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Purpose: To evaluate the fracture resistance and failure mode of implant crowns made by polyether ether ketone (PEEK), zirconia, and chromium-cobalt frames, veneered by milled composite resin. Materials and Methods: Thirty-six implant analogs were mounted in acrylic blocks, and solid abutments were secured (n = 12). Single-unit frameworks were milled from PEEK, zirconia, or chromium-cobalt, and cemented to indirect composite veneers fabricated by the rapid layering technique. After thermal cycling, the fracture resistance test was performed at a speed of 0.5 mm/min, and the results were statistically analyzed by one-way analysis of variance (ANOVA) and Tukey post hoc test (P < .05). The failure mode was evaluated by a stereomicroscope ('10). Veneer failure without damage to other components was considered desirable (repairable). Results: The mean fracture resistances of PEEK, zirconia, and chromium-cobalt specimens were 2,037.24, 2,567.05, and 2,032.10 N, respectively. The Tukey post hoc test showed no significant difference between the PEEK and chromium-cobalt groups (P = .99); however, the difference was significant between zirconia and PEEK or chromium-cobalt specimens (P = .001). Failure mode was desirable in all chromium-cobalt (12 specimens), 9 zirconia, and 7 PEEK-based specimens. Conclusion: Zirconia-composite implant crowns had significantly higher fracture resistance. Given the range of maximum occlusal forces, all the specimens had clinically acceptable results. The failure mode was more desirable in chromium-cobalt, followed by zirconia-based crowns. [ABSTRACT FROM AUTHOR]

Background. This study aimed to evaluate the final color of restorations with three different core materials (Co–Cr, Zirconia, and PEEK) veneered with heat-pressed ceramic or CAD/CAM composite. Methods. Forty cores in the form of square with dimensions of 10 × 10 mm and thickness of 0.5 mm were milled from Zirconia and Co–Cr blocks and were veneered with either A2 shade CAD/CAM composite resin or heat-press ceramic (n = 10). Ten samples from polyetheretherketone blocks were only veneered with composite resins. A2 shade veneer material with 2 mm served as control for color evaluation of samples. Color parameters were measured by spectrophotometer. The data were analyzed using one-way ANOVA and Tukey's post hoc test. Results. The mean color differences between Co–Cr, Zirconia and PEEK samples veneered with composite and the control sample were 2.91 (±0.45), 3.24 (±0.33), and 2.75 (±0.35) and for Co–Cr and Zirconia in ceramic groups were 6.46 (±0.32) and 1.97 (±0.19), respectively. One-way ANOVA and Tukey's post hoc test showed a significant difference between the core groups veneered with ceramic (P ≤ 0.001). The type of core material in the composite veneered samples, however, did not make a significant difference (P = 0.186). All groups except for Co–Cr-ceramic showed clinically acceptable results (ΔE < 3.7). Conclusion. Type of core material presented significant effect on the final color of restorations when ceramic was used as a veneer material. Conversely, the final color of composite veneer restorations is not affected by the core type. CAD/CAM composites can provide adequate color coverage for different core materials without exceeding a minimum clinically acceptable thickness. [ABSTRACT FROM AUTHOR]

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Purpose: To compare marginal adaptation before and after cementation of implant-supported metal-free frameworks fabricated from zirconia, polyetheretherketone (PEEK), or composite.Materials and Methods: Thirty-six CAD/CAM frameworks were constructed from zirconia, PEEK, or composite (n = 12 per material). Marginal gap was measured using a Video Measuring Machine (VMM) system, and repeated-measures analysis of variance was employed for data analysis (P < .05).Results: Absolute marginal discrepancies of all frameworks decreased significantly after cementation (P < .05). Zirconia and composite frameworks' marginal gap values were clinically acceptable, while PEEK frameworks were judged as being on the borderline of acceptability. Zirconia demonstrated significantly better marginal adaptation than PEEK (P < .05).Conclusion: Zirconia showed the best marginal adaptation of the three tested metal-free frameworks. [ABSTRACT FROM AUTHOR]

Introduction: The prevalence of using different esthetic methods increases the possibility of close contact between them with potential adverse interactions. This study aimed to compare the surface changes (microhardness and roughness) in two types of feldspathic porcelain after laser bleaching and post-bleach polishing. Methods: 12 standardized rectangular specimens were prepared for each porcelain group (conventionally layered and CAD-CAM milled). Vickers microhardness and roughness were evaluated before and after the bleaching procedure and after polishing. Data were statistically analyzed using repeated measures ANOVA and t test (P < 0.05). Results: The surface roughness of both groups increased significantly after laser bleaching (P < 0.001 for conventional and P = 0.004 for CAD-CAM porcelains). The polishing process reduced the roughness of both groups; the reduction was significant in conventional specimens (P = 0.020). The surface hardness values did not change significantly in the groups after bleaching and post-bleach polishing stages (P = 0.142). Generally, the average surface roughness of CAD-CAM specimens was significantly lower (P < 0.001), and the surface microhardness of the CAD-CAM group was significantly higher than conventional porcelains (P = 0.011). Conclusion: Laser bleaching significantly increased the surface roughness of feldspathic porcelains; however, it did not affect the surface microhardness significantly. Unlike CAD-CAM specimens, polishing significantly improved the surface smoothness of conventional porcelains. [ABSTRACT FROM AUTHOR]

Purpose: This study was conducted to compare the fit and retention of implant-supported, metal-free copings fabricated from zirconia, polyetheretherketone (PEEK), or composite, as well as to evaluate the possible correlation between internal adaptation and retention.Materials and Methods: A total of 36 copings were milled from zirconia, PEEK, or composite blanks (n = 12 in each group). Marginal and internal gap were evaluated by replica technique, and the pull-out test was used to evaluate retention. One-way analysis of variance, post hoc Tukey tests, and Pearson correlation coefficient test were used to analyze the data.Results: Zirconia had significantly better marginal/internal adaptation (P < .05) than the other materials. There was no statistically significant difference in mean retention force between the different groups (P > .05). No correlation was found between internal adaptation and retention.Conclusion: In the metal-free copings tested, zirconia showed the best adaptation. The retention of copings was not influenced by internal fit or material type. [ABSTRACT FROM AUTHOR]

Aims: The present study aimed to evaluate the color and translucency changes of the feldspathic porcelain samples made using the conventional or computer-aided design/computer-aided manufacturing (CAD/CAM) methods after immersion in staining solutions and laser bleaching. Materials and Methods: A total of 72 samples of feldspathic porcelain were fabricated using the conventional (n = 36) or CAD/CAM (n = 36) methods. Afterward, each group was randomly divided into three subgroups (n = 12), which underwent exposure to coffee, orange juice, or distilled water for 6 weeks. Then, the samples underwent diode laser-assisted bleaching. A spectrophotometer assessed the samples' color and translucency preintervention, after staining, and after bleaching. Statistical Analysis Used: One-way and two-way analysis of variance and independent t-test were used. The significance level was 0.05. Results: Staining for 6 weeks significantly changed the color of both types of feldspathic porcelains. Furthermore, there were significant differences between the ceramics made using different methods and immersed in different staining solutions (P < 0.001). Furthermore, laser-assisted bleaching changed the color of immersed specimens significantly (P = 0.005). However, there were no significant translucency changes in all the subgroups after staining (P = 0.215) and laser bleaching (P = 0.325). Conclusions: The staining-induced discoloration of all the subgroups was in the clinically acceptable range (ΔΕ<3.3). In addition, bleaching could effectively remove the stains in both types of ceramics while not affecting the primary color. Moreover, the translucency of the ceramics was not affected by staining or laser-assisted bleaching. [ABSTRACT FROM AUTHOR]

Objectives: Some manufacturers claim to have produced new irreversible hydrocolloids that are able to maintain their dimensional stability during storage. The present study evaluated the effect of storage time on dimensional stability of three alginates: Hydrogum 5, Tropicalgin and Alginoplast. Materials and Methods: In this experimental in-vitro trial, a total of 90 alginate impressions were made from a Dentoform model using Hydrogum 5, Tropicalgin and Alginoplast alginates. The impressions were stored in a sealed plastic bag without a damp paper towel for 0, 24, 48, 72 and 120 hours and then poured with type III dental stone. Cross-arch (facial of 6 to facial of 6 on the opposite side) and antero-posterior (distal of right first molar to the ipsilateral central incisor) measurements were made with a digital caliper on the casts. Data were analyzed by two-way and one-way ANOVA and Tukey's post-hoc test (P<0.05). Results: Alginate type and the pouring time significantly affected the dimensional stability of alginate impressions (both Ps<0.001). Pouring of Hydrogum 5 impressions can be delayed for up to 120 hours without significant dimensional changes. Alginoplast impressions may be poured after 72 hours, but Tropicalgin should be poured immediately and the storage time should not be more than 24 hours. Conclusion: Immediate pouring of alginate impressions provides the highest accuracy in reproducing the teeth and adjacent tissues; however, this study demonstrated that pouring may be delayed for up to five days using extended-pour (Hydrogum 5) alginates. [ABSTRACT FROM AUTHOR]

Objective: Failure of soft liners depends mostly on separation from the denture base resin; therefore measurement of the bond strength is very important. The purpose of this study was to compare the tensile bond strength of two soft liners (Acropars, Molloplast-B) to denture base resin before and after thermocycling. Materials and Methods: Twenty specimens from each of the two different soft liners were processed according to the manufacturer's instructions between two polymethyl methacrylate (PMMA) sheets. Ten specimens in each group were maintained in 37°C water for 24 hours and 10 were thermocycled (5000 cycles) among baths of 5° and 55°C. The tensile bond strength was measured using a universal testing machine at a crosshead speed of 5 mm/min. Mode of failure was determined with SEM (magnification ×30). Two-way ANOVA was used to analyze the data. Results: The mean and standard deviation of tensile bond strength of Acropars and Molloplast-B before thermocycling were 6.59±1.85 and 1.51±0.22 MPa, respectively and 5.89±1.52 and 1.37±0.18 MPa, respectively after thermocycling. There was no significant difference before and after thermocycling. Mode of failure in Acropars and Molloplast-B were adhesive and cohesive, respectivley. Conclusion: The bond strength of Acropars was significantly higher than Mollop-last-B (P<0.05). [ABSTRACT FROM AUTHOR]

Background and Aims: Since a large marginal opening allows more plaque accumulation, gingival sulcular fluid flow and bone loss, microleakage, recurrent caries and periodontal disease, marginal fit is of great importance in fixed restorations. The aim of this study was to compare the marginal fit of zirconium-based all ceramic (Cercon) frameworks, made by two different approaches (Direct and Wax-up scanning). Materials and Methods: An abutment analog, with 5.5 mm width and height, was selected as an experimental model. Twenty all ceramic cores were made for this model (10 specimens per each group). In the first group (Direct), experimental models were scanned directly using Computer Aided Design/Computer Aided Manufacturing (CAD/CAM). The core was then designed with the aid of a computer and machined. In the second group (Wax-up or CAM) a wax-up pattern was made on the experimental model and then scanned and milled from Cercon blocks. The marginal discrepancy of each specimen was recorded using a stereomicroscope (SZX9, Olympus, Japan) and digital camera (Mode TK, C1380E, JVC, Japan) and then measured by Adobe Photoshop CS software. The data were analyzed using T-test. Results: Mean marginal discrepancy of Direct group (85.2±3.95 μm) was significantly less than that of Wax-up group (120.2±6.91 μm). Conclusion: Improved marginal fit of zirconia ceramics was found with the direct model scanning compared with that of Wax-up scanning using CAD/CAM. [ABSTRACT FROM AUTHOR]

Background: Vinyl Polyether Siloxane is a newly introduced impression material and studies on that is scarce. Implant insertion in posterior mandible might be angulated due to anatomical considerations. The purpose of this study was to compare the dimensional and angular accuracy of impressions using full-arch versus sectional tray and Vinyl Polysiloxane versus Vinyl Polyether Siloxane in angulated implants., Material and Methods: Four implants were placed in dental areas #19, #21, #28 and #30 of a Kennedy class I mandibular acrylic model with 30° lingual angulation. Twenty sectional and 20 full-arch open trays were made on the primary cast. Impressions were taken using Vinyl Polysiloxane and Vinyl Polyether Siloxane (n=10 in 4 groups); and were poured with type IV dental stone. The coordinate measuring machine was used to measure displacements in the X, Y and Z axes and rotational discrepancies of implants. The data were analyzed using SPSS 22 and two-way ANOVA., Results: Type of tray had no significant effect on the dimensional and angular accuracy of impressions ( p >0.05). Type of impression material significantly affected linear displacement (∆r) ( P <0.05); but it did not significantly affect the rotational displacement ( P >0.05)., Conclusions: Vinyl Polysiloxane yielded more accurate impressions of angulated implants. Key words: Dental implant, impression material, impression tray, vinyl polysiloxane, vinyl polyether silicone, coordinate measuring machine., Competing Interests: Conflict of interest statement: The authors have declared that no conflict of interest exist.

Aim: Surface treatment is necessarily required for bonding of zirconia to the veneering porcelain and luting cements. Sandblasting is the most common and probably the most efficient surface treatment method. Sandblasting roughens the surface and may affect the flexural strength of zirconia. Different sandblasting protocols may yield variable results. This study sought to assess the effect of sandblasting angle and distance on the biaxial flexural strength of zirconia-based ceramics., Materials and Methods: This in vitro experimental study was conducted on 50 zirconia discs measuring 1.2 ± 0.2 mm in thickness and 15 ± 0.2 mm in diameter, which were randomly divided into five groups (n = 10) of one control and four experimental groups subjected to sandblasting with 110 μm aluminum oxide particles under 2 bar pressure for 10 seconds at 15 and 25 mm distances and 45 and 90° angles (between the nozzle head and zirconia surface). Surface roughness was measured by a roughness tester and samples were subjected to thermocycling followed by biaxial flexural strength testing according to ISO6872. The data were analyzed using one-way analysis of variance (p < 0.05)., Results: No statistically significant difference was noted in the mean biaxial flexural strength of the five groups (p = 0.40). Different sandblasting protocols yielded significantly different surface roughness values (p < 0.001). The highest and the lowest mean surface roughness belonged to 15 mm/90° (0.51 μm) and control (0.001 μm) groups respectively., Conclusion: Change in sandblasting angle and distance had no significant effect on the biaxial flexural strength of zirconia-based ceramic, but surface roughness was significantly different in the study groups. Clinical significances: Regardless of sandblasting angle, increasing distance to 25 mm significantly decreases surface roughness that may negatively affect zirconia bond strength.

Objectives: Some manufacturers claim to have produced new irreversible hydro-colloids that are able to maintain their dimensional stability during storage. The present study evaluated the effect of storage time on dimensional stability of three alginates: Hydrogum 5, Tropicalgin and Alginoplast., Materials and Methods: In this experimental in-vitro trial, a total of 90 alginate impressions were made from a Dentoform model using Hydrogum 5, Tropicalgin and Alginoplast alginates. The impressions were stored in a sealed plastic bag without a damp paper towel for 0, 24, 48, 72 and 120 hours and then poured with type III dental stone. Cross-arch (facial of 6 to facial of 6 on the opposite side) and antero-posterior (distal of right first molar to the ipsilateral central incisor) measurements were made with a digital caliper on the casts. Data were analyzed by two-way and one-way ANOVA and Tukey's post-hoc test (P<0.05)., Results: Alginate type and the pouring time significantly affected the dimensional stability of alginate impressions (both Ps<0.001). Pouring of Hydrogum 5 impressions can be delayed for up to 120 hours without significant dimensional changes. Alginoplast impressions may be poured after 72 hours, but Tropicalgin should be poured immediately and the storage time should not be more than 24 hours., Conclusion: Immediate pouring of alginate impressions provides the highest accuracy in reproducing the teeth and adjacent tissues; however, this study demonstrated that pouring may be delayed for up to five days using extended-pour (Hydrogum 5) alginates.

Objective: Failure of soft liners depends mostly on separation from the denture base resin; therefore measurement of the bond strength is very important. The purpose of this study was to compare the tensile bond strength of two soft liners (Acropars, Molloplast-B) to denture base resin before and after thermocycling., Materials and Methods: Twenty specimens fromeach of the two different soft liners were processed according to the manufacturer's instructions between two polymethyl methacrylate (PMMA) sheets. Ten specimens in each group were maintained in 37°C water for 24 hours and 10 were thermocycled (5000 cycles) among baths of 5° and 55°C. The tensile bond strength was measured using a universal testing machine at a crosshead speed of 5 mm/min. Mode of failure was determined with SEM (magnification ×30). Two-way ANOVA was used to analyze the data., Results: The mean and standard deviation of tensile bond strength of Acropars and Molloplast-B before thermocycling were 6.59±1.85 and1.51±0.22 MPa, respectively and 5.89±1.52 and1.37±0.18 MPa, respectively after thermocycling. There was no significant difference before and after thermocycling. Mode of failure in Acropars and Molloplast-B were adhesive and cohesive, respectivley., Conclusion: The bond strength of Acropars was significantly higher than Molloplast-B (P<0.05).