Keywords
Eye tracking - heat maps - incisor abrasion - perception - scan path
Introduction
For a long time, orthodontic treatment was performed mainly based on occlusal results.
The need for treatment in patients with malocclusions and the outcomes of orthodontic
treatment are typically assessed by orthodontists or the patients themselves.[[1]]
Orthodontists generally employ cephalometry, model analysis, and the index of orthodontic
treatment need in their assessments. Conversely, the patient self-evaluation methods
include the psychosocial impact questionnaire on dental esthetics and the esthetic
component of the index of orthodontic treatment need.[[2]]
Dental wear can be described as the loss of hard dental tissue resulting from a physical
or chemical cause; it is a broad term used to describe the combined processes of abrasion,
erosion, and attrition.[[3]]
In recent years, facial esthetics has become a main focus. For this reason, orthodontists
around the world are working to incorporate various tools designed to be used in improving
the esthetics of the smile into their clinical routines.[[4]] Dental and gingival asymmetries in maxillary incisors are common problems in adult
patients and are primarily caused by natural wear, fractures, or onychophagy,[[5]] with unequal crown heights being the resulting consequence.
In such a case, often, the patient has a maxillary central or lateral incisor that
is shorter or narrower than the contralateral tooth. These asymmetric changes in tooth
shape and alignment affect the perception of anterior tooth attractiveness as opposed
to symmetric changes.
For more objective orientations pertaining to the perception of smile esthetics, several
studies were carried out involving the manipulation of digital images[[6]],[[7]] and recent investigations, such as those employing eye tracking, have explored
the need for orthodontic treatment and treatment outcomes from the viewpoint of laypersons.
Importantly, these efforts present a new option for evaluation as compared with traditional
assessments based on photographs and the use of the visual analog scale.[[8]]
The eye-tracking technique has been widely used in studies of esthetic perception,
taking into account facial expression, gender, and ethnic judgment. The major advantage
of it is that, with its use, there exists the possibility of recording the movements
of the eyeballs while several stimuli compete for attention. Evaluating changes in
attention hierarchy is considered to represent a strategy for extracting facial and
cognitive information.[[9]] Eye tracking also provides an objective method for assessing what people see, and
data can establish a visual attention hierarchy[[10]] such that the use of this technology may complement the understanding of the analysis
that involves the psychosocial aspect of the esthetic sense in symmetrical and asymmetric
cases as well as in instances of facial and dental malocclusion.
As dental asymmetry in the esthetic zone is a common problem, mainly caused by tooth
wear or abrasions of the incisors and leading to unequal crown lengths, the objective
of the present study was to evaluate the visual esthetic perception of the magnitude
of abrasions in the maxillary central incisors from different categories of observers
through employing the eye-tracking technique.
Materials and Methods
The present study was analyzed and approved by the Ethics Committee of the university
(name was omitted). The study included 30 dentistry students (15 men and 15 women)
and 30 laypeople (15 men and 15 women) who did not receive prior notice of the purpose
of the study. The selected images were digitally altered using Photoshop® (Adobe Systems
Inc., San Jose, CA, USA) and included only extraoral smiling images. In addition,
Photoshop® was also used to remove imperfections (e.g., scars, props, and spots on
the skin) from the face that could draw the observer’s attention away from the primary
focus. Abrasions simulating tooth wear were edited by increasing them progressively
in increments of 0.25, 0.5, 0.75, 1.0, and 1.5 mm. In all images, the gingival margins,
papillae, and contralateral side along with the mandibular arch were kept aligned
and level.
To obtain the ocular tracing, The Eye Tribe Tracker® software (The Eye Tribe Aps,
Copenhagen, Denmark) was used in conjunction with the Ogama software (Freie Universität,
Berlin, Germany) to observe and record the ocular movement of each evaluator in a
given interest area. During the evaluation, 14 interest areas were mapped in the images:
Specifically, the right eye (target 1), left eye (target 2), right eyebrow (target
3), left eyebrow (target 4), nose (target 5), right side of the mouth (target 6),
left side of the mouth (target 7), forehead (target 8), hair (target 9), right cheek
(target 10), left cheek (target 11), chin (target 12), right ear (target 13), and
the left ear (target 14), respectively [[Figure 1]]. Before participating in the project, raters signed an informed consent form, in
which they affirmed they had good vision and were not taking any medicines that might
interfere with their cognitive or motor skills.
Figure 1: Interest area targets mapped in the face
Raters were informed that they could freely observe the images and were instructed
to sit in a chair so that they felt comfortable at a distance of 60 cm–90 cm from
a 17-inch (Dell P2317H; Dell Inc., Round Rock, TX, USA) monitor, upon which the images
at a true size were projected vertically. The Eye Tribe Tracker® was positioned just
below the monitor as recommended by the manufacturer. In the experiment itself, 12
images were projected (six images simulating central incisor abrasions that were projected
for 3 s and six transition slides that were projected for 1 s, respectively). Between
the displaying of each image, a green transition slide was included to prevent eye
fatigue and to prevent the last fixation point of the previous image from interfering
with the first fixation point of the next image – in other words, to have a “zero”
regarding the focus of the observer’s gaze. The software was calibrated to obtain
more reliable data and, as a requirement, only the “perfect” calibration was considered.
The tracing of the generated data was done on a heat map and a scanpath. The heat
map supplied information such as which areas were those most observed by the raters
in a certain interest area as selected according to a color scale ranging from cold
colors to warm colors (i.e., green to red). The report of hotter colors meant that
more fixations had occurred at that point. This was in addition to information from
the other areas that were considered to fall into the “other” category. Furthermore,
scanpaths provided tracking order information by rater category.
Results
The results indicated that, the higher the abrasion in the maxillary central incisor
was, then the greater the focus of the raters’ eyes for this region was especially
for dentistry students. In comparison, laypeople tended to diverge their gaze to other
regions such as the eyes and upper lip; however, they also observed abrasions to a
greater degree [[Figure 2]], [[Figure 3]], [[Figure 4]].
Figure 2: Heat maps. (a) No abrasion; (b) Laypeople; (d) Abrasion of 0.25 mm; (e) Laypeople;
(c and f) Students
Figure 3: Heat maps. (a) Abrasion of 0.5 mm; (b) Laypeople; (d) Abrasion of 0.75 mm; (e) Laypeople;
(c and f) Students
Figure 4: Heat maps. (a) Abrasion of 1.0 mm; (b) Laypeople; (d) Abrasion of 1.25 mm; (e) Laypeople;
(c and f) Students
By evaluating the scanpaths of the images without abrasions, students directed their
greatest amount of focus to the anterior region of the smile, diverging slightly to
the right eye. In the 0.25mm abrasion images, students placed the greatest focus again
on the anterior region, where the abrasions were present [[Figure 5]]. As a contrast, the laypeople involved in the present study concentrated on the
area of wear but often diverged their gaze to the left ear and eyes. For images containing
a 1.5mm abrasion, students had the greatest focus on the region of abrasion, diverging
slightly to the eyes [[Figure 4]]. They also fixated predominantly on the affected region, changing their focus slightly
at times to the eyes [[Figure 5]].
Figure 5: Scanpaths. Students (a) No abrasion; (b) Abrasion of 0.25 mm; (c) Abrasion of 1.5 mm;
(d). Laypeople; (e) No abrasion, 0.25 mm; (f) Abrasion of 1.5 mm
Discussion
At present, esthetic dental concerns are on the rise, with many patients seeking out
professionals to improve their smile and, consequently, their self-esteem. Eye-tracking
technology has been used previously to objectively evaluate attention paid to the
mouth, and tracking eye movements can offer insights into dentitions, faces, and smiles,
along with a few details regarding laypeople’s and dentists’ tendencies.
As dental asymmetries in the esthetic zone are common problems, mainly caused by tooth
wear or abrasions of the incisors, leading to unequal crown lengths, the objective
of the current study was to evaluate the esthetic perceptions of two different groups
(laypeople and dentistry students). Through eye tracking, the results were obtained
with heat maps and scanpaths of the images, in which there was a range of tooth presentations
from a central incisor without abrasions to a central incisor with 1.5-mm abrasions
through gradual increases (i.e., 0.25, 0.5, 0, 75, 1.0, and 1.5 mm).
When evaluating the images as a whole, a discrepancy of perception can be observed
between the two groups of evaluators. Students viewing the nonabrasion images had
a greater focus on the region of the abrasion, with little divergence to examining
other areas, while conversely, the laypeople looked at several areas, placing their
greatest focus on the region worn out in the final images in which the degrees of
abrasion were higher [[Figure 5]].
Tooth wear can be described as the loss of hard dental tissue resulting from a physical
or chemical attack; it is an all-embracing term to describe the combined processes
of abrasion, erosion, and attrition.[[3]]
Teeth worn by abrasions or any other reason usually have a favorable prognosis. The
dentist, upon encountering a case of abrasion, tends, from an esthetic perspective,
to elaborate on planning and resolution of the case. Among treatment alternatives,
direct and indirect restorations are mentioned; however, before the conclusion of
the case, one must also analyze what the cause of the problem was to potentially prevent
a recurrence by mitigating causative factors.
When faced with a case, the dentist should first locate and measure the amount of
tooth wear and then subsequently decide whether restoration is necessary, as highlighted
by Machado et al.[[11]] and Kokich et al.[[7]] Specifically, they suggested that, in certain situations, if slight deviations
are not recognized as unattractive, then the patient should perhaps not be referred
for cosmetic restorations that would eventually need to be replaced or touched up.
In the current study, the evaluators, both laypeople and students, perceived dental
disharmony in the presented images. The students tended to focus more precisely on
the teeth because such is their area of practice; however, as everyone was unaware
of the project’s intent, one can observe in the results that areas observed outside
the points of interest of the work exist. Laypeople looked more closely at the whole
face, focusing on nearby points, and others far from the area of abrasion. The image
with 0.75 mm of abrasion evaluated by laypeople was the only one that had the greatest
distance focus, which was the right eye. The rest of the images had the majority of
focus of the laypeople present on the upper lip region, which is close to the point
of interest.
Clinical situations of abrasion can be observed in individuals with the habit of onychophagia,
in which a series of rapid spasmodic bites, with the nails pressed firmly against
the cutting edge of the teeth,[[5]] cause (or not) some degree of dental wear.
It is important to note that the Ogama software has a capture capacity of approximately
85%. With this, the software may not have been totally faithful to the evaluator’s
analysis; however, the scanpaths demonstrate that the tracked eye movements were toward
the abrasion, demonstrating the effectiveness of this study.
As the results and conclusions of the present study are based on averages, it is difficult
to customize this information to a patient because of the subjectivity of evaluations
of smile esthetics.[[7]] Seeing as we used computer-manipulated patient images and the opinions of specific
types of raters, the results should be cautiously interpreted. Therefore, we suggest
that clinicians discuss the results of this study with their patients who have a dental
abrasion and then request they decide what to do on their own based on the provided
information.
Conclusions
In this study, evaluating raters’ observations of different degrees of dental abrasion,
there were differences between the two groups of raters. Dental students primarily
focused on the teeth in all images presented, with only slight differences in other
areas, while laypeople diverged further into other interest areas with higher degrees
of abrasion.
Declaration of patient consent
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms.
In the form, the patients have given their consent for their images and other clinical
information to be reported in the journal. The patients understand that their names
and initials will not be published and due efforts will be made to conceal their identity,
but anonymity cannot be guaranteed.
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