Industry Insights: No Separators, Perfect Fit — The Future of Banded Appliances

Banded orthodontic appliances are experiencing a major evolutionary leap. Enabled by selective laser sintering technology, software-aided appliance design and the proliferation of intraoral scanning technology, 3D-printed metal bands and appliances will become a core offering in a short period of time. Because of its impact on part quality, clinical workflows and laboratory operations, laser sintering technology is poised to be the future of metal orthodontic appliances. Traditionally banded appliances are deeply woven into the fabric of orthodontic practice, and the fabrication of these appliances requires acceptance of otherwise unavoidable drawbacks.

Traditional bands require separation, and thus some form of associated chair time and scheduling for the patient. This component of the banding workflow can be eliminated with laser sintering if a band does not require access to interproximal areas. A further challenge is introduced when a traditionally banded appliance is to be made in a laboratory, rather than in the office. Traditional bands interact with interproximal areas, but also regularly proceed subgingivally. Both requirements force a laboratory technician to modify areas of a stone model that are obscured to them. This creates potential error and leads to seating and fit issues.

One strategy employed to mitigate this issue is fixating already-fit bands into an impression. This method requires chair time to fit the band, and a high degree of accuracy and durability when fixating the bands in the impression. Even slight errors in fixation or disturbances during shipping will create difficulty with seating and fit. Another imperfect solution is to use scans to size bands. While this improves success when choosing a band size, it does not solve the primary issue facing technicians: concealed anatomy.

To directly address these concerns, a hypothetical appliance must require no separators, interact with only the anatomy that is visible in an impression or scan, and achieve a fit equal to a custom-fit band. Laser sintering can yield such an appliance.

Selective laser sintering (SLS) is not a new technology, but its application in orthodontic appliance manufacturing has become relevant very recently. SLS has seen applications in the crown, bridge and removable partial denture spaces for years, where it has been used to manufacture frameworks. The process uses a thin bed of cobalt-chrome (CoCr) powder spread over a metal build plate. Then, a laser selectively melts each layer of the intended device, fusing it to the previous layer, all in an inert atmosphere.

Once the parts have been grown, significant processing is required before they are ready for delivery. The parts remain attached to the build plate (Fig. 1) and are placed into a heat-treatment oven to relieve thermal stresses from the sintering process. After stress relief, the parts are separated from the build plate and support structures are removed. The bands and frameworks can then be smoothed and polished in preparation for assembly of the final appliance. Several smoothing steps are required, which can be performed either by hand or using isometric finishing.

Fig. 1

Laser sintering requires a large capital investment compared with traditional skilled fabrication, but despite this, laser sintering will become more common and accessible as the technology matures in dentistry.

The overall quality of an appliance with sintered components is superior to traditionally banded devices

To harness additive manufacturing, parts must be designed digitally. Design software allows experienced lab technicians to translate years of traditional bench experience into digital fabrication. Using a scan imparts a greater level of accuracy, but more importantly, it also allows the design of a custom band without the laborious process of a wax-up and casting. Technicians can adapt the shape of a band to visible tooth surfaces only (Fig. 2), which eliminates the most common sources of fit issues.

Fig. 2

Sintering can be wielded to fabricate entire space maintainers, bonded lingual retainers, expander frameworks and any other component requiring rigidity and strength (Fig. 3). Any components requiring precise placement in relation to tissue can be designed to stay low-profile while avoiding impingement. Additionally, any traditional components assembled onto a sintered framework are easily laser-welded, ensuring a strong connection.

Fig. 3