plan. Dental impressions are scanned in order to create a digital 3D representation of the teeth. Technicians move the teeth to the desired location with the program Treat, which creates the stages between the current and desired teeth positions. Anywhere from six to forty-eight aligners may be needed. Each aligner moves teeth .25 to .33 millimeters. A computer graphic representation of the projected teeth movements, created in the software program ClinCheck, is provided to the doctor and patient for approval or modification before aligners are manufactured. The aligners are modeled using CAD-CAM (computer-aided-design and computer-aided-manufacturing) software and manufactured using a rapid prototyping technique called stereolithography. The molds for the aligners are built in layers using a photo-sensitive liquid resin that cures into a hard plastic when exposed to a laser. The aligners are made from an elastic thermoplastic material that applies pressure to the teeth to move into the aligner's position. Patients that need a tooth rotated or pulled down may have a small, tooth-colored composite attachment bonded onto certain teeth. Since the form-fitted plastic used in clear aligners is not as rigid as the metal used in traditional braces, sometimes the flexibility in the materials need to be compensated in the areas that require movement. Alternatively, attachments may be used to facilitate movement by changing the shape of the tooth. More attachments can make the aligners less aesthetically pleasing. Reproximation, (also called interproximal reduction or IPR and colloquially, filing or drilling), is sometimes used at the contacts between teeth to allow for a better fit. Each aligner is intended to be worn an optimal 22 hours a day for one to two weeks. On average the treatment process takes 13.5 months, although treatment time varies based on the complexity of the planned teeth movements. The aligner is removed for brushing, flossing and eating. As clear aligners are made from plastic, they can be warped by hot liquids. While undergoing treatment you should limit your intake of hot liquids to protect the shape of your aligners and stop them from becoming stained. Once the treatment period has concluded, the patient is advised to continue wearing a retainer at night for the foreseeable future. When the Invisalign system was first developed, many of the aligner manufacturing processes were carried out by hand, and computer technicians had to modify each tooth in the computerized model individually. Brands Invisalign Invisalign is manufactured by