Gulden Sinmazisik

Evaluating the ability of dental technician students and graduate dentists to match tooth color

STATEMENT OF PROBLEM The ability of dental technician students to match tooth shade with the Vita 3D-Master shade guide and Toothguide Training Box has not been investigated. PURPOSE The purpose of this study was to evaluate and compare the shade-matching ability of dental technician students and graduate dentists using the Vita 3D-Master shade guide. MATERIAL AND METHODS Twenty-nine dental technician students (DTS group) and 30 graduate dentists (GD group) participated in this study. The Toothguide Training Box (TTB) was used to train the participants and test their shade-matching abilities. Shade-matching ability was evaluated with 3 exercises and a final test, all of which are components of the TTB. The number of mistakes for each participant for value (L), chroma (c), and hue (h) were recorded during the exercises and the final test, and the mistake ratios were calculated. Color difference (ΔE) values for each shade were calculated from the L*, a*, and b* values of the Vita 3D-Master shade guide for each participant in both groups. The Mann-Whitney U test was used to determine statistically significant differences between the L, c, and h mistake ratios of the 2 groups, and the Student t test was used to determine statistically significant differences between the final test scores and the ΔE values of the groups (α=.05). RESULTS The mistake ratio for L in the GD group was significantly higher than that of the DTS group (P<.05), whereas the mistake ratio for h in the DTS group was higher (P<.001). No significant differences were observed between the groups regarding the mistake ratios for c (P>.05). With regard to the final test scores and the ΔE values, no significant differences were found between the groups (P<.001), and the DTS group received higher scores than the GD group (912 and 851). The mean ΔE values for the DTS and GD groups were 1.72 and 2.92. CONCLUSIONS DTSs made more mistakes in the h parameter than GDs, and GDs made more mistakes in the L parameter than DTSs. With regard to the final test scores and the ΔE values, DTSs were more successful in shade matching than GDs.

The effect of zirconia thickness on the biaxial flexural strength of zirconiaceramic bilayered discs

The aim of this study was to assess the effect of zirconia core thickness on the biaxial flexural strength values of zirconia-porcelain bilayered discs. A total of 60 discs with 0.3, 0.4, and 0.5 mm thickness were obtained from a fully sintered zirconia block. A 1.5-mm thick layer of veneer porcelain was fired on the zirconia specimens and biaxial flexural strength tests were performed on the bilayered discs. In each group, the loading surface was the veneer porcelain in half of the specimens (core in tension) and the zirconia core surface in the other half (core in compression). The zirconia core thickness had no effect on the biaxial flexural strength of zirconiaporcelain bilayered discs when the core was in tension (p>0.05). Whereas, when the core was in compression, an increase in the zirconia core thickness resulted in an increase in the biaxial flexural strength (p<0.05).

Mechanical Properties of Endodontic Posts

This study aims to determine the stiffness, elastic limit and strength of selection of endodondic posts recently introduced on the market. Endodontic posts of ceramic (Finesse, Dentsply), zirconia (Cosmopost, Ivoclar Vivadent) and fiber reinforced composite post (FRC Postec, Ivoclar Vivadent) were cemented in a metal block and loaded an angle of 45 in an Instron type Testing Machine. From the recorded force-deflection curves the three mechanical properties were determined. The results show that considerable differencies exist with respect to mechanical properties between the investigated newer types of endodontic posts. The ceramic endodontic post (Finesse) had the lowest values of strength and elastic limit but the stiffness values of Finesse posts were between Cosmopost and FRC. The FRC post had the lowest values of stiffness but intermediate values of strength and elastic limit. The Cosmopost, had the highest strength, limit and stiffness values of all the posts investigated. Introduction In many cases, endodontically treated teeth are provided with restorations involving endodontic posts [1]. Restorations involving endodontic posts have been investigated in quite a few clinical studies in which the cause of failure have been recorded [1-4]. The main causes of failure were identified as: caries, loss of retention of the post, loss of retention of the crown, root fracture, post distortion and post fracture. Although several factors are involved, some of these failures are related to the mechanical properties of the posts. Obviously, this is the case with distortion and fracture of the post, where a relatively high elastic limit and strength will reduce the risk. Increasing the thickness of the post will make stronger, but less tooth structure remains, and the combined effect may well be a reduction of the strength of the assembly [5,6]. The mechanical properties of endodontic posts and core restorations have been studied extensively in the past [6-9]. Previously, posts which were cast in a precious alloy or prefabricated posts made of stainless steel, titanium or precious alloy were used. Recently, several new types of post material have been introduced to the dental community. These are Cosmopost (consist of zirconium oxide stabilized with small amounts of yttrium oxide), Finesse core (based on feldsphatic porcelain by leucite particles) and FRC (made of glass-fiberreinforced composite). These posts are intended to be adhesively cemented into the root canal. The literature is sparse with information on the mechanical properties of these new types of endodontic posts [1-5]. It was the aim of the present study to measure stiffness, elastic limit, and the strength of a selection of endodontic posts recently introduced to the market. Materials and Methods Three types of posts were investigated in this study. One of the posts was made of zirconia (Cosmopost, Ivoclar Vivadent, Liechtenstein; diameter = 1.6 mm) and the other post was made of glass fiber-reinforced composite material (FRC Postec, Ivoclar Vivadent; diameter = 2 mm). The Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2059-2062 doi:10.4028/www.scientific.net/KEM.264-268.2059

A Comparative Study of the Effect of Different Polishing Systems on Ceramic Dental Surfaces

Although porcelain is the most esthetic restorative material available, it is subject to fracture during function. Glazing reduces the size of flaws in the surface of the porcelain and increases its resistance to crack propagation. The purpose of this study is to compare several polishing systems and the effects on the flexural strength of the ceramic material. 28 specimens were prepared from a feldsphatic body porcelain (Finesse-Dentsply Inc.) fabricated by sintering. These specimens were randomly divided into four groups. Whereas the specimens in the first group were glazed, those in the second were autoglazed and those in third and fourth groups were mechanically polished using different diamond polishing pastes. Surface roughness and 4-point bending tests were conducted on these specimens to determine the effects of using different polishing systems on dental ceramic surfaces. The glazed group displayed the highest flexural strength values and there were no statistically significant differences in the strength and the surface roughness values of the other three groups.

The Effect of Decalcified Root Surfaces on Dentinal Bond Strength

Microtensile bond strengths of current dentin adhesives to intact and decalcified root surfaces were evaluated. Two hundred and twenty-four extracted human incisors were divided into two groups as intact (IRD) and decalcified (DRD). The roots of DRD teeth were placed in a demineralization solution to produce artificial carious-like lesions. Root surfaces were slightly ground and treated with either Scotchbond Multi-Purpose (SMP), Adper Single Bond Plus (SBP), Adper Easy Bond (AEB), Scotchbond SE (SSE), Clearfil SE Bond (CSE), Clearfil Protect Bond (CPB), Clearfil Tri-S Bond (CTS), FL-Bond II (FLB), XP Bond (XPB), iBond (IB), AdheSE Bond (ASE), Optibond Solo Plus (OSP), Prelude Dental Adhesive (PDA), and G-Bond (GB). Composite build-ups were formed on the bonded surfaces. After thermocycling, hour-glass shaped specimens with an area of 1 mm2 at the bonded interface were subjected to microtensile testing. Resin–dentin interfaces were observed with SEM. Kruskal Wallis and Mann Whitney-U tests were used for statistical analysis. There was not significant difference between bond strengths to intact and decalcified dentin, with the exception of ASE and CSE, which had higher values to IRD (p < 0.05). SSE and CTS were the adhesives that showed higher bond strengths to DRD than to IRD, however the difference was not significant (p > 0.05). The self-etch adhesives performed better on both IRD and DRD surfaces than etch-and-rinse systems.

Effect of Different Surface Applications and Adhesive Systems on Bond Strength of Porcelain Repair Material

The purpose of this study was to evaluate the effect of different surface treatments and adhesive systems on bond strength of composite resin to porcelain when there is need to repair the restoration.Materials and methods: Rectangular discs (10mm x 12mm) with a height of 2mm were prepared from leucite-reinforced feldspathic ceramic CAD/CAM blocks (Vitablocs), embedded in acrylic resin, and bur cut porcelain surfaces were created. The specimens were divided into three groups (n=20) according to the surface treatments: Er:YAG laser at 2W for 20 seconds, air abrasion with 50µm Al2O3 at 2.5 bar for 15 seconds, and the last group left untreated as control. After silane (Monobond S) application on ten specimens from each group, composite rods (Aelite Flo LV) with 4.25mm diameter and 4mm height were bonded to ceramic surfaces with a self-etch adhesive system (All-Bond SE). The remaining ten specimens from each group were etched with 36% orthophosphoric acid (Blue Etch Dental Etching Gel), and after silane and bonding agent (One-Step Plus) application composite rods with the mentioned dimensions were bonded. All groups were stored in distilled water at 37°C for one day before mechanical testing. Shear testing of all groups were performed on a universal testing machine with a load cell of 50kg and at a crosshead speed of 1.5mm/min. Results were statistically analyzed using Mann Whitney U and Kruskall Wallis tests.Results: The bond strength values of the self-etch adhesive system in the lased and control groups were statistically higher in comparison to the other adhesive system (p<0.01, p<0.05, respectively). The highest bond strength values were obtained in the Er:YAG lased and self-etch adhesive applied group.Conclusions: When there is need to repair of a porcelain restoration, a self-etch adhesive application after Er:YAG laser treatment could be the method of choice.

Mechanical Properties of CAD/CAM Manufactured and Prefabricated Endodontic Posts

The aim of this study was to evaluate the stiffness, elastic limit and strength of CAD/CAM manufactured metal and zirconia posts in comparison to prefabricated zirconia and glass-fiber posts. Materials and methods: Four types of posts were investigated in this study (n=40). Prefabricated posts made of zirconia (Cosmopost) and glass-fiber reinforced composite (FRC Postec Plus), and Cr-Co (Magnum Lucens) and zirconia (Zirkonzahn) posts manufactured with a CAD/CAM system were used. Artificial root canals with similar diameters to those of the posts were drilled on a stainless steel metal block and the posts were cemented with a self-etch/self-adhesive dual cure resin cement (Totalcem). The posts were loaded in a universal testing device at an inclination of 135 degrees at a crosshead speed of 1mm/min. The force-deflection curves were recorded, and stiffness, elastic limit and strength of the posts were determined. Data were analyzed statistically using Mann Whitney U and Kruskall Wallis tests.Results: The difference between the strength, elastic limit and also stiffness values of the groups was statistically highly significant (p<0.01). CAD/CAM Cr-Co posts showed the highest values of strength, elastic limit and stiffness amongst all the posts investigated. CAD/CAM zirconia posts had the lowest values of strength, and FRC had the lowest values of elastic limit and stiffness. Cosmopost had higher values of elastic limit and stiffness compared to CAD/CAM zirconia posts.Conclusions: If an endodontic post restoration is required, functional load and aesthetics should be considered in addition to mechanical properties of the material selected.

Microstructural Characterization and Bond Strength of the Interface Area between Dental Core and Body Porcelains

To fabricate all-ceramic fixed partial dentures with appropriate fracture strength and aesthetics, new ceramic core materials were recently introduced into the dental market. In this study, the bond strengths of the core and body porcelains of 3 different brands were determined by 4-point bending tests. Two of these brands were hot-pressed ceramics and one was glass-infiltrated presintered alumina. There were significant statistical differences in the bond strength values of the specimens of the three groups, the highest values belong to the combination of the glass-infiltrated presintered alumina as core and feldsphatic porcelain as body porcelain. Scanning Electron Microscopy investigations were carried out to examine the fracture surfaces. Introduction The use full-porcelain fixed partial dentures is still controversial, although materials for porcelain frameworks have been introduced into the market as well as new techniques and technologies[1]. In recent years, there has been a succession of new forms of full-porcelain crowns. In the case of full-ceramic crowns, the ideal design can be generalized as an inner, high strength coping with outer porcelain layers providing the aesthetic needed to reproduce the appearence of a natural tooth[2]. The interface between body porcelain and core should be free of flaws and have a strong bond[2]. In addition, interfaces play an important role in the mechanical performance of biomaterial ceramic composites such as core-veneered full-porcelain dental restorations [3]. When interface toughness exceeds the flexural stresses in the tensile surface at failure, a sharp crack will propagate and penetrate through the core-veneer interface, essentially behaving like a homogeneus material. Alternatively, when flexural stresses at failure exceed the interface toughness, the crack may deflect and extend along the interface between core and veneer with delamination resulting[3]. The aim of this study was to investigate the bond strength between the core and body porcelain of 3 different brands of full ceramic systems. Materials and Methods Three groups of core porcelain and three groups of veneering porcelains were used for this study. Two of the core materials were dewaxed hot pressed ceramics and one was glass-infiltrated alumina.(Table 1). 14 samples having the dimensions of 4 x 4 x 20 mm were prepared for each core material to obtain a total of 42 samples. These were prepared according to the manufacturer’s directions as precisely as possible. 7 samples in each group were placed 1.5 mm apart from the remaining 7 samples and the space in between was filled with the body porcelain of the system. The surfaces of the core specimens that faced the interspace were gently cleaned with 50 micron alumina at about 0.14 Mpa (20 psi). All samples were then cleaned with a steam cleaner before the application of the body porcelain and followed by sintering. The bond strength between core and body porcelain was investigated by four-point bending tests (inner span 8 mm, outer span 37 mm) in a 100 kN Servohydraulic Dartec Universal Testing Machine (Dartec Ltd., U. K.). Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 2063-2066 doi:10.4028/www.scientific.net/KEM.264-268.2063

Evaluation of Porcelain Surface Treatments and Agents for Composite to Porcelain Repair

The purpose of this study was to investigate the effects of Nd:YAG laser, air abrasion and acid-etching on the porcelain surface and repairment. Ten standard cylindrical specimens were made for each preparation (Finesse Dentsply). The specimens were lased for five seconds at a fluence of 80 mJ and a frequency of 20 Hz; air abraded for five seconds with 50 micron Al-oxide (at 60 psi); and acid etched with % 9,6 hydrofluoric acid for 120 seconds. The specimens were examined in the scanning electron microscopy (SEM) before and after the Nd:YAG laser, air abrasive and acid-etching. After silane coupling agent was applicated, two flowable restorative materials (Admira Flow, Voco; Tetric Flow, Vivadent) were bonded to the porcelain surfaces. Each group was stored in distilled water at 37oC for one day before the determination of shear bond strengths. A shear bond strength machine with 50 kg load cell and a 0.5 mm/min crosshead speed was used. The results were analyzed statistically. There was a significance between the shear bond strenth values of Admira Flow and Tetric Flow in the lased group (p<0.05). Introduction Metal-ceramic crowns combine the beauty of porcelain and the strength of metal alloys in a single restoration. Although the strength of porcelain and the bond strength of the metal substrate have improved greatly, some failures still occur under clinical conditions. The main reason for porcelain fracture is inadequate tooth preparation which results in very small interocclusal space for the metal substructure and porcelain [1]. Remaking of the crown or fixed partial denture is often inadvisable, and intraoral repair with a composite resin may be indicated [2-4]. Several intraoral porcelain repair systems are available but most of them have been only moderately succesful. Clinical procedures for nearly all systems have been complex and time consuming. Succesful repair has been an even greater problem with the metal substructure has been exposed. In this study, in vitro repair system has been evaluated. The porcelain repair systems consist of flowable composite resins (Admira Flow, Voco; and Tetric Flow, Vivadent) were used as repair materials. Materials and Methods The materials used in this study are shown in the Table 1. Porcelain discs (10 mm diameter x 3 mm) were fabricated on base metal cylinders in a porcelain furnace. The porcelain discs were then embedded in chemical-cured acrylic resin cylinders (Meliodent, Bayer) with the dimensions of 35 mm in diameter x 23 mm in height. The porcelain surfaces were polished with #600 silicon carbide papers. The porcelain specimens were divided into three groups and each group was subjected to one of the following procedures: 1) lased for five seconds at a fluence of 80 mJ and a frequency of 20 Hz; 2) air abraded for five seconds with 50 micron Al-oxide (at 60 psi); and 3) acid etched with %9,6 hydrofluoric acid for 120 seconds (Finesse All-ceramic; Dentsply, USA). Key Engineering Materials Vols. 264-268 (2004) pp. 2039-2042 online at http://www.scientific.net

Effects of Different Acid Treatments on Dental Ceramic Surfaces

In this study, effects of etching on a dental ceramic material were investigated. 9.6% hydrofluoric acid solution was used to etch 28 specimens which were prepared from the Finesse TM (trademark of Dentsply Inc.) core ceramic fabricated through ceramic hot pressing routes followed by ingot casting. The specimens were randomly divided into four groups. Three groups were etched at different times. The fourth group was the control group. 4-point bending tests and scanning electron microscopy (SEM) investigations were carried out on these specimens to determine the effects of etching on the flexural strength. Whereas the control group had better flexural strength values, there were no statistically significant differences between the strength values of the specimens of the three groups etched at different times.