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    The effect of repeated firings on the color of an alumina ceramic system with two different veneering porcelain shades
    (Mosby-Elsevier, 2010) Şahin, Volkan; Uludağ, Bülent; Üşümez, Aslıhan; Özkır, Serhat Emre
    Statement of problem Possible sources of processing variables in porcelain firing include thickness and color of the opaque, thickness, color, and translucency of the body and enamel layers, firing temperature, and number of firings Purpose The purpose of this in vitro study was to investigate the color changes of an alumina ceramic system veneered with different veneering porcelain shades and fired different numbers of times Material and methods Twenty disc-shaped ceramic specimens (10 mm in diameter, with a core thickness of 1 mm), with 2 different veneering porcelain shades (A1, A3), were fabricated from an alumina ceramic system (Turkom-Cera) (n=10) Repeated firings (3, 5, 7, or 9 firings) were performed, and color differences (Delta E) were determined using a spectrophotometer Repeated-measures ANOVA was used to analyze the data (number of firings, veneering porcelain color) The Duncan test and paired 2-tailed tests were used for multiple comparisons (alpha = 05) Results The L*a*b* values of the ceramic system were affected by the number of firings (3, 5, 7, or 9) (P < 005) and veneering porcelain shade (P < 001) Significant interactions were present between the number of firings and the veneering porcelain shade for L* (P = 002), a* (P = 001), and b* (P = 001) values A1 shade specimens maintained their L* value independent of the number of firings, whereas A3 shade specimens became lighter after an increased number of firings For both A1 and A3 veneering porcelain shades, the a* value decreased after repeated firings, which resulted in less reddish specimens, and the b* value decreased after repeated firings, which resulted in less yellowish specimens Conclusions Imperceptible (Delta E<1 6) and clinically acceptable color changes (Delta E<3 7) were demonstrated by the alumina ceramic system tested (J Prosthet Dent 2010,104 372-378)
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    Effect of Storage Time on Tear Strength of Extended-Pour Irreversible Hydrocolloid Impression Materials
    (2018) Şahin, Volkan; Jodati, Hossein; Evis, Zafer
    Objective: The aim of this in vitro study was to evaluatethe effect of prolonged storage times on the tear strength ofextended-pour irreversible hydrocolloid impression materials.Material-Method: Eighty four specimens were fabricatedfrom five commercial extended-pour irreversiblehydrocolloid impression materials (BluePrint Xcreme,Hydrogum 5, Kromopan, Alginmax and Alginelle) as wellas one experimental formula in accordance with the ISO21563:2013 standard effective for irreversible hydrocolloidimpression materials. Specimens were randomly divided intwo groups for each impression material (n=7) and subjectedto tear strength test immediately (base line) or after 120 hoursof storage. Tear strength values were obtained in N/mm anddata were analysed with two-way ANOVA (irreversiblehydrocolloid brand, storage time). Multiple comparisonswere performed with Tukey’s test (p=0.05).Results: The tear strength of the extended-pour irreversiblehydrocolloid impression materials were affected by brand(p<0.0001) and brand-storage time interaction (p=0.005).Storage time did not influence the tear strengths of theextended-pour irreversible hydrocolloid impression materialstested except Alginmax whose mean tear strengths increasedafter 120 hours of storage (p<0.05). At base line measurementsBlueprint Xcreme provided the highest mean tear strengthvalues (1.08±0.19 N/mm) whereas Alginelle provided thelowest mean tear strength values (0.51±0.3 N/mm). Hydrogum5 provided the highest tear strength values after 120 hours ofstorage (1.15± 0.12 N/mm) whereas Alginelle provided thelowest mean tear strength values (0.55±0.04 N/mm).Conclusions: All commercial extended-pour irreversiblehydrocolloid impression materials tested maintained their tearstrengths after 120 hours of storage.
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    Effects of silica coating and silane surface conditioning on the bond strength of metal and ceramic brackets to enamel
    (E H Angle Education Research Foundation, Inc, 2006) Atsu, Saadet Sağlam; Gelgör, İbrahim Erhan; Şahin, Volkan
    Objective: To evaluate the effect of tribochemical silica coating and silane surface conditioning on the bond strength of metal and ceramic brackets bonded to enamel surfaces with light-cured composite resin. Materials and Methods: Twenty metal and 20 ceramic brackets were divided into four groups (n = 10 for each group). The specimens were randomly assigned to one of the following treatment conditions of the metal and ceramic brackets' surface: (1) tribochemical silica coating combined with silane and (2) no treatment. Brackets were bonded to the enamel surface on the labial and lingual sides of human maxillary premolars (20 total) with a light-polymerized resin composite. All specimens were stored in water for 1 week at 37 degrees C and then thermocycled (5000 cycles, 5 degrees C to 55 degrees C, 30 seconds). The shear bond strength values were measured on a universal testing machine. Student's t-test was used to compare the data (alpha = 0.05). The types of failures were observed using a stereomicroscope. Results: Metal and ceramic brackets treated with silica coating with silanization had significantly greater bond strength values (metal brackets: 14.2 +/- 1.7 MPa, P < .01; ceramic brackets: 25.9 +/- 4.4 MPa, P < .0001) than the control groups (metal brackets: 11.9 +/- 1.3 MPa; ceramic brackets: 15.6 +/- 4.2 MPa). Treated specimens of metal and ceramic exhibited cohesive failures in resin and adhesive failures at the enamel-adhesive interface, whereas control specimens showed mixed types of failures. Conclusions: Silica coating with aluminum trioxide particles coated with silica followed by silanization gave higher bond strengths in both metal and ceramic brackets than in the control group.
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    Effects of the type and rigidity of the retainer and the number of abutting teeth on stress distribution of telescopic-retained removable partial dentures
    (Elsevier Taiwan, 2012) Şahin, Volkan; Akaltan, Funda; Parnas, Levend
    Background/purpose: Little is known about the force-transmission characteristics and patterns of telescopic-retained removable partial dentures (RPDs) as related to their type and rigidity (rigid and/or resilient) and the number of abutting teeth supporting the telescopic dentures. In this study, we compared the strain around the abutting teeth and edentulous ridges supporting telescopic-retained RPDs with different designs using a strain gauge technique. Materials and methods: A maxillary model including four abutting teeth (# 14, 13, 23, and 24) was constructed and is referred to as Case 1. In total, four RPD frameworks (two resilient and two rigid) were fabricated for Case 1 with a conventional telescope retainer and attachment-retained telescopic retainer (ARTR) groups. A vertical static load of 280 N was applied, and strain values obtained from the strain gauges were recorded. RPDs were modified according to the following cases-Case 2 included teeth 14, 13, and 23; Case 3 included teeth 14 and 13; and Case 4 included teeth 13 and 23-and measurements were repeated. A randomized block analysis of the variance test was conducted using a general linear model procedure with statistical software. Multiple comparisons between groups were performed using Tukey's honest significant difference test (alpha = 0.05). Results: RPDs with an ARTR produced more strain distal to the abutting teeth than RPDs with a conventional telescope retainer. Both retainer types with a rigid design produced more strain distal to the abutting teeth than did retainers with a resilient design. RPDs supported by four, three, and two unilateral abutting teeth produced similar strain patterns. RPDs supported by two bilateral abutting teeth produced the highest strain distal to the abutting teeth, but there was no significant difference between the strains produced by RPDs supported by either two unilateral or bilateral abutting teeth. The highest strain values were obtained from strain gauges distal to the "terminal" abutting teeth. Directions of the principal strain were in a vertical direction for gauges located distal to the terminal abutting teeth. More strain was produced on the posterior edentulous ridges. Conclusion: RPDs with an ARTR and both retainer types with a rigid design produced more strain distal to the abutting teeth. Using more than two abutting teeth did not improve the strain patterns of the tested RPDs. More strain was produced on the posterior edentulous ridges. Copyright (c) 2012, Association for Dental Sciences of the Republic of China. Published by Elsevier Taiwan LLC. All rights reserved.
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    A Technique for Constructing a New Maxillary Overdenture to a Nonretrievable Implant Connecting Bar
    (Allen Press Inc, 2013) Uludağ, Bülent; Polat, Serdar; Şahin, Volkan; Göktuğ, Gürkan
    The most frequent mechanical complications of the bar-implant-retained overdentures are loosening of the bar screws and the need to reactivate the retentive clips. This article describes a technique to construct a new maxillary overdenture to a nonretrievable round-profile implant connecting bar with 2 distally placed attachments. The retainer round-profile bar was nonretrievable due to a worn retaining screw head. Attachment transfer analogs are used to transfer the position of the attachments to the master cast. The technique allows the clinician to construct new overdentures without the need for removal of the implant connecting bar. Reduced chairside time, reduced treatment cost, and increased patient satisfaction are the major advantages of the technique.