Silicone Replica Technique Research Articles

Influence of porcelain firing on changes in the marginal fit of metal-ceramic fixed partial dental prostheses fabricated with laser sintering: An in vivo study.

Marginal fit is the most important criterion in the evaluation of the clinical acceptability of fixed restorations. Due to cement solubility and plaque retention, marginal gaps are potentially harmful to both the teeth and the periodontal tissues. The aim of the study was to investigate the accuracy of the fit of dental metal-ceramic bridges manufactured with the use of direct metal laser sintering (DMLS), and to explore the effects of porcelain firing on the marginal, axial and occlusal fit of metal-ceramic frameworks. The study involved 10 patients with 3-unit metal-ceramic restorations produced using the DMLS technique. Using the silicone replica technique, we examined the marginal, axial and occlusal fit of the dental bridges before and after ceramic firing. The Shapiro-Wilks normality test and Student's paired t‑test were implemented to analyze the mean differences in the marginal, axial and occlusal fit of the restorations before and after ceramic firing. A 95% confidence interval (CI) and discrepancy values at the level of 1% and 0.1% (p > 0.05) were applied. All the mean values of the measurements of marginal (156.08 μm), axial (95.75 μm) and occlusal (252.83 μm) gaps were lower before ceramic veneering than after ceramic veneering, when the mean value for the marginal gap was 178.17 μm, for the axial gap - 106.75 μm and for the occlusal gap - 266.00 μm. Porcelain firing caused no statistically significant differences in the discrepancy values of marginal, axial and occlusal fit. For clinical application, further improvement of the DMLS system is highly recommended. Marginal gaps in DLSM bridges significantly exceed the permissible inaccuracy values of 100-120 μm for prosthetic restorations.

Evaluation of the adaptation of complete denture metal bases fabricated with dental CAD-CAM systems: An in vitro study

Statement of problemConventional fabrication of complete denture metal bases is being replaced by the computer-aided design and computer-aided manufacturing (CAD-CAM) systems. However, a comparative analysis of subtractive and additive CAD-CAM manufacturing techniques is lacking. PurposeThe purpose of this in vitro study was to compare the adaptation of complete denture metal bases fabricated by milling (subtractive manufacturing) and stereolithography apparatus (SLA) and digital light processing (DLP) (additive manufacturing). Material and methodsThirty metal bases were manufactured by using the milling (MIL group), SLA (SLA group), and DLP (DLP group) techniques. The silicone replica technique was used to evaluate the adaptation of the complete denture metal bases, and 30 silicone blocks were fabricated. The silicone block was cut equally in the canine, first molar, and second molar areas. The gap between the model and the metal base was measured by using a digital microscope at the 3 locations, and the measured data were statistically analyzed by using a statistical software program (α=.05). ResultsThe gaps measured at the 3 areas showed significant differences in all 3 groups (P<.05). At the anterior, middle, and posterior areas, the SLA group showed the narrowest gap (302 ±31 μm, 241 ±39 μm, 201 ±43 μm, respectively). The SLA group also had the narrowest total gap of the metal bases (218 ±33 μm). ConclusionsThe adaptation of the fabricated metal bases varied significantly across the techniques used but fell within a clinically allowable range. The SLA group was the most precise in the fabrication of complete denture metal bases. Further studies are required to analyze the effects of the layer thickness setting, wax elimination, and casting temperature on the adaptation of metal bases manufactured by using SLA.

Effects of Trueness and Surface Microhardness on the Fitness of Ceramic Crowns

This study aims to evaluate the fitness, surface microhardness, and trueness of crowns fabricated from three types of dental ceramic blocks (HASS Rosetta, IPS e.max CAD, and VITA Suprinity) and analyze the correlations between them. A crown was first designed in computer-aided design (CAD) software. To create a crown designed model (CDM), the design file was extracted from the CAD software, and a lithium disilicate block was processed from the file with a milling machine. To create a crown scanned model (CSM), the inside of the fabricated crown was digitized using a contact scanner. Using three-dimensional (3D) inspection software (Geomagic Control X; 3D Systems), the CDM and CSM were then superimposed, and their 3D trueness was analyzed. To measure the surface microhardness of the blocks, the specimens were polished and subjected to the Vickers hardness test. The fitness of the fabricated crowns was evaluated by applying a modified silicone replica technique. Pearson correlation analysis was performed to assess the correlations between trueness, surface microhardness, and fitness. In addition, the significance of differences between the three types of dental ceramic blocks was analyzed using one-way analysis of variance (ANOVA). Significant differences in the trueness, surface microhardness, and marginal fit were observed between ceramic blocks of different types. There were also positive correlations between trueness, surface microhardness, marginal fit, and internal fit. While the marginal fit of crowns fabricated from each of the three types of ceramic blocks was in the clinically permitted range (&lt;120 µm), there were differences in the trueness and surface microhardness, depending on the type of block. However, crowns fabricated from each of the three materials have surface microhardness that is clinically applicable.

Internal and marginal discrepancies associated with stereolithography (SLA) additively manufactured zirconia crowns

Statement of problemStereolithography (SLA) additive manufacturing (AM) technologies can be selected to fabricate zirconia crowns; however, the internal and marginal discrepancies associated with these new technologies remain unclear. PurposeThe purpose of this in vitro study was to measure and compare the marginal and internal discrepancies of milled and AM zirconia crowns by using the silicone replica technique. Material and methodsAn implant custom abutment was manufactured and scanned by using a laboratory scanner (CARES Software; Institut Straumann AG). An anatomic contour crown was digitally designed, and the standard tessellation language (STLC) file was obtained. The STLC file was splinted into 2 pieces, simulating the parts of the crown that would replace the enamel (STLG1 file) and dentin (STLG2 file) structures. Three groups were determined: anatomic contour zirconia milled (CNC group), AM anatomic contour zirconia (AM group), and AM splinted zirconia (SAM group). For the CNC group, the STLC file was used to manufacture milled (CARES zirconium-dioxide crown; Institut Straumann AG) zirconia specimens. For the AM group, the STLC file was used to additively fabricate (CERAMAKER 900; 3DCeram Co) the zirconia (3DMix ZrO2 paste; 3DCeram Co) specimens. For the SAM group, the STLG2 file was selected to AM (CERAMAKER 900; 3DCeram Co) the zirconia (3DMix ZrO2 paste; 3DCeram Co) specimens. Ten specimens per group were manufactured. The silicone replica technique was used to measure the marginal and internal discrepancies. The cement gap was measured on images captured by using a digital microscope at ×100 magnification. For the internal gap, 50 measurements were made for each specimen, and for the marginal gap, 25 measurements were made for each specimen. The normality test, Shapiro-Wilk test, was conducted. The results indicated that the distributions were not normal; therefore, nonparametric Kruskal-Wallis H and pairwise Mann-Whitney U-tests were used to analyze the data. The Spearman correlation coefficient was used to determine the correlation between marginal and internal discrepancies in all 3 groups. ResultsSignificant differences were found in marginal and internal discrepancies among the groups. The CNC group had the least marginal and internal discrepancies compared with the AM and SAM groups. The SAM group had significantly lower values for marginal and internal discrepancies than the AM group. The AM group showed the highest marginal and internal discrepancies. The CNC group had a weak correlation coefficient of 0.13 (P=.046), the AM group had a moderate correlation coefficient of 0.32 (P<.001), and the SAM group had a nonsignificant correlation coefficient of 0.12 (P=.051). ConclusionsCNC and SAM groups had clinically acceptable marginal and internal discrepancies, while the AM group had a clinically unacceptable marginal and internal crown discrepancies. Furthermore, a weak correlation was encountered between the marginal and internal discrepancies measured in all groups.

Marginal and internal fit of 3D printed provisional crowns according to build directions.

PURPOSEThis study aimed to fabricate provisional crowns at varying build directions using the digital light processing (DLP)-based 3D printing and evaluate the marginal and internal fit of the provisional crowns using the silicone replica technique (SRT).MATERIALS AND METHODSThe prepared resin tooth was scanned and a single crown was designed using computer-aided design (CAD) software. Provisional crowns were printed using a DLP-based 3D printer at 6 directions (120°, 135°, 150°, 180°, 210°, 225°) with 10 crowns in each direction. In total, sixty crowns were printed. To measure the marginal and internal fit, a silicone replica was fabricated and the thickness of the silicone impression material was measured using a digital microscope. Sixteen reference points were set and divided into the following 4 groups: marginal gap (MG), cervical gap (CG), axial gap (AG), and occlusal gap (OG). The measurements were statistically analyzed using one-way ANOVA and Dunnett T3.RESULTSMG, CG, and OG were significantly different by build angle groups (P<.05). The MG and CG were significantly larger in the 120° group than in other groups. OG was the smallest in the 150° and 180° and the largest in the 120° and 135° groups.CONCLUSIONThe marginal and internal fit of the 3D-printed provisional crowns can vary depending on the build angle and the best fit was achieved with build angles of 150° and 180°.

Fabrication of Dental Crown by Optical Coherence Tomography: A Pilot Study

Digital impressions have been studied for better gingival retraction in including the under subgingival finish line condition. Here, we employed swept-source optical coherence tomography (SS-OCT) of 1310 nm wavelength, which is capable of noninvasive, high-resolution, and high-speed, to discern the utilization-possibility for supporting the fabrication of the dental crown. A three-dimensional (3D) abutment was used at the 0.5 mm of the subgingival finish line below the level of the gingiva. The SS-OCT system scanned a field of view of 10 mm × 10 mm using the 3D working model by the depth-directional three focal points. The obtained 1500 images of OCT cross-sections, which are 1221 × 1220 pixels, were rendered to the 3D model for the effective design of a virtual crown. Then, the ceramic crown was fabricated through a milling machine with a computer-aided design and computer-aided manufacturing (CAD/CAM) software. The marginal fit of the crown was evaluated 219.1 ± 48.9 μm by a silicone replica technique. Although the marginal fit is not sufficient for the clinical allowable gap at one resin typodont, this study can be anticipated to encourage further researches for the enhanced fabrication of dental crown under subgingival finish line conditions.

Effect of digital scans on marginal and internal discrepancies of zirconia crowns

Statement of problemA few studies have compared the accuracy of newly introduced intraoral scanners (IOSs); however, limited evidence is available concerning which system provides the best marginal and internal adaptation of zirconia crowns. PurposeThe purpose of this in vitro study was to compare the marginal and internal discrepancies of zirconia crowns fabricated with 4 digital scanners by a silicone replica technique. Material and methodsA maxillary central incisor was prepared for a ceramic crown and duplicated to form 10 metal abutments. Four groups of zirconia crowns with different scanning methods were produced for each die: 1 laboratory scanner, L (Ceramill Map 400), and 3 different IOSs, CS (CS3600), TR (TRIOS3), and CE (CEREC Omnicam). The marginal and internal discrepancies were measured by a silicone replica technique under a static load of 50 N. The replica specimens were sectioned buccolingually and mesiodistally and then examined by using a stereomicroscope (JTZ-7XT) at ×200 magnification. Fifteen reference points were measured on each specimen. One-way ANOVAs with the Duncan multiple range tests were used for statistical analysis of the data (α=.05). ResultsThe mean marginal discrepancies of zirconia crowns were 12.7 μm for group L, 12.6 μm for group CS, 14.8 μm for group TR, and 15.8 μm for group CE. No significant differences were found in marginal and incisal discrepancies among 4 groups. However, groups CS and L showed significantly better cervical and axial discrepancies than groups TR and CE. Group TR showed significantly better axial discrepancy than group CE. ConclusionsZirconia crowns made by using the CS3600 and the laboratory scanner with a conventional impression showed significantly better internal discrepancies than those made by using TRIOS3 and CEREC Omnicam.

Assessment of the Adaptation of Interim Crowns using Different Measurement Techniques.

To compare the internal fit and marginal discrepancy of acrylic resin interim crowns fabricated by different manufacturing methods, and to test the consistency of measuring marginal discrepancy and internal fit between different measuring techniques. A dentoform mandibular left first molar was prepared for an all-ceramic crown. Thirty-six interim crowns were fabricated and divided into three groups (n = 12): group BAC (Bis-acrylic composite, fabricated manually), group CAM (CAD/CAM polymethylmethacrylate resin, milled), and group 3DP (3D printed methacrylic oligomers, printed). The internal fit of the interim crowns was evaluated by the silicone replica technique and by X-ray microcomputed tomography (µCT) technique. The marginal discrepancy of the interim crowns was evaluated by the vinyl polysiloxane (VPS) (Aquasil Ultra XLV) impression technique and by optical coherence tomography (OCT) technique. Data were statistically analyzed using ANOVA and Turkey tests at α = 0.05. Pearson correlation test was used to evaluate the correlation between the different measurement techniques and marginal discrepancy/internal fit. The manually fabricated interim crowns (group BAC) had significantly greater discrepancy of internal fit than did the digitally fabricated crowns (group CAM and group 3DP) measured by both silicone replica technique and µCT 2-dimensional (2D) image measurement. There were no statistically significant differences in the cement space volume values obtained by the µCT image technique between group BAC and group 3DP (p = 0.285). The coefficientof determination between the two volumetric measurement techniques was low (R2 = 0.30). For marginal discrepancy, the manually fabricated interim crowns had a wider absolute marginal discrepancy than both digitally fabricated groups (p < 0.05). In both the VPS impression and OCT assessment, there was no statistically significant difference between group CAM and group 3DP (p = 0.798 and 0.994, respectively). The coefficientof determination between the VPS impression and OCT techniques for marginal discrepancy measurement was low (R2 = 0.23). Digitally fabricated interim crowns (group CAM and group 3DP) had better internal fit and smaller marginal discrepancy than manually fabricated interim crowns (group BAC). For comparison of the different evaluation techniques, the silicone replica technique and µCT measurements had low correlation for internal fit assessment, as did the PVS impression and OCT techniques for marginal discrepancy test.

Implant-abutment fit influences the mechanical performance of single-crown prostheses

ObjectivesTo evaluate the three-dimensional fit of abutments fabricated by the industry to those either milled or cast by a commercial laboratory and to correlate the implant-abutment connection fit with stress at fatigue failure of prostheses. Probability of survival (reliability) and fractography to characterize failure modes were also performed for cemented and screw-retained prostheses. MethodsOne-hundred and twenty-six maxillary central incisor crowns were milled to restore implants and divided in 3 cemented and 3 screwed-retained groups (n = 21/each), as follows: [Digital-Sc]: milled one-piece monolithic abutment/crown; [TiB-Sc]: milled crowns cemented onto Ti-base abutments; [UCLA]: screw-retained crown using UCLA abutments; [Digital-Ce]: milled two-piece assembly comprised by screwed monolithic abutment and a cemented crown; [TiB–Ce]: milled coping cemented onto Ti-base abutments to receive a cemented crown; [UCLA-Ce]: UCLA abutments that received an overcast coping and a cemented crown. Implant-abutment volume misfit was assessed by micro-computed tomography using the silicone replica technique. Implant/crown systems were subjected to step-stress accelerated life testing (SSALT) in water. The use-level probability Weibull curves and reliability for a mission of 50,000 cycles at calculated stress at failure of 2,300, 3300 and 4300 MPa were plotted. Fractographic analysis was performed with scanning electron microscopy. Internal misfit was analyzed through one-way ANOVA following post-hoc comparisons by Tukey test (p < 0.05). Correlation between misfit volume and the stress at fatigue failure was assessed by Pearson test. ResultsSimilar misfit volumes were observed for TiB-Sc (0.458 mm3), TiB–Ce (0.461 mm3), UCLA (0.471 mm3) and UCLA-Ce (0.480 mm3), which were significantly lower than Digital-Sc (0.676 mm3) and Digital-Ce (0.633 mm3). The mean β values were: 1.68, 1.39, 1.48, 2.41, 2.27 and 0.71 for Digital-Sc, TiB-Sc, UCLA, Digital-Ce, TiB–Ce and UCLA-Ce, respectively, indicating that fatigue was an accelerating factor for failure of all groups. Higher stress at failure decreased the reliability of all groups, more significantly for screw compared to cement-retained groups, especially for Digital-Sc that demonstrated the lowest reliability. The failure mode was restricted to abutment screw fracture. A negative correlation was observed between misfit values and stress at failure (r = -0.302, p = 0.01). ConclusionsAbutments milled by a commercial lab presented higher misfit compared to those provided by the industry and a moderate correlation was observed between higher misfit and lower stress at failure during fatigue. Probability of survival decreased at higher stress, especially for screw compared to cement-retained groups, and failures were confined to abutment screws.

Chairside measurement of the marginal and internal fit of crowns: a new intraoral scan-based approach.

To investigate the marginal and internal fit of crowns, a new intraoral scanner-based digital approach for chairside measurement (D-IOS) was systematically analysed and compared with the conventional silicone replica technique (CV-SR) and digital 3D analysis software (D-GOM). Two models, representing different clinical situations, were constructed, and the first molar was prepared for a full-coverage crown. On the basis of an intraoral scan (Trios3), copings of three different materials (non-precious alloy, zirconium dioxide, and resin composite) with two different cement spaces (80μm, 50μm) were manufactured. The fit of the copings was investigated by all three methods (CV-SR, D-IOS, D-GOM). Therefore, the cement space was visualized with low-viscosity silicone and digitalized with a second intraoral scan. Evaluation of fit by the D-IOS-method was measured in the intraoral scanner software, whereas for analysis by D-GOM, both intraoral scan datasets were transferred to 3D analysis software (GOMInspect). The CV-SR-method was used as a control group. For all copings, the measurements were repeated five times. The data were analysed with ANOVA. No significant differences between the three evaluation methods and the coping materials were shown. However, in the occlusal area, the internal gap was significantly higher compared to the internal gap in the marginal and axial areas regardless of the cement space setting (p < .05). The target parameter of the cement spaces did not match the actual measured internal gaps. All three evaluation methods and coping materials can be used for the measurement of fit within different clinical situations. The digital chairside measurement implemented in the intraoral scanner software enables an easy, applicable evaluation of fit of crowns without additional laboratory devices or special software applications.

Effect of tooth preparation design on marginal adaptation of composite resin CAD-CAM onlays

Statement of problemAlthough different preparation designs have been proposed for onlays fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM), their effect on marginal adaptation is unclear. PurposeThe purpose of this in vitro study was to investigate the effect of tooth preparation designs on the marginal and internal adaptation of ceramic-reinforced composite resin CAD-CAM onlays. Material and methodsA traditional preparation with a heavy chamfer on the functional cusp and a contrabevel on the nonfunctional cusp and a shoulder preparation with equal reduction on all cusps were used for mesial-occlusal-distal (MOD) onlay preparations. Ceramic-reinforced composite resin onlays were designed and milled based on the scanned prepared teeth. A digital silicone replica technique was used to determine marginal discrepancies between preparations and onlay restorations. A total of 100 numeric distances (representations of the fit in each region) were measured in 3 distinct regions: the buccal margin, lingual margin, and internal area. Independent Student t tests were used to determine significant differences (α=.05). ResultsTraditional preparation designs resulted in significantly smaller overall discrepancies (50.9 ±0.5 μm and 139.1 ±5.4 μm, P<.001) and smaller marginal discrepancies in the buccal (49.7 ±1.4 μm and 135.8 ±2.2 μm, P<.001) and lingual areas (47.1 ±1.0 μm and 133.4 ±1.1 μm, P<.001). ConclusionsThe marginal adaptation of ceramic-reinforced composite resin CAD-CAM onlays was affected by the preparation design. The traditional preparation design offered better marginal adaptation; therefore, it is recommended in clinical practice.

A clinical comparison of digital and conventional impression techniques regarding finish line locations and impression time.

This study compared digital and conventional impression techniques regarding impression time, frequency of adjustments, and adaptation of cobalt-chromium (Co-Cr) copings with supragingival and subgingival finish lines. Thirty premolars prepared for single-unit metal-ceramic restorations with supragingival and subgingival finish lines (n = 15). Conventional impression and digital scan of prepared teeth were made. Using computer aided design/computer aided manufacturing (CAD/CAM) system the copings were produced by a milling machine from Co-Cr blocks and internal and marginal discrepancies were measured using silicone replica technique. Data were analyzed using repeated measures ANOVA and Mann-Whitney test (alpha = .05). The impression technique had a significant effect on the magnitude of gap (P < .001). The internal and marginal gaps in the digital technique (49.43 μ and 60.07 μ, respectively) were significantly lower than the values in the conventional method (91.88 μ and 96.96 μ, respectively-P < .001). Finish line positions had no significant effect on the fit and marginal gap of copings (P = .54 and .243, respectively). The mean impression time (19':27″ in conventional technique and 10':31″ in digital technique) was significantly shorter (P < .001) and the mean frequency of adjustments (2.2 times for conventional and 1.3 times for digital technique) was significantly lower in the digital technique (P < .001). The gingival biotype (thick or thin) had no significant effect on marginal and internal fit (P = .052 and .319, respectively). The digital technique was superior in terms of fit, impression time, and frequency of adjustments. Finish line positions had no significant effect on the fit of copings. Using intraoral scanner promotes the fits of restorations in supragingival and subgingival finish lines.

Assessment of the internal fit and marginal integrity of interim crowns made by different manufacturing methods

Statement of problemThe adaptation of interim crowns made by subtractive and additive manufacturing has not been well investigated. PurposeThe purpose of this in vitro study was to evaluate the internal fit and marginal discrepancy of interim crowns made by different manufacturing methods. Material and methodsA dentoform mandibular left first molar was prepared for a ceramic crown and scanned for the fabrication of 48 stereolithical resin dies and interim crowns. Group CAM included 16 ZCAD interim crowns made by computer-aided design and computer-aided manufacturing (CAD-CAM) technology; group 3DP, 16 NextDent MFH interim crowns made by digital light processing technology; and group APP, 16 Jet interim crowns manually made by using autopolymerizing acrylic resin and used as controls. The silicone replica technique was used to determine the internal discrepancy volume before definitive cementation. All crowns were cemented with Temp-Bond NE under a 50-N load and bench set for 10 minutes before microcomputed tomographic (μCT) scan assessment. The volume of cement space was measured by using the μCT scan 3-dimensional (3D) images, and gap distance at assigned locations was recorded by using the μCT scan 2-dimensional (2D) images. The marginal discrepancy was measured by the polyvinyl siloxane (PVS) impression technique and using a stereomicroscope. Data were analyzed by ANOVA and the Tukey honestly significant difference tests (α=.05). The association between different measuring techniques was analyzed by the Pearson correlation test. ResultsThe gap distance between interim crowns and dies from all 3 groups measured by using the μCT scan 2D images ranged from 0.13 mm to 0.55 mm, with the highest value found at the central occlusal location in group APP. The total average gap distance values recorded for group APP were significantly higher than those for group CAM and group 3DP (P<.05). No significant differences were found in internal discrepancy and cement space volume between group CAM and group 3DP (P>.05). The Pearson correlation test showed a moderate correlation (r=0.69) between the silicone replica technique and the μCT scan technique in determining cement space volume. When the PVS impression technique was used to measure the marginal discrepancy, the mean values obtained from group APP were statistically significantly higher than those from group CAM and group 3DP (P<.05). No statistically significant difference in marginal discrepancy was found between group CAM and group 3DP (P=.70). ConclusionsDigitally fabricated interim crowns had better internal fit and smaller marginal discrepancy than manually constructed interim crowns. The silicone replica technique and μCT scan technique measurements had a moderate correlation in assessing the adaptation of cemented interim crowns.

A Comparison Study of Marginal and Internal Fit Assessment Methods for Fixed Dental Prostheses.

Numerous studies have previously evaluated the marginal and internal fit of fixed prostheses; however, few reports have performed an objective comparison of the various methods used for their assessment. The purpose of this study was to compare five marginal and internal fit assessment methods for fixed prostheses. A specially designed sample was used to measure the marginal and internal fit of the prosthesis according to the cross-sectional method (CSM), silicone replica technique (SRT), triple scan method (TSM), micro-computed tomography (MCT), and optical coherence tomography (OCT). The five methods showed significant differences in the four regions that were assessed (p < 0.001). The marginal, axial, angle, and occlusal regions showed low mean values: CSM (23.2 µm), TSM (56.3 µm), MCT (84.3 µm), and MCT (102.6 µm), respectively. The marginal fit for each method was in the range of 23.2–83.4 µm and internal fit (axial, angle, and occlusal) ranged from 44.8–95.9 µm, 84.3–128.6 µm, and 102.6–140.5 µm, respectively. The marginal and internal fit showed significant differences depending on the method. Even if the assessment values of the marginal and internal fit are found to be in the allowable clinical range, the differences in the values according to the method should be considered.

Marginal fit of metal-ceramic crowns fabricated by using a casting and two selective laser melting processes before and after ceramic firing

Statement of problemFew studies have investigated changes in the marginal fit of metal-ceramic restorations fabricated by selective laser melting (SLM) techniques after the application of veneering ceramic. PurposeThe purpose of this in vitro study was to evaluate the marginal fit (silicone replica technique) and internal porosity (cross-section analysis) of cobalt-chromium (Co-Cr) alloy metal crowns prepared by using 2 SLM processes together with a casting technique before and after ceramic veneering. Material and methodsCast single Co-Cr crowns and SLM-processed crowns with large (SLML) or small (SLMS) porosity were prepared (n=20/group), and half were subjected to ceramic veneering. On a single Co-Cr master die, the marginal discrepancy (MD) and absolute marginal discrepancy (AMD) of the crowns were measured by using the silicone replica technique, in which each replica was cut into 4 sections before and after ceramic veneering (n=10 for each subgroup). After marginal fit measurements, each metal coping was cross-sectioned into 4 parts, and 5 rectangular optical microscope images were acquired on both outer corners of each quarter. The porosity was then calculated as the ratio of the black-to-white pixels on the binarized images. The data were analyzed by 2-way ANOVA and the post hoc test (Tukey or Student t test) (α=.05). ResultsBefore ceramic veneering, the 2 SLM groups showed significantly larger MDs than the casting group (56.4 ±10.4 μm) (P<.05). A significant increase in MD after ceramic veneering was detected only in the SLML group (P<.001). The AMD values showed a similar trend with MD values. The 2 SLM groups (in particular, SLML) showed a significantly higher amount of porosity than the casting group before ceramic veneering (P<.001). Only the SLML group showed a significant decrease in the amount of porosity after ceramic veneering (P<.001). ConclusionsWithin the limitations of this in vitro study, large internal porosity within the SLM-fabricated Co-Cr metal copings affected the marginal fit of the metal-ceramic crowns. However, all the MD values of the 3 groups were lower than the acceptable range even after the application of veneering ceramic.

Comparison of marginal and internal fit of 3-unit zirconia frameworks fabricated with CAD-CAM technology using direct and indirect digital scans

Statement of problemAccurate marginal and internal fit of dental restorations are essential for their long-term success. The fit of zirconia restorations prepared using digital scan systems has not been fully evaluated. PurposeThe purpose of this in vitro study was to compare the marginal and internal fit of 3-unit zirconia frameworks fabricated using direct and indirect digital scans. Material and methodsIn a maxillary model, the left first premolar and first molar were prepared to receive 3-unit zirconia fixed dental prostheses. Conventional impressions were made using stock trays and 2-step putty/wash polyvinyl siloxane material and were scanned using laboratory scanner (Conventional Impression-Laboratory scanner [CIL] group). The impressions were then poured, and the stone casts were scanned (Dental Cast-Laboratory scanner [DCL] group). Digital scans were made using TRIOS (TRIOS Intraoral scanner [TRI] group) and CS3600 (CS3600 Intraoral scanner [CSI] group) scanners (n=10). Zirconia copings were designed and milled from presintered blocks and subsequently sintered. Marginal, mid-axial, axio-occlusal, and mid-occlusal discrepancies were measured using the silicone replica technique with stereomicroscopy at ×50 magnification. The data were analyzed using 1-way ANOVA (α=.01). ResultsThe ANOVA revealed significant differences among the studied groups in terms of all studied characteristics (P≤.01). Marginal gap was significantly higher in the DCL group (106 ±45 μm) compared with all other groups (P≤.01). However, no significant differences were observed in marginal gap between the TRI (60 ±15 μm) and CSI (55 ±13 μm) groups (P>.01). Internal gap in the mid-occlusal and axio-occlusal regions were significantly higher in the CIL (238 ±92 μm and 227 ±95 μm) and DCL (248 ±71 μm and 216 ±68 μm) groups than those recorded in the TRI (104 ±27 μm and 126 ±31 μm) and CSI (128 ±16 μm and 147 ±28 μm) groups (P≤.01). Internal discrepancies in the mid-axial position were similar between the TRI (70 ±15 μm) and CSI (72 ±23 μm) groups (P>.01), but these values were significantly lower than those recorded in the CIL (88 ±31 μm) and DCL (85 ±30 μm) groups (P≤.01). ConclusionsWithin the limitations of this study, zirconia frameworks in the TRI and CSI groups had lower marginal and internal gaps compared with those in the DCL and CIL groups. Marginal gap in all groups was within a clinically acceptable range.

Performance of a repair service set for the retrieval of fractured abutment screws: a pilot in vitro study.

To report the success of a repair service set for the retrieval of fractured screws and to compare three clinical assessments to an in vitro assessment to verify the completeness of removal of the fractured screws. Twelve clinicians were asked to remove fractured implant abutment screws from prepared specimens by means of a repair service set. The completeness of the removal of any abutment screw material was measured by the fit of an impression post, a dental surgery microscope, and the use of an elastomeric impression material. After the participants attempted to remove the fractured screw with the repair service set, 100%, 83.3%, 66.7%, and 75% of the fractured screws were considered successful in the impression post, dental surgery microscope, silicone replica, and stereomicroscope assessments, respectively. The retrieval of fractured screws succeeded in 75% of the cases. The silicone replica technique and the dental surgery microscope had similar diagnostic values to the stereoscopic microscope assessment.

Evaluation of the Marginal and Internal Fit of Implant-Supported Metal Copings Fabricated with 3 Different Techniques: An In Vitro Study.

To compare the marginal and internal fit of cobalt-chromium (Co-Cr) alloy copings fabricated by with lost wax technique (LW), computer-aided design and computer-aided manufacturing (CAD/CAM), and direct metal laser sintering (DMLS). Thirty-six tissue level, straight titanium abutments were screwed onto implant replicas. All specimens were embedded in acrylic resin and randomly divided into 3 subgroups according to the fabrication of metal coping: LW, CAD/CAM, and DMLS. In total, 36 (n = 12/group) Co-Cr implant-supported metal copings were prepared. Marginal, intermarginal, axial, and occlusal fits of each coping were measured using the silicone replica technique. The data were evaluated statistically using one-way ANOVA and Bonferioni post-hoc test (α = 0.05). The CAD/CAM group showed significantly lower marginal fit than the LW group and DMLS groups (p < 0.001). The marginal fit of the LW group was not significantly different from the DMLS group (p = 0.721). No significant difference found among the fabrication methods in terms of intermarginal fit (p = 0.913). The CAD/CAM group showed lower axial fit than the LW group (p = 0.026), but there was no statistical difference between the DMLS group and the LW (p = 0.999) and CAD/CAM groups (p = 0.247). No significant differences found among the fabrication methods in terms of occlusal fit (p = 0.158). The LW and DMLS groups showed better marginal fit compared to the CAD/CAM group; however, the CAD/CAM group was better than the LW group in terms of axial fit. All fabrication methods demonstrated similar intermarginal and occlusal fit.

Effect of manufacturing techniques on the marginal and internal fit of cobalt-chromium implant-supported multiunit frameworks

Statement of problemSubtractive and additive computer-aided design and computer-aided manufacturing (CAD-CAM) systems have been used in the fabrication of cobalt-chromium (Co-Cr) long-span restorations. However, the accuracy of fit of multiunit frameworks is unclear. PurposeThe purpose of this in vitro study was to compare the marginal and internal fit of implant-supported, cement-retained 3-unit, 4-unit, and 5-unit Co-Cr metal frameworks fabricated by the lost wax (LW), CAD-CAM milling, and selective laser melting (SLM) techniques. Material and methodsA total of 90 Co-Cr metal frameworks were fabricated for 3-unit, 4-unit, or 5-unit implant-supported cement-retained restorations on stock abutments with 3 different manufacturing technique subgroups (LW, CAD-CAM milling, and SLM). The silicone replica technique was used to evaluate the marginal and internal discrepancy values. By using a light microscope at ×45 magnification and a digital measurement program, the thickness of the silicone layer was measured at 16 reference points on each abutment for a total of 3360 measurements. The effect of manufacturing techniques and number of units (groups) on discrepancy values was evaluated using a full factorial ANOVA model. Group and manufacturing technique effects were analyzed separately by 1-way ANOVA in case of significant interactions. Pairwise comparisons were evaluated using the Tukey post hoc test (α=.05). ResultsThe mean marginal discrepancy of 3-unit frameworks showed no statistically significant differences in the LW (35 μm) and SLM (25 μm) techniques; however, the frameworks manufactured by CAD-CAM milling (68 μm) had the highest marginal discrepancy values (P<.001). The mean marginal discrepancy values were 40 μm (LW), 33 μm (CAD-CAM milling), and 25 μm (SLM) for 4-unit frameworks, and no significant differences were found among the manufacturing techniques. For 5-unit frameworks, CAD-CAM milling techniques had the widest mean marginal discrepancy values (85 μm), and copings manufactured by the LW technique had the lowest mean marginal discrepancy values (36 μm). For all manufacturing techniques, axial discrepancy values were not affected with respect to the unit number (P=.526). The highest internal discrepancy values were measured at the occlusal area in all groups. ConclusionsCAD-CAM milling had the poorest marginal fit values for 5-unit frameworks, whereas the LW technique demonstrated the best results. Unit number had no significant influence on the marginal and internal fit of the LW manufactured frameworks.

Influence of repeated firings on marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic restorations fabricated with different techniques

Statement of problemIll-fitting restorations can jeopardize dental, periodontal, and systemic health. Repeated ceramic firing may influence the fitting accuracy of restorations, but scientific information regarding this issue is lacking. PurposeThe purpose of this in vitro study was to assess and compare the influence of repeated firings on the marginal, axial, axio-occlusal, and occlusal fit of metal-ceramic 3-unit fixed partial dentures (FPDs) manufactured with different framework methods, including casting, fully sintered hard alloy milling (FHAM), presintered soft alloy milling (PSAM), and selective laser sintering (SLS). Material and methodsA total of 60 Co-Cr metal frameworks for 3-unit FPDs were fabricated with 3 different computer-aided design and computer-aided manufacturing (CAD-CAM) techniques and conventional casting for a typodont model. The discrepancy values for premolar and molar abutments were measured by using the silicone replica technique after fabrication of the framework, second firing, fourth firing, and seventh firing. The replicas were separated into mesiodistal and buccolingual cross-sections, and digital images of the cross-sections were obtained with a stereomicroscope at ×80 magnification. The measurement points were examined to record the discrepancy values (μm) with in-built measuring software. The recorded data were subjected to repeated-measures 4-way ANOVA and the Bonferroni post hoc test (α=.05). ResultsFor all measurement periods, the marginal, axial, axio-occlusal, and occlusal discrepancy values differed significantly among the manufacturing groups (P<.001). Moreover, the repeated firings had a statistically significant influence on the discrepancy values of PSAM, FHAM, and SLS groups (P<.05). The cast group was not significantly affected by repeated firings (P>.05). The PSAM group revealed the lowest discrepancy values at all measurement periods (P<.05), except after the second firing in the marginal and axial locations. ConclusionsThe PSAM-fabricated restorations demonstrated superior fitting accuracy. All manufacturing groups were influenced by repeated firings, except the cast group. The marginal discrepancy values of all manufacturing groups were within the range of clinical acceptability (<120 μm).