In this post, we are going to discuss a unique material and its usage; lithium disilicate (IPS e.max, Ivoclar Vivadent).

It is a ceramic material with high esthetic potential that also offers good strength. In fact, amongst the major indications of the product are individual anterior restorations and adhesive cementation. This material can be used with both pressed ceramic technology and CAD/CAM systems.



What is IPS e.max?

Lithium disilicate-based glass-ceramic, with a 70% crystalline component and a higher resistance to flexion (around 360 MPa), was first introduced by Ivoclar as Empress II. It is currently available as IPS e.max, with two versions: one for pressing, and the other for CAD/CAM milling. Although it has a high ratio of crystalline phase, the material is translucent enough to be used in esthetic restorations (veneers, crowns) because of the low refraction index of the lithium disilicate crystals. Furthermore, because of its high mechanical resistance, it can be used as a ceramic core that will be layered with a special ceramic containing fluorapatite crystals.


Why IPS e.max?

  1. Compatible with the economic realities of most laboratories.
  2. Suitable for etching and bonding with hydrofluoric acid (real bonding); this explains why, despite the 400 MPa flexural strength compared to the 1,000 MPa of zirconia, lithium disilicate ceramics bonded to enamel have almost 75% of the mechanical strength of zirconia (Ma et at, 2013).
  3. Proven mechanical properties for more than 15 years.
  4. Can be used monolithic or layered.
  5. Can be used in analog (pressed) or digital (milled block) versions
  6. Ability to select translucency and opacity.
  7. Precise fit.




Depending on the esthetic needs the technician may decide to use three different
laboratory techniques:

  1. Painting technique
  2. Cut-back technique click this link
  3. Layering technique.

Considerations regarding these different techniques include:

  • Lithium disilicate is available in different degrees of opacity; therefore, it is possible to maintain the natural translucency of a healthy tooth if the preparation is also healthy, while also achieving good results in cases of discolored tooth preparations with metallic or titanium restorations.
  • In the selection of the raw material, it is of fundamental importance to consider the color of the tooth and the thickness of the disilicate, two aspects that drastically affect the final esthetic result.

Indications:

  • Veneers with a thickness of 0.3 mm.
  • Minimally invasive inlays and onlays.
  • Partial and complete crowns.
  • Short-span anterior partial dentures on natural teeth end implants.
  • Partial dentures of three to four dental units (zirconia substructure and disilicate superstructure).

Advantages:

  • Possibility of calibrating the degree of translucency in each individual restoration.
  • Optimal results even in minimum thickness.
  • Minimally invasive preparations.
  • Possibility of adhesive cementation.
  • Unique technical capabilities in monolithic forms

One shade .. many options
To illustrate the importance of the choice of ingot for this clinical case, a black line was traced on the prepared tooth. Six 0.4 mm veneers were manufactured in IPS e.max Press using different ingots for each sample. Each veneer, therefore, presented unique optical properties (different masking power) related to the type of material used.
It can be seen that only one type of ingot was capable of masking the dyschromia of the substrate (represented by the black line) and reflecting the light sufficiently to reproduce the luminosity of the adjacent teeth.





Fluorescence


What is the purpose of the fluorescence of ceramic restorations?

Fluorescence offers a significant reduction in metamerism. Metamerism characterizes an object that has different optical behavior depending on the light source (chair light, natural sunlight, daylight with clouds, artificial light, etc).
  • Natural dentin is very fluorescent; natural enamel is only a little fluorescent.
  • The basic ingots HO (high opacity), MO, LT, and HT (high translucency) have weak intrinsic fluorescence depending on the dyes and pigments incorporated, although they all have the same fluorescence in their raw state. These ingots are generally laminated with ceramic powders (IPS e.max Ceram), which contain fluorescent particles (fluorapatite for dentin masses) and give the final restoration a degree of fluorescence that is close to that of the natural tooth.
  • Newer ingots (MT [medium translucency], Opal) have a higher fluorescence and are intended for monolithic use. They are therefore indicated for very thin veneers and then colored.







Choice of material and thickness

The esthetic objective of the treatment is to choose the right ingot to achieve the desired final color. It is important to note that for a single tooth restoration, the ingot choice affects the thickness of the preparation.
In this case, the preparation thickness is increased due to the choice of the medium opacity (MO) ingot, which requires 0.8 mm not 0.5 mm thickness due to its average opacity - the only one able to match the brightness of the adjacent tooth.

The thickness of a preparation is directly correlated to the choice of material ..


If the realization of ceramic veneers is now a standard procedure thanks to the technique of Galip GΓΌrel, proposed almost 20 years ago, the predictability of obtaining perfect veneer color is still a difficult element to achieve.
Indeed, the final color is a combination of the veneer, the substrate and the resin cement.
The choice of the level of translucency or opacity of the ceramic will have a significant impact on the final brightness of the restoration.
Therefore thorough knowledge of the different types of ingot and the resulting light transmission is an essential prerequisite for the clinician and the dental technician.



Normal luminosity: LT ingot

When using a low translucency (LT) veneer, light penetrates the veneer and passes through it, then meets the underlying enamel that will reflect the light. An external observer perceives normal brightness ( amount of white reflected by the different layers encountered - the veneer and the underlying substrate ).
Veneer materials with a thickness of 0.5 mm allow the underlying substrate to be visualized through the veneer thanks to this translucency. This leads to a natural color (A1, BI , A2) if the veneer has a thickness of 0.5 mm, and the preparations are therefore minimal in the enamel layer. If the thickness of the veneer is greater than 0.5 mm (for example, 0.8 to 1 mm), the translucency through this thickness results in too much light transmission and too little reflection, leading to restorations with low luminosity, therefore teeth appear gray.

In this clinical case, the LT ingot does not have the necessary brightness to match the adjacent whitened teeth.

LT ingots are indicated for the treatment of four, six, eight, and ten veneers. LT A1, A2 or B1 ingots can be selected according to the desired final color.




High luminosity: MO ingot

When using an MO veneer, light penetrates less far into the veneer and does not meet the underlying enamel because of its opacity. An external observer perceives a high brightness (only the amount of white reflected by the veneer).
Veneer material with a thickness of 0.5 mm does not allow sufficient ceramic layering to obtain a satisfactory final color. With this thickness, the opacity of the material is not satisfactory. Therefore a greater thickness (0.8 mm instead of 0.5 mm) is required to obtain an aesthetic result (0.4 mm for the framework and 0.4 mm for the layering). This allows a natural color (A1, B1, A2) to be obtained for an MO 1 ingot if the veneer has a thickness of 0.8 mm and the preparations are minimal. If a higher brightness (color obtained after whitening) is required, the MO 0 ingot is recommended.

The clinical case presented requires the use of an M0 0 ingot on a 0.8 mm (similar to the initial tooth shape). This allows matching the luminosity of the whitened adjacent teeth.

 

MO ingots are indicated for single-tooth restorations as well as very additive treatment.



C
onclusion
  • The use of lithium disilicate (IPS e.max) due to its versatility and ease of use.
  • Single tooth: use of the MO ingot because of its ability to match the luminosity of the adjacent teeth, especially after whitening.
  • Restoration of the anterior region: use of LT ingot. Preparation of 0.5 mm.
  • The best esthetic result is obtained by layering.
  • Fluorescent ingots are more likely to be indicated in monolithic form and then colored.

The following posts describe different cases where the choice of lithium disilicate indication.
Stay tuned..
  • Ref.
  1. Laminate veneers 20 recipes for smile design, Stefen Koubi
  2. Modern esthetic dentistry an A to Z guided workflow, Vincenzo Musella
  3. Comprehensive esthetic dentistry.