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ARIFA HASSAN 2 ND YEAR

Effects of two surface FInishes on the color of cemented and colored anatomic-contour zirconia crowns ;LEE et al, (J Prosthet Dent 2016;116:264-268). ARIFA HASSAN 2 ND YEAR

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ARIFA HASSAN 2 ND YEAR

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  1. Effects of two surface FInisheson the color of cemented and colored anatomic-contour zirconia crowns ;LEE et al, (J Prosthet Dent 2016;116:264-268) ARIFA HASSAN 2ND YEAR DEPT OF PROSTHODONTICS

  2. INTRODUCTION • Zirconia has excellent aesthetic quality, biocompatibility, and mechanical property. Thus, zirconia is getting attention as a proper material for posterior teeth restoration to replace the existing ceramic. • Recently, the introduction of new CAD/CAM milling technology and new zirconia made it possible to manufacture anatomic contour zirconia crown, enabling the forming of occlusal surface anatomically instead of in the form of porcelain veneer. • Anatomic contour zirconia crowns have excellent fracture resistance property because it does not have superstructure

  3. Statement of problem • The esthetic appearance of anatomic-contour zirconia restorations is influenced by the shade of the coloring liquid and the optical properties of the luting cements.

  4. PURPOSE • The purpose of this in vitro study was to investigate the effects of surface finishing methods on the color distribution of colored anatomic-contour zirconia crowns before and after being cemented onto abutments.

  5. A single implant-supported restoration is a well-established solution for replacing a missing tooth because of its high survival rates, good esthetics, and improved phonetics. • To address esthetic demands, restoring a dental implant with ceramic materials has drawn considerable interest in recent years. • High strength zirconia in the form of industrially prefabricated blocks milled to shape using computer-aided design and computer-aided manufacturing (CAD-CAM) technologies has been widely applied as a core material for ceramic restorations

  6. Zirconia is a white, semitranslucent material. Zirconia-based restorations have, therefore, been fabricated with zirconia cores layered or pressed with feldspathic porcelain to achieve acceptable esthetics. • This bilayered structure of the core-porcelain system may alter the mechanical characteristics of the zirconia substructures and induce veneer porcelain chipping. • Currently, there is a trend toward anatomical-contour zirconia restorations without veneering porcelain.

  7. To achieve comparable esthetic levels with layered zirconia restorations, different methods have been proposed. • Among them, the color shading of anatomic-contour zirconia in the presintering stage enables the color to be reflected from the inner structure to improve the optical properties and obtain a more estheticcolor match. • Two main approaches have been developed for coloringzirconia restorations

  8. In one approach, metallic pigments are added to the initial zirconia powder before or after pressing the milling blocks. • In the other approach, anatomic-contour zirconia restorations are immersed in coloring liquids containing rare earth elements. • The selected coloring liquid plays a determining role in achieving color matching with the intended shade. Thereafter, polishing and glazing are 2 surface-finishing methods to obtain the glossy surfaces of ceramic restorations. • Different finishing protocols applied to ceramic systems result in changes to both color and translucency.

  9. The esthetic appearance of anatomic-contour zirconia restorations is influenced by the shade selection of the coloring liquid and the optical properties of the luting cements. Kim et al14 compared the surface textures produced by glazing and polishing techniques with coloredzirconia specimens and demonstrated that both polishing and glazing decreased the lightness but that glazing also increased the yellowness. Fazi et al found that significantcolor changes occurred after cementation of thin Lava Frame zirconia

  10. MATERIAL AND METHODS • Crown-shaped specimens for color measurements were prepared with CAD-CAM fabricated anatomic-contour zirconia crowns. • The study involved the fabrication of 24 crowns from titanium abutments representing a maxillary right first premolar. • Each abutment was scanned (D900; 3Shape A/S), and a digital impression was obtained. • The crown was designed using CAD software (DWOS; Dental Wings) and milled (340i; imes-icore) from presinteredzirconia blocks

  11. The milled zirconia crowns were immersed in the A3 shade of coloring liquid in plastic holders for 30seconds, except for the control group (denoted group C, n = 6). • All of the zirconia crowns were then sintered in a sintering furnace (6000 MS; VITA Zahnfabrik). • The thickness of the middle third of each crown was measured, and the mean thickness was controlled to 2.48 ±0.24 mm, as verified with a crown gauge (Miltex Gauge; Lake Success).

  12. The coloredzirconia crowns were randomly separated into 3 experimental groups (n=6) according to the surface-finishing methods: • no treatment (N), polished (P), and glazed (G). • In group N, no surface-finishing method was applied to the colored crowns. • In group P, the crowns were polished using a polishing kit (HP321; EVE Ernst Vetter) with a slow-speed handpiece (7000 to 12000 rpm). • In group G, the crowns were glazed in a ceramic furnace (P500; IvoclarVivadent AG) using a glazing paste (DD Nature Zr Glaze & Glaze liquid; Dental Direkt).

  13. The surface roughness (Ra) was measured with a profilometer (ET-3000; Kosaka Laboratory). • A tungsten carbide stylus with a tip radius of 0.5 mm was drawn over the surface of the specimen, and the mean value of 6 measurements was obtained for each specimen. • Each zirconia crown was ultrasonically cleaned in distilled water for 5 minutes and directly seated onto its corresponding abutment for color measurements.

  14. For each crown, the color was recorded with a dental spectrophotometer (EasyShade; VITA Zahnfabrik) over a gray background. • The spectrophotometer was calibrated using a standard white tile before each group of color measurements. • The spectral reflectance of a color was recorded and converted into the Commission International de l’Eclairage (CIE) 1976 color system (CIELab). • In this system, color is expressed as 3 coordinates: the L* value is the lightness of an object, the a* value represents the red or green chroma, and the b* value represents the yellow or blue chroma. The color difference (DE) between 2 measured crowns was calculated

  15. After the color measurement, each zirconia crown was fixed onto its corresponding titanium abutment with A2-self-adhesive resin cement (Rely X U200; 3M ESPE) . • The internal walls of the crown were degreased with 80% ethanol. A thin layer of cement was evenly applied to the inner surface of the crown with an automix syringe, and the crown was firmly seated on the abutment. Each surface was light-polymerized (3M Elispar ESPE) for 20 seconds from the occlusal and any excess cement was removed. • The color measurements were repeated, and the DE was calculated as previously described.

  16. For each crown, 3 color measurements were made, and their average was recorded. • A paired t test was used to determine whether the difference in the total color change of a zirconia crown was because of the coloring liquid or the cement application.

  17. RESULTS The result showing that immersion in the coloring liquid did not alter the surface roughness of the zirconia crowns. There was a significant difference in Ra between groups P and G (P=.01).

  18. Before cement application, no significant differences were noted in the mean values of L*, a*, and b* between groups C and N nor among groups, except for the L* value between groups P and G (P=.041). The mean DE values and standard deviations obtained for each group are summarized in table.

  19. Untrained observers distinguished differences between groups N and P. Hence, a DE value of 2.72 was considered the perceptibility threshold in the present study Clinically perceptible color differences were observed for all colored groups compared with group C. Color differences between each pair of colored groups were also perceptible in clinical settings

  20. Statistically significant differences were found for the a* values of all groups and b* values of all groups, except group G. For color difference (DE), a statistically significant difference was found only in group G, while cement application highly influenced the color perception of coloredzirconia ceramics in all groups.

  21. DISCUSSION • Based on the results of the present study, the null hypothesis that different surface-finishing protocols and luting cements applied to coloredzirconia crowns would not affect their color parameters was rejected. • The color parameters of a restoration should be similar to those of natural teeth. • Surface factors, such as the texture (smooth or rough) and luster (glossy or dull), affect the color of ceramic materials, especially the CIE L* value. • No statistical differences in CIE a* or b* values were found in the present study, indicating that surface-finishing methods did not change the hue

  22. A statistically significant difference in L* values between polishing and glazing was expected because a smooth surface reflects a greater amount of light than a rough surface, resulting in an increase in lightness values. Untrained observers distinguished differences between groups N and P. Hence, a DE value of 2.72 was considered the perceptibility threshold in the present study

  23. The color difference between groups N and G was higher than that between groups N and P. • Excluding the influence of DL*, there was also a large shift in the yellow-blue coordinate (Db*). • The use of composite resin luting cements masked the underlying color and modified the esthetic outcome of the restoration

  24. The results of the present study showed that the shift in the L* coordinate was relatively small when cement was applied. • However, the shade of the cement seemed to influence the color appearance of the restoration.

  25. Limitations • The present study has limitations. Only a single shade of luting cement was used, and the immersion period in the coloring liquid was limited to 30 seconds. • Coloring effects with regard to various shades of luting cements and immersion periods should be investigated in further studies. • The thickness of the cement layer was controlled to 300 mm. Further studies are needed to test the effect of different thicknesses of luting cements on color distribution.

  26. CONCLUSIONS • Within the limitations of the present study, the following conclusions were drawn: • 1. The polished surfaces of zirconia crowns were rougher than glazed surfaces (P=.002), which resulted in larger and more perceptible color differences between no treatment and polishing (DE= 25.36). • 2. When a luting cement was used, perceptible color differences could be detected for the zirconia crowns (DE=2.79 for group C; DE=3.14 for group N; DE=2.75 for group P, and DE=3.47 for group G).

  27. Effect of polishing and glazing on the color and spectral distribution of monolithic zirconia • Kim et al ; [J Adv Prosthodont 2013;5:296-304]

  28. PURPOSE • The aim of this study was to evaluate the effect of polishing and glazing on the color and spectral distribution of monolithic zirconia.

  29. MATERIALS AND METHODS • Forty-five monolithic zirconia specimens (16.3 mm × 16.4 mm × 2.0 mm) were fabricated • These specimens were divided into five groups according to the number of coloring liquid applications. • • Group I: One time of application • Group II: Two times of application • Group III: Three times of application • Group IV: Four times of application • Group V: Five times of application

  30. Each group was divided into 3 subgroups according to the method of surface treatments (n=3): N: no treatment; P: polishing; G: glazing. • Color and spectral distribution of five different areas of each specimen were measured according to CIElab (Commission International de l’Eclairage (CIE) 1976 color system) , color space in the reflectance mode relative to the standard illuminant D65 on a reflection spectrophotometer

  31. RESULTS. • There was a significant difference in CIE L* between Subgroup N and P, and in CIE b* between Subgroup P and G in each group. • Spectral reflectance generally decreased in Subgroup P and G in comparison with Subgroup N. • Color differences between Subgroup P and G were within the perceptibility threshold (ΔE*ab< 3.7) in most groups. • Highly significant correlation was found between CIE b*and each subgroups as the number of coloring liquid applications increased (R2>0.88, P<.001).

  32. CONCLUSION • A perceptible color difference can be detected after polishing of monolithic zirconia. • Polishing decreases the lightness, and glazing also decreases the lightness, but increases the yellowness of monolithic zirconia • The increased number of coloring liquid applications makes monolithic zirconia darker and more yellowish, this tendency was not changed even after polishing or glazing procedure.

  33. For a perfect color match of zirconia restorations, clinicians should take into account the possible color deviations after polishing or glazing at the time of shade selection • The use of composite resin luting cements masked the underlying color and modify the esthetic outcome of the restoration. Therefore, cements used when fabricating crowns, especially in anterior areas, should closely approximate the color of the prepared tooth structure.

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