Dental Tribune Untited Kingdom Edition

April 16-22, 201218 Lab Tribune United Kingdom Edition A s dentistry continues to evolve, new tech- nologies and materi- als are continually being of- fered to the dental profession. Throughout the years, restor- ative trends and techniques have come and gone. Some material developments have transformed the face of aes- thetic dentistry, while other initial concepts have phased out and died. Today all ce- ramic restorations continue to grow in the area of restora- tive dentistry, from pressed ceramic techniques and ma- terials to the growing use of zirconia, and new materials that can be created from CAD/ CAM technology. This article will explore new uses for the all-ceramic material, known as lithium disilicate, and the use of a digital format to de- sign and process this material in new and exciting ways. An overview of the material and unique clinical procedures will be presented. Introduction Embracing proven alterna- tive solutions and transform- ing traditional methods can be challenging to dental restora- tive teams facing increasing patient demands while being tasked with delivering high- strength restorative options without compromising the aesthetic outcomes. Tradi- tionally, dental profession- als have used a high-strength core material made of either a cast metal framework or an oxide-based ceramic (such as zirconia or alumina). This ap- proach has two disadvantages. Compared with glass-ce- ramic materials, the substruc- ture material has high value and increased opacity but may not be aesthetically pleasing.1 This is especially an issue in conservative tooth prepara- tion when the core material will be close to the restora- tion’s exterior surface. The other disadvantage is that although the high- strength material has great mechanical properties, the layering ceramic with which it is veneered exhibits a much lower flexural strength and fracture toughness.2, 3 The zir- conia core (with a 900 to 1,000 MPa flexural strength) is less than half of the cross-sec- tional width of a restoration; it must be completed with a veneering material with a flexural strength in the range of 80 to 110 MPa (depending on delivery method).4 The veneering material tends to chip or fracture during func- tion. Also, such restorations depend significantly on the ability to create a strong bond interface between the dissimi- lar materials of oxide-ceramic and silica-based glass-ceram- ic, a bond that is not difficult to create.5 However, the qual- ity of the bond interface can vary substantially because of cleanliness of the bond sur- face, furnace calibration, user experience and other issues. In today’s industry, mono- lithic glass-ceramic struc- tures can provide exceptional aesthetics without requiring a veneering ceramic. Greater structural integrity can be achieved by eliminating the veneered ceramic and its req- uisite bond interface.6 The relative strength of the avail- able glass-ceramic material has traditionally been the dis- advantage of these restora- tions. Owing to their flexural strength of 130 to 160 MPa, they are limited to single- tooth restorations, and adhe- sive bonding techniques are needed for load sharing with the underlying tooth.6 This has been resolved through the development of highly aes- thetic lithium-disilicate glass- ceramic materials. The 70 per cent crystal phase of this unique glass- ceramic material refracts light very naturally, while also providing improved flexural strength (360 to 400 MPa).7 This gives more indications for use and the ability to place restorations using tradition- al cementation techniques, while also having strength and aesthetics. Lithium disilicate, the restorative material of multiple options Lee Culp and Prof Edward McLaren Fig. 1 Pre-existing clinical condition of mandibular molar to be restored Fig. 2 Mandibular molar restored with CAD/CAM-designed and -milled e.max resto- ration, using stain and glaze technique for aesthetics Fig. 3 Pre-existing clinical condition of maxillary posterior quadrant to be restored Fig. 4 Maxillary posterior quadrant restored with CAD/CAM-designed and -milled e.max restorations, using a micro-layering tech- nique for aesthetics. Clinical dentistry in Figure 3 & 4 was done by Dr Michael Sesseman ‘Embracing proven alternative solu- tions and trans- forming traditional methods can be challenging to dental restora- tive teams facing increasing patient demands’