1.Tinschert,-J; Natt,-G; Mautsch,-W; Spiekermann,-H; Anusavice,-K-J.Marginal fit of alumina-and zirconia-based fixed partial dentures produced by a CAD/CAM system.Oper-Dent 26(4):367-74
Abstract:Clinical long-term success of all-ceramic dental restorations can be significantly influenced by marginal discrepancies. As a result, this in vitro study evaluated the marginal fit of alumina- and zirconia-based fixed partial dentures (FPDs) machined by the Precident DCS system. Different master steel models of three-, four- and five-unit posterior FPDs with an 0.8 mm chamfer preparation were produced. FPDs made of DC-Zirkon and In-Ceram Zirconia core ceramics were machined by the Precident DCS system. The marginal fit of the milled frameworks placed on the master steel models was determined by a replica technique using a light-body silicone to fill the discrepancies between crown and tooth and a heavy-body material to stabilize the light-body impression material. The impressions were poured into an epoxy resin material and each model was cross-sectioned with a low speed diamond saw to better visualize marginal discrepancies. The marginal fit of the FPDs was evaluated by scanning electron microscopy. The measurements of the marginal fit exhibited mean marginal discrepancies in a range between 60.5 and 74.0 microm, mean marginal gaps in a range from 42.9 to 46.3 microm, mean vertical discrepancies in a range from 20.9 to 48.0 microm and mean horizontal discrepancies in the range of 42.0 to 58.8 microm. Statistical data analysis was performed using the non-parametric test of Kruskal-Wallis and Mann-Whitney. The analysis revealed no significant differences (p>0.05) between the mean marginal gaps and vertical and horizontal discrepancies. However, for some FPDs the mean values of the marginal discrepancies were significantly different (p < or =0.05). The wide range of the measured values may be attributed to the complex geometrical design of long span FPDs and difficulties regarding the milling process of brittle ceramic materials. Based on the selection of 100 microm as the limit of clinical acceptability, the results of this study can conclude that the level of marginal fit for alumina- and zirconia-based FPDs achieved with the Precident DCS system meet the clinical requirements.
2.Bindl,-A; Mormann,-W-H.Clinical and SEM evaluation of all-ceramic chair-side CAD/CAM-generated partial crowns.Eur-J-Oral-Sci 111(2):163-9
Abstract:The effect of hardware and software on the quality of Cerec all-ceramic partial crowns was investigated in this cross-sectional study. Partial crowns (n = 818) had been adhesively placed in 496 patients between 1993 and 1997 using Cerec 1 and Cerec 2 units (groups 1 and 2) as well as Cerec 2 with wall-spacing software (group 3). From each group, 25 randomly selected partial crowns were evaluated using modified United States Public Health Service (USPHS) criteria. Of these, 12 were randomly selected in each group, replicas taken and examined in a scanning electron microscope for marginal interfacial width and for continuous margin adaptation. Interfacial width of group 1 (308 +/- 95 micro m) was significantly larger than those of groups 2 (243 +/- 48 micro m) and 3 (207 +/- 63 micro m). Continuous margin adaptation at the tooth-luting composite and luting composite-restoration interfaces showed only minor differences in groups 1 (94.5 +/- 8% and 95.5 +/- 2%), 2 (98.1 +/- 1% and 97.5 +/- 1.4%) and 3 (96.8 +/- 3% and 96.8 +/- 2%). Pooled clinical rating was excellent or good at 97% for all groups, indicating acceptable restoration quality except for one breakage in group 1.
3.Bronwasser PJ, Mormann WH, Krejci I, Lutz F.Schweizer Monatsschrift fur Zahnmedizin 101(2):162-9, 1991
Abstract icor MGC Cerec inlays were placed in 53 teeth clinically and in 24 extracted teeth. Both main groups were subdivided into the following four test subgroups: 1. monofunctional dentin adhesive without linings. 2. bifunctional dentin adhesive without linings. 3. monofunctional dentin adhesive with linings. 4. bifunctional dentin adhesive with linings. The marginal adaptation of the occlusal surfaces of the restorations placed clinically was evaluated from replicas using the scanning electron microscope at x 200 magnification. In contrast, the marginal adaptation of all the restored enamel surfaces and the disto-cervical dentinal margins of the restorations placed in the extracted teeth were similarly evaluated. These margins were examined before and after thermomechanical stressing. The restorations were stressed 120,000 times at 300 cycles of 5-55-5 degrees C, chemically degraded by immersion in ethanol of 75% for 20 h and brushed for 30 min with a toothbrush at 1,96 N load. The in-vitro restorations were also subjected to dye penetration tests. The percent "excellent margin" recorded along the enamel-composite interface of the occlusal surfaces of the clinically placed restorations varied between 83.6 and 88.2%. The corresponding scores for the in-vitro specimens were at least 95% before and 90% after the thermomechanical and chemical stressing. The bifunctional dentin adhesive "Prisma Universal Bond 2" had a 93.6% "excellent margin" along the dentin-composite margin before stressing which decreased to 84.4% after stress. These scores were not significantly different.
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