Why Tooth Preparation Matters in Chairside CAD/CAM Dentistry

Chairside CAD/CAM has streamlined the process of designing and manufacturing dental restorations. However, the digital workflow does not actually begin with the intraoral scanner. It begins with tooth preparation.

The quality of the preparation affects how clearly the margin can be scanned, how the restoration can be designed, and how accurately it can be manufactured. In other words, digital technology can improve the workflow, but it cannot completely compensate for an unclear or inadequate preparation.

1. Tooth Preparation Is the Starting Point of the Digital Workflow

A typical chairside CAD/CAM workflow follows this sequence:

Tooth Preparation → Scanning → CAD Design → CAM Milling → Finishing → Clinical Placement

Each step depends on the information generated by the previous one.

If the preparation margin is unclear, the scanner may have difficulty capturing it. If there is insufficient restorative space, the CAD design may be restricted. If the internal geometry is unsuitable, milling may become more challenging.

This is why preparation should be considered part of the digital workflow rather than a separate clinical step.

2. Preparation Margin: Make the Boundary Clear

A clearly defined preparation margin is essential for digital scanning.

The scanner needs to distinguish the prepared tooth from the surrounding tooth structure and soft tissue. A continuous and accessible finish line generally makes digital margin identification easier.

Several factors can interfere with this process:

• Poorly defined finish lines
• Deep subgingival margins
• Bleeding or excessive moisture
• Soft-tissue interference
• Irregular preparation contours

This is why soft-tissue management remains important in a digital workflow.

A margin must first be clinically visible before it can be digitally captured.

Repeated scanning cannot always compensate for a preparation that is difficult to see clinically.

3. Restorative Space Matters for CAD Design

The preparation must also provide adequate space for the planned restoration.

If the tooth is insufficiently reduced, the available space for the restoration may be limited. This can affect the anatomical form and thickness that can be designed in CAD.

The basic relationship is:

Insufficient Reduction → Limited Restorative Space → Restricted CAD Design

The exact preparation requirements depend on the restoration type, material, and clinical situation. Therefore, preparation should always follow the appropriate clinical and material-specific guidelines.

The key principle is simple: the digital design can only work within the physical space created by the preparation.

4. Preparation Geometry Affects Milling

Tooth preparation should also be considered from a manufacturing perspective.

Sharp internal angles, narrow areas, or inaccessible geometry can make it more difficult for milling tools to reproduce the intended restoration design.

Smooth and appropriately rounded internal transitions can provide a more practical relationship between:

Tooth Preparation → Restoration Design → Milling

The goal is not simply to make the preparation easy to scan. It should also provide geometry that can be properly designed and manufactured.

5. Scanning and Preparation Work Together

A well-designed preparation still needs appropriate scanning conditions.

Before scanning, clinicians should consider:

• Is the preparation margin clearly visible?
• Is the field sufficiently dry?
• Is soft tissue covering the margin?
• Can the scanner access the proximal and cervical areas?
• Is the preparation clearly distinguishable from the surrounding structures?

Deep or narrow areas may require additional attention because the scanner needs sufficient access and viewing angles to capture the surface.

Therefore, clinical preparation and digital scanning should be considered together.

6. Common Preparation Problems in Chairside CAD/CAM

These problems do not necessarily make a digital restoration impossible, but they may introduce additional adjustments and uncertainty into the workflow.

7. A Simple Chairside CAD/CAM Preparation Checklist

Before scanning, it is useful to check four areas:

Preparation

• Adequate restorative space
• Appropriate preparation geometry
• No unnecessary undercuts

Margin

• Clearly defined
• Continuous
• Sufficiently accessible

Soft Tissue

• Adequate tissue management
• Controlled moisture
• No bleeding obscuring the margin

Digital Access

• Scanner can reach the preparation
• Proximal and cervical areas are visible
• Preparation can be clearly distinguished from surrounding structures

Conclusion

Chairside CAD/CAM is often associated with scanners, CAD software, milling machines, and restorative materials. But the digital workflow starts before any of these technologies are used.

It starts with tooth preparation.

A clear margin supports scanning. Adequate restorative space supports CAD design. Appropriate preparation geometry supports CAM milling.

The better the preparation connects with the requirements of digital acquisition and manufacturing, the more predictable the overall chairside CAD/CAM workflow can become.

The digital workflow begins with the preparation.