Marginal accuracy of press-ceramic veneers influenced by preparation design and fatigue.
ABSTRACT To investigate the influence of preparation design and mouth motion fatigue on the marginal accuracy of press-ceramic veneers bonded to human maxillary central incisors.
Forty-eight extracted human maxillary central incisors divided in three groups of 16 specimens each, received veneer preparations. In Group WP a window preparation (WP) was performed. Specimens in Group IOP were prepared with an incisal overlap (IOP) of 2 mm without palatal chamfer. For Group CVP, specimens received a complete-veneer preparation (CVP) of 3 mm incisal reduction and 2 mm palatal extension. Veneers were fabricated with IPS Empress and bonded adhesively with dual polymerizing composite Variolink II. The discrepancies of marginal fit were examined on epoxy replicas before and after mouth motion fatigue at x200 magnification.
The mean (geometrical) (95% confidence limits) marginal accuracy after cementation was recorded as follows: WP-46 (43-49) microm, IOP-46 (44-49) microm and CVP-54 (51-58) microm. Fatigue led to a significant decrease of marginal accuracy in all groups (P < 0.036) [WP-47 (44-50) microm, IOP-51 (48-53) microm and CVP-63 (59-67) microm]. Group CVP demonstrated significantly higher marginal gap values than groups WP and IOP, before and after fatigue (P < 0.004). No significant differences were found between groups WP and IOP.
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ABSTRACT: OBJECTIVES: A novel three-dimensional scanning technique was used to investigate the effects a one-step and a two-step impression method can have on the three-dimensional fit of ceramic partial crowns. METHODS: 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 finishline 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 color-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). RESULTS: 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. CONCLUSIONS: OS/SV and OS/DV impressions resulted in statistically significantly smaller marginal and internal discrepancies than the two-step technique. CLINICAL SIGNIFICANCE: 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.Journal of dentistry 12/2012; · 2.00 Impact Factor
Article: Marginal and internal fit of pressed lithium disilicate partial crowns in vitro: a three-dimensional analysis of accuracy and reproducibility.[show abstract] [hide abstract]
ABSTRACT: The objective of this in vitro study was to visualize and to quantify the marginal and internal fit of heat-pressed ceramic restorations by a novel three-dimensional procedure. Accuracy and reproducibility of the employed measuring method were determined. An acrylic model of a lower left first molar was prepared to receive a partial crown and duplicated by single step dual viscosity impressions. Corresponding working casts were formed from Type IV die stone and indirect restorations were fabricated from heat-pressable lithium disilicate ceramics (IPS e.max Press, Ivoclar Vivadent AG, Schaan, Liechtenstein). The acrylic tooth model and the ceramic partial crowns were digitized by a structure light scanner with a measurement-uncertainty of 4 μm and subjected to computer-aided quality inspection. Visual discrepancies in marginal and internal fit were displayed with colors. For quantitative analysis, mean quadratic deviations (RMS) were computed and analyzed by Student's t-test (n=5, α=0.05). Mean RMS-values for accuracy (reproducibility) ranged from 34 (14) μm for internal areas to 78 (23) μm for marginal surfaces. Differences in accuracy (p=0.003) and reproducibility (p<0.001) were statistically significant. In general, areas with sharp internal line angles such as occlusal ridges and the preparation finish line exhibited oversized dimensions, whereas areas with rounded and soft internal line angles were undersized. The viability of a computer-aided and three-dimensional approach for assessing marginal and internal fit of indirect restorations was demonstrated. Thereby, the obtained results track complex form changes as they occur during laboratory processing.Dental materials: official publication of the Academy of Dental Materials 03/2012; 28(3):320-6. · 2.88 Impact Factor