Handan Yilmaz

Flexural strength and fracture toughness of dental core ceramics

STATEMENT OF PROBLEM Many different strengthened all-ceramic core materials are available. In vitro study of their mechanical properties, such as flexural strength and fracture toughness, is necessary before they are used clinically. PURPOSE The purpose of this study was to evaluate and compare the mechanical properties of 6 commonly used all-ceramic core materials using biaxial flexural strength and indentation fracture toughness tests. MATERIAL AND METHODS Specimens of 6 ceramic core materials (Finesse, Cergo, IPS Empress, In-Ceram Alumina, In-Ceram Zirconia, and Cercon Zirconia) were fabricated (n=25) with a diameter of 15 mm and width of 1.2 +/- 0.2 mm. For each group, the specimens were tested to compare their biaxial flexural strength (piston on 3 balls) (n=15), Weibull modulus, and indentation fracture toughness (n=10) (IF method). The data were analyzed with 1-way ANOVA test (a=.05). The Tamhane multiple comparison test was used for post hoc analysis. RESULTS Mean (SD) of biaxial flexural strength values (MPa) and Weibull modulus (m) results were: Finesse (F): 88.04 (31.61), m=3.17; Cergo (C): 94.97 (13.62), m=7.94; IPS Empress (E): 101.18 (13.49), m=10.13; In-Ceram Alumina (ICA): 341.80 (61.13), m=6.96; In-Ceram Zirconia (ICZ): 541.80 (61.10), m=10.17; and Cercon Zirconia (CZ): 1140.89 (121.33), m=13.26. The indentation fracture toughness results showed that there were significant differences between the tested ceramics. The highest fracture toughness values (MPa x m(0.5)) were obtained with the zirconia-based ceramic core materials. CONCLUSIONS Significant differences were found in strength and toughness values of the materials evaluated. Cercon Zirconia core material showed high values of biaxial flexural strength and indentation fracture toughness when compared to the other ceramics studied.

Influence of surface treatments on surface roughness, phase transformation, and biaxial flexural strength of Y-TZP ceramics

The aim of this study was to evaluate the influence of surface grinding and sandblasting on surface roughness, phase chances, and biaxial flexural strength of yttria-stabilized tetragonal zirconia (Y-TZP) materials. Thirty disk specimens of Cercon (C), DentaCAD (DC), Zirkonzahn (ZZ) were fabricated. The specimens were divided into three groups according to surface treatment (control, ground, and sandblasted). Surface roughness was measured, and X-ray diffraction analysis was performed. Finally, biaxial flexural strength was determined. The data was analyzed by two-way ANOVA. Weibull statistics was used to analyze the variability of strength. The effects of surface treatments on surface roughness values were different for each material. X-ray diffraction analysis revealed that control groups of C and ZZ were composed of tetragonal zirconia. Relative amount of monoclinic zirconia (SD) was 7.366 (0.716)% in the DC control group. In all materials, transformation occurred after treatments. Grinding decreased and sandblasting increased the strength of control groups in all materials. Ground C and DC specimens had higher Weibull modulus than control groups while lower m was found for ground ZZ. Sandblasting, resulted in lower m compared with grinding for all materials although increased strength. The roughness and crystalline phase of Y-TZP materials were influenced by surface treatments. Biaxial flexural strength of materials decreased after grinding and increased after sandblasting. The low m of sandblasted groups may indicate further weakening of the materials, resulting in unexpected failures.

In Vitro Evaluation of Cytotoxicity of Soft Lining Materials on L929 Cells by MTT Assay

The aim of this in vitro study was to evaluate five commonly used soft lining materials, Viscogel (VG), Ufi Gel P (UGP), Softliner (S), Coe-Soft (CS), and Molloplast-B (MB) in terms of cytotoxicity by MTT assay, using L929 mouse fibroblasts. Sixteen disk-shaped specimens from each material were prepared (according to the manufacturers instructions) in stainless steel mold (10 mm diameter and 1.5 mm thick). The specimens were incubated for 24, 48, 72, and 96 h in Dulbeccos Modified Eagle Medium Hams F12 (DMEM/F12) and following each incubation interval, cytotoxicity of the extracts to cultured mouse fibroblasts (L929) were measured by MTT assay. Data were statistically analyzed by two-way analysis of variance (ANOVA), and Duncans test, at a significance level of p < 0.05. Group CS revealed significantly high cytotoxic effect at all incubation periods (p < 0.05). Although no cytotoxic effect for Group S was found at 24, 48, 72 h periods, it has been raised at 96-h incubation period (p > 0.05). Group VG, UGP, S (except at 96 h period), and Group MB demonstrated high cell survival rates at incubation periods.

Effect of fatigue on biaxial flexural strength of bilayered porcelain/zirconia (Y-TZP) dental ceramics

OBJECTIVES The aim of this study was to evaluate the effect of fatigue on biaxial flexural strength of bilayered disks of two Y-TZP cores. METHODS Twenty bilayered veneer/zirconia disks were fabricated from each material (Lava veneer+core, 3M/ESPE, and Cercon veneer+core, Densply). Ten specimens from each material were tested for biaxial flexural strength either with or without being subjected to fatigue (20,000 cycles, 2 Hz, 200 N load) in a universal testing machine (1mm/min). Stresses generated at the core and the veneer, at the top and the bottom surfaces, and the interface of bilayered disk were calculated using Hueshs solutions. Data were statistically analyzed using Weibull statistics. The fractured core was also examined via Raman spectroscopy and the monoclinic fraction was calculated at the top, the middle of thickness, and the bottom of the cross-section of fractured core. The results of monoclinic fraction were statistically analyzed by Three-Factor ANOVA with Repeated Measures on One Factor. RESULTS Weibull modulus (m) of Cercon control (CC), Cercon fatigue (CF), Lava control (LC) and Lava fatigue (LF) were between 11.8 and 14.3, 7.1 and 13.1, 9.4 and 13, and 7.1 and 8.2, respectively. There were no significant differences between characteristic strength (σ(0)) of CC (970.9 MPa) and CF (947.7 MPa) (p>0.05). For Lava, σ(0) of LF (1444.8 MPa) was significantly higher than LC (1240.5 MPa) (p<0.05). At the interfaces, σ(0) values of CC and CF groups were not significantly different while LF showed significantly higher σ(0) than LC. The monoclinic zirconia was significantly lower for CF than CC and significantly higher for LF than LC. SIGNIFICANCE Fatigue showed different effects on the strength of Cercon and Lava ceramic systems. Decreases in m values were observed at the interfaces of two materials after fatigue.

Effect of fatigue on fracture toughness and phase transformation of Y‐TZP ceramics by X‐ray diffraction and Raman spectroscopy

The aim of this study was to evaluate the effect of fatigue on fracture toughness and phase transformation of yttria-stabilized zirconia polycrystal materials (Cercon and Lava). The specimens were tested for indentation fracture toughness either with or without being subjected to fatigue (20,000 cycles, 2 Hz, 200 N load). X-ray diffraction (XRD) analysis was used to examine the phase composition of specimens. The indentation images were analyzed using Raman spectroscopy at indentation center (p1), indentation corner (p2), points on crack 100 μm (p3), and 200 μm (p4) away from the corner and a point ∼80 μm away from the crack (p5). Fracture toughness results were statistically analyzed by two-way analysis of variance (ANOVA); XRD and Raman spectroscopy results were analyzed by three-way ANOVA. Fracture toughness of Cercon control (CC) and fatigue (CF) groups were 6.8 and 6.9 MPa√m, respectively, with no significant difference (p > 0.01). Fracture toughness of Lava fatigue (LF; 7.3 MPa√m) was significantly higher than Lava control (LC; p < 0.01). XRD analyses showed CC and LC consisted of tetragonal zirconia, monoclinic zirconia detected after fatigue. After indentation, relative amount of monoclinic phase significantly increased in CC, CF, and LC; decreased in LF. The Raman spectroscopy results indicated that monoclinic fraction was the highest at p2, subsequently at p1 and decreased at p3, p4, and p5 for all groups. Mechanical cycling increased fracture toughness of Cercon and Lava, the second being significant. Phase transformation was also detected after fatigue, which is higher in Lava. Analysis of indentations showed that transformation was highest was at the corner, second at center.

Finite element analysis of stress distribution with splinted and nonsplinted maxillary anterior fixed prostheses supported by zirconia or titanium implants.

PURPOSE The aim of the present study was to evaluate the effect of splinting titanium (Ti) or zirconia (Zr) implants supporting maxillary anterior fixed prostheses on the stress levels and patterns in the implants, prostheses, and the surrounding bone; and to compare the effects of Zr and Ti implant materials on the stress distribution in splinted and nonsplinted designs via finite element modeling. MATERIALS AND METHODS Zr and Ti dental implants and the anterior maxilla were modeled. In the nonsplinted design (D1), implants were placed into the maxillary left central incisor and canine regions, and a three-unit zirconia fixed prosthesis was modeled. In the splinted design (D2), a symmetric model of D1 was generated and the two prostheses were splinted together to create a six-unit prosthesis. Loading was applied horizontally and obliquely. Von Mises, tensile, and compressive stresses were evaluated in the implants, prostheses, and surrounding bone. RESULTS Under both loading conditions, the stresses on the D2 implants were lower than those in the D1 implants. Stresses were concentrated on the neck of the implant and decreased through the apex. All of the stress values in cortical bone in D1 were slightly higher than in D2 for both implant materials under both loading conditions. CONCLUSION When the implants were splinted together, stresses were reduced in the supporting bone and implants in both loading conditions, but increased stress was observed in the prostheses under oblique loading. Intense stress concentrations were found in the connector of the splinted prosthesis and the cervical region of the nonsplinted prosthesis. Zr and Ti implants showed very similar stress distributions in all materials. Under oblique loading, lower stresses occurred in implants and the prosthesis core material when Ti implants were used.

Effect of surface treatments on the biaxial flexural strength, phase transformation, and surface roughness of bilayered porcelain/zirconia dental ceramics

STATEMENT OF PROBLEM Veneered zirconia restorations are widely used in prosthetic applications. However, these restorations often fail because of chipping of the veneer porcelain. Surface treatments of zirconia core materials may affect the connection between the 2 layers. PURPOSE The purpose of this study was to evaluate the effect of surface treatments on the biaxial flexural strength, phase transformation, and mean surface roughness of different bilayered porcelain/zirconia ceramics. MATERIAL AND METHODS Forty disk-shaped specimens were obtained for each material (Kavo and Noritake) and divided into 4 (n=10) groups (control, airborne-particle abraded, ground, and ground and airborne-particle abraded). Airborne-particle abrasion was performed with 110-μm Al2O3 particles for 15 seconds and at 400 kPa. Diamond rotary instruments with 100-μm grain size were used for grinding. The monoclinic phase transformation and surface roughness of the specimens were measured. Then, the specimens were veneered and subjected to a biaxial flexural strength test to calculate the Weibull moduli (m values) and the stresses occurring at the layers, outer surfaces of the bilayer, and interfaces of the layers. RESULTS The Kavo airborne-particle abraded group showed higher strength values in both layers (P<.05) than those of all experimental groups. The Kavo airborne-particle abraded group showed the lowest m values at the core and veneer layers. According to the phase analysis, significantly higher Xm values were found in the ground and airborne-particle abraded groups for both materials (P<.05). In both materials, except in the airborne-particle abraded groups, the relative monoclinic phases showed no difference (P<.05). CONCLUSION Surface treatments affected the phase transformation, surface roughness, and biaxial flexural strength of Kavo and Noritake zirconia ceramics differently. Surface treatments increased the relative monoclinic phase content and average surface roughness.

A single-tooth, two-piece zirconia implant located in the anterior maxilla: A clinical report

It can be difficult to achieve a natural appearance in the anterior region with implant-supported restorations because metal components may show through the soft tissue. Zirconia implants, therefore, should be considered as an alternative treatment for improved esthetics. The goal of this clinical report was to evaluate a new 2-piece zirconia implant system for the maxillary anterior region. A 2-piece zirconia dental implant was placed in the maxillary left lateral incisor position and left in place for 6 months to osseointegrate. Panoramic and periapical radiographs were examined for bone-implant osseointegration. The plaque control record (PCR), bleeding on probing (BOP), and probing depth (PD) were measured after the cementation of the definitive restoration and a 6-month follow-up period. The PCR, BOP, and PD values were compared and the marginal bone level was also evaluated by making standardized periapical radiographs. The results showed that over the 6-month follow-up period, the marginal area was healthy and presented no bleeding on probing, no plaque accumulation, and no change in periimplant marginal bone level.

An Overview of Zirconia Dental Implants: Basic Properties and Clinical Application of Three Cases

Due to the possible aesthetic problems of titanium implants, the developments in ceramic implant materials are increasing. Natural tooth colored ceramic implants may be an alternative to overcome aesthetic problems. The purpose of this article is to give information about the basic properties of dental zirconia implants and present 3 cases treated with two-piece zirconia implants. Two-piece zirconia dental implants, 4.0 mm diameter and 11.5 mm in length, were inserted into maxillary incisor region. They were left for 6 months to osseointegrate. Panoramic and periapical radiographs were obtained and examined for bone-implant osseointegration. During the follow-up period the patients were satisfied with their prosthesis and no complication was observed.

An impression technique for implant-retained orbital prostheses.

This article describes an impression technique to transfer implant positions to the definitive cast using magnetic attachments splinted with acrylic resin for an implant-retained orbital prosthesis. The acrylic resin transfer device that incorporated the magnets was also used as the acrylic resin magnet substructure for the silicone orbital prosthesis.