Colour measurements of all ceramic crown systems

Effects of shade and thickness on the translucency parameter of anatomic-contour zirconia, transmitted light intensity, and degree of conversion of the resin cement

STATEMENT OF PROBLEM

Anatomic-contour zirconia prostheses are usually cemented with resin cement. However, information regarding the effects of the zirconia shade and thicknesses on the translucency of the prosthesis, the intensity of the transmitted light beneath the prosthesis, and the subsequent degree of conversion in the resin cement is sparse.

PURPOSE

The purpose of this in vitro study was to investigate the translucency parameter in 3 anatomic-contour zirconia specimens of 2 shades at 5 different thicknesses and to investigate the transmitted light intensity and degree of conversion of the resin cement beneath the ceramic specimens by using a traditional zirconia and a lithium disilicate glass-ceramic as controls.

MATERIAL AND METHODS

Ceramic specimens from 1 anatomic-contour zirconia in a generic shade (CAP FZ) and 2 anatomic-contour zirconias in A2 shade (Zirlux and Luxisse) were used. Lithium disilicate in HT A2 shade (IPS e.max CAD) and traditional zirconia in a generic shade (CAP QZ) were used as controls. A total of 125 ceramic specimens (n=25) were fabricated to a final specimen dimension of 12×12 mm and in thicknesses of 1.0, 1.25, 1.5, 1.75, and 2.0 mm according to the manufacturers' recommendations. The CIELab color space for all specimens placed against a white and black background was measured with a spectrophotometer (CM-2600D), and the translucency parameters were calculated for the materials at various thicknesses. A light-polymerizing unit (DEMI LED) was used to polymerize the resin cement (Variolink II) placed beneath the ceramic specimens. Transmitted light intensity from the polymerization unit beneath the ceramic specimens was measured by using a spectrophotometer (MARC Resin Calibrator), and the transmittance of each specimen was calculated. The coefficient of absorption of each material was calculated from the regression analysis between the natural log of transmittance and specimen thickness. The degree of conversion of resin cement was measured by using a Fourier transformation infrared (FTIR) spectrophotometer. The results were analyzed by using 2-way ANOVA (α=.05). The relationship between the transmittance and the translucency parameter was evaluated by plotting the transmittance against the translucency parameter value of each specimen.

RESULTS

The translucency parameter decreased with increasing thickness in all 5 material groups. All anatomic-contour zirconia had lower translucency parameters than e.max CAD (P<.001). The same results were found for the intensity of the transmitted light (P<.001). Both A2 shade anatomic-contour zirconia (Zirlux and Luxisse) showed significantly lower light transmittance than a generic shade anatomic-contour zirconia (CAP FZ) (P<.001). The coefficients of absorption were found to range from 0.63 to 1.72 mm^-1, and reflectance from 0.10 to 0.25. The results from the degree of conversion of resin cement after polymerization through 1 to 2 mm of specimens showed a significantly higher degree of conversion in the e.max group than in all other groups (P<.001). The correlation between translucency parameter and the intensity of the transmitted light suggested that the relationship was shade dependent.

CONCLUSIONS

The translucency parameter and the transmitted light intensity of ceramic material were influenced by the type of ceramic and the shade and thickness of the ceramic. The combined effects of layer thickness and the intensity of the transmitted light in the A2 shade anatomic-contour zirconia (Zirlux and Luxisse) resulted in a lower degree of conversion in resin cement than in a generic shade anatomic-contour zirconia (CAP FZ) at layer thicknesses of 1.75 and 2 mm.

Cement opacity and color as influencing factors on the final shade of metal-free ceramic restorations

OBJECTIVE

To investigate the influence of opacity and color of luting cements on the final shade of metal-free restorations.

MATERIALS AND METHODS

Five resin cement colors in combination with four different thicknesses of CAD/CAM ceramic materials were tested, and a composite substrate was used as dentin color reference (n = 3). Specimen color was measured with a spectrophotometer equipped with an integrating sphere before and after cementation (CIELAB). Cement and ceramic color and opacity (TP) were assessed by measuring the tested ceramic thickness as a 1-mm thick disk for each of the cement shades. The differences in color were evaluated (ΔE₀₀ ). Data were statistically analyzed by a Two-Way ANOVA followed by the Tukey Test for post-hoc comparison (P < .05) and multiple comparison Pearson's test (P < .05); the acceptability and perceptibility threshold were evaluated.

RESULTS

Statistically significant influence was found for factors ceramic thickness and cement shade (P < .001). Perceptible and unacceptable color changes were induced on the final restoration by resin cements (ranging from ΔE₀₀  = 0.69 ± 0.54 to ΔE₀₀  = 5.53 ± 0.46), the correlation between factors became strong (r²  > 0.6) in case of mismatch between color and translucency of cement and ceramic. Only the clear shade in combination with the thickest ceramic, resulted in an imperceptible color change (ΔE₀₀  = 0.69 ± 0.54).

CONCLUSIONS

The final shade of ceramic restorations can be influenced by resin cements; the magnitude of influence is related to the cement optical properties.

CLINICAL SIGNIFICANCE

In order to influence the final shade of a ceramic restoration, a cement more opaque than the restorative material should be used. Conversely, in the case of a fitting shade of the restoration, a cement more translucent than the restoration should be used to avoid undesired changes.

Effect of 5.25 % sodium hypochlorite on color stability of acrylic and silicone based soft liners and a denture base acrylic resin

The purpose of the current study was to investigate the effect of a chemical disinfectant (sodium hypochlorite 5.25 %) on color stability of a denture base acrylic resin and two processed soft denture lining materials of two different types (acrylic-based and silicone-based). Ten specimens from each type of materials tested were made (2 × 20 × 20 mm). All specimens were immersed in sodium hypochlorite (5.25 %). Colorimetric measurements for each specimen were taken before immersion, and after 24 h and 7 days of immersion. Color changes were evaluated using the CIE L*a*b* colorimetric system. Data were statistically analyzed with one-way analysis of variance (ANOVA) (α = 0.05). ANOVA was followed by Bonferroni test to determine which groups differed from each other. ΔE and ΔL* of the silicone-based liner at the 1st and 7th days of immersion were significantly more than of denture base acrylic resin and acrylic-based liner. Change in ΔL* values of denture base acrylic resin and acrylic-based liner was small and statistically insignificant after 24 h of its immersion. However, the increase in ΔL* values of the acrylic-based liner after 7 days of immersion was considerably more than of denture base acrylic resin. Color changes in denture base acrylic resin and soft denture liners tended to increase with longer immersion times, and the color stability of the soft denture liners was influenced by its chemical type.

Effect of veneering techniques on color and translucency of Y-TZP

PURPOSE

This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) all-ceramic restorations.

MATERIALS AND METHODS

Thirty disc specimens (10-mm diameter, 0.50 +/- 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10-mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat-pressing IPS e.max ZirPress fluorapatite glass-ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low-fusing nano-fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (tau) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (DeltaE) were calculated using color difference formula. One-way analysis of variance (ANOVA) combined with a Tukey multiple-range test were used to analyze the data (alpha= 0.05).

RESULTS

As to ZP, ZPC, and ZC groups, the value of a* increased (-1.35 +/- 0.07, -0.64 +/- 0.06, -0.36 +/- 0.05, respectively) (p < 0.05); b* decreased (27.01 +/- 0.07, 25.48 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 +/- 0.08, 25.49 +/- 0.11, 23.28 +/- 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 +/- 0.48, 1.64 +/- 0.03, respectively), and lowest in ZPC group (82.14 +/- 0.18, 1.47 +/- 0.01, respectively) (p < 0.05).

CONCLUSIONS

Y-TZP all-ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.

Effects of chemical disinfectants on surface characteristics and color of three fixed prosthodontic crown materials

STATEMENT OF PROBLEM

Dental restorations should reproduce similar optical effects as natural tooth structure to achieve a good color match. Mismatch can result in unsatisfactory shade matching.

PURPOSE

This study determined whether chemical disinfectants affected the surface texture and color of 3 fixed prosthodontic materials.

MATERIAL AND METHODS

Five chemical disinfectants (Clorox, Banicide, Cidex-7, Biocide, and Multicide) in combination with 3 restorative materials (Dicor, Vita VMK ceramometal porcelain, Midas ADA type III noble casting alloy) were evaluated at 4 different times of immersion (10 minutes, 30 minutes, 24 hours, and 7 days). Changes from baseline for surface roughness and color were evaluated. Surface roughness data were recorded with a surface analyzer and color data in CIE L*a*b* color space were measured with a colorimeter. Data were analyzed with repeated measures analysis of variance and single factor analysis of variance.

RESULTS

There were no statistical differences in surface roughness among disinfectants and restorative materials. However, there were statistical differences of changes in color, increase in deltaE and decrease in deltaL, among disinfectants and the noble casting alloy.

CONCLUSION

Only 2 of the 3 materials evaluated, Dicor and Vita VMK ceramometal porcelain, can be used with all 5 disinfectants up to 7 days of immersion. Three chemical disinfectants (Biocide, Clorox, and Multicide) caused clinically significant color changes with the noble casting alloy after 7 days of immersion.

Effects of chemical disinfectants on the surface characteristics and color of denture resins

PURPOSE

Because dentures are disinfected repeatedly and for various amounts of time, it was of clinical interest to determine whether chemical disinfectants altered the surface texture or inherent color.

MATERIAL AND METHODS

Five chemical disinfectants (Clorox, Banicide, Cidex-7, Biocide, and Multicide) in combination with five denture resins (Dentsply reline material, Hygenic HyFlo, Hygenic Perm, Lucitone 199, and Triad VLC reline resin) were evaluated at four different times of immersion (10 minutes, 30 minutes, 24 hours, and 7 days). Changes from baseline for surface roughness and color were recorded. Surface roughness data were recorded with a surface analyzer. Color data in CIE L*a*b* color space were measured with a colorimeter. Data were analyzed with repeated-measures analysis of variance and single-factor analysis of variance.

RESULTS

Although statistical differences were demonstrated among disinfectants and resins for both measured parameters, the magnitudes of change in color and roughness was most often clinically insignificant.

CONCLUSIONS

One disinfectant (Multicide) cannot be used on all five resins, and the remaining four disinfectants can be used on any of the five resins for up to a period of 30 minutes. All resins tested can be immersed in the four remaining disinfectants for up to 30 minutes without appreciable alteration to surface texture or color. Lucitone 199 resin can be immersed in any of the four disinfectants for up to 7 days without perceivable color change.

Influence of lamination on the flexural strength of a dental castable glass ceramic

This study evaluated the effect of veneering Dicor castable ceramic with Vitadur N and Dicor Plus feldspathic porcelains. A biaxial flexure test was conducted on five groups of specimens (Dicor castable ceramic, Vitadur N dentinal porcelain, Dicor Plus dentinal porcelain, Dicor core veneered with Vitadur N and Dicor core veneered with Dicor Plus castable ceramic). Each group consisted of 10 disks of nearly identical dimensions with a 1.98 +/- 0.04 mm thickness and 15.7 +/- 0.35 mm in diameter. Statistical analysis indicated that there was neither significant difference (p > 0.05) between mean flexural strength of Dicor Plus and Vitadur N ceramic or Vitadur N and Dicor/Vitadur N ceramic specimens. The mean flexural strength of Dicor/Vitadur N specimens was significantly lower than the mean flexural strength of Dicor ceramic specimens. Conversely, there was no significant difference between mean flexural strength of Dicor ceramic and Dicor/Dicor Plus ceramic specimens. Scanning electron microscope (SEM) examinations of Dicor/Dicor Plus ceramic specimens suggested better wetting of Dicor core by Dicor Plus ceramic with lower incidence of porosity at the interface. However, Dicor/Vitadur N ceramic specimens exhibited a higher incidence of porosity at the interface. This indicated that lamination of Dicor castable ceramic material with feldspathic porcelain for esthetics could be attained without sacrificing strength of the original material, provided that appropriate veneering material was selected.

Use of an in vitro model to assess the effects of APF gel treatment on the staining potential of dental porcelain

Porcelains and resin composites exposed to acidulated phosphate fluorides (APF) have been reported to result in increased roughness, loss of weight, and loss of specular reflectance (gloss). Six samples of five commercial porcelains were subjected to five four-minute treatments with APF gels. Samples were then subjected to a nine-day cyclic staining procedure that utilized a tea, coffee, and mucin mixture. Changes in reflectance were then measured by means of a Minolta Chromameter (CR121) and converted to CIE L* a* b* values at illuminant D65 against a white background. delta L*, delta a*, delta b*, and delta E values were calculated. There was a substantial decrease in the L* value (lightness) for all porcelains. The average L* value for APF-treated and then stained porcelains was 43.6, for the stained-untreated samples, 48.2, and for untreated-unstained porcelain, 53.5. For three of the five porcelains, the differences in L* between treated and untreated stained porcelains were statistically significant. Changes in a* and b* values were also found to be consistent with but not as large as the changes in L*.

Duration of tooth color change after bleaching

Tooth color change was monitored after a single, in-office bleaching technique using a colorimeter. Twenty young adults participated in the double-blind study at The Ohio State University College of Dentistry. Half of the participants had their maxillary anterior teeth bleached and half were controls. By one month, the large initial color change was considerably reversed and only noticed by one subject. After six months, the effect of bleaching was small, but still measurable.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The growth in the dental literature continues to escalate, as evidenced by the publication of at least 326 new books in 1988 and 1989 and more than 20 new journals in 1989. There still appears to be undue emphasis on quantity instead of quality of research. This proliferation in the literature poses ever increasing difficulties to this Committee in filtering out the articles that are of particular interest to the members of the Academy and identifying those that are most likely to have a major impact on dental practice and service. The subjects covered include periodontics, caries and preventive dentistry, craniomandibular disorders, occlusion, pulp biology, ceramics, and restorative dental materials.