Influence of sterilization on the retention forces of lithium disilicate and polymer-infiltrated ceramic-network crowns bonded to titanium base abutments: An in-vitro study.

OBJECTIVES: The aim of this study was to evaluate the effect of sterilization on the retention forces of lithium disilicate (LD) and polymer-infiltrated ceramic network (PICN) crowns bonded to titanium base (Ti-base) abutments. MATERIALS AND METHODS: Forty LD and 40 PICN crowns were milled and then bonded to 80 Ti-bases with two resin composite cements: Multilink Hybrid Abutment (mh) and Panavia V5 (pv) for a total of 8 groups (n = 10). Half of the specimens (test) underwent an autoclaving protocol (pressure 1.1 bar, 121°C, 20.5 min) and the other half not (control). Restorations were screw-retained to implants, and retention forces (N) were measured with a pull-off testing machine. The surfaces of the Ti-bases and the crowns were inspected for the analysis of the integrity of the marginal bonding interface and failure mode. Student's t-test, chi-square test, and univariate linear regression model were performed to analyze the data (α = 0.05). RESULTS: The mean pull-off retention forces ranged from 487.7 ± 73.4 N to 742.2 ± 150.3 N. Sterilized groups showed statistically significant overall higher maximum retention forces (p < .05), except for one combination (LD + mh). Sterilization led to an increased presence of marginal gaps and deformities compared to no-sterilization (p < .001), while no statistically significant relationship was found between failure mode and sterilization (p > .05). CONCLUSIONS: Sterilization may have a beneficial effect on the retention forces of LD and PICN crowns bonded to titanium base abutments, although it may negatively influence the integrity of the marginal bonding interface.

Effect of implant type on the stability of cantilever fixed dental prostheses: An in vitro study.

OBJECTIVES: To simulate the replacement of a premolar with an implant-supported cantilever fixed dental prosthesis (ICFDP) and how the fracture load is affected by implant type, positioning within the zirconia blank, and aging protocol. MATERIALS AND METHODS: Seventy-two ICFDPs were designed either within the enamel- or dentin layer of a 4Y-PSZ blank for bone-level and tissue-level titanium-zirconium implants. Fracture load was obtained on the cantilever at baseline (no aging) or after aging in a chewing simulator with the load applied within the implant axis (axial aging) or on the cantilever (12 groups with n = 6). A three-way ANOVA was applied (α = .05). RESULTS: A three-way ANOVA revealed a significant effect on fracture load values of implant type (p = .006) and aging (p < .001) but not for the position within the zirconia blank (p = .847). Fracture load values significantly increased from baseline bone level (608 ± 118 N) and tissue level (880 ± 293 N) when the implants were aged axially, with higher values for tissue level (1065 ± 182 N) than bone level (797 ± 113 N) (p < .001). However, when the force was applied to the cantilever, fracture load values decreased significantly for tissue-level (493 ± 70 N), while values for bone-level implants remained stable (690 ± 135 N). CONCLUSIONS: For ICFDPs, the use of bone-level implants is reasonable as catastrophic failures are likely to be restricted to the restoration, whereas with tissue-level implants, the transmucosal portion of the implant is susceptible to deformation, making repair more difficult.

Small-diameter titanium grade IV and titanium-zirconium implants in edentulous mandibles: Ten-year results from a double-blind, randomised controlled split-mouth core-trial.

The goal of this extension study was to compare the 10-year outcome of 3.3 mm diameter titanium-zirconium (TiZr) or grade IV titanium (Ti) implants in mandibular implant-overdentures. MATERIALS AND METHODS: This study is the 10-year follow-up from a randomised, controlled, double-blind, split-mouth multicentre clinical trial. Patients with edentulous mandibles had received two implants in the interforaminal region (bone-level, diameter 3.3 mm, microrough surface), one of TiZr (test) and one of Ti (control). Implant survival and success, plaque and sulcus bleeding indices, probing pocket depth, gingival margin, clinical attachment level and radiographic crestal bone levels were evaluated. RESULTS: Fifty of 91 patients with implants were available for the 10-year examination and 36 patients were valid for the intent-to-treat (ITT) analysis. The implant success rate was calculated as 94.6% and 91.9% for the TiZr implants and the Ti implants respectively. Four implants were lost (TiZr = 1; Ti = 3) in the entire study period. Kaplan-Meier survival analyses estimated 10- year implant survival rate for TiZr to 98.9% and Ti 95.8%.The mean of total and functional crestal bone loss was 1.49 mm (±1.37 mm) and 0.82 mm (±1.09 mm) in the TiZr group and 1.56 mm (±1.34 mm) and 0.85 mm (±1.16 mm) in the Ti group. CONCLUSIONS: This split-mouth design RCT on mandibular implant-overdentures evidenced, bearing in mind its follow-up time-related reduced cohort size, high 10-year implant success- and survival rates. These results confirm TiZr as well-suited implant material for realising small-diameter implants. Registered on www. CLINICALTRIALS: gov: NCT01878331.

A randomized clinical trial on zirconia versus titanium implants in maxillary single tooth replacement.

OBJECTIVES: This RCT aimed to compare zirconia and titanium dental implants in the maxillary premolar region. The comparison was based on marginal bone level (MBL) changes, clinical parameters, aesthetic outcomes, and patient related outcome measures (PROMs) 1 year after prosthetic loading. MATERIALS AND METHODS: Fifty patients were randomly assigned to receive either a zirconia (ZrO2, n = 25) implant or a titanium (Ti, n = 25) bone-level implant. Implants were provided with a lithium disilicate crown 3 months after placement. Follow-up was at 1 month and after 1 year. The primary outcome pertained to changes in MBL. Reported secondary outcomes consisted of implant survival, peri-implant tissue health, aesthetics, and PROMs. RESULTS: Mean MBL change after 1 year was 0.01 mm (SD = 0.45; min = 0.72, max = 0.86) for ZrO2 and -0.09 mm (SD = 0.34; min = 0.53, max = -1.06) for Ti (p = .439). Scores for the other clinical outcome parameters and PROMs were generally favorable, with no significant differences. However, significant differences were found for the aesthetic outcomes regarding two criteria: (a) level of facial mucosa (p = .022), in favor of Ti, and (b) root convexity/soft tissue color and texture (p = .005) in favor of ZrO2. CONCLUSION AND CLINICAL IMPLICATIONS: The ZrO2 and Ti implant types used in this study, replacing a single missing maxillary premolar, show a comparable outcome in terms of MBL change after 1 year. Clinical and aesthetic parameters, as well as PROMs, are favorable and similar between both implant types after 1 year of prosthetic loading. These short-term study results suggest that both are suitable for clinical use.

Evaluation of bond strength between zirconia milled ceramic material and veneered dental porcelain.

This study aimed at examining the bond strength between zirconia and ceramic veneer, following the ISO 9693 guidelines. A total of fifty specimens of zirconia/ceramic-veneer system were produced using two commercial zirconias (VITA YZ-HTWhite and Zolid HT+ White, referred to as Group A and Group B, respectively) and a ceramic-veneering material (Zirkonia 750). The microstructure (via x-ray diffraction analysis, XRD and Secondary Electron mode, SEM) and the mechanical properties (via 3-point bending tests) of the two groups were assessed. Then, experiments were conducted according to the ISO 9693 and conventional protocols applied for producing zirconia/ceramic-veneer restorations. Bond strength values, measured by 3-point bending tests, were 34.42 ± 7.60 MPa for Group A and 31.92 ± 6.95 MPa for Group B. SEM observations of the cohesively fractured surfaces (on the porcelain side) and the examination for normality using the Shapiro-Wilk test suggested the use of Weibull statistical analysis. Median strength (σ50%) for Group A and Group B was 34.76 and 32.22 MPa, while the characteristic strength (σ63.2%) was 35.78 and 33.14 MPa, respectively. The Weibull modulus disparity between groups (12.69 and 13.07) was not significant. Bond strength exceeded the ISO 9693 minimum of 20 MPa, suggesting satisfactory strength for clinical use.

Microstructure, physical and mechanical properties of dental polychromic multilayer zirconia of uniform composition.

The present study aimed to compare the microstructure, physical, and mechanical properties of three commercially available dental polychromatic multilayer zirconia materials of uniform composition: Dima Mill Zirconia ML, VITA YZ/ST Multicolor, and VITA YZ/XT Multicolor (with 3, 4, and 5 mol% Y2 O3 , respectively); thus, the influence of Y2 O3 content on the above properties of the produced materials was experimentally studied. Homogeneous zirconia ceramics with a dense micro- and nanostructure, without pores or defects, were produced after milling the blocks and sintering, which resulted in yttrium-stabilized tetragonal and cubic zirconia. Statistical analysis of the results of measurable magnitudes was performed by the one-way ANOVA test. The increase of Y2 O3 content (from 3 to 5 mol%) favored larger grain and crystallite sizes and a decrease of the values of the mechanical properties; yet, the differences were statistically insignificant. Clinically, these differences are expected to have no impact on their function in the oral cavity, both in terms of their fracture propensity and the damage that can be caused to the opposing teeth. Accordingly, the experimental results qualify the polychromic multilayer zirconia ceramics of uniform composition fabricated by milling technology for use in dental restorations.

Finishing technique effect on strength of zirconia-reinforced lithium silicate ceramic.

The aim of this study was to evaluate the effect of two finishing techniques, glazing or polishing, in comparison with the as-cut condition, on the biaxial-flexural-strength (BFS) of a zirconia-reinforced lithium silicate ceramic (ZLS). Cylinders were milled from CAD/CAM blocks and sliced to obtain disc-shaped specimens (ISO6872:2015). Polished and glazed specimens were processed following the manufacturer's instructions. Thirty-three specimens were obtained for each condition and microstructural and BFS/fractographic characterizations were performed. BFS and roughness data were analyzed using Weibull statistics and ANOVA one-way with Tukey post-hoc test, respectively. While a rougher surface was observed for as-cut specimens, smoother surfaces were observed for polished and glazed ZLS at microscopical evaluation and confirmed through surface-roughness evaluation. X-ray spectra depicted a glass phase for all groups and characteristic metasilicate, lithium disilicate, and lithium phosphate peaks for the as-cut and polished specimens. Glazed specimens showed higher characteristic strength than polished and as-cut specimens, which did not differ significantly. While higher Weibull-modulus was observed for the polished than for the as-cut specimens, no statistically significant differences were noted between glazed and polished, and between glazed and as-cut specimens. ZLS presents higher strength when glazed, and polishing increases the structural reliability of the material relative to the as-cut condition. Both finishing techniques reduced surface roughness similarly.

Impact of Auxiliary Features on Retention of Short Dental Crowns: An In-Vitro Analysis of Box and Groove Preparations.

BACKGROUND Several auxiliary features have been proposed to achieve sustainable retention for short-prepared dental crowns; however, achieving retention is challenging. This study aimed to assess the impact of increased total occlusal convergence and auxiliary preparation factors like box and groove on the retention form of short tooth preparations. MATERIAL AND METHODS Eighty resin machine-milled dies with a height of 3 mm and a deep chamfer margin of 1 mm were prepared to mimic the short-prepared molar. Initially, 2 teeth were prepared following the guidelines, and the total occlusal convergence was kept at 10° and 20°, respectively. Auxiliary features such as the proximal box and buccal groove were prepared on separate 20° dies. Eighty dies were prepared with 10 samples each for 10°, 20°, 20° with proximal box and 20° with buccal groove for zirconia (n=40) and metal crowns (n=40). Cementation was done with glass ionomer luting cement, and a pull-off test was conducted. Data were analyzed using one-way analysis of variance and post hoc fisher least significant difference test (P<0.05). RESULTS The highest mean was observed in the proximal box group with the metal crown (14.59), and the lowest in the group with 20° zirconia crowns (9.12). Within groups, the highest retentive values were found for the 20° taper with proximal box preparation; the lowest was for the 20° taper group. CONCLUSIONS Within the study limitations, it could be concluded that incorporating a proximal box or buccal groove in short tooth preparations with an increased total occlusal convergence improved retentive values.

Influence of Chairside Simulated Adjustment (Finishing and Polishing) Protocol and Chlorhexidine Mouthwash Immersion on Color Stability and Translucency of 2 and 3 Preshaded Multilayered Monolithic Zirconia.

BACKGROUND Preshaded monolithic zirconia (MLZ) is reported to have high translucency. This study aimed to assess the effect of chlorhexidine gluconate (ChG) mouthwash on color and translucency parameter (TP) of 2 different preshaded MLZ dental ceramics after clinical adjustment. MATERIAL AND METHODS Two MLZ disk-shaped specimens [NPM (Nacera Pearl Multi-Shade) (n=72) and CZM (Ceramill Zolid FX Multilayer)] (n=72) were simulated for clinical adjustment, finished, and polished using 2 adjustment kits [recommended kit, third-party kit: Diasynt Plus and SUN (n=12 each)] and later immersed in ChG mouthwash (Avohex) for 2 weeks. Difference in color (ΔE) and TP (Y) were calculated using the CIELab formula after measuring the coordinates (Lab) with a colorimeter. Individual changes in color and TP were assessed on the Clinical acceptance (perceptible) threshold (CAT/CPT) and Translucency perception threshold (TPT), respectively. Differences between the 2 ceramics were assessed using one-way ANOVA and post hoc tests, with all differences considered significant at P<0.05. RESULTS NPM and CZM differed in color at baseline despite having the same Vita shade combination. Between the 2 preshaded MLZ ceramics, NPM showed significant changes in color when adjusted with a third-party kit. Chlorhexidine produced changes in color and TP that were designated as clinically perceptible (ΔE=1.0 to 3.3) on the CAT/CPT and TPT scales, irrespective of the adjustment kit used. ChG produced the least or no changes in glazed MLZ specimens. CONCLUSIONS ChG mouthwash, whenever prescribed for preshaded MLZ restoration, should be adjusted prior to final glazing to avoid clinical adjustments that adversely affects color and translucency of the restoration.

Factors Influencing Dentists' Choice of Restorative Materials for Single-Tooth Crowns: A Survey Among Saudi Practitioners.

BACKGROUND Material selection is crucial in restorative dentistry, influenced by aesthetics, material properties, and tooth location. This understanding is key for advancing dental practices and patient outcomes. The present study aimed to assess dentists' preferences for restorative materials in single-tooth crowns (SC) and how abutment tooth location and preparation margins influence these choices. MATERIAL AND METHODS A web-based pre-validated questionnaire survey was conducted among 811 actively practicing dentists in Saudi Arabia. RESULTS In posterior teeth, we found that ceramic was the most preferred material for SC regardless of the abutment tooth location and location of margins, followed by porcelain fused to metal (PFMs). In anterior teeth, ceramics were preferred, followed by CAD/CAM-based resin SC. Among the choice of ceramics in teeth for both supra-gingival margins, monolith zirconia was the most-preferred material for SC fabrication in posterior teeth, followed by zirconia-reinforced lithium silicate ceramic. Similarly, for sub-gingival margins, monolith zirconia crowns were the most popular option in posterior teeth among the respondents, with the highest in the mandibular molar region. In the anterior region, layered zirconia was the least preferred, and lithium disilicate ceramics was the most-favored option. A statistically significant difference existed between supra- and subgingival preparation for teeth 11 (P=0.01), 16 (P=0.03), and 34 (P=0.02). CONCLUSIONS Ceramic was the material of choice among Saudi dentists for replacement of SC, irrespective of the location and preparation margin. Monolith zirconia was usually selected for posterior teeth and lithium disilicate ceramics was the top choice in anterior teeth.

The Impact of Repeated Steam Sterilization Cycles on the Efficacy of Chairside Adjustment Kits for Polishing Monolithic Multi-Layered Zirconia Dental Restoration Material.

BACKGROUND Before insertion, chairside adjustment kits are heat sterilized for positioning and polishing dental restorations. This study aimed to evaluate the effects of 2 steam sterilization cycles on the efficacy of polishing highly translucent monolithic zirconia (HTMLZ) dental restoration material. MATERIAL AND METHODS 100 HTMLZ disc-shaped specimens were adjusted (grinding, finishing, polishing) with EVE Diacera kit. Two steam sterilization techniques [standard (Gp S), immediate/flash (Gp (F)] of CAK were further subgrouped based on number of sterilization cycles [cycle 1 (control), cycle 5, 10, 15, and 20 (experimental)] (n=10 each). Each subgroup accordingly was evaluated for average surface roughness (Ra) and root mean square roughness (Rq) using a profilometer. Mean and standard deviation of 5 subgroups were statistically analyzed using one-way ANOVA/post hoc Tukey's test. Scanning electron microscopy complemented Ra, Rq measurements. Statistical differences of P≤0.05 were considered significant. RESULTS HTMLZ specimens in both groups showed increased (Ra/Rq) values after repeated sterilization of EVE Diacera kit, with Gp F showing lesser increase than Gp S (20 cycles). Gp F at 10 cycles and Gp S at 15 cycles showed clinically unacceptable roughness threshold (0.25 µm). Differences between subgroups for Ra and Rq values were significant (P≤0.05) with less differences within groups observed in early cycles (1, 10). Results validate the manufacturer's recommendations of using flash sterilization/10 cycles for EVE Diacera kit. CONCLUSIONS Repeated sterilization reduces efficacy of chairside adjustment kit to produce smooth surfaces on HTMLZ. This study recommends flash sterilization to a maximum of 10 times to get the clinically acceptable results of Ra and Rq.

Initial damage and failure load of zirconia-ceramic and metal-ceramic posterior cantilever fixed partial dentures.

OBJECTIVES: The aim of this study was to compare failure load and initial damage in monolithic, partially veneered, and completely veneered (translucent) zirconia cantilevered fixed partial dentures (CFPDs), as well as completely veneered metal-ceramic CFPDs under different support and loading configurations. MATERIALS AND METHODS: Eight test groups with anatomically congruent CFPDs (n = 8/group) were fabricated, differing in CFPD material/support structure/loading direction (load applied via steel ball (Ø 6 mm) 3 mm from the distal end of the pontic for axial loading with a 2-point contact on the inner cusp ridges of the buccal and oral cusps and 1.3 mm below the oral cusp tip for 30° oblique loading): (1) monolithic zirconia/CoCr abutment teeth/axial, (2) monolithic zirconia/CoCr abutment teeth/oblique, (3) partially veneered zirconia/CoCr abutment teeth/axial, (4) partially veneered zirconia/CoCr abutment teeth/oblique, (5) completely veneered zirconia/CoCr abutment teeth/axial, (6) completely veneered CoCr/CoCr abutment teeth/axial (control group), (7) partially veneered zirconia/implants/axial, and (8) partially veneered zirconia/natural teeth/axial. Restorations were artificially aged before failure testing. Statistical analysis was conducted using one-way ANOVA and Tukey post hoc tests. RESULTS: Mean failure loads ranged from 392 N (group 8) to 1181 N (group 1). Axially loaded monolithic zirconia CFPDs (group 1) and controls (group 6) showed significantly higher failure loads. Oblique loading significantly reduced failure loads for monolithic zirconia CFPDs (group 2). Initial damage was observed in all groups except monolithic zirconia groups, and fractography revealed design flaws (sharp edges at the occlusal boundary of the veneering window) in partially veneered zirconia CFPDs. CONCLUSIONS: Monolithic zirconia CFPDs might be a viable alternative to completely veneered CoCr CFPDs in terms of fracture load. However, oblique loading of monolithic zirconia CFPDs should be avoided in clinical scenarios. Design improvements are required for partially veneered zirconia CFPDs to enhance their load-bearing capacity. CLINICAL RELEVANCE: Monolithic zirconia may represent a viable all-ceramic alternative to the established metal-ceramic option for CFPD fabrication. However, in daily clinical practice, careful occlusal adjustment and regular monitoring should ensure that oblique loading of the cantilever is avoided.

Effect of zirconia surface conditioning before glazing on the wear of opposing enamel: an in vitro study.

OBJECTIVES: This in vitro study aimed to evaluate the wear of natural teeth opposing 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with different surface conditions. MATERIALS AND METHODS: Sixty 3Y-TZP specimens were randomly assigned to six groups (n = 10), differing in surface condition. In three groups, the samples underwent glazing-with the glaze applied to roughened (i.e., 106-µm-grit diamond-finished), as-sintered, and polished zirconia. The three remaining groups consisted of unglazed specimens: solely polished samples and diamond-finished samples (106-µm-grit and 46-µm-grit) without further conditioning. Two-body wear was evaluated at extracted, non-carious molars (n = 60), which served as antagonists in chewing simulation (10,000 masticatory cycles, 49N load). As a control, natural teeth with intact enamel surfaces were tested against natural molars (n = 10). All samples were 3D-scanned before and after the chewing simulation (7 Series, Straumann). Volume loss was calculated (Inspect Software, GOM), and statistically analyzed (SPSS Statistics 24, IBM). RESULTS: Volume loss of the natural antagonists decreased in the following order: 106-µm-grit diamond-finished zirconia (4.6 ± 2.5 mm3), glazed 106-µm-grit diamond-finished zirconia (3.8 ± 1.1 mm3), glazed as-sintered zirconia (3.5 ± 0.9 mm3), 46-µm-grit diamond-finished zirconia (1.7 ± 0.6 mm3), control (1.6 ± 0.7 mm3), glazed polished zirconia (1.4 ± 0.5 mm3), and solely polishing (0.4 ± 0.2 mm3). Even when polishing the surfaces before glazing, volume loss was not mitigated to the same extent as after polishing alone. CONCLUSIONS: The zirconia surface condition beneath the glazing influences antagonist wear. Although polishing before glazing resulted in acceptable levels of antagonist wear, this approach did not yield as favorable results as polishing alone. CLINICAL RELEVANCE: For operators favoring glazing, pre-polishing the zirconia surface could be advantageous to reduce wear.

Biaxial flexural strength of 3D-printed 3Y-TZP zirconia using a novel ceramic printer.

OBJECTIVES: To compare the strength and reliability of 3D-printed 3Y-TZP zirconia manufactured with various printing orientations and staining. MATERIALS AND METHODS: A total of one-hundred cylindrical zirconia specimens were designed and fabricated using 3D printing and processed according to ISO 6872 standards. Of these specimens, 80 were 3D printed using the new ZIPRO-D (ZD) 3D ceramic printer. In this ZD group, 60 specimens were printed in a vertical orientation and were either stained after debinding (ZD1, x-orientation, n = 20) or not stained (ZD2, x-orientation, n = 20; ZD3, y-orientation, n = 20) and the remaining 20 specimens out of n = 80 were printed in a horizontal orientation (ZD4). Further 20 specimens out of the entire sample N = 100 were printed vertically with the CeraFab7500 3D ceramic printer (LC). All completed specimens were loaded until fracture using a universal testing machine. Biaxial flexural strengths and Weibull parameters were computed for the ZD groups and for the LC group. Group and sub-group effects were evaluated using Welch ANOVA (alpha = 0.05). RESULTS: The mean (standard deviation, SD) biaxial flexural strengths of vertically oriented ZD samples with (ZD1) and without (ZD2/ZD3) staining were 811 (197) and 850 (152) MPa, respectively (p > 0.05). The ZD4 (horizontally printed), 1107 (144) MPa, and LC (1238 (327)) MPa samples had higher mean (SD) flexural strengths than the ZD1-3 specimens. No difference was observed between the ZD4 and LC group (p > 0.05). Weibull moduli were between m = 4.6 (ZD1) and 9.1 (ZD4) in the ZD group and m = 3.5 in the LC group. CONCLUSIONS: All tested 3D-printed zirconia specimens exceeded the flexural strengths required for class 5 restorations according to ISO 6872 standards. While the flexural strengths of zirconia printed using the novel ZD device in the vertical orientation are lower than those of zirconia printed using the LC printer, the ZD printer shows at least comparable reliability. CLINICAL RELEVANCE: 3D-printing of zirconia is a new technology in dental application. Based on the presented strengths values, clinical application of 3D-printed zirconia for fixed dental protheses can be recommended.

Effect of water glass treatment for zirconia and silane coupling on bond strength of resin cement.

OBJECTIVE: To evaluate the ability of the water glass treatment to penetrate zirconia and improve the bond strength of resin cement. MATERIAL AND METHODS: Water glass was applied to zirconia specimens, which were then sintered. The specimens were divided into water-glass-treated and untreated zirconia (control) groups. The surface properties of the water-glass-treated specimens were evaluated using surface roughness and electron probe micro-analyser (EPMA) analysis. A resin cement was used to evaluate the tensile bond strength, with2 and without a silane-containing primer. After 24 h in water storage at 37 °C and thermal cycling, the bond strengths were statistically evaluated with t-test, and the fracture surfaces were observed using SEM. RESULTS: The water glass treatment slightly increased the surface roughness of the zirconia specimens, and the EPMA analysis detected the water glass penetration to be 50 µm below the zirconia surface. The application of primer improved the tensile bond strength in all groups. After 24 h, the water-glass-treated zirconia exhibited a tensile strength of 24.8 ± 5.5 MPa, which was significantly higher than that of the control zirconia (17.6 ± 3.5 MPa) (p < 0.05). After thermal cycling, the water-glass-treated zirconia showed significantly higher tensile strength than the control zirconia. The fracture surface morphology was mainly an adhesive pattern, whereas resin cement residue was occasionally detected on the water-glass-treated zirconia surfaces. CONCLUSION: The water glass treatment resulted in the formation of a stable silica phase on the zirconia surface. This process enabled silane coupling to the zirconia and improved the adhesion of the resin cement.

Repair of monolithic zirconia restorations with different direct resin composites: effect on the fatigue bonding and mechanical performance.

OBJECTIVE: The study aims to evaluate the shear bond and flexural strength fatigue behavior of yttrium-stabilized zirconia (4YSZ) repaired using different resin composites. MATERIALS AND METHODS: Cylindric specimens of 4YSZ were obtained for the bond strength (Ø = 6 mm, 1.5 mm of thickness) and biaxial flexural strength (Ø = 15 mm, 1 mm of thickness) fatigue tests and divided into 3 groups according to the repair resin composite: EVO (nanohybrid), BULK (bulk-fill), and FLOW (flowable). The zirconia surface was air-abraded with alumina particles, a 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) primer was applied, and the resin composite was build-up over the zirconia. Fatigue shear bond strength and flexural fatigue strength tests were performed (n = 15). One-way ANOVA and Tukey post hoc tests were carried out for both outcomes, besides scanning electron microscopy and finite element analysis. RESULTS: The repair material affected the fatigue shear bond strength of zirconia ceramic. The BULK group (18.9 MPa) depicted higher bond strength values than FLOW (14.8 MPa) (p = 0.04), while EVO (18.0 MPa) showed similar results to both groups. No effect was observed for the mechanical behavior (p = 0.53). The stress distribution was similar for all groups. CONCLUSION: The repair of yttrium-stabilized zirconia (4YSZ) ceramics with bulk-fill resin composites was the best option for high fatigue bond strength. However, the fatigue mechanical performance was similar regardless of the applied repair material. CLINICAL RELEVANCE: The repair of yttrium-stabilized zirconia (4YSZ) monolithic restorations may be performed with nanohybrid and bulk-fill resin composites in order to promote longevity in the treatment.

Dental implant and abutment in PEEK: stress assessment in single crown retainers on anterior region.

OBJECTIVE: Stress distribution assessment by finite elements analysis in poly(etheretherketone) (PEEK) implant and abutment as retainers of single crowns in the anterior region. MATERIALS AND METHODS: Five 3D models were created, varying implant/abutment manufacturing materials: titanium (Ti), zirconia (Zr), pure PEEK (PEEKp), carbon fiber-reinforced PEEK (PEEKc), glass fiber-reinforced PEEK (PEEKg). A 50 N load was applied 30o off-axis at the incisal edge of the upper central incisor. The Von Mises stress (σvM) was evaluated on abutment, implant/screw, and minimum principal stress (σmin) and maximum shear stress (τmax) for cortical and cancellous bone. RESULTS: The abutment σvM lowest stress was observed in PEEKp group, being 70% lower than Ti and 74% than Zr. On the implant, PEEKp reduced 68% compared to Ti and a 71% to Zr. In the abutment screws, an increase of at least 33% was found in PEEKc compared to Ti, and of at least 81% to Zr. For cortical bone, the highest τmax values were in the PEEKp group, and a slight increase in stress was observed compared to all PEEK groups with Ti and Zr. For σmin, the highest stress was found in the PEEKc. Stress increased at least 7% in cancellous bone for all PEEK groups. CONCLUSION: Abutments and implants made by PEEKc concentrate less σvM stress, transmitting greater stress to the cortical and medullary bone. CLINICAL RELEVANCE: The best stress distribution in PEEKc components may contribute to decreased stress shielding; in vitro and in vivo research is recommended to investigate this.

Zirconium as a Promising Synovial Biomarker for Loose Cemented Knee Prosthesis.

BACKGROUND: Aseptic loosening is the most common mode of failure after total knee arthroplasty. Despite this, the diagnosis often remains challenging and mainly relies on imaging modalities. Until today, no biomarker exists to aid in diagnosing loosening of the implants. As zirconium (Zr) is often found in bone cement, where it serves as radiopacifier, this study aimed to establish Zr as a synovial biomarker for loosened cemented knee prostheses. METHODS: A total of 31 patients scheduled for revision of a cemented knee prostheses were included. In all patients, the initial used cement contained Zr. After arthrotomy, specimens of synovial fluid were taken and levels of Zr were measured by inductively coupled plasma mass spectrometry. Depending on the necessary amount of force for explantation, the implants were graded "loose" or "well-fixed". Preoperative radiographs were evaluated by 2 independent physicians. RESULTS: The concentration of Zr in the synovial fluid differed significantly (P < .001) between the "loose" (mean 170.9 µg/L, range 0 to 1941 µg/L) and the "well-fixed" (mean 0.6 µg/L, range 0 to 6 µg/L) implants. The receiver operating characteristic analysis revealed 0.25 µg/l as an optimal cutoff value leading to a sensitivity of 0.84, a specificity of 0.92, a positive predictive value of 0.94, and a negative predictive value of 0.79. There was no significant difference in the diagnostic performance compared to radiographs (P = .66). CONCLUSIONS: Zirconium proved to be a reliable novel synovial biomarker for diagnosing aseptic loosening of knee prothesis fixed with cement containing Zr. This biomarker should not be interpreted in isolation, but in combination with existing diagnostic tools.

Influence of different abutment materials on the color of implant-supported restoration: A laboratory study.

PURPOSE: To investigate the effect of different abutments and crowns on the color of implant-supported restorations. METHODS: Zirconia and lithium disilicate (e.max) disks with A2 shade were fabricated to represent two crowns. The implant abutments were untreated titanium, opaqued titanium, anodized titanium, A2 shade zirconia and white zirconia. 4.0 mm-thickness zirconia and e.max specimens were used as references respectively. The crowns were placed on tested abutments with a drop of clear glycerin between them and the color was measured using a digital spectrophotometer. CIELab values were recorded to evaluate color differences (ΔE) between tested specimens and the references. RESULTS: Titanium abutments presented higher color differences than zirconia. The ΔE values with untreated titanium were higher than those with opaqued titanium. No differences were found between untreated titanium and anodized titanium for zirconia crowns. The ΔE values of zirconia crowns showed no significant differences between shade A2 zirconia and white zirconia abutments; e.max crowns showed a significant difference. The zirconia crown ΔE values were lower than those of e.max for all titanium and A2 zirconia abutments. Lithium disilicate crowns and zirconia abutments may be more suitable for implant-supported restorations. Opaqued titanium abutment may improve color in esthetic regions when a ceramic abutment cannot be used. CLINICAL SIGNIFICANCE: Lithium disilicate crowns and zirconia abutments may be an effective method to achieve excellent color matching in esthetic regions with implant-supported restorations.

Effect of toothbrushing with conventional and whitening dentifrices on monolithic zirconia after finishing procedures.

PURPOSE: To evaluate the effect of toothbrushing with conventional and whitening dentifrices on the color difference (ΔE00), gloss (Δgloss), and surface roughness (SR) of stained stabilized zirconia with 5 mol% of yttrium oxide (5Y-TZP) after polishing or glazing. METHODS: Specimens were divided into four groups (n=20): C (control), S (staining), SG (staining and glazing) and SP (staining and polishing). 50,000 toothbrushing cycles were performed with conventional (n=10) and whitening (n= 10) dentifrice slurries. The ΔE00 and Δgloss were measured using a spectrophotometer and CIEDE2000 system while SR was measured by laser confocal microscope. The ΔE00 and Δgloss data were analyzed using 2-way ANOVA, and SR data were analyzed using the linear repeated measures model, with Bonferroni's complementary test (α= 0.05). RESULTS: The ΔE00 values were beyond the acceptability threshold and no differences were found among the groups. There was no difference among groups to Δgloss after toothbrushing with conventional dentifrice while SP presented the highest values of Δgloss after toothbrushing with whitening dentifrice. Conventional dentifrice decreased the SR of stained groups and whitening dentifrice decreased SR of S and SG. The toothbrushing with conventional and whitening dentifrices promoted color difference, but did not impair gloss and surface roughness of stained 5Y-TZP. CLINICAL SIGNIFICANCE: Monolithic zirconia has been routinely used for esthetic restorations, however the type of finishing procedures that is carried out on it must be taken into consideration, in addition to the fact that brushing can influence the color difference of the material as well as interfere with surface roughness and gloss.