Dr. Mohamed shares the essential principles of ‘Prep Criteria’ for perfect scanning. This video provides a concise overview of the key points discussed in his recent webinar.
Basic Principles of Teeth Prep for Digital Impression
Dr. Mohamed discusses several critical aspects of teeth preparation that are vital for achieving accurate digital impressions.
Total Occlusal Convergence (TOC)
The Total Occlusal Convergence (TOC) is the angle between two opposing walls of the tooth prep. Ideally, this angle should be between 10 to 22 degrees. A TOC less than 10 degrees can cause undercuts, while more than 22 degrees can affect the restoration’s resistance and retention. Therefore, ensuring the correct TOC allows for a smooth scanning process without missing any critical areas.
Preparation Height
Active Preparation Height is the distance from the finish line to the occlusal surface. Ideally, it ranges from 3 to 4 millimeters. This height is crucial for ensuring good resistance and retention, especially when the TOC angle is optimal. If the adjacent teeth are longer, increasing the TOC angle helps the scanner capture all necessary details. This prevents noise and inaccuracies in the scan.
Rounded Line Angles
Rounded line angles for the axial wall and occlusal surface are essential to minimize milling errors. Sharp angles can lead to seating issues for crowns because scanners may struggle to read these edges accurately. Conversely, rounded margins are easier for scanners to read and for milling machines to reproduce accurately, helping ensure the restoration is properly seated and reduces the risk of undermilling.
Interproximal Spaces
Adequate interproximal space is crucial for successful milling. If the space is less than 0.3 to 0.5 millimeters, the milling machine cannot accurately mill the restoration, which leads to tight contacts and incomplete seating. Understanding the limitations of the milling machine and ensuring sufficient interproximal space can prevent these issues.
By adhering to these prep criteria—maintaining the correct TOC, ensuring proper preparation height, rounding line angles, and maintaining adequate interproximal space—dentists can achieve precise digital impressions and successful restorations. These principles help avoid common pitfalls in the scanning and milling process, leading to better outcomes for patients and less frustration for dental professionals.
For more detailed insights, watch the full version of Dr. Mohamed’s webinar on Preparation Criteria for Digital impressions and Guided preps.
