Introduction to CAD/CAM Techniques

  • CAD/CAM stands for Computer-Aided Design and Computer-Aided Manufacturing.
  • CAD/CAM systems are technologies used to plan and produce prostheses with the aid of a computer.
  • Developed in the 1960s primarily for the aircraft and automotive industries.
    • First CAD/CAM dental restoration was produced by Dr. Francois Duret in 1983.
    • In 1987, Mörmann and Brandestini discovered the CEREC system, which was the first dental system combining digital scanning with milling units.

Components of CAD/CAM Systems

  • Every CAD/CAM system consists of three primary components:
    1. Digitalization Tool:
    • Responsible for collecting data from the prepared teeth area, along with adjacent and opposing areas.
    • Utilizes intra-oral or extra-oral scanners that convert physical manifestations into virtual impressions.
    1. Software:
    • Processes the collected data and, depending on the application, produces a dataset to facilitate fabrication of the product.
    1. Production Technology:
    • Transforms processed data into the final desired product.

Evolution of Dental Impressions

  • Despite advancements in impression materials, conventional methods remain uncomfortable for patients and time-consuming for clinicians.
  • The introduction of CAD/CAM technologies in the late 1980s and developments in intra-oral scanning over the past two decades have presented alternatives to traditional impressions.

Types of Imaging Technologies in Optical Scanners

  • Four types of imaging technology currently employed:
    1. Triangulation
    2. Parallel Confocal Imaging
    3. Active Wave Front Sampling
    4. Three-Dimensional In-Motion Video
    • These technologies determine the measurement speed, resolution, and accuracy of the scanner.

Intra-Oral Digital Impression

  • Also known as Direct Digital Impression.
  • Replicates the intra-oral situation using a 3-D camera to capture data in digital format, leading to the generation of a virtual model.
  • Restoration designs are based on this virtual model, and manufacturing is completed with a milling machine.
    • Direct intra-oral digital impressions are more precise than conventional impressions, minimizing errors.
    • Benefits include time-saving and elimination of several steps:
    • At the dental office: Tray selection, material dispensation, impression disinfection, and impression shipping.
    • At the dental lab: Plaster pouring, die cutting, trimming, articulation, and extra-oral scanning.
    • Digital impressions enhance patient comfort and increase treatment acceptance, especially for patients with gag reflex issues.
    • Reduces distortion and offers enhanced 3-D pre-visualization of tooth preparation.

Limitations of Intra-Oral Digital Impression

  • Considerations include:
    • Finish line location, periodontal health, saliva flow rate, and sulcus bleeding can affect accuracy.
    • The camera only captures visible structures; anything obscured by saliva, blood, or soft tissue may be inaccurately recorded.
    • Accessibility for the scanner wand is crucial; limitations may occur in retro-molar regions, especially in patients with restricted mouth opening.

Extra-Oral Digital Impression

  • Known as Indirect Digital Impression or Die Scanning Technique.
  • A laboratory procedure requiring a conventional stone model to initiate the CAD/CAM process:
    • Procedure: An initial clinical impression is taken, and after pouring the impression, the cast model is scanned using an optical or mechanical scanner.
    • A 3-D virtual image is displayed, allowing restoration design from the digital data obtained.

Data Processing Software

  • The computer unit includes software for visualizing scanned data, planning, and designing restorations on-screen.
  • Data is collected in Standard Transformation Language (STL) or Standard Tessellation Language format.
  • The software allows for the design of various dental restorations:
    • Examples: Veneers, inlays, onlays, individual crowns, bridges, copings, and partial denture frameworks.
  • Once the restoration design is complete, the CAD software converts the virtual model into commands for the CAM unit, leading to fabrication.

Computer-Aided Manufacturing (CAM)

  • The final stage of CAD/CAM can be divided into two main manufacturing techniques:
    1. Subtractive Manufacturing
    2. Additive Manufacturing
    • A hybrid technique combining both methods is also utilized.

Subtractive Manufacturing Technology

  • Based on milling a product from a block using a Computer Numeric Controlled (CNC) machine.
  • CAM software converts the CAD model into a tool path for the CNC machine:
    • This includes computations and commands dictating CNC milling operations.
    • Classification of milling units:
    • Based on axes: 3-axes, 4-axes, or 5-axes devices.

Processing Techniques in Subtractive Manufacturing

  • Classifications based on processing technique:
    • **Dry Milling:
    • Used primarily for zirconium oxide blanks with low pre-sintering to prevent moisture absorption.**
    • **Wet Milling:
    • Involves cool liquid spray to protect tools during milling and is applied for metals, glass ceramics, and pre-sintered zirconium oxide.**

Additive Manufacturing Technology

  • Also known as 3D Printing, this technique creates physical objects directly from 3D CAD data:
    • Adds material (liquid, sheet, wire, or powder) layer-by-layer to form parts.
    • Advantages include:
    • Nearly 100% material utilization.
    • Reduced production times.
    • Exceptional geometric design freedom.