EMM 514 - The metal framework design is very important for dental restorations to be successful. PDF

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The metal framework design is very important for dental restorations to be successful. The alloys used also affect how successful the veneering is since they have to meet certain requirements. The biological requirements include how compatible they are to the oral tissues, the functionality requirem...

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METAL FRAMEWORKS AND VENEERING OF METAL CERAMIC RESTORATION

By (Name) The Name of the Class (Course) Professor (Tutor) The Name of the School (University) The City and State where it is located The Date

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Table of Contents Abstract......................................................................................................................................................3 1.0 Introduction.........................................................................................................................................3 1.1 Objectives.............................................................................................................................................4 1.2 Requirements of metal alloys used in metal-ceramic restorations...................................................5 1.3 Alloys used in metal-ceramic restoration...........................................................................................5 1.4 The framework design of the metal framework................................................................................6 1.5 Requirements of veneering porcelain.................................................................................................6 1.6 Comparisons of bonding mechanisms between metal and veneering porcelain.............................6 1.7 Forms of failure between metal and veneering porcelain.................................................................7 Conclusion..................................................................................................................................................7 Bibliography..............................................................................................................................................8

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Abstract The metal framework design is very important for dental restorations to be successful. The alloys used also affect how successful the veneering is since they have to meet certain requirements. The biological requirements include how compatible they are to the oral tissues, the functionality requirements determine how they function when placed in the oral cavity of the patient, the working requirements involve the ease of working when the prosthodontist is carrying out the veneering procedure. The most commonly used alloys in metal-ceramic restorations include titanium, gold-based, cobalt-chromium, stainless steel, and nickel-chromium. The veneering porcelain should be compatible with the metal alloy, biocompatible with the oral tissues, possess the ability to be divided and used thinly, and be durable among other requirements. Color change, fracture of the porcelain, gum recession, and marginal expansion are the failures that can occur between metal alloys and veneering porcelain.

Keywords: Veneering, framework, metal-ceramic. 1.0 Introduction Metallic elements are those that ionize into cations when in solution. An alloy is a combination of two or more metals where every metal in the combination contributes some of its best properties. These metal alloys are shaped using the dental casting technology that was developed by Taggart as the lost wax technique. The alloys used in dentistry are soluble in each other both in the liquid and solid state. They are used to make inlays, on lays, bridges, and dental implants whenever a patient has experienced loss of teeth or part of their teeth have been destroyed due to decay, accidents and other issues. The replacement of lost teeth is important for restoration of chewing functions, preventing misalignment of the other teeth, offering support to the mouth, and for aesthetic purposes to restore the patient’s self-esteem. Metals and ceramics are highly biocompatible with the oral tissues and are popular options for veneering. [ CITATION Mic07 \l 1033 ] For metal alloys to be used in dental restorations, they have to possess a set of attributes that would lead to their successful use in the procedures. The requirements they should meet are divided into biological, functional, and working requirements. Biological requirements are those that relate to the reaction of the patient with the use of the alloys. Functional requirements are those that they should meet when the patient uses them while working requirements are those that

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they should possess when the dentist is working with them. Titanium, gold-based, stainless steel, cobalt-chromium, and nickel-chromium alloys are commonly used as the base metal alloys for ceramic restorations. [ CITATION Mic07 \l 1033 ]

Figure 1 Metal-ceramic restorations [ CITATION Fai14 \l 1033 ]

1.1 Objectives 1. To list the requirements of metal alloys used in metal-ceramic restorations

2. To list the possible alloys used in metal-ceramic restoration 3. To describe the framework design of the metal framework 4. To list the requirements of veneering porcelain used in metalceramic restorations

5. To compare between the bonding mechanisms between metal and veneering porcelain

6. To clarify the possible forms of failure between metal and veneering porcelain and mention the possible causes of each failure

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1.2 Requirements of metal alloys used in metal-ceramic restorations Biocompatibility with the oral tissues of the patient is a very important requirement for them to possess. For them to be compatible, they should be hypoallergenic, they should be known to be safe for use when considering the patient’s health, and they should not get tarnished or corroded because the production of rust poses a risk to the oral health of the patient and makes the metal alloys less aesthetically pleasing than intended. The metal alloys used should also have high ductility, toughness, high resistance to sagging, high fatigue strength, high resistance, high yield strength, high transverse strength, high cantilever bending strength, high modulus of elasticity and high impact strength. They should be elastic so as not to get deformed by the masticatory movements in the mouth since the mouth moves a lot during mastication and can easily stretch them. They should have a high fatigue strength and toughness to prevent them from breaking due to the forces in the mouth. They should have a high transverse strength to manage the sideward movement of the mouth during chewing. [ CITATION Fai14 \l 1033 ] When the prosthodontists are working with the alloys, they are required to be easy to solder, cast (shape), and burnish. The high ductility that they should possess also makes burnishing them easier. Their solidus-liquidus range should be narrow so that they do not form oxides during casting, their melting point should be low so that a simple technique is used to melt them and low temperatures are involved so that the casting shrinkage is low, and they should also possess a high density so that little force is used in casting them. To avoid flowing when being soldered, the metal alloys should have a high sag resistance. [ CITATION YuZ18 \l 1033 ]

1.3 Alloys used in metal-ceramic restoration The most commonly used alloys in metal-ceramic restorations include titanium, gold-based, cobalt-chromium, stainless steel, and nickel-chromium.

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1.4 The framework design of the metal framework The metal alloy may get deformed when its solidus point is lower than the firing temperature of the ceramic preventing the margin from expanding. Marginal integrity, contour control, and design of the metallic lingual band are the most important parts of the framework design that should be considered. The marginal fit should be as closed as it can get through it is impossible to reach a completely closed margin. This helps to prevent bacteria and other germs from getting into the restorations and cause diseases. It also allows for the easy cleaning of the restorations. A torpedo diamond is used to reduce the lingual axial wall. The contours should be smooth, well-rounded, and convex-shaped. To contain the porcelain, the ledge of the metal should be well-rounded, and the finish line between the metal and the ceramic used should be 900. [ CITATION KHO97 \l 1033 ]

1.5 Requirements of veneering porcelain The veneering porcelain should be translucent and appear like an enamel to provide the aesthetics of the teeth that are required by the patient. The porcelain should have the ability to be divided and used thinly in the teeth. It should be compatible with the metal alloy used. It should have a high maintenance capability so that it does not lose its aesthetics over time. It should be biologically compatible with oral tissues so that it does not cause allergic or other negative reactions. It should be strong and tough to resist abrasion caused by the chemicals in the cleaners and resist impact forces when the patient experiences an accident. They should have a high melting point so that they are not deformed when the patient takes in hot food or drinks. Its coefficient of thermal expansion should match that of the alloy to prevent restoration failure, it should be insoluble in oral fluids and other ingested fluids, and non-adherent to dental cement. [ CITATION EAM97 \l 1033 ]

1.6 Comparisons of bonding mechanisms between metal and veneering porcelain The metal and the ceramic are bonded to each other chemically, mechanically, by applying thermal expansion mismatch, and by applying bonding paste. In the mechanical bonding, the fused ceramic is made to flow on to the irregularities of the metal alloy. Sandblasting and the use of plastic beads for waxing are important processes for this type of bonding. An ionic bond is formed between the thin oxide layer and the porcelain. Metal degassing is necessary for

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the creation of the oxide layer in this type of metal-ceramic bond. When the metal cools down, it contracts and forms a bond with the porcelain through the process of thermal expansion mismatch. It may be necessary to apply a bonding paste on the alloy’s surface before putting porcelain on top of it. [ CITATION PCG08 \l 1033 ]

1.7 Forms of failure between metal and veneering porcelain The forms of failure in this case include cracking and fracturing of the porcelain, marginal expansion, gum recession, and change of color of the porcelain. The cracks and fractures have a variety of causal agents that include tensile stress, poor marginal integrity, and rigidity of the materials when stretching masticatory forces are applied to them. [ CITATION Liu14 \l 1033 ] When a patient undergoes root canal treatment, the color of the porcelain is highly likely to change. The porcelain’s shade and thickness have a large influence on whether the porcelain will change color in the functional period. [ CITATION Die14 \l 1033 ] The marginal expansion takes place when the firing temperature of the ceramic is higher than the solidus point of the metal alloy. Gum recession is largely caused by the mistreatment of the restorations by patients. [ CITATION PCh15 \l 1033 ]

Conclusion In conclusion, the requirements of metal alloys used in dental ceramics include biocompatibility with the oral tissues, high ductility, toughness, high resistance to sagging, high fatigue strength, high resistance, high yield strength, high transverse strength, high cantilever bending strength, high modulus of elasticity and high impact strength. They should also have high elasticity, high fatigue strength, toughness, and be easy to solder, cast (shape), and burnish. The most commonly used alloys in metal-ceramic restorations include titanium, goldbased, cobalt-chromium, stainless steel, and nickel-chromium. Marginal integrity, contour control, and design of the metallic lingual band are the most important parts of the framework design that should be considered. The veneering porcelain should be translucent and appear like the enamel, have the ability to be divided and used thinly, have a high maintenance capability, be biologically compatible with oral tissues, be strong and tough to resist abrasion, have a high melting point, its coefficient of thermal expansion should match that of the alloy, it should be insoluble in oral and other ingested fluids, and be non-adherent to dental cement. The metal and the ceramic are bonded to each other chemically, mechanically, using thermal expansion mismatch, and by applying bonding paste. The forms of

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failure that are presented in these cases include cracking and fracturing of the porcelain, marginal expansion, gum recession, and change of color of the porcelain

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