Digital technology in dental clinical practice is increasingly mature and widely adopted, providing valuable support for the quality and efficiency of dental diagnosis and treatment. It to a certain extent reduces the reliance on clinical experience and can provide technical support and assistance for the rapid growth of young doctors, promoting technological homogenization in grassroots dental diagnosis and treatment in China.
At the same time, digital technology-assisted chairside treatment in dentistry is gradually becoming possible, reducing the number of patient visits and offering a more patient-friendly treatment experience. With the deep integration of digital technology and dental medicine, the production of various dental prostheses and auxiliary treatment devices using CNC machining and 3D printing technology has become an important application area of digital technology in dentistry. The emergence of various new “digital dental materials” has attracted attention from dental professionals, becoming one of the important directions in dental material science.
From the perspective of material formation, dental materials can be divided into non-preformed materials (such as impression materials, filling materials, bone powder, adhesives, etc.), preformed materials (such as orthodontic brackets, implants, artificial teeth, etc.), and custom-formed materials (including casting, hand-bending, machining, 3D printing, etc.). Among them, materials related to digital technology generally refer to CNC machining (also known as subtractive manufacturing) materials and 3D printing (also known as additive manufacturing) materials in custom-formed materials, which can be further categorized into metal materials, resin materials (polymeric compounds), ceramic materials, etc.
Generally, industrially preformed materials (blocks, discs, etc.) have more homogeneous materials and better mechanical properties than casting processes. 3D printing technology has high raw material utilization, is environmentally friendly, and has advantages in batch production, especially suitable for complex shaping processes. Its mechanical performance is comparable to casting and has become one of the key technologies in industrial manufacturing.
The following sections provide a detailed overview of the classification of digital dental materials based on material types and processing methods, systematically outlining the mechanical properties of various types of related materials and the digital processing characteristics, aiming to provide guidance for the clinical application and selection of digital technology-related materials. From a biomimetic perspective, all types of dental restorative materials should be close to the performance of natural tooth tissues to avoid stress interruption (shielding) and achieve a continuous and reasonable stress distribution.
1. Digital Dental Ceramic Materials
Digital dental ceramic materials are currently mainly processed by cutting and grinding (Numerical Control). Cuttable dental ceramic materials mainly include feldspathic ceramics, glass ceramics, alumina ceramics, zirconia ceramics, glass-infiltrated composite ceramics, etc. Feldspathic ceramics and glass ceramics belong to glass-based ceramics, with good translucency and aesthetics, able to mimic the optical properties of enamel and dentin, and are mostly used for anterior aesthetic restorations.
Multilayer or even sculpted prefabricated ceramic blocks allow for excellent aesthetics in fully anatomical restorations produced by cutting, simplifying or even replacing traditional manual veneering steps to some extent. However, glass-based ceramics have lower fracture resistance and higher brittleness, so strict adherence to indications is necessary during clinical use. Highly dense polycrystalline zirconia ceramics, represented by zirconium oxide, have developed rapidly and can be directly machined into anatomical-shaped restorations made of full-contour zirconia, presenting distinct technological characteristics.
There are two methods for processing zirconia restorations using dental CAD/CAM systems: one is to cut fully sintered zirconia, and the other is to cut presintered zirconia followed by secondary sintering. Each of these techniques has its strengths: fully sintered zirconia is very hard, but direct machining is costly; presintered zirconia offers high cutting efficiency, but there is usually about 20% material shrinkage during secondary sintering, making it the mainstream processing technology.
Zirconia ceramics exhibit high strength, and by adjusting the yttrium content, their translucency can be improved for high-translucent restorations, such as full-contour zirconia crowns in the molar region and implant superstructures (abutments, frameworks, restorations, etc.). Multilayered gradient biomimetic zirconia ceramics have also made significant progress, better meeting the physiological needs of dentistry. Zirconia ceramics can also be used for implants and abutments to avoid shortcomings of titanium (aesthetics, etc.).
Dental ceramic materials have made preliminary progress in 3D printing technology in China, obtaining national medical device registration certificates, and clinical application research is ongoing (Medical Device Registration 20223171660). Dental ceramic 3D printing technology achieves nearly 100% raw material utilization, is environmentally friendly, and offers advantages in batch processing, making it an area worth focusing on for research.
2. Digital Dental Composite Resin Materials
Composite resin is a reinforced polymer compound composed mainly of organic resins and inorganic fillers. In recent years, the application of nanofillers has led to the development of a new type of composite dental restorative resin material reinforced with ceramic nanoparticles, significantly improving the performance of composite resins. These materials have properties close to glass ceramics, also known as resin-based ceramics.
These resin-based ceramics are mainly divided into two categories: one involves adding inorganic fillers to the resin matrix, and the other involves adding resin to the ceramic network structure. Resin-based ceramics have excellent load-bearing capacity and fatigue resistance, along with an elastic modulus similar to composite resin and dentin. They exhibit excellent cutting machinability, but from a medical device registration perspective, these materials strictly do not belong to ceramics, and their wear resistance is not as good as true ceramic materials. Currently, resin-based ceramics used clinically follow the same standards of color and types as dental ceramics, often named as “certain ceramics” (such as Vita Enamic, Katana Avencia, etc.).
Cuttable composite resins used for CNC machining are industrialized preformed resin materials for indirect restorations. Typically in rectangular resin blocks or circular resin discs, they offer excellent machinability without the need for secondary firing, thus outperforming materials clinically cured by light polymerization in terms of performance. Composite resin materials can be used in various indirect restorations in dental clinical settings, such as inlays, veneers, dental crowns, etc., for rapid chairside production, as well as in pediatric deciduous crown pre-fabrications (especially in general anesthesia procedures). Their wear resistance is much lower than ceramics, close to the hardness of natural teeth, and they have special indications in clinical use, such as in pediatric dental restorations, geriatric dental restorations, transitional restorations, etc.
Light-curable composite resins suitable for 3D printing are composite resin liquids containing photosensitive materials, used to produce diagnostic or working models, various resin restorations (temporary dentures, denture baseplates, etc.), and various surgical guides (implant guides, orthodontic appliance guides, tooth extraction guides, bone harvesting guides, bite guides, etc.), meeting the clinical needs.
Currently, light-curable resin 3D printing technology has significantly improved in printing speed and accuracy, with ultra-fast light-curable resin 3D printing technologies such as selective area light-curing technology (LCD) and continuous digital light manufacturing technology (CDLM) being capable of chairside printing dental models or guides within 15 minutes, providing strong support for chairside digitalization in various dental disciplines (restorative, orthodontics, pediatric, implantology, etc.). The main mechanical properties of various dental composite resins.
3. Digital Dental Metal Materials
Metal materials used for dental restorations mainly include medical nickel-chromium alloy, cobalt-chromium alloy, gold alloy, titanium alloy, and pure titanium. The CNC machining technology of metal materials is relatively mature, with processing equipment having up to 5 or 7 axes, high processing precision, and the ability to process complex surface forms (such as personalized implant bases, edentulous implant restoration frameworks, etc.), mainly used for making copings, personalized abutments, denture frameworks, implant bridges, as well as orthodontic or pediatric space maintainers.
Metal 3D printing is a rapidly developing important direction, directly processing metal powders to form various dental restorations or components, with significant advantages such as high efficiency, high precision, high stability, good material physicochemical properties, environmentally friendly processing environment, low long-term costs, and batch processing advantages (a single run can process up to 200 metal crown restorations), among others.
Selective laser melting (SLM) is one of the main metal 3D printing technologies, capable of producing very dense metal parts with strengths exceeding or equalling those produced by conventional casting methods. It can currently be used for processing various surgical guides, metallic orthodontic auxiliary devices and retainers, as well as personalized implant components (such as titanium mesh, titanium plates, artificial joints), showing promising prospects. Pure titanium is a biocompatible metal material suitable for dental restoration requirements. Personalized titanium meshes and plates for implants or jawbone reconstructions are commonly produced using 3D printing technology, as compared to machining processes, considerations need to be made for heat dissipation and oxidation during processing.
4. Other Digital Dental Materials
Traditional wax materials that are custom-made into dedicated blanks can be used for mechanical cutting, and a mixture of light-curable liquid materials can be used for 3D printing. The wax restoration models generated through processing are similar to composite resin materials and can be used for diagnosis, treatment planning, or casting models. Usually, CAM technology offers higher processing accuracy and efficiency than manual production. Polyetheretherketone (PEEK) is a new material that has gained attention in the dental field in recent years. PEEK material is characterized by high temperature resistance, corrosion resistance, wear resistance, acid resistance, and good cutting machinability, making it suitable for 3D printing.
PEEK resin is a semicrystalline polymer with mechanical strength similar to human bone tissue and good biocompatibility. It has been used to produce various orthopedic implants (such as hip joints, intervertebral discs, femurs, etc.). In the field of dentistry, PEEK material has been used to make dentures, frameworks, implant bridges, children’s removable retainers, bite guards, etc. Its wear resistance is lower than ceramics, and its hardness is close to natural teeth, with specific indications in clinical settings such as pediatric dental restorations, geriatric dental restorations, transitional restorations, etc.
5. Outlook
Appropriate dental materials directly affect the aesthetic results and long-term success of dental treatments. Dentists should pay attention to and understand the mechanical properties of these commonly used dental materials and the digital processing characteristics to achieve optimal clinical indications. From personalized implantable metal 3D printing to personalized ceramics or resin restorations that match individual needs (such as strength, wear resistance, etc.), to 3D printed ultra-thin ceramic restorations for surface enhancement, multi-colored integrated processing materials (such as full-mouth dentures, removable partial dentures), biologically active 3D printed materials for tissue engineering, and time-related 4D biomaterials, etc., it is believed that with the continuous development of dental material technology and digital processing technology, the two will mutually promote each other, leading to the development of new dental digital materials with the goals of aesthetics, biomimicry, and functional gradients.
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