MONOLITHIC LITHIUM-DISILICATE GLASS-CERAMIC RESTORATIONS

Abstract

In a pursuit for perfect esthetic and natural appearance of restorations in contemporary dentistry, porcelain fused to metal restorations are gradually being replaced by all-ceramics. All-ceramic restorative systems are not a new concept. They were first introduced with the so-called “porcelain jacket crown” in the 1900s by Charles H.Land, fabricated with high-fusing feldspathic porcelain on platinum foil matrix. Because of the low strength of this porcelain, the failure rate was very high and they were slowly abandoned. In the last 10 years with the introduction of lithium-disilicate class ceramics IPSe.max System (Ivoclar Vivadent) with a strength of 470 MPa monolithic restorations made a big comeback. Monolithic or full-contour lithium-disilicate restorations can be stained and glazed for more natural tooth colour look. The ideal restoration shade is optimally reproduced by means of the IPS e.max Shade Navigation App. It facilitates the material selection, leads to results that feature optimum shade match and thus provides efficiency and reliability. This material has two forms: a homogeneous ingot with various degrees of translucency and opacity used with hot-pressed technology Emax Press and a pre-crystallized block used with CAD/CAM technology Emax CAD. Regarding the strength of the material, pressed lithium disilicate is 11% stronger than the CAD/CAM lithium disilicate according to Ivoclar’s 2011 scientific report. Pressable lithium disilicate restorations demonstrated a 98.4% survival rate. Machineable lithium disilicate restorations (IPS e.max CAD) demonstrated a 97.9% survival rate. The pressing technique demonstrated a significantly smaller marginal gap than the CAD/CAM technique. Some in vitro studies have pointed out that lithium disilicate monolithic crowns and FDPs, both CAD/CAM and hot-pressed, are more resistant to fatigue fracture compared to bilayered, hand veneered ones, showing higher fracture loads (1900 N), that are comparable to the metal-ceramic standard. Clinical outcomes of different IPS e.max lithium disilicate prostheses like single crowns, 3 unit bridges, veneers, inlays and onlays, both in the bilayered and monolithic forms, in a 4-year retrospective study reported: 0.91% for monolithic and 1.83% for bilayered single crowns (twice the rate of the monolithic); 4.55% for monolithic FDPs; 1.3% for monolithic and 1.53% for bilayered veneers; and 1.01% for monolithic inlays/onlays. This research supports the use of monolithic lithium disilicate restorations in everyday treatment of choice for high-strength and esthetic indirect treatments, whether for the anterior or posterior regions of the mouth. The material offers specific advantages to dentists such as the ability to provide strong and durable restorations with highly esthetic characteristics without metal. More clinical studies for the esthetic outcome of monolithic restorations are needed in the future.