Within the limitations of this study, the method of direct digitalisation seems to have the potential to improve the accuracy of impressions for four-unit FDPs.

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Regarding the accuracy, all tested intraoral scanning technologies seem to be able to reproduce a single quadrant within clinical acceptable accuracy. However, differences were detected between the tested systems.

The results of this in vitro study show that digital impressions made with the Lava(TM) C.O.S. system and its digital workflow are suitable for fabricating four-unit zirconia frameworks, with regard to marginal and internal fit requirements.

Implant-supported prosthodontics requires precise impressions to achieve a passive fit. Since the early 1990s, in vitro studies comparing different implant impression techniques were performed, capturing the data mostly mechanically. The purpose of this study was to evaluate the accuracy of three different impression techniques digitally. Dental implants were inserted bilaterally in ten polymer lower-arch models at the positions of the first molars and canines. From each original model, three different impressions (A, transfer; B, pick-up; and C, splinted pick-up) were taken. Scan-bodies were mounted on the implants of the polymer and on the lab analogues of the stone models and digitized. The scan-body in position 36 (FDI) of the digitized original and master casts were each superimposed, and the deviations of the remaining three scan-bodies were measured three-dimensionally. The systematic error of digitizing the models was 13 μm for the polymer and 5 μm for the stone model. The mean discrepancies of the original model to the stone casts were 124 μm (±34) μm for the transfer technique, 116 (±46) μm for the pick-up technique, and 80 (±25) μm for the splinted pick-up technique. There were statistically significant discrepancies between the evaluated impression techniques (p ≤ 0.025; ANOVA test). The splinted pick-up impression showed the least deviation between original and stone model; transfer and pick-up techniques showed similar results. For better accuracy of implant-supported prosthodontics, the splinted pick-up technique should be used for impressions of four implants evenly spread in edentulous jaws.

Dental restorations are increasingly manufactured by CAD/CAM systems. Currently, there are two alternatives for digitizing dental implants: direct intra-oral data capturing or indirect from a master cast, both with transfer caps (scanbodies). The aim of this study was the evaluation of the fit of the scanbodies and their ability of reposition. At the site of the first molars and canines, implants were placed bilaterally in a polymer lower arch model (original model), and an impression was taken for fabricating a stone cast (stone model). Ten white-light scans were obtained from the original and the stone model with the scanbodies in place. The scanbodies were retrieved after each scan and re-attached to the same implant or lab analogue. The first scan of the series served as control in both groups. The subsequent nine scans and control were superimposed using inspection software to identify the discrepancies of the four scanbodies in both experimental groups. The systematic error of digitizing the models was 13 μm for the polymer and 5 μm for the stone model. The mean discrepancy of the scanbodies was 39 μm (±58 μm) on the original implants versus 11 μm (±17 μm) on the lab analogues. The difference in scanbody discrepancy between original implants and lab analogues was statistically significant (p < 0.05, Mann-Whitney U test). Scanbody discrepancy was higher on original implants than on lab analogues. Fit and reproducibility of the scanbodies on original implants should be improved to achieve higher accuracy of implant-supported CAD/CAM fabricated restorations.

Full-contour zirconia restorations are gaining in popularity. Highly translucent zirconia materials and multi-coloured zirconia blocks might help to overcome the aesthetic drawbacks of traditional zirconia. This study evaluated the transmittance of visible light (400-700 nm) through the four different layers (Enamel Layer EL, Transition Layer 1 TL1, Transition Layer 2 TL2, Body Layer BL) of a multi-coloured zirconia block (KATANA™ Zirconia Multi-Layered Disc (ML)) using a spectrophotometer. Forty specimens (thickness of 1±0.05 mm) from each layer were examined and statistically evaluated at a confidence-level of 5%. Light transmittance was expressed as a percentage of the through-passing light. The following mean values (SD) were found: EL 32.8% (1.5), TL1 31.2% (1.3), TL2 25.4% (1.3) and BL 21.7% (1.1). Significant differences were found between all groups (ANOVA, Student-Newman-Keuls). This multi-coloured zirconia block showed four layers with different light transmittance capabilities. It might therefore be useful for enhancing the aesthetic appearance of full-contour zirconia restorations made from this material.