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CAD CAM Made Simple

As dentistry goes digital, CAD CAM will play an ever more prominent role in the way that prosthetic dentistry is carried out. But how does it work? What does it stand for? Two spanish students give you an introduction to this innovative technology.



In the past few years, the barriers of communication and success have been pushed with the help of technology. The field of dentistry is no exception. New technologies and methods have been developped to replace the analogue work flow. According to Van Noort in November 2011, computers are making artisanal task easier, faster, cheaper and more predictable. The final restoration made through the analogue sequence: impression – plaster pouring – trimming – lost wax technique – layering, includes a high risk of errors in each step. A fully digital workflow can overcome difficulties associated with conventional techniques through 3 steps:

  1. Digital Scanner

  2. Software to treat prosthesis data: CAD

  3. Computer data -> final prosthesis : CAM

Intraoral Scanner

The first step in the process of fabricating a restoration is the replication of the hard and soft intraoral tissues. A traditionnal impression is usually made with an alginate tray placed and maintained in the mouth of the patient during the setting time of the material (5-8 minutes). After desinfection, the impression is sent to the laboratory. This process typically involves discomfort of the patient and gag reflex. Dimensional variation due to setting expansion and contraction of the cast and die result in poor accuracy, often leading to the retake of the impression. In spite of their cost and learning curve, intraoral scanners are important tool in the digital workflow. After scanning, we obtain a computerized image with the details of the patient’s mouth. Some scanners can even also automatically detect the colour. Therefore, storage of plaster models and communication with the laboratory technician is improved. Digital impressions do not involve any materials and poor details areas can be rescanned specifically. The comfort of the patient is ensured by pausing the sequence of image capture (3-5 minutes per quadrant). However, the sum of images can lead to errors. Further studies are needed to assess IOS accuracy in full mouth rehabilitatation. Depending on the brand, sucessful scan may require a coating of the teeth or soft tissue. Powder spray enhances the quality of the image. A proper scanning would not be possible with saliva contamination. A cheek retractor and a tongue guard can be used in small patient or in children. More studies are also needed on children.

Extra-oral

Extraoral scanning can be used in a wide variety of dental applications. In the laboratory, the extra oral scanner reads the information on a cast. Two types of extra oral scanners exist : optical scanners, which scans with light, and contact scanners, touching the cast with a pin. Most of the laboratories have an optical one, as it is easier and quicker to use than the contact one, which is used for specific tasks such as implant reading.

In the dental clinic, static and dynamic occlusion can be analysed with facial extraoral scanners.

Facial scanning allow the virtual replication of realistic mandibular movement to diagnose temporomandibular joint diseases

CAD : Computer Aided Design

After the replication of the patient’s mouth, the next step is to design the future prosthetic. In the conventionnal technique, the design of the future prosthesis was dependant on the dental technician. With the loss wax technique, wax sprouts and metal framework sometimes did not match. In the digital workflow, a computer system is used to assist in the creation, modification, and analysis of a design. The dentist can simulate different treatment options and discuss it with the patient as the CAD technlogy allow to display the tissues in a 3D image system on screen. It is a more convenient experience for the patient, who can visualize their future restoration. With the computer aided design, the dentist or the technician design adjust the prosthesis parameters with the computer. The marginal line is highlighted digitally and can be modified if the software chooses it incorrectly. The thickness of the restoration is also managed digitally. Some programmes analyse and offer an objective support in shade match selection. The choice of the material is made during this step. To ensure functionnal occlusion, articulation in static and dynamic movement is assessed. Hua et al, evaluated the digital articulator as being as accurate as the analogue one.

CAM : Computer Aided Manufacture

Once the design of the restoration is complete, the manufacturing process can start. With CAM, the manufacturing process can be done through a milling, a substractive process ; milling, or laser sintering, an additive process.

With the laser sintering additive technique, cobalt chromium layers are added from scratch. It is a less expensive technique as there is no waste. The surface of the material is rough and allows more retention but tends to retain bacteria. With the milling process, material is substracted from a block of ceramic to obtain the final restoration. Results are precise and allow an accurate connection tooth-prosthesis. The lost of the material cannot be reused, contrary to the laser sintering. Its use is indicated in cases with restoration made of zirconia or lithium disilicate ceramic.

3D printing

Intraoral scanning takes the physical information of the mouth and transforms it into numerical data. This data can be then translated into physical information thanks to the 3D printer. This allows the cast to be printed by the technician, avoiding the physical transfer by the use of digital file or by the dentist. This cast can then be further analysed or be a base for wax ups or restorative purposes.

There are multiple uses of stereolitography. An application can carry out the printing of temporary complete denture for try in purpose and send to the laboratory as additional useful information. In implant placement surgery, the success requires detailed planning. Stereolitography allows to print 3D drill guide that help to place the implant with precise direction. According to Coachman, ideal gingival curve can be designed digitally and used during crown lenghtenning procedures. Incision of the soft tissue curve is made through the previously digitally designed gingival guide.

Conclusion

A digital workflow in dentistry have become increasingly popular in order to operate more efficiently. CAD/CAM increases the patient’s satisfaction and can be an ergonomic tool for the dentist. Reduced chair time and fewer number of visits contributes to improve patient satisfaction. Clinical outcomes are satisfatory both for the patient and dentist. Digital work flow can be used in restorative dentistry, implantology and orthodontics.

By using CAD/CAM, the fabrication of inlays, onlays, veneers, crowns, dentures, implant abutments and orthodontics appliances can be easier, quicker and more accurately carried out. In orthodontics, the possibility to obtain a following of the impression with a digital storage and the possibility to print them with 3D printers is of great interest. The transfer of the data offers a faster aligner treatment plan. Intra-oral scanned images can be integrated in a multidisciplinary open system, incorporating CBCT, facial scanner, and digital jaw motion record.

The concept of fully digital restorations open new horizons like the possibilty of using scanned natural teeth from a donator instead of handmade shape to offer more natural smile to patients. Natural shapes can then be adjusted to the patient’s face. Extraoral facial scanner datas and digital smile donor datas can be integrated on a programme to show the patients the final results. None of this would be possible in the analogue world. The future of dentistry is definitely a combination of the analogue and digital workflow, but it will be the digital technology driving it forward.

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