[1] Tooth preparation
- Tooth preparation: A zirconia-made crown should have a minimum thickness of greater than 1.0mm.
- For a zirconia inlay, the shape of the cavity should be a simple “open box” without an undercut.
- If a J margin is created, it needs to be corrected during the margin finish. If not, the shape cannot be milled accurately, resulting in a faulty fit on the margin area. Sharp cusps should be avoided as they are difficult for the milling bur to go in, which may cause the final product to be too thin.
- You should take the bur thickness of the milling machine into account, and make sure the anterior teeth’s incisors and posterior teeth’s cusps aren’t prepped too sharply. If it is too sharp, the zirconia crown will get thinner as the inside would have been excessively milled.
- In case of equigingival or subgingival margins, gingival retraction is necessary.
[2] Gingival condition
- Check if there is bleeding or swelling for the area that you're going to scan.
- Especially in implant cases, you need to check if it reveals a healthy soft-tissue collar around the implant site, which has been guided by the healing abutment since the implant placement. If you scan the implant site when there is bleeding, the scan data may not be accurate because the emergence profile cannot be properly acquired.
[3] Fluid control
- It is essential to control saliva and blood before scan. You should remove stagnant saliva on the teeth. Although you don’t want the mouth to be completely dry, it needs to be dry enough to eliminate any fluid on the teeth’s surface and prevent bubble creation. Make sure to control for blood. Remember that blood will also be scanned, and it would lower scan accuracy.
[4] Gingival retraction
- With silicone impressions, a gap between the tooth and the gingiva is caused by the pressure of the impression material. Digital impressions, unlike silicone impressions, require gingival retraction before scan.
- Gingival retraction can be done by either cordless gingival displacement techniques (gingival incision using laser or gingival retraction using Expasyl or Gingimaster) or a cord packing technique.
- In cases where a single-cord technique is not enough to make the margin exposed, you can insert another cord for proper gingival retraction, and then remove the second cord before scan.
- In case of the double retraction cord technique, It is required to check whether tissue health is compromised to avoid the risk of bleeding that could occur when the second cord is removed.
[5] Scanbody
- Before scanning a scanbody, make sure it is fixed correctly to the fixture.
- It is important that the unique shape of the scanbody is facing the lingual or buccal side because it will make the scanbody matching process easier later on in exocad. Furthermore, if it is facing the proximal direction, it is difficult to scan the scanbody.
[6] Necessary scan areas by case
- Crown: prepped teeth, distal and mesial surface of adjacent teeth, contact surface
- Inlay: the cavity of a prepped tooth
- Implant: emergence profile, adjacent teeth, scanbodies
- Orthodontics: the deepest molar, attached gingiva, interproximal area
[7] Light control
- When the hard light comes into a scanning area, It affects scanning performance. Ensure to prevent intensive light coming from a dental chair or any other light sources.
- Enable the Warning For External Light(Beta) feature in Medit Scan for Clinics > Settings. When this is enabled, the user will be notified instantaneously when the system detects any external light.
[8] Scanner tip
- Clean the tip using soapy water and a brush, and inspect the mirror found in the tip. If the mirror appears stained, smudged or has a milky haze, it may affect the quality of scan results. Clean the mirror using a soft brush and soapy water, or replace it with the new one.
[9] Proper scanning angle
- When you scan the lingual(buccal), tilt the tip toward the lingual(buccal) side so that the lingual(buccal) side of the teeth, the lingual(buccal) gingiva, and the occlusal surface appear as 1:1:1.
- Gingiva scan data should be sufficiently acquired for the occlusion stage.
[10] Scan results
- Check the scan data from various angles using the reliability map.
- Remove all unnecessary data using trimming tools.
- If you missed out anything, perform additional scan to complete the data.
- Check margin line, undercut, and tooth reduction for prepped teeth.
