Shade Change Research Articles

The influence of porcelain layer thickness on the final shade of ceramic restorations

Statement of problem Ceramic restorations should be made of porcelain layers of different opacity, shade, and thickness in order to provide a natural appearance. By means of CAD/CAM layering technology such as CICERO, it is feasible to produce all-ceramic crowns with porcelain layers of predetermined thickness. However, it is not yet known whether changes in thickness of these porcelain layers within the clinically available space can perceivably influence the overall shade of the restoration. Purpose The purpose of this study was to determine, quantitatively, the effect of different thickness ratios of opaque porcelain (OP) and translucent porcelain (TP) layers on the overall shade of all-ceramic specimens. Material and methods The CIELAB values of 5 assembled specimens, each consisting of 2 or 3 discs (CORE 0.70 mm/OP - 0, 0.25, 0.50, 0.75, or 1.00 mm/TP 1.00, 0.75, 0.50, 0.25, or 0 mm) were determined with a spectrophotometer for the Vita shades A1, A2, and A3. Distilled water was used to attain optical contact between the layers. Black or white backgrounds were used to assess the influence of the background on the final shade. Color differences (ΔE) between layered specimens were determined. Correlation between the thickness ratio and the L*, a*, and b* values was calculated by 2-tailed Spearman correlation analysis. Results The results indicated that small changes in OP/TP thickness ratio can perceivably influence the final shade of the layered specimens (ΔE >1). Redness a* and yellowness b* increased with the thickness of OP for all shades. Redness a* ( P < .01 for all shades) correlated more strongly with thickness than yellowness b* ( P < .01 for A1 and A3; P < .05 for A2). The lightness (L*) was shade dependent. The correlation (r) between OP/TP thickness and L* was 0.975 ( P < .01) for shade A1, 0.700 (not statistically significant) for shade A2, and 0.900 ( P < .05) for shade A3. Conclusion Small changes in thickness and shade of opaque and translucent porcelain layers can influence the final shade of the layered porcelain specimen.

Influence of Microwaves on Nonformaldehyde DP Finished Dyed Cotton Fabrics

An alternative approach to formaldehyde-releasing conventional N-methylol com pounds is based on the use of nonformaldehyde durable press polycarboxlic acid (PCA) finishing agents. Another alternative approach, investigated here, is using microwave energy to impart durable crease resistance to dyed cotton fabric. The bifunctional dyes C.I. Reactive Red 195, C.I. Reactive Yellow 145, and C.I. Reactive Blue 221 are used in the study, and the isocratic HPLC method is employed to quantify the PCA reacted with the cellulosic material for two different curing procedures. Shade change evaluation reveals that microwave curing has a greater influence on the dE values than conventional curing. In all other aspects, primarily wrinkle recovery and deformation resistance, microwave curing offers much better results.

Sulphur dyes on nylon 6,6—part 2: the effects of reductant, oxidant and wash-off

Nylon 6.6 was dyed with five commercial suphur dyes using seven different reducing systems and three oxidation systems and the dyeings were subected to repeated wash testing and to light fastness assessment. It was found that the different reductants effected not only the colour strength of the dyeings but also influenced the colour of the dyeings. Two of the reducing systems studied had a deleterious effect on colour strength achieved for some of the dyes. From a wash fastness viewpoint, while the same two reducing systems had a deliterious effect on both the extent of shade change and staining of adjacent multifibres, overall, the dyeings displayed very good fastness to the five repeated wash tests. There was very little difference between the three oxidising systems examined in terms of the colour strength of the dyeings, with the f( k) values obtained for the five dyes being virtually identical for each of the three oxidation systems used. However, the colour of the dyeings differed for the three oxidation systems studied. The wash fastness of the dyeings was little effected by the type of oxidant used. The wash-off of dyeings markedly reduced the extent of staining of adjacent multifibre strip but did not improve the colour change that occurred upon repeated washing. With the exception of the black dye, the dyes displayed poor fastness to light and this was, in general, little influenced by reductant, oxidant and wash-off.

Effect of liquor ratio on the shade change and cross‐staining observed in the ISO 105‐C08 test†

The effect of liquor ratio on the amount of cross‐staining and shade change in the ISO 105‐C08 wash fastness test has been studied in order to improve the correlation between the results from the laboratory test and to those obtained in a domestic washing machine. It has been shown that the correlation obtained for cross‐staining but not shade change is improved when the liquor ratio is reduced below the 50;1 currently in use. A revised setting of 20;1 is recommended for an international ring test to confirm repeatability and reproducibility.

Bleaching effect on pulpless tooth with simultaneous use of Nd:YAG laser

The purpose of this study is to report some knowledge gained from experiments in which we tried tooth bleaching using laser and bleaching agents on pulpless tooth due to trauma. We conducted in vitro experiments using extracted teeth of lower permanent central incisors with the following four conditions: (1) using 30% hydrogen peroxide (H 2O 2) and Nd:YAG laser, without Indian ink; (2) in addition to the condition of (1), with Indian ink; (3) using laser in conjunction with H 2O 2 and sodium perborate, without Indian ink; (4) in addition to the conditions of (3), with Indian ink. The bleaching agents that used 30% H 2O 2 and sodium perborate had more bleaching effects than the one with 30% H 2O 2 only. Furthermore, translucency was not lost in the cases in which Indian ink was not used. Obtaining above results, we conducted clinical trials under condition (3). In three trial cases, changes in shade were observed after the bleaching treatment. Largely satisfactory results were gained with over three times radiation in two clinical cases. After the bleaching treatment, the patients had no perceptive or apparent symptoms. Little recurrence of discoloration was found.

Sulphur dyes on nylon 6,6—part 1: the effects of temperature and pH on dyeing

Nylon 6.6 was dyed with five commercial sulphur dyes at different pH values and various temperatures. It was found that over the pH range 6–12, maximum colour strength was achieved at pH 7 and the colour of the dyeings was influenced by the pH at which dyeing had been carried out. The latter observation was explained in terms of the effect of pH on the state of reduction of the dyes and their subsequent oxidative condensation. The five dyes varied in terms of the effect of dyeing temperature, over the range 50–120 °C, on colour strength. Generally, within the range 70–98 °C, temperature had little effect on the colour of the dyeings whereas both lower dyeing temperatures (50 and 60 °C) and, especially, higher temperatures (110 and 120 °C) resulted in colour change. In terms of wash fastness, dyeing temperature had little influence on shade change or staining of adjacent multifibre material. With the exception of the black dye used, the dyeings displayed poor fastness to light; dyeing temperature had little effect on light fastness.

Reaction between pH indicators with a large pKa value and human serum albumin and its application to the determination of the serum albumin concentration

The reaction between four pH indicators with a large pKa value and human serum albumin and its application to the determination of the serum albumin concentration were studied. In the reaction of Bromothymol Blue (BTB), Phenol Red, Cresol Red and Thymol Blue with serum albumin, although a change in the color shade did not occur, the absorbance of the reaction mixture decreased. Since this absorbance decrease was largest in the reaction of BTB(the molar absorbance decrease at pH 7.4 was 7.59×104 l mol−1 cm−1), which was sufficiently sensitive to measure the serum albumin concentration, the BTB color reagent at pH 7.4 was applied to its determination. The measurement values by the BTB method correlated with those by the dye-binding method using the Bromocresol Green method(r = 0.965, y = 1.21x−4.25, n = 90) and with those by a method using Bromocresol Purple(r = 0.953, y = 1.04x + 3.56, n = 90). The mean value of the BTB method (41.8 g/l) was higher than those of the Bromocresol Green method (38.1 g/l) and the Bromocresol Purple method(36.6 g/l). Since the reaction of BTB was carried out at pH 7.4, where serum protein does not precipitate, the addition of a detergent for preventing the precipitation of serum protein is not required. Therefore, the use of this color reagent contributes to decreasing water pollution by the detergent and acid used in the conventional methods.

Tooth whitening is effective, with neither adverse nor beneficial effects to gingiva or plaque

Objective To assess the efficacy and safety of dentist-prescribed, home-applied tooth whitening agents Data sources Medline 1989–1999 inclusive Study selection Placebo controlled clinical trials of 10% carbamide peroxide using a custom-fitted tray, which reported efficacy using a change in shade guide units were included. Data extraction and synthesis Shade guide unit change was evaluated to reflect efficacy, and both gingival and plaque indices to reflect safety. All 3 were analysed for the significance of 4 variables: treatment group, daily application time, the duration of treatment, and brand of bleach were examined . Number needed to treat was calculated. Results 28 trials evaluated tooth bleaching, 20 of which were dentists-prescribed, and patient applied agents. 7 met all the criteria. The data indicated that home-applied agents using a 10% carbamide peroxide gel delivered in a custom-fitted tray whitened teeth significantly, when compared to a placebo control. Conclusions Within the caveats discussed in the paper, the results indicate that, on average, dentist-prescribed, home-applied tooth whitening will whiten teeth 2 shade guide steps for six months, and neither adversely nor beneficially affect the gingiva or plaque.

Quantitative light-induced fluorescence: a potential tool for general dental assessment.

Current dental diagnostic methods can detect caries but cannot quantify the mineral status of a lesion. Quantitative light-induced fluorescence (QLF) measures the percentage of fluorescence change of demineralized enamel with respect to surrounding sound enamel, and relates it directly to the amount of mineral lost during demineralization. Development of caries-like lesions and subsequent remineralization of the lesions were monitored by QLF. The results showed that the percentage of fluorescence change (Delta Q) increased linearly with the demineralization time and decreased with increased remineralization time. Stained teeth were whitened with a bleaching agent and the change in stain intensity (Delta E) was quantified using QLF. The results showed that Delta E decreased linearly as the tooth regained its natural color. Factors that might affect the use of QLF to detect and quantify caries were also examined. It was concluded that QLF could be used to detect and longitudinally monitor the progression or remineralization of incipient caries, however lesion detection may be limited by the presence of saliva or plaque and enhanced by staining. The change in shade of discolored teeth by whitening agents could be quantitatively measured by QLF.

Riparian gravel banks of upland and lowland rivers in Victoria (south-east Australia): arthropod community structure and life-history patterns along a longitudinal gradient

Riparian sand and gravel banks are inhabited by a fauna that is well adapted to varying river water levels and frequent inundation of the banks. Arthropods found in these habitats were studied from November 1998 to January 1999 in the upper and lower floodplains of the main rivers and tributaries in ten major catchments in the Victorian Alps. Wolf spiders (Lycosidae, 68%) and ground beetles (Carabidae, 7.8%) were the most abundant arthropods, with densities averaging 14.6 ± 1.8 (s.e.) and 2.3 ± 0.4 individuals m–2 respectively. Species composition and wolf spider densities changed substantially between upland and lowland rivers. These differences correspond with changes in altitude, shading, and gravel and gravel bank size. Comparison of our results with similar studies conducted in temperate Northern Hemisphere floodplains showed significant differences. Carabidae, not Lycosidae, are the dominant arthropod group in Northern Hemisphere floodplains. Wolf spider densities are higher in upper than lower reaches of rivers in the Victorian Alps, but do not change along rivers in the Northern Hemisphere. In contrast, carabid beetles showed similar densities between upland and lowland floodplains in Victoria, but increase in density along rivers in the Northern Hemisphere. A second, monthly sampling program on gravel banks along the Avon River (Gippsland) over a one-year period in 1996 and 1997 provided information on the life histories of eight common gravel-bank arthropods: Venatrix lapidosa, V. arenaris, two undescribed Artoria species (‘A’, ‘B’) (Lycosidae), Eudalia macleayi, Elaphropus ovensensis, Perileptus constricticeps and an unidentified Loxandrus species (‘B’) (Carabidae). Artoria sp. A and sp. B are diplochronous. Despite its smaller size, Artoria sp. B matured one month after Artoria sp. A. Lower temperatures at upland streams and rivers, the typical habitat for Artoria sp. B, may delay its development in comparison with Artoria sp. A, which is generally found further downstream. The life histories of both lycosid spiders and carabid beetles, characterised by prolonged reproductive period and short larval development, appear to have some adaptive value in regard to the disturbance-prone environment.

Guidance for selecting the measurement conditions in the dye-binding method for determining serum protein: theoretical analysis based on the chemical equilibrium of protein error.

A methodology for selecting the measurement conditions in the dye-binding method for determining serum protein has been studied by a theoretical calculation. This calculation was based on the fact that a protein error occurs because of a reaction between the side chains of a positively charged amino acid residue in a protein molecule and a dissociated dye anion. The calculated characteristics of this method are summarized as follows: (1) Although the reaction between the dye and the protein occurs up to about pH 12, a change in the color shade, called protein error, is observed only in a pH region restricted within narrow limits. (2) Although the apparent absorbance (the absorbance of the test solution measured against a reagent blank) is lower than the true absorbance indicated by the formed dye-protein complex, the apparent absorbance correlates with the true absorbance with a correlation coefficient of 1.0. (3) At a higher dye concentration, the calibration curve is more linear at a higher pH than at a lower pH. Most of these characteristics were similarly observed experimentally in the reactions of BPB, BCG and BCP with human and bovine albumins. It is concluded that in order to ensure the linearity of the calibration curve, the measurement should be performed at a higher dye concentration and sufficiently high pH where the detection sensitivity is satisfied.

Spatial and temporal patterns of territorial mate locating behaviour in Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae)

Male Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae) defend perch sites as a method of visually locating receptive females. In this study we charted the spatio-temporal activity of perching males in tropical Australia to investigate (a) the extent to which male activity is thermally constrained, and (b) the physical attributes of selected perching sites. Butterflies were surveyed along two 5-15m wide open corridors through dense vegetation, and this allowed the prediction that males should favour narrower corridor sections in order to maximize their visual search capability. This prediction was supported. Beyond corridor width, the distribution of favoured perches was not explained any further by patterns of shading, larval food plant distribution, or the presence of nectar resources. Males were active from 0800 to 1700 h, but the number of perching individuals varied throughout the day, and this pattern varied between the two transects. Most individuals perched along one transect in the morning (0900-1100 h), whereas activity along the other peaked around midday (1100-1300 h). This between-transect difference in male activity followed changes in shading between the transects, however this variable did not predict male distribution at the territory scale. Although ambient and black body temperatures were significantly related to population-level activity, these variables only predicted 15-55% of the variance in male counts in individual transects. This result, viewed in conjunction with the limited available information on female receptivity, suggests that the timing of mate location in H. bolina may be primarily influenced by the daily pattern of female availability.

Durable press finish of cotton/polyester fabrics with 1,2,3,4‐butanetetracarboxylic acid and sodium propionate

AbstractSodium hypophosphite (SHP) is widely used as an effective catalyst for the esterification reaction of cellulose with 1,2,3,4‐butanetetracarboxylic acid (BTCA). However, catalysts containing phosphorus cause significant shade changes in dyed fabrics because of their reductive nature, and the effluents containing phosphorus cause eutrophication in rivers and lakes. Hence, their commercial application as catalysts in textile processing is limited. In this study sodium propionate and its catalytic activities as a nonphosphorous catalyst were investigated. The evidence for esterification and crosslinking of cellulose with BTCA in the presence of sodium propionate was shown by an improved wrinkle recovery angle and durable press rating of treated fabrics. The presence of ester groups in the treated fabrics was confirmed by FTIR analysis. The performance of sodium propionate as a catalyst for BTCA was comparable to that of SHP. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 81: 654–661, 2001

Effect of temperature and bath composition on the dyeing of cotton with catalase‐treated bleaching effluent

Conventional rinsing to remove residual hydrogen peroxide after the bleaching of cotton fabric can be replaced by enzymatic cleaning using catalases. Our previous study showed that dyeing in such catalase‐treated bleaching baths results in a shade change on the dyed fabrics. The aim of this present study was to investigate the reasons for the unacceptable colour differences of the dyed fabrics. Experiments were performed to study the possible temperature‐dependent dye interactions in the standard dyebath, and in the dyebath prepared with bleaching effluent. Fluorescence emission spectra were used to detect changes in the structure of the catalase related to the thermal unfolding and denaturing of the protein. It was found that the colour difference on the dyed textiles could be attributed to the temperature‐dependent dye‐enzyme interaction and precipitation, as well as to the complexity of the bleaching bath composition.

Thermodynamics of the Digital Transfer Printing Process

The digital transfer printing process is divided into two steps: i) the digital print of an image on the transfer paper and ii) the thermal transfer (sublimation process) of the printed image onto the textile or other polymer substrates.Based on the sublimation model the thermal transfer process is explained and the critical physical parameters are evaluated: affinity of the dye to the paper and sublimation enthalpy of the dye.Analyzing the spectral behavior of transfer dyes transferred at different temperatures the activation energy for the transfer printing process is evaluated and compared to the sublimation enthalpy of the dye.The spectral behavior of transfer papers before and after transfer show a dramatic change in shade. This clearly indicates a fixation of the transfer dye on / in the paper surface. As a conclusion to evaluate the whole transfer printing process it is necessary to take the distribution equilibrium between the paper and the substrate into account: The higher the affinity of the paper to the dye, the lower is the color strength on the substrate.Based on the physical properties of transfer disperse dyes the consequences on color generation and reproducibility are discussed.

A CLINICAL EVALUATION OF 10 PERCENT VS. 15 PERCENT CARBAMIDE PEROXIDE TOOTH-WHITENING AGENTS

Agents with carbamide peroxide, or CP, in various concentrations are widely prescribed for at-home tooth whitening. It is not clear, however, if the more concentrated gels will whitening teeth to a greater extent, as no controlled clinical trials have been reported. The authors conducted a double-blind study of human subjects to evaluate whether a 15 percent CP tooth-whitening system was more effective than a 10 percent CP system, and to determine if tooth sensitivity increased with use of the higher concentration. The authors recruited 57 subjects with maxillary anterior teeth of shade A3 or darker (as gauged against a value-oriented shade guide). The subjects were 18 to 65 years of age and in good general and dental health. After matching the subjects by sex and age, the authors randomly assigned them to either a control group, which used a 10 percent CP whitening agent, or an experimental group, which used a 15 percent CP agent. The results indicated that there was no significant difference in shade change between the groups after one week of treatment (t = 1.455, P = .05), but there was a significant difference at the end of the treatment period (t = 2.303, P < .05), as well as two weeks after treatment concluded (t = 2.248, P < .05). There was no significant difference in sensitivity (t = 1.399, P > .05). There was a significant difference in color change between the 10 percent CP and 15 percent CP groups at the end of the study period. There was no significant difference in level of tooth sensitivity between the two groups, and the incidence was equal; there was, however, a significant difference in variability of tooth sensitivity between the two groups. If performed under the careful guidance of a dentist, at-home whitening is an effective treatment, regardless of whether 10 percent CP or 15 percent CP is used. There may be added color change and varying sensitivity with the use of 15 percent CP.

Dye distribution in the dyeing of mixed denier polyester fabrics

Microfibre polyester is sometimes blended with higher denier fibres to achieve good aesthetic effects at lower cost. Two polyester yarns of 1.4 and 0.7 denier were dyed singly and together with a range of depths of CI Disperse Blue 79, and the dye distribution over the course of the dyeings was examined. The uptake is initially greater on the microfibre, but as dyeing is continued the distribution becomes more even, and eventually the same concentration of dye is present on both fibres. Based on the common observation that a given concentration of dye produces a lighter shade on a microfibre, the redistribution of dye during the process causes a continuing shade change even though the bath exhaustion is constant. A mixture of three dyes produced a stable hue on a fabric of 1.0 denier polyester after 20 min at a fixed dyeing temperature, but when dyed on a fabric of 1.0 and 0.5 denier yarns, a change in hue continued for more than 60 min.

Teaching nightguard bleaching and other tooth‐whitening procedures in North American dental schools

Tooth-whitening using carbamide peroxide delivered in a custom-fitted tray (nightguard bleaching) is a relatively new procedure, yet it is currently one of the most commonly used types of esthetic dental treatment in private practice. This study determined the extent that nightguard bleaching (NGB) has been included in dental school curricula. All sixty-five dental schools in North America were surveyed about curriculum content and treatment protocol for the use of nightguard and other bleaching procedures, generating an 82 percent response. The survey covered eighteen subject areas related to NGB ranging from clinical requirements and indications to products and recall intervals used. The most commonly taught tooth-whitening procedure was NGB, which was most often taught by operative and restorative faculty. Although no schools had clinical requirements for NGB, 92 percent taught it. The most common indications for NGB were esthetic shade change and pre-restorative lightening of teeth. Unrestored caries, defective restorations, and pre-existing sensitivity were common contraindications. Most schools do not use a specific NGB consent form, but most use written patient instructions. Most schools use at least two different NGB products, bleach for two to four weeks, and use reservoired and scalloped trays. An average of 25 percent of NGB patients were estimated to develop sensitivity, for which treatment recommendations include fluoride, desensitizing toothpaste, and reduced exposure time. Curriculum time and safety concerns were reasons for not teaching NGB (8 percent schools). Most schools indicated that the relative importance of NGB in the curriculum was increasing.

The Effects of pH and Heat Treatment Processing on the Stability of Natural Food Colours used in Dairy Products

This study was carried out to investigate the effects of pH and heat treatment processing on stability and natural food colours used in dairy products. A repeated laboratory experiment was conducted in which loss of colour intensity or change in shade of natural food colours used in acid and nearly neutral dairy products at low and at boiling temperatures was investigated. Five (5) natural food colours out of the fourteen (14) in the study were applied to small-scale industrial processing of UHT milk drinks and laboratory-scale yoghurt making. All the fourteen natural food colours studied were stable to pH changes. Only one natural food colour (Beet root) was destroyed at boiling temperatures while two of the colours (Beet root and Cochineal) were destroyed at UHT (136oC/4Seconds) processing. It was then concluded that pH changes and Heat Treatment processing do not contribute very much to the destruction of natural food colours used in dairy products. The Journal of Food Technology in Africa Volume 5 Number 2 (April - June 2000), pp. 59-61 KEY WORDS: pH, Heat, Stability, Food Colours

Nightguard Vital Bleaching of Tetracycline‐Stained Teeth: 54 Months Post Treatment

The purpose of this longitudinal whitening study was to determine the stability, post-treatment side effects, and patient satisfaction after 6 months of active treatment of tetracycline-stained teeth with 10% carbamide peroxide at 0 and 54 months post treatment. Twelve patients who completed the study (80%) were contacted and asked to participate in a survey concerning their whitening experience. Subjects were asked whether there had been any change in the shade of their teeth after treatment, and if they had experienced any side effects that they believed were treatment-related. Eight of the twelve patients underwent clinical examination. Ten patients (83%) reported no obvious shade change or only a slight darkening not noticed by others. Two (17%) reported a slight darkening that is probably noticeable by other people, but no one reported moderate darkening or significant darkening back to original shade. All respondents (n = 12) denied having to have a crown or root canal that they believed was treatment-related. Examiners who compared preoperative and post-treatment photographs and Vita shade values were in agreement with the patient's perceptions of shade change. The degree of improvement was significant for both the immediate (0 mo) and the 54-month post-treatment comparison with the pretreatment shade (p < .005 and p < .01 respectively). Results of this nightguard vital bleaching study indicate that tetracycline-stained teeth can be whitened successfully using extended treatment time, and that shade stability may last at least 54 months after treatment. Patients who participated in this study were overwhelmingly positive about the procedure in terms of shade retention and lack of post-treatment side effects.