Kenneth B. May, ES, DDS, MW Michael E. Razzoog, Andrew Koran III, DDS, MS,” and Emerson Robinson, University of Michigan, School of Dentistry, Ann Arbor, Mich.
of color stability
DDS, MS, MPH,b BS, DDS, MPHd
Several denture base resins have been recently introduced that provide easier or faster processing. Although these materials have adequate strength properties, the color stability is also of interest. This study evaluated the color stability of five denture base acrylic resins and one denture base repair resin. The samples were subjected to conditions of accelerated aging to test color stability. Five samples of each material were processed and aged for 100 and 300 hours. The color stability was quantitatively measured using the Minolta Chroma Meter II. Color measurements were made before weathering and at 100 and 300 hours the color difference AE was calculated for all samples. At 300 hours the color change of the materials was significantly different at p < 0.01. It was found that: (1) the color of Lucitone Hy-pro and Acron was least affected by conditions of accelerated aging; (2) Triad, Aecelar 20, and Perm demonstrated noticeable color changes; and (3) Compak-20 bad an appreciable color change and was the least color-stable of the materials tested. (J PROSTHET DENT 1992;68:78-82.)
any new resinshave beenrecently introduced for prosthodontic applications. These new materials include visible light-activated resins(VLAR), fast heat-cure resins, chemically activated resins,and microwave-activated resins. They are now competing with conventional denture base acrylic resins becauseof their easeof handling and their physical and mechanical properties.
In an attempt to shorten the processingtime of heatcured denture base resins, modified pour-type materials were deve1oped.lWhile processingtime was shortened to lessthan 1 hour, theseresinsexhibited a color changewith time. In responseto this, manufacturers developed rapid cure heat-activated resins.2-4These materials can be polymerized in lessthan 1/2hour, and this has appeal to dentists and laboratory technicians who prefer heat-activated resins. Another approach to reducing processingtime is to use chemically-activated resins (cold-cured materials). These materials react chemically to initiate the polymerization reaction. They are similar chemically to pour-type resins except for polymer particle size, monomer/polymer ratio,
Presented at the Academy of Complete Denture Prosthetics meeting, Wintergreen, Va. Material in this article is based on a thesis submitted in partial fulfillment of the requirements for a Master of Science degree in Prosthodontics, Horace H. Rackham School of Graduate Studies, University of Michigan. aAssistant Professor. bProfessor, Department of Prosthodontics. CProfessor, Department of Prosthodontics. dProfessor, Department of Prosthodontics. 10/l/37526
and the monomer used. The color stability of chemically activated denture baseacrylic resinsvaries with the chemical composition of the monomer5and, as a group, chemically activated denture baseresinshave been found to be lessstable than conventional acrylic resins.@’ VLARs are yet another form of chemically-activated denture baseresinsthat combinesa photoinitiator, a urethane dimethacrylate matrix, an acrylic copolymer, and microfine silica fillers.l* VLARs have been shown to be equalto autopolymerizing methacrylates in physical properties.ll The chemistry of the initiation to that of light-activated composites.
However, VLARs have been reported to have different water absorption, variable dimensional accuracy, and significantly greater staining characteristics.12 Microwave-activated denture base resins have also recently beenmarketed to competewith conventional acrylic resins. In comparison
resins are reported to have greater accuracy13and less cross-palatalcontraction in the palatal sealarea.l” In the evaluation of three physical properties (porosity, hardness, and transversestrength), microwaveacrylic resinmaterials that are processedin lessthan 5minutes showno difference in properties when compared with conventional resins processedat a thickness of 2.5 mm or less.15-17 This study determinesquantitatively the color stability of four new denture baseresins,one repair resin, and one conventional heat-cured resin as a function of accelerated aging.Thesedata will be usefulto dentistswho desireto use materials that are color stable.
Six acrylic resin materials were examined. Five are denture baseresinsand one a denture baseacrylic repair material
and Perm were included
I. Brand names and manufacturers of denture base resins and denture base repair resins studied
Dentsply International, Inc., York, Pa. Dentsply International, Inc. The Hygenic Corp., Akron, Ohio Modern Materials, Columbus Dental, Miles
Chemical activated repair resin Fast heat-cure acrylic resin
Fast heat-cure acrylic resin
Acron G C
VLAR, Visible light-activated
II. Color change (AE) meansand standard deviations (SD) at 100and 300 hours of accelerated aging Table
Louis, MO. Dentsply International, Inc. G-C Dental, Tokyo, Japan
Time 100 Materials
Hy-pro Perm VLAR (Triad) Accelar 20 Compak 20 Acron GC
1.53 (0.31) 1.49 (0.52)
1.84 (0.34) 1.03 (0.87)
0.99 (0.28) 2.33 (0.81)
1.54 (0.38) 1.79 (0.76) 3.29 (0.34) 1.43 (0.46)
as in Table I.
ANOVA of AE data on materials at 100and
300 hours Source
100 hours Material Error Total 300 hours Material Error Total
to compare the color stability of the newer materials to materials that have beenusedfor sometime. Sampleswere prepared in disks50 mm in diameter by 1.0mm thick. Five samplesweremadefor eachmaterial studied. The samples were 0.5 mm thicker than the dimensionrequirementsfor color stability testing asdescribedin the American Dental Association’s(ADA) Specification No. 1218to more accurately evaluate color changesas a function of accelerated aging. The materialswere hydrated for a period of 30 days in distilled water and were then desiccatedto a constant weight. Test sampleswere identified by placing a seriesof identification notches signifying the type of material and samplenumber, and all evaluations were conducted using a double-blind procedure. The color change(AE) was determined using a Minolta Chroma Meter II with data processorDP-100 (Minolta CameraCo.,Ltd., Osaka,Japan) to quantify the color of the samplesand calculate the difference from baselinecolor of the samplesbefore and after 100and 300hours of exposure to acceleratedaging conditions. Color measurementswere made in three randomly selectedareasnear the center of each sample. The average of the three readings was recorded and the mean of eachmaterial wascalculated. In all, there were 30 samplesthat provided a total of 90 readings for statistical analysis. After the initial color measurement,sampleswereplaced in a weathering chamber (Weather-O-Meter 25 WR, Atlas
the ultraviolet/visible light spectrum of a 2500 W xenon lamp at 905%humidity and 110’ F temperature. The samplesweresprayed with distilled water for 18minutes every 102minutes accordingto ASTM test D2565for accelerated aging of polymers. After 100 and 300 hours of aging, the color measurementsof all sampleswere repeated.The statistical analysis consistsof: (1) descriptive statistics, (2) analysis of variance for the change of color (AE) at each time, and (3) repeated measurementanalysisto assess the overall effect of material on the color change. To determine the average color change after 100 hours and 300hours, the mean and standard deviation of each of the six materials were calculated (Table II). The six materials were comparedwith respectto the meancolor change at 100hours and 300hours, using the analysisof variance (ANOVA) methodi (Table III). The final and the more important statistical technique performed in the data analyseswasthe repeated measurementanalysis.20In this analysis, the color changesmeasuredafter 100 hours and 300 hours were consideredas repeated measurementson the same experimental unit and thus were assumedto be correlated. An overall comparisonof the meancolor changes at both times was made. The significancetests of time ef-
fect and the interaction
Device Co., Chicago,
Ill.) and were exposed to
at level of p