Supervisors info:
Παπάζογλου Ευστράτιος, Αναπληρωτής Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ.
Γεώργιος Πετράκος, Αναπληρωτής Καθηγητής, Τμήμα Δημόσιας Διοίκησης, Σχολή Πολιτικών Επιστημών, Πάντειο Πανεπιστήμιο.
Paravina Rade, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, Πανεπιστήμιο του Τέξας.
Summary:
Introduction: A smile plays a major role in the assessment of facial attractiveness and in the overall evaluation of a smiling person. Several studies have shown that poor dental esthetics is considered to be less attractive overall, including social attractiveness. The success of each restoration is heavily determined by the uniformity and color resemblance, that they have while opposed to the adjacent teeth or restorations. The perception of color in the space related to dentistry, is a complex phenomenon that involves three factors: the observer, the illuminant and the object. It is well established that dentistry employs mathematic equations, as a mean to ‘quantify’ color and subsequently ‘calculate’ the color difference between two distinct surfaces. Digital technology, using the computer-aided image manipulation, has been used in order to investigate the impact of specific changes in dental appearance, without altering other facial or smile characteristics. In order to interpret, color difference, usually perceptibility and acceptability thresholds are estimated. Perceptibility threshold refers to the smallest color difference, that can be detected by an observer. A 50:50% perceptibility threshold, refers to the situation in which 50% of observers notice a difference in color, between two objects while the other 50% notice no difference. Accordingly, the difference in color that is acceptable for 50% of observers corresponds to a 50:50% acceptability threshold. Except from these thresholds, the influence of color difference in smile attractiveness is an important factor. However, the effect of the discoloration of tooth types (central incisor, canine) on the overall facial attractiveness, has not yet been investigated. Moreover, the association between perceptibility and acceptability frequencies and smile attractiveness, still has not been evaluated.
Objectives. The first purpose of this study, was to evaluate the influence of lightness difference, of a single anterior maxillary tooth on smile attractiveness, using the CIELAB system on digital simulated facial portraits. The second aim was to assess the visual perceptibility and acceptability thresholds, for lightness differences of a single maxillary central incisor, and to investigate possible differences in these thresholds between the type (i.e. dentists vs laypersons), the gender and the age, in order to estimate the boundaries, within which a singled restoration prosthesis can remain undetectable or with an acceptable difference compared to the remaining teeth of the smile. The third purpose was to investigate the association between the attractiveness of the smile and perceptibility and acceptability frequencies would be investigated.
Material & Methods: A series of images with varying lightness (L), were created by altering the anterior teeth of a male Caucasian, on a frontal view of full-portrait image. For each one of the three anterior teeth the shade was modified, to create 15 different images, one image serving as the control and half with increased and half with decreased lightness, were created by modifying digitally in each step 1 ΔL unit (ΔL=ΔΕ=1). The images were presented in random order in a digital calibrated monitor. 160 participants (80 dentists, 80 laypersons) were instructed to fill out a questionnaire, giving a score using a Visual Analog Scale and evaluating every image for a perceptibly or an acceptable mismatch of central incisor color. All participants were screened using Ishihara’s test for color deficiency, in order to ensure judgements validity in the perceptibility and acceptability questions regarding the color changes.
Results: For central incisors difference in lightness, ΔL≥1 negatively affected attractiveness. There was a higher tolerance for lightness mismatch, when one lateral incisor is lighter and the same applies when the canine was darker. Difference in lightness affected smile attractiveness, both for dentists and laypersons. No difference between males and females was observed for the dentists. For laypersons, females perceived smiles with lightness difference, as significantly less attractive compared to males. Dentist's age did not affect perception of smile attractiveness. Younger laypersons perceived darker color, as less attractive. 50% perceptibility thresholds were significant lower in dentists compared to laypersons. There was found a significant difference, regarding 50% acceptability thresholds between the type of observer. Dentist group presented a high false rate compared to layperson. Smile attractiveness score presented a different curve, compared to perceptibility and acceptability frequencies.
Conclusion: Changes in lightness of a single anterior tooth significantly affected smile attractiveness in a different way for the central vs lateral vs canine. For the dentists, age and gender did not significantly affect smile perception, in contrast to laypeople. Difference in lightness between the two central incisors, is tolerated with various degrees among dentists and laypersons. The age and the gender of the observer plays an important role in the perception of differences in lightness. Perceptibility thresholds were significantly lower than acceptability thresholds. The assessment of smile attractiveness complement the perceptibility and acceptability estimation, assisting in a better interpretation, of the influence of color difference in clinical reality, overcoming problems, as high false alarm rates and the bias that is created when the observers are informed that they have to assess a difference in color. Digital simulation of differences in the color of the teeth on human portraits, constitute a significant tool in order to assess color difference thresholds, especially in the era of social media, where a major part of communication is performed via digital images. However, image simulation, is a technique that presents also limitations compared to in vivo circumstances, when the results has to be expanded in the clinical reality.
Clinical significance: Lightness differences of a single anterior tooth affects smile attractiveness, in an individualized way for each tooth. The assessment of smile attractiveness complements the perceptibility and acceptability estimation of visual thresholds, assisting in a better interpretation, of the influence of color difference in clinical reality
