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    Comparison of the effects of different loading locations on stresses transferred to straight and angled implant-supported zirconia frameworks: a finite element method study
    (Taylor & Francis Ltd, 2015) Guven, Sedat; Atalay, Yusuf; Asutay, Fatih; Ucan, Musa Can; Dundar, Serkan; Karaman, Tahir; Gunes, Nedim
    The paper presents three-dimensional (3D) finite element models of straight and angled implants and their zirconium-based superstructures. The key objective was to compare the influence of different loading conditions on the stress distribution of straight and angled implants and the zirconia frameworks. 3D finite element straight- and angled-implant models of a mandibular section of bone with missing second molars and their zirconium-based superstructures were used. The straight and angled implants were 4.7 x 13-mm screw-type dental implant systems. Total loads of 300 N were applied in a vertical direction and in an oblique (30 degrees to the vertical) direction buccolingually. Maximum and minimum von Mises stress values of the titanium structures (abutment and implant body) and zirconia frameworks were calculated. When the two groups were examined, the highest stress value was in the zirconia framework of the angled implant-supported model with an oblique loading force (731.46 MPa). The lowest stress values were concentrated in the straight implant-supported model. Thus, the stress values in the angled implant-supported crown were higher than those in the straight implant-supported model. Stress values with oblique loading forces were higher than the values with vertical loading forces. The highest stress value in the zirconia framework was similar to the ultimate strength of the zirconia.
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    The Effect of Ytterbium-Doped Fiber Laser with Different Parameters on Physical Properties of Zirconia Surface
    (Mary Ann Liebert, Inc, 2017) Unal, Server Mutluay; Ozkir, Serhat Emre; Polat, Zelal Seyfioglu; Guven, Sedat; Asutay, Hilal
    Objective: Laser irradiation is an alternative surface treatment method for roughening zirconia surfaces. The aim of this study was to evaluate the effects of ytterbium-doped fiber laser (YbPL) on zirconia. Background: Zirconia surfaces are resistant to many surface treatment methods, but surface roughness is crucial for adhesion of veneering materials and cements to zirconia. Methods: The zirconia discs were prepared and divided into four groups according to the power of the laser irradiation (5, 12, 17, and 20W). These groups were divided into five subgroups according to the frequency (25, 40, 60, 80, and 100kHz). Surface roughness values were measured with a noncontact profilometer, and the mean Ra values were calculated. Wettability was measured with a goniometer. The surface morphology was observed with a scanning electron microscope (SEM). The changes in the surface crystalline structure were analyzed with X-ray diffractometry. Results: Ra values of all groups were higher than the control group. The highest surface roughness value was at 20W and 100kHz. Best wettability characteristic was observed at 5W and 60kHz. The correlations between Ra and wettability were low but significant. SEM examination of 5W with different frequencies showed no microcracks, however, melted areas were observed. Remaining groups had microcracks and melted layers. A significantly lower T/M-phase transformation was observed in some groups. Conclusions: YbPL irradiation was effective at roughening the zirconia surface. Although laser treatment affected zirconia surfaces and provided surface roughness, the power and frequency should be adjusted to achieve optimum results.
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    Evaluation and comparison of the marginal adaptation of two different substructure materials
    (Korean Acad Prosthodontics, 2015) Karaman, Tahir; Ulku, Sabiha Zelal; Zengingul, Ali Ihsan; Guven, Sedat; Eratilla, Veysel; Sumer, Ebru
    PURPOSE. In this study, we aimed to evaluate the amount of marginal gap with two different substructure Materials using identical margin preparations. MATERIALS AND METHODS. Twenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables. REAMS. According to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, 24.47 +/- 5.82 mu m before and 35.11 +/- 6.52 mu m after cementation; in the laser-sintered Co-Cr structure, it was, on average, 60.45 +/- 8.87 mu m before and 69.33 +/- 9.03 mu m after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface. CONCLUSION. Marginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.
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    Examination of stress distribution and fracture resistance in five-unit tooth- nd implant-supported partial fixed zirconia prosthesis
    (Taylor & Francis Ltd, 2015) Guven, Sedat; Aguloglu, Suleyman; Beydemir, Koksal; Dundar, Serkan; Atalay, Yusuf; Ucan, Musa Can; Asutay, Fatih
    In this study, stress distribution and fracture strength values of zirconia frameworks were compared in five-unit tooth- and implant-supported fixed zirconia prosthesis. Three-dimensional finite element stress analysis and static non-linear analysis were used. Because of the boundary conditions determined for these methods, the tooth- and implant-supported models only included the regions of tooth numbers 43-47. The highest stress value (901.845 MPa) was measured in Model 1 (five-unit tooth-supported fixed zirconia bridge) at the mesial gingival neck area of restoration number 45. This stress value was within the ultimate strength of zirconia (900-1200 MPa). Stress values for connector regions were not in the ultimate strength value of zirconia. Stress values in the tooth-supported fixed zirconia bridge were more than the values in the implant-supported fixed zirconia bridge. The highest stresses in Model 2 (five-unit implant-supported fixed zirconia bridge) occurred in the restoration that the model was installed on. The obtained results showed that five-unit tooth-supported posterior zirconia fixed bridge prostheses are not recommended and that the second premolar region is most seriously affected in terms of stress.
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    Long-term effects of antihypertensive medications on bone mineral density in men older than 55 years
    (Dove Medical Press Ltd, 2014) Agacayak, Kamil Serkan; Guven, Sedat; Koparal, Mahmut; Gunes, Nedim; Atalay, Yusuf; Atilgan, Serhat
    Introduction: In this study, we investigated the effects of long-term antihypertensive treatment with calcium channel blockers or beta blockers on the bone mineral density of maxilla, as determined by cone-beam computed tomography (CBCT). Material and methods: This retrospective study was conducted on CBCT images of men older than 55 years who had received different dental indications. Data were grouped into three categories according to the antihypertensive medication history of the patients: group A included patients who had been taking beta-blocker treatment for more than 5 years, group B included patients who had been taking calcium channel blocker treatment for more than 5 years, and the control group included patients who had never used any hypertensive medications before. Results: Statistically significant differences were observed between the beta blocker and calcium channel blocker groups. Conclusion: In hypertension treatment, beta blockers may be preferred to calcium channel blockers in patients at high risk for osteoporosis and bone resorption. Keywords: bone mineral density, CBCT, beta blockers, calcium channel
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    Three-dimensional finite-element analysis of a single implant-supported zirconia framework and its effect on stress distribution in D4 (maxilla) and D2 (mandible) bone quality
    (Taylor & Francis Ltd, 2015) Guven, Sedat; Demirci, Fatih; Yavuz, Izzet; Atalay, Yusuf; Ucan, Musa Can; Asutay, Fatih; Altintas, Eyyup
    The aim of this in-silico study was to compare stress distributions in implants and zirconia frameworks of mandibular and maxillary implant-supported crowns. For comparison, vertical and oblique loading forces were used. Three-dimensional finite-element implant models of a mandibular section of bone (D2) and a maxillary section of bone (D4) with missing second molars and their zirconium-based superstructures were used. Zimmer dental implants of 13 mm in length and 4.7 mm in diameter were modelled. A load of 200 N was applied toward vertical and oblique (30 degrees to the vertical) directions. Maximum and minimum von Mises stress values of the implants and the zirconia framework were calculated. The highest stress value was concentrated in the zirconia framework of the maxillary implant-supported model with the oblique loading force (301.17 MPa). The lowest stress value was concentrated in the mandibular implant-supported model. And the stress values in the maxilla were higher than in the mandible. The maxilla (D4) showed higher stress values than in the mandible (D2), because the trabecular bone is weaker and less resistant to deformation than the cortical bone. Stress values with oblique loading forces were higher than with vertical loading forces. Because of the high Young's modulus of zirconia (low elastic properties), zirconia frameworks showed higher stress values than the implants.
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    Three-dimensional finite-element analysis of two ceramic inlay restorations with different cavity designs
    (Taylor & Francis Ltd, 2015) Guven, Sedat; Akdogan, Mehmet; Oz, Cihan; Dogan, Mehmet Sinan; Unal, Mehmet; Unal, Server; Sahbaz, Cafer
    The aim of this in silico investigation was to examine the influence of two ceramic inlay materials with different cavity designs on stresses in the inlay. Finite-element analysis and three-dimensional modelling were used to examine the stress in ceramic inlays resulting from a 250-N point load on occlusal surfaces. The adhesion properties and von Mises stress values in the enamel, dentin, ceramic materials and cement linings were simulated. Two ceramic inlay materials: porcelain ceramic (Empress II, Ivoclar Vivadent, Liechtenstein) and zirconia ceramic (ICE Zirkon, Zirkonzahn SRL, Gais, Italy), as well as two cavity corner designs: rectangular and rounded, were evaluated. The obtained von Mises stress results indicated that the maximum and minimum forces were concentrated in the enamel and dentin, respectively. The stress values in the dentin and inlay material were similar in the porcelain ceramic and zirconia ceramic groups. However, in the enamel, the stress values in the zirconia ceramic group were significantly lower than those in the porcelain ceramic group. Additionally, cavities with rounded corners were subject to significantly less stress compared to those with rectangular corners. Thus, the zirconia ceramic inlay demonstrated better performance under applied stress, based on the reduced stress values in the tooth structure. Cavities with rounded corners showed less stress than those with rectangular corners, which could be attributed to the enhanced stress distribution capabilities of rounded corners.