Welcome to the May Q&A Roundup webinar summary, presented by Dr. Keun-Young Jang and Chae-yeon Lee.
This month’s theme focused on the Modeless Crown, addressing three essential questions from the Medit user group. Each question was explored in detail with practical solutions, actual cases, and instructional videos.
Q1. What is the Best Technique to Get Accurate Scans of the Contact Areas?
Our first question came from Mark, who found it challenging to scan the contact areas without layering data and causing inaccuracies. This issue is common among practitioners working on Modeless Crowns. Dr. Jang and Ms. Lee discussed several techniques to overcome this problem.
User Insights and Expert Protocols
Mark and other users in the Medit user group had already noted the importance of using the lock function and maintaining communication with the lab. Dr. Jang provided a detailed protocol in response, which he explained in five steps during the webinar.
- Determine the Targets: Focus on specific scanning points like mesial and distal contacts in margins, rather than the entire crown. This precision helps avoid random, inefficient movements that can lead to unnecessary data layering.
- Decide on the Scanning Sequence: Complete the scan of contact areas in one shot and lock them to prevent layering. Margins can be scanned in multiple passes, starting from the mesial contact and ending with the distal contact, to capture a rough outline initially.
- Set Focal Length and Perform the Primary Scan: Set the focal length based on the crown length and space between adjacent teeth. The primary scan should aim to capture approximate data of the entire crown with a spiral movement, ensuring accurate data for both distal and mesial contacts.
- Analyze the Primary Scan and Lock Properly Scanned Areas: Evaluate the primary scan results and lock accurately captured areas. If contact areas are not properly obtained, delete the scan data and start over to avoid inaccurate data from multiple rescans.
- Rescan Areas with Insufficient Data Using HD Scan Mode: After locking accurate areas, focus on scanning insufficient data in HD mode. Use a rolling motion to hit the target from various angles, achieving green colors on the reliability map for all margin areas.
These steps ensure a systematic and efficient scanning process, minimizing the chances of inaccuracies.
Practical Tips from Chae-yeon
Chae-yeon shared her method of performing a pre-scan and then cutting out the contact area before the final scan. She emphasizes a single sweeping motion and using the lock function to prevent data layering.
Q2. What Clinical Difference Does the Blurry Effect Have on the Final Crown Margin?
The second question is about how blurry margins can affect the final crown result. This is a common issue, especially when dealing with deep margins, and it’s crucial to understand both the causes and solutions to ensure accurate crown margins.
Understanding Blurry Margins
Blurry margins often result from insufficient rolling motion during scanning or challenging scanning environments, such as deep subgingival margins. When the margin appears blurry, it can lead to inaccuracies in the final prosthesis, impacting fit and longevity.
Causes of Blurry Margins and Solutions
- Soft Tissue Undercut: Soft tissue undercuts are a primary cause of blurry margins. They can obstruct scanning light, making it challenging to capture deep margins accurately. Whenever possible, create supra-gingival margins. If subgingival margins are necessary, use provisional restorations to enhance scanning conditions or perform a gingivectomy.
- Moisture Control: Moisture from saliva or gingival crevicular fluid can distort scan data by causing erratic reflections of the scanning light. To manage moisture, use cotton rolls, suction, and hemostatic agents like DryZ. Perform pre-scans, trim data, and keep the area dry with gauze. An assistant can help with retraction and moisture control.
- Wet Retraction Cord: Leaving retraction cords in place for too long can cause them to absorb moisture and swell, leading to distortion and reflection issues that result in blurry margins. To avoid this, use a combination of two retraction cords and complete the scan without removing them. Scan quickly to prevent the cords from swelling and affecting scan quality.
Q3. What’s the Best Way to Avoid Surface Artifacts and Edge Smoothening?
The third question addressed the issue of margins appearing rounded instead of sharp in scan data. This can be a concern when aiming for precision in crown preparation.
Understanding the Issue
Dr. Jang explained that this rounding effect is due to the mesh density in scan data, which can smooth out fine details. While higher resolution settings can provide more detail, the default medium resolution is usually sufficient for clinical purposes. When mesh density is set to a medium level, the scanner captures the general shape but may not reflect the intricate details of the margin. This is why margins can appear rounded rather than sharp.
Solutions to Avoid Artifacts and Smoothening
- Use HD Mode: Switch to HD mode for scanning margin areas. This setting increases the resolution for critical parts of the scan, capturing finer details.
- Manual Margin Line Creation: Specify margins through the margin line creation function for higher resolution processing.
- Adjusting Resolution Settings: Change the default resolution settings to high resolution. This will result in larger file sizes but will provide the detailed, sharp scan data desired.
Clinical Relevance
Dr. Jang reassured that the rounding effect, though visible under magnification, does not affect the clinical outcome. The rounding of margins due to mesh density usually falls within a clinically acceptable range. Dental restorations, like crowns, do not require nano-scale precision. The acceptable margin of error in prosthodontics is often around 50 micrometers, while milling machines typically operate within a 10-micrometer precision range. The rounding observed in scans is usually much smaller than these tolerances, meaning it does not significantly impact the fit and function of the final prosthesis.
The May Q&A session delved deeply into the practical challenges and solutions associated with Modeless Crowns. From addressing the intricacies of scanning contact areas to overcoming issues with blurry margins and avoiding surface artifacts, the session provided valuable, actionable insights.
Stay tuned for future sessions as we continue to explore the questions and challenges from our Medit user group!
Watch the full May Q&A session here
