The Evolution of High-Strength Ceramics: the Role of Microstructure and Manufacturing

Abstract

In the quest for highly esthetic and strong restorative material, dental technicians, practitioners, and manufacturers have produced several compositions of ceramic materials. Increasing the strength of ceramics without compromising their translucency remains a major challenge. Like porcelain-fused-to-metal crowns, veneering the strong and opaque ceramic cores with a translucent porcelain may improve the strength of porcelain crowns. However, frequent chipping of this weak veneering layer was a major problem. Recently, the advent of computer-aided design/computer-aided manufacturing (CAD/CAM) has allowed the production of stronger ceramics while minimally increasing their translucency and eliminating the need for the veneering layer. Therefore, the current review aims to provide an overview and a critique of the evolution and development of all-ceramic restorations, while also focusing on the material properties and considerations related to their use in restorative dentistry.

Keywords

esthetics - dental ceramics - translucency - veneers - CAD/CAM

Introduction

For successful integration of a restorative material into the oral cavity, it must possess adequate strength and good esthetics. Although traditional dental ceramics were highly esthetic, their clinical performance in restorative dentistry was limited by inherent brittleness.[1] Therefore, various ceramic compositions and fabrication techniques were developed to improve mechanical properties. However, these modifications compromised their esthetic properties, particularly translucency. With the increase in patients' awareness and demand for highly esthetic restorations, even in the posterior area of the mouth, the development of all-ceramic restorations with both high strength and esthetics has become necessary. This review will illustrate the development of all-ceramic restorations, focusing on the material properties and considerations for their use in restorative dentistry.

Method

A narrative review approach was adopted. Literature search was conducted using the following search engines: PubMed, Scopus, Otago Library Ketu, Web of Science, and google scholar using the keywords “dental ceramics,” “lithium disilicate,” “zirconia,” “hybrid ceramics,” “high-strength ceramics” “CAD/CAM,” and “all-ceramic restorations.” Articles from last 10 years were screened for relevance to material composition, mechanical properties, manufacturing advances, and clinical performance. Additional landmark and historical references were incorporated to provide context.

Early Dental Ceramics

Traditional all-ceramic restorations were known as “the porcelain jacket crown.” Primarily composed of porcelain, it was introduced by Charles Land in 1886 by building up layers of moist feldspathic porcelain powder, using a brush, on a substructure of burnished platinum foil, followed by firing the crown in a furnace at a controlled high temperature.[2] Feldspathic porcelain is a composite of three materials: clay or kaolin (hydrated aluminosilicate), quartz (silica), and feldspar, a naturally occurring potassium, sodium, or calcium-aluminosilicate.[3] When potassium feldspar (K₂Al₂Si₆O₁₆) is fired at high temperatures, leucite crystals and a glassy phase are generated. At the firing temperature, leucite crystals exist in the cubic phase; however, upon cooling to room temperature, they undergo a transformation to the tetragonal phase. This phase transition is accompanied by a volumetric expansion of approximately 1.2%.[4] This expansion generates thermal stresses that result in internal microcracking during cooling, reducing the strength of the material. Although this restoration was highly esthetic, its use in restorative dentistry was limited by its low strength, which resulted from high feldspathic glass content and high porosity.[1] Incorporating insights from fundamental literature on dental ceramics, a detailed classification has been added[5] [6] ([Fig. 1]).

Fig. 1 Classification scheme of dental ceramics based on microstructure, chemical composition, ISO 6872 clinical indications, processing techniques, and firing temperature.[5] [6]

Dr. Abraham Weinstein developed the first porcelain-fused-to-metal (PFM) crown in the late 1950s[7] with the aim of improving overall crown strength while retaining esthetics. As shown in [Fig. 1], the PFM consists of a metal core layered with ceramic. The addition of leucite to feldspathic porcelain increased the coefficient of thermal expansion to match that of the metal core, thus allowing its fusion to gold containing alloys (between 84 and 88%) to form complete crowns and fixed partial dentures.[8] The alloy used in contemporary PFM restoration differs from that used in traditional PFM restorations. Early alloys were developed with reduced gold content to improve mechanical properties.[8] PFM eventually became popular due to their combination of the esthetics of a porcelain layer and the strength of a metal core, with the esthetics of feldspathic porcelain, extending feldspathic porcelain to include posterior crowns and anterior and posterior bridges. Since their introduction in the 1960s, the PFM restorations have enjoyed great success and become the gold standard for restoring teeth.[9] However, the esthetics of the PFM restoration are constrained by the lack of light transmission through the metal casting, thereby reducing its translucency. This is particularly problematic in the esthetic zone. Therefore, dental researchers have worked on developing materials with adequate strength as well as optimal esthetics. The layering steps required to fabricate all-ceramic crowns are illustrated in [Fig. 2].

Fig. 2 A schematic diagram of a porcelain-fused-to metal (PFM) crown. In all-ceramic crowns, the metal core is replaced by porcelain, or the tooth is covered by a single-piece (monolithic) porcelain veneer (Biorender).

All-Ceramic Crowns

By 1965, a bi-layered restoration was introduced by Mclean and Hughes. However, this time, it was a metal-free, all-ceramic restoration. It was produced by adding aluminum to feldspathic porcelain to create a stronger, modified version of the porcelain jacket crown.[10] [11] In this technique, a core of aluminous porcelain (containing 40–50% alumina crystals) was applied and fired over a platinum foil substrate, followed by successive layers of more translucent but mechanically weaker porcelain, which were applied and fired until the crown form was completed ([Fig. 3]).[12] Although this material had double the strength of the early porcelain jacket crown, it was used primarily in the anterior region because of its low strength.[1] The high opacity of this material was also a major drawback.[10]

Fig. 3 Layering technique: (A) Polycrystalline framework; (B) Feldspathic ceramic build-up (wash bake); (C) Feldspathic ceramic build-up (intensive chroma + dentin); (D) Feldspathic ceramic build-up (enamel layer); (E) Feldspathic ceramic after firing; (F) Feldspathic ceramic after thermal and mechanical glazing.[12]

Modern Dental Ceramics

Afterward, alternative manufacturing methods have been developed, allowing the production of all-ceramic restorations in monolithic form. These methods were: casting (Dicor Dentsply/York Division, York, Penn) and injection molding (Cerestore, Coors Biomedical, Lakewood, Colo. and IPS Empress1, 2 and E.max, Ivoclar AG, Schaan, Liechtenstein).

Dicor is a castable glass − ceramic system, which combines the accuracy of casting technique and the esthetics of high ceramics to provide restoration with superior esthetics to PFM and better marginal adaptation than feldspathic porcelain.[13] This system is based on the growth of fluorine-containing, tetra-silicic mica crystals, which were first reported in a patent by Grossman in 1973.[13] In the Dicor technique, a mica-strengthened glass is cast into a lost-wax form and later converted into ceramic using a special heat treatment that initiates controlled crystallization in the glass. The crystals increase the strength and toughness of the glass ceramic. However, the Dicor crowns had a high number of failures and were withdrawn from the market.[1]

Fracture of early dental porcelain was often related to the shrinkage on cooling, leading to marginal inaccuracy, distortion of the platinum matrix, and decreased strength.[14] In 1983, a shrink-free monolithic ceramic Cerestore (Coors Biomedical, Lakewood, Colo.) was introduced to overcome this problem. Unlike early dental porcelain, Cerestore did not undergo considerable shrinkage after cooling to room temperature. Its formulation was such that chemical and crystalline transformations occurred during firing to compensate for the reduced shrinkage volume ordinarily experienced with traditional dental ceramics.[14] It was manufactured using an injection-molding technique on a special epoxy die.[14] Because of the high failure of this material, it was replaced by Alceram, a new core material with a flexure strength of 162 MPa, nearly twice as high as that (88 MPa) of the Cerestore. However, because of their high clinical failure rate, the products were also withdrawn from the market.[1]

IPS Empress 1 (Ivoclar AG, Schaan, Liechtenstein) is a glass ceramic reinforced with leucite crystals (KAlSi₂O6 or K₂O • Al₂O₃ • 4SiO₂) in amounts varying from 35 to 55% by volume. The flexural strength of this material ranges from 95 to 180 MPa, and the fracture toughness is approximately 1.3 MPa √m making it suitable for inlays, onlays, veneers, and anterior crowns.[15] [16] [17] Leucite-reinforced glass − ceramic crowns have exhibited a low clinical failure rate and excellent esthetics after a follow-up period of up to 11 years.[18] IPS Empress 1 inlays and onlays have also demonstrated a high survival rate, even in large defects after 8-year follow-up.[19]

In 1998, Ivoclar released IPS Empress 2, a lithium disilicate (Li₂Si₂O₅)-reinforced glass–ceramic processed with the same laboratory procedure and equipment used for Empress 1. However, Empress 2 prostheses have higher flexural strength (340 − 400) MPa and fracture toughness (2 − 3.3 MPa √m) than IPS Empress I,[16] [17] which allows their use as posterior crowns and anterior 3-unit bridges. Empress 2 crowns have a satisfactory long-term survival rate.[20] [21] However, anterior bridges made of Empress 2 have exhibited lower 5- and 10-year survival rates than PFM bridges, mainly due to a low fracture resistance.[20] [22]

The slip casting technique was then utilized to fabricate strong cores by applying an aluminum oxide (Al₂O₃) slip (a dispersion of Al₂O₃ particles in water) onto a gypsum die, followed by sintering to create a 3D porous network composed mainly of crystalline structures. The porous network was then infiltrated with molten glass in a second step to increase strength and limit crack propagation sites.[23] This technique was used to produce a series of products known as In-Ceram Ceramics (Vita Zahnfabrik, Bad Säckingen, Germany). The first of these products was In-Ceramic Alumina, which was introduced in 1989. It contains 80 to 82 wt.% pure Al₂O₃ and has a flexural strength of 442 MPa, the strongest of ceramic materials at that time,[1] which is three to four times stronger than feldspathic porcelains.[24] It was one of the first all-ceramic materials used for anterior bridges and anterior and posterior crowns. However, its use for posterior bridges has not been recommended because of the high failure rate, mainly because of fractures at the connector area.[25] This material's main disadvantage is its high opacity; therefore, it is primarily used as a core veneered with more translucent ceramic.[26] [27]

To improve the translucency, slips made from magnesium spinel (In-Ceram Spinell) were introduced in 1994. They were fabricated using the same technique as previous In-Ceram systems. However, the framework contained a mixture of magnesia and alumina (MgAl₂O₄) to improve the material's translucency.[28] [29] The higher translucency of the In-Ceram Spinell expanded its use to include inlays, onlays, and veneers.[30] However, the trade-off resulted in a decrease in flexural strength to 250 MPa, limiting its use to anterior crowns.[30] Furthermore, the translucency of this material was insufficient for monolithic restorations, so it had to be veneered with feldspathic porcelain.[28] [29]

In-Ceram Zirconia was developed by incorporating 33% cerium oxide (12 mol% CeO₂) partially stabilized zirconia into In-Ceram Alumina, to enhance strength through the transformation toughening mechanism of zirconia.[16] In some studies, In-Ceram Zirconia has been reported as the strongest of the three slip-cast cores, with a flexural strength of approximately 600 MPa.[31] However, some studies indicated no significant difference in the strength of In-Ceram Zirconia and In-Ceram Alumina.[27] [32] Posterior FDPs made of In-Ceram Zirconia exhibited performance similar to PFMs after 5-year and 10-year follow-up. However, higher chipping rates and biological complications were also reported.[33] [34] Other disadvantages of the material include its high opacity[35] and the large minimum required connector dimension of 25 mm², which is difficult to achieve intraorally.[34] Due to the increase in popularity of lithium disilicate and yttria-stabilized zirconia (Y-TZP), particularly for computer-aided design/computer-aided manufacturing (CAD/CAM) technology, the use of this class of materials diminished.

Later, IPS e.max Press (Ivoclar Vivadent) was introduced in 2005. It was an improved version of IPS Empress 2 in terms of strength and translucency, enabling it to be used as a monolithic restoration. The excellent mechanical properties of this material are due to the tightly interlocked distribution of the disilicate crystals and the mismatch between the coefficients of thermal expansion of lithium-disilicate crystals and the glassy matrix, which induces a compressive stress around the crystals, limiting crack propagation.[4] H. IPS e.max Press has a flexural strength of 370 to 460 MPa and fracture toughness of 2.8 to 3.5 MPa √m, permitting its use for inlays, onlays, crowns, and 3-unit anterior bridges. IPS e.max crowns demonstrated a 95% success rate in the medium term (3 − 5 years).[36] Three-unit FDPs made from monolithic IPS e.max showed 5- and 10-year survival and success rates similar to those of conventional metal − ceramic FDPs, provided a connector area of 4 × 4 mm was achieved.[37] Inlays and onlays made of lithium disilicate ceramics have performed well in the medium and long-term follow-up, particularly when they were provided with 2-mm occlusal thickness.[38] IPS e.max CAD was released in 2006 to allow the fabrication of restorations by milling partially crystallized lithium-disilicate blocks. Besides coming in a wide variety of colors, IPS e.max CAD is also available in three levels of translucency: medium opacity, high translucency, and low translucency, which is achieved by altering the crystals' size. IPS e.max can be used in the form of monolithic and bilayer restorations; however, chipping of the veneering material is a common complication in bilayer restorations.[39] However, the existing literature does not clearly distinguish between IPS Empress 2, IPS e.max Press and IPS e.max CAD when reporting survival and failure rates. Instead, the above materials are commonly categorized as “lithium-reinforced ceramics,” “lithium disilicate ceramics,” or “glass ceramics,” assigning similar survival and failure rates. Therefore, such generalization does not account for these products' compositional and microstructural differences, significantly affecting clinical performance. Conflating these materials under umbrella terms may have led to misrepresentation of their actual long-term outcomes.

High Strength Dental Ceramics

In order to use metal-free, all-ceramic restorations in all areas of the mouth and for all types of restorations, high-performance ceramics with high flexural strength and fracture toughness were developed. Compared to other dental ceramics, these ceramics consisted of densely packed crystals with no glass phase in between; hence, they were given the name “polycrystalline ceramics.” Because of the absence of the glassy phase in these materials, all the atoms are densely packed into regular arrays that are much more difficult to drive a crack through, making them more robust than other types of ceramics.[2] High-strength ceramics include polycrystalline alumina (Al₂O₃) and zirconia (ZrO₂). Traditionally, these ceramics were used to fabricate restoration cores or frameworks, which are then veneered with more translucent glass ceramics to improve the esthetics. High-strength ceramics such as alumina- and zirconia-based systems exhibit superior mechanical properties due to their fully crystalline or predominantly crystalline microstructures. Densely sintered alumina (99.5% Al₂O₃) demonstrates flexural strengths between 487 and 699 MPa and fracture toughness values of 4.5 to 6 MPa·√m, while tetragonal zirconia polycrystals (3Y-TZP) reach flexural strengths around 1,000 MPa and toughness values near 10 MPa·√m. The absence of a glassy matrix contributes to their increased strength but limits their ability to be etched, requiring alternative bonding strategies.[5] [6] Recent manufacturing advancements, including multi-axis CAD/CAM milling, green-state zirconia machining, and hot isostatic pressing, have further enhanced the accuracy, density, and mechanical performance of high-strength ceramics. The introduction of cubic-phase zirconia (4Y-, 5Y-PSZ) has improved translucency, although their strength is reduced compared to traditional 3Y-TZP.[40] Additionally, glass-infiltrated alumina and zirconia systems produce interpenetrating ceramic networks that enhance crack resistance.[40]

Alumina

Pure Al₂O₃ powder (99.9%) was used to fabricate these restorations, initially using the dry pressing technique against enlarged models of the prepared teeth[41] and later by using CAD/CAM technology (Procera system) which was developed by Nobel Biocare (Goteborg, Sweden). The flexural strength of Procera all-ceramic crown is 687 MPa,[42] and the fracture toughness is 6 MPa √m.[43] Posterior and anterior all-ceramic crowns fabricated from Al₂O₃ demonstrated a low failure rate after 5 years[18] [42] and 10 years of service, especially for anterior crowns.[18] [44] Alumina-based ceramics represent one of the earliest and most widely investigated classes of high-strength dental ceramics, distinguished by their fully polycrystalline microstructure and excellent mechanical performance. According to Ho & Matinlinna, alumina used in dental restorations is typically composed of 99.5% Al₂O₃, with minimal or no glassy phase present.[5] This high level of crystallinity contributes directly to its superior mechanical properties, including flexural strength values ranging from 487 to 699 MPa and fracture toughness values of 4.5 to 6 MPa·√m, placing alumina among the earliest high-performance ceramics capable of replacing metal frameworks in all-ceramic crowns and short-span fixed prostheses. Unlike silica-based ceramics, alumina does not rely on a glassy matrix for structural integrity; instead, its strength is derived from the densely packed crystal grains that resist crack initiation and propagation.

Talibi et al further classify alumina within the polycrystalline ceramic family, a group characterized by the absence of an amorphous glass phase and by densely sintered crystalline structures.[6] This microstructural arrangement limits light transmission, making alumina inherently more opaque than feldspathic or lithium disilicate ceramics. Despite this aesthetic limitation, alumina's mechanical reliability made it a vital precursor to modern zirconia frameworks. Earlier systems such as In-Ceram Alumina introduced the concept of a glass-infiltrated alumina network, where a porous alumina matrix was infiltrated with lanthanum aluminosilicate glass. This hybrid microstructure enhanced flexural strength and created an interlocking network that improved crack resistance through crack deflection mechanisms. In terms of processing technologies, alumina ceramics were historically produced through slip casting, glass infiltration, or pressure sintering. Advances in CAD/CAM expanded alumina's usability by enabling the milling of densely sintered blocks. However, Talibi et al note that milling alumina presents challenges due to its intrinsic hardness; tool wear and prolonged machining times limit its practicality compared with modern zirconia systems.[6] Bonding protocols for alumina also differ significantly from those for glass-based ceramics. Because alumina lacks silica, it cannot be etched with hydrofluoric acid, making resin bonding dependent on micromechanical surface treatments (e.g., airborne-particle abrasion) combined with chemical primers such as 10-MDP. This reinforces the need for material-specific bonding strategies in clinical practice.

Zirconia

Zirconia is composed of densely packed polymorph crystals that occur in three forms: monoclinic (M), cubic (C), and tetragonal (T). Zirconia crystals take the monoclinic form at the room temperature and up to 1,170°C. Above this temperature, they transform into the tetragonal and cubic forms at 2,370°C. Several oxides were used to stabilize zirconia at room temperature; however, it was found that Yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP) is by far the strongest of all ceramic compositions, with a flexural strength of >1 GPa and fracture toughness of 5 to 10 MPa √m.[45] The excellent mechanical properties of zirconia have expanded the clinical use of all-ceramic materials, from single crowns and short-span anterior fixed dental prostheses to include fabrication of multiunit, long-span posterior bridges and full-arch frameworks as well as implants, implant abutments, and complex implant superstructures to support fixed and removable prostheses.[46] [47]

Two main drawbacks for zirconia restorations were noted.[48] The first is the high incidence of veneering porcelain fracture, manifesting clinically as chipping fractures,[49] [50] [51] and the second is an inherent tetragonal to monoclinic phase transformation (ageing) problem that has been identified to occur in zirconia in the presence of water. A high level of monoclinic phase may be detrimental to mechanical characteristics such as strength and toughness.[52] Therefore, the long-term clinical success of zirconia-based restorations may be impaired. At present, monolithic zirconia restorations, which have been manufactured mainly by CAD/CAM technology, possess several advantages such as high flexural strength, minimal wear on the antagonists, satisfactory esthetics, requiring less laboratory time and utilizing fewer dental sessions. Furthermore, the introduction of full-contour monolithic zirconia with improved translucency has solved the problem of veneering porcelain chipping and opacity. Although monolithic zirconia is a new alternative to veneered zirconia restorations, there are limited studies about its translucency. However, multicolor monolithic zirconia ceramics present considerably improved esthetics and translucency; further research is necessary to evaluate their long-term potential to preserve these outstanding properties. Tuncel et al concluded that monolithic zirconia may not be the most esthetic material for the anterior region. However, it may serve as an alternative to the bilayered zirconia restorations in the superior posterior region due to the larger grain size and lower translucency.[53] New compositions of Y-TZP claimed different optical and mechanical properties for dental CAD/CAM machining systems, which were recently introduced to the market, with the indication for monolithic restorations with limited span and conservative tooth preparation. Due to the increased translucency and adequate mechanical properties, the “high translucent” zirconia has been proposed as an alternative material to lithium disilicate for monolithic restorations.

The composition, processing methods, and resulting microstructure play a crucial in determining the properties and performance of ceramic materials. Pure zirconia, due to its allotropic nature, exists in three temperature-dependent crystalline phases:

• (1) a monoclinic phase, stable from room temperature up to about 1,170°C; (2) a tetragonal phase, stable up to around 2,370°C; and

• (3) a cubic phase, which remains stable from 2,370°C to its melting point.

The above phases not only differ from the crystal structure but also in its optical and mechanical characteristics.

These variations have been strategically leveraged to develop restorative materials with tailored properties suited for a wide range of clinical applications. Furthermore, the recent generation of Y-TZPs with varying yttria stabilizer concentrations directly influences the cubic-to-tetragonal crystal ratio. Y-TZPs consist predominantly of the tetragonal phase. This phase is retained at room temperature by incorporating 3 mol% yttrium oxide, producing what is commonly known as 3Y-TZP. 3Y-TZP was introduced as an alternative to metal − ceramics restorations, providing high mechanical properties and improved aesthetics. Subsequent generations of dental zirconia were developed by increasing the yttrium oxide content to improve translucency. Stabilization of approximately 25% of the cubic phase with 4 mol% of yttrium oxide resulted in partially stabilized zirconia with increased translucency compared to 3Y-TZP, making it suitable for monolithic applications.[40] The increase in yttrium oxide (5–8% mol) in zirconia materials and the stabilization of higher amounts of the cubic phase, led to the development of “ultra-translucent zirconia.” However, stabilizing over 50% of the cubic phase leads to a notable reduction in the flexural strength and fracture toughness compared to 3Y-TZP. Therefore, “ultra-translucent zirconia” is recommended for partial or full single-unit reconstructions and for short-span fixed dental prostheses in the anterior region.[40] Currently, various manufacturing techniques are employed to enhance marginal accuracy, strength distribution, and shade integration. For example, hot isostatic pressing increases density, eliminates internal flaws, and improves long-term reliability, whereas Cold Isostatic Pressing ensures uniform compaction of zirconia powders. Nano-grain engineering controls optical scattering and enhances polishability.[40] [Table 1] summarizes the composition and structural characteristics of the major dental ceramic systems used in restorative dentistry.

Table 1 Composition and structural characteristics of major dental ceramic systems used in restorative dentistry

Ceramic type	Composition	Strength (Flexural/MPa)	Fracture toughness	Aesthetic properties	Indications
Feldspar-based (porcelain)	SiO2, KAlSi3O8, Kaolin	50–75 MPa	Very low	Excellent translucency	Veneers, inlays/onlays
Leucite-reinforced	45% leucite crystals	approx. 120 MPa	1.6–1.8 MPa·√m	High translucency	Veneers, anterior crowns
Lithium disilicate	70% Li2SiO5 crystals	350–450 MPa	2.8–3.5 MPa·√m	Moderate translucency	Crowns, short-span bridges
Alumina	99.5% Al2O3	487–699 MPa	4.5–6.0 MPa·√m	Low translucency	Core substructure
Zirconia	ZrO2 (monoclinic/tetragonal)	approx. 1,000 MPa	Up to 10 MPa·√m	Opaque	Posterior crowns, FPD cores
Glass-infiltrated ceramics	Alumina + glass	300–500 MPa	2.5–3.5 MPa·√m	Moderate	Crowns, short-span bridges

Abbreviation: FPD, fixed partial denture.

Hybrid Ceramics

The recent classification of CAD/CAM machinable composite materials as “hybrid ceramics” is controversial, as evidenced by the new classification that was introduced, in which they proposed the term “resin matrix ceramics” as part of the overall classification of dental ceramic materials.[54] In the author's opinion, these materials should not be classified as such because they cannot withstand a thermal cycle: the resin matrix begins to break down above 250°C,[55] and their percentage filler content is similar to that of dental composites used for direct and indirect restorative techniques. Their only difference is that they come in a form suitable for milling using a CAD/CAM process. Despite this, the authors have chosen to include these materials as part of the overall history of the development of ceramic systems.

The idea behind introducing hybrid ceramics was to combine the tooth-like physical properties of resin and the high esthetic properties of ceramics to produce a restorative material with similar mechanical and optical properties to the natural tooth structure. The anticipated improvements include reduced brittleness, rigidity, and hardness coupled with improved flexibility, fracture toughness, and better machinability compared to ceramics.[56] Two products were developed to achieve this goal: VITA Enamic (Vita Zahnfabrik, Bad Säckingen, Germany) and LAVA Ultimate (3M ESPE, Saint Paul, Minnesota, United States). VITA Enamic is composed of two interpreted networks of organic resin and ceramic. Therefore, it is known as a “polymer infiltrated ceramic network” or PICN. It is quite similar to In-Ceram products, in which a ceramic network is infused with glass. Contrary to conventional composites, the lower ceramic fraction in PICNs decreases the elastic modulus and hardness while increasing the flexural strength and strain at failure.[56] PICNs have a modulus of elasticity similar to that of dentine and adhesive bonding cement, resulting in better stress distribution to the tooth structure and more uniform strain generation.[56] [57] PICN can be used for crowns, inlays, onlays and veneers. PICN crowns performed well in short-term follow-up.[58] [59] Inlays and partial-coverage restorations have demonstrated high survival rates over an observation period of 3 years.[59] Although promising, clinical studies on PICN are scarce and short-term; therefore, further long-term studies are needed to prove its efficacy as an alternative to feldspathic porcelains.

Lava Ultimate is a machinable resin nanoceramic (RNC) consisting of approximately 80% nanoceramic fillers (silica, zirconia, and silica − zirconia nanoclusters), all embedded into a highly cross-linked polymeric matrix. Industrial manufacturing and additional curing of composites reduce the porosity and the number of flaws, which is claimed to result in higher fatigue and flexural resistance compared to direct composites fabricated with conventional layering and curing processes.[60] Advantages of RNC include reduced milling time, lower milling bur wear, improved polishability, and ease of repair.[61] In-vitro testing of Lava Ultimate demonstrated high fatigue resistance, similar to IPS e.max CAD and higher than IPS EmpressCAD.[62] This was theorized to be attributed to the reduced modulus of elasticity and increased flexibility.[61] Partial crowns made of Lava Ultimate demonstrated a clinical success rate of 85.7% after 24-month follow-up.[63] Similar to Vita Enamic, clinical studies on Lava Ultimate are scarce or are short-term; therefore, more studies with long-term results are required to prove its efficacy as an alternative to feldspathic porcelains.

Conclusion

Dental ceramics and their associated processing technologies have undergone remarkable advancements over the past 15 years. Much of this evolution has centered on deliberate microstructural modifications and the rapid adoption of CAD/CAM-based production methods. The introduction and maturation of high-strength ceramics, particularly alumina- and zirconia-based polycrystalline materials, have transformed the clinical capabilities of ceramic systems. These materials now support the fabrication of posterior crowns, multi-unit fixed partial dentures, long-span bridges, full-arch implant-supported prostheses, and even implant abutments, expanding the clinical indications beyond what was previously achievable with conventional feldspathic systems.

At the same time, traditional bilayered restorations composed of a strong core veneered with highly aesthetic porcelain are gradually being replaced by monolithic ceramic solutions. This paradigm shift is driven by the reduced incidence of veneer chipping, simplified manufacturing workflows, and the increasing availability of high-strength, high-translucency ceramics. The development of cubic-phase zirconias (4Y-PSZ and 5Y-PSZ) and reinforced lithium-silicate ceramics reflects the ongoing effort to balance optical performance with mechanical integrity, an area that continues to evolve with improvements in material science

Conflict of Interest

None declared.

Data Availability

Data available on request from the authors.

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Publication History

Article published online:
05 February 2026