The effect of adjustment and finishing procedure on roughness, strength, and phase transformation of monolithic zirconia.

OBJECTIVE: To evaluate the effect of adjustment and finishing procedures and thermal aging of monolithic zirconia on the surface roughness, phase transformation, and flexural strength. MATERIAL AND METHODS: One hundred disk-shaped monolithic zirconia specimens were randomly divided into 5 groups: control, received only glazing; group Gr, was grinded; group GrP, was grinded and polished; group GrG, was grinded and re-glazed; group GrPG, was re-glazed after grinding and polishing. Half of the each group were stored in distilled water for 24 h and the remaining were thermocycled for 5000 cycles. Topographic evaluations were done with profilometer and scanning electron microscope. Phase changes were assessed through X-ray diffractometer. The biaxial flexural strength test was calculated by universal test machine. Statistical analysis was performed by using two-way ANOVA and Tukey multiple comparison test (p < 0.05). RESULTS: Group Gr showed statistically higher surface roughness and flexural strength values than the other groups (p < 0.001). However, no significant differences were observed between finishing groups (p >0.05). Phase transformation was occurred in all groups but the differences were not statically significant (p >0.05). Artificial aging had no effect on surface roughness, flexural strength, and phase transformation (p >0.05). CONCLUSION: Surface roughness significantly increased after grinding, but finishing procedure approximated it to the control group. Glazing after grinding decreased the flexural strength, but polishing did not. Zirconia polishing system may be an alternative to re-glazing for monolithic zirconia. CLINICAL RELEVANCE: Polishing is one of the most effective finishing procedures that can improve the physical properties of the material without damaging its mechanical properties.

Artifact expression of polyetheretherketone in cone beam computed tomography: An in vitro study.

STATEMENT OF PROBLEM: Dental prosthetic materials can cause artifacts in cone beam computed tomography (CBCT) images, adversely affecting diagnostic quality, although the problem may be less with polyetheretherketone (PEEK). Studies evaluating the artifacts caused by frequently used prosthetic materials are lacking. PURPOSE: The purpose of this in vitro study was to compare the artifacts in CBCT images caused by PEEK, zirconia, cobalt-chromium (Co-Cr) alloy, and titanium (Ti). MATERIAL AND METHODS: A polymethylmethacrylate phantom (Ø4.0×4.0 cm) with a central cylindrical aperture (Ø0.5×0.5 cm) was produced. Co-Cr, Ti, zirconia, and PEEK cylinders (0.5×0.5 cm) were manufactured, and CBCT images of the empty phantom (control group) with the test cylinders inside were made 3 times. In all images, the axial sections passing through the middle of the materials were evaluated. Eight regions of interest (ROI) area were determined around the materials (0.5×0.5 cm). The presence of artifacts was evaluated by making gray value standard deviation (SD) calculations in these ROI areas. The average SD values of 8 ROI fields from the 3 CBCT scans were made, and the materials were compared with each other in terms of the presence of artifacts by using 1-way analysis of variance (α=.05). RESULTS: The difference between the SD values of the control and the PEEK cylinder was not statistically significant (P>.05). The SD values of both the control and PEEK groups were significantly lower than those of the zirconia, Co-Cr, and Ti groups (P<.05). CONCLUSIONS: Zirconia, Ti, and Co-Cr caused artifacts in CBCT images, but the artifacts with PEEK were similar to those in the control group, suggesting it was the optimal choice in terms of achieving diagnostic quality.

An In Vitro Evaluation of the Effect of Various Adhesives and Surface Treatments on Bond Strength of Resin Cement to Polyetheretherketone.

PURPOSE: To investigate the effect of various surface pretreatments and adhesive systems on bond strength of resin cement to polyetheretherketone (PEEK). MATERIALS AND METHODS: 360 PEEK specimens were divided into 4 groups to receive the following pretreatments (n = 90): no pretreatment, sandblasting, silica coating and Er:YAG laser. Surface roughness (SR) and scanning electron microscopy (SEM) evaluations were conducted after mechanical pretreatments for topographical surface evaluations. After the pretreatments, each group was divided into 3 subgroups (n = 30) according to the adhesive system used: no adhesive system, Visio.link, and Signum PEEK Bond. Resin cement was applied, and specimens underwent 5000 thermocycles (5-55°C) before shear bond strength (SBS) test. One-way ANOVA and Tukey test were used to analyze the SR data; 2-way ANOVA and Fisher's LSD test were used to analyze the SBS data at the confidence interval of 95% (α = 0.05). RESULTS: The sandblasting group demonstrated the highest SR values (p < 0.05). No significant differences in SR values were identified among silica coating, laser, and control groups (p ˃ 0.05). Conditioning with Visio.link after sandblasting group exhibited the highest SBS values (p < 0.05). No significant differences in SBS values were found between laser and control group (p ˃ 0.05). Conditioned groups presented higher SBS values than unconditioned groups (p < 0.05). Between the two adhesive systems, Visio.link demonstrated statistically significant higher SBS values than Signum PEEK Bond (p < 0.05). CONCLUSION: Silica coating and sandblasting were shown to provide superior pretreatment of PEEK surface. Laser pretreatments showed no effectiveness on bond strength of resin cement to PEEK. Adhesive systems improved the resin bonding to PEEK.

The effect of various polishing systems on surface roughness and phase transformation of monolithic zirconia.

PURPOSE: The purpose of this study was to evaluate and compare three polishing systems on the surface roughness and phase transformation of monolithic zirconia. MATERIALS AND METHODS: 100 disk shaped specimens (10 mm diameter, 3 mm thickness) were fabricated from monolithic zirconia blocks. 20 specimens were left as a control group and remaining specimens were grinded by diamond bur to simulate the occlusal adjustments. Grinded specimens were randomly divided into 4 groups: group G (no polishing), group M (Meisinger, zirconia polishing kit), group E (EVE Diacera, zirconia polishing kit), and group P (EVE Diapol, porcelain polishing kit). Surface roughness was measured with profilometer and surface topography was observed with SEM. XRD analysis was performed to investigate the phase transformation. Statistical analysis was performed with one-way ANOVA and Tukey's post hoc tests at a significance level of P=.05. RESULTS: All polishing groups showed a smoother surface than group G. Among 3 polishing systems, group M and group E exhibited a smoother surface than the group P. However, no significant differences were observed between group M and group E (P>.05). Grinding and polishing did not cause phase transformations in zirconia specimens. CONCLUSION: Zirconia polishing systems created a smoother surface on zirconia than the porcelain polishing system. Phase transformation did not occur during the polishing procedure.

The effect of ultrafast fiber laser application on the bond strength of resin cement to titanium.

The purpose of this study was to investigate the effect of ultrafast fiber laser treatment on the bond strength between titanium and resin cement. A total of 60 pure titanium discs (15 mm × 2 mm) were divided into six test groups (n = 10) according to the surface treatment used: group (1) control, machining; group (2) grinding with a diamond bur; group (3) ultrafast fiber laser application; group (4) resorbable blast media (RBM) application; group (5) electro-erosion with copper; and group (6) sandblasting. After surface treatments, resin cements were applied to the treated titanium surfaces. Shear bond strength testing of the samples was performed with a universal testing machine after storing in distilled water at 37 °C for 24 h. One-way ANOVA and Tukey's HSD post hoc test were used to analyse the data (P < 0.05). The highest bond strength values were observed in the laser application group, while the lowest values were observed in the grinding group. Sandblasting and laser application resulted in significantly higher bond strengths than control treatment (P < 0.05). Ultrafast fiber laser treatment and sandblasting may improve the bond strength between resin cement and titanium.

The effect of Er:YAG laser irradiation on the bond stability of self-etch adhesives at different dentin depths.

The aim of this study was to evaluate the effect of Er:YAG laser irradiation on the micro-shear bond strength of self-etch adhesives to the superficial dentin and the deep dentin before and after thermocycling. Superficial dentin and deep dentin surfaces were prepared by flattening of the occlusal surfaces of extracted human third molars. The deep or superficial dentin specimens were randomized into three groups according to the following surface treatments: group I (control group), group II (Er:YAG laser; 1.2 W), and group III (Er:YAG laser; 0.5 W). Clearfil SE Bond or Clearfil S3 Bond was applied to each group's dentin surfaces. After construction of the composite blocks on the dentin surface, the micro-shear bond testing of each adhesive was performed at 24 h or after 15,000 thermal cycles. The data were analyzed using a univariate analysis of variance and Tukey's test (p < 0.05). Laser irradiation in superficial dentin did not significantly affect bond strength after thermocycling (p > 0.05). However, deep-dentin specimens irradiated with laser showed significantly higher bond strengths than did control specimens after thermocycling (p < 0.05). Thermocycling led to significant deterioration in the bond strengths of all deep-dentin groups. The stable bond strength after thermocycling was measured for all of the superficial-dentin groups. No significant difference was found between the 0.5 and 1.2 W output power settings. In conclusion, the effect of laser irradiation on the bond strength of self-etch adhesives may be altered by the dentin depth. Regardless of the applied surface treatment, deep dentin showed significant bond degradation.

The effect of veneering on the marginal fit of CAD/CAM-generated, copy-milled, and cast metal copings.

OBJECTIVE: This in vitro study investigated the marginal fit of metal and zirconia copings before and after veneering on dies with shoulder/chamfer (s/c) finish lines. MATERIALS AND METHODS: Using CAD/CAM, ten (n = 10) each s/c zirconia (NZ) copings and ten (n = 10) each s/c metal (MM) copings were generated. As controls, ten (n = 10) each s/c zirconia copings were copy-milled (ZZ) and ten (n = 10) each s/c metal copings were cast (CC). The vertical marginal discrepancy of the copings was measured at 20 predefined spots of the circular shoulder and chamfer finish lines in microns (µm) before and after a first and a second veneering firing using a stereomicroscope at ×40 magnification. Data were statistically analyzed, and the comparisons of CAD/CAM-milled (NZ, MM), copy-milled (ZZ), and cast (CC) copings before and after veneering were made at a significance level of p < 0.05. RESULTS: Gap width at s/c finish lines of ZZ was (91 ± 11/100 ± 28) and increased significantly (109 ± 21/141 ± 18) after the first firing (ZZ1). NZ showed significantly smaller gaps than ZZ (36 ± 6/46 ± 12) and (NZ1) after the first firing (61 ± 16/71 ± 29). Gap widths of CC groups (36 ± 8/25 ± 4) were not significantly different from NZ but were significantly lower after the (CC1) first veneering firing (40 ± 8/42 ± 7). MM copings showed gap values similar to NZ. Second firings did not significantly increase gaps in all groups except ZZ2 of chamfer finish line. CONCLUSION: Veneering increased the marginal gap width of copings. CLINICAL RELEVANCE: Within the limits of this in vitro study, aesthetic ceramic veneering of CAD/CAM-generated copings caused a statistically significant but tolerable loss of marginal fit precision.

The Effect of Sandblasting, Er:YAG Laser, and Heat Treatment on the Mechanical Properties of Different Zirconia Cores.

OBJECTIVE: The purpose of this study was to evaluate the effect of surface and heat treatments on the mechanical properties and phase transformation of yttria-stabilized tetragonal zirconia (Y-TZP) materials. BACKGROUND DATA: Zirconia is exposed to several treatments during dental application process. Knowing the effect of applied treatments on zirconia is essential for clinical success. MATERIAL AND METHODS: Forty disk specimens of Zirkonzahn (Z) and DC-Zirkon (DC) materials were fabricated. The specimens were randomly divided into four groups according to surface [control, sandblasting, Erbium: Yttrium Aluminum Garnet (Er:YAG) laser irradiation] and heat (firing) treatments. The surface roughness (Ra, µm) was measured using a surface profilometer. The relative amount of the transformed monoclinic (m) phase was analyzed by X-ray diffractometry (XRD). Biaxial flexural strength was tested using piston-on-three-ball technique. The data were analyzed with the Kruskal-Wallis H test with Bonferroni correction, and the Mann-Whitney U test was used for pairwise comparisons. RESULTS: There were no significant differences in surface roughness among the treated groups (p > 0.05), whereas sandblasting showed higher surface roughness than other treatments for both materials. Scanning electron microscopic (SEM) analyses revealed changes in surface morphology after surface treatments, especially in laser groups with the formation of cracks, and in sandblasting groups with the formation of microretentive grooves. The greatest amount of the monoclinic phase was measured after sandblasting (8.13%) for Z and (19.8%) for DC. The monoclinic phase reverted to the tetragonal phase after heat treatment. Heat treatment groups showed significantly lower flexural strength than other treatments (p < 0.05). CONCLUSIONS: Heat and surface treatments influenced the mechanical properties of zirconia ceramic. The biaxial flexural strength and crystalline phase of materials decreased after heat treatments.