Vertical Misfit Research Articles

EVALUATION OF ACCURACY OF TWO DIFFERENT IMPRESSION MATERIALS AND THREE DIFFERENT IMPRESSION TECHNIQUES ON THE VERTICAL MISFIT OF A THREE UNIT IMPLANT SUPPORTED FIXED DENTURE PROSTHESES


 
 
 AIM: The aim of the study is to evaluate the accuracy of two different impression materials and three different impression techniques on the vertical misfit of a three-unit implant supported fixed denture prostheses.Materials and Methods: A total of 60 casts were fabricated for the present study with a closed tray, open tray and open tray splinted abutment impression technique. Two different commercially available impression materials were used - polyether and addition silicone. Both the materials were used for all the above impression techniques.Results: Accordingtotheresultderivedfromthisstudypolyethershowedleastmarginalgap.On the other hand on the basis of impression techniques open tray impression with splinted transfer coping also exhibited a minimum marginal gap.Conclusion: 1. Higher marginal accuracy was found in impressions made by polyether compared to polyvinyl siloxane. 2. Open tray splinted technique exhibited a minimum marginal gap when used with polyether as impression material compared to open tray non splinted technique and closed tray technique.
 
 

Effectiveness of Sealing Gel on Vertical Misfit at the Implant-Abutment Interface and Preload Maintenance of Screw-Retained Implant-Supported Prostheses.

This in vitro study evaluated the effectiveness of a sealing agent on vertical misfit of the implant-abutment interface in an external hexagon implant system before and after mechanical cyclic loading. Effects on preload maintenance of retaining screws after mechanical cycling were also assessed. External hexagon implant systems were divided into two groups (n = 12) according to the presence of an anaerobic sealing gel (control group-no sealing gel; experimental group-sealing gel applied). A prefabricated UCLA abutment was attached to the external hexagon implant with a digital torque wrench in accordance with the recommendations of the manufacturer. Specimens were tested through mechanical cyclic loading (1 × 106 cycles, 2 Hz, and 130 N). Vertical misfit of the implant-abutment interface was analyzed using a stereomicroscope, and reverse torque values were obtained using a digital wrench. Misfit and reverse torque data were measured and analyzed via analysis of variance (ANOVA) and the Tukey least significant difference test (α = .05). The sealing gel promoted lower vertical misfit values in the test group after mechanical cycling compared with before cycling (P = .009). The control group showed lower reverse torque values for retaining screws compared with the initial torque after mechanical cyclic loading (P < .0001). However, sealing gel application promoted higher reverse torque values in the test group postcycling (P = .0003). Anaerobic sealing agent application improved vertical misfit of the implant-abutment interface and preload maintenance of screw-retained implant-supported prostheses post-mechanical cycling.

Torque Maintenance Capacity, Vertical Misfit, Load to Failure, and Stress Concentration of Zirconia Restorations Cemented or Notched to Titanium Bases

Different titanium bases for implant-supported prostheses can present different mechanical behavior. The goal of this study was to evaluate the torque before and after fatigue, the load to failure, and stress concentration of zirconia restorations cemented or notched to a titanium base. Forty implants were included in polyurethane cylinders and divided into two groups: zirconia restoration cemented on a titanium base and zirconia restoration notched on a titanium base. The specimens had their torque loosening and vertical misfit evaluated before and after cyclic fatigue (200 N/2 Hz/2 × 106 cycles/37°C). Load to failure was evaluated in a universal testing machine (1 mm/min, 1,000 kgf). Failures were evaluated by scanning electron microscopy. Three-dimensional models were created, and the stress concentration was calculated using the finite element method. Data from the in vitro tests were submitted to two-way analysis of variance and Tukey test (α = .5). The cemented restorations presented less torque loosening (19.79 to 15.95 Ncm), lower vertical misfit (3.7 to 10.5 μm), lower stress concentration in the restoration (88.2 to 99.8 MPa), and higher fracture load (451.3 to 390.8 N) than notched restorations. The presence of a cement layer between the restoration and titanium base reduced the susceptibility to abutment screw loosening, improved the resistance to compressive load, and reduced the stress concentration in the restoration.

Fit of 3Y-TZP complete-arch implant-supported fixed dental prostheses before and after porcelain veneering

Statement of problemTo minimize technical complications, implant-supported fixed dental prostheses must fit well. The fit of complete-arch veneered zirconia frameworks has not been fully evaluated. PurposeThe purpose of this in vitro study was to evaluate the fit of screw-retained zirconia implant-supported complete-arch maxillary frameworks for fixed dental prostheses before and after porcelain veneering. Material and methodsTen stone casts simulating an edentulous maxilla and provided with 6 abutment analogs were produced. For each stone cast, 1 zirconia framework was fabricated by computer-aided design and computer-aided manufacturing. The fit was analyzed by using a coordinate measuring machine in 3 dimensions (x, y, and z axes) using best fit by virtual matching of center point coordinates before and after porcelain veneering. Also, the horizontal distances between implant position pairs P1–P6, P2–P5, and P3–P4 were measured. Furthermore, an optical microscope was used to evaluate vertical fit at the terminal abutments after porcelain veneering. ResultsBefore the porcelain veneering procedure, the frameworks had a mean horizontal misfit of 27.7 μm in the x-axis and 12.0 μm in the y-axis. In the vertical dimension (z-axis), the mean misfit was 2.4 μm and the mean 3D misfit value was 32.3 μm before veneering. Porcelain veneering increased the mean misfit by 0.2 μm in the horizontal plane (x and y axes), 0.4 μm in the vertical plane, and 0.4 μm in 3D; the difference before and after veneering was not statistically significant (P>.05). The mean ±standard deviation vertical misfit at the terminal abutments was 9.2 ±2.9 μm, optically recorded after porcelain veneering. The measured horizontal distances between implant position pairs P1–P6, P2–P5, and P3–P4 increased to 0.9 μm, 2.0 μm, and 1.9 μm, respectively, after porcelain veneering. The difference for the implant position pair P2–P5 was statistically significant (P<.05). ConclusionsScrew-retained zirconia implant-supported complete-arch maxillary frameworks for fixed dental prostheses have a fit well within the range of 30 μm in the horizontal plane and 10 μm in the vertical plane. The porcelain veneering procedure did not affect the fit of the frameworks.

CAD/CAM vs Conventional Technique for Fabrication of Implant-Supported Frameworks: A Systematic Review and Meta-analysis of In Vitro Studies.

To compare the marginal vertical misfit between implant-supported frameworks fabricated using CAD/CAM systems and the conventional technique (lost-wax casting). This review was performed according to PRISMA criteria and registered on PROSPERO (CRD42017055685). An electronic search was performed independently by two examiners in the MEDLINE (Pubmed), Embase, Web of Science, and Cochrane Library databases to find studies published up to April 2018. The database search yielded 507 references. After removing duplicate references, 384 studies remained. Eleven in vitro studies were selected according to the eligibility criteria (inter-reader κ = 0.88). Nine different CAD/CAM systems were used to fabricate 172 frameworks of different materials, including zirconia, monolithic lithium disilicate, and metallic alloys. Subgroup analyses were performed for different types and retention systems of the frameworks. In the general analysis, marginal misfit observed with the CAD/CAM systems was lower than with the conventional method (P = .003), as was observed in the subgroup analysis for single-unit frameworks (P < .00001). For fixed (P = .89), cemented (P = .60), and screwed (P = .18) frameworks, no significant difference was observed between the evaluated techniques. The CAD/CAM systems showed improved marginal fit over the conventional lost-wax casting technique for fabricating single-unit frameworks; however, in the subgroup analyses, no difference was observed for the fixed implant-supported type or for the retention systems evaluated.

Analysis of Vertical Misfit of Crowns Fabricated with CAD/CAM Technology using Two Scanning Techniques: Direct and Indirect

The study evaluated the marginal vertical misfit of feldspathic ceramic crowns fabricated by the computer-aided design (CAD)/computer-aided manufacturing (CAM) technology and compared the two methods of scanning techniques: direct digital impression and indirect digital impression. The titanium specimens were divided into two groups: scanning with the direct digital impression (DDI) at the milled prosthetic abutment level and indirect digital impression (IDI) at the cast model and after milled feldspathic ceramics blocks. Vertical marginal misfit was analyzed. The t-test was used for the analysis of the comparison factor between the groups and the one-way analysis of variance (ANOVA) test, and post hoc Tukey test was used to compare the variance of crown analysis regions within the group. A significance level of 5% was considered for the analyses. There was no significant difference in vertical marginal misfit between the groups of DDI and IDI (p = 0.345). In relation to each region measured within the studied groups, it was observed the similarity between the six regions analyzed in the DDI group (p >0.05) and IDI group, a significant difference between two areas. The vertical marginal adaptation was similar between digital scanning methods. Based on the data evaluated, vertical marginal adaptation indices were within acceptable clinical standards. The direct digital scanning in unit bodies was reliable, pointing that the coating of titanium dioxide in the titanium abutment did not negatively influence the vertical marginal adaptation of the feldspathic ceramic crowns.

Mechanical Behavior of Different Micro Conical Abutments in Fixed Prosthesis.

To evaluate the biomechanical behavior between two different micro conical abutments: two-piece and one-piece abutments. Four groups were divided according to the prosthetic connection (internal or external hexagon) and abutment type. The vertical misfit between the abutment and implant was evaluated under stereomicroscope. Next, the implants were divided into pairs and embedded in polyurethane to receive two-element prostheses. The initial removal torque was measured for abutments and for prosthesis fixation. The samples were mechanically cycled (200 N, 2 Hz, 2 × 106 cycles) before measuring the torque loss in the same regions. For stress verification, a finite element analysis was used. For vertical misfit, one-piece (4.70 ± 0.26 μm) < two-piece (16.8 ± 0.32 μm). For preload in abutment screw, two-piece = one-piece. For prosthetic screw, a higher percentage of preload was found for two-piece, but no statistical difference was observed after fatigue cycling between the groups. For stress analysis, no difference (10%) was observed for abutments, retention screw, or for the bone. The one-piece abutment maintained even amounts of preload after cyclic loading and presented less vertical misfit in comparison with the two-piece abutment for both implant connections. The use of one-piece abutments did not increase the stress and strain concentration, suggesting acceptable biomechanical behavior.

Influence of vertical misfit in screw fatigue behavior in dental implants: A three-dimensional finite element approach.

Misfit is unavoidable in dental implant-supported prostheses due to machining process or inappropriate assembling, and the definition of an admissible misfit is still a controversial issue. This work aims to understand the behavior of the screws in dental implant-supported prostheses to estimate an admissible vertical misfit value in terms of screw fatigue failure. For that purpose, a finite element model of a dental implant-supported prosthesis was created and analyzed. Vertical misfits were introduced in different positions, the lower and upper screws were tightened to the bolting force values recommended by the manufacturer, and two different occlusal loads were analyzed. In addition, two different prosthesis materials were studied. Screw load variations were reported and a fatigue analysis was performed. As a result, it was observed that the screw tightening sequence closed small vertical misfits (equal to or less than 40 µm), whereas larger misfits (more than 40 µm) remained open. If the vertical misfit is closed by the end of the tightening sequence, it may be considered equivalent to the ideal fit situation in regard to screw fatigue failure. The prosthesis material had no significant influence on the fatigue behavior.

Evaluation of Vertical Misfit of CAD/CAM Implant-Supported Titanium and Zirconia Frameworks.

This study compared the vertical misfit of fixed implant-supported titanium (Ti6Al4V) and yttria-stabilized tetragonal zirconia frameworks milled using the computer-aided design/computer-aided manufacturing (CAD/CAM) Zirkonzahn system. An aluminum mandibular master cast was used, and four analogs of the Regular CrossFit implant for straight multibase titanium alloy abutments (Institut Straumann) were fixed with self-curing acrylic resin in mandibular canine and second premolar tooth locations with the aid of a parallelometer. Scan abutments were placed over the four straight multibase Regular CrossFit abutments to determine their correct three-dimensional (3D) positioning in the virtual model. Implant frameworks were designed virtually, and five frameworks of each material (titanium alloy or yttria-stabilized tetragonal zirconia) were milled using the CAD/CAM system. Scanning electron microscope (SEM) images, with magnifications of 50×, 250×, and 1,000×, were obtained from three points on the buccal surface, three points on the lingual surface, and three points on the mesial surface of each abutment. The measurements were performed in the center of each of the thirds, thus defining points one, two, and three. The degree of vertical misfit at the framework-abutment interface was determined using ImageJ software and analyzed using the Student t test (P = .05). The mean misalignment value was 6.011 ± 0.750 μm for the titanium group and 9.055 ± 3.692 μm for the zirconia group. Within the limitations of this study, there was no significant difference in vertical misfit between the titanium and zirconia implant frameworks produced using the CAD/CAM system. Regardless of the material used, the CAD/CAM frameworks achieved an adequate vertical fit.

Influence of Cross-Section Design and Vertical Misfit on Stress Distribution in Overdenture Retaining System: 3-Dimensional Finite Element Analysis.

To evaluate by 3-dimensional (3-D) finite element analysis the stress generated on overdenture-retaining bar system with different cross sections (round, ovoid, or Hader) and misfit levels (50, 100, and 200 μm) manufactured with different metallic alloys (Au type IV, Ag-Pd, Ti cp, and Co-Cr). Three-dimensional finite element models were modeled using specific 3-D software (SolidWorks) and imported into mechanical simulation software (ANSYS). A displacement simulating the settlement of the screw was performed until the infrastructure was settled properly on the prosthetic platform. Higher misfit levels caused higher stress on the overdenture-retaining bar system components, where (1) Hader bar presented the highest values (bar = 730.71; screw = 59.66, and periimplant bone tissue = 42.96, in megapascal) and (2) round bars made with type IV Au alloy presented lower stress values on the bar framework (193.99 MPa) and screw (10.27 MPa). Higher vertical misfit increased the stress values on the overdenture-retaining bar system; complex cross-sectional designs increased stress values on the bar framework, prosthetic screw, and periimplant bone tissue; stiffer alloys caused higher stress values on all the studied conditions.

Comparison between open and closed-tray impression techniques on the implant transfer accuracy

Objective: This in vitro study aimed to determine and compare the dimensional accuracy of open and closed-tray impression techniques for implant-supported prosthesis. Material and Methods: On a edentulous master model, four external hexagonal implants were parallelly installed and associated with four multi unit coping transfers and four multi unit rotational caps. A master superstructure was constructed and splinted all implants (control group). Five customized trays were constructed to perform ten open (n=5) and closed-tray (n=5) impressions. The obtained models were submitted to the dimensional analysis on three points in the center of the labial face of each implant (A, B, C, and D) with the aid of Stereoscopic Magnifying Glass with x60 magnification. The vertical misfit between the metallic structure and the implant analogues was measured on each point. The obtained results were submitted to Dixon’s normality test and Kruskal-Wallis test for independent samples (p &lt; 0,05) with the aid of Bioestat 5.0 software. Results: The means and standard deviation were: open tray technique – 24.6474 ± 14.8883 µm; closed-tray technique – 26.2257 ± 9.7421 µm; and control group 22.445 ± 7.7106 µm. Conclusion: The accuracy of open and closed-tray impression techniques showed no statistically significant differences and both techniques were effective for implant transfer.

Influence of Manufacturing Methods of Implant-Supported Crowns on External and Internal Marginal Fit: A Micro-CT Analysis.

Aim To evaluate the influence of different manufacturing methods of single implant-supported metallic crowns on the internal and external marginal fit through computed microtomography. Methods Forty external hexagon implants were divided into 4 groups (n = 8), according to the manufacturing method: GC, conventional casting; GI, induction casting; GP, plasma casting; and GCAD, CAD/CAM machining. The crowns were attached to the implants with insertion torque of 30 N·cm. The external (vertical and horizontal) marginal fit and internal fit were assessed through computed microtomography. Internal and external marginal fit data (μm) were submitted to a one-way ANOVA and Tukey's test (α = .05). Qualitative evaluation of the images was conducted by using micro-CT. Results The statistical analysis revealed no significant difference between the groups for vertical misfit (P = 0.721). There was no significant difference (P > 0.05) for the internal and horizontal marginal misfit in the groups GC, GI, and GP, but it was found for the group GCAD (P ≤ 0.05). Qualitative analysis revealed that most of the samples of cast groups exhibited crowns underextension while the group GCAD showed overextension. Conclusions The manufacturing method of the crowns influenced the accuracy of marginal fit between the prosthesis and implant. The best results were found for the crowns fabricated through CAD/CAM machining.

Abutment misfit in implant-supported prostheses manufactured by casting technique: An integrative review.

The aim of this study was to perform an integrative review of the literature on the clinically usual prosthesis-abutment misfit over implant-supported structures manufactured by conventional casting technique. The present integrative review used the PRISMA methodology. A bibliographical search was conducted on the following electronic databases: MEDLINE/PubMed (National Library of Medicine), Scopus (Elsevier), ScienceDirect (Elsevier), Web of Science (Thomson Reuters Scientific), Latin American and Caribbean Center on Health Sciences Information (BIREME), and Virtual Health Library (BVS). A total of 11 relevant studies were selected for qualitative analysis. The prosthetic-abutment vertical misfit considered clinically usual ranged from 50 to 160 μm. The vertical misfit depends on several steps during technical manufacturing techniques, which includes the materials and technical procedures. Lower values in misfit are recorded when precious metal or titanium alloys are utilized. Although a vertical misfit mean value of 100 μm has been considered clinically usual, most of the previous studies included in this revision showed lower mean values.

Influence of scanner, powder application, and adjustments on CAD-CAM crown misfit

Statement of problemThe manufacturers of computer-aided design and computer-aided manufacturing (CAD-CAM) systems emphasize that new technologies can improve the marginal fit of dental crowns. However, data supporting this claim are limited. PurposeThe purpose of this in vitro study was to investigate the differences among the following fabrication methods on the marginal discrepancy of dental crowns: intraoral optical scanners, powder application, and adjustments of intaglio surface. Material and methodsA single human premolar was fixed on a typodont and prepared to receive crowns prepared by the CEREC CAD-CAM system. Three fabrication techniques were used: digital scans using the CEREC Bluecam scanner with titanium dioxide powder (TDP), digital scans using the CEREC Omnicam scanner without TDP, and digital scans using the Omnicam scanner with TDP. Five experimental groups (n=10) were designated: Bluecam (group B), Bluecam with adjustments (group BA), Omnicam (group O), Omnicam with adjustments (group OA), and Omnicam with TDP (group OP). The specimens were scanned using microcomputed tomography to measure the vertical, horizontal, and internal fit and volumetric 3-dimensional (3D) internal fit values of each luting space. The paired t test was used to evaluate mean marginal fit change after adjustments within the same group. One-way analysis of variance and post hoc tests were used to compare groups B, O, and OP (α=.05). ResultsMean vertical fit values ±standard deviations of group B=29.5 ±13.2 μm; BA=26.9 ±7.7 μm; O=149.4 ±64.4 μm; OA=49.4 ±12.7 μm; and OP=33.0 ±8.3 μm. Adjustments in the intaglio surface and TDP application statistically influenced the vertical fit of group O (P<.001). The percentage of vertical fit values <75 μm in group B=89.3%, BA=92.7%, O=31.0%, OA=73.5%, and OP=92.0%. Mean horizontal fit values for group B=56.2 ±21.5 μm; 85.8 ±44.4 μm for group BA; 77.5 ±11.8 μm for group O; 102.5 ±16.2 μm for group OA; and 91.4 ±19.4 μm for group OP. Results from group B were significantly different from those of the other test groups (P<.05). The percentages of horizontal misfit were 61.2% in group B; 73.5% in group BA; 88.1% in group O; 92.4% in group OA; and 85.0% in group OP. Volumetric 3D internal fit values in group B were 9.4 ±1.3 mm3; 10.7 ±1.0 mm3 in group BA; 11.8 ±2.1 mm3 in group O; 11.0 ±1.3 mm3 in group OA; and 9.6 ±0.9 mm3 in group OP. The overall results from groups B and OP were better than those of group O, with regard to vertical misfit and volumetric 3D internal fit. ConclusionsDifferent intraoral optical scanners, powder application, and internal adjustments influenced the marginal discrepancy of crowns. Crowns fabricated using the Omnicam system had significantly higher vertical discrepancy and volumetric 3D internal fit than those fabricated using the Bluecam scanner with TDP. Adjustments of the intaglio surface improved the vertical fit of crowns made using the Omnicam scanner; however, TDP application before Omnicam scanning improved the vertical fit as well as the volumetric 3D internal fit value of the luting space of crowns.

Influence of angulation and vertical misfit in the evaluation of micro-deformations around implants

Objective: This in vitro study was to evaluate micro-strains around of implant, under the influence of angulations and vertical misfit in three-element implant-supported fixed partial dentures during axial loading by using strain gauge analysis. Materials and Methods: Three external hexagon implants with straight configuration and three external hexagon implants with angled (17°) configuration were inserted into two polyurethane blocks. To measure micro-strain, four strain gauges were bonded onto the surface of each block. Plastic copings were adapted to a standard wax pattern and cast. An axial load of 30 kgf was applied on the center of each implant for 10 seconds, using a load application device. The vertical misfit was measured at six different points by using a stereo microscope with 100-X magnification. Results: The results showed that the values for different implant angulations were significant (P= 0.0086). The Pearson’s correlation test between micro-strain and vertical misfit revealed no correlation between angled configuration (P= 0.891) and straight configuration (P= 0.568). Conclusion: The micro strain was higher for angled implants; no correlation was found between the vertical misfit and the micro strain values.

Microscopic evaluation of implant platform adaptation with UCLA-type abutments: in vitro study

Abstract Introduction The fit between abutment and implant is crucial to determine the longevity of implant-supported prostheses and the maintenance of peri-implant bones. Objective To evaluate the vertical misfit between different abutments in order to provide information to assist abutment selection. Material and method UCLA components (N=40) with anti-rotational system were divided as follows: components usinated in titanium (n=10) and plastic components cast proportionally in titanium (n=10), nickel-chromium-titanium-molybdenum (n=10) and nickel-chromium (n=10) alloys. All components were submitted to stereomicroscope analysis and were randomly selected for characterization by SEM. Result Data were analyzed using mean and standard deviation and subjected to ANOVA-one way, where the groups proved to statistically different (p=&lt;0.05), followed by Tukey’s test. Conclusion The selection of material influences the value of vertical misfit. The group machined in Ti showed the lowest value while the group cast in Ni Cr showed the highest value of vertical misfit.

Effect of technique and impression material on the vertical misfit of a screw-retained, three-unit implant bridge: An in vitro study.

Introduction:A dental impression is a negative imprint of an oral structure that can be used to produce a positive cast of a patient's teeth as a permanent record. The accuracy of the impression affects the accuracy of the cast, and a precise impression is needed in order to create prosthesis with optimal fitting. Minimization of misfit is an important aim in prosthesis science and dental implants. The aim of this study was to evaluate the effects of the materials and techniques used to take an impression on the vertical misfit of implant-supported, screw-retained, three-unit bridges.Materials and Methods:The principal model used was an acrylic block with two ITI implants. A 1.5-mm abutment was attached to fixtures with torque of 25 N.cm. A base-metal framework was built on the abutment in the acrylic block. The abutments of the acrylic model were unscrewed and fixture-level impressions were made. The impression techniques included open/closed-tray techniques and the impression materials were polyether and polyvinyl siloxane. Forty acrylic custom trays were built for each impression. The marginal gap in the framework at three points (buccal, lingual, and distal) was measured using an optical microscope with ×250.Results:It is demonstrated that in all 360 evaluated samples, the mean vertical misfit in polyether samples of molar and premolar teeth was significantly lower than in polyvinyl siloxane (P < 0.001 and P = 0.017, respectively) in all three locations of the molar and lingual premolar examined (buccal, lingual, and distal), the mean vertical misfit of the polyether samples was significantly lower than those of polyvinyl siloxane (P < 0.01). On the other hand, although the mean vertical misfit using the open-tray technique in the molar teeth was significantly lower than with the closed-tray method (P = 0.002), no statistical difference was seen between the open-tray and closed-tray technique in general (P = 0.87).Conclusion:Within the limitations of this study, the following conclusions can be drawn: The impression method had no effect on marginal discrepancy of 3-unit screw retained fixed partial dentures. A higher marginal accuracy was obtained using polyether impression material compared to polyvinyl siloxane.

Precision Fit of Screw-Retained Implant-Supported Fixed Dental Prostheses Fabricated by CAD/CAM, Copy-Milling, and Conventional Methods

The aim of this study was to evaluate the effectiveness of fabrication methods (computer-aided design/computer-aided manufacture [CAD/CAM], copy-milling, and conventional casting) in the fit accuracy of three-unit, screw-retained fixed dental prostheses. Sixteen three-unit implant-supported screw-retained frameworks were fabricated to fit an in vitro model. Eight frameworks were fabricated using the CAD/CAM system, four in zirconia and four in cobalt-chromium. Four zirconia frameworks were fabricated using the copy-milled system, and four were cast in cobalt-chromium using conventional casting with premachined abutments. The vertical and horizontal misfit at the implant-framework interface was measured using scanning electron microscopy at ×250. The results for vertical misfit were analyzed using Kruskal-Wallis and Mann-Whitney tests. The horizontal misfits were categorized as underextended, equally extended, or overextended. Statistical analysis established differences between groups according to the chi-square test (α = .05). The mean vertical misfit was 5.9 ± 3.6 μm for CAD/CAM-fabricated zirconia, 1.2 ± 2.2 μm for CAD/CAM-fabricated cobalt-chromium frameworks, 7.6 ± 9.2 μm for copy-milling-fabricated zirconia frameworks, and 11.8 (9.8) μm for conventionally fabricated frameworks. The Mann-Whitney test revealed significant differences between all but the zirconia-fabricated frameworks. A significant association was observed between the horizontal misfits and the fabrication method. The percentage of horizontal misfits that were underextended and overextended was higher in milled zirconia (83.3%), CAD/CAM cobaltchromium (66.7%), cast cobalt-chromium (58.3%), and CAD/CAM zirconia (33.3%) frameworks. CAD/CAM-fabricated frameworks exhibit better vertical misfit and low variability compared with copy-milled and conventionally fabricated frameworks. The percentage of interfaces equally extended was higher when CAD/CAM and zirconia were used.

Vertical Misfit of Single-Implant Abutments Made from Different Materials Under Cyclic Loading.

Little information is available in the literature regarding the accuracy of marginal fit of abutments made from different materials. The aim of this study was to compare the level of vertical misfit in abutments made from different materials before and after cyclic loading. Thirty external hexagon implants, 3.75-mm diameter and 13-mm length, were embedded in epoxy resin and divided into three groups according to abutment type (n = 10): (1) machined titanium (Ti) abutments; (2) premachined gold-alloy (Au) abutments; and (3) machined zirconia (Zr) abutments. The abutments were attached to their respective implants by titanium alloy screws at the manufacturer's recommended torque. A cyclic loading (0.5 × 10(6) cycles; 15 Hz) between 11 and 211 N was applied at an angle of 30 degrees to the long axis of the implants. Implant-abutment vertical misfits (μm) were measured at four predetermined points before and after loading with a stereomicroscope at 60× magnification. The group means were compared using a three-way repeated-measure analysis of variance (ANOVA) and Tukey test (α = .05). The results from the ANOVA identified significant effects of the abutment type (P < .001). However, there were no significant effects of cyclic loading (P = .978) or measured surfaces (P = .955). When the abutment groups were compared regardless of cyclic loading and measured surfaces, the Au group showed the highest value of vertical misfit (14.93 ± 0.78), followed by the Ti group (8.53 ± 0.44) and the Zr group (5.64 ± 0.73), with statistically significant differences among them (P < .05). The abutment groups showed statistically significant differences in vertical misfit. Zr abutments showed the highest accuracy in terms of marginal fit, and Au abutments showed the lowest. Cyclic loading did not significantly change the level of vertical misfit. All experimental groups presented acceptable values of marginal misfit.

Accuracy of Digital Versus Conventional Periapical Radiographs to Detect Misfit at the Implant-Abutment Interface.

Misfit is a risk factor for rehabilitation with implants, and its detection is of fundamental importance to the success of treatment with implants. The use of appropriate radiographic imaging is key for a good prognosis. The aim of this study was to compare the efficacy of film and digital radiographs for the detection of misfit at the implant-abutment interface. Digital and conventional (manual and automatic processing) radiography was performed in seven test specimens, each one with a different vertical misfit between the abutment and the platform of the implant. Scanning electron microscopy was used to confirm the misfit and to measure it. Five dental radiologists independently and blindly evaluated the images. Cohen's kappa with linear weighting was calculated to determine interexaminer and intraexaminer concordance. Statistical analyses were performed using the Cochran's Q test and the receiver operating characteristic curve (ROC). Interexaminer analysis showed that the kappa value was equal to 0.74, whereas the average kappa value in the intraexaminer evaluation was 0.90. Digital imaging showed the largest area on the ROC graph, and conventional images with manual processing showed the smallest area. The images obtained through conventional radiography with both manual and automatic processing showed statistically significant differences from the measurement of the gold standard (P < .05). Digital imaging can be used to evaluate misfit at the implant-abutment interface. Conventional systems of radiographic imaging do not provide sufficient information to evaluate misfit at the implant-abutment interface.