Effect of different surface treatments on the biaxial flexural strength of zirconia ceramics.

STATEMENT OF PROBLEM: Different surface treatments have been applied to zirconia restorations in clinical practice to increase the bond strength between zirconia and cement, but their effect on flexural strength is unknown. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different surface treatments before and after sintering on the flexural strength of zirconia. MATERIAL AND METHODS: Sixty disk-shaped specimens with an initial diameter of 18.6 ±0.1 mm and thickness of 2 ±0.1 mm were prepared from preshaded presintered 3Y-TZP blocks. The specimens were randomly divided into 3 groups (n=20) according to surface treatments (Group Laser, Group APA, Group Rocatec), and the groups were then divided into 2 subgroups (n=10) according to surface treatment before and after sintering. The phase compositions of the groups were examined by using an X-ray diffractometer (XRD) with 3 randomly selected specimens from each group. Biaxial flexural strength testing was conducted using a universal testing machine to examine the flexural strength of the zirconia specimens. Two-way ANOVA and post hoc least significant difference tests were performed (α=.05). RESULTS: According to the XRD analysis, no monoclinic phases were determined on the surface of the presintered laser-treated specimens, but tetragonal phases were observed on the surface of the postsintered specimens. Surface treatment type and application stage (presintering to postsintering) have a significant effect on the biaxial flexural strength of the specimens (P<.05). The lowest biaxial flexural values were observed in the Laser group, and postsintered specimens showed higher biaxial flexural strength than presintered specimens (P<.05). CONCLUSIONS: Postsintered specimens showed higher monoclinic content than presintered specimens. Laser-treated specimens showed the lowest biaxial flexural strength for both presintered and postsintered specimens.

The effect of different cleaning agents and resin cement materials on the bond strength of contaminated zirconia.

The purpose of this study was to examine the effect of different cleaning methods and resin cements on the shear bond strength (SBS) of contaminated zirconia. A total of 92 disc-shaped zirconia specimens were contaminated with different procedures. Then, the specimens were grouped according to cleaning methods and resin cements: no cleaning + Variolink Esthetic DC (CNV ), no cleaning + Panavia V5 (CNP ), sandblasted + Variolink Esthetic DC (SBV ), sandblasted + Panavia V5 (SBP ), Ivoclean + Variolink Esthetic DC (ICV ), Ivoclean + Panavia V5 (ICP ), Katana Cleaner + Variolink Esthetic DC (KCV ), and Katana Cleaner + Panavia V5 (KCP ). Following an aging protocol in a 37°C for 1 week, SBS analysis was performed with a universal test machine. For the surface topography and elemental analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) were used. Significance was evaluated as p < .05 and p < .01. The highest SBS results were found in the SBP group, showing a statistically significant difference from all other groups (p < .05). For the same cleaning method, Panavia V5 showed statistically significantly higher SBS values than Variolink Esthetic DC (p < .01), except the CNP -CNV (p = .880) and KCP -KCV (p = .082) groups. The most detected surface elements by EDS were Zr, O, C, and N, respectively. The contaminated zirconia surfaces must be cleaned for successful adhesion. The use of phosphate-containing adhesives in combination with sandblasting will increase the adhesion strength, and universal cleaning agents can be a good alternative to sandblasting.

Effects of denture cleaning solutions on the retention of Hader bar clips.

STATEMENT OF PROBLEM: The clinical performance of implant-retained overdentures (IODs) with plastic bar clips made of different materials in the same design and dimensions may vary according to the patient's daily home care procedures. However, information about the effects of denture cleaning solutions on the retention of Hader bar clips is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the retention of Hader bar clips made of different polymers after being soaked in denture cleaning solutions. MATERIAL AND METHODS: Ninety Hader bar clips made of polyamide (PA, n=30), polytetrafluoroethylene (PTFE, n=30), and polyetherketoneketone (PEKK, n=30) materials were tested. Two multiunit abutments were screwed onto the implant analogs and embedded into an acrylic resin block in a standardized position. The digital scanning of the abutments was acquired, and the bar patrix of each material system milled from a cobalt-chromium (Co-Cr) alloy disk by using computer-aided design and computer-aided manufacturing (CAD-CAM). After the milled bar patrices were screwed onto abutments and the metal housings of the bar clips were embedded into acrylic resin blocks, they were connected passively at the same angulation to a universal testing machine. The initial retention values of all Hader bar clips were measured, and each material system was divided into 3 subgroups (n=10) before soaking in the cleaning solutions: distilled water (DW), 5% sodium hypochlorite (NaOCl), or sodium bicarbonate-sodium perborate (SBSP). Each material was soaked for the equivalent of 3 months of clinical use. The final retention values of each Hader bar clip were measured. The data were statistically analyzed by using a 2-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) test, and the paired sample t test (α=.05). RESULTS: The 2-way ANOVA showed that the denture cleaning solution, the clip material, and their interactions led to significantly different retention values (P<.001). A decrease was observed for the retention values of all test groups after soaking in the cleaning solutions (P<.05). No retention was observed for the PTFE clips after soaking in the 5% NaOCI solution. CONCLUSIONS: The denture cleaning solutions negatively affected the retention of Hader bar clips, regardless of the type of solution and clip material. The 5% NaOCI solution not only decreased the retention of PTFE clips but also completely degraded it. It is recommended that 5% NaOCI solution be avoided for the daily care of IODs with PTFE clips.

Influence of bleaching agents on the color change and translucency of resin matrix ceramics.

OBJECTIVE: The aim of this study was to investigate the color change, translucency, and whiteness index of three different resin matrix ceramics and a resin composite subjected to different bleaching agents. MATERIALS AND METHODS: Twenty disc-shaped specimens (A2 shaded) for three different resin matrix ceramic brands (Groups Ena, Ulti, and Cera) (totally 60) were prepared using the CAD/CAM technique and 20 nanofiller composite specimens (Group Comp) (A2 shaded) with the same dimensions were prepared as the control group. The color change (∆E00 ), relative translucency parameter (RTP), and whiteness index (WID ) of the specimens initial and after different bleaching procedures (home-bleaching and office-bleaching) were calculated using ∆E00 , TP00 , and WID formulas. Two-way analysis of variance (ANOVA) and multiple comparison test with Bonferroni correction (α = .05) at the significance level of P < .05 were performed for the comparisons of ∆E00 values. The RTP and WID values were evaluated by using repeated measures ANOVA and multiple-comparison test with Bonferroni corrections (α = .05) at the significance level of P < .05. RESULTS: Bleaching procedure and material type were found to be significant regardless of bleaching type for RTP and WID values. Material type has a significant effect on the ∆E00 values. The highest color change values were determined in Group Comp (P < .05). CONCLUSIONS: Bleaching procedures significantly affected the RTP values of Groups Ulti and Cera (P < .05). ∆E00 values for the resin matrix ceramics after the bleaching procedures were below the clinically acceptable values, regardless of the bleaching agent. CLINICAL SIGNIFICANCE: Optically, materials such as resin matrix ceramics have properties different from not only enamel and dentin but also among themselves. The possible effect of bleaching agents on these materials should be considered carefully while choosing the restorative material.

Influence of heating rate on the flexural strength of monolithic zirconia.

PURPOSE: Fabrication of zirconia restorations with ideal mechanical properties in a short period is a great challenge for clinicians. The purpose of the study was to investigate the effect of heating rate on the mechanical and microstructural properties of monolithic zirconia. MATERIALS AND METHODS: Forty monolithic zirconia specimens were prepared from presintered monolithic zirconia blanks. All specimens were then assigned to 4 groups according to heating rate as Control, Group 15℃, Group 20℃, and Group 40℃. All groups were sintered according to heating rates with the sintering temperature of 1500℃, a holding time of 90 minutes and natural cooling. The phase composition was examined by XRD analysis, three-point bending test was conducted to examine the flexural strength, and Weibull analysis was conducted to determine weibull modulus and characteristic strength. Average grain sizes were determined by SEM analysis. One-way ANOVA test was performed at a significance level of 0.05. RESULTS: Only tetragonal phase characteristic peaks were determined on the surface of analyzed specimens. Differences among the average grain sizes of the groups were not statistically significant. The results of the three-point bending test revealed no significant differences among the flexural strength of the groups (P>.05). Weibull modulus of groups was ranging from 3.50 to 4.74. The highest and the lowest characteristic strength values were obtained in Group 20℃ and Control Group, respectively. CONCLUSION: Heating rate has no significant effect on the flexural strength of monolithic zirconia. Monolithic zirconia restorations can be produced in shorter sintering periods without affecting the flexural strength by modifying the heating rate.

Effect of surface treatments on the bond strength of indirect resin composite to resin matrix ceramics.

PURPOSE: The purpose of this study was to evaluate the shear bond strength (SBS) of an indirect resin composite (IRC) to the various resin matrix ceramic (RMC) blocks using different surface treatments. MATERIALS AND METHODS: Ninety-nine cubic RMC specimens consisting of a resin nanoceramic (RNC), a polymer-infiltrated hybrid ceramic (PIHC), and a flexible hybrid ceramic (FHC) were divided randomly into three surface treatment subgroups (n = 11). In the experimental groups, untreated (Cnt), tribochemical silica coating (Tbc), and Neodymium-Doped Yttrium Aluminum Garnet (Nd:YAG) laser irradiation (Lsr) with 3 W (150 mJ/pulse, 20 Hz for 20 sec.) were used as surface treatments. An indirect composite resin (IRC) was layered with a disc-shape mold (2 × 3 mm) onto the treated-ceramic surfaces and the specimens submitted to thermal cycling (6000 cycles, 5 - 55℃). The SBS test of specimens was performed using a universal testing machine and the specimens were examined with a scanning electron microscope to determine the failure mode. Data were statistically analyzed with two-way analysis of variance (ANOVA) and Tukey HSD test (α=.05). RESULTS: According to the two-way ANOVA, only the surface treatment parameter was statistically significant (P<.05) on the SBS of IRC to RMC. The SBS values of Lsr-applied RMC groups were significantly higher than Cnt groups for each RMC material, (P<.05). Significant differences were also determined between Tbc surface treatment applied and untreated (Cnt) PIHC materials (P=.039). CONCLUSION: For promoting a reliable bond strength during characterization of RMC with IRC, Nd:YAG laser or Tbc surface treatment technique should be used, putting in consideration the microstructure and composition of RMC materials and appropriate parameters for each material.

Shear Bond Strength of Nanohybrid Composite to the Resin Matrix Ceramics After Different Surface Treatments.

OBJECTIVE: The purpose of this study was to evaluate the effects of different surface treatments on the shear bond strength (SBS) of a composite resin to the various resin matrix ceramics (RMC). BACKGROUND: Clinical applications of physical and chemical surface conditioning methods may be required for RMC to optimize the adhesion of additional resin materials. MATERIALS AND METHODS: Ninety-nine RMC specimens (6 × 6 × 2 mm) were prepared from a resin nanoceramic (RNC), a polymer-infiltrated hybrid ceramic (PIHC), and a flexible hybrid ceramic (FHC) block with a cutting machine under copious water. All specimens divided randomly into three surface treatment subgroups (n = 11): (1) untreated (Cnt), (2) tribochemical silica coated (Tbc), and (3) neodymium-doped yttrium aluminum garnet (Nd:YAG) laser irradiated with 3 W (150 mJ/pulse, 20 Hz) for 20 sec. A nanohybrid composite resin was layered with a disc-shape mold (2 × 3 mm) onto the ceramics and submitted to thermal cycling (3000 cycles, 5-55°C). The SBS test of specimens was performed using a universal testing machine. Data were statistically analyzed with two-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). RESULTS: The type of RMC, surface treatments, and their interactions was statistically significant on SBS, according to the ANOVA (p < 0.05). Both the Tbc and Lsr surface treatments significantly increased the SBS values of FHC (p < 0.001), while significant increases were observed only for Lsr0applied RNC and Tbc applied PIHC groups (p < 0.001). CONCLUSIONS: The tribochemical silica coating and laser irradiation techniques may be suitable for improving the surface topography of specific types of RMC. While the same surface treatment technique may not provide similar successful results for all types of RMC, it is recommended to choose the most effective and reliable technique for clinical application.

Experimental evaluation of stress distribution with narrow diameter implants: A finite element analysis.

STATEMENT OF PROBLEM: Narrow diameter implants were developed to allow placement in narrow alveolar ridges. Clinicians may have concerns about the durability and function of such implants. PURPOSE: The purpose of this finite element study was to compare the stress values occurring on the implant and at the implant bone interface after the application of the static and dynamic forces on narrow diameter, titanium and titanium-zirconia implants in the maxillary and mandibular second premolar region. MATERIAL AND METHODS: Titanium (Ti) and titanium-zirconium (Ti-Zr) narrow diameter implants (3.3 mm in diameter, 10 mm in length) were simulated in the maxillary and mandibular second premolar region, and metal-ceramic crown restorations were designed. Forces of 100 N were applied to crowns in a vertical and oblique (45-degree angle to the long axis) direction. Maximum and minimum principal stresses in the cortical and trabecular bone and the von Mises stresses and fatigue strength of the implants were evaluated with 3-dimensional finite element analysis. RESULTS: In vertical and oblique static loading, Ti and Ti-Zr implants showed similar stress distribution within the same jaw models. However, the von Mises stresses in Ti-Zr implants were slightly higher than for Ti implants in all models. In oblique static and dynamic loading, all stresses were found higher than vertical loading, and fatigue failure results were found to be more critical than vertical forces. CONCLUSIONS: Based on a numerical simulation, Ti and Ti-Zr alloys can be used successfully as narrow diameter implants in the second premolar area.

Evaluation of the skeletal and dental effects in orthodontic patients with maxillary lateral incisor agenesis.

OBJECTIVE: The purpose of this study was to evaluate the transverse dimension of the dentoalveolar and skeletal widths in both unilateral (UMLIA) and bilateral (BMLIA) maxillary lateral incisor agenesis groups. MATERIALS AND METHODS: The study sample consisted of 59 patients (34 females and 25 males) divided into three groups as UMLIA group (16 patients; 14.94 ± 1.37 years), BMLIA group (21 patients; 14.46 ± 1.53 years) and control group (22 patients; 15.28 ± 1.70 years) without tooth agenesis. Transversal measurements (maxillary and mandibular intercanine, interpremolar, intermolar, intercanine alveolar, interpremolar alveolar, intermolar alveolar widths) were done on dental casts. Craniofacial skeletal measurements were done with posteroanterior cephalometric radiographs. Statistical testing was performed with the one-way variance analysis, Kruskal-Wallis and post hoc tests. RESULTS: UMLIA and BMLIA groups had statistically significantly narrower skeletal apical base of the maxilla, maxillary intercanine and intercanine alveolar widths compared with the control group (P < .05). Moreover, UMLIA and BMLIA groups had statistically significantly similar dental, alveolar and skeletal features (P > .05). CONCLUSIONS: The UMLIA and BMLIA groups showed statistically significantly smaller values for maxillary intercanine, maxillary intercanine alveolar and skeletal maxillary widths compared with the control group. CLINICAL SIGNIFICANCE: This study provides information the transverse dimension of the dental, alveolar and skeletal widths with maxillary lateral incisor agenesis patients. Knowledge of transverse dimension of the dental, alveolar and skeletal widths with maxillary lateral incisor agenesis patients is important for diagnosis and treatment planning.

Influence of the color of composite resin foundation and luting cement on the final color of lithium disilicate ceramic systems.

STATEMENT OF PROBLEM: Lithium disilicate restorations are commonly used, particularly in the anterior region. The color of the underlying composite resin foundation (CRF) and luting cement may negatively affect the color of lithium disilicate ceramic restorations. PURPOSE: The purpose of this in vitro study was to investigate the effect of CRF and resin cement materials on the color of lithium disilicate ceramics in 2 different translucencies. MATERIAL AND METHODS: Twenty disks (11×1.5 mm, shade A2) were fabricated from medium-opacity (mo) (n=10) and high-translucency (ht) (n=10) lithium disilicate (Lds) blocks (IPS e.max Press). Five CRF disks (11×3 mm) were fabricated in 5 different shades (A1, A2, A3, B2, C2) and 30 resin cement disks (11×0.2 mm) in the shades of translucent (Tr), universal (Un=A2), and white-opaque (Wo). Ceramic specimens were placed on each CRF, and the resin cement combination and color was measured with a spectrophotometer. CIELAB color coordinates were recorded, and the color coordinates of both ceramics on the shades of the A2 CRF and resin cement were saved as the control. Color differences (ΔE00) between the control and test groups were calculated. Data were analyzed with 3-way analysis ANOVA and compared with the Tukey HSD test (α=.05). RESULTS: The ΔE00 values were influenced by the shades of the CRF, resin cement materials, and also their interactions (P<.05). The ΔE00 values were not affected by the ceramic type. The ΔE00 values of the Wo cement groups (1.73 to 2.96) were significantly higher than those of the other cement shades (0.88 to 1.29) for each ceramic type and CRF shade (P<.05). CONCLUSIONS: Lithium disilicate ceramics in 2 different translucencies were similarly influenced by the color of the underlying cement and CRF. When translucent and universal cement shades were used, the core shade did not affect the final color of the ceramics. White opaque cement caused clinically unacceptable color changes in both ceramics on all shades of CRFs except the C2 CRF and when high translucency ceramic was used on the A2 CRF. These changes were clinically acceptable, but perceptible.

Evaluation of bond strength of various epoxy resin based sealers in oval shaped root canals.

BACKGROUND: The aim of this study was to evaluate the bond strength of AH plus, Acroseal, and Adseal to the root canal dentin. METHODS: A total of 36 single-rooted, mandibular premolar teeth were used. Root canal shaping procedures were performed with ProTaper rotary instruments (Dentsply Maillefer) up to size F4. The prepared samples were then randomly assembled into 3 groups (n = 12). For each group, an ultrasonic tip (size 15, 0.02 taper) which was also coated with an epoxy resin based sealer and placed 2 mm shorter than the working length. The sealer was then activated for 10 s. A push-out test was used to measure the bond strength between the root canal dentine and the sealer. Kruskal-Wallis test to evaluate the push-out bond strength of epoxy based sealer (P = 0.05). The failure mode data were statistically analyzed using Pearson's chi square test (P = 0.05). RESULTS: Kruskal-Wallis test indicated that there were no statistically significant difference among the push out bond strength values of 3 mm (p = 0.123) and 6 mm (P = 0.057) for groups, there was statistically significant difference push out bond strength value of 9 mm (P = 0.032). Pearson's chi square test showed statistically significant differences for the failure types among the groups. CONCLUSION: Various epoxy resin based sealers activated ultrasonically showed similar bond strength in oval shaped root canals. Apical sections for all groups have higher push out bond strength values than middle and coronal sections.

Influence of implant abutment material on the color of different ceramic crown systems.

STATEMENT OF PROBLEM: Ceramics are widely used for anterior restorations; however, clinical color reproduction still constitutes a challenge particularly when the ceramic crowns are used on titanium implant abutments. PURPOSE: The purpose of this in vitro study was to investigate the effect of implant abutment material on the color of different ceramic material systems. MATERIAL AND METHODS: Forty disks (11×1.5 mm, shade A2) were fabricated from medium-opacity (mo) and high-translucency (ht) lithium disilicate (IPS e.max) blocks, an aluminous ceramic (VITA In-Ceram Alumina), and a zirconia (Zirkonzahn) ceramic system. Disks were fabricated to represent 3 different implant abutments (zirconia, gold-palladium, and titanium) and dentin (composite resin, A2 shade) as background (11×2 mm). Disk-shaped composite resin specimens in A2 shade were fabricated to represent the cement layer. The color measurements of ceramic specimens were made on composite resin abutment materials using a spectrophotometer. CIELab color coordinates were recorded, and the color coordinates measured on composite resin background served as the control group. Color differences (ΔE00) between the control and test groups were calculated. The data were analyzed with 2-way analysis of variance (ANOVA) and compared with the Tukey HSD test (α=.05). RESULTS: The ceramics system, abutment material, and their interaction were significant for ΔE00 values (P<.001). Clinically unacceptable results (ΔE00>2.25) were observed for lithium disilicate ceramics on titanium abutments (2.46-2.50). The ΔE00 values of lithium disilicate ceramics for gold-palladium and titanium abutments were significantly higher than for other groups (P<.05). CONCLUSION: The color results (ΔE00>2.25) of an implant-supported lithium disilicate ceramic restoration may be clinically unacceptable if it is fabricated over a titanium abutment. Zirconia may be a more suitable abutment material for implant-supported ceramic restorations.

Influence of abutment material and luting cements color on the final color of all ceramics.

PURPOSE: The purpose of this study is to evaluate the effects of different abutment materials and luting cements color on the final color of implant-supported all-ceramic restorations. MATERIALS AND METHODS: Ten A2 shade IPS e.max Press disc shape all-ceramic specimens were prepared (11 × 1.5 mm). Three different shades (translucent, universal and white opaque) of disc shape luting cement specimens were prepared (11 × 0.2 mm). Three different (zirconium, gold-palladium and titanium) implant abutments and one composite resin disc shape background specimen were prepared at 11 mm diameter and appropriate thicknesses. All ceramic specimens colors were measured with each background and luting cement samples on a teflon mold. A digital spectrophotometer used for measurements and data recorded as CIE L*a*b* color co-ordinates. An optical fluid applied on to the samples to provide a good optical connection and measurements on the composite resin background was saved as the control group. ΔE values were calculated from the ΔL, Δa and Δb values between control and test groups and data were analyzed with one-way variance analysis (ANOVA) and mean values were compared by the Tukey HSD test (α = 0.05). RESULTS: One-way ANOVA of ΔL, Δa, Δb and ΔE values of control and test groups revealed significant differences for backgrounds and seldom for cement color groups (p the 0.05). Only zirconium implant abutment groups and gold palladium abutment with universal shade cement group were found to be clinically acceptable (ΔE ≤ 3.0). CONCLUSION: Using titanium or gold-palladium abutments for implant supported all ceramics will be esthetically questionable and white opaque cement will be helpful to mask the dark color of titanium abutment.