Historical Survey of Dental Restorative Materials

Historical Survey of Dental Restorative Materials Historical Survey of Dental Restorative Materials Introduction: Dental restorative material is a biomaterial used to restore the shape and function of damaged or missing tooth (caused by caries or trauma). Restorative materials can be divided into two types depending on whether they are designated to be applied directly to the injured tooth or fabricated in the lab firstly. 1. Direct Dental Restoration: Direct restoration means the usage of dental materials to save injured tooths function. A filling is a way to restore a damaged tooth by decay to recover its function and shape again (1). There are several kinds of materials which are used as filling. The right choice is determined by many factors; such as: extent of required repair, cost, having allergies to specific materials, etc Metallic Fillings: Gold fillings: gold has used as filling material. It is prepared in a laboratory and after that it is cemented into required place. Gold inlays are well compatible by gum tissues. Gold is considered the best filling material because it may last more than twenty years (1). However, gold filling often requires many visits to dentist as well as it is the most expensive choice. The following figure is for tooth with gold filling: Fig. (1): Gold filling Amalgam Fillings: first introduction of amalgam was in the United States in 1830, then this material was developed in both England and France. The amalgam fillings consist of silver, copper, zinc, tin and mercury. After starting of using amalgam as filling, controversy arose because of adding the mercury to fillings. At the beginning, this material is not embraced in the USA by the organized dentistry. In 1840, many members of dental surgeons of the American Society refused to use amalgam as filling material(2). In fact, the amount of mercury which was added to fillings was harmful to the health of patients. The mercury exists in filling may seep into the patients system and lead to a number of health concerns, for example: cancers or multiple sclerosis. Therefore, nowadays a lots of precautions have been taken to be sure that amalgam fillings are safe as possible as for patients (3). Generally, amalgam fillings are resistant to wear and inexpensive. But, according to their dark color, they are not desirable like other filling materials as well as they are not used in visible areas, like front teeth. The following figure is for tooth with amalgam filling: Fig. (2):Amalgam filling Non-metallic Fillings: Resin-Based Composite (RBC) fillings: composite fillings are closely to be the same color of natural teeth and these fillings are used where a natural appearance is required. The components are mixed and then placed directly into the tooth cavity, after that they harden. Actually, many experiences have approved that composites are not the ideal filling for large cavities because they may wear over time. As well, composites may become stained from tobacco or drinks like coffee or tea. They do not last more than three to ten years, however, recent research has suggested that the longevity of resin-based composites could be equally to amalgam (4). The following figure is for tooth with composite filling: Fig. (3):Composite filling Porcelain fillings: these fillings could be inlays or onlays. They are produced to order in a dental laboratory and then bonded to the damaged tooth. Porcelain fillings can be resist staining and matched to the natural tooth color. Generally, porcelain restorations cover most of the tooth. However, the cost of these fillings is similar to gold fillings. Glass-ionomer cements/water-based cements: Self-setting which is pure glass ionomers, or light cured which is resin modified glass-ionomers. Glass ionomer restoratives become popular with dentists because of their adhesive properties as well their ease of handling. They are relatively poor in resistance to moisture. These fillings have adequate compressive strength to be used as core build-up. However, flexural strength and fracture toughness of these materials are low. Therefore glass ionomer cements are suitable to place where there is tooth substance remaining to support the filling material and where resistance could be obtained from tooth tissue. Cermet cements do not supply advantages more than glass ionomers and they usually have poor adhesion to tooth structure(5). In general, the longevity of glass-ionomers is lower than that of amalgam or RBCs (4). Long-term temporary fillings; for example: reinforced zinc oxide-eugenol cements (4). 2. Indirect Dental Restoration: Indirect restorations are prepared in laboratory away from the injured tooth. Indirect restorations include inlays which are intracoronal, crowns and bridges that are extracoronal, or onlays which is considered as a combination of intracoronal- extracoronal. Crowns: Crowns could cover all/ partially the surfaces of tooth. After making a decision which restoration should be done for patient, materials and methods should be determined to begin the fabrication (5). Design and Materials Selection for Indirect Restorations: Gold: For more than 4 thousand years, gold has used as a restorative material in dentistry. The first gold fixed bridges were introduced by Romans and then its dental applications have published widely (6). The selection of restoration type and design will depend on the clinical situation details. However, gold is considered as one of the most efficient restorative material especially as extracoronal. Fig 4,5 show Cast gold crown (7,8). Fig (4): Cast gold crown Fig (5): Cast gold crown Advantages Disadvantages Having a hardness which is similar to the normal enamel Gold crown is fabricated by cast process from molten that may sometimes lead to microgaps at margins which are liable to decay Contours of occlusal and axial are built up clearly in the wax Visibly different from the color of natural teeth long-lasting High sensitivity hot/cold Used for complete/partial tooth coverage. long procedures for preparation (cast) and treatment Avoiding problems caused by using dissimilar metals High cost Porcelain: For many years, porcelain has used as a dental restorative material. Porcelain is a brittle material that requires special treatment for surface, such as: etching and silanisation. Porcelain crowns require restriction to anterior teeth excluding some types such as, Empress II, Inceram and Procera which are considered high-strength ceramics. Advantages Disadvantages Strong hardness of porcelain is more than natural enamel, that may cause damaging to the other natural teeth (for example; clench and grind) Natural looking Small thickness makes porcelain brittle and fracture No conductivity of (heat-cold) More reduction of tooth structure should be done Suitable for metal sensitivity-patients Fig 6 shows porcelain crowns (8). Fig (6): porcelain crowns Porcelain metal: Porcelain metal crowns combine between durability strength of the metal, and good aesthetics of the porcelain, Fig.(7): shows porcelain gold crown (8). Fig (7): Porcelain Gold Crown Advantages Disadvantages Comparing with full porcelain it is Stronger more durable Opacity because of the metal base Better aesthetic than full metal Existence of dark metal edge at the gum line Bonding techniques used are less sensitive than techniques used for full porcelain Porcelain and metal base could separate during use Limitation because of metal allergies of some Patients Composites: Recently, Composites are used widely in dentistry according to their high strength, high wear resistance and less expensive than other materials like: porcelain, gold, or zirconia. As well, composites used in onlay/crowns have permanent form stability comparing with other materials (5). However, sometimes a material less wear-resistant is more favorable to be sacrificial to nature. Fig. (8) shows a composite crown (5): Fig (8):A composite crown Table (1) illustrates comparison of materials used for indirect restoration (9): table (1): Comparison of materials used for crown manufacturing Porcelain Porcelain metal Gold alloys Metal alloys Biocompatibility Well tolerated. some patients may show allergenic sensitivity to base metals. Well tolerated. Well tolerated, but some patients may show allergenic sensitivity to base metals. Esthetic natural color translucency limits translucency because of metal. desirable color Durability Brittle Strength is related to bond to underlying. strong durable. High strength toughness Fracture Resistance Weak under tension impact. metal improve the strength. Highly resistant. Wear Resistance Highly resistant, except when porcelain surface becomes rough. Resistant Sensitivity Low thermal conductivity High thermal conductivity Implants: First introduction of dental implants was in the 1960s by Brà ¥nemark. Dental implants are fabricated to replace missing teeth. The chemical and physical properties (composition characteristics of the implant surface and its microstructure, in addition to the design of implant) determine the factors which influence the implant therapy. Many criteria should be achieved such as, strength, biocompatibility, toughness, resistance of wear, corrosion, and fracture. The design principles and the physical properties of the material must be compatible. Table 2 includes materials used to produce dental implants due to their chemical composition (10). Table (2): Chemical composition of implant material Titanium Titanium Alloys: Several metals and metallic alloys including: gold, cobalt chromium, and stainless steel are used to produce dental implants. Last research declare that titanium is the gold standard metal to fabricate dental implants. This material approves long-term survival during experiments (10) and totally inertia to fluids of the mouth (11). Table (3): shows the mechanical and physical properties of biomedical titanium alloys. Table (3): Mechanical and physical properties of biomedical titanium alloys Material Modulus (GPa) Tensile Strength (MPa) Yield Strength (MPa) Elongation (%) Density (g/cc) Type of Alloy Cp Ti grade I 102 240 170 24 4.5 ÃŽÂ ± Cp Ti grade II 102 345 275 20 4.5 ÃŽÂ ± Cp Ti grade III 102 450 380 18 4.5 ÃŽÂ ± Cp Ti grade IV 104 550 483 15 4.5 ÃŽÂ ± Ti-6Al-4V- ELI 113 860 795 10 4.4 ÃŽÂ ± + ÃŽÂ ² Ti-6Al-4V 113 930 860 10 4.4 ÃŽÂ ± + ÃŽÂ ² Ti-6Al-7Nb 114 900-1050 880-950 8-15 4.4 ÃŽÂ ± + ÃŽÂ ² Ti-5Al-2.5Fe 112 1020 895 15 4.4 ÃŽÂ ± + ÃŽÂ ² Ti-15Zr-4Nb-2Ta-0.2Pd 94-99 715-919 693-806 18-28 4.4 ÃŽÂ ± + ÃŽÂ ² Ti-29Nb-13Ta-4.6Zr 80 911 864 13.2 4.4 ÃŽÂ ² The ÃŽÂ ± + ÃŽÂ ² alloy is the most commonly used for the manufacturing of dental implants. This alloy is made up of 6% aluminum 4% vanadium (Ti-6Al-4V) (10). Reports indicate that incidence ranging of titanium implant fracture from 0% to 6%,on the other hand, it is an uncommon occurrence. Fig (9): shows the titanium implant fracture. Fig (9): Titanium implant fracture. Recently, there are some concerns that titanium could evoke an undesirable host reaction; however, little evidence is available about that. Ceramics First introduction of ceramics to dental implants were in the form of coatings onto metal-based implants. They were used to improve osseointegration. Recently, various forms of ceramic coatings have been used for dental implants. Table 4 illustrates ceramic materials used as dental implants (10): Table 4: Ceramic materials used as dental implants Material Chemical Composition Hydroxylapatite (HA) Ca10(PO4)6(OH)2 Tricalcium phosphate (TCP) ÃŽÂ ±, ÃŽÂ ²,Ca3(PO4)2 Fluorapatite (FA) Ca10(PO4)6F2 Tetracalcium phosphate Ca4P2O9 Calcium pyrophosphate Ca4P2O7 Brushite CaHPO4, CaHPO4 ·2H2O Bioglasses SiO2-CaO-Na2O-P205-MgO, Aluminium oxide Al2O3 Zirconium oxide ZrO2 Zirconia is the most favorable among oxide ceramics according to its excellent mechanical properties. Yttria stabilised tetragonal zirconia polycrystalline (Y-TZP) materials exhibits high corrosion wear resistance, in addition to its high flexural strength (800 to 1000 MPa) comparing with other dental ceramics (10). An understanding of the bio-mechanical failure modes of zirconia implants is essential so that an optimal zirconia implant design can be developed. Based on more fundamental studies in the biomaterials science field, the physical mechanism of ceramic implant failure can be either chemical and/or mechanical in nature. Mechanical failure can occur either during the surgical placement of the implant or subsequent functional loading. Clinical examples of fracture modes of zirconia implants are shown in fig. 10,11: Fig (10): zirconia implant fractured during surgery Fig (11): zirconia implant fractured after loading. References: 1. Colgate. Oral Care Centre, 2016. Weblog. Available from: http://www.colgate.com/en/us/oc/oral-health/procedures/fillings/article/what-is-a-filling 2. WOLFE B. Energetic Healthcare and Dentistry. Weblog. Available from: http://www.drwolfe.com/dentistry/mercury_fillings 3. The 123 Community Dentist Network. The History of Dental Fillings, 2013. Weblog. Available from: The History of Dental Fillings 4. Report of the meeting convened at World Health Organization. Future Use of Materials for Dental Restoration. Switzerland, 2009. 5.. Restoration of teeth (complex restorations) 6. KNOSP H., HOLLIDAY R. J., CORTI C.W..Gold in Dentistry: Alloys, Uses and Performance,2003. 7. Donaldson J. A. The Use of Gold in Dentistry, AN HISTORICAL OVERVIEW. PART I, 1980. 8. RICH M.A Comparison of Dental Crown Materials. Health Centered Dentistry. Weblog. Available from: http://drmartharich.com/resources/a-comparison-of-dental-crown-materials 9.American Dental Association. Oral Health Topics- Dental Materials. Weblog. Available from: http://www.ada.org/en/member-center/oral-health-topics/dental-materials 10. OSMAN R. B., SWAIN M. V. A Critical Review of Dental Implant Materials with an Emphasis on Titanium versus Zirconia, 2015. 11. CROITORU S. M., MIHAILESCU I. N., POPOVICI I. A. Materials and Technologies Used in Present Dental Implants Manufacturing, 2014.

Business Law I Chapter 9 Answers Essay

1. Consideration consists of mutual exchange of gains and losses between contracting parties. In the exchange, a gain by the offer is at the same time a loss to the offeror. The legal term used to designate the gain that each party experiences is that party’s legal benefit. Consideration has three characteristics 1) The agreement must involve a bargained-for exchange; 2)the contract must involve adequate consideration; and 3) the benefits and detriments promised must themselves be legal. 2. A legal detriment can be any of the following: 1) doing something that one has a legal right not to do; 2) giving up something that one has a legal right to keep; and 3) regaining from doing something that one has a legal right to do. 3. The law will not enforce an agreement that has not been bargained for. An agreement involves a bargained-for exchange when 1) a promise is made in exchange for another promise, 2) a promise is made in exchange for an act, or 3) a promise is made for forbear ance of an act. 4. A court may refuse to enforce a contract or any clause of a contract if is considers the contract or clause unconscionable, that is, the consideration is so ridiculously inadequate that it shocks the court’s conscience. This designation usually happens when there is a great inequality in bargaining power between the two parties. 5. Consideration can be a promise not to sue. A promise not to sue, when there is right, or at least the apparent right, to sue, is enforceable when it is supported by consideration. Promising not to sue is forbearance. Acceptance of an agreement not to sue, supported by consideration, terminates one’s right to continue any lawsuit, presently or on the future, on grounds described in the agreement. 6. There are three ways that the courts can seek to uphold charitable pledges. The first way involves actual consideration, which occurs when charitable contributions are made on the condition that the promisor be remembered for the gift by having his or her name inscribed in some way on a memorial associated with the project. Another approach is to use either promissory estoppel or public policy to support the claim. Also, when there is no promise to carry out a specific project, the courts have held each pledge made is supported by the pledges of all others who have made similar pledges. This concept of consideration is used in support of all promises of money for undefined causes. 7. If a creditor accepts as full payment an  amount that is less than the amount due, the dispute has been settled by an accord and satisfaction. Accord is the implied or expressed acceptance of less than what has been billed the debtor. Satisfaction is the agreed-to settlement contained in the accord. Only if the dispute is honest, and the offer to settle made in good faith, and not superficial or trivial will the courts entertain arguments based on accord and satisfaction. 8. The agreements that be enforceable by a court of law even though they lack consideration are: a) Promises under seal – enforceable in some states for contracts not involving goods Unenforceable under UCC for contracts involving goods. b) Promises after discharge in bankruptcy – enforceable in most states. c) Promise to pay debts barred by statute of limitation – enforceable. d) Promises enforced by promissory estoppel – enforceable only if offeror knew that offeree would rely on the promise and offeree places himself in a different and difficult position as a result of that promise. e) Option – enforceable under UCC if made by a merchant, in writing, stating the time period over which the offer will remain. 9. Promissory estoppel is a legal doctrine that restricts a party from denying that a promise was made under certain conditions, even though consideration has not been exchanged to bind an agreement. To be effective, promissory estoppel requires that the party making the promise know, or be presumed to know, that the other party might otherwise make a definite and decided change of position in contemplation of those promises. In reaching this doctrine, courts have accepted the principles of justice and fairness in protecting the party receiving the promise from otherwise unrecoverable loses. 10. Shopping online is one of the fastest growing market places on record. Despite its many advantages (quick & efficient, comparison shopping, availability of hard-to-get products) , there are many difficulties: – Cyber-payment option: Wide variety of methods. One of the most popular methods is by credit/debit card. Most online sellers will accept the major credit cards such as Visa, Master Card. This type of system protects both the buyer and the seller. This process may become the most acceptable process because most of the times when people buy and sell in  cyberspace they are dealing with strangers. The online payment process eliminates the identity verification problem. This is important because one of the biggest concerns about online shopping is security. – Cyber-Payment Security Issues: the ease and efficiency of using credit/debit cards is frequently offset by the security concerns associated with their use. The US is not up-to-date as the EU in providing data and privacy protection to its consumers. The EU Data Protection Directive along with EU E-Privacy Directive guarantee the rights of European citizens while at the same time ensuring the smooth exchange of data among those nation-states that honor the privacy and data protection standards themselves. US corporations that are involved with EU corporations must demonstrate that, despite the lack of legislation in the US, the companies themselves will promise to honor the same degree of protection to data and to privacy as guaranteed by the EU. These guarantees have been labeled the Safe Harbor Principles. They are enforced by the US Department of Commerce. It is best for a consumer to check directly with the US Department of Commerce to determine the true status of a company rather than just relying on the company’s blanket assertion that they follow the safe harbor standards.

Warning Signs on Research Topics about Social Issues You Need to Know About

Warning Signs on Research Topics about Social Issues You Need to Know About There's no need to select a topic that is likely to make your academic life so complicated. The type of topic you select will ascertain the degree of success you'll get. It's really simple to use in addition to self explanatory. Utilize your example to back up your opinion and explain it. To totally understand the political process an individual should have lots and tons of understanding of the way our society operates. This social issue is a quality case of a problem that will resonate with a massive audience. Topics like the psychology of persuasion, peer pressure, conformity, and obedience are merely a few of those studied in this region of social psychology. When picking your social problems topic, don't forget that it's always far better to write about something you're already more or less acquainted with. Introducing Research Topics about Social Issues There are a lot of things to consider and most importantly, is the dependability of the service you decide to use. After discovering our website, you will no longer will need to bother friends and family with these kinds of requests. You desire a subject that is going to keep you motivated and create in you the urge to move to the next level. Being part of society, you see and feel various troubles and tr ends which occur constantly and mean something to various groups of individuals. To compose a great research paper you want to be confident in your argument. If you're writing about social problems, you will typically be writing about the way the topic affects larger groups of people, including how poverty affects a whole generation. Researching any issue about government or laws can get overwhelming because of the intricacy of the issues and even due to the wording of some laws. Make using the suggested research paper topic ideas and you'll be prosperous. There's well-known that you aren't going to have the ability to compose a great insightful research paper if you're not interested in the subject overall and in the subject particularly. Writing a research paper even though may appear challenging is a considerable portion of routine student life. To begin researching local problems, head straight to local newspapers and internet sources. Top Choices of Research Topics about Social Issues A superb subject is probably to cause a superb project. The excellent thing with an intriguing research topic is that it's going to grow your interest throughout the research practice. You cannot comprehensively take care of an industry research topic which is too wide. 1 thing you ought to realize is that choosing the ideal research topic is the most crucial step in writing your dissertation, thesis, or research report. Perform extensive research on the subject of your choice and make an impressive persuasive speech that individuals will remember for long. There isn't any doubt your future employers will want to learn what your key research project focused on. If you're confused with a number of interesting topics to research online, it's far better to choose what interests you the most. You may find almost all of these research materials online while some are easily available in your nearby library. The Argument About Research Topics about Social Issues Suicide prevention is a critical part of therapy and treatment for mental health problems, particularly for those people who are inpatients in hospitals. Men and women who have survived cancer may have physical, emotional, and societal problems that affect their quality of life, no matter what sort of cancer they've been treated for. Check with your physician before you begin, stop, or adjust the dose of any medication. When you look around, you will observe social troubles that affect society each day. The entire research should be constructed around or from the subject. When you decide on a research topic, make certain it is one which you understand and have a firm grasp on. These topics will be helpful for individuals who need to compose essays about the subject mentioned above in the shape of a normal job. Don't hesitate to use our sample topics to produce your own! If you would like to compose a controversial essay, you definitely must look for the greatest social issues topics or satire topics. Writing an intriguing essay about trendy topics is an opportunity to reveal your understanding of the planet. You have to make sure you've picked an adequate topic so you may submit a high-quality essay. To begin with, make certain you decide on a topic which will be interesting to both you and the reader. It isn't important to us, whether you're too busy on the job concentrating on a passion undertaking, or simply tired of a seemingly infinite stream of assignments. Don't be concerned if you don't have good writing skills because you always ought to seek the services of an expert to finish your assignment punctually. In today's world, there are lots of social difficulties. They have always been an integral part of the human condition.

The Role Of Sports For Athletes And Women Athletes

Marketisation and commoditisation provide leverage for powerful nations to assert their dominance over their sport competitors by, for instance, buying their best athletes from the dominated countries and sometimes offering those athletes citizenship. There are instances when international corporate entities sponsor and own clubs in other countries, make all management decisions, and secure profits which they return to their home countries thereby leaving host countries further impoverished (Nauright 2012:54).The above global pattern has not favored most womens’ national and local teams as most corporate entities prefer to sponsor national mens’ teams. Both the commodification and corporatization of sport reduce especially womens’†¦show more content†¦Local leagues face serious challenges due to inability to raise funds as a result of reduced quality of play resulting in poor stadium attendance that mean fewer facilities, and as indicated earlier, this l ack of facilities has a trickle-down effect on accessibility of facilities for women in sports. Due to globalisation, national teams go into a stage of â€Å"dependent development† an example is the English soccer teams as a result of the presence of foreign players in the league system denying most of the local clubs eventually has a negative effect the national team (Maguire 2013:200). Globalisation has also impacted on local sport participation by way of administrative practices. For example, Carter (2002) documents the rise of global administrative bodies (such as FIFA and OIC) and FIVF (Vanderhoof 2011) that oversee and regulate various sports. Similarly, MacAloon (1984) discusses how the modern Olympic movement highlights the diffusion of sports forms and organisation across the globe. These organisations also continue empowering males (e.g., the amount of money FIFA gives to mens’ soccer teams during the World Cups is greater than the amount they give to womens’ teams). Such inequities sometimes serve as deterrents to female participants and thereby compromise efforts to create equality between the sexes (Grainey 2012:23). The internationalisation as well as the internationality of sports can