Rapid manufacturing produces custom lingual orthodontic appliances.

In the past, the path to perfectly aligned teeth meant a smile marred by a mouthful of metal brackets and wire. A solution to this problem is to hide the braces on the inside of the teeth, but this simple idea poses unique challenges and difficulties.

T.O.P. Service for Lingualtechnik GmbH, Bad Essen, Germany, overcame those challenges with its unique approach incorporating custom appliances produced with rapid manufacturing technology.

Lingual (tongue side) orthodontic appliances are mounted on the inner surfaces of the teeth and require precise bracket positioning and high precision in the brackets' archwire slots. Because the appliance is on the inside, the lingual brackets must have a smaller profile to avoid discomfort or speech impairment.

In 2001, T.O.P. Service introduced custom lingual brackets, which are designed patient-by-patient and tooth-bytooth to deliver precision and control for improved results and patient comfort.

Each orthodontic appliance requires up to 16 brackets. The lingual brackets measure 0.200 x 0.118 x 0.079 in. (5 x 3 x 2 mm) and have only a 0.016 in. (0.4 mm) wall thickness. Production of these small, detailed brackets is complicated by the archwire slot. Measuring only 0.018 x 0.025 in. (0.46 x 0.64 mm), the archwire slot must be extremely precise.

To aid in rapidly manufacturing the brackets, T.O.P. Service selected the ModelMaker II system from Solidscape, Merrimack, N.H., for creation of investment casting patterns.

Over the past four years, the company has expanded its operations to include eight Solidscape T66 Benchtop systems, which enables it to deliver 150 custom-made orthodontic appliances each week.

Production of lingual appliances begins with malocclusion models cast from impressions of the patient's teeth. One model becomes the setup after it is manipulated to align the teeth to the target positions. This setup is reverse engineered with a white light scanner (Fig. 1) to create a digital model that is loaded into T.O.P. Service's design software. Selecting from a library of brackets, T.O.P. Service technicians position the brackets and adjust their features for optimal results (Fig. 2). The bracket design is output as an STL file for building patterns for investment casting.

[FIGURE 1 AND 2 OMITTED]

The T66 Benchtop, which can build with 13 micron (0.0005 inch) layers, constructs the bracket patterns with proprietary thermoplastic ink jetting technology. The thermoplastic, which has wax-like properties, is deposited as small droplets. For precise layer thickness and flatness, a cutter mills the horizontal plane. When complete, the patterns are post processed by dissolving the support material and wiping off any debris.

Next, cast pipes are attached to the patterns, and the casting tree is assembled. The tree is embedded in a "speed plaster" to create the investment casting shell. The shell is heated to 1,274F (690C) to burn out the patterns, and then dental gold is cast into the investment.

After cooling, the shell is broken away to yield the metal brackets (Fig. 3). The runners (cast pipes) are removed, and the brackets are tumbled in a polishing compound to smooth the surfaces.

[FIGURE 3 OMITTED]

To complete the process, the brackets are mounted to the malocclusion model (Fig. 4), and a transfer tray is cast. T.O.P. Service's rapid manufacturing process, from treatment planning to shipment of the lingual appliance, takes only 10 to 15 days.

[FIGURE 4 OMITTED]

Select No. 002 at www.moderncasting.con/info