Laird Harrison

March 28, 2012

March 28, 2012 (Tampa, Florida) — Zirconia crowns with veneers made with digital impressions fit better than those made with conventional impressions, researchers reported here at the American Association for Dental Research 2012 Annual Meeting.

Although digital impression techniques are becoming more widespread, few studies have directly compared veneers made with digital impressions with those made with the conventional approach.

"The digital impression technique led to a significantly better margin fit and internal adaptation in all measured locations," said Dennis Fasbinder, DDS, from the School of Dentistry at the University of Michigan in Ann Arbor.

To see which approach resulted in better-fitting crowns, the researchers made a crown with a zirconia core and a crown with a ceramic veneer for each of 50 cases, for a total of 100 crowns.

The surface veneers were made with 2 different processes. One crown in each matched pair was made with a conventional polyvinylsiloxane (PVS) impression, in which a stone die was made to fabricate the veneer by hand. The other crown was made with a digital impression — an intraoral scanner was used to create a veneer made with computer-aided design and manufacturing.

The researchers also used PVS as part of the study to measure which crown fit better. They injected a light PVS material into the crown and seated the crown on the tooth preparation to record the cement space.

After the light material was set, they removed the crown and injected a heavy PVS material into the crown lined with the light PVS.

The light PVS recorded the space available for the cement between the preparation and the crown, and the heavy material replicated the crown preparation.

They next sectioned the PVS material faciolingually into 3 pieces. The sections were measured with a microscope at 20× magnification for margin fit, axial wall adaptation, and occlusal wall adaptation.

The crowns made with PVS impressions had margins of 78.62 µ (±25.62). In contrast, the digital crowns had margins of 51.45 µ (±18.59).

The crowns made with PVS impressions had axial adaptation of 93.75 µ (±35.89), whereas the digital crowns had axial adaptation of 79.06 µ (±23.98).

The crowns made with PVS impressions had occlusal adaptation of 162.03 µ (±47.22). The digital crowns had occlusal adaptations of 119.91 µ (±38.18).

These results were statistically significant (P < 0.05).

The investigators also recorded the time needed to cement the crowns in place, and found no difference between the conventional and digital crowns. The total time for PVS crowns was 6.63 minutes (±5.04), whereas the total for digital crowns was 6.04 (±4.76) (P > 0.05).

Half of the crowns made with each process were Lava DVS and half were Lava Zirconia (both by 3M Espe). The researchers found no statistical difference between the 2 in cementation time or fit.

Asked to comment, session moderator Frederick Trevor Burke, DDS, MS, BDS, MDS, told Medscape Medical News that the results made a good case for the digital impression techniques.

"I think it's very impressive," he said. "For him to show that these actually provide a good fit is a good statement. We are one step closer to making all restorations digitally."

Dr. Fasbinder and Dr. Burke have disclosed no relevant financial relationships.

American Association for Dental Research (AADR) 2012 Annual Meeting: Abstract 644. Presented March 23, 2012.

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