Porcelain vs Lithium Disilicate: Flexural Strength Explained

When choosing materials for dental restorations, porcelain and lithium disilicate are two popular options, each with distinct strengths. Porcelain is valued for its natural look, making it ideal for front teeth. However, its flexural strength (60–180 MPa) limits its use in high-stress areas. Lithium disilicate, on the other hand, offers much higher flexural strength (360–440 MPa), making it better suited for molars and other areas subject to heavy chewing forces. While porcelain excels in aesthetics, lithium disilicate balances durability with a tooth-like appearance, providing a versatile solution for both anterior and posterior restorations.

Quick Comparison:

Choosing the right material depends on the location of the restoration, functional demands, and aesthetic priorities.

Dental Ceramics in 2022 – Which Ceramic Should I Use? – PDP117

What is Flexural Strength in Dental Materials

Flexural strength refers to how well a dental material can bend without breaking, representing the maximum stress it can handle before failing. This property is crucial for dental restorations like crowns, bridges, and veneers, which must withstand the repeated forces of daily activities such as chewing and biting ^[2][3].

How Flexural Strength is Measured

To determine flexural strength, dental labs typically use standardised tests like three-point or biaxial bending methods. In these tests, a sample is gradually stressed until it fractures. The maximum load it endures, relative to its size, is then used to calculate its flexural strength. These tests adhere to international standards, such as ISO 6872:2008, ensuring reliable and consistent results. Flexural strength is measured in megapascals (MPa), where 1 MPa equals approximately 145 pounds per square inch. These precise calculations help dentists and technicians select materials that ensure long-lasting restorations.

Why Flexural Strength Matters for Your Dental Health

When comparing materials like porcelain and lithium disilicate, understanding flexural strength can guide better choices. Restorations with higher flexural strength are generally more durable, reducing the chances of chipping or cracking, especially in areas exposed to heavy chewing forces. Factors like material composition, microstructure, and processing methods can impact flexural strength. For instance, heat treatments can improve strength, while mismatches in elastic modulus between the restoration and the tooth structure can weaken performance ^[1][4]. If you need restorations in high-stress areas, opting for materials with stronger flexural properties can help ensure their durability and long-term success ^[2][3].

1. Porcelain

Flexural Strength

When it comes to strength, feldspathic porcelain, a conventional dental material, offers flexural strength in the range of 60 to 120 MPa. In contrast, leucite-reinforced porcelains, an upgraded version, boast a higher flexural strength of 120–180 MPa ^[3].

Several factors play a role in determining the final flexural strength of porcelain restorations. These include the material’s composition, the presence of flaws or porosities, the thickness of the restoration, and the firing process ^[4]. Additionally, surface treatments like glazing and polishing, as well as the method of cementation, can influence strength. Understanding these variables is key to predicting how porcelain performs in clinical scenarios.

Aesthetic Qualities

Porcelain is celebrated for its translucency and ability to replicate natural tooth enamel, making it a top choice for aesthetically demanding restorations, especially in the anterior region ^[5]. Feldspathic porcelain, in particular, blends seamlessly with natural teeth, delivering lifelike results. This quality has solidified porcelain’s role in cosmetic dentistry for over a century ^[3]. Its combination of biocompatibility, colour stability, and visual appeal makes it ideal for procedures like smile makeovers and anterior restorations, including veneers.

Durability and Longevity

With proper care, porcelain restorations can last anywhere from 5 to 15 years or more. However, their longevity is often limited by their relatively lower flexural strength ^[4]. Common failure modes include chipping and cracking, which may result from occlusal overload, improper preparation, or inherent material weaknesses. Due to its brittle nature, porcelain is more prone to fractures under heavy occlusal forces compared to stronger alternatives ^[3]. This underscores the importance of precise placement and careful management of biting forces.

Clinical Applications

Porcelain is particularly suited for restorations where aesthetics are a priority and functional demands are lower. It is commonly used for veneers, inlays, onlays, and anterior crowns ^[4]. However, its application in posterior crowns and bridges is limited due to its lower strength and increased risk of fracture under heavy chewing forces ^[4]. For highly aesthetic, low-stress applications – such as anterior veneers – porcelain remains unmatched in delivering natural-looking results ^{[3] [4]}. A classic example includes patients seeking cosmetic enhancement for their front teeth, where porcelain veneers are often the go-to choice for achieving a natural appearance.

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2. Lithium Disilicate

Flexural Strength

Lithium disilicate ceramics stand out for their impressive flexural strength, far surpassing that of traditional porcelain materials. One of the most commonly used products, IPS e.max CAD, boasts flexural strength values ranging from 360 MPa for milled restorations to 400 MPa for pressed versions ^[3]. In some studies, these values climb as high as 440 MPa under ideal conditions ^[6].

This exceptional strength comes from its unique microstructure: a glass matrix packed with approximately 70% elongated, interlocking lithium disilicate crystals by volume ^[6]. The heat treatment process following milling is key to enhancing these mechanical properties through crystallisation ^[4]. When compared with other dental ceramics, IPS e.max CAD recorded a mean fracture strength of 1,698.52 ± 237.5 N, significantly outperforming alternatives ^[2]. These characteristics make lithium disilicate a go-to choice for high-stress applications. On top of its strength, it also delivers aesthetics that meet the demands of modern restorations.

Aesthetic Qualities

Lithium disilicate doesn’t just excel in strength – it also offers outstanding aesthetics that rival traditional porcelain. Known for its translucency and natural tooth-like appearance, it closely mimics the look of enamel ^[8]. Available in a variety of shades and translucency levels, it allows dental professionals to achieve precise colour matching and seamless integration with the patient’s existing teeth. This makes it an excellent choice for anterior restorations, where appearance is especially critical.

Durability and Longevity

Lithium disilicate restorations are well-regarded for their durability, showing strong resistance to fractures and chipping ^[4][2]. Clinical studies confirm that these restorations retain their structural integrity over long periods, with high survival rates even after extensive testing. For example, laboratory fatigue testing involving 250,000 cycles at 100 N demonstrated its ability to withstand repeated stress ^[2]. Additionally, its wear resistance is superior to many other ceramic options ^[7], contributing to restorations that last longer and require fewer replacements.

Clinical Applications

Thanks to its balanced properties, lithium disilicate is widely used in various dental procedures. It is suitable for single crowns, veneers, inlays, onlays, and even short-span bridges ^[4][3]. Its strength, which surpasses traditional porcelain, allows it to be used not only for anterior restorations but also for posterior applications where the occlusal forces are greater ^[6]. This combination of strength and aesthetics makes it a versatile material for both the front and back teeth.

In Australia, dental practices like Complete Smiles Bella Vista often choose lithium disilicate for its consistent performance in CAD/CAM restorations. Its compatibility with digital workflows further enhances its appeal for creating custom restorations. That said, proper case selection is crucial. While lithium disilicate is stronger than traditional porcelain, it falls short of zirconia in terms of robustness and may not be the best choice for long-span bridges or extremely high-stress scenarios ^[1].

Advantages and Disadvantages

Knowing the strengths and weaknesses of porcelain and lithium disilicate helps dentists choose the right material for each patient and clinical situation. Both materials have their own strengths, and selecting the right one is key to achieving long-lasting results. Here’s a closer look at the pros and cons of each.

Porcelain: The Go-To for Aesthetics

Porcelain stands out for its ability to replicate the natural translucency of enamel, making it a top choice for veneers and anterior crowns where appearance is critical ^[3][6]. Its ability to blend seamlessly with surrounding teeth makes it a popular option for patients focused on aesthetics.

But porcelain does have its limits. Its flexural strength is relatively low (<150 MPa), which means it’s more prone to fractures under heavy chewing forces. This makes it less suitable for posterior restorations or for patients who grind their teeth (bruxism). Additionally, porcelain requires precise technique during application, adding to its challenges.

Lithium Disilicate: Strength Meets Versatility

Lithium disilicate, on the other hand, offers impressive strength (360–440 MPa) thanks to its interlocked crystal structure. This makes it a versatile option for crowns, bridges, inlays, and onlays. Its durability allows it to perform well in areas under high stress, offering flexibility in treatment planning.

Clinical studies back this up, with lithium disilicate showing 100% survival rates after 250,000 loading cycles at 100 N ^[2]. It’s also compatible with CAD/CAM technology, which simplifies the fabrication process and improves precision.

However, lithium disilicate isn’t without its downsides. Its translucency, while good, doesn’t quite match the optical properties of porcelain, which can make it less ideal for cases where aesthetics are the top priority ^[4][6]. It’s also more expensive and often requires specialised equipment, which can make it less accessible for some practices.

Comparing Clinical Performance

Here’s a quick snapshot of how these materials stack up in key areas:

Choosing the Right Material

The decision between porcelain and lithium disilicate often comes down to balancing aesthetics with durability. Porcelain is ideal for low-stress areas where appearance matters most, such as veneers or anterior crowns. Lithium disilicate, on the other hand, is better suited for high-stress areas like posterior crowns and bridges, where strength is a priority.

In Australian dental clinics, such as Complete Smiles Bella Vista, both materials are used strategically. Porcelain is often chosen for its unmatched aesthetics in the front teeth, while lithium disilicate is preferred for its durability in areas that endure greater stress.

Conclusion

Research consistently highlights lithium disilicate as a stronger option compared to porcelain, particularly in terms of flexural strength. With a flexural strength range of 360–440 MPa, lithium disilicate significantly outperforms conventional porcelain, which falls below 200 MPa ^[3][6]. This strength advantage makes it an excellent choice for high-stress applications like posterior crowns, bridges, and restorations for patients with bruxism. Dynamic loading tests further validate its durability ^[2].

When choosing materials, it’s important to weigh strength against aesthetics. Porcelain, with its superior translucency, is often the go-to for anterior veneers where appearance is key. On the other hand, lithium disilicate is better suited for areas that endure higher stress. The final decision should consider factors like the restoration’s location, the patient’s bite force and habits, and their aesthetic preferences. This evidence highlights the importance of tailoring material selection to the specific functional and aesthetic needs of each case.

Navigating these choices requires professional expertise. Dental professionals, such as Dr. James Hanna at Complete Smiles Bella Vista, carefully evaluate flexural strength data alongside tooth structure and occlusal patterns to recommend the most appropriate material. This thorough approach ensures that the chosen material aligns perfectly with the clinical demands.

Both porcelain and lithium disilicate have proven their value in modern dentistry. The key lies in selecting the right material for the right application, ensuring that restorations combine durability with a natural appearance to promote long-term oral health and satisfaction. Matching material properties to the specific demands of each restoration is essential for achieving the best possible outcomes.

FAQs

What should I consider when deciding between porcelain and lithium disilicate for dental restorations?

When deciding between porcelain and lithium disilicate for dental restorations, several factors come into play, such as flexural strength, appearance, and the type of restoration needed. Porcelain is known for its excellent appearance, making it a great choice for veneers or crowns in areas with less bite pressure. On the other hand, lithium disilicate stands out for its higher flexural strength, which makes it better suited for restorations in high-stress areas like molars.

Your dentist will carefully assess factors like the location of the restoration, your bite force, and your preferences for aesthetics to recommend the most suitable material. It’s essential to have an open conversation with a qualified dental professional to ensure the choice aligns with your specific oral health needs.

What role does flexural strength play in choosing materials for dental restorations?

Flexural strength plays an important role in choosing materials for dental restorations, as it reflects how well a material can handle bending forces without breaking. Two of the most commonly used materials in this field are porcelain and lithium disilicate, each offering unique benefits for different dental applications.

Porcelain is highly valued for its natural, lifelike appearance, making it a popular choice for veneers and crowns in areas where aesthetics matter most, like the front teeth. Meanwhile, lithium disilicate stands out for its superior flexural strength, making it a better option for restorations in high-pressure areas, such as molars, where chewing forces are more intense. Ultimately, your dentist can guide you in selecting the most suitable material based on your specific needs and the type of restoration required.

What care is needed to maintain porcelain and lithium disilicate dental restorations for long-term durability?

To keep porcelain and lithium disilicate restorations in top shape, consistent care and maintenance are key. Start with regular brushing using a soft-bristled toothbrush and fluoride toothpaste, paired with daily flossing. This helps to prevent plaque from building up around the restorations. Be sure to steer clear of abrasive toothpaste, as it can gradually scratch the surface.

Certain habits can also put these restorations at risk. Avoid grinding your teeth, biting your nails, or using your teeth as tools to open packages – these actions can cause unnecessary stress on the restorations. For those who grind their teeth, a custom-fitted night guard can provide essential protection.

Don’t skip your regular dental check-ups and professional cleanings. These appointments are crucial for keeping an eye on the condition of your restorations and catching any potential issues early.

With these practices, you can help ensure your restorations stay strong and look great for years.

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• Ceramic Materials in Crowns and Bridges
• Fatigue Resistance of CAD/CAM Dental Materials
• Zirconia vs. Ceramic: Biocompatible Dental Materials