The Right Cut

The Right Cut | Image Credit: © Andriy - stock.adobe.com

Whenever they find themselves in a pickle and need help getting out of the jar, James Bond and Batman can always turn to their trusty gadgets. Whether it’s Bond’s laser watch, pen grenade, or a tricked-out Aston Martin, or Batman’s smoke pellets, Batarang, or Batmobile, there is always a gizmo.

While not a matter of life or death, dental labs are faced with a range of options when it comes to machining and tooling, given different materials and applications. Finding the best tool depends on a variety of factors that lab owners must keep in mind.

Familiar Faces

In the lab, the tools used by milling machines to carve shapes out of materials share a common form factor.

“Most of these tools are made out of tungsten carbide,” Chris Urist, president and partner at Primotec USA, notes. “That’s the best-quality raw material to use. Different machines have different sizes and dimensions of tools, but for example let’s just say the most common mill is a Roland Mill, and those have a 4-mm shank diameter where the chuck holds the tool. The first tool that the machine will grab is a roughing tool, which is the biggest tool, and removes the most material the fastest.”

The machines that do the heavy lifting of CAM work are the mills themselves.

“First and foremost, you need the mill,” Lisa Aguirre, dental marketing manager at Roland DGA, says. “It’s like if you want to print something at home, you must have a file to send and a device to send it from, but you need a printer to produce the print. It works the same way for dental milling, where the mill creates the final product.”

Milling machines work in wet or dry capacities, depending on which material is used and what is being produced.

“The type of hardware you use is going to depend on the type of product that you’re looking to produce,” Aguirre says. “For example, if you’re producing zirconia or dentures—or for anything removable—you’re looking at a dry milling solution. Whereas if you’re using a glass ceramic material, a lithium disilicate, or a custom titanium abutment, things of that sort, you’re going to be looking for a wet milling solution.”

“There are a variety of mills out there that handle multiple materials,” adds Matt Viens, CAD/CAM training supervisor, Zahn Dental. “Some of the major manufacturers include Roland DGA, VHF, Amann Girrbach, Imes, and imes-icore. Each major manufacturer typically has 1 model dedicated to milling wet-milled materials only, then other models that are suitable for milling multiple materials. This includes dry-only mills or mills that can function as a wet and dry combination. For these combination mills, the best rule of thumb regarding matching the hardware to the materials is to stick to milling either wet or dry materials for as long as possible within the production workflow, before having to switch over to the other.”

While there are mills that can handle both wet and dry applications, they tend not to be very efficient.

“The process of having to clean out the mill between materials can be tedious and time-consuming,” Viens says. “Not to mention that if not done correctly, it can and will lead to premature wear and tear on the integral parts of the mill itself. With wet-only mills, it is imperative to keep up with required daily cleaning and maintenance routines to ensure that any additional buildup is not going to cause issues with the normal function of the equipment. With dry-only mills, vacuuming and minimizing the amount of debris left within the milling chamber will help to reduce the influence that the particles can have on the units being milled and on parts of the mill itself. In short, keeping up with cleaning and maintenance is key, no matter the material type.”

Architectural Considerations

Labs also have the opportunity to select tools and equipment based on whether they can interoperate with other manufacturers’ products. Those pieces of hardware and equipment that work only with a single manufacturer’s products are said to be “closed architecture.” On the other hand, those that can work with other vendors’ offerings are said to be “open architecture.”

“Our solutions at Roland DGA are all open architecture,” Aguirre notes. “This allows you the freedom to choose your preferred materials, whereas a closed system would limit you to using the particular materials approved for that unit. Open architecture means that from scan to design to the actual milling of the material, it’s open, so if a new material comes out on the market tomorrow—as long as it’s FDA validated or 510(k) certified—you would be able to mill that material, whether it be wet or dry, depending on the solution you’re working with. Using a milling solution with open architecture is a good way to ensure you are getting the most bang for your buck.”

There are, naturally, pros and cons to each architectural philosophy. Supports of closed systems tout their solutions as more predictable and reliable. Open systems, on the other hand, allow for more flexibility.

“Obviously, with open architecture solutions, you’re going to have more restorative options and more possibilities as far as materials and also with tooling,” Aguirre says. “As far as materials, for example, if you’re working with a closed system, you may only have 5 or 6 materials to choose from, whereas from a laboratory standpoint, there may be a better material out there that would better suit this case, based on the patient’s function or other variables. With an open milling system, the laboratory would be able to offer that other material to the clinician as a recommendation for their patient.”

There doesn’t seem to be a strong pull, one way or the other, as far as which type of system is most prevalent.

“It’s still 50/50,” Aguirre adds. “For instance, 3D printers. They’re about 50/50 right now. You have some companies that believe if they lock you into materials, hardware and software, it’s a more controlled production environment.

“My background is clinical,” she continues. “I always talk to clinicians about avoiding becoming a cookie-cutter practice. You don’t want a consultant that’s going to come in and cookie-cutter your practice with that solution. You want to be able to make the best decisions for your patients based on their unique situation, because no 2 mouths are the same. It’s like a fingerprint, whether it be the bite, the anatomy, the function, whether they have dry saliva vs more of a wet mouth, or the foods they eat. I could go on and on, but closed architecture really narrows down your options. You’ll see it even more on the 3D printing side, because they’re basically forcing you to buy their consumable materials as well.”

Doing It All

Can any one machine do it all? That is, can a lab get by with just 1 mill that can handle wet and dry cases? The answer is a resounding, “It depends.”

“There are hybrid milling machines which mill both wet and dry,” Aguirre says. “At Roland DGA, we don’t presently manufacture hybrid machines, only because it requires a significant amount of maintenance when you go from wet to dry. Take zirconia milling as an example. If zirconia dust were to enter the milling chamber, because they’re milled in the same chamber, and there’s any amount of moisture left in that machine, which happens more often than you’d think, and you start milling zirconia, you’re going to have concrete in your mill. Anybody who’s ever touched zirconia dust knows what I’m talking about. It is fine. It makes a mess. So obviously, it’s not something that’s meant to be wet milled, unless it’s fully sintered, and there are not too many of those products available.”

Tools seem to be best used with a specific material.

“There is no such thing as an all-purpose tool,” Viens says. “There are tools, like carbide tools, that can handle a variety of materials such as zirconia, wax, polymethyl methacrylate (PMMA), and other types of ‘soft’ materials. But due to their composition, these tools are not suited for lasting a long time and they degrade faster than specialized tools for the particular materials. Typically, carbide tools are the cheaper option among the tools available. Therefore, the versatility and advantage of such a tool is quickly overrun by the constant need for replacement. Tools are designed and produced to be effective and efficient against specific materials. Though it may cost more to run multiple sets of tools to cover the variety of materials, the cost over the long run is greatly lessened due to their durability.”

While tools may be able to handle different materials, they can wear faster if they’re not used properly.

“You can have 1 tool that does everything, but that’s one of the least efficient ways of milling, because again, if it’s just that carbide material, it’ll be fine for wax and PMMA. It’s OK for zirconia, but not great,” Urist says. “It does not last very long. And most people are milling zirconia out of their machines the majority of the time. So, with zirconia, we—and most manufacturers—recommend a diamond coating. That diamond coating will make the tools last way longer for milling zirconia; it could be up to 10 times as long as a carbide tool. So, it is more expensive, but it’s a higher-quality coating. It just really makes the surface and the sharpness of that edge last a long time. But that’s specifically for zirconia milling. If you were to go and start milling another material, like PMMA with that, it does not last quite as long.”

Mistakes

Labs can extend the life and the function of their tools by avoiding some common mistakes.

Using the correct tooling for the job tops Aguirre’s list.

“The No. 1 mistake, I would say, is not using the proper tooling,” Aguirre says. “Tooling is so important to the success of the milling job. I think in our industry, a lot of times we don’t put a lot of emphasis on it, but using the right tools and using quality tools are really, really important in the long run. Again, our systems are open, so they can use any appropriately sized tool—and there are a lot of them out there. We can guarantee our Roland DGA, DGSHAPE tools are authentic; they’re high quality. Sometimes users think that they’re saving money by using less expensive tools—kind of the no-name knockoffs. We see these cheaper brands in implant parts, tools, and materials. And they’re less expensive for a reason. There is value in using quality tools and making sure that you’re using the right tools for the job.

“There are actually 3 things to keep in mind when choosing your tools,” she continues. “The first one is, are you using quality tools? Because if you don’t use quality tools, you’re going to be swapping those tools out much more frequently. And that’s something that in any mill is going to require an actual technician to do. Those frequent replacements eat into your profits, reducing your [return on investment] and increasing your overhead. Typically, lower-quality tools also break more frequently, and not when they’re supposed to. Maybe the tool has this many hours and maybe it’s getting close to its estimated lifetime. Lower-quality tools can be unpredictable, which can also cost lab owners time and money.”

Tools, Aguirre adds, should be appropriate for the material being milled.

“The second question to ask yourself is, are you using the right tools for the material that you’re milling?” she says. “For example, are you trying to mill zirconia with a PMMA tool or vice versa? More often than not, when we see chipping in zirconia, for example, we’ll see users using carbide tools. Although there is an indication for using carbide tools, the best tool to mill zirconia with is a diamond-coated tool. And then same thing for PMMA. You’ll see somebody saying, ‘Oh, I don’t know why this tool keeps breaking,’ and they’re milling a PMMA puck with a diamond tool, which is not the right tool for that application.

The third consideration is paying attention to your CAM software. CAM software will always tell the user what tool slot each tool belongs in,” she continues. “Sometimes while setting up their milling session, people are so busy clicking that they may not notice that something changed, because each setup is based on the design that’s created. It’s best to always take the time to ensure that your tool setup mimics what you see on your screen and your CAM software.”

There are several variables at play when it comes to selecting the right tool for a given material and job.

“Relative to tools, the most common issue is putting the wrong tool size in the wrong slot or labeling the tool in that slot incorrectly in the CAM software,” Viens adds. “For example, placing a 1-mm bur in the placement where a 2-mm burr is meant to be or mislabeling a 1-mm bur as a 2-mm bur in the CAM software. Some mills are able to detect the type of bur and will let you know that the wrong one is in the current slot and allows for you to correct this error. But other mills or software are only as capable as the information that is input into them. So, the mill assumes that the correct bur is in the correct slot, and when it goes to mill it either breaks the bur or overmills certain areas because of the difference in size.”

“I would recommend that [dental labs] use a different tool for their different materials,” Urist adds. “Some labs will just use the carbide tools, and they’ll use it for everything that they’re milling. And again, they are the least expensive, but they won’t be the most efficient and cost-effective over the life of the tool. So, if you had one set for zirconia, a diamond coated set, and then another set for the other stuff you’re milling—PMMA and wax—it may be more up front of a cost for them, but it will help them in their tool longevity over the life span of that set of tools.”

He also advises labs to be mindful of bur coating materials.

“There are diamond coatings for zirconia, but there are other coatings as well,” Urist adds. “We make a gold coating for metal milling. Different coatings add different hardnesses to the tool, and they just help milling different materials. So, we have a Blue Line coating, which is good for PMMA and PEEK, and then a Gold Line, which is good for metals. Finding the right tool for the right material really just helps with the longevity of the tool.”

Price

Tooling costs are, of course, important. And while it may seem that the lab will get a longer life out of a more expensive tool, Urist observes that there may be cases where it’s more efficient to buy less expensive tools and chalk up frequent replacements as more efficient for the business.

“It might go in the other direction in that labs will just want to use a set of diamond tools and they’ll end up using that for everything,” Urist says. “But in that case, it would make more sense to also buy a less expensive set of tools for the other materials that you’re milling that don’t need that coating. So, if they mill a lot of PMMA or wax, for example, then there’s no need to buy that more expensive coated tool. It just really depends on the material they’re looking to mill, because I would always recommend a diamond-coated tool for zirconia but not for other materials. But again, there are different types of diamond coating, and they can find much less expensive ones that are manufactured in China or India, but usually the coating isn’t quite as good as other coatings that are done here in the US or in Germany, for example. And that, honestly, doesn’t always depend on where it’s manufactured or what tools you’re using. A lot of it also depends on the CAM software and the strategy that they’re using. Two different labs might have the exact same milling machine and using the exact same tools, but they have one as a strategy from Company A and one strategy from Company B, but Company A’s will be much faster. They will be able to mill a crown out in, let’s say, 12 minutes, and then Company B will sell you one that takes 20 minutes. And typically, when this is the case, the lab that’s milling with Company B, the tools are lasting way longer. They’ll get hundreds of hours out of a tool, and Company A will get, let’s just say, half the amount of time out of a tool. And again, that just depends on the strategy that’s being used in basically how hard and fast that tool is working. There’s no right or wrong answer, because some labs just say, ‘I don’t care. I’d rather go through tools a lot faster and have these crowns milled out in 10, 12 minutes, because we’re a production lab and we need to pump these units out.’ And others would say ‘I’d rather have a higher-quality milled restoration and have the tools last a lot longer.’ So, there are many different variables, but really the longevity comes down to the CAM strategy and how fast you’re manufacturing your parts.”

More expensive does not always mean better.

“The most expensive tool is not always the best option,” Viens says. “You have to look at the yield of the product relative to its cost. If it is able to produce similar-quality units as cheaper burs but last a great deal longer, then it may be worth it. If it cannot match the quality but lasts longer, then it may not be the best option. As mentioned before, the carbides are going to be the cheapest to start out with, but they will not last the longest. The diamond-coated tools or similar are specifically engineered to last longer and are better suited toward all budgets, both in cost and effectiveness.”

Dental labs’ tools may not be quite as cool as James Bond’s or Batman’s, but there is always the right tool for the job.