Proper Integration of Milling Machines and Services

Dental mills are distinguished according to the degree of precision that can be obtained in their final products. They range from 3 to 5 axes and can mill wet, dry, or both, depending on the milling machine. The precision is within the range of +/-50 microns to +/-5 microns, with an average repetition precision of +/-20 microns. Simple dental restorations, such as copings and routine dental prosthetics, can be milled utilizing a 3-axis milling machine. However, when complicated geometries and/or complex tool strategies are needed, enhanced milling axes are required. Implant abutments, implant bars, Prettau® bridge cases, and the like that require a sophisticated degree of geometric milling will demand the use of 5-axis milling machines to achieve the appropriate dimensions for creating the dental prosthesis. Some advanced milling machines have the ability to toggle between 3 axes for simpler geometries to 5 axes with the more sophisticated of milling needs. The range of price points for the different milling machines varies. Therefore, depending on the business’ model and clientele, an educated decision can be made as to which milling machine would best suit that laboratory’s needs.

Quality and durability is another imperative factor for choosing a milling machine. The amount of the machine’s output needs to be aligned with its build and quality in order to sustain appropriate output. Some milling machines are tabletop professional mills that can produce a significant output typically in line with most typical dental laboratories (Figure 2). However, if the business requires a continuous long output run, such as at a milling center, then an industrial milling machine may be better suited (Figure 3). Industrial milling machines are produced to have a high rate of output, including different features (discussed below) to effectively allow for an increase in output. The number of unit output the laboratory or milling center completes is directly correlated to the efficiency and longevity of the milling machine. Choosing a milling machine that would satisfy the output needs of the business today and the projected output of tomorrow is how to obtain long-lasting success. A milling machine that is not built for long runs should not be forced to produce high output rates. Doing this would diminish the viability of the machines and subsequently the ROI on the milling machine.

When contemplating the build of the milling machine, certain attributes are paramount when deciding the best fit for the specific business model. The milling mechanism is directly responsible for generating efficient outputs with regard to revolutions per minute (RPM) of the spindle and position/tool changer. Certain milling machines are manufactured with either belt-driven, magnetic, ball-screws linear guides, or manual spindles, by which the chuck is housed. Depending on the manufacturing milling mechanism, this will dictate the spindle’s RPM and maintenance protocols. To further illicit efficiency, many milling machines have enhanced attributes such as automatic blank changers and extensive multiple tool changers (Figure 4). The more robust these attributes, the greater and more efficient outputs can be generated without major human involvement. Greater efficiency outputs in the absence of human interaction provide an enhanced profit stream and a greater ROI for the milling machines. The price of these features has to be compatible with the business model and level of output. Such characteristics are incredibly relevant for a milling center, but perhaps not so for a smaller dental laboratory with significantly less output.

Physical space is yet another consideration when seeking the ideal milling machine. Milling machines are available as compact (tabletop), chairside, and floor (foot space). Again, depending on a laboratory manager or owner’s reflection of the business model, the appropriate milling machine will become apparent. Typically the chairside milling machine is among the most uncomplicated—it can mill simple restorations and requires little space. This milling machine is best suited for a small laboratory or dental office looking to do chairside milling. The chairside machines can be versatile, but limited to the attributes they possess because of the need to make these machines compact. These are typically found in small- to medium-sized dental laboratories or small milling centers. They are able to mill out most dental geometries and typically are equipped with either wet or dry capabilities or both (Figure 5). The larger, industrial-sized floor milling machines are incredibly versatile and can mill out an assortment of products. These machines with all their attributes require a bit more setup, but once operational, can create outputs at an efficient large-scale rate. The floor space required is significant, and these machines are best suited for a milling center that needs to produce high volume. The price points on these milling machines vary from entry-level chairside on the lower price point spectrum to the more expensive robust industrial multidisc changer.

Finally, when considering the last element prior to integrating a milling machine into the dental solutions of an existing business, some thought needs to go into the type of consumables or products that will be milled or offered through this technology. Not all materials can be milled in the same fashion; some require being in a clean, dry environment, while others require the use of a wet, lubricating, and/or cooling solution. The softer millable materials such as green-stage zirconia, wax, and PMMA need to be in a clean and dry milling environment, while the harder substances such as CrCo, titanium, and lithium disilicate necessitate the use of a cooling/lubricating solution sprayed onto the material and burs while milling. Some machines offer a dual-modality milling, whereby all materials may be used whether wet or dry. The downside is that many of these machines cannot be toggled back and forth between wet and dry within a daily cycle. If one is to mill dry, directly after a wet mill, or vice versa, often the dry materials will gunk the machine once wet, making for extra maintenance.

All milling machines are not alike, nor do they need to be because the products we provide our clients are not alike. A well-thought–out strategy to incorporate a digital solution in terms of milling solutions is imperative. Clearly understanding the ramifications of digital technologies as they pertain to the respective business model, clientele, and entity would help ensure optimal ROI and ease of integration into a business.

Daniel Alter, MSc, MDT, CDT, is a Professor of Restorative Dentistry at the New York City College of Technology, City University of New York in Brooklyn, NY.