Accuracy of ceramic restorations made using an in-office optical scanning technique: an in vitro study.

The present in vitro study concerns determination of the pre-cementation gap width of all-ceramic crowns made using an in-office digital-impression technique and subsequent computer-aided design/computer-aided manufacturing (CAD/CAM) production. Two chairside video camera systems were used: the Lava Oral scanner and Cadent's iTero scanner. Digital scans were made of a first molar typodont tooth that was suitably prepared for an all-ceramic crown. The digital impressions were sent via the Internet to commercial dental laboratories, where the crowns were made. Also, an impression of the typodont tooth was made, poured, and scanned in order to evaluate the pre-cementation gap of crowns produced from scanning stone dies. These methods and systems were evaluated by creating replicas of the intermediate space using an addition-cured silicone, and the gap widths were determined using a measuring microscope. Hot-pressed leucite-reinforced glass-ceramic crowns were selected as a reference. The mean value for the marginal measuring points of the control was 170 µm, and the values for all the evaluated crowns ranged from 107 to 128 µm. Corresponding figures for the internal measuring points were 141-210 µm and 115-237 µm, respectively. Based on the findings in the present study, an in-office digital-impression technique can be used to fabricate CAD/CAM ceramic single crowns with a marginal and internal accuracy that is on the same level as that of a conventional hot-pressed glass-ceramic crown. In the present study, however, slight differences could be seen between the two types of ceramic crowns studied with respect to the internal fit obtained.

Formation of several stable complexes between the minor components of the cyclic tetrapeptide cyclo-(-Pro1-Ala2-D-Phe3-Leu4-) and some specific Boc-amino acids.

The cyclic tetrapeptide cyclo (-Pro1-Ala2-D-Phe3-Leu4-) was modeled and synthesized to be used for molecular interactions and chiral discrimination studies in CDCl3. Total correlation spectroscopy and nuclear Overhauser effect spectroscopy spectra of the cyclic tetrapeptide showed the presence of one dominant stereoisomer-1- and three minor ones--2a, 2b, and 2c--in a relationship of 92:6:1:1. They formed three- to five-hydrogen bond complexes with Boc-D-Ser, Boc-L-Ser and Boc-L-Thr (Boc: t-butyloxylcarbonyl). These three Boc-amino acids interact more strongly with 2a, 2b, and 2c than with 1, altering their relative concentrations to 48:40:6:6. In the complex between the cyclic tetrapeptide and Boc-D-Ser, the stereoisomer 2a exchanged chemically with 1, 2b, and 2c, while 1 did not exchange with either 2b or 2c. This chemical exchange is due to cis-trans isomerization of the peptide bonds. The chiral discrimination of 2a, 2b, and 2c was stronger than that of 1. No complexation occurred with Boc-L-Ala or Boc-L-Trp.