 met the inclusion criteria. Direct view technique was used by 47.5% of the articles followed by cross-sectioning (23.5%), and impression replica (20.2%) techniques. The marginal gap values reported by these techniques varied among individual crown systems and across different systems because of variations in study type (in vivo vs. in vitro), sample size and measurements per specimen, finish line design, and stage at which the marginal gap was measured. Conclusion: There was a substantial lack of consensus relating to marginal adaptation of various crown systems due to differences in testing methods and experimental protocols employed. Direct view technique was the most commonly used method of reproducible results. Also, conducting an experimental set-up of testing a minimum of 30 specimens at 50 measurements per specimen should produce reliable results. Additionally, using a combination of two measurement methods can be useful in verification of results.
Accuracy of marginal fit and axial wall contour for lithium disilicate crowns fabricated using three digital workflows
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Ibragimov TI, Aristova lYa, Ataeva SD, Baskov DV, Batrak IK, Kuznetsov OE, Novichkova MS, Tsalikova NA. A method for clinical evaluation of the accuracy of manufacturing fixed dentures. Patent RF No. 2491033, 2013.
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