Page 563 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 20.5 Direct Manufacturing and Rapid Tooling 543

CASE STUDY 20.l lnv|sal|gn® Orthodontic Allgners

Orthodontic braces have been available to straighten The Invisalign product uses a combination of
teeth for more than 50 years. The braces involve advanced technologies in the production process,
metal, ceramic, or plastic brackets that are bonded shown in Fig. 20.16. The treatment begins with an
adhesively to teeth with fixtures for attachment to a orthodontist or a general dentist creating a polymer
wire, which then forces compliance on the teeth and impression of the patient’s teeth (Fig 20.16a). These
straightens them to the desired shape within a few impressions then are used to create a three-dimensional
years. Conventional orthodontic braces are a well~ CAD representation of the patient’s teeth, as shown in
known and successful technique for ensuring long- Fig. 20.16b. Proprietary computer~aided design
term dental health. However, there are several software then assists in the development of a treatment
drawbacks to conventional braces, including the facts strategy for moving the teeth in an optimal manner.
that (a) they are aesthetically unappealing; (b) the Once the treating doctor has approved the
sharp wires and brackets can be painful; (c) they trap treatment plan and it has been developed, the
food leading to premature tooth decay; (d) brushing computer-based information is used to produce the
and flossing teeth are far more difficult and less aligners. This is done through a novel application of
effective with braces in place; and (e) certain foods stereolithography. Although a number of materials
must be avoided because they will damage the braces. are available for stereolithography, they have a
One solution is the Invisalign system, made by characteristic yellow~brown shade to them and
Align Technology, Inc. It consists of a series of aligners, therefore are unsuitable for direct application as an
each of which the person wears for approximately two orthodontic product. Instead, the Align process uses a
weeks. Each aligner (see Fig. 20.15) consists of a stereolithography machine that produces patterns
precise geometry that incrementally moves the teeth to of the desired incremental positions of the teeth
the desired positions. Because the aligners can be (Fig. 20.16c). A sheet of clear polymer is then
removed for eating, brushing, and flossing, most of the thermoformed (see Section 19.6) over these patterns
drawbacks of conventional braces are eliminated. to produce the aligners, which are sent to the treating
Furthermore, since they are produced from a orthodontist. With the doctor’s supervision, patients
transparent plastic, the aligners do not seriously affect are instructed to change the next set of aligners every
the person’s appearance. two weeks.

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FIGURE 20.l5 (a) An aligner for orthodontic use, manufactured by a combination of
rapid tooling and thermoforming. (b) Comparison of conventional orthodontic braces
with the use of transparent aligners. Source: Courtesy of Align Technology, Inc.