Tool Capacity and Types
As indications become more complicated, more tool types are needed to address new part features. For standard crown-and-bridge applications, ball-nose cutters handle a majority of the organic shapes that need to be milled. Any sharp corners on the inside of copings are compensated for in the CAD software. However, with laboratories and milling centers producing more implant-related parts in their own facilities, a need exists for flat end mills and drills to manufacture these geometric shapes. Some milling strategies for screw-retained bridges in titanium and chrome cobalt utilize as many as 10 tools, so without the respective capacity in a machine, these parts cannot be milled as a single job.
Another way to ensure the machine is effective at milling new applications is by integrating proper tooling for the job. A popular new request for in-house milling is full dentures in wax and PMMA. Regarding an acceptable milling time, denture bases present new challenges for machines currently on the market because they require a significant amount of material removal before finishing the surface area and tooth pockets. To most effectively do this, a tool that is uncommon to the dental market should be used — a single flute, highly polished end mill. This tool properly manages the increased chip load while removing a larger amount of material, and it will cut very cleanly without generating as much heat due to its sharper cutting edge.
As dental laboratories continue to push their production equipment’s capacities, machine manufacturers are looking for more ways to accommodate the increased usage. Automation is a great way to optimize workflow and efficiency. Denture base milling is a perfect example of how automation can significantly increase a laboratory’s ability to justify the added expense of an automatic blank-changer when choosing a machine. They are one of the largest parts being milled in-house, and in most cases they’ll take up a whole blank. Milling times can range from 30 minutes to four hours depending on the machine, CAM software, and desired surface finish.
This creates a unique new problem for laboratories that want to add the ability to mill multiple denture bases at one time. If the machine has already reached its full capacity during the day, the most opportune time to mill parts with longer milling times is overnight. However, because only one denture base can fit per blank, unattended blank changes are necessary to produce multiple parts each night.
Evaluating New Equipment
Popular milling indications being brought in-house by dental laboratories and milling centers include hybrid abutments with angulated screw channels, full-arch screw-retained hybrid bridges, denture bases, preform abutments, and titanium bars. Different machine features should be considered for each indication.
As previously noted, laboratories looking to add single hybrid abutments with angulated screw channels should look for either a 5-axis machine or the ability to use a fourth axis to mill the divergent occlusal direction.
Laboratories looking to add full-arch screw-retained hybrid bridges with titanium bases should look for a 5-axis machine that will address the potential for larger angulations; 25° or above is ideal.
To mill denture bases, investigate machines with slightly higher-powered spindles and faster movements to handle the increased amount of material removal and larger surface area finishing required for these types of parts. Another good consideration is an automation cell to enhance the unique workflow when the laboratory can only fit one part per 98.5-mm blank.
To mill preform abutments, look for a machine that effectively holds the preform blanks in quantities that make sense in a particular environment. For small laboratories that mill just a few abutments a day, a single blank holder is sufficient. However, some laboratories produce a large number of titanium custom abutments and would benefit from a six-blank holder and an automatic puck changer. In either case, a coolant or lubricant must be used. Industrial-grade features that add weight, power, and stability are also recommended.
To mill titanium bars, consider machines with similar attributes to preform milling equipment, but with an even higher level of accuracy and more tool positions. In these cases, additional weight and vibration dampening will also ensure that tool wear is acceptable and does not affect the fit.
Many factors must be considered when evaluating a new piece of CAD/CAM equipment. To ensure the most effective and impactful decision is being made, ask more questions. Don’t just ask which machine is the best fit. A laboratory needs to understand the hows and the whys of a new process before a purchasing decision can be made with confidence.
About the Author
Jordan Greenberg is Managing Director of FOLLOW-ME! Technology North America.