Ceramics in Dentistry: Principles and Practice

By J. Robert Kelly

The use of ceramics in dentistry holds enormous potential for restoring dentitions, but ceramics can be difficult to master because of the common problems of chipping and fracture. This book unlocks the mystery behind successful use of dental ceramics and lays bare the science behind this high technology. The author shows how and why fracture occurs and explains why choosing the right material, design and processing method are vital to the success of any ceramic restoration and why certain ceramic systems are most suitable for certain clinical situations. The author also details how to achieve esthetic excellence without compromising strength. The book concludes with a chapter on the use of ceramics in implant dentistry and how CAD/CAM technology can be used to revolutionize this field. Thumbnails featured throughout point to extra online content.

• Language: English
• Publisher: Quintessence Publishing Co, Inc
• Release date: Jun 17, 2020
• ISBN: 9780867157277

Book preview

Preface

Welcome to the Kelly Lectures on Ceramics—aimed at general dentists, prosthodontists, high-end laboratory technicians, and prostho-cadets—meant to harken back to the Feynman Lectures on Physics. (Alas, I do not play bongo drums like he did.) This book is designed to teach what this stuff is, what it is good for (from clinical data), and how to maximize durability and esthetics.

Before I headed off to Harvard to study prosthodontics and MIT as a cross-registration student studying glass science and ceramic engineering, I knew that I faced a pivotal career choice: to focus my doctoral work on either resin-based composites or ceramics. I had been introduced to both along with metallurgy and mechanics in my superb materials masters degree program mentored by Bill Brantley at Marquette University. Obviously ceramics won, in part due to inspiration from the two-volume series on the art and science of dental ceramics by Dr John McLean (Quintessence, 1979). At that time my interest in all-ceramic systems and high-end esthetics was warming up.

In Boston, Ted Riley and Ralph Sozio, working with Coors Biomedical, had introduced the first net-shape (ie, nonshrinking) ceramic to dentistry along with the first high technology ceramics processing equipment into the dental laboratory. Shortly thereafter, David Grossman from Corning Glass Works, working in partnership with Dentsply, introduced Dicor, the first glass-ceramic dental material. Also in Boston, Kenneth Malament was just beginning his phenomenal in-depth clinical study of many aspects of all-ceramic prostheses. About this time, my MIT professor, Kent Bowen, received a letter from Dr Werner Mörmann, the inventor of the CEREC machine, wanting a better ceramic. It was my job to write the answer and to host Werner at the MIT Ceramics Processing Research Laboratory. Next to visit was Henry Rauter, owner of Vita Zahnfabrik, along with Wayne Whitehill, President of Vident. With the sponsorship of Vita and working closely with their top inorganic chemist, Norbert Thiel, we invented the Vita Mark II block for CEREC—still a high-technology material on today’s market with wonderful wear kindness (trade secret). In the meantime, I attended the first CEREC course taught in English (at the University of Zurich) and learned to appreciate flying to Europe in business class!

Over the years I have developed quite some teaching material on dental ceramics, including organizational approaches; simplified concepts of strength, toughness, and durability; and even a new classification system used in the international dental standard, ISO 6872. Many, many lecture opportunities presented themselves, and slowly I came to have sufficient material to fill all-day programs—and now a book.

My wife has been encouraging me to write a book for years. I found that as I sat down to put keyboard to paper, I was simply lecturing through my fingertips with the wonderful opportunity to expand the content. Even more exciting was the idea to use either scannable codes or links to allow interested readers to sample extra visual content that is both humorous and informative. And best yet, the folks at Quintessence liked the idea (although Lisa Bywaters once suggested my appearing as a cartoon character). Thus, this book has the potential to be a living book as we can add to and enhance the linked content.

Acknowledgments

Key individuals helped in providing encouragement and proofreading of the manuscript, including Drs Werner Mörmann of Zurich, Switzerland, and David Burnham of Edmonton, Canada. And, of course, thanks Patrice for the gentle wifely push !

1

Introduction to Ceramics in Dentistry—Where Did This Stuff Come From?

Craft Art or High Technology

When I have the opportunity to lecture on the history of ceramics in dentistry, I enjoy challenging audiences to commit by a raise of hands as to whether they think dentistry borrowed ceramic technology from craft art or pursued it through innovation and high technology. To further develop the point, I draw a clear distinction between high technology and craft art by providing some defining characteristics of each. Many would agree that high technology should include: (1) dentistry borrowing materials/processes shortly after their development by an unrelated industry, (2) incorporation of new learning from recent scientific literature outside of dental medicine, and (3) the spread of outright new inventions within dentistry. Craft art, on the other hand, brings to mind materials and techniques borrowed from highly skilled artisans involved in jewelry making, the arts, and the manufacture of everyday goods. More than 90% of people vote for an origination through craft art, as I would have done prior to my literature search!

It is useful to review how and why ceramics came to be used in dentistry, and this introduction serves three purposes: (1) to alert practitioners to the fact that the use of ceramics has always represented the adoption of high technology, not borrowed craft art; (2) to reinforce the concept that ceramic technology and improved ceramics were introduced to solve specific problems or to increase restorative versatility; and (3) to provide some background into the nature and science of ceramics. (Astute readers will also find clues about where to watch for the emergence of new ceramic technologies.)

In the Beginning

In the late 1600s and early 1700s, many European rulers and aristocrats were dispensing enormous sums to import porcelain from China and Japan. Schloss Charlottenburg in Berlin has an impressive assortment of porcelain, and Fig 1-1 represents just a small portion of the collection. Augustus II of Saxony (who was the reigning King of Poland and Elector of Saxony at the time) amassed one of the largest collections in Europe; it is now on display at Dresden’s Zwinger Museum housed in his former palace. Such expensive activity led China to be characterized as the bleeding bowl of Europe. Between 1604 and 1657 alone, over 3 million pieces of Chinese porcelain reached Europe.¹ In just one day in 1700, East Indiamen ships unloaded 146,748 pieces of porcelain in a European port as the market for porcelain became insatiable.¹

Fig 1-1 A small portion of the china collection from Schloss Charlottenburg in Berlin.

One response to this situation involved state-sponsored research into porcelain discovery. Notable European leaders, including Augustus II the Strong and the Medici family of Florence, were independently sponsoring research into the development of a European porcelain to match the hard, translucent, and sonorous material developed in Eastern Asia nearly 1,100 years earlier. Europeans strived for porcelain discovery without much success for about 200 years, and this activity is credited with the growth of modern analytical chemistry from its roots in alchemy. Figure 1-2 shows the historical timeline of porcelain discovery.

Fig 1-2 Timeline for the development of several related porcelains.

State-sponsored research into porcelain discovery initiated in France and the Germanic state of Saxony in the late 1600s. The efforts of Count Walther Von Tschirnhaus in developing the mineral resources of Saxony on behalf of Augustus II were particularly important for dentistry. He used a series of large burning lenses (magnifying glasses up to 1 meter in diameter) to create a solar furnace; these lenses directed to a focal spot, allowing Von Tschirnhaus to subject minerals to extensively high temperatures, easily in excess of 1,436°C.²

Meanwhile in Berlin (in the Germanic state of Prussia), Johann Friedrich Böttger was manipulating metals as a journeyman apothecary. Böttger’s parlor trick involved melting base metals such as silver coins and then adding a dose of the Arcanum of the philosopher’s stone.³ When poured into molds and cooled, the resulting product was analyzed to be pure gold! Böttger inadvisably performed this transmutation demonstration at his employer’s house to impress some important guests, resulting in a summons by King Frederick I of Prussia for a command performance. Placing discretion ahead of valor, Böttger fled south to Saxony, where he attempted to study medicine at Wittenberg University. Wanted posters appeared in Berlin, and a price was put on the head of Böttger. For the local representative of Augustus II in Wittenberg, the arrival of a contingent of a dozen troops from King Frederick seemed excessive for the capture and return of a supposedly common criminal. Therefore, Böttger was placed under house arrest for months while Augustus was alerted and the situation explored. With the presence of foreign troops confounding the situation, Böttger was finally spirited away by coach in the dead of night, using back roads to avoid Prussian troops, and delivered to Augustus in Dresden. To further deceive the Prussians, the Saxons continued to bring food to the room of Böttger. For any state needing to support armies, Böttger’s ability to turn base metals into gold was simply too important to let slip away, so Böttger was held as a prisoner under the wing of Von Tschirnhaus to perfect gold production.

Serendipity and a clever intuition prevailed to save Böttger from certain execution following over 3 years of unsuccessful gold making, a project costing Augustus a small fortune. Experimenting with his burning lenses, Von Tschirnhaus had discovered that while neither sand nor lime (calcium oxide) would fuse individually, they would do so when combined; in fact, the resulting white product looked suspiciously like porcelain. What had been discovered was the use of a flux to create lower melting intermediate compounds, promoting glass formation and allowing the fusion of the high-silica sand. Because it was known that high-quality clay was a major ingredient in Chinese porcelain, Saxony was secretly scoured for sources of the purest clay. Böttger, whose expertise in chemistry was by then extensive, realized that porcelain had to have a glassy component resulting from very high–temperature reactions. Building on the discovery of Von Tschirnhaus, he reasoned that lime added to clay was worth exploring.

Between 1704 and 1708, research was conducted under extreme secrecy beginning in the Albrechtsburg Castle, which still exists in the city of Meissen, Germany (Fig 1-3), and then in the dungeon basement of the feared Jungfernbastei (Maiden’s Bastion) in Dresden (Fig 1-4a). Böttger used what is known today as the Edisonian approach, whereby a wide variety of formulations are systematically tried. Figure 1-4b shows a page from his laboratory notebook memorializing the successful mixture of clay and lime (obtained from calcined alabaster that was pulverized and heated to drive off water and sulfur, leaving fine calcium oxide powder).

Fig 1-3 Recent photograph of Albrechtsburg Castle in Meissen, Germany, the site of an early porcelain discovery laboratory and the first manufacturing site of European porcelain rivaling