Various Factors Affect Quality of CAD/CAM Custom Abutments
Process requires good software, hardware, and FDA compliance
By Calvin Shim
Computer-aided design (CAD) and computer-aided manufacturing (CAM) have significantly changed and impacted the dental industry’s approach to restorative treatment. The evolution of automated technologies used in dental prosthetics now allows even the smallest of dental laboratories to manufacture CAD/CAM restorations that were once only feasible from major milling centers or corporations. Today, laboratories of all sizes can digitally design and mill full-contour crowns and bridges, wax forms for casting, even custom implant abutments. The historical barriers to entry have always been the capital investment required to purchase the equipment, the technical proficiency to operate and maintain both the equipment and software, and, in the case of in-house milled custom implant abutments, FDA compliance.
Julian Osorio, DMD, pioneered CAD/CAM custom abutments. In 1993, working with MIT engineers, he was the first to file a patent detailing a CAD/CAM custom abutment manufacturing system that made it possible for practitioners and technicians to achieve predictable, superior esthetic results, while eliminating the complexity associated with traditional implant solutions.1 Three years later, Osorio founded Atlantis Components Inc., now owned by DENTSPLY Implants. The company uses technology that is exclusive to its products and is still a leader in the marketplace. Today, advancements in CAD software and sophistication in milling technology have produced an endless list of companies in the industry that offer commercially available CAD/CAM abutment design software, milling machines, and milled custom implant abutment services.
Currently, the two primary types of CAD/CAM-milled, patient-specific abutments being manufactured are full titanium abutments and hybrid zirconia abutments with a titanium base.
Several factors impact the quality of digitally designed and milled patient-specific abutments, including CAD software, CAM software, milling machine technology, availability of qualified dental abutment design technicians, and FDA compliance.
CAD/CAM Software
Results can vary significantly depending on which abutment design software is used. Some CAD platforms have limitations in terms of abutment shape, contouring, and sharpness. Others handle particular types of abutment cases better than their competitors. Each CAD software program has its strengths and weaknesses. Only through experience and the knowledge to use the right software program for the specific type of case being fabricated will consistent great results be achieved.
Some manufacturers of milling machines offer advanced CAM software that can range in price up to $12,000, with the functions and tools varying drastically depending upon the monetary investment made. As with purchasing most anything else, the more you pay, the more you get. Many of the advanced capabilities that are required to produce quality abutments, regardless of the material being milled, are not available in the lower-cost machines (Figure 1 and Figure 2). Ultimately, what software you choose impacts the quality of the end product.
For example, milling titanium in a high-production environment requires high-level resolution in the positioning of the milling tool. Without a software program that can position the milling tool for this high-level smooth movement, the end results are not ideal (Figure 3 through Figure 6). CAD/CAM technology is not as plug-and-play as many people might assume. Using advanced CAM software, marginal detail can be inspected and corrections made before the actual milling process begins.
Milling Machines
The machine used for milling custom implant abutments also greatly impacts abutment quality. While some might believe any milling unit can consistently mill quality abutments, many limitations exist in terms of milling power, consistency, accuracy, and maintenance. If you are milling titanium abutments, for example, spindle power is extremely important. The torque and movement resistance of the spindle greatly impacts the finely milled quality of the abutment surface and also impacts the longevity of the spindle. The other important factor to keep in mind when milling metal is the type of motor that is powering the unit. Lower-cost machines use step motors, which feature a high probability of drift. If the motor is not strong enough to push to position 3 and can only achieve position 2.8, the entire tool path after this point of drift will be incorrect. More robust milling machines use very powerful servomotors with encoders that are capable of detecting drift as it happens and modifying milling tool paths to adjust for discrepancies.
A Matter of FDA Compliance
One of the primary barriers to entry and points of confusion in the industry is the matter of FDA compliance as a medical-device manufacturer. Although further clarification may be forthcoming, according to the FDA at press time, a facility is considered a medical-device manufacturer, regardless of the material being milled, if it is either using CAD/CAM technology to create an entire abutment including the implant/abutment interface, or CAD/CAM milling a custom abutment from a blank that already has the implant/abutment interface on one end. Medical-device manufacturers fall under FDA regulation, meaning they must be registered with the FDA and must have 510(k) clearance for milling such devices. This registration requires full compliance with 21 CFR 820 Quality Management System and can be extremely costly and time-consuming to achieve. Compliance requires quality checks, staffing, documentation, verification, training, maintenance, and audits.
The FDA makes a distinction between hand milling and CAD/CAM milling of implant abutments. There are no abutment blanks with or without the implant interface/abutment interface or titanium-base abutment blanks that have been cleared for CAD/CAM milling custom abutments. There are abutment blanks that have been approved for hand milling. This technical difference often causes confusion and misunderstanding.
Currently, Sirona Dental is the only CAD/CAM software and system that has been 510(k) cleared for milling the top half of a titanium-base, 2-piece zirconia hybrid abutment system using only Sirona CAD/CAM equipment and materials. The equipment and materials can be purchased and utilized by any laboratory without obtaining a 510(k) clearance. Other CAD/CAM systems have been cleared for the design only of the abutment, but milling must be completed at a 510(k) cleared milling facility.
Reference
1. Meet Dr. Julian Osorio – Boston Cosmetic Dentist. Osorio Dental Group. https://osoriodentalboston.com/dr-julian-osorio-boston-cosmetic-dentist/. Accessed August 27, 2015.
Calvin Shim is Managing Director of CreoDent Prosthetics in New York, NY.
