Evaluation of the marginal adaptation and debonding strength of two types of CAD-CAM implant-supported cement-retained crowns

BACKGROUND

In-vitro data from a clinically well-known lithium disilicate ceramic reference was used to assess the expected performance of resin-based materials in implant dentistry. The purpose of the study was to compare the bond strength and marginal adaptation of nano-ceramic hybrid composite crowns cemented to stock cement-retained abutments to lithium disilicate crowns.

METHODS

Twenty abutment analogs were embedded into auto-polymerizing acrylic resin blocks. The blocks were divided into 2 groups according to the restorative crown material. The 2 groups were divided as follows: Resin nano-ceramic group and lithium disilicate group. Abutment analogs in both groups were scanned using a laboratory scanner, and the restorations were designed, manufactured, and cemented with resin cement over the corresponding group. All samples were tested for marginal adaptation and bond strength after storage for 24 hours at 37 °C in 100% humidity. Data were collected, tabulated, and statistically analysed using the appropriate tests. Normality was checked using Shapiro Wilk test and Q-Q plots. Data were normally distributed. Variables were presented using mean, 95% Confidence Interval (CI) and standard deviation in addition to median and Inter Quartile Range (IQR). Differences between groups regarding debonding forces was assessed using independent t test. Two Way ANOVA was performed to assess the effect of material and bonding on marginal gap. All tests were two tailed and p value was set at < 0.05.

RESULTS

Marginal gap and debonding force values were significantly different according to the type of material used (P < .05). Resin nano-ceramic crowns presented lower marginal gap values before (20.80 ± 8.87 μm) and after (52.11 ± 22.92 μm) bonding than lithium disilicate crowns. The debonding force value for resin nano-ceramic crowns (284.30 ± 26.44 N) was significantly higher than that for lithium disilicate crowns (253.30 ± 33.26 N). Adhesive failure mode was detected in all the specimens in both groups.

CONCLUSIONS

The type of material used for implant-supported cement-retained crowns had a statistically significant effect on marginal adaptation and bond strength. Resin nano-ceramic implant-supported cement-retained crowns had better marginal adaptation and higher bond strength than those manufactured using lithium disilicate.

Misfit of Implant-Supported Zirconia (Y-TZP) CAD-CAM Framework Compared to Non-Zirconia Frameworks: A Systematic Review

Objective: The aim of the study was to systematically review the overall outcomes of studies comparing the misfit of yttria-stabilized zirconia (Y-TZP) CAD-CAM implant-supported frameworks with frameworks fabricated with other materials and techniques. Methods: An electronic literature search of English literature was performed using Google Scholar, Scopus, Web of Science, MEDLINE (OVID), EMBASE, and PubMed, using predetermined inclusion criteria. Specific terms were utilized in conducting a search from the inception of the respective database up to May 2022. After the search strategy was applied, the data were extracted and the results were analyzed. The focused question was: Is the misfit of the implant-supported zirconia CAD-CAM framework lower than that of non-Y-TZP implant-supported fixed restorations? Results: Eleven articles were included for qualitative assessment and critical appraisal in this review. In the included studies, Y-TZP CAD-CAM implant-supported frameworks were compared to Titanium (Ti), Ni-Cr, Co-Cr, PEEK and high-density polymer, and cast and CAD-CAM frameworks. The studies used scanning electron microscopy, one-screw tests, digital or optical microscopy, 3D virtual assessment, and replica techniques for analyzing the misfit of frameworks. Six studies showed comparable misfits among the Y-TZP CAD-CAM frameworks and the controls. Three studies showed higher misfits for the Y-TZP CAD-CAM frameworks, whereas two studies reported lower misfits for Y-TZP CAD-CAM implant frameworks compared to controls. Conclusion: Y-TZP CAD-CAM implant-supported frameworks have comparable misfits to other implant-supported frameworks. However, due to heterogeneity in the methodologies of the included studies, the overall numerical misfit of the frameworks assessed in the reviewed studies is debatable.

Marginal gap and fracture resistance of implant-supported 3D-printed definitive composite crowns: An in vitro study

OBJECTIVES

To compare the marginal gap and fracture resistance of implant-supported 3-dimensional (3D) printed definitive composite crowns with those fabricated by using 3 different millable materials.

MATERIAL AND METHODS

A prefabricated abutment was digitized by using a laboratory scanner (E4 Lab Scanner) and a complete-coverage maxillary first premolar crown was designed (Dental Designer). Forty crowns were fabricated either by 3D printing (Saremco Print Crowntec, SP) or milling (Brilliant Crios, BC; Vita Enamic, VE; Cerasmart 270, CS) (n = 10). Baseline marginal gap values were evaluated by measuring 60 predetermined points on an abutment (15 points for each side) with a stereomicroscope at ×40 magnification. Marginal gap values were reevaluated after adhesive cementation. Load-to-fracture test was performed by using a universal testing machine. Two-way analysis of variance (ANOVA) was used to evaluate the effect of material type and cementation on marginal gap values. While Tukey HSD tests were used to compare the materials' marginal gap values before and after cementation, the effect of cementation on marginal gap values within each material was analyzed by using paired samples t-tests. Fracture resistance data were analyzed by using 1-way ANOVA (α=0.05).

RESULTS

Material type and cementation significantly affected marginal gap values (P < .001). Regardless of cementation, SP had the lowest marginal gap values (P < .001), while the differences among milled crowns were nonsignificant (P ≥ .14). Cementation significantly increased the marginal gap values (P < .001). Material type did not affect fracture resistance values (F = 1.589, P = .209).

CONCLUSION

Implant-supported 3D-printed composite crowns showed higher marginal adaptation compared with the milled crowns before and after cementation. In addition, all crowns endured similar forces before fracture.

Marginal fit of 3-unit CAD-CAM zirconia frameworks fabricated using cone beam computed tomography scans: an experimental study

Whether cone beam computed tomography (CBCT) scans can be used for the fabrication of computer-aided design and computer-aided manufacturing (CAD-CAM) fixed dental prostheses (FDPs) is not known. The purpose of the present study was to compare the marginal fit of 3-unit zirconia FDPs fabricated by using CBCT or 3-dimensional (3D) laboratory scanning. Extracted second premolar and molar teeth in a maxillary typodont model were prepared. The first molar was removed and the typodont model was scanned with a laboratory or a CBCT scanner to generate two virtual 3D cast groups (3DL and CBCT). Forty four 3-unit zirconia FDPs were designed on virtual casts and milled. The vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy at seven locations on each abutment. A total of 616 measurements were made at 14 fixed locations in two groups of 22 specimens. The VMD data for 3DL and CBCT groups were statistically analyzed using the Mann-Whitney U test (α = 0.05). The mean VMDs on premolar ranged between 44 and 55 µm (median: 43-55 µm) in 3DL, and 74 and 100 µm (median: 72-93 µm) in CBCT; and on the molar, between 47 and 114 µm (median: 46-114 µm) in 3DL, and 91 and 162 µm (median: 93-156 µm) in CBCT. There was a significant difference between the gaps in 3DL and CBCT groups (p < 0.001). FDPs fabricated using 3D laboratory scanner had significantly smaller VMDs. Nevertheless, the 3-unit zirconia FDPs fabricated using CBCT scans presented promising marginal integrity.

Implant framework misfit: A systematic review on assessment methods and clinical complications

BACKGROUND

The fit of implant-supported prostheses is of prime importance for the long-term success of implant therapy.

PURPOSE

This systematic review aimed to evaluate recent evidence on current techniques for assessing implant-framework misfit, its associated strain/stress, and whether these misfits are related to mechanical, biological, and clinical consequences.

MATERIALS AND METHODS

An electronic search for publications from January 2010 to October 2020 was performed using the Pubmed, Embase, Web of Science, and Cochrane Library databases with combined keywords on implant-framework misfit assessments and related clinical complications. Inclusion and exclusion criteria were applied. After full-text analyses, data extraction was implemented on current techniques of misfit assessment and the relationship between the misfit and the induced strain/stress.

RESULTS

A total of 3 in vivo and 92 in vitro studies were selected, including 47 studies on quantifying the degree of implant-framework misfit with dimensional techniques, 24 studies measuring misfit-induced strain/stress with modeling techniques, and 24 studies using both methods. The technical details, advantages, and limitations of each technique were illustrated. The correlation between the implant-framework misfit and the induced strain/stress has been revealed in vitro, while that with the biological complications and implant/prostheses failure was weak in clinical studies.

CONCLUSIONS

Dimensional and modeling techniques are available to measure the implant-framework misfit. The passivity of implant-supported fixed prostheses appeared related to the induced strain/stress, but not the clinical complications. Further studies combining three-dimensional (3D) assessments using dimensional and modeling techniques was needed.

Digital versus conventional workflow for the fabrication of multiunit fixed prostheses: A systematic review and meta-analysis of vertical marginal fit in controlled in vitro studies

STATEMENT OF PROBLEM

Limited evidence is available for the marginal fit of multiunit fixed dental prostheses (MFDPs) fabricated with digital technologies compared with those fabricated with conventional techniques.

PURPOSE

The purpose of this systematic review and meta-analysis was to answer the following question: Does digital workflow for the fabrication of tooth-supported or implant-supported MFDPs provide better marginal fit than the conventional workflow?

MATERIAL AND METHODS

PubMed, SCOPUS, EBSCO, and Web of Science databases were searched for controlled in vitro studies addressing direct comparison of the fit of MFDPs produced with digital or conventional workflows and excluding studies addressing interim restorations, MFDPs on mixed abutments (teeth and implants), or studies in which reproduction of the basic master cast was performed in 1 group. Vertical and horizontal marginal fit were the primary outcomes; meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, with subgroup analysis for tooth- or implant-supported MFDPs.

RESULTS

Four studies published between 2011 and 2015 met the inclusion criteria and were included in the review. They investigated 3-unit partial fixed dental prostheses, exhibited a high degree of heterogeneity, and reported data only regarding vertical marginal fit. MFDPs fabricated with digital techniques presented a nominally higher vertical marginal discrepancy than those fabricated with the conventional technique, but the mean difference (MD) (19.8 μm, 95% confidence interval [CI]: -12.1; 51.7) has no statistical significance. The same is also applicable to subgroup analysis for a tooth-supported (MD=45.8 μm, 95% CI: -45.4; 137.0) or implant-supported (MD=14.7 μm, 95% CI: -38.6; 68.1) MFDP.

CONCLUSIONS

Digital technologies offer a reliable alternative to conventional techniques for the fabrication of tooth- or implant-supported 3-unit fixed partial dentures; additional studies with up-to-date technologies and for prostheses with more than 3 units are recommended to provide stronger evidence.

Discrepancy of complete-arch titanium frameworks manufactured using selective laser melting and electron beam melting additive manufacturing technologies

STATEMENT OF PROBLEM

Titanium frameworks for implant-supported prostheses can be additively manufactured using different powder-based fusion technologies, including selective laser melting (SLM) and electron beam melting (EBM). Some manufacturers have developed a technique that combines the printing of the framework with the subsequent machining of the implant interface. Whether these technologies produce frameworks with acceptable accuracies is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the discrepancy obtained from the digitizing procedures of the definitive cast, the implant-prosthesis discrepancy, and the distortion of the manufacturing processes in the fabrication of titanium frameworks for implant-supported complete-arch prostheses manufactured using SLM and EBM additive manufacturing technologies.

MATERIAL AND METHODS

A completely edentulous mandibular definitive cast with 4 implant analogs and a replica of a screw-retained interim restoration was obtained. A standard tessellation language (STL) file of the framework design was prepared using dental software (Exocad). Six frameworks were manufactured using either SLM (3D Systems) or EBM (Arcam) technologies. Discrepancy (μm) was measured at the x- (mesiodistal), y- (buccolingual), and z- (occlusogingival) axes by using the formula 3D=x²+y²+z² three times by best-fit superimposure of the definitive cast STL file, the definitive cast titanium framework, and the framework STL file by using a coordinate measuring machine (CMM) controlled by software (Geomagic). The Kruskal-Wallis and Mann-Whitney U statistical tests were used (α=.05).

RESULTS

The digitizing procedures of the definitive cast showed a mean accuracy of 3 ±3 μm. Except for the z-axis (P<.05), no significant differences were observed between the SLM and EBM technologies for implant prosthesis discrepancy for the x- or y-axis (P>.05). The most favorable results were obtained in the z-axis, representing the occlusogingival direction. Three-dimensional discrepancy measurements in all comparisons ranged between (60 ±18 μm and 69 ±30 μm) and were not statistically significant (P>.05). The highest discrepancy was observed in the y-axis (37 to 56 μm), followed by the x- (16 to 44 μm) and z- (6 to 11 μm) axes (P<.05).

CONCLUSIONS

The titanium frameworks analyzed for a complete-arch implant-supported prosthesis fabricated using either the SLM or EBM additive technologies showed a clinically acceptable implant-prosthesis discrepancy, where similar discrepancies on the x-, y-, and z-axes were found between the additive manufacturing technologies. Both technologies showed comparable abilities to manufacture the STL file additively on the x-, y-, and z-axes.

Passivity of conventional and CAD/CAM fabricated implant frameworks

The objective of this research was to evaluate the passivity by measuring the passive fit and strain development of frameworks screwed on abutments, made by CAD/CAM technology, and to compare these parts with samples manufactured by conventional casting. Using CAD/CAM technology, four samples were made from zirconia (Zircad) and four samples were manufactured from cobalt-chrome (CoCrcad). The control groups were four specimens of cobalt-chrome, made by one-piece casting (CoCrci), with a total of 12 frameworks. To evaluate the passive fit, the vertical misfit at the abutment-framework interface was measured with scanning electron microscopy (250×) when only one screw was tightened. The mean strain in these frameworks was analyzed by photoelasticity test. A significant difference in the passive fit was observed between the control and sample groups. CoCrcad exhibited the best value of passive fit (48.76±13.45 µm) and CoCrci the worst (187.55±103.63 µm); Zircad presented an intermediate value (103.81±43.15 µm). When compared to the other groups, CoCrci showed the highest average stress around the implants (17.19±7.22 kPa). It was concluded that CAD/CAM-fabricated frameworks exhibited better passivity compared with conventionally fabricated frameworks. CAD/CAM-fabricated Co-Cr frameworks may exhibit better passive fit compared with CAD/CAM-fabricated zirconia frameworks. Even so, similar levels of stress were achieved for CAD/CAM-fabricated frameworks.

In vitro assessment of the marginal and internal fits of interim implant restorations fabricated with different methods

STATEMENT OF PROBLEM

The fit of an interim implant restoration (IIR) is important for the effective treatment of patients with partial edentulism. However, no clinical trials have evaluated the marginal and internal fittings achieved with various fabrication methods.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the marginal and internal discrepancies in IIRs produced with 3 different methods.

MATERIAL AND METHODS

Partially edentulous maxillary and mandibular casts from a transfer abutment were used. Prostheses were prepared by applying wax to the implant abutment. Shapes were copied using putty. IIRs were fabricated from poly(methyl methacrylate) for a conventional system with thermoplastic resin (CTR, n=40), a 4-axial milling machine with a crown-designed standard template library for a subtractive manufacturing system with Pekkton milling (SPM, n=40), and a 3-dimensional printer for an additive manufacturing system with digital light processing (ADL, n=40). The marginal and internal discrepancies were evaluated in each group using the silicone replica technique. The space between the abutment and the intaglio surface of the prosthesis was evaluated with a digital microscope (×160 magnification). Results were analyzed with nonparametric 2-way analysis of variance using rank-transformed values and Tukey post hoc test (α=.05).

RESULTS

The fabricated IIRs were significantly different at all points (P<.001). Moreover, ADL was superior to CTR and SPM. IIRs were significantly different only at the intermarginal discrepancy (the vertical discrepancy between the crown and the point where the margin becomes round and changes to the axial wall), the axiogingival discrepancy (the vertical discrepancy between the internal surface and the axial wall adjacent to the gingival wall of the abutment), and the occlusal discrepancy (the vertical discrepancy between the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P<.001). No significant differences were found among the IIRs at the marginal discrepancy (the vertical discrepancy between the abutment margin and the crown; P>.111) and the axio-occlusal discrepancy (the vertical discrepancy between the axial wall adjacent to the occlusal wall of the abutment and the internal surface; this discrepancy comprises the internal discrepancy; P>.257).

CONCLUSIONS

ADL was superior to the other 2 fabrication methods. However, all 3 methods were suitable because they produced a marginal fit which was within the clinically acceptable range.

Clinical Advantages and Limitations of Monolithic Zirconia Restorations Full Arch Implant Supported Reconstruction: Case Series

Purpose. The purpose of this retrospective case series is to evaluate the clinical advantages and limitations of monolithic zirconia restorations for full arch implant supported restorations and report the rate of complications up to 2 years after insertion. Materials and Methods. Fourteen patients received implant placement for monolithic zirconia full arch reconstructions. Four implants were placed in seven arches, eleven arches received six implants, two arches received seven implants, two arches received eight implants, and one arch received nine implants. Results. No implant failures or complications were reported for an implant survival rate of 100% with follow-up ranging from 3 to 24 months. Conclusions. Monolithic zirconia CAD-/CAM-milled framework restorations are a treatment option for full arch restorations over implants, showing a 96% success rate in the present study. Some of the benefits are accuracy, reduced veneering porcelain, and minimal occlusal adjustments. The outcome of the present study showed high success in function, aesthetics, phonetics, and high patient satisfaction.

Influence of CAD/CAM on the fit accuracy of implant-supported zirconia and cobalt-chromium fixed dental prostheses

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.