Fantastic Voyage: Take a trip though the research and development process of orthodontic appliances by Mark Payne

Header: Fantastic Voyage
by Mark Payne

Let's go on a journey—an adventure, if you will—into a fascinating world where small, intricate and often complicated assemblies are created. Orthodontic appliances, minute in their structures yet precise and eminently functional, are fashioned from an alchemy of exotic metal alloys, interesting chemistries, the algorithms of virtual reality and the ingenuity of progressive thinkers (both orthodontists and engineers).

The research and development department at Henry Schein Orthodontics (HSO) deploys several innovative technologies, including 3-D appliance design and virtual testing, additive printing, slow-motion videography and advanced manufacturing techniques. Each progressive step of the technological engineering process infuses another layer of precision into appliance design and fabrication.

Together, these technologies realize three specific goals: to bring innovative, high-quality orthodontic appliances to market, to do so more quickly than ever before, and, perhaps more importantly, to offer a high degree of confidence that the appliances will perform effectively from their initial launches, not in their second or third generation.

We're about to go behind the scenes at HSO to observe how the engineering team applies methodologies to design, test and manufacture orthodontic appliances. When I compare the technology we've incorporated into the research and development process with how companies operated when I started in the business more than 25 years ago, I wonder how we managed without these tools. (Try remembering how you functioned before you had a smartphone: It's hard to recall, isn't it?)

Step 1:
Virtual simulation and testing
The initial design phase has a kind of "animation" feel to it. While computer-aided design (CAD) has been a standard in engineering for decades, being able to test CAD designs in a virtual world using finite element analysis (FEA) has been a game-changer. FEA has been generalized to a wide variety of engineering disciplines, all the way to the testing of bridges and airplane wings, where stress analysis predictions are life-and-death issues.

At HSO, the FEA software allows engineers to foresee in the virtual world how a particular oral-appliance design will react to real-world physical effects such as stress, strain, heat and vibration. They can simulate on computers the pencil-chewing, ice-crunching machinations of patients to determine where such real-life stresses would concentrate on an appliance. Once they understand those stressor locations, they can enhance the design to mitigate the probability of product failure.

In the past, engineers would have to do tedious calculations by hand, or use digital spreadsheets to determine theoretical stresses and strains in predetermined locations in any particular product design. They'd then perform bench tests on appliances once they were in prototype form, several weeks and many thousands of dollars into the development process. And if an appliance prototype didn't measure up in real-world bench testing, the process had to start all over again. This trial-and-error methodology was costly and time-consuming. FEA software allows them to avoid many weeks—sometimes months—of work and considerable expense to discover this valuable information. Its efficiency enables engineers to analyze design features for the greatest assurance that they'll launch to exacting standards while shortening lead time to introduction.

When the FEA of where a product showed greatest stress in the virtual environment is compared with real-life bench testing of a prototype, the prototype consistently mimics the FEA predictions (Figs. 1a–b). I call it "no-surprises" engineering.

That said, although FEA is dependably accurate, it's not the end-all, be-all. It's still critical for engineers to test all appliances under real-life conditions to ensure real-world functionality and strength. But we're not there yet—the next step is to create an enlarged scale model of the design.

Fig. 1a

Fig. 1a: A 3-D CAD model of Henry Schein Orthodontics’s Carriere SLX bracket, with the door in the closed position. The arrows indicate pincers that will need to spring or flex over the lollipop when moving between the open and closed positions.
Fig. 1b
Fig. 1b: The virtual finite element analysis of the door shows the maximum deflection the pincers will need to move when opening and closing the mechanism. This FEA proved that the door would operate like a coplanar spring and not take a permanent set during operation.

Step 2:
A 3-D printed oversize model
Once the engineers have drafted and satisfactorily tested a design in the virtual environment, they upload the 3-D CAD file to the additive printer (often called a 3-D printer). Additive printing/manufacturing has become the standard of care in dentistry for prostheses, dental models, partial dentures, and crown and bridge applications.

Additive-printed, enlarged-scale models are another essential aspect of HSO's appliance design and manufacturing process. The time and savings garnered from using this method is phenomenal. In the past, it took a highly skilled machinist somewhere between a week and a month to fabricate a conventional scale model, depending on the complexity of the appliance. The additive printer makes an appliance in roughly 16 hours. HSO typically starts a print job at the end of a workday and, with the printer working overnight, the scale model is ready the next day.

The enlarged-scale model—usually five to 15 times actual size, depending on needs (Figs. 2a–2d, p. 32)—is constructed one layer at a time, with each pass of the 3-D printer head adding roughly 0.0006 inch of material. (For comparison, a typical human hair, at 0.003 inch, is five times as big.) By this means, additive printing offers exacting, high-resolution scale model fabrication.

Looking at a 3-D design on a flat computer screen pales in comparison to being able to hold a model of an appliance in your hands. To touch and manipulate actual parts is vital to evaluating the interaction of complex assemblies (e.g., in a self-ligating bracket), as well as gauging overall functionality and tolerances. It's like the difference between watching a video of someone and interacting with him or her in person.

Step 3:
Slow-motion video analysis
For many years, movie directors have used slow motion to turn chaotic scenes into things of beauty. Videographers can now shoot with great clarity things that were once too fast for film—think of the slow-motion capture of a bullet piercing a plank in some action/adventure movie. For HSO, slow-motion video is another indispensable tool in the engineering process.

Slow-motion video cameras capture images at an exceedingly fast rate—from 120 frames per second (fps) all the way up to 10,000 and even 100,000 or more fps. When the video is played back at a rate friendly to the human eye—24 to 30 frames per second—slow motion is born. An action that was filmed at 300 fps for 1 second will last approximately 10 seconds in slow-motion playback. (A camera that takes 10,000 fps was likely used to capture that gunshot impact into a plank.)

HSO uses slow-motion cameras to slow the quick action of real-world appliance bench testing to see definitively how a mechanism functions or fails when stressed, and whether the FEA virtual-world stress analysis was predictive (Figs. 3a–b). Slow motion is particularly useful in observing failure modes of appliances and the actuation of mechanisms. For example, it's nearly impossible to see the fast movement of a spring mechanism that might be used in a self-ligating bracket while it's being activated and deactivated. Utilizing this technology provides the opportunity to observe, in close-up conditions and precise detail, how a mechanism functions, deforms or fractures. This priceless information allows engineers to iterate through final designs efficiently, which means they get new products—that function as planned—to the market more expediently than ever before.

Fig. 2a

Fig. 2a: A 15x scale model of the SLX self-ligating bracket, still on the build table
Fig. 2b
Fig. 2b: The 3-D printed model of the bracket, immediately out of the additive printer, with a penny to show scale
Fig. 2c

Fig. 2c: Enlarged scale models are essential in gauging overall appliance functionality and tolerances. This shows the SLX bracket, with door closed.
Fig. 2d
Fig. 2d: The bracket, with door open

Step 4:
Manufacturing with injection molding
When I think back to the beginning of my career, when orthodontic manufacturing was synonymous with machined parts, I marvel at the tremendous complexity and inflexibility of that process. Machining is an outmoded means of high-volume production that can be very labor-intensive, yielding boxy brackets with sharp edges. It entails multiple machining operations performed in separate manufacturing cells, followed by joining and assembly processes. The sharp edges machining produces necessitates tedious tumbling procedures that take hours to soften the brackets.

HSO uses metal injection molding (MIM) and its counterparts, plastic injection molding (PIM) and ceramic injection molding (CIM), for fabricating brackets and most intraoral appliances. MIM involves developing a mixture of finely powdered metal, a binder and a plasticizer (to facilitate molding) that compose a "feedstock." This feedstock is capable of being injection-molded into small, complex parts. MIM combines the material flexibility of powder metallurgy with the design flexibility of injection molding. The molds are made from hard, wear-resistant materials that allow for a high number of production cycles before they need to be refabricated. CIM and PIM utilize a similar process with different feedstock materials.

The advantages of injection-molded manufacturing are legion. MIM, PIM and CIM are the perfect technologies for manufacturing high-volume-production small orthodontic parts. They offer virtually unlimited design freedom to form complex parts and intricate geometries—including undercuts, bores, threads and blind holes—while minimizing the need for costly joining and assembly operations. There's significant material flexibility, relatively low production costs (aside from the considerable expense of the initial molds) and short production cycles by utilizing the legions.

Moreover, injection molding offers smooth surface finishes right from the mold, with rounded contours on all planes that reduce archwire binding, improve efficiency and enhance patient comfort and satisfaction (Figs. 4a–b). The importance of rounded contours—specifically at the entrance to the archwire slot—cannot be emphasized enough, because they eliminate archwire notching, which is the greatest contributor to friction in an orthodontic system. Injection-molded manufacturing represents the culmination of a cutting-edge technological engineering process that serves to shorten lead time in bringing orthodontists the most advanced appliances in the industry.

Fig. 3a

Fig. 3a: The virtual-world FEA of the Carriere Motion CL III appliance being subjected to 2.5 times more load than it would ever be expected to endure. Doing this reveals the points most vulnerable to stress at such extreme conditions.
Fig. 3b
Fig. 3b: Slow-motion video captures the moment the appliance fractured, at the location predicted by the FEA.
Important note: These images reflect a load of over 50 pounds being applied virtually and in the real-world bench test. One goal is to ensure that while in the oral cavity, the appliance would debond long before it would actually break.
Fig. 4a

Machined bracket
Fig. 4b
HSO Maestro MIM Bracket

If you've been an orthodontist for any length of time, you understand how apprehensive certain clinicians have been about adopting first-generation orthodontic appliances, which all too often have been problematic because of limitations in engineering and manufacturing processes. The state-of-the-art technologies in HSO's research and development are designed to give its engineers confidence that the products they introduce will function effectively at launch—giving you, the orthodontist, confidence that the smiles you create are not only gratifying to you, your staff and the patients themselves, but will become an ongoing referral source to keep the practice growing.

When I talk with doctors about HSO's latest technologies and take them on a tour through the manufacturing facility, their intrigue and fascination makes me shake my head in wonder about how we ever got along without these methods. It also fuels my anticipation of groundbreaking products we hope to introduce in the not-so-distant future!

Dr. Samuel L. Bobek As director of engineering for Henry Schein Orthodontics, Mark Payne is responsible for the development of new product innovations and manufacturing engineering for the company. He has over 25 years of experience in the orthodontic profession, including 18 years at Ormco, where he moved through the ranks to become the director of product and process development. He was at the forefront in the development of patient-specific appliances, with numerous patents to his credit. Payne is an accomplished technical leader, with claim to many successful inventions in both the medical device and consumer markets. He earned his degree in manufacturing engineering from California Polytechnic University in Pomona, California.

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