March 2013, Volume 9, Issue 3
Published by AEGIS Communications
Go Deep with Digital Impressions
Digital optical impressions allow dentists to achieve an intimate fit without gingival retraction
Day-to-day dentistry sometimes presents surprises. Although usually manageable, these surprises can induce stress and lead to lengthened appointment times. When used appropriately, technology can help the clinician reduce the anxiety produced by unforeseen occurrences.
During a new patient examination, an open margin was discovered at the mesial surface of a full gold crown on tooth No. 31. There was no bleeding on probing, but there was a 5-mm probing depth at the distolingual surface. An explorer could easily get under the margin, so a replacement crown was planned (Figure 1).
After the crown was removed, recurrent caries was discovered as anticipated, but the distolingual portion of the prior build-up simply fell off with no adhesion. The previous gold crown had held the build-up in place (Figure 2). This explained the 5-mm probing depth, although it had been assumed it was a submerged area of gingiva around a distal molar. In hindsight, this could be seen on the preoperative radiographs; however, it was assumed that the prior build-up existed wholly within the tooth.
The patient could not remember the original reason for her crown but estimated it to be at least 10 years old. Most likely, the distolingual cusp fractured subgingivally, and a build-up and crown were completed for her. Whether or not crown lengthening was needed when the original crown was placed was not known at this time. In any case, the current situation involved a very deep subgingival margin that required treatment. A decision had to be made.
It was possible to place a matrix band around the tooth for a build-up, but it would be difficult without customization of the matrix band, and it could disrupt the gingival attachment. This would certainly induce hemorrhaging, as it would be placed subgingivally at the distolingual areas as well as circumferentially. In addition, a matrix band would not be able to adapt to the beginning of the furcation area, leaving a bulky surface and margin. Achieving a reliable margin seal in the area would also be questionable.
Another option would be to complete a build-up and prepare the crown margin back to the tooth structure, thereby seating the prosthetic completely to the tooth structure. However, the same problem—gingival retraction—would occur when setting up for the physical impression. Ways to accomplish this—eg, cord placement, laser troughing, etc—were considered. If a cord were placed in the sulcus, the gingival attachment would be disrupted. Also, because it would be very close to bone level at the distolingual, there might not be space for a cord. While this treatment would be possible, it would be difficult and time-consuming. In the end, this potentially difficult case was completed simply with a digital optical impression rather than a physical impression.
Because the gingiva was relatively healthy, there was only crevicular fluid to address. This was easily controlled chemically using ViscoStat® (Ultradent Products, Inc., ultradent.com). A build-up was completed with a glass ionomer restorative (GC Fuji II™ LC, GC America Inc., gcamerica.com) while leaving the preoperative post. Preparation of the tooth was completed to allow at least 2 mm of occlusal reduction and a chamfer margin to the tooth structure even at the deep distolingual area. After preparation, ViscoStat was again used for controlling crevicular fluid and slight hemorrhaging from iatrogenic abrasion of the gingiva from the diamond bur. After the preparation was completed and the fluid controlled, only a digital image was needed. Using the CEREC® Omnicam (Sirona, cereconline.com), the digital impression was completed in a couple of minutes.
The Omnicam is very much like a typical intraoral video camera and does not require a reflective medium. Because the Omnicam displays the color of 3-dimensional data (ie, the impression), it was very easy to differentiate the tooth structure from the gingiva (Figure 3); physical retraction of the tissue was not required to see past the margin. If the camera can see the margin, the milling chamber can mill the ceramic to the margin. Therefore, if it can be seen by the camera, it can be restored. This technology made handling a difficult clinical situation very easy and very efficient.
The crown was designed (Figure 4) and milled from IPS e.max CAD (Ivoclar Vivadent, ivoclarvivadent.com). Because the preparation had adequate mechanical resistance and retention forms, along with enough occlusal reduction, the crown was cemented with a luting cement (GC Fuji PLUS™, GC America Inc., gcamerica.com) (Figure 5). The postoperative radiograph reveals the intimate fit of the ceramic crown to the tooth, even in the deep distolingual area (Figure 6).
Technological advancements in dentistry continue to help the clinician in the most difficult restorative situations. In this case, the author used a digital impression to replace a crown without gingival retraction, even with a deep distolingual area. Intimate fit was achieved without disrupting the gingival attachment. In short, current technology made it possible to achieve the desired result easily and efficiently, without surprises.
The author is a Beta tester for Sirona Dental Systems and Ivoclar Vivadent.
About the Author
Todd Ehrlich, DDS