DNT-Theses-MSc

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Accuracy of working Models and Marginal Fit of tooth Supported Provisional Dental Prosthesis Fabricated by Three Dimensional Printing Compared to CAD/CAM Milling System : (In Vitro Study) /
Sidhom, Marina Fayek Fathallah,; Supervisor : Ihab El-Sayed Mosleh, Hanaa Zaghloul.
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Bioactive Cement versus Resin Cement Regarding the Perceived Shade of E-Max Restorations : (An In Vitro Study) /
Nagy, Amira Gehad,; Supervisor : Omaima Elmahallawy, Lomaya Ghanem
Esthetics is becoming the main concern for patients and professionals. Demands for creating a natural appearing smile has increased as it reflects youth and acceptance. The goal of esthetic dentistry is to restore teeth to meet the natural form, biocompatibility and appearance. To create a dental restoration that gives a natural looking requires accurate replication of size, shape, surface texture, contouring, translucency and color of natural dentition. Shade is an essential parameter that attracts attention of patients, they judge and accept their dental restorations based on shade matching especially in the anterior esthetic zone. For dental restoration with acceptable shade, translucency and fluorescence it should match that of natural dentition to mimic the vitality. In the past decades, porcelain fused to metal fixed prosthesis was the material predominantly used to restore teeth. But, unfortunately the metal layering acts as a barrier for light transmission giving the restoration dark opaque appearance. The introduction of metal free restorations all-ceramic restorations, have proved to be an excellent alternative for porcelain fused to metal. These restorations utilize more conservative preparation because of the continuous improvements in their mechanical, physical properties and processing methods. Ceramic type, thickness, shade, firing temperature and bonding affects the final appearance of restoration. Lithium disilicate was launched in 1998 by Ivoclar Vivadent; it is one of the most famous glass- ceramics. It has adequate mechanical properties and offers attractive esthetic quality. One of the most important factors that affect the color of dental restorations is the cement used. Type, thickness, curing method and shade affects the perceived shade of the restoration and it’s stability over time. Resin cements are widely used for cementation of lithium disilicate as it bonds chemically to underlying glass- ceramic increasing strength and longevity of dental restoration. Furthermore, it has a clinically accepted color effect and stability. Newly introduced bioactive dental cement with ionic resin matrix is claimed to mimic the physical and chemical properties of natural teeth. In addition, it releases and recharge of calcium, phosphate and fluoride. It would be challenging to investigate the shade of lithium disilicate samples cemented with bioactive cement and comparing it with samples cemented with resin cement.
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Debonding of ceramic restorations using erbium chromium YSGG laser : "A Comparative In-Vitro Study"
Abuosa, Reham Ahmed Mohamed,; Supervisor : Lamia Sayed Kheiralla, Rana Mahmoud Sherif
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Effect of Diode Laser Irradiation of Bonding Agents Before Curing Versus Standard Bonding Protocol on the Shear Bond Strength Between Resin Cement and Dentin /
El-Hakim, Nada Maged Mohammed Mahmoud,; Supervisor : Ashraf Hassan Mokhtar, Tamer A. Hamza.
It has been more than half a decade since Buonocore and later Nakabayashi developed the concepts behind the most popular branch in restorative dentistry, dental adhesion. Owing to its ability to create intimate contact between the tooth and the restoration, adhesion theoretically eliminates marginal gaps, reduces micro-leakage, and prevents secondary caries. With the spread of the adhesive concept, came the development of resin cements, enabling bonding of indirect tooth-colored restorations through micro-mechanical interlocking instead of the conventional luting method employed by acid-based cements. Adhesive bonding, through appropriate surface treatment protocols, not only provides superior bond quality, but also increases the flexural properties of ceramic restorations. Flexural properties such as modulus of elasticity and strength prevent de-bonding of cemented restorations during function. However, due to the nature of adhesive bonding, it has been proven that the quality of adhesion is proportional to the performance of the bonding agent. Unfortunately, the performance of contemporary bonding agents is still flawed when it comes to dentin. Unlike enamel, which has about 96%wt inorganic material, dentin has a more complex heterogeneous structure, composed of about 70%wt inorganic material and up to 30%wt organic content and water. The dentinal structure is further complicated by its structural variability according to location, as it changes not only with differences in depth, but also from region to region within the same tooth. Moreover, the dentinal composition and structure constantly changes throughout life according to local factors such as age, trauma, and caries. This complex structure renders it challenging to achieve a reliable bond to dentin, and due to its hydrophilic nature, nano-leakage occurs at some point within the hybrid layer, resulting in eventual bond deterioration and failure. According to the recent literature, self-etch adhesive systems (6th, 7th, and 8th generation adhesives), also called simplified bonding systems, seems to outperform the etch and rinse adhesive systems in dentinal bonding. However, numerous studies still reported water-related bond deterioration after aging. The presence of HEMA, water, and ethanol, as well as the differences in molecular weights between acidic and cross-linking monomers have been blamed for the breakdown of adhesive interfaces created by simplified bonding systems. In light of these problems, improvements in bond formulations are constantly being attempted through diverse laboratory studies and clinical trials. But till now, manufacturers have yet to produce an adhesive system or technique that prevents dentin bond deterioration by time. Dental lasers have recently been gaining popularity, and their use have been incorporated into multiple restorative procedures, including dental adhesion. SE Gonçalves et al (1999) suggested an adhesive protocol in which a soft tissue laser irradiated on an uncured adhesive before polymerization resulted in a statistically significant increase in shear bond strength to dentin. The use of laser energy on the bonding agent before its curing has since been evaluated in further studies and has been further hypothesized to increase bond penetration, help evaporate the solvent, increase its degree of conversion (DC), and increase the modulus of elasticity of the hybrid layer. Some authors, however, obtained negative results, finding the laser to have no effect whatsoever on the bond strength. Others found an increase in immediate bond strength that dropped dramatically after aging. Nevertheless, achieving sustainable high dentin bond strengths is the ultimate goal of adhesive dentistry. The idea of incorporating laser energy to reach this goal is interesting as it is debatable. Therefore, in an attempt to further asses the validity of laser use in dentinal bonding, the aim of this study is to evaluate the effect of a soft tissue laser irradiated on uncured bonding agents on the dentin bond strength.
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Effect of Er, Cr : YSGG Laser Versus Acid Etching Surface Treatment on the Surface Roughness and Optical Properties of Two Pressable Lithium Disilicate Ceramics with Different Thicknesses : In-Vitro Study /
Morsi, Mohamed Tarek Anwar,; Supervisor : Ihab Mosleh Mostafa, Hanaa Hassan Zaghloul.
The increased demand for high esthetics initiated the development of tooth colored restorative materials having superior esthetic and mechanical properties to withstand the occlusal forces. Dental ceramic restorations provide high esthetics that mimic the dental appearance of natural dentition producing satisfactory results to the patients and clinicians. Dental ceramics have variable compositions with different crystalline content such as feldspathic glass porcelain, zirconia, lithium disilicate, fluroapatite or leucite-reinforced ceramics. Glass ceramics consist of glassy matrix with imbedded crystalline structures. As the glassy matrix increases, the ceramics become more translucent. The crystalline content provides strength on the expense of its esthetic appearance. IPS e.max Press (first introduced into the market in 2005) consists of lithium disilicate crystalline structures (70% by volume) embedded into a glassy matrix7,8. The crystals have plate-like shape that are randomly distributed in the glassy matrix. The random distribution and the needle-like structure of the crystals would deflect cracks and prevent their propagation. GC InitialTM LiSi Press is a newly introduced lithium disilicate pressable ceramic, which is empowered by HDM technology (high density micronization) to provide improved physical properties (unsurpassed flexural strength of more than 450 MPa) while obtaining superior esthetics. With the advent of adhesive dentistry, ceramic veneers can be produced with high optical and mechanical properties in a minimum thickness up to 0.3 mm13–16. Aside from the layering fabrication technique, ceramic veneers can be constructed from ingots or blocks by heat pressing technique and computer assisted design/ computer assisted manufacturing (CAD/CAM) technique. The ceramic’s thickness has a noticeable effect on the optical properties of the ceramic restoration. Increased thickness affects color and translucency, making the ceramic darker more reddish/yellowish and increases the ceramic’s opacity. The bonding between the restoration and the dental structure is enhanced by the surface treatment of the ceramic surface. However, the modification of the internal surface of the ceramic by creating microporosities that would increase the surface area for bonding. The different surface treatments of ceramics affect the surface roughness which influences the optical properties of the ceramics. The roughness on the ceramic’s surface makes the light that goes through the ceramic pass with the different incidence and direction. Using Hydrofluoric acid etchant as a surface treatment is considered a standard classic method. Hydrofluoric acid removes the glassy matrix of ceramic material. Once the glassy matrix has been removed, the crystalline content is exposed creating micro-roughness on the surface of the ceramic. However, Hydrofluoric acid etchant as a surface treatment is considered hazardous to the dentist and the patient31. Er,Cr:YSGG Laser irradiation is a new technology that has been introduced lately to different fields of dentistry. Er,Cr:YSGG laser can make surface roughness on the glass ceramics as a surface treatment prior to bonding similar to that made by hydrofluoric acid etching. Reviewing the dental literature, there is a considerable debate regarding the effect of Er,Cr:YSGG Laser as a surface treatment protocol for producing surface roughness on the ceramic’s surface and its effect on the optical properties of the ceramic. In view of the unreported health hazards of laser irradiation in dentistry, it is worth to assess its effect as a surface treatment protocol on the surface roughness, color and translucency parameters of two pressable lithium disilicate ceramic materials with different thicknesses before and after aging.
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Effect of Surface Treatment of Different Ceramic Materials by Er, Cr : YSGG Laser Irradiation on The Shear Bond Strength to Resin Cement : A Comparative in-Vitro Study /
Mandil, Shahd Taha Hussein Adam,; Supervisor : Hesham Katamish, Tarek Salah.
People’s interests for a beautiful smile have been greatly increased lately which led to the appearance of veneers. The high outstanding esthetic properties of all ceramic restorative materials that simulate the appearance of natural teeth, plus its high mechanical properties that can tolerate and protect the teeth against different occlusal forces inside the mouth for long time, makes it number one material used for veneers restorations. Although ceramics have the best esthetic proper ties, high wear resistance, and are biocompatible and can retain their color for long time, they are brittle and can get fractured. Additionally, ceramics may cause severe wear of the opposing natural teeth. A new novel material polymerinfiltratedrestor ation called (hybrid ceramics) combines the positive properties of both the ceramic and resin composite restorations composed of mainly ceramic network of (86 wt%) and reinforced with an acrylate polymer network of (14 wt%) and can be used for veneer rest orations. The surface treatment of the ceramic surface has been a major breakthrough owing to its significance in increasing the surface roughness of ceramics to enhance the micromechanical bond with adhesive resin cement. With the introduction of erbium lasers (Er:YAG and Er,Cr:YSGG) in dentistry, many studies have been performed to test the effect of laser in changing the surface texture of ceramic materials Clinically, due to many variable factors inside oral cavity, chipped or fractured veneers are one of the most frequently reported problems. In cases of small fracture it is not necessary to totally replace chipped veneers. Due to the high cost and difficulty of total replacement, many studies suggested that intra oral repair with composite resin is m ore conservative and cause less trauma to teeth and surrounding tissues. Different intra oral repair methods have been applied and developed to improve the fractured surface and optimize its bond strength with composite resin. However, the traditional meth ods containing acid are hazardous for both patient and clinicians, as the acid may cause damage to eyes and the skin, so special protective equipment is needed. Therefore, another more biofriendly technique is preferred. Nowadays, since the introduction o f the idea of laser for ceramic surface treatments many authors studied the effect of Nd:YAG and Er:YAG lasers for increasing surface roughness of some ceramic materials. However, Er,Cr:YSGG laser still needs more studies to prove its efficiency to be used as an alternative surface treatment method to improve bonding of etched ceramic with adhesive resin. The effect of Er,Cr:YSGG laser in producing surface roughness of glass ceramics and composite materials is still questionable. So, in the current study th e effectiveness of Er,Cr:YSGG laser as an alternative method to the traditional ceramic surface treatment techniques was to be examined to prove if the Er,Cr:YSGG laser irradiation could enhance the shear bond strength of different ceramic materials with a dhesive resin cement. This would be more beneficial and less harmful to oral tissues during intra repair of fractured ceramic restorations.
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Effect of Surface Treatments on the Pull-out Bond Strength of the Glass Fiber Post to Toot Dentin : "A Comparative In-Vitro Study"
Mekky, Amr Ahmed,; Supervisor : Maged El-Hakim, Tamer Elhamy Shokry.
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Effect of Surface-Polishing Techniques and Aging on The Roughness and Optical Properties of Different Ceramic-Polymer Systems : In-Vitro /
Abonema, Abdullah Adel Abdullah,; Supervisor : Ihab Mosleh Mostafa, Hanaa Hassan Zaghloul.
Dental restorations should possess certain criteria and characteristics to be acceptable. Biocompatibility to oral tissues, resistance to fracture under masticatory forces and superior esthetic properties of the material are among the most important characteristics. Dental ceramics are one of the most popular and successful fixed dental restorations because of their biocompatibility and optimal esthetic properties. Ceramics are included in the fabrication of fixed and removable tooth- and implant-supported prosthodontics. Dental ceramics can mimic natural tooth color, translucency and gloss. Ceramic restorations could be fabricated as one full contoured unit of the same material, referred as ‘monolithic”, or fabricated in the form of a material with higher strength as a substrate and veneered to a full contour with other ceramic material for esthetic purposes, then referred as “bilayered” ceramic restorations. The latter case, as zirconia substrate veneered with lithium disilicate or feldspathic porcelain, which combines both strength and high fracture resistance (zirconia substrate) and esthetics (lithium disilicate or feldspathic porcelain). One of the main drawbacks of dental ceramics is their fracture tendency when subjected to tensile stresses. Polymer infiltrated ceramic materials have been introduced to the market to combine the advantages of both ceramics and resins to overcome some of the mechanical drawbacks of ceramics. 3–6 The innovation in computer aided design/computer aided manufacturing (CAD/CAM) systems has a motivating influence in developing new ceramic blocks. Accuracy, time-saving and superior esthetics are benefits gained of these new products. Polymer infiltrated ceramic CAD/CAM blocks have been recently introduced as a chairside restorative material.7,8 Manufacturers claim that the polymer integrated within the ceramic structure would provide elasticity to the restoration.9 Hybrid ceramic restorations can be used as anterior and posterior single tooth- or implant-supported restorations. The construction of hybrid polymer ceramics is a one-step CAD/CAM procedure, which means, they do not need a heat treatment or furnace for setting or sintering. Moreover, no need for heat glazing or even a glaze layer to be applied as claimed by the manufacturers. Esthetic consideration of newly introduced materials is an important factor to determine the acceptance and durability. The importance of polishing procedure and aging of polymer-ceramic materials and their effect on the surface roughness, consequently the optical properties, are the objectives of this study.
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Evaluation of different oral conditions on the color stability and surface roughness of CAD/CAM hybrid ceramics versus IPS e.max : An In vitro study /
ELSayed, Alaa Hamed,; Supervisor : Lamia sayed Kheiralla, Rana Mahmoud Sherif.
Color matching and long-lasting color stability of dental materials are two of the major factors that influence the success or the failure of any esthetic dental restoration. In addition, the surface texture of a tooth colored restoration has a major effect on plaque accumulation, discoloration, wear and the esthetic appearance. Ideally, for any material to be used, it should fulfill four main criteria; esthetics, strength, accuracy and passive fit. Dental ceramics set ground as the most natural in appearance, texture, color, reflectance, and translucency, where distinguishing them from the natural teeth is sometimes even impossible. Moreover, it was approved that ceramics have optimum biocompatibility to oral tissues and reduced tendency of maintaining bacterial plaque as well as it does not absorb water nor conduct heat. A Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) was introduced to dentistry in the mid-1980s. Several types of CAD/CAM ceramic blocks have been developed for restoration fabrication, including feldspathic ceramic, leucite-reinforced ceramics, lithium disilicate ceramics, and zirconium oxide ceramics. CAD/CAM offer high esthetic demands, short chair side time, and less number of visits. Although dental ceramics are widely used for inlays, onlays, single crown and fixed partial dentures, they still have some disadvantages, such as high cost, the risk of fracture due to their brittleness, high wear to the opposing natural dentation, handling concerns (fragility during trial insertion and cementation) and veneer failure. Therefore, there has been an increasing interest in the use of newly introduced hybrid ceramic blocks to overcome some of dental ceramics drawbacks, due to their optimal resilience, stiffness, and wear characteristics together with their excellent esthetics. Currently, there is no much documentary evidence available regarding the effect of the different oral media on the milled CAD/CAM hybrid ceramic regardless to glass ceramic restorations. Thus, it was worthy to investigate the color stability and surface roughness of a recently introduced CAD/CAM hybrid ceramic (CERASMART) to lithium disilicate (IPS e.max CAD) ceramic under two beverage solutions (coffee – Mirinda orange juice) and a home-bleaching agent.
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Evaluation of Edge Strength of two Hybrid Ceramics as Compared to a Glass Ceramic Veneer with Different Marginal Thickness : "An in Vitro Study" /
Fahmy, Dorotea Ashraf,; Supervisor : Maged El Hakim, Tarek Salah Morsi.
The demand for treating esthetics within anterior teeth continues to grow. Available options to restore their aesthetics include conservative treatments, such as bleaching and direct composite laminate veneers. Improvements in adhesive systems and the development of new-generation porcelain technology have supported the growing demand for treating unaesthetic teeth with porcelain laminate veneers. The problem of combining esthetics and strength has been strategic especially with the development of minimal thickness of laminate veneers. Throughout the years dentistry has gone through numerous developments in knowledge, techniques and technology. Due to increasing concerns about the aesthetics and biocompatibility of dental restorations, patients and dentists have become more and more interested in metal-free tooth-colored materials, ceramic materials were developed in response to this increasing demand. Newly introduced dental ceramics allow mimicking the natural tooth color and translucency. However, ceramics remain weak under tension due to its inherent brittleness and therefore their thickness has a major influence on their strength. Laminate veneers has greatly replaced other alternatives that were used to treat tooth discoloration. However, during long term evaluation clinical failure tends to appear. The most frequent failure that appeared in laminate veneers were incisal chipping and the development of inner flaws. This refers to the main problem that ceramics remain a brittle material. As a conclusion, due to the inherent brittleness of ceramics the material must be compensated by applying a desirable sufficient thickness to help the material perform adequately. As for edge strength, it is defined as the ability of the restorations to withstand forces at a thin edge and it is evaluated by measuring the force to fracture at 0.5 mm distance of the sample edge, since it is the most susceptible area for breakdown in the clinical performance of the restoration. A previous study has concluded that the force required for chip formation increases with distance from the edge and the process of chipping starts first with a small indentation that propagates and as a result a flake drops out. Throughout many previous papers, the edge strength was measured at a progressively increasing distance with 0.1 mm intervals, and they have shown that the most common two modes of failure were cracking and chipping. A different study has classified failure into a group that can be repaired and another group of complete replacement of the restoration. A similar classification was present in a study which graded failure from 1-3. Grade 1 represented minor chipping that can be modified by polishing, grade 2 was moderate chipping which is treated in the oral cavity by photo activated resin composite followed by grade 3 which is severe chipping or fracture by which the only line of treatment was removal of the restoration and remake. Recently introduced CAD/CAM materials offer an alternative solution, that is composed of 2 phases (resin and ceramic) with different percentage in each material. The combined solution of ceramic and polymer has improved the mechanical properties and with great attention to the improvement of the resiliency of these materials that led to fabrication of thin sections without chipping. A variety of all-ceramic systems are commercially available and can offer a new esthetic dimension, particularly in anterior teeth.(8) Recently introduced the polymer infiltrated ceramic materials like Vita Enamic that combines the properties of ceramic and polymer, it belongs to a new substance class, known as “hybrid-ceramic.” It consists of a hybrid structure with two interpenetrating networks of ceramic and polymer, a so- called double network hybrid (DNH) that combined the advantages of both ceramic and polymer that improved the mechanical properties, the material can be milled very thin (0.2 - 0.5 mm) for the preservation of tooth structure. A previous study has concluded that the mechanical properties (flexural strength and strain at failure) of feldspar ceramic can be enhanced by infiltration of a second phase (polymer) into porous ceramic precursor and that these materials are considered to more closely imitate natural tooth properties compared with existing dental restorative materials. Another hybrid ceramic material will be used is Cerasmart (from GC Dental Products) which is a high-density composite resin material containing 71% filler particles by weight. It consists of flexible nano ceramic matrix with an even distribution of nano ceramic for better strength and force absorption, the material can be milled in thin section as it is indicated for veneers. Since there is a limitation in the previous studies about these hybrid ceramics, a control group of IPS Empress CAD, (from IvoclarVivadent) was used to compare the results as it contains a microstructure of leucite, which gives the restoration its mechanical and esthetic properties and many studies have used this glass ceramic. Thus, this study was conducted to evaluate the edge strength of the three different ceramic materials mentioned in minimal veneer thickness, as during milling, cementation and function the material is subjected to forces that should be evaluated to determine the capability of the material to withstand forces in minimal thicknesses.
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Fatigue Resistance of Custom Made Resin-Ceramic, One-Piece and Two-Piece Implant Abutment/Crown : (In Vitro Study) /
Issa, Fady Alfred Boulos Nakhla,; Supervisor : Hesham Katamish, Tarek Salah.
In recent years, social emphasis on esthetics and general appearance has reached an all-time high focus. Every practitioner is now faced with patients that care more about the appearance of their teeth than the actual treatment plan presented. The increased demand for esthetics by both patients and clinicians has revolutionized the treatment procedures taken in dental practice. High awareness and research was implemented towards conservatism and dental practice is now focusing on minimally invasive techniques in all procedures undertaken. Dental Implants are now the cornerstone for restoration of missing teeth and oral rehabilitation. Showing a 95-97% success rate of single implant-supported restorations.1 Providing favorable biomechanical properties, titanium implants and abutments are the golden standard for implant-supported restorations2. However, this causes an esthetic disadvantage, especially in highly esthetic zones. Titanium abutments cause an unnatural bluish-gray appearance to the surrounding soft tissue, specifically around thin layered gingiva. Therefore a tooth-colored abutment is needed to provide acceptable esthetics. For this reason several types of esthetic all ceramic abutments were introduced, offering a variety of tooth-colored shades and stains to accommodate a metal-free natural and esthetic look. In comparison to titanium abutments, ceramic abutments are more aesthetic with less, yet acceptable strength. 3–5 The introduction of Computer Aided Design/Computed Aided Manufacturing (CAD/CAM) technologies in the 1980s provided access to a standardized manufacturing process. Offering a more predictable, accurate and reproducible restoration with reduced production cost. As a result, a new generation of ceramic and composite materials was introduced to the market, opening the door for various uses and restorative designs to be introduced in dental practice.6 CAD/CAM materials (ceramics & zirconia) were tested and used for various prosthetic restorative modalities, including crown and implant abutments. Due to the brittle nature of ceramics, the abutments were shown to exhibit high stress propagation and concentration on their respective implants and bone specifically in high load areas such as posterior teeth. They also cause abrasion to the opposing dentition. The highly condensed particle nature of zirconia while exhibiting high strength and acceptable mechanical properties, they still provided an esthetic complication due to their dull opaque shade.7,8 Composite resin material, on the other hand, suffer from increased material wear, loss of surface polish, and color instability. Most recently, a new polymer infiltrated hybrid ceramic material has been developed by several companies for CAD/CAM application. Specifically, the VITA Company produced the VITA ENAMIC CAD/CAM blocks. The material is composed of a porous feldspathic ceramic mesh infiltrated by an acrylic polymer network material, providing mechanical properties similar to natural tooth properties. To the best of our knowledge, the hybrid ceramic material was not tested as an implant abutment. The fatigue behavior and the fracture resistance of the material as an implant supported abutment is unknown and was not investigated yet.
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Fracture Resistance of E max Crowns Bonded with Bio-actice Cements : In Vitro Study /
Mahdi, Omar Moutaz Elsayed Ahmed,; Supervisor : Maged Elhakim, Lomaya Ghanem.
At present, there is a trend to develop biomaterials that have bioactive functions, in addition to their basic properties. Bioactive glass was added to glass ionomer cements to stimulate bone growth, to replace bone, and to decrease dentine hypersensitivity. Incorporation of bioactive glass into commercial GICs to enhance bioactivity was examined. Bio active material introduce a specific biologic response at tissue surface interface. Once bioglass particles attach to dentine surface they form a surface hydroxycarboappetiate layer sealing the tubules, decreasing dentine hypersensitivity and dissolve ions that initiate the cell growth factors that cause cell regenerative and reconstructive capacity which is commonly known as regenerative dentistry. One of the bio active cements that is gaining attention nowadays is Ceramir crown and bridge. Many recent studies reported that ceramir crown and bridge showed no loss of retention, secondary caries or marginal discolorations, furthermore concerning the margins of all observed restorations the integrity was clinically sound, no sensitivity or gingival inflammation. This is why the study of bio active cements in comparison to other cements is of great importance nowadays.
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Fracture Resistance of Nano Hybrid Ceramic versus Lithium Disilicate Endocrowns Cemented with Twoo Bonding Approaches : An In Vitro Study /
Hassan, Fayrouz Abd ElHassieb,; Supervisor : Ashraf Hassan Mokhtar, Tamer Abd ElRehim Hamza.
Endodontically treated molars are considered a challenge in restorative dentistry. Such teeth are more susceptible to fracture because of their inherently poor structural integrity by the carious lesions, trauma and extensive cavity preparation. There are a lot of debates about the ideal treatment for endodontically treated teeth. Although dowels are used to retain coronal buildup materials, nowadays it is agreed that dowel do not reinforce remaining tooth structure and may even lead to excessive weakening. The endocrown restoration is an alternative for restoring endodontically treated molars which presented in 1999 by Bindl and Mörmann. This monolithic, ceramic adhesive restoration needs specific preparation designs to satisfy criteria aiming for the success of these restorations. The endocrown restorations are achieving a biomechanical concept by a cervical margin in the form of a butt joint and preparation of the pulp chamber that does not reach the root canals conserving root dentin. The remaining tooth structure helps in increasing the durability and strength. Recently there are new dental ceramic materials and new processing techniques, specifically CAD/CAM and milling technology that facilitated the development and application of recently introduced dental ceramics. CAD/CAM helps in using different materials that cannot be used by conventional dental processing techniques. Perfectly controlled industrial ceramic processing can allow for producing of increased microstructural uniformity, higher density, and lower porosity and decreased residual stresses in restorations. Such improvements have the potential to improve clinical predictability and satisfactory outcome. For chairside cases where strength is a consideration, lithium disilicate CAD restorations offer the strength of 400 Mpa as compared with the leucite-reinforced ceramic, with Mpa ranging from 120 to 160, and still having good esthetic results. Lithium disilicate ceramic material used in the form of monolithic material and provide better strength. (5) Recently introduced CAD/CAM block based on the integration polymer network and ceramics. Hybrid material offers the ease of handling of a composite material with the surface gloss and optimum finish similar to porcelain. The microstructural analyses suggested that this hybrid material composed of interconnected networks: a dominant ceramic and a polymer. Endocrowns restricted to the silica-based ceramic material, which can be acid etched ceramic to obtain a good bond to the prepared tooth structure by using of adhesive cementation system, and ensure the stability of this monolithic restoration. Pressed or machined lithium disilicate ceramic showed favorable results. As they have high mechanical strength and satisfactory esthetic results. The bond strength of hybrid ceramics to composite resin cement is thought to be superior to that found with ceramics. The presence of resin matrix in blocks of hybrid ceramics facilitates bonding to resin composite luting materials, giving more even and uniform distribution of forces when compared to feldspathic and reinforced ceramics and therefore better fracture resistance. The recently introduced dentin adhesives allowed for increased bond strength and claimed by the manufacture to be eighth generation dentin bonding agent (Futurabond DC, Voco, Germany). These bonding agents contain valuable amounts of highly functional nano- sized cross- linking agents, silica particles and offer the advantage to be dual -cured and having higher bond strength than sixth and seventh generations.
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Fracture Resistance of Nano Hybrid Ceramics Versus Lithium Di-Silicate Restorations with Two Finish Line Curvatures : (In Vitro study) /
Selim, Osama Selim Mohammed,; Supervisor : Jihan Farouk Younis, Tamer Abd El Rehim Hamza.
Beauty is chased and demanded by the population as the technology and the media expands. The visual perception of esthetics is relative, though people seek what they believe is beauty. A good smile has a great impact of a person’s impression received by others. Thus, the increased esthetic demands of patients requires seeking dental cosmetic treatments.1 The introduction of dental ceramic restorations passed through many developmental steps that started with porcelain fused to metal (PFM). At that time, the porcelain used for restorations didn’t show optimum mechanical properties to be used by itself. The porcelain itself is biocompatible with the oral tissues and showed promising physical propertied. Its main drawback is the surface flaws and voids, brittleness, low fracture toughness and low tensile strength, thus required a metal core. A thickness of 1.5 mm is required to produce a mechanically and physically acceptable metal-ceramic restoration. Designing a new ceramic material that can withstand occlusal forces without metal core made a significant impact in dental technology and market. The goal to fabricate a ceramic restoration was to eliminate the drawbacks of PFM as metal showing at the margins, color and shade mismatch and chipping of veneered porcelain. Since mid 1980’s dental ceramic technology has changed by producing pressable ceramics to fabricate ceramic restorations. To withstand forces, fillers were added to the glass matrix, such as leucite, aluminium and zirconia as a method of strengthening glass ceramics. Hybrid ceramics are combination of two or more ceramic materials or a combination of ceramic and resin polymer material. The concept of hybrid ceramics was invented to gain the advantages of the two mixed materials together without compromising mechanical nor physical properties of the final resultant material.5–7 Since Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) technology have been introduced into the dental field, dental restoration fabrication became faster and easier. Dental ceramics manufacturers’ aims were directed to invent ceramic blocks that can be fabricated with less laboratory steps, less wasted materials and to diminishing the human errors. Conservatism is one of the main objectives and principles of modern dental approaches, treatments and methods. As dental cosmetic treatments begin from a conservative scaling and polishing procedure ending with implant-supported restorations, dental ceramics plays a leading role with many esthetically restorative options. Tooth preparation, especially finish line design has an influence on the marginal fit of ceramic restorations and their fracture resistance. Clinically and during preparation, curvatures may be present at the finish line configuration. The influence of the finish line curvature on the marginal gap of restoration has been investigated. Though, its impact on the fracture resistance of ceramic restoration lacks documentation.
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Marginal Fit and Microleakage of Monolithic Zirconia Crowns Cemented by Bio-active Cements : An In Vitro Study /
Hassan, Radwa Hamdy,; Supervisor : Ashraf Hassan Mokhtar, Hanaa Hassan Zaghloul.
Esthetics and biocompatibility are crucial factors that increased the demand for metal free restorations among patients. Zirconia-based ceramics are a rapidly growing type of esthetic restorations. They are characterized by superior mechanical properties and superior resistance to fracture. The use of zirconia ceramics has increased rapidly with the evolution of computer- aided design and computer-aided manufacturing (CAD/CAM) technology. This technology improved the marginal fit, mechanical durability and predictability of the final restorations. Veneering of zirconia-based ceramic restorations with feldspathic ceramics is mandatory as they suffer from deficient translucent properties. The introduction of monolithic zirconia “translucent zirconia” offers improvement in the esthetic appearance and durability of the final restorations without fracture compared to veneered zirconia. Clinical longevity of translucent zirconia full coverage restorations is a multi-factorial. The marginal fit and microleakage are critical factors in determining the durability of the final restoration. Any marginal gap reflects the quality of the marginal adaptation and can influence the amount of leakage which may be one of the main causes of failure of monolithic zirconia full coverage restorations. The proper selection of luting agent considered to be the key factor for long-term success of any fixed dental prosthesis. Different luting agents were analyzed and only those containing organophosphate ester monomer groups have shown a significant durable bond to zirconia. In the dental field, bioactive materials were recently introduced and referred to a property of new cements to form hydroxy- apatite when immersed in a simulated body fluid (SBF) and saliva. Ceramir bioactive cement is a modification of glass ionomer cement with addition of calcium aluminate which has a remineralizing characteristic. Such limited number of studies were found using Ceramir as a luting agent with monolithic zirconia, therefore the aim of the present study was to evaluate the marginal fit and microleakage of monolithic zirconia crowns cemented by bio-active cement (Ceramir).
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Marginal Fit of Nanohybrid Ceramic Versus Emax Monolithic Restoration With Two Finish Line Curvatures : An In Vitro Study /
El Shennawy, Sally Mohammed Mansour,; Supervisor : Ahmed Hassanien Khalil, Tamer Abd ElRehim Hamza.
Dental ceramics are used to restore missing or damaged structures because of their high translucency, esthetics, biocompatibility, better hardness that gives the restoration its wear resistance, resistance to disintegration in oral fluids, and low thermal diffusivity, however ceramics are brittle, which means that they display a high compressive strength but low tensile strength. This subjects such restoration for failure in the oral environment. Improvements in the mechanical properties and methods of fabrication in order to improve strength was achieved by adding different types of crystal and metal oxide which obstruct crack propagation and hence increase the strength, but as strength increased the translucency decreases which had a negative effect on the overall esthetics, so there was always a need to have an outer coat from glass ceramics. The delamination of esthetic veneer usually occur, to overcome such failure the use of monolithic restoration was introduced. By definition monolithic means it is fabricated in full contour out of a single material. Monolithic crowns can be fabricated from lithium disilicate, and full contour zirconia restorations. While zirconia offers significantly greater fracture strength (more than 900 MPa compared with 400 for lithium disilicate), lithium disilicate has generally been considered to be a better choice for use in the esthetic zone because of its high translucency and a more natural appearance. In order to combine the strength and reliability of zirconia together with esthetics of lithium disilicate, Zirconia-reinforced lithium silicate glass-ceramics was introduced. It has a homogeneous structure that offers good material quality and consistency, high load capacity and long-term reliability. Resin restorations are less expensive than other crown types. However, they wear down over time and are more subjected to fractures than porcelain fused to metal crowns. Moreover, they tend to be less esthetic than ceramic crowns. Therefore, to overcome this problem and to enhance esthetic properties, a new type of hybrid ceramics was introduced named as resin-reinforced lithium silicate glass ceramics, a hybrid dental ceramic with a dual network structure that combines ceramic and composite material properties. Due to its high strength, resinreinforced lithium silicate glass ceramics is resistant to the shear and compressive forces. Used in treatment of severely abraded dentition or erosion and with bruxers , due to its high reliability causing improved edge stability leading to finer and more accurate results than with conventional dental ceramics. Moreover, it can be easily finished and polished. It is also etchable, viscoelastic, has acceptable flexure strength and provides acceptable marginal fit. Marginal misfit has many severe outcomes which may cause prospective failure of the prosthesis. Marginal fit of the crown is defined as the gap between the prepared tooth and the inner surface of the restoration. Absolute marginal discrepancy is the distance between the cavosurface finish line of the preparation and the margin of the restoration. Marginal discrepancy can be measured through different methods such as direct view of the crown on a die, cross-sectional view, impression replica technique, and clinical examination. In order to obtain a proper marginal fit, there should be an appropriate marginal design and curvature according to the type of restoration being used. A study done to evaluate the effect of finish line curvature on marginal fit of all ceramic CAD/CAM crowns had concluded that the finish line curvature had no effect on marginal fit of all ceramic crowns. However, this study was conflicted by another study that determined the greater the finish line curvature, the wider the marginal gap widths. Marginal fit differs between different types of restorations and different finish line curvatures. The hypothesis of this study is to prove that the finish line curvature and type of ceramic restoration will affect the marginal fit.
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Micro-Shear Bond Strength of Bioactive Cement to Translucent Zirconia After Thermocycyling : A Comparative In-Vitro Study
El Gendy, Mennatalla Ahmed Emad,; Supervisor : Ehab El-Sayed Mosleh, Hanaa Hassan Zaghloul.
The increased demand for esthetic dentistry and the rising question regarding the biocompatibility of dental alloys lends to the introduction of new esthetic materials. Ceramic materials are nowadays an attractive alternative to metal based restorations. With greater success and reliability, the applications of metal-free ceramic restorations have been extended due to the introduction of zirconia in dentistry. Because of the introduction of CAD/CAM system, the production of zirconia restorations has become a fully digitalized process which is faster and more accurate. Zirconia restorations suffer of decreased translucent properties. However; this problem could be overcome by esthetic optimization of veneered restorations with pronounced anatomic structure. However, research reports have documented ceramic veneer fractures (chipping) and fractures of the zirconia substructure as well. To overcome these problems of veneered zirconia fractures, the full contoured monolithic zirconia “translucent zirconia” was introduced as an alternative approach. Translucent zirconia offers improvement in esthetics. Moreover, this restoration is defined by a significantly reduced material thickness in comparison with veneered restorations or other monolithic materials. As the restoration can be colored individually prior to sintering, followed by staining and characterization, good esthetic could be achieved. Bonding to zirconia is challenging as it tends to be difficult to etch with hydrofluoric acid due to the absence of glassy matrix. However, bonding to zirconia ceramic can be improved via many surface treatments such as selective infiltration etching technique, laser etching, alumina Introduction 2 coating, tribochemical silica coating, silica ceramic coating and airborne particle abrasion. 1–4 The airborne particle abrasion with alumina has been used for mechanical interlocking claiming that a durable strong zirconia based ceramic bond could be achieved. The type of luting agent, biocompatibility, insolubility and resistance to degradation contributes to the long term success of fixed dental prosthesis. Different cementing agents have been produced and only those containing organophosphate ester monomer groups have shown a significant durable bond to zirconia.5 Aging and thermo-cycling are two significant factors to be considered in the bond strength tests. It was found that the minimum number of thermal cycles for metal/resin bond is 5000 cycles. This is based on ISO 10477.6 Adhesive ability can predict the longevity of a restoration which can be measured by bond strength testing. An accurate and clinically reliable bond strength test must be less technique sensitive and it should involve the use of relatively inexpensive protocol. A newly introduced calcium aluminate based cement, referred to its bioactive properties, with claims to form hydroxyapatite, as well as the release and recharge of calcium, phosphate and glass ionomer. It would be worthy however, to investigate the micro-shear bond strength of air-abraded translucent zirconia cemented with bioactive cement after thermocycling.
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Micro-shear strength of hybrid ceramics : the effect of different surface treatments and universal adhesives in vitro study /
Yacoub, Tarek Anwar Ibrahim,; Supervisor : Ashraf Hassan Mokhtar, Hanaa Hassan Zaghloul.
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Micro-Tensile Bond Strength of a New Bioactive Cement to Lithium Disilicate and Hybrid Ceramics Before and After Thermocycling : In-Vitro Study /
El-Sharkawi, Noran Mohammad Mostafa,; Supervisor : Hesham Katamish, Tarek Salah Morsi.
The use of dental ceramics has increased enormously due to the rising demands by patients for better appearance, leading to the development of metal-free restorations. Dental ceramics attain high esthetics qualities, color stability and good biocompatibility to the oral tissues. Yet, they are brittle, liable to fracture and they cause wear to the opposing enamel. On the other hand, resin composite restorations are soft, compliant and they do not cause wear to the opposing dentition. However, they are subjected to their own wear and discoloration over time. Researchers and recent advances have led to the discovery of new materials having the advantages of both dental ceramics and resin composites, known as hybrid ceramics, or also known as ceramic-reinforced polymer systems. These hybrid materials are believed to be of higher flexibility and better fracture toughness while retaining less brittleness, rigidity, and hardness than the original materials. Dental ceramics are classified into: Glass-matrix ceramics, Polycrystalline ceramics and resin-based ceramics. Glass ceramics include lithium disilicates (LDC) which are available in the form of ingots (heat pressed), and CAD/CAM blocks. Two main types of the hybrid ceramics are present in the dental market, polymer-infiltrated ceramic network material (PICN) and the resin nanoceramic (RNC) which is based on the nanotechnology. Resin nanoceramics include Cerasmart and Lava Ultimate. Ceramics are known for being brittle; this is why their long-term success depends mainly on adhesive cementation. Resin cements are the most commonly cements used with ceramic materials due to the combination of vitreous and crystalline phases structure of ceramic which allow for etching and provide excellent adhesion. Recently, bioactive cements have been introduced as an innovation in the field of dental cements. Activa BioActive cement is t considered to be an enhancement of the RMGI cement. It is composed of; a bioactive resin matrix, shock absorbing resin component and reactive glass fillers which have physical and chemical properties similar to natural teeth. Durable bonding between ceramic materials and the underlying cement is very important as it improves retention, fracture resistance, marginal adaptation and prevents any leakage or decay. Activa has a different mechanism for bonding than conventional cements. This has to be assessed and investigated by a number of physical and mechanical tests to conclude its properties as there are no enough studies about it. Our goal in this study was to evaluate the micro-tensile bond strength of the newly introduced Activa BioActive cement with LDC e.max and hybrid Cerasmart ceramics in comparison to the conventional resin cements before and after thermocycling.
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Shear Bond Strength of Bioactive Cement versus Resin Cement to Tooth Structure in Two Humid Conditions : (In Vitro Study)
Elattar, Mohamed Arafa Ali,; Supervisor : Ahmed Hassanein Khalil, Jihan Farouk Younes.
Cementation is a critical step that determines the success and longevity of the indirect ceramic restorations anteriorly or posteriorly such as, ceramic inlays, onlays, veneers and complete crowns. Retention and durable seal of the gap between the prepared tooth substrate and the restoration is one of the main functions of the cement that governs the success of the overlying restoration that finally enhances the optical properties of the restored tooth. There is a myriad of cementing agents that have been used in dentistry starting from zinc phosphate cement and were followed by zinc polycarboxylate, glass ionomer, resin modified glass ionomer and resin cement. Success of adhesive bonding in dentistry is multifactorial; it depends on type of substrate, type of adhesive substance, operator skills to bond the restoration successfully and humidity of the working area. Regarding the different substrates for instance, enamel is highly mineralized, which facilitates bonding procedure. On the other hand, dentin is not as of harmonious structure as enamel, it is composed of inorganic, organic components and water that demands ideal moisture conditions to ensure proper bonding by avoidance of collapse of the organic part of the dentin (collagen fibers). Humid condition of the substrate affects majorly the bond strength between the restorations and tooth substrate. There are many contaminants that could interfere with the process of bonding such as saliva, gingival fluid, blood and handpiece lubricant. Glass ionomer cements were introduced with great ease of usage without need for additional step, but it had one main disadvantage that was inadequate strength and toughness. That is the reason why resin modified glass ionomer was presented to improve the mechanical properties of conventional glass ionomer with enhanced strength like that of resin cements. For resin cements, using resin cements for bonding is a technique sensitive procedure because it requires multi-step protocol of primer acid etching and finally bond to establish effective bond joint between the tooth and restoration. To solve this drawback, self-adhesive resin cement was introduced which requires only single-step application, reduces manipulation time and improves bond effectiveness. Despite of the development of cements, there was lack of bioactivity potential of the existing cements and self-sealing ability against bacterial leakage that eventually prevent secondary caries and failure of the restoration. Diverse formulas of bio-active cements were submitted like calcium aluminate and calcium silicate products to form hydroxy apatite and maintain the tooth- restoration interface for a durable and successful restoration. Due to the increase demands for esthetic restorations, ceramic materials have evolved including the glass ceramic and zirconia-based ceramic restorations. Zirconia is a polycrystalline material with better mechanical and physical properties that is used in different dental prosthesis such as, single crowns, adhesive bridges and fixed partial dentures. Bonding zirconia-based restorations is a critical issue; it cannot be etched with hydro-floric acid because of its polycrystallinity composition. It can be sandblasted which increases the mechanical bond strength. Another method of enhancing bond strength is, silane coupling agents with tribochemical treatment. Self-adhesive resin cements are used with zirconia restorations without a preceding step to prepare the surface. The aim of this study was to evaluate the bond strength of the bioactive resin modified glass ionomer cement when bonded to enamel and dentin in wet and dry conditions in comparison to self-adhesive resin cement.