Cosmetic/Esthetic - A Quarterly Newsletter on Dental SpecialtiesJADA

Perceptible and acceptable difference in color

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Appraising color variance is of great interest in dentistry and reinforced by increasing esthetic demands of patients and dental professionals. Determining color difference thresholds for both perceptibility (just noticeable differences) and acceptability (higher differences called acceptable color differences or color tolerances) are of great importance in advancing dental research in areas that include bleaching efficacy, color stability and dental shade.  

According to scientists publishing in the March/April 2015 issue of the Journal of Esthetic and Restorative Dentistry, perceptibility and acceptability thresholds can be helpful aides for selecting dental materials, as well as to evaluate their clinical performance, interpret visual and instrumental findings in clinical dentistry and dental research and assist in standards development.

To determine human color perceptibility and acceptability thresholds of dental ceramic in a simulated clinical setting, scientists at the University of Texas School of Dentistry at Houston coordinated a prospective study carried out at seven research sites around the world—Spain, Brazil, Germany, Hungary, U.S., Japan and Saudi Arabia. Scientists sought to determine at what point observers in the study differentiate a change in color of a dental ceramic and what on average is an acceptable change.

To investigate, scientists measured and calculated color values for 63 monochromatic ceramic specimens within the tooth color range. The specimens were then combined into specimen pairs. Of possible specimen pairs (1,953), 60 were selected for observation and further divided into three sets of 20 specimen pairs. The three sets were medium to light shades; medium to dark shades; and dark shades.

Five groups of five observers each—dentists, dental students, dental auxiliaries, dental technicians and lay people—were recruited from each of the seven research sites for a total of 175 evaluating participants. Each had normal color vision and passed a dental color matching competency test. Once scientists randomized the order of specimen pairs with each of the three sets, they presented specimen pairs in the same order to all observers and performed color comparisons using a viewing booth under standardized settings.

“Can you see a difference in color between these two specimens?”  If the answer was yes to this perceptibility threshold question, scientists asked the acceptability question: “Would you consider this difference in color acceptable in a patient’s mouth?”  Fifty percent “yes” responses were considered as the threshold level by the researchers.

Among results were differences between perceptibility thresholds and acceptability thresholds among groups of observers and among research sites. Perceptibility threshold differences by observer group revealed differences among the dentist, dental auxiliaries, dental technician and lay groups as compared with the perceptibility threshold for all observers. The acceptability threshold for dentists, dental students and auxiliaries was not significantly different. Dental technicians were more discriminating, whereas lay people were less discriminating compared with the overall acceptability threshold found.

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Color perception

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Despite instrumental methods of color evaluation, visual color matching is still the primary method for selecting and evaluating the color of teeth and restorations. Although accurate shade matching is essential to successful clinical practice, dentists’ visual perception is not routinely tested or systematically trained.

Finding that most studies focus on the physical and physiological variables that limit proper color selection, researchers at the University of Sao Paulo, Brazil, conducted a study to investigate the effects of an individual’s emotional aspects on color discrimination. They aimed to investigate color discrimination among dental students with regard to gender, symptoms of anxiety and depression and quality of life. Considering previous research showing potential effects of estrogenic activity, the scientists also evaluated whether the use of hormonal contraceptives might affect color perception.

The research team analyzed perception of color discrimination by exploring differences among 61 dental student volunteers (45 women and 16 men) without color perception-deficiency. From 25 sets of swatches, the volunteers were asked to group together identical swatches displaying the colors of blue, red and green at five different levels of saturation, as well as an achromatic set (gray), and a beige set representing colors similar to teeth.

Researchers assessed volunteers for the presence and severity of anxiety and depression symptoms, quality of life and psychological factors via well-recognized diagnostic tools and a psychiatrist who was part of the research team. Women were asked about hormonal contraceptive use. Each volunteer was also asked about their physical health and activities associated with the visual arts.

The primary finding was that there was no significant difference in color perception between the genders. The study did not demonstrate that psychosocial symptoms, such as anxiety and depression, interfered with perceptions of color difference. Also among findings with respect to the contraception variable, women who used hormonal contraception made more errors than women who did not, particularly with green and red colors and in regard to gray scale (brightness). When men were compared to women who used hormonal contraception, scientists did not see a significant difference between the groups. However, when men were compared with women who did not use contraception, women made more errors than the men.

Authors noted that some of the basis for the gender difference in color visualization seen in the literature can be associated with the cone photoreceptor coding genes. The coding genes for the long-wavelength light and medium wavelength light cone photoreceptors are present on the X chromosome. In discussion, authors also reported on previous research showing that the differences in color perception on the red-green axis between genders are more dependent on estrogen than testosterone.

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Dental morphology and occlusion education

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A new method of learning dental morphology and occlusion that emphasizes the visual arts and uses drawing, waxing and layering exercises was published in the Spring 2015 issue of the International Journal of Esthetic Dentistry.

The body of dental literature has established students’ longstanding problems with learning morphology and occlusion and understanding its value in their future careers. Attempts have been made to shift towards “more clinically applicable learning, the improvement of conceptual understanding and the acquisition of psychomotor skills,” the author said.

The report outlines what is called the “2D-3D-4D” concept approach, which is also intended to allow practicing dentists, dental technologists and their youngest team members to develop a strong sense of morphology, function and esthetics. Among its aspects is a conceptual part of the module which requires drawing in 3D using an approach involving the five perceptual skills of drawing—edges; spaces; relationship; light and shadows and gestalt. The perceptual skills were adapted to tooth drawing—frame; contour; elements; shadows and highlights; and composition.

“This enhances the learners’ creativity by stimulating the creative language mode of the right side of the brain,” according to the report.
Another among the important aspects of the module is material upgrades: “In many programs, students are expected to perform with excellence but are not necessarily using the most appropriate materials devices and techniques.”

The revisionary module “provides a practical and progressive learning methodology regarding dentin and enamel shape, function and distribution,” the author said. “The methodology is accompanied by state-of-the-art, clinically relevant materials, devices and techniques, as well as detailed instructional manuals and films for all laboratory exercises.”

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Less invasive treatment for amelogenesis imperfecta

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A case report describing a minimally invasive approach to treating amelogenesis imperfecta (AI) was reported about in the Spring 2015 issue of the International Journal of Esthetic Dentistry. Researchers achieved a full-mouth adhesive rehabilitation with direct composite restorations, veneer/onlays and facial/palatal veneers.

A hereditary disorder affecting enamel’s structure and appearance, AI results from a disruption in at least one of the three stages of normal enamel formation. The most widely used classification system for AI is based on appearance and developmental defects and distinguishes AI into one of four main types: hypoplastic, hypomaturation, hypocalcified and hypomaturation-hypoplastic. Due to affected patients’ psychological struggle, clinicians are generally inclined to address the problem as soon as possible. However, when and how to start treatment is challenging for clinicians because the bulk of the literature provides limited follow-up reporting, authors said.

In the published case describing treatment of a 24-year-old female with hypoplastic AI, the bonding did not show signs of degradation after five years,  “…which is encouraging to clinicians as it shows that adhesive techniques may be reliable even in the presence of a compromised enamel layer,” according to authors. The interdisciplinary treatment plan involved orthodontics, periodontics and restorative treatments.

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Wet Bonding Dilemma Now Solved

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When using the Total Etch (etch and rinse) adhesives technique, it’s critical that the dentin is dried to the appropriate degree before the bonding agent is applied. Highly moist dentin will affect the quality of the bond because it’s difficult to bond anything to a wet surface.  

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