Advances in Dental Restorations: A Comprehensive Review of Machinable and 3D‐Printed Ceramic‐Reinforced Composites

ABSTRACT

Objective

This review aims to evaluate the current understanding and clinical applications of machinable ceramic‐reinforced composites (CRCs) and the emerging first generation of 3D‐printed CRCs in dental restorations.

Overview

Machinable CRCs, introduced over a decade ago, have shown moderate success in short‐ to medium‐term clinical applications, particularly in low‐stress areas. However, their long‐term durability limitations, such as increased wear and marginal deterioration, restrict their use in high‐stress situations and full crowns. The first generation of 3D‐printed CRCs offers customization advantages but is still in early development and exhibits lower mechanical strength and higher wear rates than CAD‐CAM CRCs and traditional ceramics. Additionally, the classification and definitions surrounding CRCs remain ambiguous, as ADA categorizations do not clearly differentiate CRCs from ceramics, complicating clinical indication, usage, and billing practices.

Conclusion

Machinable CAD‐CAM CRCs are moderately successful in low‐stress applications, while 3D‐printed CRCs show limitations in wear resistance and durability, raising concerns for their use in definitive restorations. Both require further research and clinical validation.

Clinical Significance

Machinable CAD‐CAM CRCs are best suited for low‐stress applications, while 3D‐printed CRCs may be more appropriate for provisional use. Until long‐term clinical data are available, ceramics should be preferred for high‐stress or full‐coverage restorations. Clearer definitions for porcelain/ceramic and comprehensive application guidelines are urgently needed to support clinician decision‐making and improve patient outcomes.

1. Introduction

The pursuit of restorative materials that closely mimic the properties and appearance of natural dental tissues has long been a focal point in dental materials science. Over the past decade, ceramic‐reinforced composites (CRCs) have emerged as a promising category of materials, combining the esthetic qualities of ceramics with the flexibility and handling characteristics of composite resins [1, 2, 3]. Machinable CRCs, in particular, have gained widespread acceptance in clinical practice, supported by extensive laboratory research and clinical trials that have established their indications, limitations, and clinical performance [3, 4, 5, 6, 7]. These materials have been suggest for a wide range of applications, including inlays, onlays, veneers, and even full‐coverage crowns, offering a versatile solution for dental restorations to a myriad of clinical challenges.

In recent years, the advent of 3D printing technology has introduced a new generation of CRCs, designed to offer the same benefits as their machinable counterparts but with the added advantages of customization and reduced material waste. Although it has been stated manufacturing generates significantly less waste a recent study showed only a 20% difference from subtractive method [8]. Despite the excitement surrounding these 3D‐printed CRCs, their clinical use is still in its infancy, and much remains unknown about their long‐term durability, optimal indications, and overall performance in the oral environment. The initial investigations suggest that while they hold promise, these materials may be better suited for provisional rather than definitive restorations at this stage.

This manuscript aims to provide a comprehensive review of the current understanding of machinable and 3D‐printed CRCs, focusing on their mechanical properties, clinical applications, and the need for standardized definitions and classifications. By exploring the strengths and limitations of these materials, this review seeks to inform clinical practice and guide future research in this evolving field.

2. Classification of Machinable and 3D Printed Ceramic‐Reinforced Resin Materials

The definition of what constitutes a hybrid ceramic material has been a source of confusion and debate. The 2013 American Dental Association (ADA) Code on Dental Procedures and Nomenclature defined “porcelain/ceramic” as “pressed, fired, polished, or milled materials predominantly composed of inorganic refractory compounds, including porcelains, glasses, ceramics, and glass‐ceramics” [9]. In 2023, the ADA's Council on Dental Benefit Programs revised this definition, describing porcelain/ceramic as “materials containing predominantly inorganic refractory compounds, including porcelains, glasses, ceramics, and glass‐ceramics” [10]. It “was revised to be inclusive of materials used in prostheses fabrication using 3D printing technology” [11]. Since most materials currently used in 3D printing technology are resin‐based, along with certain CAD‐CAM machinable blocks, there is an inadvertent overlap with “resins,” which the ADA Code on Dental Procedures defines “resin” as “any resin‐based composite, including fiber or ceramic‐reinforced compounds, and glass ionomers” [10]. The recently revised and released American Dental Association CDT 2025: Current Dental Terminology retains the same 2023 definitions for “porcelain/ceramic” and “resin,” with no additional clarification provided [12]. Although this change supports the inclusion of 3D‐printed resin‐based materials as viable options for restorative applications, the revised definitions introduce ambiguity in the classification, indication, usage, and billing between resin‐based CAD‐CAM and 3D printed materials versus true ceramic materials.

In contrast, the 10th edition of the Glossary of Prosthodontic Terms [13], published in 2023, defines ceramics as “compounds of one or more metals with a nonmetallic element, usually oxygen; they are composed of chemically and biochemically stable substances that are strong, hard, brittle, and inert nonconductors of thermal and electrical energy.” Porcelain is defined as “a ceramic material formed of infusible elements joined by lower‐fusing materials; most dental porcelains are glasses.” The glossary further clarifies novel materials, defining CRC resin as a “resin (i.e., polymer) composite with a phase of polymer in which mineral particles (fillers) are introduced to reinforce the material; new processing methods for CAD‐CAM technology have introduced highly cross‐linked resin matrices reinforced by a very high percentage of mineral particles.” Hybrid ceramic (HyC), dual‐network ceramic polymer, and resin‐modified ceramic are described as “terms used to refer to a porous ceramic network infiltrated by a polymer.” This provides more specific guidance on the composition required for a material to be classified as “ceramic” or “resin,” or “hybrid.”

Given these considerations, adopting a more precise classification of resin‐containing indirect restorative materials (resin‐matrix ceramics) aligned with the Glossary of Prosthodontic Terms is needed [1, 2, 14]. This classification can be divided into two categories:

1. Ceramic‐reinforced composite (CRC): Indirect restorative materials that consists of a cross‐linked resin matrix reinforced with ceramic fillers, which can be subcategorized by their method of fabrication into

   1. Machinable (subtractive manufacturing) or
   2. 3D‐printed (additive manufacturing)

2. Hybrid ceramic (HC): Indirect restorative materials composed of a porous ceramic network infiltrated by a polymer, currently fabricated exclusively using milling technology.

CRCs were designed based on the structure of conventional composites, while HC was developed with a unique microstructure that emphasizes the inclusion of feldspathic ceramic. Therefore, this refined classification provides greater clarity for the proper identification, usage, fabrication methods, and billing of these materials in the clinical practice. Table 1 specify different mechanical properties of these materials following the proposed classification.

TABLE 1.

Comparison of mechanical properties among natural dental tissues, machinable CRC, 3D‐printed CRC, and other dental restorative materials.

	Material	Elastic modulus (GPa)	Fracture toughness (MPa√m)	Flexural strength (MPa)	Hardness (VH)
Dental tissues	Enamel	87–100 [15]	0.6–1.5 [16]	470 (intra rod)‐978 (multiple rods) [17]	354 [18]
	Dentin	17–40 [19]	2.3 [20]	212 [21]	60 [22]
Machinable glass‐ceramic	IPS e.max CAD (Ivoclar Vivadent)	95 [23]	2.2 [24]	360 [23]	574 [25]
Hybrid ceramic	Vita Enamic (Vita Zahnfabrik)	30 [26]	1.2 [24]	148 [27]	181–235 [27]
Machinable ceramic‐reinforced composite (CRC)	Lava Ultimate (3M)	12.8 [28]	1.3–2.0 [24]	184–200 [25, 28]	95–115 [27]
	Cerasmart (GC)	10.4 [29]	0.6–1.2 [24, 30]	205 [30]	68 [27, 31]
3D‐printed ceramic‐reinforced composite (CRC)	Ceramic Crown (SprintRay)	5.9 [25]	2.1 [32]	117–150 [25, 33]	42 [25]
	CrownTec (Saremco)	4 [34]	1.4 [32]	135 [35]	30 [36]
	Varseo Smile Crown Plus (Bego)	4 [37]	1.1 [32]	116 [37]	23 [32]
3D‐printed resin for provisional restorations	C&B MFH (NextDent)	2 [25]	NA	97 [25]	14.1 [25]
Nanohybrid resin composite	Omnichroma (Tokuyama Dental)	7.9 [38]	1.4 [39]	102 [40]	76 [41]
Nanofilled resin composite	Filtek Supreme Ultra (3M)	13 [25]	1.4 [42]	157 [25]	91 [25]

For this review, the patient, intervention, control, outcome (PICO) question was: “Do machinable (CAD‐CAM) or 3D printed CRCs demonstrate clinically acceptable surface roughness, wear resistance, bonding effectiveness, and long‐term clinical success compared to ceramics?”. Online research was conducted in the PubMed and Scopus databases using search terms such as “resin nano ceramic,” “hybrid ceramic,” “machinable composite,” “3D printed composite,” “surface roughness,” “wear,” “bonding,” “clinical trial,” and their variations. Only original articles, in English, published in peer‐reviewed journals between 2010 and 2024 were included based on the following inclusion criteria: resin nanoceramics, ceramic‐reinforced polymers, 3d printed resin composites, hybrid ceramics, in vitro and in vivo studies, machinable and 3D printed manufacturing methods, studies comparing CRC materials with ceramic materials, studies on surface roughness, wear, and bonding properties, systematic reviews and meta‐analysis. The exclusion criteria included animal studies, studies on zirconia or implant supported restorations. All abstracts of retrieved articles were analyzed. Articles that met the inclusion criteria were selected for full analysis, and their bibliographic references were also analyzed for potential inclusion.

2.1. Machinable CRC

Machinable CRCs were introduced in 2011, with claims that these materials perform similarly to or better than glass‐ceramics and composite materials [28]. Lava Ultimate (3M) is often recognized as the first machinable CRC to utilize nanotechnology for its filler content (Figure 1), building upon the foundation of the same manufacturer's nanofilled composite resin (Figure 2). This material, also known as a resin nano‐ceramic, was designed to bridge the gap between traditional glass‐ceramics and composite resins, offering a blend of the esthetic qualities of ceramics with the flexibility and ease of use characteristic of composites. Unlike conventional ceramics, which require firing to achieve their final form, Lava Ultimate and similar materials were engineered to be machined subtractively directly into their final shape without additional processing. Initially, this category of material was marketed for a broad range of applications, including full‐coverage crowns and fixed partial dentures. However, in 2015, the manufacturer decided to limit its indications to inlays, onlays, and veneers, due to the poor clinical performance of full coverage restorations with this material. More recently, other manufacturers of machinable CRC propose that their materials can withstand occlusal stress and are therefore suitable for use as crowns [43, 44, 45, 46, 47]. Thus, understanding the short‐term (up to 2 years), medium‐term (3–5 years), and long‐term (6 years or more) clinical performance of machinable CRCs is essential for establishing clear indications and recognizing the limitations of these materials.

FIGURE 1.

Machinable CAD‐CAM ceramic‐reinforced composite: Lava Ultimate (3M) showing spherical silica nanofillers (20 nm) and spherical zirconia (4–11 nm) distribution within the polymeric matrix as (1) dispersed, non‐aggregated individual particles, and (2) nanoclusters made of loosely bound aggregated silica/zirconia nanoparticles (ranging from 0.6 to 10 μm) (magnification ×25,000).

FIGURE 2.

Nanofilled composite resin: Filtek Supreme Ultra (3M) depicting a combination of nonagglomerated/nonaggregated spherical silica fillers (20 nm), nonagglomerated/nonaggregated zirconia fillers (4–11 nm), and aggregated spherical zirconia/silica cluster fillers (magnification ×25,000).

Short term clinical trials revealed that machinable CRC may serve as an alternative to ceramic restorations, though concerns remain over marginal integrity and discoloration within a 2‐year evaluation period [48, 49, 50, 51, 52, 53, 54]. At 1‐year evaluation for treatment of severe tooth, wear machinable CRC showed similar causes of complications [7]. The overall success rate decreases overtime for this type of restoration, starting at 95% after 12 months and dropping to 85.7% after 24 months [55].

Medium‐term clinical studies have identified a series of possible complications with machinable CRC. A 4‐year retrospective study found that 25% of crowns made from machinable CRC experienced complications, such as: debonding (74.5%), fracture (4.7%), and chipping (1.9%) [56]. Another study highlighted the challenges with hybrid ceramic crown restorations, reporting a 6.5% loss within 3‐year period due to clinically unacceptable fractures [57]. Similarly, endocrowns made of machinable CRC reported comparable complications over a 5‐year period, with an overall success rate of 70.8% and a survival rate of 87.5% [58]. It was also found a 8.3% probability of fracture for machinable CRC onlays over 5 years, highlighting a moderate long‐term risk for machinable CRC under clinical conditions [59]. Machinable CRC used to fabricate occlusal veneers showed 84.7% survival rate over 3 years, with minor chipping fractures affecting marginal integrity but remaining repairable, contrasting with ceramic restorations made of lithium disilicate glass–ceramic which maintained a 100% survival rate during the same period [4]. Thus, medium‐term evaluations (3–5 years) suggest that partial‐ and full‐coverage restorations made from machinable CRC may pose clinical challenges due to increased risks of complications such as debonding, fractures, and marginal chipping.

To date, there are limited long‐term clinical studies exceeding 6 years on machinable CRC. A 5.5 year clinical evaluation on patient with severe tooth wear revealed that success rate for indirect RBC restorations ranged from 70.7%–97.1%, depending on the tooth type and failure criteria [60]. Anterior teeth exhibited the highest success rate (97.1%), followed by premolars (87.4%), with molars exhibiting the lowest success rate (70.7%). For molars, annual failure rates increased progressively over the study period, from 2.5% at 1 year to 5.4% at 3 years, and reaching 8.1% at 5.5 years [60]. A 7‐year clinical observation of machinable CRC in patients with moderate to severe tooth wear revealed a higher incidence of technical failures (24.1%) compared to lithium disilicate glass–ceramic (5.5%), with issues such as fractures (6.2%), discoloration (14.2%), and increased susceptibility to occlusal wear (91.1%) [61]. The study also reported an overall failure rate of 25.3% for the machinable CRCs over the 7‐year period, while lithium disilicate restorations, observed over a longer 13‐year period, demonstrated a significantly lower overall failure rate of 5.5% [61].

Based on these clinical findings, machinable CRCs are best suited for provisional or moderate‐term clinical use, such as interim restorations or lower‐stress partial coverage restorations, where replacement of the restoration anticipated within a few years. These materials may be appropriate for partial coverage restorations, such as inlays and onlays, especially in cases with lower occlusal load demands. While marginal integrity and retention are generally manageable in these settings, regular monitoring remains essential.

For longer‐term and full‐coverage restorations, however, machinable CRCs present limitations including increased risks of debonding, fractures, and marginal deterioration, which become more evident after 3 years. The success rate of machinable CRC is significantly influenced by the tooth type, with molars being more susceptible to failures and requiring more frequent maintenance than other teeth. Therefore, these materials are not recommended as definitive options for full crowns or high‐stress areas, where ceramics consistently provide superior durability and longevity.

2.1.1. Microstructural Characterization

Machinable CAD‐CAM CRC contains a high ceramic content, typically 65% or higher, with the remaining portion consisting of a cross‐linked polymeric matrix. The polymerization process for these materials is conducted under controlled industrial conditions, utilizing standardized high‐pressure (250 MPa for 60 min) and high‐temperature parameters (180°C) [62]. This method results in a highly homogeneous internal structure and significantly reduces the presence of unreacted monomers [3, 14].

The filler size, shape, and content vary significantly among the CAD‐CAM materials and tends to be larger than that of conventional resin composites. Lava Ultimate (3M, St Paul, MN, USA) is a CAD/ CAM block made with engineered spherical silica, with mean filler size of 20 nm diameter, and spherical zirconia with particle size ranging from 4 to 11 nm diameter. Nanofillers are then distributed within the polymeric matrix as (1) dispersed, non‐aggregated individual particles, and (2) nanoclusters made of loosely bound aggregated silica/zirconia nanoparticles (ranging from 0.6 to 10 μm) (Figure 1). Katana Avencia (Kuraray) blocks are composed of compressed aluminum oxide and silica nanofillers with spherical and rounded shapes, ranging from 20 to 40 nm in size (Figure 3a). Shofu Block HC (Shofu) consists of silica and zirconia silicate nanofillers between 20 and 100 nm, as well as nanoclusters varying from 0.4 to 12 μm (Figure 3b). Cerasmart (GC) (Figure 3c), Brilliant Crios (Coltene) (Figure 3d), and Tetric CAD (Ivoclar Vivadent) blocks contain silica and barium glass fillers, primarily in irregular shapes. However, most of the machinable CRC present differences in the mean size of the particles and filler content that slightly differs from those provided by the manufacturer [63, 64, 65]. Table 2 provides a detailed description of machinable CRC organic and inorganic composition, filler size, shape, and content.

FIGURE 3.

(a) Machinable CAD‐CAM ceramic‐reinforced composite: Katana Avencia (Kuraray) showing compressed spherical and rounded shapes aluminum oxide and silica nanofillers ranging from 20 to 40 nm in size (magnification ×25,000). (b) Machinable CAD‐CAM ceramic‐reinforced composite: Shofu Block HC (Shofu) depicting silica and zirconia silicate nanofillers (20 and 100 nm) and nanoclusters made of nanofilled fillers (ranging from 0.4 to 12 μm) (magnification ×25,000). (c) Machinable CAD‐CAM ceramic‐reinforced composite: Cerasmart (GC) showing silica (20 nm) and irregular shaped barium glass fillers (100–300 nm) (magnification ×25,000). (d) Machinable CAD‐CAM ceramic‐reinforced composite: Brilliant Crios (Coltene) showing amorphous silica (20 nm) and irregular shaped barium glass fillers (≥ 1.0 μm) (magnification ×25,000).

TABLE 2.

Organic and inorganic composition, filler size, shape, and content of different ceramic‐reinforced composites.

	Material	Organic composition	Inorganic composition	Filler size	Filler shape	Filler/ceramic content
Hybrid ceramic (polymer‐infiltrated ceramic network PICN)	Vita Enamic (Vita Zahnfabrik)	UDMA and TEGDMA (14%)	Feldspar glass‐ceramic (SiO2 58%–63%; Al2O320%–23%; Na2O 9%–11%; K2O 4%–6%; B2O3 0.5%–2%; ZrO2 and CaO) sintered network (86 wt%)	Feldspar (leucite‐based), zirconia reinforced ceramic network	Porous (network of finely branched channels) compacted block of presintered leucite‐based feldspar with minor crystalline phase of zirconia	86 wt%
Machinable ceramic‐reinforced composite resin	Lava Ultimate (3M)	Bis‐GMA, bis‐EMA, UDMA, and TEGDMA	Silica (SiO2) and zirconia (ZrO2) fillers, dispersed silica and zirconia nanofillers	Silica (20 nm), zirconia (4–11 nm) fillers Nanoclusters (0.6–10 μm)	Spherical	80 wt%
	Cerasmart (GC)	Bis‐MEPP, UDMA, and DMA	Silica and barium glass fillers	Silica (20 nm) Barium glass (300 nm)	Irregular	65 wt%
	Tetric CAD (Ivoclar Vivadent)	Cross‐linked dimethacrylate (Bis‐GMA, Bis‐EMA, TEGDMA, UDMA)	Barium aluminum silicate glass, silicon dioxide	Barium aluminum silicate glass (< 1 μm) silicon dioxide (< 20 nm)	Irregular	71–74 wt%
	Shofu Block HC (Shofu)	UDMA, TEGMA	Zirconia silicate, silica powder, microfused silica	Zirconia silicate and silica fillers (20–100 nm) nanoclusters (0.4–12 μm)	Spherical	61 wt%
	Brilliant Crios (Coltene/Whaledent)	Cross‐linked methacrylates	Amorphous silica and barium glass	Silica (20 nm) Barium glass (> 1.0 μm)	Irregular	70.7 wt%
	Katana Avencia (Kuraray Noritake Dental)	UDMA, TEGDMA	Aluminum oxide and SiO2	Aluminum oxide (20 nm), SiO2 (40 nm)	Rounded and spherical	62 wt%
3D‐printed ceramic‐reinforced composite resin	Ceramic Crown (SprintRay)	Methacrylate, proprietary oligomers, photo initiators and pigments	Silica (SiO2) and ytterbium oxide (Yb2O3)	SiO2 and Yb2O3 (1.0–5.0 μm) SiO2 (0.05–0.5 μm) (mean = 1.24 μm)	Irregular and some rounded fillers	50 wt%
	CrownTec (Saremco)	Bis‐EMA, trimethylbenzoyldiphenylphosphine oxide, photo initiators and pigments 4,4‐Isopropylidiphenol, ethoxylated and 2‐methyl prop‐2enoic acid	Rounded glass fillers and pyrogenic silica	0.04–1.50 μm (mean = 0.49 μm)	Mostly rounded and some irregular fillers	30–50 wt%
	VarseoSmile Crown Plus (Bego)	4,4′‐Isopropylidiphenol, ethoxylated and 2‐methylprop‐2enoic acid. methyl benzoylformate, diphenyl (2,4,6‐trimethylbenzoyl) phosphine oxide, photo initiators and pigments	Glass fillers	0.07–1.21 μm (mean 0.4 μm)	Mostly rounded and some irregular fillers	19–24 wt%
3D‐printed resin for provisional restorations	C&B MFH (NextDent)	7,7,9 (or 7,9,9)‐Trimethyl‐4, 13‐dioxo‐3, 14‐dioxa‐5, 12‐diazahexadecane‐1, 16‐diyl bismethacrylate, ethylene dimethacrylate, 2‐hydroxyethyl methacrylate, and diphenyl (2,4,6‐trimethylbenzoyl)‐phosphine oxide, 4‐methoxyphenol, hydroquinone monomethyl ether	SiO2, TiO2, and flakes of (C, O, Al, Si, and Ti)	1–2 μm flakes of (C, O, Al, Si, and Ti) and 0.2–0.5 μm SiO2 [25]	Irregular and spherical	3 wt%
Nanohybrid resin composite	Omnichroma (Touyama Dental)	UDMA, TEGDMA	Silica and zirconia fillers	260 nm	Spherical	79 wt%/68 vol%
Nanofilled resin composite	Filtek Supreme Ultra (3M)	Bis‐GMA, bis‐EMA, UDMA, and TEGDMA	Silica (SiO2) and zirconia (ZrO2) fillers	Silica (20 nm), zirconia (4–11 nm) fillers Nanoclusters (0.6–10 μm)	Spherical	80 wt%

Abbreviations: Bis‐EMA, ethoxylated bisphenol A‐dimethacrylate; Bis‐GMA, bisphenol A‐glycidyl methacrylate; Bis‐MEPP, bisphenol‐A ethoxylate dimethacrylate; DMA, dimethacrylate; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate.

Filler morphology influences the mechanical and optical properties of the composites. Spherical fillers tend to improve mechanical bonding with the polymer matrix, while irregularly shaped fillers can affect wear, color, and translucency. Inhomogeneities such as pores microstructures, microcracks, and large radiopaque fillers were identified in some CAD‐CAM machinable CRC. These defects, although large, had a minor impact on the total volume of the material (< 0.01 vol.%) [63]. Despite the industrial manufacturing process, these materials are not entirely homogeneous and may contain significant defects that could affect their performance.

2.1.2. Surface Roughness

Surface roughness is a significant factor influencing the long‐term performance of CAD‐CAM CRCs. These materials showed varying degrees of surface roughness both before and after simulated toothbrushing [66, 67, 68]. Machinable CAD‐CRC exhibited initial lower surface roughness; however, they experienced significant increases in roughness post‐toothbrushing [68, 69]. In contrast, glass–ceramic materials and hybrid ceramic, which possess a higher glass content, maintained lower roughness values after brushing [66, 68]. This suggests that materials with higher ceramic content may offer better resistance to surface degradation, reducing the need for repolishing in clinical settings.

Moreover, the correlation between surface roughness and gloss was evident across the studies, with higher roughness generally corresponding to a decrease in gloss [69, 70]. This deterioration was more pronounced in composite resins, especially those with larger and irregular filler particles. The findings underscore the importance of selecting materials with appropriate surface properties for long‐term esthetics and functionality. Given that surface roughness can lead to increased plaque accumulation and potential biofilm formation [71], repolishing of machinable CRCs, as part of regular maintenance, is mandatory to maintain their clinical performance over time. Clinicians must inform their patients of this requirement to ensure they understand the importance of regular follow‐up and maintenance for the longevity of their restorations.

2.1.3. Wear

A recent systematic review concluded that while resin‐ceramic materials generally exhibit lower wear resistance compared to lithium disilicate glass–ceramics, they cause less wear on opposing teeth, which can be advantageous in certain clinical situations [72]. However, alterations in anatomic form and increased occlusal wear should be expected for CAD‐CAM CRC. One clinical study revealed that CAD‐CAM machinable CRC yielded 67% more wear compared to lithium disilicate glass‐ceramic and 15% more wear than hybrid ceramic (PICN) over a 6‐month period [6]. This is indicative of wear starting relatively early with resin‐based materials, even when fabricated with CAD‐CAM machinable techniques, and progressing over the restoration's lifetime. This wear pattern has been reported in multiple clinical studies with evaluation periods ranging from 2 to 7 years, demonstrating that CAD‐CAM CRC are significantly less resistance to abrasion than ceramic materials [5, 57, 61]. Long‐term evaluation revealed substantial surface deterioration, with 91.1% of CAD‐CAM CRC restorations displaying extensive occlusal wear after 6 and 7 years [61].

Clinical success of CAD‐CAM machinable CRC was shown to be 86.7% after 24 months for single tooth restorations [55]. The clinical performance of CAD‐CAM CRC used to rehabilitate patients with severe tooth wear pointed to a success rate between 97.2% and 100% [7]. The authors indicated that polishing to remove discoloration or roughness were not considered failures, and 5.46% of the restorations required some form of intervention during the study. Another clinical study revealed 84.7% survival rate for ultra‐thin CAD‐CAM CRC and 100% for CAD‐CAM lithium disilicate glass‐ceramic over a 3‐year period [4]. Regarding wear, a 3‐year clinical study showed a mean vertical loss of 186 μm in the premolar region and 342 μm in the molar region, in contrast to lithium disilicate glass‐ceramic of mean vertical loss of 90 μm in the premolar region and 93.6 μm in the molar region [5]. Further analysis revealed that CAD‐CAM CRC had significantly higher wear rates, especially in the molar region (premolar: first year 107% and third year 207%, molar: 265% and third year 179% more wear than pressed lithium disilicate glass‐ceramic) [5]. These findings underscore the importance of a clear and accurate distinction between materials in the ADA classification, as differences in wear and clinical performance can significantly impact treatment outcomes and material selection.

Our clinical observations revealed that most issues with CAD‐CAM CRC occur between 18 and 36 months after placement (Figure 4a–f). Scanning electron microscopy analysis revealed progressive wear in machinable CAD‐CAM CRC (Lava Ultimate, 3M), with early wear characterized by nanocluster filler plucking and initial degradation at the filler/resin matrix interface (Figure 5a), advancing to extensive surface disorganization, significant filler plucking, resin matrix exposure, interface degradation, and surface cracking in later stages (Figure 5b). While minor failures in CAD‐CAM CRC restorations can be repaired, larger full‐mouth reconstructions using CAD‐CAM CRC should be approached with caution. Excessive wear of CAD‐CAM CRC overtime may result in decrease of the patient's vertical dimension of occlusion. Patients should be clearly informed that these restorations are considered transitional and may need to be replaced with ceramic restorations in the future. This suggests that resin‐ceramic materials may be less durable in terms of wear resistance over time, highlighting the need for careful clinical case selection and constant maintenance. Table 3 outlines some of the key advantages and limitations of CAD‐CAM machinable CRCs, providing a comprehensive overview of advantages and limitations for definitive dental restorations.

FIGURE 4.

Clinical sequence depicting increasing wear of CAD‐CAM CRC (Lava Ultimate, 3M) onlay (a–c) and CAD‐CAM CRC (Lava Ultimate, 3C) tabletop occlusal veneer (d–f) immediately after bonding, 18‐months and 36‐months after placement.

FIGURE 5.

(a) Initial stages of wear of machinable CAD‐CAM ceramic‐reinforced composite (Lava Ultimate, 3M) showing nanocluster filler plucking (white arrows), with exposure of the underlying resin matrix and early signs of degradation at the filler/resin matrix interface (red arrows) (magnification ×5000). (b) Advanced stages of wear of machinable CAD‐CAM ceramic‐reinforced composite (Lava Ultimate, 3M) revealing extensive surface disorganization, including significant nanocluster filler plucking, exposure of the resin matrix, degradation at the filler/resin matrix interface, and surface cracking (magnification ×5000).

TABLE 3.

Advantages and limitations of CAD‐CAM machinable CRC versus 3D‐printed CRC for definitive restorations.

	Machinable CRC	3D‐printed CRC
Fabrication precision	High precision due to controlled industrial milling processes.	Precision can vary depending on the 3D printer type, quality, calibration, ethanol rinse procedures, curing device, and settings.
Material homogeneity	Generally uniform, with fewer defects due to pre‐fabrication under controlled conditions.	Potential for inhomogeneities, such as voids or inconsistent layers, depending on printing quality.
Mechanical properties	Higher mechanical properties compared to 3‐printed CRC, but lower than ceramics.	Generally lower mechanical strength and wear resistance compared to CAD‐CAM CRC, and significant inferior to ceramics.
Optical properties	Monochromatic but minor changes in translucency over time.	Monochromatic, but susceptible to discoloration in a short period of time.
Surface	Maintains smoother surface short‐term with less roughness progression compared to 3D‐printed CRC Requires higher maintenance with constant finishing and polishing steps than ceramic.	Increased susceptibility to surface roughness progression, especially after aging, leading to higher wear rates. Requires higher maintenance with constant finishing and polishing steps than machinable CRC.
Steps	Scan, design, mill, finish, and polish.	Scan, design, print, wash, dry, polymerize, finish, and polish.
Time efficiency	Faster turnaround for single units once blocks are milled. Must consider finishing and polishing steps.	Must consider printing and post‐processing times, finishing and polishing steps. Can be faster for complex or multiple units.
Cost	Higher investment due to the cost of CAD‐CAM software, milling software, milling machine, burs, and blocks.	Lower material costs but requires investment in 3D printing technology (3D printer, wash and dry machine, and curing device). Does requires constant calibration of the printer.
Material waste	Generates more waste due to milling from a solid block.	20% less waste than machinable CRC as material is added layer by layer.
Bonding	Established protocols with predictable outcomes.	Bonding protocols are still evolving, with potential variability in outcomes.
Clinical longevity	Moderate clinical longevity in low‐stress applications; not ideal for high‐stress or full‐coverage restorations.	No long‐term data available; long‐term independent clinical trials are necessary. Could be better suited for provisional applications.

2.1.4. Bonding

The success of machinable CRC restorations heavily depends on the effectiveness of the adhesive luting process, which involves meticulous surface preparation and the use of advanced adhesive systems. Airborne‐particle abrasion, using 50 μm aluminum oxide particles at 1–2 bar pressure, is recommended as a intaglio surface treatment [1, 73]. This process creates micro‐retentive areas on the surface of the composite resin, increasing the surface area available for bonding and enhancing mechanical interlocking between the restoration and the adhesive.

Following airborne‐particle abrasion, the application of a silane coupling agent is advised, particularly when dealing with CRC resins [1]. Silane acts as a chemical bridge between the inorganic filler particles and the organic adhesive, improving the bond strength. In some cases, a universal adhesive system containing 10‐MDP (methacryloyloxydecyl dihydrogen phosphate) can be used as an alternative or in conjunction with silane. However, the efficacy of silane coupling agents or silane‐containing universal adhesive as pretreatment differs based on the type of CAD‐CAM CRC [74]. Resin‐based adhesives are preferred over conventional cements due to their superior bonding capabilities and their ability to withstand the stresses encountered in the oral environment. These adhesives penetrate the micro‐retentive surface created by the airborne‐particle abrasion, forming a strong micromechanical and chemical bond with the composite resin.

The occurrence of debonding of CAD‐CAM machinable CRC clinically after adhesive luting is minimal when the bonding steps are performed accurately [55, 60]. With precise execution of the bonding protocol, long‐term clinical success is likely, as the risk of debonding in adhesive restorations is minimal. However, over 5 years, machinable CRC (Lava Ultimate) onlays exhibit a gradual reduction in ideal margin quality, decreasing from 100% at baseline to 23.2%, with an increasing percentage (76.8%) showing minor yet detectable marginal discrepancies [59]. This trend indicates a slow but steady decline in margin integrity, though the margins may remain intact without significant gap formation.

2.2. 3D Printed CRC

Newer 3D‐printed CRCs have been recently developed specifically for fabrication of definitive dental restorations, offering an alternative to traditional subtractively manufactured CAD‐CAM materials. The first generation of 3D‐printed CRC is now available for clinicians and dental technicians to fabricate dental restorations, expanding the material options for restorative dentistry.

The 3D printing process for 3D‐printed CRC involves vat layer‐by‐layer polymerization, where a digital model guides the precise layer‐by‐layer polymerization of the material. The 3D printer platform moves incrementally, stacking each newly cured layer on top of the previous one until the desired restoration is completed. There are different types of vat polymerization, including stereolithography (SLA), digital light processing (DLP), and continuous liquid interface production (CLIP). After printing, the restoration requires cleaning with ethanol and a post‐polymerization step to remove any excess resin and ensure an appropriate degree of conversion. This additive manufacturing approach allows for highly customized restorations with complex geometries, reduced material waste, and faster production times.

The integration of ceramic particles into the resin matrix enhances the material's wear resistance, mechanical strength, and esthetic properties. According to the manufacturers 3D‐printed CRC are suitable for long‐term clinical use in anterior and posterior crowns, veneers, inlays, onlays, and as artificial teeth for dental prosthesis (complete dentures and/or partial dentures) [35, 37, 75, 76].

Currently, there is a scarcity of short‐term randomized clinical trials evaluating the effectiveness of definitive 3D‐printed CRC restorations. Furthermore, the few studies that exist have tested materials no longer commercially available, making it challenging to establish their clinical effectiveness [77, 78]. This lack of data on clinically viable, commercially accessible materials highlights an essential gap in the literature and emphasizes the need for robust, clinical studies on currently available 3D‐printed CRC options.

2.2.1. Microstructural Characterization

3D‐printed CRC resins present with less ceramic content, varying from 3% to 50%, and increased methacrylate polymeric matrix compared to that of CAD‐CAM machinable CRC [25]. This fact can be a cause of concern for producing definitive restorations. Not all manufacturers provide clear details regarding the specific filler content or composition of their products, often offering only a range of filler content or vague information about the components used.

The distribution, content, size, and shape of fillers are crucial factors in determining the material‐specific properties of 3D‐printed CRC. Although stabilizing agents can aid in achieving a uniform dispersion of ceramic fillers, this uniformity cannot be fully assured, as the fillers may settle or separate within the liquid resin over time. During the printing process, filler distribution can become non‐homogeneous, leading to the formation of dispersed fine particles alongside larger agglomerates/clusters of the same fillers, which the latter tends to align predominantly parallel to the printing orientation [79]. Filler agglomeration and clustering result in increased inter‐particle spacing, which exposes more of the resin matrix, potentially leading to its degradation [80, 81]. Proper mixing of the printable resin components is essential to reduce heterogeneity in the final structure of the restoration. To address this issue, manufacturers have adopted various strategies, such as incorporating mechanical roller or tilting resin stirring devices to maintain consistent mixing (i.e.: NextDent LC‐3D Mixer, NextDent, PrograPrint PR5, Ivoclar Vivadent), or by minimizing the amount of resin in the bottles while employing press SLA (i.e.: Midas, SprintRay). These approaches help to mitigate the risk of developing an inhomogeneous microstructure during the printing process.

A minimum filler load of 50 wt% for 3D‐printed CRC has been said to be necessary for acceptable clinical outcomes [82]. However, the filler content of commercially available 3D printed CRC is significant lower than that found in clinically established CAD‐CAM machinable CRC or current direct composite resins [25, 83]. Increasing the filler content in 3D‐printed CRC can offer both benefits and challenges in the fabrication of dental restorations. While higher filler content can enhance the elastic modulus, this improvement is highly dependent on the size and distribution of the fillers [84]. At the same time, increasing the filler content can also raise viscosity [85], which may negatively impact printability, leading to issues such as clogging, inconsistent flow, and reduced printing precision [86]. This could explain why most available 3D‐printed CRCs exhibit a relatively low elastic modulus. The elastic modulus of 3D‐printed CRCs ranges from 2 to 6 GPa (Table 2), which is up to 150% lower than that of human dentin. Moreover, there is no clinical study that compares the clinical outcomes of 3D‐printed CRC and the importance of filler content on the survival or success rate of these types of restorations.

The filler shape and size are quite variable for 3D‐printed CRCs. Filler sizes ranged from 5.0 to 0.04 μm, depending on the material studied. Ceramic Crown (SprintRay) displayed large irregular silica fillers ranging from 1.0 to 5.0 μm and smaller rounded 0.5 μm ytterbium oxide fillers, with a mean filler size of 1.24 μm (Figure 6). Varseo Smiles Crown Plus (Bego) revealed mostly rounded and some irregular filler with size ranging from 0.07 to 1.21 μm with a mean filler size of 0.4 μm (Figure 7). Crowntec (Saremco) also presented with rounded and some irregular filler with size ranging from 0.04 to 1.50 μm with a mean filler size of 0.49 μm (Figure 8). The shape and size of the fillers are directly related with gloss retention and wear. Resin‐based materials with larger or irregular particles tend to have rougher, less glossy surfaces and are less wear‐resistant compared to those with small, spherical particles [87]. Table 2 provides a detailed description of 3D‐printed CRC organic and inorganic composition, filler size, shape, and content.

FIGURE 6.

3D‐printed ceramic‐reinforced composite: Ceramic Crown (SprintRay) displaying large irregular silica fillers ranging from 1.0 to 5.0 μm and smaller rounded 0.5 μm ytterbium oxide fillers, with a mean filler size of 1.24 μm (magnification ×25,000).

FIGURE 7.

3D‐printed ceramic‐reinforced composite: Varseo Smiles Crown Plus (Bego) showing mostly rounded and some irregular filler with size ranging from 0.07 to 1.21 μm with a mean filler size of 0.4 μm (magnification ×25,000).

FIGURE 8.

3D‐printed ceramic‐reinforced composite: Crowntec (Saremco) showing rounded and some irregular filler with size ranging from 0.04 to 1.50 μm with a mean filler size of 0.49 μm (magnification ×25,000).

2.2.2. Surface Roughness

Tests conducted in our laboratories showed that Ceramic Crown (SprintRay) achieved smoother surfaces when polished with ceramic polishing kits, while Varseo Smiles Crown Plus (Bego) and Crowntec (Saremco) can be effectively polished using conventional composite polishing rotary burs. Nevertheless, all 3D‐printed CRCs benefited from a final polishing step with a goat hairbrush [88]. The surface roughness of the permanent 3D‐printed CRCs was found to be comparable to that a specific resin‐based CAD/CAM block (i.e., Grandio, Voco); however, the 3D‐printed resins exhibited lower microhardness, which could potentially impact their clinical success [89]. Aging significantly affected the surface roughness of 3D‐printer CRC, resulting in up to 66.7% increase after a 2‐year laboratory aging simulation [90]. One study found that 3D‐printed CRC initially exhibited a 43.5% higher surface roughness than CAD‐CAM lithium disilicate glass‐ceramic [91]. However, post‐aging assessments revealed that while the ceramic maintained relatively low roughness with only a 21.7% increase, the 3D‐printed CRC showed a substantial 63.6% increase in roughness [91].

High‐resolution, high‐magnification scanning electron microscopy performed in our laboratory has revealed that the inhomogeneous microstructure of 3D‐printed composites becomes apparent after polishing procedures (Figures 9, 10, 11). Microgaps, voids, and porosities are visible across the entire surface, including evidence of filler fracture, all of which could lead to reduced mechanical strength, increased wear, higher susceptibility to staining and plaque accumulation, and a greater risk of bacterial infiltration, potentially compromising the longevity and esthetics of the restoration.

FIGURE 9.

Polished surface of 3D‐printed ceramic‐reinforced composite Ceramic Crown (SprintRay) revealing inhomogeneous microstructure with microcracks (white arrow) and evidence of filler fracture (red arrow) (magnification ×15,000).

FIGURE 10.

Polished surface of 3D‐printed ceramic‐reinforced composite Varseo Smiles Crown Plus (Bego) revealing inhomogeneous microstructure with microgaps, voids, and porosities (magnification ×15,000).

FIGURE 11.

Polished surface of 3D‐printed ceramic‐reinforced composite Crowntec (Saremco) revealing inhomogeneous microstructure with microgaps, voids, porosities, and filler plucking (magnification ×15,000).

The application of a light‐cured low‐viscosity glaze material has been suggested to enhance the surface quality of dental restorative or to provide further characterization to a monolithic material [92]. To ensure long‐term adherence to the 3D‐printed CRC surface, pre‐treatment with airborne particle abrasion for 5 s (27 μm) followed by the application of a silane for 60 s is recommended (Figure 12). After placement of pigments and glazing resin (Figure 13), the surface can be effectively polished with goat hairbrush (Figure 14).

FIGURE 12.

Surface pre‐treatment of a 3D‐printed ceramic‐reinforced composite surface for characterization and glazing: (a) Pre‐treatment with airborne particle abrasion for 5 s (27 μm), (b) Steam clean of the surface, and (c) Application of a silane for 60 s and air‐dry.

FIGURE 13.

Surface characterization of a 3D‐printed ceramic‐reinforced composite. (a) Blue pigment is applied to the incisal third to simulate incisal translucency. (b) Opaque pigment is applied to the incisal edge to simulate the incisal halo effect. (c) White pigment is applied to the line angles and mamelons to increase light reflection. (d) Red pigment is applied to the gingival third to increase chroma.

FIGURE 14.

Examples of 3D‐printed ceramic‐reinforced composite veneers before (left) and after characterized, glazed, and polished (right).

While the application of glaze improves the surface smoothness and wear resistance of 3D‐printed composites, there are some limitations. Incomplete polymerization of the resin glaze layer could compromise the restoration mechanical properties [88]. Over time, the glaze can chip, especially under stress, which might reduce its protective effects (Figure 15a–f). This chipping can lead to exposure of the underlying material, potentially compromising the glaze's long‐term effectiveness [92]. Additionally, the glaze's performance may vary under different conditions, meaning its benefits might not be as reliable in all situations. Overall, while glazing provides initial advantages, its durability over time is a concern.

FIGURE 15.

Surface roughness of polished and glazed 3D‐Printed ceramic‐reinforced composites. After polishing and glazing, half of the specimens were left intact, while the other half was subjected to 80,000 cycles of simulated toothbrushing abrasion using a toothpaste slurry containing distilled water and toothpaste (Colgate 2 in 1 Whitening with Stain Lifters, Colgate; RDA 200). (a) Polished and glazed ceramic crown revealing the glazing covering (magnification ×5000). (b) Lower magnification (×500) of polished and glazed ceramic crown, showing the two halves of the specimen (intact and toothbrushing abrasion). (c) Polished and glazed ceramic crown after toothbrushing abrasion simulation (magnification ×5,000) note the partial removal of the glaze, exposure of the fillers, and increased porosities. (d) Polished and glazed Varseo Smile Crown Plus revealing the glazing covering (magnification ×5000). (e) Lower magnification (×500) of polished and glazed Varseo Smile Crown Plus, showing the two halves of the specimen (intact and toothbrushed). (f) Polished and glazed Varseo Smile Crown Plus after toothbrushing abrasion simulation (magnification ×5000) note partial removal of the glaze, increased porosities, and surface microcracks.

Surface roughness of 3D‐printed CRCs is significantly affected by toothbrushing abrasion (Figure 16a–f). Depending on the composition of the 3D‐printed CRC roughness can increase by approximately 16%–60%, due to abrasive wear from toothbrushing [93]. Additionally, 3D‐printed CRC is vulnerable to discoloration and is significantly affected by artificial aging. A recent study showed that the gloss of 3D‐printed veneers decreased by approximately 32.6% after artificial aging in coffee and by about 34.4% after aging in tea [94]. These percentages reflect a significant reduction in gloss that occurred within just 7 days of being subjected to these staining solutions. Overall, our clinical observations indicated an increase in surface roughness and a decrease in gloss retention within just a few weeks of clinical placement.

FIGURE 16.

Surface roughness of polished 3D‐printed ceramic‐reinforced composites. After polishing, half of the specimens were left intact, while the other half was subjected to 80,000 cycles of simulated toothbrushing abrasion using a toothpaste slurry containing distilled water and toothpaste (Colgate 2 in 1 Whitening with Stain Lifters, Colgate; RDA 200). (a) Polished ceramic crown (magnification ×5000). (b) Lower magnification (×500) of polished ceramic crown, showing the two halves of the specimen (intact and toothbrushing abrasion). (c) Polished ceramic crown after toothbrushing abrasion simulation (magnification ×5000) note the exposure of the fillers, filler plucking, and increased porosities. (d) Polished Varseo Smile Crown Plus (magnification ×5000). (e) Lower magnification (×500) of polished Varseo Smile Crown Plus, showing the two halves of the specimen (intact and toothbrushing abrasion) (f) Polished Varseo Smile Crown Plus after toothbrushing abrasion simulation (magnification ×5000) note the increased porosities.

A recent multicenter randomized controlled clinical trial evaluating 3D‐printed CRC crowns for primary molars reported a survival rate of 82% after 12 months, along with increased discoloration, higher gingival and plaque indices [77]. The latter may be attributed to the inherent increase in surface roughness of 3D‐printed resins.

High‐magnification scanning electron microscopy analysis revealed that polished 3D‐printed CRCs exhibit multiple voids, particularly around the filler particles. These defects may result from either compromised polymerization of the resin matrix or inadequate silanization of the ceramic fillers, leading to poor binding between the fillers and the polymeric matrix. These voids create pathways for the penetration of water molecules, which then interact with the polymeric structure of the resin, causing plasticization of the resin matrix. Water molecules can position themselves between the polymer chains, reducing the intermolecular forces, increasing the material's elasticity, decreasing its mechanical strength, and softening the resin, potentially accelerating the degradation of the restoration.

2.2.3. Wear

The quality of the bond between the fillers and the polymeric matrix is critical for the long‐term durability of resin‐based materials [82, 95]. When the covalent bond between the filler and polymer matrix is compromised, it creates a pathway for water uptake, which can lead to chain degradation, polymer swelling, and monomer leaching [96, 97]. Additionally, interactions of water with unreacted monomers and/or their hydrophilic groups can lead to polymer/monomer leaching and corrosive degradation of the composite resin [96]. If a 3D‐printed CRC exhibits less than 50 wt% filler content, it may fail to achieve the necessary mechanical properties and resistance to degradation, potentially compromising its clinical performance [82]. Figures 17 and 18, respectively, illustrate the significant wear observed on Ceramic Crown (SprintRay) and Varseo Smile Crown Plus (Bego) under 120,000 cycles of chewing simulation.

FIGURE 17.

Wear of 3D‐printed ceramic‐reinforced composite Ceramic Crown (SprintRay) revealing extensive surface disorganization, including significant filler exposure, filler plucking, exposure of the resin matrix, degradation at the filler/resin matrix interface, increased porosity, and surface cracking (magnification ×5000).

FIGURE 18.

Wear of 3D‐printed ceramic‐reinforced composite Varseo Smiles Crown Plus (Bego) revealing extensive surface disorganization, including significant filler plucking, exposure of the resin matrix, degradation at the filler/resin matrix interface, increased porosity, and surface cracking (magnification ×5000).

A recent study showed that 3D‐printed resin crowns exhibited adequate strength to endure typical masticatory forces in children, regardless of whether fabricate with 0.4 or 0.6 mm thick [98]. However, after simulated chewing, these crowns exhibited increased surface wear, including microcracks, debris deposition, and discoloration [98].

Scarce information is available in the literature regarding the wear behavior of the so called “definitive” 3D‐printed CRC. Crowntec (Saremco) showed significantly greater volumetric wear compared to Varseo Smile Crown Plus (Bego), with approximately 154% higher wear under artificial saliva conditions [92]. The significantly higher volumetric wear observed in some 3D‐printed CRCs, compared to others, may be largely attributed to plastic deformation [92], which plays a crucial role in the material's wear resistance under artificial saliva conditions. Additively manufactured materials, such as Crowntec (Saremco) and VarseoSmile Crown Plus (Bego), exhibited approximately 16%–19% higher volumetric wear compared to machinable CAD‐CAM CRC materials like Brilliant Crios (BC) and Vita Enamic (Vita) [99]. Another study revealed that 3D‐printed CRC (FormLabs Permanent Crown Resin) exhibited a volumetric loss that was approximately 11.7% lower than Grandio Voco, 70% higher than GC Cerasmart, and 134.5% higher than Vita Enamic [90]. When the wear of a 3D‐printed CRC (Varseosmile Crown Plus) was compared to CAD‐CAM fabricated lithium disilicate glass‐ceramic (e.max CAD, Ivoclar Vivadent), the 3D‐printed CRC was nearly twice as susceptible to surface wear (95.5%) [91].

The wear behavior of 3D‐printed CRC is highly susceptible to post‐printing treatment. Specifically, post‐curing restorations using curing devices with wavelengths of 405 nm and chamber temperatures above 60°C can enhance monomer conversion and improve wear resistance [83, 100]. All these facts underscore the difference in wear resistance between the two manufacturing approaches, with 3D‐printed CRC demonstrating greater susceptibility to wear.

Different authors highlighted the need for judicious clinical application and careful consideration for patient needs [79, 81, 88, 92]. There is increasing concern that the first generation of 3D‐printed CRCs may not yet be considered a reliable alternative to machinable materials (machinable CRC, HC, or glass‐ceramics) for definitive restorations [81], but they can be appropriately indicated for use as provisional or temporary restorations.

2.2.4. Microstructure of the 3D Printed Layers

The choice of layer thickness can directly influence the clinical performance of 3D‐printed restorations, particularly in terms of wear resistance and structural integrity. Thinner printing layers (50 μm) lead to superior overall physical and mechanical properties in 3D‐printed resins, including higher flexural strength, Vickers hardness, improved wear resistance, and smoother surface roughness compared to layers printed at 100 μm [101]. Assuming that the 3D printer is fully calibrated.

The orientation of filler particles and agglomerates parallel to the printing layers may enhance the compressive and flexural strength of the printed restorations [79]. However, the irregular distribution and alignment of these particles could also negatively affect the overall mechanical integrity, polishability, fracture resistance, and color stability of the material. Thus, proper consideration of printing orientation and the potential for filler agglomeration is essential to optimize the durability and effectiveness of these restorations [79].

When 3D printing composite resins, maintaining the right viscosity is crucial for ensuring smooth, even flow during the printing process. The resin must flow easily into the gaps between layers as the platform moves. However, for definitive 3D‐printed CRC, the need for a high filler content increases viscosity, and the resulting surface tension can prevent the resin from spreading smoothly. This can lead to uneven distribution, creating an irregular surface and potentially causing interstitial gaps or incomplete layers in the printed restoration. Consequently, the material may have a less uniform structure, compromising its mechanical properties and overall performance, particularly in terms of wear resistance.

The orientation of printing layers significantly impacts the mechanical properties and fracture behavior of 3D‐printed composite materials. Printing at a 45° angle, rather than horizontally (0° angle) or vertically (90° angle), enhances the material's strength, wear, and resistance to fracture, making it a crucial consideration in dental restoration design [79, 102]. Layers printed at a 45° angle exhibit higher flexural strength and modulus compared to vertically printed layers. In vertically printed restorations, cracks tend to propagate along layer boundaries, increasing the risk of delamination [79]. In contrast, a 45° layer orientation offers more uniform stress distribution across the layers, reducing the likelihood of such issues [102]. Conversely, recent findings suggest that a 90° print orientation yields higher flexural strength and modules compared to 0° and 45° orientations, with results meeting the minimum flexural strength of 80 MPa required by ISO 4049 standard specifications [103]. The authors also emphasized that machinable CAD‐CAM CRC still exhibits superior mechanical properties compared to 3D‐printed CRC [103].

A correct 3D‐printing strategy is essential for achieving a clinically acceptable restoration, as layer thickness and orientation during printing process must be carefully controlled. However, there is still a lack of standardized guidelines on optimal layer thickness and orientation for all 3D‐printed CRCs leading to variability in the mechanical performance and, consequently, affecting the longevity of 3D‐printed restorations. Table 3 outlines some of the key advantages and limitations of 3D‐printed CRCs, providing a comprehensive overview of advantages and limitations for definitive dental restorations.

2.2.5. Bonding

Similar to machinable CAD‐CAM CRC, 3D‐printed restorations must be adhesively luted instead of cemented. Airborne‐particle abrasion (50 μm at 1–2 bar) is recommended surface treatment for bonding 3D‐printed restorations [104, 105, 106]. Application of silane agent or universal adhesive system containing 10‐MDP is also recommended [105]. It is important to note that different 3D‐printed resins may yield varying bonding strengths depending on their composition. However, due to their mechanical properties, it is not advisable to use non‐adhesive cements for delivering 3D‐printed restorations.

3. Conclusions

The primary goal of any restorative material is to closely replicate the properties and appearance of natural dental tissues. This review aimed to provide insights into the clinical applications of machinable CRCs and the emerging first generation of “definitive” 3D‐printed CRCs in dental restorations. Based on the available evidence, the following conclusions were drawn:

• Machinable CAD‐CAM CRCs: Machinable CRCs have demonstrated moderate clinical success in short‐ to early medium‐term applications, particularly in low‐stress areas. These materials are therefore better suited for partial restorations, such as inlays, onlays, or veneers, and for provisional applications where lower occlusal stress is anticipated. However, the use of CAD‐CAM CRCs for full‐coverage restorations should be approached with utmost caution, as they present limitations in long‐term durability, including higher risks of wear, marginal deterioration, and fracture, especially in high‐stress areas.

• Emerging potential and limitations of the first generation of “definitive” 3D‐printed CRCs: The first generation of so called “definitive” 3D‐printed CRCs introduces valuable advancements in customization and material efficiency. Nonetheless, current evidence indicates that these materials exhibit significantly higher wear rates and surface roughness progression compared to machinable CRCs and ceramics, especially under prolonged functional loading. This wear susceptibility highlights the need for cautious use in definitive restorations. Thus, their use as long‐term provisional restorations appears to be a logical approach, whereas considering them as definitive porcelain/ceramic materials remains highly controversial.

• Comparative performance of CAD‐CAM machinable CRC and 3D‐printed CRC: CAD‐CAM machinable CRCs demonstrate superior wear resistance, surface stability, and overall durability compared to first‐generation 3D‐printed CRCs. Studies indicate that 3D‐printed CRCs experience faster surface roughness progression and higher susceptibility to wear under occlusal loading, making them less suited for high‐stress applications. While machinable CAD‐CAM CRCs are still limited in long‐term success rate compared to traditional ceramics, they outperform 3D‐printed CRCs in resistance to surface degradation.

• Comparative analysis of CAD‐CAM and 3D‐printed CRCs with traditional ceramics: It is evident that resin composite based CRC materials—whether machinable or 3D‐printed—cannot yet rival the physical properties (wear resistance, surface roughness, and longevity) of ceramic restorations. While both CAD‐CAM and 3D‐printed CRCs may provide some esthetic benefits, their clinical indication remains limited by their increased susceptibility to degradation.

• Classification, definition, and standardization needs: The ambiguity and inadvertent overlap in current ADA classifications for “porcelain/ceramics” and “resins” highlights the necessity for refined definitions that distinguish between true ceramic materials, resin‐based composite materials, and hybrid materials. A standardized classification system, as proposed in this review, is essential for ensuring clarity in clinical indication, usage, and billing practices, ultimately guiding appropriate material selection and patient care.

• Recommendations for clinical applications: Based on available evidence, machinable CAD‐CAM CRCs are best suited for cases requiring lower occlusal stress and 3D‐printed CRCs for provisional applications. Until further long‐term clinical data are available, ceramics should remain the preferred choice for definitive restorations in high‐stress or full‐coverage situations, given their superior performance.

These conclusions underscore the importance of ongoing research and clearer material definitions to support clinicians in making evidence‐based material choices, ensuring both patient satisfaction and restoration longevity. This will ensure that clinicians, dental technicians, and patients are better informed, fostering more transparent and effective decision‐making regarding the materials used in dental restorations.

Conflicts of Interest

The authors declare no conflicts of interest.

Data Availability Statement

Research data are not shared.