In a captivating presentation at the EAO Digital Days, Markus Blatz, Chairman of the Department of Preventive and Restorative Sciences at the University of Pennsylvania School of Dental Medicine, delved into the significance of manufacturing techniques in dental restorations. Focusing primarily on subtractive manufacturing methods, Blatz shared valuable insights into digital dentistry's evolution and the advantages of various materials and techniques.
Embracing Digital Technologies Blatz highlighted the University of Pennsylvania's commitment to integrating digital technologies into dental education. From pre-clinics to advanced clinical training, students are equipped with skills in intraoral scanning, digital restoration design, and appropriate material selection. The digital workflow encompasses everything from digital records and diagnostics, often utilizing AI technologies, to treatment planning and manufacturing.
Subtractive Manufacturing: Milling Techniques Subtractive manufacturing, particularly milling, remains a preferred method for creating dental restorations. Blatz emphasized the versatility of milling, which allows for the use of a wide variety of materials including ceramics, metal alloys, polymers, composite hybrid ceramics, acrylics, and waxes. The ability to mill from industrially fabricated blocks ensures homogeneity, reducing porosity and enhancing both physical and optical properties.
Milling machines vary from large laboratory-based systems capable of handling full-mouth constructions to smaller units suitable for in-office fabrication. Chairside milling machines offer significant advantages in terms of cost and speed, allowing for rapid production of restorations, often within minutes. For example, a zirconia crown can be milled and sintered in less than 30 minutes, enabling same-day restorations.
Advantages of Industrially Fabricated Blocks The industrial fabrication of blocks used in milling ensures greater homogeneity compared to conventionally mixed materials. This homogeneity leads to superior physical properties and improved optical qualities, as the more consistent material allows light to travel through it more effectively. Additionally, the smoother surface of milled materials reduces bacterial adhesion, as demonstrated in studies comparing CAD/CAM milled PMMA with conventionally fabricated PMMA restorations.
Challenges and Comparisons with 3D Printing While 3D printing holds promise for the future of dental restorations, Blatz noted that current technologies still fall short in precision and material stability compared to milling. For devices requiring high precision, such as full-mouth rehabilitations and implant frameworks, milling remains superior. Studies comparing CAD/CAM milled frameworks with cast frameworks showed significantly higher precision in milled zirconia and titanium bars.
The precision of milled abutments also surpasses that of conventionally cast abutments. Milled titanium abutments demonstrate higher accuracy and reduced bacterial adhesion compared to cast titanium, enhancing their biological compatibility. Similarly, zirconia abutments, popular for their aesthetic and biological benefits, show less soft tissue remodeling and bacterial adhesion.
Advancements in Zirconia Compositions Recent developments in zirconia compositions have introduced more translucent formulations with higher amounts of yttria and cubic particles. While these new zirconias offer improved aesthetics, they come at the cost of reduced flexural strength. Nevertheless, they remain stronger than silica-based ceramics. Studies have shown that milled zirconia, due to its manufacturing process, maintains superior physical properties compared to printed zirconia.
Biological and Aesthetic Integration The biologic properties of milled materials are crucial for successful implant restorations. Zirconia surfaces, when properly polished, exhibit excellent soft tissue adherence, reducing bacterial adhesion and promoting healthy tissue integration. The importance of surface topography was emphasized, with polished zirconia surfaces showing better soft tissue attachment compared to glazed surfaces.
Conclusion In conclusion, while the future may hold advancements in additive manufacturing, subtractive manufacturing methods currently provide the best combination of precision, material versatility, and biological integration. The high precision, reduced cost, and improved physical and optical properties of milled restorations make them the preferred choice in modern dental practice. As Blatz aptly summarized, what truly matters is delivering restorations that are aesthetic, durable, and biologically integrated, ensuring optimal patient outcomes.
Markus Blatz's insights underscore the importance of embracing digital technologies and the continued evolution of materials and techniques in dental restorations. His expertise and research provide a valuable guide for practitioners seeking to enhance their clinical outcomes through advanced manufacturing methods.