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E-Max Crowns – A Detailed Overview

Natural aesthetic rendition is a key aim of restoring teeth with full-coverage crowns. Therefore, an ideal dental material for the fabrication of crowns would allow the control of substrate colour and translucency.

Traditional metal ceramic crowns exhibit a lack of light exchange with the surrounding soft tissues caused by the reflection of their metal frameworks and their opaque layers.

Thus, they often present a compromised aesthetic appearance compared to natural teeth.

With the increased demand for aesthetics, all-ceramic restorations have become very popular over the last decades.

Such restorative all-ceramic systems must fulfil biomechanical requirements and should provide longevity like metal ceramic restorations while providing enhanced aesthetics.

Advancements in ceramic material science have resulted in more enhanced physical properties of modern ceramics, leading to a significant increase in the clinical use and practice of all-ceramic restorations.

Lithium disilicate glass ceramic material has been introduced by Ivoclar Vivadent (Amherst, N.Y.) for use in all ceramic restorations.

Introduced in 2005, this material is available as an ingot that can be processed using either lost-wax hot pressing techniques or press-fit (IPS e-max Press, Ivoclar Vivadent) and as a block that can be milled with computer-aided design/computer-aided manufacturing (CAD/CAM) technology (IPS e-max CAD, Ivoclar Vivadent).

Per the manufacturer, it combines high flexural strength along with optimal aesthetics and recommends its use for anterior or posterior crowns, implant crowns, inlays, onlays or veneers.

The e-max/lithium disilicate glass ceramic system, whether CAD/CAM processed or heat-pressed, is indicated either as a full-contour (monolithic) restoration or as a core for subsequent porcelain veneering.

The range of indication is supposed to include anterior and posterior teeth. IPS e-max Press not only can be used as a core material with aesthetic layering but also allows ceramic crowns to be fabricated fully anatomical without the need for veneering (staining technique).

Recent 2-years clinical study on full-contour e-max crowns have shown favourable results in terms of structural integrity, with no mechanical failures such as fracture or chipping. In harmony with these clinical findings, 2-mm-thick full-contour molar crowns of IPS e-max CAD subjected to sliding contact fatigue-testing have demonstrated significantly higher reliability than porcelain-layered yttrium oxide partially stabilised tetragonal zirconia polycrystalline (Y-TZP) crowns.

Although the clinical results are promising, occlusal clearances of less than 2 mm may reduce the reliability of full-contour e-max crowns. This issue necessitates further investigation. In addition, the use of veneering porcelains to improve aesthetics would need a reduction in core thickness that could also limit crown mechanical performance in the posterior region.

Since metal ceramic crowns are generally considered the “gold standard”, and Y-TZP restorations are of significant interest for clinical use, both materials should be compared with e-max/lithium disilicate crowns.

Considering these, in a recent study it has been proved that the reliability of reduced-thickness monolithic lithium disilicate crowns is higher when compared with that of Y-TZP and at least comparable with those of metal-ceramic systems. Moreover, clinical results for lithium disilicate crowns are promising, but longer observation periods and comparison between monolithic and multilayer systems are still required and should be approached with caution.

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