Color stability and aging of plastic veneering materials

Accelerated Aging Effects on Color and Translucency of Bleaching-Shade Composites

PURPOSE

This study was performed to evaluate the influence of accelerated aging on the color and translucency parameter (TP) of bleaching-shade resin composites.

MATERIALS AND METHODS

Thirty-three bleaching shades and two control conventional shades of microhybrid (MH) and microfill (MF) resin composite specimens (n = 5) were aged in an accelerated aging chamber set to standard CAM 180 cycles. One side of each specimen was evaluated for surface color and TP changes compared with baseline in increments of 150 kJ/m2 for intervals up to 450 kJ/m2 using a spectrophotometer. A deltaE* > or = 3.7 was considered to be a poor match, and the total TP range was divided into three equal parts representing low, medium, and high translucency. Data were analyzed with analysis of variance.

RESULTS

Compared to the baseline, deltaL*, deltaa*, deltab*, and deltaE* ranges at 450 kJ/m2 were -0.8 to 5.0, -0.6 to 1.2, -8.3 to 0.0, and 0.7 to 8.6 for MH and 0.2 to 1.3, 0.1 to 1.3, -2.5 to 1.1, and 1.7 to 2.7 for MF composites. Scheffé's S intervals (p = .05) for comparisons of deltaL*, deltaa*, deltab*, and deltaE* values of MH composites between baseline and 450 kJ/m2 were 1.6, 0.6, 1.7, and 1.5, respectively. Corresponding Tukey-Kramer intervals for MF composites were 0.7, 0.3, 0.6, and 0.6, respectively. TP values at baseline ranged from 0.9 to 4.3 for MH and from 1.4 to 2.2 for MF composites, whereas deltaTP for baseline minus 450 kJ/m2 ranged from -1.1 to 1.7 for MH and from -0.1 to 0.3 for MF composites. Scheffé's S interval (p = .05) for comparisons of deltaTP values of MH composites for baseline minus 450 kJ/m2 was 1.0. Corresponding Tukey-Kramer interval for MF composites was 0.4.

CONCLUSIONS

Aging-dependent color changes at 450 kJ/m2 were above the limit that indicated a poor match for 18/26 MH, while corresponding values for microfills were within acceptable range. Accelerated aging generally caused decreases in L* (specimens became darker) and a* values (specimens became redder), while b* values increased (specimens became more chromatic) for both MH and MF composites. TP was relatively stable during aging for both MH and MF composites.

Color stability of new-generation indirect resins for prosthodontic application

STATEMENT OF PROBLEM

Several new-generation indirect resins are being advocated for full contour restoration of teeth. Previous indirect resin systems have failed in this application, due in part to color instability.

PURPOSE

This study evaluated and characterized the color stability of various new-generation indirect resins (ceramic-polymers) when subjected to accelerated aging.

MATERIAL AND METHODS

Four new-generation indirect resin systems, 1 direct resin system, and 1 dental porcelain control were subjected to accelerated aging for a period of 300 hours. Initial specimen color parameters were determined in the Commission International de l'Eclairage Lab (CIELAB) color order system with a colorimeter. Color changes (DeltaE) were calculated between baseline color measurements and measurements made after 150 and 300 hours of accelerated aging. Color difference data were subjected to a 1-way analysis of variance to examine the interaction between material and time interval of aging. Where significant interactions occurred, a least-squared means test was performed to identify differences in the color stability between the materials (P </=.05).

RESULTS

After 300 hours of accelerated aging, color changes of the indirect resins ranged between 0.62 and 3.40 DeltaE units. Two of the products tested demonstrated color stability that was not significantly different from the porcelain control.

CONCLUSION

All the indirect resins tested demonstrated color stability at or below a quantitative level that would be considered clinically acceptable. Color changes of ceramic-polymers occurred because of changes in chroma, rather than alterations in lightness.

Mastique laminate veneers: results after 4 and 10 years of service

The purpose of the present study was to evaluate the clinical quality over 4 years and the longevity over 10 years of 77 Mastique laminate veneers (DeTrey, Dentsply). The veneers were bonded to incisors and canines with a light-cured composite resin, using the acid-etch technique, and examined every 1/2 year in accordance with USPHS criteria. Anatomic form and marginal adaptation were rated excellent in more than 50% of the veneers throughout the study. Moderate surface wear was seen in most of the veneers after 4 years of service. Marginal discoloration and color match were recorded as not acceptable in 20% of the veneers at the 4-year control. No significant difference was found in the gingival index between veneer and control teeth. The cumulative retention rate was 40% after 4 years and 20% at the 10-year recall. Owing to the high frequency of spontaneous loss, Mastique laminate veneers cannot be recommended as permanent restorations.

Color stability of hybrid ionomers after accelerated aging

PURPOSE

The color stability and surface roughness of three commercial hybrid ionomers were determined in vitro after accelerated aging. Three shades of each hybrid ionomer prepared in light-cured and dark-cured conditions were tested.

MATERIALS AND METHODS

Samples were aged in an artificial aging chamber by subjecting them to total ultraviolet light irradiation of 150 kJ/m2 over a period of 77 hours. Color (CIE LAB system) was measured before and after aging on a reflection spectrophotometer. Surface roughness was measured with a profilometer.

RESULTS

After accelerated aging, all samples became lighter. Photac-Fil Aplicap (ESPE-Premier, Norristown, PA) and Fuji II LC (GC America, Chicago, IL) also became less chromatic (less red and less yellow). Among the light-cured samples, Fuji II LC had the greatest change in color followed by Photac-Fil Aplicap and Vitremer (3M Dental Products, St Paul, MN). For the dark-cured samples, Fuji II LC had the greatest change in color followed by Vitremer and Photac-Fil Aplicap. There were no differences in delta E* between the two lightest shades, but the darker shades of each product showed the greatest changes in color. All samples became significantly rougher after aging.

CONCLUSIONS

Hybrid ionomers changed color significantly and perceptibly after in vitro accelerated aging. Surfaces became significantly rougher and showed evidence of cracking and degradation.

Evaluation of hard direct reline resins

Peak curing temperatures of hard, direct, autopolymerizing reline resin materials tested were all within ADA specification guidelines. A temperature range of 10 degrees C was demonstrated among materials, with the highest polymerization temperatures recorded for Perm and Lang's Self-Curing Rebase Acrylic, and the lowest for KOOLiner, Flexacryl, and COE-Rect. This temperature difference is probably clinically detectable. However, intraoral testing of polymerization temperatures yielded lower peak values than those observed with specification testing, and the temperature peaks occurred earlier with intraoral conditions. There were significant color changes with simulated aging for three of the products tested: Flexacryl, COE-Rect, and Lang's Self-Curing Rebase Acrylic. The color changes occurred after only 24 hours of accelerated aging. Although there was only a small change in color with aging for Perm and KOOLiner, there was a moderate shift in the color of KOOLiner (delta E = 2.2) before aging. Thus only Perm demonstrated little color change with simulated aging. Of the reline products, one material, KOOLiner, demonstrated lower bond tensile strengths to denture base materials. However, the clinical significance of this was not known. One denture base material (Astron) recorded significantly higher bond strength values for all reline products and failure always took place within the denture base.