Emax: Uncovering the Real Strength of a Lithium Disilicate Material like LiSi Press

This lithium disilicate material, Emax, isn’t just another glass-ceramic; it was a revolution in a small ingot. It blended strength and beauty in a way I had never seen before.

In this post, we’ll explore what makes this material, Emax, so special. We will look at its amazing flexural strength and how it gets that strength from its tiny crystal structure. If you are a dentist, a lab technician, or even a patient curious about the crown in your mouth, this article is for you. I’ll break down the science into simple terms and share what I know about this game-changing material, including other great products like LiSi Press.

What Is Lithium Disilicate, Anyway?

Let’s start with the basics. What is lithium disilicate? At its heart, it’s a type of glass-ceramic. Think of it as a special kind of glass filled with a huge number of tiny, needle-shaped crystals. The specific chemical formula is Li2Si2O5. This is important because it’s the key to its strength. These ceramics are part of a family of dental materials that have transformed how we restore teeth. The company Ivoclar Vivadent was a true pioneer in this field, and they really set the standard for what these materials could do.

Before lithium disilicate, our all-ceramic options were mostly weaker porcelain. They looked nice but could chip easily. This new lithium disilicate glass ceramic promised both beauty and power. It has excellent biocompatibility, which means it’s safe and gets along well with the tissues in your mouth. This makes it a top choice in restorative dentistry. The lithium disilicate itself is very stable.

These ceramic materials are made through a controlled process of heating. This process creates a dense network of Li2Si2O5 crystals inside a glassy matrix. This structure is what stops cracks from spreading. So, when you choose a lithium disilicate crown, you’re getting a material that is designed from the molecule up to be tough and long-lasting. It’s one of the most trusted materials available for dental restorations today. Lithium disilicate is also known for its great bond to tooth structure.

Why Is Emax So Popular in Modern Dentistry?

So why did Emax become the celebrity of the dentistry world? For example, a patient with a cracked front tooth needs a perfect, esthetic result. A traditional porcelain veneer feels risky. A stronger material like zirconia wouldn’t have the same translucency. When choosing to use an Emax restoration, the result is incredible. You can’t tell which tooth is the crown and which were natural.

The popularity of Emax comes from this amazing balance. It has the high flexural strength needed for a posterior tooth but also the beautiful esthetics needed for an anterior veneer. This versatility is a huge advantage. You can use this single lithium disilicate material for a wide range of jobs, from a full crown to a thin veneer or even an inlay. This makes life easier for both the dentist and the dental laboratory. The material gives us confidence that the restoration will look good and last for a very long time.

It’s one of the most commonly used all-ceramic materials for a reason. Emax allows for minimally invasive restorations. This means we can save more of the natural tooth structure, which is always the goal. The material can be made very thin, as little as 1.0 mm for a crown, yet still be incredibly strong. This combination of features makes Emax a go-to choice for so many situations in dentistry. It truly delivers on its promise of a strong and beautiful smile.

How Strong Is Lithium Disilicate? Let’s Talk Flexural Strength.

When we talk about strength in dentistry, one of the most important numbers is flexural strength. What does that mean in simple terms? Imagine trying to bend a small beam of the material. The flexural strength is the amount of force, or pressure, it can take before it snaps. We measure this force in megapascals, or MPa. A higher MPa number means a stronger material. This is a critical property for any restoration that has to withstand chewing forces.

So, how does lithium disilicate stack up? The flexural strength of lithium disilicate ceramics is very impressive. Most Emax products have a flexural strength of around 400 to 500 MPa. To put that in perspective, older dental ceramics might have a flexural strength of only 100-150 MPa. This means lithium disilicate is three to five times stronger. This high strength is why we can use it for a posterior molar crown and trust it not to break under pressure.

This high flexural strength is a direct result of its internal structure. The dense, interlocking crystal network I mentioned earlier acts like rebar in concrete. It stops tiny cracks from growing and causing a fracture. This gives Emax and other lithium disilicate ceramics the power to last for years, even in the tough environment of the mouth. The impressive flexural strength is a key reason why lithium disilicate has earned its place as a top-tier all-ceramic material. The modulus is also well-balanced.

What Are the Key Mechanical Properties of Lithium Disilicate?

While flexural strength gets a lot of attention, it’s not the whole story. To truly understand a material, we need to look at all the mechanical properties of lithium disilicate. One of these is fracture toughness. Think of fracture toughness as a material’s resistance to an existing crack spreading. Lithium disilicate has excellent fracture toughness due to its high crystal content. This makes the restoration more forgiving if a small flaw develops.

Another key property is the modulus of elasticity. The modulus is basically a measure of stiffness. A material with a very high modulus is very rigid, while one with a low modulus is more flexible. The modulus of lithium disilicate is similar to that of natural tooth dentin. This is a huge advantage. It means that when you bite down, the Emax crown flexes in a way that is very similar to a real tooth. This reduces stress on the underlying tooth structure and the cement holding the crown in place.

These good mechanical properties combine to give lithium disilicate restorations their fantastic durability. The properties of lithium disilicate glass-ceramics also include good thermal expansion characteristics and color stability. This means the restoration won’t expand or contract too much with hot and cold foods, and it won’t change color over time. It’s this complete package of flexural strength, modulus, and toughness that makes lithium disilicate so reliable.

Can It Really Look Like a Real Tooth? (A Look at Translucency and Esthetics)

Strength is great, but in dentistry, looks matter just as much, especially for an anterior tooth. This is where lithium disilicate truly shines. The secret is a property called translucency. Translucency is the ability of a material to let some light pass through it, just like natural enamel.

Emax and other lithium disilicate products come in various levels of translucency and opacity. For example, Ivoclar Vivadent makes ingots labeled HT (High Translucency) and LT (Low Translucency). An HT ingot is great for an inlay or a veneer where you want the natural color of the tooth to show through. An LT ingot is better for a crown where you need to block out a dark underlying tooth. This control over optical properties allows a skilled technician to create a restoration with amazing, life-like esthetics.

The esthetic quality is not just about translucency. It’s also about how the material reflects light and the fine details that can be added. The surface of a lithium disilicate crown can be stained and glazed to perfectly mimic the subtle textures and colors of a real tooth. This level of artistry, combined with the material’s inherent esthetic potential, is why lithium disilicate is the gold standard for beautiful dental restorations. The final crystalline structure is key to these esthetics.

How Do You Make an Emax Restoration? (Press vs. Mill)

So how do we turn a piece of lithium disilicate into a perfectly fitting veneer or crown? There are two main ways to fabricate an Emax restoration: pressing and milling. Both methods are used all the time, and each has its own advantages. The choice often depends on the type of restoration and the equipment in the dental laboratory.

The first method is the pressing technique, which uses products like IPS e.max Press. This is a bit like the classic “lost wax” technique. First, a wax model of the crown is made. This wax model is then surrounded by an investment material. After the wax is burned away, a small lithium disilicate ingot is heated until it becomes like thick honey. This molten glass-ceramic is then pressed into the mold. It’s a very precise way to fabricate a restoration and is excellent for getting a perfect fit.

The second method is milling, which uses a CAD/CAM machine. This is a high-tech approach. The tooth is scanned, either in the mouth (intraoral scanner) or from a model. A computer then designs the restoration, and a machine carves the crown or veneer out of a solid block of lithium disilicate material, such as an IPS e.max CAD block. This method is very fast and allows for same-day dentistry in some cases. You can mill a beautiful all-ceramic crown in under an hour.

What’s the Real Difference Between IPS e.max Press and CAD?

At first glance, IPS e.max Press and IPS e.max CAD might seem like just two different ways to make the same thing. But there are some key differences in the materials themselves. The main difference is the state of the lithium disilicate when you start. The IPS e.max Press ingot is a fully crystallized lithium disilicate glass ceramic (Li2Si2O5). It already has its final, high flexural strength.

The IPS e.max CAD block, on the other hand, is delivered in a partially crystallized state. It is a softer, bluish material made of lithium metasilicate crystals (Li2SiO3). This material has a much lower flexural strength, around 130 MPa, which makes it easy for the machine to mill quickly and without wearing out the tools. After the restoration is milled, it must go into a special oven for a firing cycle. This is the final crystallization step. During this firing, the lithium metasilicate (Li2SiO3) transforms into the much stronger lithium disilicate (Li2Si2O5), and the crown turns into the correct tooth color.

So, which one is better? It depends. IPS e.max Press is often said to have a slightly higher flexural strength (around 470 MPa vs. 400 MPa for CAD) and is preferred for more complex cases or a three-unit bridge. IPS e.max CAD offers incredible speed and convenience. Both methods, when done correctly, produce a fantastic and strong all-ceramic restoration. The fabrication method is just a different path to the same excellent result.

Are There Other Options Besides Emax? What About LiSi Press?

While Ivoclar Vivadent and its Emax brand are the big names in lithium disilicate, they are not the only players in the game. Competition is a great thing in dental materials, and other companies have developed their own excellent lithium disilicate glass ceramics. One of the most well-known alternatives is GC’s LiSi Press. This is another pressable lithium disilicate that competes directly with IPS e.max Press.

LiSi Press boasts similar properties, including high flexural strength and beautiful esthetics. Some technicians love the way the LiSi Press ingot flows and the vitality they can get in their all-ceramic restorations. It uses a similar pressing technique and is designed to create a strong, monolithic restoration or be layered with porcelain for custom characterization. The existence of products like LiSi Press pushes all manufacturers to keep innovating and improving their dental ceramics.

Whether a lab chooses Emax or LiSi Press often comes down to personal preference, experience, and relationships with the manufacturers. The important thing is that we have choices for high-strength ceramic materials that allow us to provide the best possible care for our patients. This is a great time for periodontics and restorative work.

What’s the Secret on the Inside? (A Peek at the Microstructure)

I’ve mentioned the crystal structure a few times, but let’s take a closer look. The real secret to the flexural strength of lithium disilicate is its microstructure. Imagine a pile of needles thrown on a table. Now imagine filling all the space between those needles with glue. That’s a simple way to picture the microstructure in lithium disilicate glass. The “needles” are tiny, elongated crystals of lithium disilicate (Li2Si2O5). The “glue” is the glassy matrix that holds them all together.

This interlocking crystalline structure is incredibly effective at stopping cracks. When a force is applied to the crown, a tiny crack might start in the glass matrix. But as soon as it hits one of the many Li2Si2O5 crystal needles, it has to change direction. It gets deflected and blunted. To break the material, a crack would have to find a path through this dense, tangled forest of crystals. This gives the material its amazing fracture toughness and flexural strength. The study of the crystallization and microstructure in lithium is fascinating.

The chemical process is also key. The heat treatment on crystallization is precisely controlled. Some research, like a vitro study on the effect of P2O5, shows how tiny additions of other chemicals can influence crystal growth. The p2o5 on the crystallization can affect the size and density of the crystals. All this science, from p2o5 and heat treatment to the final treatment on crystallization and microstructure, is done to create the ideal monolithic structure. It’s a world away from a weaker lithium silicate like li2sio3.

Is Lithium Disilicate the Right Choice for Everything?

It is not the perfect solution for every single situation. The biggest consideration is for long-span bridges, especially in the posterior area of the mouth where biting forces are highest. While an Emax crown is great for a single posterior tooth, a bridge that replaces two or more teeth requires even more flexural strength. The connector areas of a bridge are where stress is concentrated.

For a long posterior bridge, a stronger material like monolithic zirconia is often a better choice. Zirconia can have a flexural strength of over 1000 MPa, more than double that of lithium disilicate. However, zirconia typically has lower translucency, so it can be a trade-off between ultimate strength and the best esthetics. So, where is lithium disilicate the hero? It’s perfect for almost any single-tooth restoration. This includes anterior and posterior crowns, veneers, inlays, and onlays.

You can also fabricate a short, three-unit bridge with lithium disilicate if it’s in the anterior region (front of the mouth). The decision always comes down to the specific clinical situation. We have to consider the patient’s bite (occlusal forces), the location in the mouth (anterior vs. posterior), and the desired esthetic outcome. But for the vast majority of all-ceramic single-unit dental restorations, lithium disilicate material is a fantastic, reliable, and beautiful choice.

Things to Remember

• Strong and Beautiful: Lithium disilicate (Emax, LiSi Press) offers a great mix of flexural strength (400-500 MPa) and life-like esthetics.
• Crystal Power: Its strength comes from a dense structure of interlocking Li2Si2O5 crystal needles in a glass matrix.
• Versatile Use: It’s great for a single crown, veneer, inlay, and onlays in both the anterior and posterior parts of the mouth.
• Two Ways to Make: Can be fabricated using a pressing technique (IPS e.max Press) or milled with a CAD/CAM machine (IPS e.max CAD).
• Not for Everything: For long bridges in the back of the mouth, a stronger material like zirconia is often a better choice.