The CAD in CAD/CAM

CAD design software's powerful tools continue to expand.

By Patrick Bever, and Chris Brown, BSEE

As many dental laboratories consider adding CAD/CAM processes to their production workflow, understanding the difference between the two should be the first line of business. CAD is computer-aided design, and CAM is computer-aided manufacturing. CAD involves the use of a computer and software to digitally design a part. CAM software is used to take that design and manufacture it, either by milling or printing. Laboratories using CAD software are often referred to as design centers because they are strictly designing restorations. Milling centers typically use both CAD and CAM software.

Dental CAD software is most associated with designing crown-and-bridge substructures and full-contour restorations. However, in recent years, the design software has evolved to include custom implant abutments, removable prostheses, and orthodontic appliances.

Case Management

Nearly all CAD software programs have an integrated case management/tracking system. Instead of technicians relying solely on traditional case pan colors or shelf placement to identify case status, software case management screens provide icons such as notepaper (case entered), scanners (case scanned), or teeth (case designed) to identify case status.

Case entry typically involves entering the doctor’s name, patient’s name, restoration type, material, shade, and tooth number into a “record.” That record becomes part of a database that holds information on every case processed. Some case management modules also support case entry and access from multiple computers on a network. For busier laboratories and milling centers, administrative staff can enter cases, allowing technicians to focus on case processing rather than data entry.

Because case information is retained in a database, it is usually very easy to search for specific details. Finding cases with certain types of restorations, materials, or even previous cases for the same patient can be quite simple to locate. The low cost and small physical footprint of hard drives these days make long-term storage of cases far easier to manage.

CAD Software and Scanners

Before a computer and software (CAD) can be used to design restorations, the model has to be available in a digital form by one of the following three methods:

• Method 1: A digital impression from the 3M LAVA™ C.O.S. or Cadent iTero™ dedicated systems, or from the Sirona Cerec^® AC Connect or the E4D Dentist acquisition units.
• Method 2: A 3-dimensional (3D) scan of a poured model from a traditional impression.
• Method 3: A direct scan of a traditional impression.

For doctor-scanned digital impression cases, most CAD programs include a software utility to import scan files. This utility is usually part of the Case Management module and often will automatically populate all of the necessary case information into the case record.

For cases where a model or impression must be scanned, most CAD software programs are bundled with a 3-D scanner interface. Once a case is entered into the “Case Management” module, the scanner interface can be used to digitize the model.

Restoration Type and Materials

Restoration type and materials are normally selected during case entry. This means selecting from simple copings (uniform thickness), anatomical copings with specified cutback for porcelain, bridge frameworks, full-contour, custom abutments, and removable frameworks. Once selected, pre-configured design parameters, such as cement gap, are loaded into the case.

Case Design

Case design may be the most intimidating part of the process for many technicians. However, it is not as difficult as it might seem. There is a digital equivalent for every step that technicians usually go through during a case. Below are common features of today’s typical crown and bridge CAD software.

Insertion Path

Every CAD program provides the ability to set the insertion path for a restoration. Many programs propose an optimal insertion path to provide minimal undercuts. A graphical representation of the undercuts based on the insertion path is provided. However, be aware that sometimes, in order to minimize undercuts, the proposed insertion path may create an undercut on the margin. It is actually a great example of why software still needs a technician to operate it.

Blocking Out Undercuts

Early versions of CAD software required manual blocking out of undercuts. Just about all CAD programs today automatically block out undercuts with a click of a button or check of a checkbox.

Margin Identification

Each CAD software program provides a utility to identify the margin. Some programs auto-detect the margin, while others may require the user to click a point on the margin and the software detects the rest. All programs allow for manual editing of the proposed margin. With a computer screen providing an effective 25x to 50x magnification of the trimmed die, margin identification takes a new turn in terms of accuracy.

Cement Spacer, Margin Reinforcement

Painting of die spacer is no longer necessary with CAD software. Cement gaps are now defined in software and loaded automatically with each case. While the terminology may vary, most programs provide the ability to specify the cement spacer thickness near the margin, and specify different thicknesses on the walls and occlusal surface. If a given preparation or doctor requires a more passive fit, it is only a click of the mouse to increase the default cement gap settings.

A term that may be new to some dental laboratories is “margin reinforcement.” The margin, being at the edge of the coping and with minimal thickness, is the area most prone to chipping or damage during the milling process. To improve viability, additional thickness is added to the margin to strengthen it during milling. The additional material can be specified in thickness, height, and angulation. The milling center should be contacted for the optimal settings for their mills and materials. While the margin reinforcement feature is helpful during milling, it must be manually removed afterward as part of the margin-finishing process.

Shaping and Sculpting

Each CAD software program provides various tools to shape and sculpt restorations. The tools range from a digital equivalent of a waxing pen to a scaling tool that allows entire surfaces to be stretched or compressed. Most technicians usually find a preferred digital tool to achieve a desired effect.

Libraries

An exciting feature of most CAD software programs is that they support library teeth from which a technician may choose when designing full-contour restorations. Some programs support the creation and use of a personal tooth library, while others are limited to libraries supplied by the software supplier.

Virtual Articulation

Another exciting feature in recent releases of CAD software is virtual articulation. Often this feature is integrated with the scanner module, but it should become more mainstreamed, particularly with the increasing popularity of chairside scanners. Virtual articulators allow for programmable protrusive and excursive movements to enable technicians to see occlusal interferences and design accordingly.

Abutments

Custom abutment design is relatively new in today’s mainstream CAD software packages. In most cases, a scan locator must be scanned by either the doctor or the laboratory scanner to identify the precise location of the implant. The same sculpting and shaping tools are used to design the abutment. One advantage some programs offer is the ability to design the custom abutment and the substructure or final restoration simultaneously. This can improve turnaround time because the restoration is being fabricated at the same time the abutment is being milled. Simultaneous design also improves fit and accuracy because the abutment does not need to be scanned.

Removable Prostheses

CAD software for removable prostheses is also relatively new. While some programs are dedicated to removable design, others are traditional crown-and-bridge design programs with added removable design modules. Many of the designs tools are the same, just adapted for the specific requirements of designing denture frameworks.

Conclusion

CAD software gives laboratories the ability to design their own restorations or substructures. It distributes design responsibilities to the laboratories that are most familiar with their client’s preferences while leveraging the milling center’s manufacturing capacity and efficiency to produce more restorations in a shorter period of time at a lower cost. Laboratories designing their own restorations often save $20 per unit compared to typical milling center scan/design/mill pricing. That can be a significant cost-savings over a year.

Which CAD software is best for your laboratory? Consider the cost of the scanner and software. Look at the volume of production and types of restorations anticipated over the next 2 years. Make sure that the software supports the types of restorations you produce and that the initial purchase price and maintenance fees are manageable.

About the Authors

Chris Brown, BSEE, is the manager of the Apex Dental Milling in Ann Arbor, Michigan

Patrick Bever is an Advanced CAD/CAM Dental Technician at Apex Dental Milling in Ann Arbor, Michigan.