In this article, we will walk you through the preparatory steps to scan general prosthodontics.
 Tooth Preparation
- Tooth preparation: Keep zirconia’s properties in mind when making a prosthesis with an oral scanner. Zirconia is hard but thin, and therefore fragile. A zirconia-made crown should have a minimum thickness of greater than 1.0mm.
- Inlay preparation: In the case of a zirconia inlay, the shape of the cavity should be a simple “open box” without an undercut.
- You need to be careful with regard to two aspects.
: Firstly, if the margin line is sharp like a ‘J’ shape (J margin or fin), it will need to be removed during the margin preparation. If not, the shape will not be milled accurately, resulting in a faulty fit on the margin area.
: Secondly, sharp cusps should be avoided as they will be 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 prepared too sharply. If it is too sharp, the zirconia crown will get thinner as the inside would have been excessively milled.
- Margin Placement: In case of equigingival or subgingival margins, gingival retraction is necessary. If the margin is subgingival, the line will not be easy to scan as it is under the gingiva.
 Gingiva Control
- With silicone impressions, there is a gap between the tooth and the gingiva, caused by the pressure of the impression material. However, digital impressions require gingival retraction because you will scan the oral condition as it is at the time. Therefore, thorough gingiva conditioning is required to capture accurate scan data.
- Gingival retraction can be done by either cordless gingival displacement techniques (gingival incision using laser or gingival retraction using Expasyl/Gingimaster) or a cord packing technique.
- In cases where the margin is subgingival or 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 right before scanning.
- It is required to check if tissue health is compromised because spontaneous bleeding might occur when the second cord is removed.
 Fluid Control
- It is essential to control saliva and blood before scanning. 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, which would lower scan accuracy and even if scanned, the data will not be usable. The gingiva should also be healthy. Unhealthy gum tissue makes it tougher to obtain accurate scan data due to liquid leaking from the tissue.
 Scan Data Check
- After scanning, there are four points to check: the prepared tooth, soft tissue, adjacent teeth, and occlusion.
- While checking the scan data, remove all the unnecessary data by using trimming tools.
- If you missed out anything, perform additional scan to complete the data.
(1) The prepared tooth
: Check the margin line, undercut, and tooth reduction.
(2) Soft tissue
: With soft tissue, some parts are deleted automatically but recognition is slower without proper soft tissue retraction such as: did not align well during the scan, did not locate the bite well and incorrectly aligned it, the soft tissue data was attached to the teeth scan, or the data volume was too large (post-processing speed slows down as the data volume increases). When retracting soft tissue, use a mirror or finger to ensure enough retraction.
(3) Adjacent teeth
: As is the case with silicone impressions, digital impressions need adjacent teeth information to make an accurate prosthesis. If a prepared tooth is a posterior tooth, you will have to scan two adjacent teeth. If it is an anterior tooth, it would be better to get the full anterior scan data.
: After the occlusion scan, check if it is aligned in the same position as the physical occlusion.
: In the case of a full arch, it is recommended to acquire the equivalent amount of the occlusion scan data from both sides.