A wide range of polymers are commonly used for various applications in prosthodontics. Polymethyl methacrylate (PMMA) is commonly used for prosthetic dental applications, including the fabrication of artificial teeth, denture bases, dentures, obturators, orthodontic retainers, temporary or provisional crowns, and for the repair of dental prostheses. Additional dental applications of PMMA include occlusal splints, printed or milled casts, dies for treatment planning, and the embedding of tooth specimens for research purposes. The unique properties of PMMA, such as its low density, aesthetics, cost-effectiveness, ease of manipulation, and tailorable physical and mechanical properties, make it a suitable and popular biomaterial for these dental applications. To further improve the properties (thermal properties, water sorption, solubility, impact strength, flexural strength) of PMMA, several chemical modifications and mechanical reinforcement techniques using various types of fibers, nanoparticles, and nanotubes have been reported recently. The present article comprehensively reviews various aspects and properties of PMMA biomaterials, mainly for prosthodontic applications. In addition, recent updates and modifications to enhance the physical and mechanical properties of PMMA are also discussed.

Prosthodontic Applications of Polymethyl Methacrylate (PMMA): An Update.

Objective To review materials available in computer-aided design/computer-aided manufacturing (CAD/CAM), their various properties and accuracy are compared to conventional materials/methods when available. Overview CAD/CAM in dentistry is constantly growing and becoming a user- and patient-friendly technology and service using intraoral scanners and laboratory/chairside milling units to manufacture dental restorations and appliances from multiple materials including wax, metals, composite resins, and ceramics. Properties of these materials may vary when compared to restorations prepared from conventional and additive manufacturing methods. Understanding the differences in these properties is important for material and fabrication method selection. Additive manufacturing is becoming an alternative to subtractive manufacturing in many applications. However, chemical composition, mechanical and physical properties of these materials are still lacking. 3D printed materials require a considerable amount of research and time to prove their clinical efficacy. Conclusion The current developments in, and possibilities of, CAD/CAM technology is exciting and is transforming restorative dentistry. With all this excitement, it is crucially important to ensure that proper testing and evaluation of the various materials are warranted before making definite claims and decisions to replace conventionally prepared materials. Clinical significance CAD/CAM materials are versatile and emerging as the material of choice for many restorations and appliances. For recently introduced CAD/CAM materials, it is important to ensure that proper clinical- and research-based evidence confirming the success and durability of these materials are available before recommending them in patient care.

Materials in digital dentistry-A review.

Purpose To evaluate and compare the mechanical properties (flexural strength and surface hardness) of different materials and technologies for denture base fabrication. The study emphasized the digital technologies of computer-aided design/computer-aided manufacturing (CAD/CAM) and three-dimensional (3D) printing. Materials and methods A total of 160 rectangular specimens were fabricated from three conventional heat-polymerized (ProBase Hot, Paladon 65, and Interacryl Hot), three CAD/CAM produced (IvoBase CAD, Interdent CC disc PMMA, and Polident CAD/CAM disc), one 3D-printed (NextDent Base), and one polyamide material (Vertex ThermoSens) for denture base fabrication. The flexural strength test was the three-point flexure test, while hardness testing was conducted using the Brinell method. The data were analyzed using descriptive and analytical statistics (α = 0.05). Results During flexural testing, the IvoBase CAD and Vertex ThermoSens specimens did not fracture during loading. The flexural strength values of the other groups ranged from 71.7 ± 7.4 MPa to 111.9 ± 4.3 MPa. The surface hardness values ranged from 67.13 ± 10.64 MPa to 145.66 ± 2.22 MPa. There were significant differences between the tested materials for both flexural strength and surface hardness. There were also differences between some materials with the same polymerization type. CAD/CAM and polyamide materials had the highest flexural strength values. Two groups of CAD/CAM materials had the highest surface hardness values, while a third, along with the polyamide material, had the lowest. The 3D-printed materials had the lowest flexural strength values. Conclusions Generally, CAD/CAM materials show better mechanical properties than heat-polymerized and 3D-printed acrylics do. Nevertheless, a material's polymerization type is no guarantee of its optimal mechanical properties.

Comparison of Mechanical Properties of 3D-Printed, CAD/CAM, and Conventional Denture Base Materials.

Purpose CAD/CAM complete dentures have increased in popularity and a wide variety of systems are currently available. These prostheses present many advantages for clinicians, technicians and patients. Subtractive manufacturing is used by most of the available systems while a few manufacturers use an additive manufacturing technique. This article describes the currently available systems and materials available for the fabrication of CAD/CAM complete dentures and reviews the literature relative to their physical properties. Methods A comprehensive review of the literature was completed to enumerate the currently available techniques to fabricate CAD/CAM complete dentures and discuss their physical properties. A search of English language peer-reviewed literature was undertaken using MEDLINE and PubMed on research articles published between 2000 and 2019. A hand search of relevant dental journals was also completed. Results The literature indicates the physical properties of CAD/CAM milled poly(methylmethacrylate) or PMMA as it is commonly described is superior to conventionally processed PMMA for the fabrication of complete dentures. Conclusion The incorporation of CAD/CAM technology into complete denture design and fabrication streamlines the clinical and laboratory processes and provides improved physical properties that enhance denture quality.

CAD/CAM Complete Denture Systems and Physical Properties: A Review of the Literature

Statement of problem High flexural strength is one of the desirable properties for denture base resins, yet only few studies have evaluated the physical properties of newer denture bases such as computer-aided design and computer aided manufacturing (CAD-CAM) milled products. Purpose The purpose of this in vitro study was to compare the flexural strength of 3 different types of denture base resins: compression molded, injection molded, and CAD-CAM milled. Material and methods Three groups (n=10) of acrylic denture base resins were tested: injection molded, compression molded, and CAD-CAM milled resin. ISO-compliant, rectangular specimens were fabricated (64×10×3.3 mm) (n=30). Specimens were stored in water for 1 week, and flexural strength was measured by using a 3-point bend test until failure. The Student t test was used to evaluate differences in the flexural strength and modulus of elasticity among specimen groups. The Bonferroni formula was used to set significance at α=.017 to account for multiple comparisons among the 3 groups. Results The flexural strength of the CAD-CAM milled group was significantly higher than that of the other 2 groups (P Conclusions CAD-CAM milled denture bases may be a useful alternative to conventionally processed denture bases in situations where increased resistance to flexural strength is needed.

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Flexural strength of denture base acrylic resins processed by conventional and CAD-CAM methods.

Purpose The introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) technology to the field of removable prosthodontics has recently made it possible to fabricate complete dentures of prepolymerized polymethyl methacrylate (PMMA) blocks, which are claimed to be of better mechanical properties; however, no published reports that have evaluated mechanical properties of CAD/CAM PMMA. The purpose of this study was to compare flexural strength, impact strength, and flexural modulus of two brands of CAD/CAM PMMA and a conventional heat-cured PMMA. Materials and methods 45 rectangular specimens (65 mm × 10 mm × 3 mm) were fabricated (15 CAD/CAM AvaDent PMMA specimens from AvaDent, 15 CAD/CAM Tizian PMMA specimens from Shutz Dental, 15 conventional Meliodent PMMA specimens from Heraeus Kulzer) and stored in distilled water at (37 ± 1°C) for 7 days. Specimens (N = 15) in each group were subjected to the three-point bending test and impact strength test, employing the Charpy configuration on unnotched specimens. The morphology of the fractured specimens was studied under a scanning electron microscope (SEM). Statistical analysis was performed using one-way ANOVA and Tukey pairwise multiple comparisons with 95% confidence interval. Results The Schutz Dental specimens showed the highest mean flexural strength (130.67 MPa) and impact strength (29.56 kg/m2 ). The highest mean flexural modulus was recorded in the AvaDent group (2519.6 MPa). The conventional heat-cured group showed the lowest mean flexural strength (93.33 MPa), impact strength (14.756 kg/m2 ), and flexural modulus (2117.2 MPa). Differences in means of flexural properties between AvaDent and Schutz Dental specimens were not statistically significant (p > 0.05). Conclusions As CAD/CAM PMMA specimens exhibited improved flexural strength, flexural modulus, and impact strength in comparison to the conventional heat-cured groups, CAD/CAM dentures are expected to be more durable. Different brands of CAD/CAM PMMA may have inherent variations in mechanical properties.

A Comparison of the Flexural and Impact Strengths and Flexural Modulus of CAD/CAM and Conventional Heat-Cured Polymethyl Methacrylate (PMMA).

Purpose
To compare surface properties of 2 brands of pre‐polymerized resin blocks for complete dentures (CAD/CAM PMMA) to conventional heat‐polymerized PMMA.
Materials and Methods
A total of 45 rectangular specimens (25 × 25 × 3 mm) were fabricated from 3 brands of PMMA (n = 15/group): AvaDent CAD/CAM PMMA, Tizian‐Schutz CAD/CAM PMMA, Meliodent conventional PMMA. Specimens were examined for wettability using the sessile drop method, surface roughness using a digital contact profilometer, and microhardness using Vickers hardness number. Statistical analysis was performed using one‐way ANOVA and Tukey pairwise multiple comparisons. p‐Values of ≤0.05 were considered significant. 
Results
AvaDent specimens demonstrated the highest mean contact angle (72.87 ± 48°) and the highest mean Vickers hardness number (20.62 ± 0.33). The conventional heat‐polymerized specimens showed the highest mean surface roughness (0.22 ± 0.071 μm). Tizian‐Schutz specimens showed the lowest mean surface roughness (0.12 ± 0.02 μm).
Conclusions
As CAD/CAM PMMA groups exhibited significantly more favorable surface properties in comparison to the conventional heat‐polymerized groups, CAD/CAM dentures are expected to be more durable. Different brands of CAD/CAM PMMA may have inherent variations in surface properties.

https://www.zora.uzh.ch/id/eprint/183156/1/37.pdf

Kawkab Y. Tahboub

Papers

A Comparison of the Flexural and Impact Strengths and Flexural Modulus of CAD/CAM and Conventional Heat-Cured Polymethyl Methacrylate (PMMA).

A Comparison of the Surface Properties of CAD/CAM and Conventional Polymethylmethacrylate (PMMA).