FULL AND PARTIAL COVERAGE CROWNS

Chapter 2HISTORY

Metals form a large part of the earth on which we live, nearly 80% of the known elements are metals in the earths crust. Most of the metallic elements occur in compounds and not in the metallic state. A few of the least reactive metals may be found in the metallic state in the earths crust, these metals include gold, copper, mercury and platinum. Ancient people knew how to use many native metals and gold was used for ornaments, plates, jewelry and utensils as early as 3500 BC, gold objects showing a high degree of culture have been excavated at the ruins of the ancient city of europe in mesapotamia. Silver was used as early as 2400 BC. Native copper was also used at an early date for making tools and utensils. Since about 1000 BC iron and steel have been the chief metals of construction. The earliest known use of dental materials can be traced to approximately 700B.C. The Etruscans made teeth of ivory and bone that were held in place by a gold framework. Animal bone and ivory from the hippopotamus or elephant were used lot many years thereafter. Later, human teeth sold by the poor and teeth obtained from the dead were used, but dentists generally disliked this option. Fauchard suggested porcelain as an improvement upon bone and ivory for the manufacture of artificial teeth, a suggestion which he obtained from R. A. F. de Reaumur, the French savant and physicist, who was a contributor to the royal porcelain manufactory at Sevres. An improved version of that product "mineral paste teeth" that was produced in 1774 by Duchateau, was introduced in England soon. A French dentist De Chemant patented the first porcelain tooth material in 1789. In 1808 Fonzi, an Italian dentist invented a "terrometallic" porcelain tooth that was held in place by a platinum pin or frame. Although fixed prosthodontic crown and bridge work dates to as back as 300 to 400 BC where in one of the oldest tombs of Sidon, a Phoenician specimen was found consisting of gold wire fastened around six anterior teeth, two of them being pontics. But crown and bridge fixed partial prosthesis was indeed in a crude state of development till as late as 1850.The early crowns were not fabricated by casting. It was made by flowing solder over gold foil that had been adapted to the tooth preparation, with wrought wire staples in the preparation grooves. In 1907 William H. Taggart announced his method of making gold castings, using a disappearing wax pattern and it was known as lost wax technique. This application of an old method revolutionized the technical aspect of restorative dentistry. It made possible exceptional refinements in the construction of fixed partial prosthetic appliances. The stainless steel crown has been around about 50 years, give or take a few. Dr. William Humphrey of Denver, Colorado, gets credit for developing and popularizing the crown around the world. The birth of the stainless steel crown ended years of frustration for dentists who were trying to treat extensive caries of the primary dentition.For many years dentists caring for children had searched for a restorative solution to multisurface caries in the primary dentition. Amalgam was the mainstay, but when a tooth became more amalgam than hard tissue, failure was inevitable. Only the very rich could afford a gold crown. Orthodontic bands filled with amalgam were a last resort when little tooth structure remained above the gingiva, but this technique provided little form or retention. It may have been the orthodontic band that provided the idea for the crown of the same material. Dr. Humphreys relationship with the Rocky Mountain Orthodontic Company provided him an opportunity to see the bands made. A small piece of steel was placed over a die that vaguely resembled a tooth and the dies form was impressed into the metal, creating something looking like a small tin can. All but the most gingival portion was discarded as the orthodontic band was severed from the primordial crown. Dr. Humphrey began to work with some of the precut blanks to restore teeth. The first crowns looked like something which resembles a used shell casings rather than the anatomic contoured and festooned versions we have today. Over the years, the crowns have been shortened and some anatomy added, but the original concept has remained the same.The full metal crown has been in some controversy and criticism. Over these 50 years we have accused it of many things, including allergenicity and gingival irritation, called it unesthetic, and argued about whether its margins should stay above or extend below the gingiva. In spite of it all, the metal crown has continued to serve us and our patients well.

Looking back on the many restorative techniques that have come and gone, its hard to find a match for the full metal crown. Its easy to do, lasts as long as the tooth, doesnt leak or break, and fits just about every tooth whereas gold has its cost, amalgam its controversy, and plastic its limits. Then came ceramics which play an integral role in dentistry. Their use in dentistry dates as far back as 1889 when Charles H. Land patented the all porcelain jacket crown.This new type of ceramic crown was introduced in 1900s. The procedure consisted of rebuilding the missing tooth with porcelain covering, or jacket as they called it. The restoration was extensively used after improvements were made by E.B. Spaulding and publicised by W.A. Capon. To reduce the risk of internal microcracking during the cooling phase of fabrication, the porcelain fused to metal (PFM) crown was developed in the late 1950s by Abraham Weinstein.2The bond between the metal and porcelain prevented stress cracks from forming. While PFM crowns have a decrease in porcelain failures, but the addition of a metal brings an opaque layer which diminishes the esthetics of these restorations.Partial veneers were invented by California dentist Charles Pincus in 1928 to be used for a film shoot for temporarily changing the appearance of actors' teeth.[1]Later, in 1937 he fabricated acrylic veneers to be retained by denture adhesive, which were only cemented temporarily because there was very little adhesion. The introduction of etching in 1959 by Dr. Michael Buonocore aimed to follow a line of investigation of bonding porcelain veneers to etched enamel. Research in 1982 by Simonsen and Calamia[2]revealed that porcelain could be etched withhydrofluoric acid, and bond strengths could be achieved between composite resins and porcelain that were predicted to be able to hold porcelain veneers on to the surface of a tooth permanently. This was confirmed by Calamia[3]in an article describing a technique for fabrication, and placement of Etched Bonded Porcelain Veneers using a refractory model technique and Horn[4]describing a platinum foil technique for veneer fabrication. Additional articles have proven the long-term reliability of this technique.[5][6][7][8][9][10][11][12][13]Today, with improved cements andbonding agents, they typically last 1030 years. They may have to be replaced in this time due to cracking, leaking, chipping, discoloration, decay, shrinkage of the gum line and damage from injury or tooth grinding. The cost of veneers can vary depending on the experience and location of the dentist.A resurgence of an all ceramic restoration came in 1965 with the addition of industrial aluminous porcelain (more than 50%) to feldspathic porcelain manufacturing. J.W. McLean and T.H. Hughes developed this new version of the porcelain jacket crown that had an inner core of aluminous porcelain containing 40% to 50% alumina crystals.3Although it had twice the strength of the traditional PJC, but still the strength was not enough so it could be used in the anterior region only. Its higher opacity was also major drawback.4Another development in the 1950s by Corning Glass Works led to the creation of the castable Dicor crown system. Glass was strengthened with various forms of mica. The process involved the use of the lost wax casting technique, which produced a casted glass restoration. Then this was heat treated or cerammed. The ceramming process provided a controlled crystallization of the glass that resulted in the formation and even distribution of small crystals. The resultant monochromatic crown was shaded with an application of a superficial color layer. The processing difficulties and high incidence of fracture were factors that led to the abandonment of this system.6Leucite was first added to feldspathic porcelains to raise the coefficient of thermal expansion to match the metals to which they were fired. The crystalline leucite phases also helped feldspathic porcelain to slow crack propagation. High leucite-containing ceramics Empress and optimal pressable glass (OPC) were introduced in the late 1980s and were the first pressable ceramic materials. Although the initial steps for fabrication for Empress and OPC were similar to Dicor and Cerestore in which the restoration was formed in wax, a heated leucite-reinforced ceramic ingot was pressed into the mold using a specially designed pressing furnace, whereas the Dicor crown was created using centrifugal casting. Despite the increase in strength of leucite-reinforced pressed Empress material, fracture was still possible when used in the posterior region.3 During this time, a glass infused ceramic core system was developed. Vita used a slip-casting process in which the core achieved an 85% sintered alumina by volume and introduced the In-Ceram system. This glass infused alumina core had a flexural strength of 352 MPa. The change of infused oxides slightly reduced the flexural strength but produced a restoration more fitting for the anterior region. Vita also added a variation of the infused core by mixing alumina with zirconium oxide crystals, which increased the flexural strength to 700 MPa. It was intended for posterior crowns and bridges.In the mid 1990s Nobel Biocare introduced the Procera AllCeram core, which was the first computer-aided design/computer-aided manufactured (CAD/CAM) substructure. This core consisted of 99.9% alumina to which a feldspathic ceramic was layered. The use of CAD/CAM technology spurred a whole new generation of ceramic substructures consisting of zirconium dioxide. Several manufacturers (Lava, 3M ESPE; Procera Forte, Nobel Biocare; and Cercon, DENTSLY) introduced crown and bridge frameworks milled from blocks of pre-sintered yttrium stabilized zirconium dioxide blocks. The oversized milled frame works were then sintered for 11 hours at 1500C providing excellent fit with 900 MPa to 1300 MPa of flexural strength. Other manufacturers (Everest, KaVo, DC-Zirkon, Precident DCS) milled fully sintered zirconium dioxide blocks to overcome the shrinkage factor, which one study found to have a superior marginal fit.8In 1998 Ivoclar introduced IPS Empress II, which was a lithium disilicate ceramic material used as a single and multiple unit framework indicated for the anterior region. The frame-work was layered with a veneering ceramic specially designed for the lithium disilicate. A 5-year study revealed a 70% success rate when used as a fixed partial denture framework.9Authentic, a second-generation, low-fusing, high-expansion, leucite glass-reinforced ceramic material, was introduced into the European market in 1998 by Ceramay GmbH & Co. Laboratory technician Brian Lindke experimented with pressing Authentic to specific alloys. Ceramic pressable ingots with a compatible coefficient of thermal expansion were developed for this technique.Lithium disilicate re-emerged in 2006 as a pressable ingot and partially crystalized milling block (Cerec for chairside and inLab milling units for laboratories).10 The flexural strength of the material was found to be more than 170% higher than any of the currently used leucite reinforced ceramics. Later IPS e.max was introduced to dentistry in 2007, which quickly became the fastest-growing product. Thus dental material manufacturers seem to be leaning away from metal alloy-containing restoratives and favoring all-ceramic restorative dentistry. Research and development appears to be heading in two directionsimproving the strength and esthetics References1. Taylor JA.History of Dentistry: A Practical Treatise for the Use of Dental Students and Practitioners.Philadelphia, PA: Lea & Febiger; 1922: 142-156.2. Asgar K. Casting metals in dentistry: past-present-future.Adv Dent Res.1998;2(1):33-43.3. Kelly JR, Nishimura I, Campbell SD. Ceramics in dentistry: historical roots and current perspectives.J Prosthet Dent.1996;75(1): 18-32.4. Leinfelder KF, Kurdziolek SM. Contemporary CAD/CAM technologies: the evolution of restorative systems.Pract Proced Aesthet Dent.2004;16(3):224-231.5. Krishna JV, Kumar VS, Savadi RC. Evolution of metal-free ceramics.J Indian Prosthodont Soc.2009;9:70-75.6. Powers JM, Sakaguchi RL.Craigs Restorative Dental Materials 2011, 12th Edition, St. Louis, MO: Mosby Elsevier; 20:444.7. Wagner WC, Chu TM. Biaxial flexural strength and indentation fracture toughness of three new dental core ceramics.J Prosthet Dent.1996;76(2):140-144.8. Ariko K. Evaluation of marginal fitness of tetragonal zirconia polycrystal all-ceramic restorations.Kokubyo Gakkai Zasshi.2003;70(2):114-1239. Marquardt P, Strub JR. Survival rates of IPS Empress 2 all-ceramic crowns and fixed partial dentures: results of a 5-year prospective clinical study.Quintessence Int.2006;37(4):253-259.10. Sol-Ruiz MF, Lagos-Flores E. Survival rates of a lithium disilicate-based core ceramic for three-unit esthetic fixed partial dentures: a 10-year prospective study. International journal of prosthodontics 2013; Mar-Apr;26(2):175-80