The total number of samples (45) were divided into three main groups cured according to three curing cycles (The standard short cycle, rapid was subdivided into three subgroup: The control group (without additives), samples prepared with the addition of Nigella Sativa, and samples prepared with the addition of Thyme oil. Color was measured for all the samples. Results were analyzed statistically by (Descriptive statistics, ANOVA and Duncan’s multiple range test) and showed that both additives(Nigella Sativa and Thyme oil) showed significant changes in the color of denture base. conclusion Both additives (Nigella sativa and Thyme oil) showed significant changes in the color of acrylic resin denture base material. The addition of Thyme oil to the samples cured by the regular heat curing cycle showed color change (ΔE=3.376) in relation to the standard (ADA) cycle which is an acceptable range in vitro.
This study were to evaluate the effect of Nigella sativa and Thyme oil on The color of Acrylic Resin Denture Base Material.
The number of denture wearers is increasing as the number of elderly people continually growing, and polymethylmethacrylate (PMMA) is still the most frequently used material in denture base fabrication(1 ).
Color stability is a required characteristic of denture base polymers, whether hard acrylic or soft lining materials, specified by various national and international standards typically as ADA specification No.12(2 ).
The color and translucency should be maintained during processing and these resins should not get stained or change in color through the clinical use. The color stability criteria may provide an important information on the service ability of the dental materials (3,4,5,6,7,8 ).
Various additives [(ethylene glycol dimethacrylate (EGDMA)
(9 ),glass flake(10 ), rigid rod polymer (RRP) fillers(11 ), Chlorohexidine gluconate powder(12 )] were added to acrylic resin to improve its flexural strength and modulous, microhardness, water sorption , solubility and flexibility.
Medical plant extracts (Nigella sativa and Thyme oil) were used as additives, as these oils were recommended to give suitable properties when added with certain concentrations on the heat cured acrylic resin (13,14).
Also these medical oils have antibacterial activity, Nigella sativa has greater effect, which may be due to the complex chemical structure of these seeds. These little seeds have over than one hundred different chemical components, including abundant sources of all the essential fatty acids, thougt that is often used medically. For example the essential oil of black cumin has an antimicrobial effect(15,16 ).
Materials and Methods
The total number of samples (45), were prepared from vertex heat cured denture base resin material according to manufacturer's instructions powder/liquid mixing ratio (2/1) . Samples were divided into three main groups:
1.The first group (15 samples) cured according to the standard short cycle(2 ) at 74 °C for 90 minutes, then at 100 °C for 30 minutes (5 samples were the control prepared without additives, 5 samples prepared with the addition of Nigella Sativa oil and 5 samples prepared with the addition of Thyme oil).
2. The second group (15 samples) cured according to the standard rapid simplified manufacturer’s instruction curing cycle at 70 °C for 10 minutes, then at 100 °C for 20 minutes (5 samples were the control prepared without additives, 5 samples prepared with the addition of Nigella Sativa oil and 5 samples prepared with the addition of Thyme oil).
3. The third group (15 samples) cured according to the standard regular manufacturer’s instructions at 100 °C for 30 minutes (5 samples were the control prepared without additives, 5 samples prepared with the addition of Nigella Sativa oil and 5 samples prepared with the addition of Thyme oil).
The concentrations at which these additives added were 1.5% by weight(13 ). The oil was added gradually (drop by drop) to the polymer with continuous mixing, then the monomer was added gradually to the mixture.
Note: The symbol (N) was added to the samples prepared with the addition of Nigella sativa and (T) for the samples prepared with the addition of Thyme oil.
1.Color Test (by the use of VITA Easyshade):
Acrylic samples were prepared with dimensions of (20x30x1.5) ± 0.03 mm(17 ). Five samples were used for each group. After curing, the samples were stored in distilled water at 37 ± 1°C for 7 days before testing.
When the Easyshade device is warming up, the bottom of the screen displays a “presets” selection box. Touching “presets” allows Easyshade’s default mode of operation to be selected and saved. This is achieved by the touch screen of the Easyshade.
The appropriate mode of measurement must be selected, and data reported are mode specific. In the measurements, “tooth single” mode of operation was selected and the device is adjusted to display the results of a measurement as L (Lightness), C (Chroma) and H (Hue).
The device must be calibrated each time when the unit was power - up, but not required between each measurement. Calibration is achieved by placing the 5 mm probe against a calibration block housed within the machine (Figure 1), according to the manufacturer’s instructions.
The background color affects the color of denture base resins(18 ).So many trials were made to determine the standard method of color measurement of acrylic resin denture base material by using VITA Easyshade device.
1. Five samples of the standard short cycle (ADA) were measured with the presence of a white background .
2.The color of the above samples were measured without background and by placing additional samples of the same dimensions, starting by placing one by one and the number of additional samples was increased gradually until no change in measurements (lightness, chroma and hue) was detected and this is obtained by placing seven pieces under the measured sample .
3. Three edentulous patients with good oral health and normal color of the mucosa were selected and the above samples were measured intraorally on the three patients (the control method).
The results of color measurements (extraorally and intraorally) were statistically analyzed. It is shown that the measurements with one additional sample under the measured sample showed no significant difference from the intraoral measurements(Figure. 2,3,4). So this method was depended in this study for color measurements of all the samples .
(CIE L*a*b*) color difference metrics were used for the performance analysis of the samples in the current study. The measured values of L, C and H for each sample were transformed into baseline L*, a*, b* values. The total color change (ΔE) of each sample was calculated for each sample at each evaluation using the formula(19,20,21,22 )
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