fa Three-dimensional fit of lithium disilicate partial crowns in vitro پروتزهای دندانی Prothtodontics پژوهشي Research <p> <strong>Objectives</strong></p><p>  A novel three-dimensional scanning technique was used to investigate the effects a one-step and a two-step impression methods can have on the three-dimensional fit of ceramic partial crowns. </p><p> <strong>Methods</strong></p><p>  An acrylic model of a mandibular first molar was prepared to receive a partial coverage all-ceramic crown (mesio-occlusal-distal inlay preparation with reduction of all cusps and rounded shoulder finish line of buccal wall). Type IV plaster replicates were cast based on one-step single viscosity (OS/SV), one-step dual viscosity (OS/DV), and two-step dual viscosity (TS/DV) impressions. Five partial crowns were fabricated per impression method using hot-pressed lithium disilicate ceramics. Then, preparation and restorations were digitized using a non-contact, white-light scanner featuring self-calibrating optics (overall measurement uncertainty of <5μm). Data were entered into quality inspection software which superimposed the records (best-fit-algorithm), calculated fit-discrepancies for every pixel, and colour-coded the results to aid visualization. Furthermore, mean quadratic deviations (RMS) were computed and analyzed statistically with a 1-way ANOVA. Scheffé’s procedure was applied for multiple comparisons (α=0.05). </p><p> <strong>Results</strong></p><p>  Mean RMS-values for marginal (internal) surfaces were: OS/SV 70 (20)μm, OS/DV 78 (34)μm, and TS/DV 107 (52)μm. Differences among impression techniques were statistically significant at p=0.006 (0.001). Qualitatively, occlusal ridges and preparation finish lines were over contoured, whereas inner occlusal boxes and the proximal–occlusal isthmus were under contoured.</p><p> <strong> Conclusions</strong> </p><p> OS/SV and OS/DV impressions resulted in statistically significantly smaller marginal and internal discrepancies than the two-step technique. <strong></strong></p><p> <strong>Clinical significance</strong></p><p>  Marginal and internal fit of hot-pressed lithium disilicate partial crowns depended on the employed impression technique. One-step impressions are preferred over two-step techniques in many day-to-day clinical situations, especially for the fabrication of partial coverage crown restorations. </p><hr><p></p><p> <strong>Source: </strong>Journal of Dentistry</p><p> <a href="http://www.jodjournal.com/article/S0300-5712(12)00316-8/abstract" target="_blank"><font color="#0000ff">Full Text</font></a></p> Marginal fit, Internal fit, Dental ceramics, Computer-aided analysis 0 0 http://idai.ir/browse.php?a_code=A-10-32-2123&slc_lang=fa&sid=1 Oliver Schaefer 10031947532846009952 10031947532846009952 Yes Policlinic of Prosthetic Dentistry and Material Science, Centre for Dental Medicine, Jena University Hospital, An der Alten Post 4, 07743 Jena, Germany Harald Kuepper 10031947532846009953 10031947532846009953 No Policlinic of Prosthetic Dentistry and Material Science, Centre for Dental Medicine, Jena University Hospital, An der Alten Post 4, 07743 Jena, Germany Bernd W. Sigusch 10031947532846009954 10031947532846009954 No Policlinic of Conservative Dentistry, Centre for Dental Medicine, Jena University Hospital, An der Alten Post 4, 07743 Jena, Germany Geoffrey A. Thompson 10031947532846009955 10031947532846009955 No School of Dentistry, Marquette University, 1801 West Wisconsin Avenue, Milwaukee, WI 53233, USA Arthur F. Hefti 10031947532846009956 10031947532846009956 No School of Dentistry, Marquette University, 1801 West Wisconsin Avenue, Milwaukee, WI 53233, USA Arndt Guentsch 10031947532846009957 10031947532846009957 No Policlinic of Conservative Dentistry, Centre for Dental Medicine, Jena University Hospital, An der Alten Post 4, 07743 Jena, Germany