Ferhan Egilmez

Factors affecting the mechanical behavior of Y-TZP

AIM The aim was to evaluate the influence of sandblasting with various propulsion pressures on the phase transformation, flexural strength and Weibull modulus of a yttria stabilized tetragonal zirconia polycrystalline ceramic (Y-TPZ). In addition, the susceptibility of cyclic loading and low-temperature degradation under two different conditions (chemical and thermal aging) was investigated. MATERIALS AND METHODS The specimens [105bar-shaped specimens (19.3×14.5×1.3mm(3))] were equally divided into seven groups (n=15) according to the test protocols. The specimens in control group received no surface treatment (Group A). Groups B1, B2 and B3 were airborne-particle abraded with 110μm Al2O3 particles at 200kPa, 400kPa and 600kPa (2bar, 4bar and 6bar) pressure, respectively. Group C was submitted to mechanical cyclic loading under 200N 20,000 times sinusoidal loading/unloading at a frequency of 10Hz between 10% and 100% load in distilled water at 37°C. Group D was submitted to thermal degradation in an autoclave at 134°C under additional 200kPa pressure for 5h. Group E was immersed in 4% acetic acid at 80±5°C for 168h as chemical degradation testing. Following each treatment protocols, the three-point flexure test was used to calculate the flexural strength. Additionally, X-ray diffraction analysis was used to estimate the relative amount of monoclinic phase. The reliability of strength was assessed through the Weibull distribution. Statistical analysis was conducted with one-way ANOVA and Tukey׳s pairwise multiple comparisons. The treated and fractured surfaces were observed with SEM. RESULTS Statistical analysis revealed that there were significant differences among the flexural strength results of all tested groups (F=4.510, p<0.05). Group B2 demonstrated the highest strength values, whereas Group E showed the lowest (625.86±123.57; 466.56±91.50, respectively). Weibull moduli of all tested groups were statistically significant and ranging from 4.3 to 8.3. A greater amount of monoclinic phase was determined in the specimens of D, E and B3 groups (25.43%, 20.89% and 19.71%, respectively). However, lower amount was observed in groups A, B1 and B2 (10.02%, 13.35% and 15.19%, respectively). CONCLUSIONS The present study suggested that flexural strength of zirconia was significantly decreased by chemical degradation. In addition, surface conditioning, cyclic fatigue and thermal, chemical degradation conditions significantly changed the structural reliability of the materials strength.

Micro-shear bond strength of different resin cements to ceramic/glass-polymer CAD-CAM block materials.

PURPOSE The aim of this study was to evaluate the effects of hydrofluoric acid treatment on bond strength of resin cements to three different types of ceramic/glass containing CAD-CAM block composite materials. METHODS CAD-CAM block materials of polymer infiltrated (Vita Enamic), resin nanoceramic (Lava Ultimate) and nanoceramic (Cerasmart) with a thickness of 1.5mm were randomly divided into two groups according to the surface treatment performed. In Group 1, specimens were wet-ground with silicon carbide abrasive papers up to no. 1000. In Group 2, 9.6% hydrofluoric acid gel was applied to ceramics. Three different resin cements (RelyX, Variolink Esthetic and G-CEM LinkAce) were applied to the tubes in 1.2-mm thick increments and light-cured for 40s using LED light curing unit. Half of the specimens (n=10) were submitted to thermal cycling (5000 cycles, 5-55°C). The strength measurements were accomplished with a universal testing machine (Lloyd Instruments) at a cross-head speed of 0.5mm/min until the failure occurs. Failure modes were examined using a stereomicroscope and scanning electron microscope. The data were analyzed with multivariate analysis of variance (MANOVA) and Tukeys post hoc tests (α=0.05). RESULTS There were significant differences between ceramics and resin cements (p<0.001). However, hydrofluoric acid gel treatment had no effect on bond strength values (p=0.073). In addition, thermal cycling significantly decreased bond strength values of resin cements to ceramics (p<0.001). CONCLUSIONS Use of appropriate resin cement systems with different ceramic/glass-polymer materials might promote the bonding capacity of these systems.PURPOSE The aim of this study was to evaluate the effects of hydrofluoric acid treatment on bond strength of resin cements to three different types of ceramic/glass containing CAD-CAM block composite materials. METHODS CAD-CAM block materials of polymer infiltrated (Vita Enamic), resin nanoceramic (Lava Ultimate) and nanoceramic (Cerasmart) with a thickness of 1.5mm were randomly divided into two groups according to the surface treatment performed. In Group 1, specimens were wet-ground with silicon carbide abrasive papers up to no. 1000. In Group 2, 9.6% hydrofluoric acid gel was applied to ceramics. Three different resin cements (RelyX, Variolink Esthetic and G-CEM LinkAce) were applied to the tubes in 1.2-mm thick increments and light-cured for 40s using LED light curing unit. Half of the specimens (n=10) were submitted to thermal cycling (5000 cycles, 5-55°C). The strength measurements were accomplished with a universal testing machine (Lloyd Instruments) at a cross-head speed of 0.5mm/min until the failure occurs. Failure modes were examined using a stereomicroscope and scanning electron microscope. The data were analyzed with multivariate analysis of variance (MANOVA) and Tukeys post hoc tests (α=0.05). RESULTS There were significant differences between ceramics and resin cements (p<0.001). However, hydrofluoric acid gel treatment had no effect on bond strength values (p=0.073). In addition, thermal cycling significantly decreased bond strength values of resin cements to ceramics (p<0.001). CONCLUSIONS Use of appropriate resin cement systems with different ceramic/glass-polymer materials might promote the bonding capacity of these systems.

Effect of Surface Modification on the Bond Strength between Zirconia and Resin Cement

PURPOSE This study aimed to evaluate the micro push-out (μ-PO) bond strength between zirconia and resin cement after addition of zirconia particles to increase the surface roughness. MATERIALS AND METHODS Y-TZP zirconia specimens in three experimental groups were subjected to Y-TZP particle deposition via dipping into the milling residue suspension at different times prior to the sintering process. The dipping procedure was repeated twice for each specimen in group B, six times in group C, and ten times in group D. The specimens subjected to airborne-particle abrasion (110 μm Al2 O3, Rocatec Pre) acted as the control group (group A). All of the specimens were then bonded using adhesive resin cement (RelyX Ultimate). A μ-PO test was used to determine the bond strength values. One-way ANOVA at a 5% confidence level was performed for data analysis. Optical microscopy and scanning electron microscopy (SEM) were used to evaluate the failure modes and surface structure. RESULTS Y-TZP particle deposition did not have a significant effect on the bond strength of the resin cement to zirconia specimens when compared to the control (p = 0.141). Higher bond strength values were observed in groups C and D than in control. The surface layer presented blister-like porosities with openings of various diameters ranging between 2 and 4 μm. CONCLUSION Y-TZP particle deposition after dipping six and ten times did not improve the mean bond strength statistically but presented surface topography that may be favorable for increased micromechanical retention for adhesive resin cement. CLINICAL SIGNIFICANCE Y-TZP particle deposition may create a more retentive surface than airborne-particle abrasion for adhesive bonding between zirconia surface and resin cement.

Effect of reduced exposure times on the cytotoxicity of resin luting cements cured by high-power led.

Objective Applications of resin luting agents and high-power light-emitting diodes (LED) light-curing units (LCUs) have increased considerably over the last few years. However, it is not clear whether the effect of reduced exposure time on cytotoxicity of such products have adequate biocompatibility to meet clinical success. This study aimed at assessing the effect of reduced curing time of five resin luting cements (RLCs) polymerized by high-power LED curing unit on the viability of a cell of L-929 fibroblast cells. Material and Methods Disc-shaped samples were prepared in polytetrafluoroethylene moulds with cylindrical cavities. The samples were irradiated from the top through the ceramic discs and acetate strips using LED LCU for 20 s (50% of the manufacturers recommended exposure time) and 40 s (100% exposure time). After curing, the samples were transferred into a culture medium for 24 h. The eluates were obtained and pipetted onto L-929 fibroblast cultures (3x104 per well) and incubated for evaluating after 24 h. Measurements were performed by dimethylthiazol diphenyltetrazolium assay. Statistical significance was determined by two-way ANOVA and two independent samples were compared by t-test. Results Results showed that eluates of most of the materials polymerized for 20 s (except Rely X Unicem and Illusion) reduced to a higher extent cell viability compared to samples of the same materials polymerized for 40 s. Illusion exhibited the least cytotoxicity for 20 s exposure time compared to the control (culture without samples) followed by Rely X Unicem and Rely X ARC (90.81%, 88.90%, and 83.11%, respectively). For Rely X ARC, Duolink and Lute-It 40 s exposure time was better (t=-1.262 p=0,276; t=-9.399 p=0.001; and t=-20.418 p<0.001, respectively). Conclusion The results of this study suggest that reduction of curing time significantly enhances the cytotoxicity of the studied resin cement materials, therefore compromising their clinical performance.

Bond strength of self-adhesive resin cements to dentin after antibacterial and chelating solution treatment

OBJECTIVE The aim of this study was to evaluate the effect of tetracycline HCl, 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) and chlorhexidine digluconate (CHX) on micro push-out (µ-PO) bond strengths of two self-adhesive resin cements on dentin. MATERIALS AND METHODS Sixty discs of 1.25 mm thickness (middle dentin) were prepared from human molars perpendicular to the tooth axis. Two standardized occlusal cavities of 2.20 mm occlusal diameter and 1.25 mm cervical diameter were prepared in each disc. The cavities were divided into three groups in accordance with the surface treatment (50 mg/ml tetracycline HCl, 18% HEBP and 2% CHX solutions). Following the treatment of the discs for 5 min, cavities were filled with two different self-adhesive resin cements (Clearfil(™) SA Cement and RelyX(™) Unicem). After light polymerization of cements, µ-PO bond strength tests were performed. Failure modes were examined and dentin morphologic assessments were done. Statistical significance was determined by a multivariate analysis of variance (MANOVA) followed by Tukeys post-hoc test (p < 0.05). Additionally, a paired-samples T-test was used to compare the µ-PO bond strengths of self-adhesive resin cements (p < 0.05). RESULTS Paired-samples T-test revealed that there was no significant difference between tested self-adhesive resin cements (p = 0.612). No significant two-factor interaction was observed between Clearfil(™) SA Cement and chemical agents (p = 0.457). Similarly, tetracycline HCl and CHX did not have a significant effect on the bond strength of RelyX(™) Unicem (p > 0.05). However, HEBP significantly decreased the bond strength of RelyX(™) Unicem when compared to the control (p < 0.05). Conclusion. The tetracycline HCl and CHX solutions do not have beneficial effects on µ-PO bond strengths of self-adhesive resin cements. Additionally, the results of this study do not justify the use of self-adhesive resin cements, following HEBP treatment of dentin. CLINICAL SIGNIFICANCE The application of topical HEBP solution treatment to dentin could have adverse effects on the µ-PO bond strengths of RelyX(™) Unicem.

Light transmittance of zirconia as a function of thickness and microhardness of resin cements under different thicknesses of zirconia

Objective: The objective of this study was to compare microhardness of resin cements under different thicknesses of zirconia and the light transmittance of zirconia as a function of thickness. Study design: A total of 126 disc-shaped specimens (2 mm in height and 5 mm in diameter) were prepared from dual-cured resin cements (RelyX Unicem, Panavia F and Clearfil SA cement). Photoactivation was performed by using quartz tungsten halogen and light emitting diode light curing units under different thicknesses of zirconia. Then the specimens (n=7/per group) were stored in dry conditions in total dark at 37°C for 24 h. The Vicker’s hardness test was performed on the resin cement layer with a microhardness tester. Statistical significance was determined using multifactorial analysis of variance (ANOVA) (alpha=.05). Light transmittance of different thicknesses of zirconia (0.3, 0.5 and 0.8 mm) was measured using a hand-held radiometer (Demetron, Kerr). Data were analyzed using one-way ANOVA test (alpha=.05). Results: ANOVA revealed that resin cement and light curing unit had significant effects on microhardness (p < 0.001). Additionally, greater zirconia thickness resulted in lower transmittance. There was no correlation between the amount of light transmitted and microhardness of dual-cured resin cements (r = 0.073, p = 0.295). Conclusion: Although different zirconia thicknesses might result in insufficient light transmission, dual-cured resin cements under zirconia restorations could have adequate microhardness. Key words:Zirconia, microhardness, light transmittance, resin cement.

Comparison of light transmittance in different thicknesses of zirconia under various light curing units

PURPOSE The objective of this study was to compare the light transmittance of zirconia in different thicknesses using various light curing units. MATERIALS AND METHODS A total of 21 disc-shaped zirconia specimens (5 mm in diameter) in different thicknesses (0.3, 0.5 and 0.8 mm) were prepared. The light transmittance of the specimens under three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) was compared by using a hand-held radiometer. Statistical significance was determined using two-way ANOVA (α=.05). RESULTS ANOVA revealed that thickness of zirconia and light curing unit had significant effects on light transmittance (P<.001). CONCLUSION Greater thickness of zirconia results in lower light transmittance. Light-emitting diodes light-curing units might be considered as effective as Plasma arc light-curing units or more effective than Quartz-tungsten-halogen light-curing units for polymerization of the resin-based materials.

Does artificial aging affect mechanical properties of CAD/CAM composite materials

PURPOSE The purpose of this study was to determine the flexural strength and Weibull characteristics of different CAD/CAM materials after different in vitro aging conditions. METHODS The specimens were randomly assigned to one of the six in vitro aging conditions: (1) water storage (37°C, 3 weeks), (2) boiling water (24h), (3) hydrochloric acid exposure (pH: 1.2, 24h), (4) autoclave treatment (134°C, 200kPa, 12h), (5) thermal cycling (5000 times, 5-55°C), (6) cyclic loading (100N, 50,000 cycles). No treatment was applied to the specimens in control group. Three-point bending test was used for the calculation of flexural strength. The reliability of the strength was assessed by Weibull distribution. Surface roughness and topography was examined by coherence scanning interferometry. Evaluated parameters were compared using the Kruskall-Wallis or Mann-Whitney U test. RESULTS Water storage, autoclave treatment and thermal cycling significantly decreased the flexural strength of all materials (p<0.05), whereas HCl exposure or cyclic loading did not affect the properties (p>0.05). Weibull moduli of Cerasmart™ and Lava™ Ultimate were similar with control. Vita Enamic® exhibited similar Weibull moduli in all aging groups except the HCl treated group (p>0.05). Ra values of Cerasmart™ and Lava™ Ultimate were in the range of 0.053-0.088μm in the aged groups. However Ra results of Vita Enamic® were larger than 0.2μm. CONCLUSIONS Flexural strength of newly developed restorative CAD/CAM materials was significantly decreased by artificial aging. Cyclic loading or HCl exposure does not affect to the flexural strength and structural reliability of Cerasmart™ and Lava™ Ultimate.

Micro-shear bond strength of resin cement to dentin after application of desensitizing toothpastes

Abstract Objectives. The aim of the study was to evaluate the effect of three desensitizing toothpastes on bonding of resin cements to dentin. Materials and methods. The occlusal surfaces of 72 maxillary third molars were ground to obtain flat dentin surfaces and then divided into three groups according to three desensitizing toothpastes used: Sensodyne Rapid Relief (GlaxoSmithKline, SmithKline Beecham Ltd., Slough, UK), Signal Sensitive Expert (Unilever Sanayi ve Ticaret Türk A.Ş., Ümraniye, İstanbul, Turkey) and Colgate Sensitive Pro-Relief (Colgate Palmolive, New York, NY). Following bonding of the resin cement (Clearfil™ SA Cement, Kuraray Co, Osaka, Japan) to dentin, the specimens were light cured for 40 s with a LED (Elipar S10, 3M Espe, St. Paul, MN). The strength measurements were accomplished with a micro-shear testing machine (Bisco, Schaumburg, IL) at a cross-head speed of 0.5 mm/min until the failure occurs. Failure modes were examined using a stereomicroscope and scanning electron microscope. The data were analyzed with one-way analysis of variance (ANOVA) and Tukey HSD test (α = 0.05). Results and conclusion. ANOVA revealed that the application of desensitizing toothpastes had significant effects on bond strength of the resin cement tested to dentin (p < 0.05). Mixed failures were observed in all of the groups. Clinical significance. The use of a desensitizing toothpaste before cementation might alter the bond strength of adhesively luted restorations.

Effect of Platelet-Rich Plasma on the Outcome of Early Loaded Dental Implants: A 3-Year Follow-up Study

This study evaluated the effect of local application of platelet-rich plasma (PRP) on the outcome of early loaded implants. Two implants were placed in the posterior region or bilaterally symmetric to the median line of the maxilla. Then, PRP was either applied or not applied to the implant sockets. Outcome measures were prosthesis and implant success as well as biological and prosthetic complications. Stability of individual implants was assessed manually and with a resonance frequency analysis device. The implant stability quotient (ISQ) was recorded on the operation day, on postoperative day 4, and at postoperative week 1. At the end of the first postoperative week, implants with ISQ values >60 were early loaded on day 7 with metal-ceramic crowns. Measurements were repeated at postoperative weeks 2, 3, and 4 and at postoperative months 6, 12, 24, and 36. One of the 64 implants was dropped out after 3 months of loading. No prosthesis failed. There were no prosthetic complications. Statistical analysis r...