Effect of personality characteristics on perception of tooth whitening outcome in young adults in long-term: a randomised, double-blind, placebo controlled trial

Abstract

Background

Tooth whitening is a popular cosmetic procedure; however, its perceived effectiveness and long-term psychosocial impact remain underexplored. This study investigated perceptions of tooth color change and the associated psychological and social effects over a one-year period, with particular attention to the role of individual personality traits.

Methods

Fifty participants aged 19 to 28 were randomly assigned to either an experimental group or a control group. The experimental group received a light-activated whitening gel, while the control group received an inactive gel. Evaluations were conducted at baseline, one week post-treatment, and one year post-treatment. Tooth color was measured using spectrophotometry. Standardized questionnaires were employed to assess psychosocial effects and personality traits. Data were analyzed using analysis of variance with Bonferroni post hoc tests and independent samples t-tests.

Results

The experimental group showed a significantly greater improvement in tooth color shortly after treatment compared to the control group. Although this improvement diminished over time, it remained above baseline levels at the one-year follow-up. In the short term, participants in the experimental group reported reduced psychological and social concerns, while the control group reported a decrease in psychological impact only. After one year, the experimental group experienced a return of psychosocial concerns, whereas the control group continued to report improvements. Personality traits influenced these outcomes: lower neuroticism and higher perfectionism were associated with enhanced short-term benefits, while higher conscientiousness was linked to more sustained long-term improvements.

Conclusions

Participants demonstrated limited ability to accurately perceive improvements in tooth color, often noticing relapse over time. The psychosocial impact of tooth whitening was influenced by personality traits, highlighting the importance of a personalized approach in cosmetic dental treatments. Practitioners should consider individual psychological profiles when managing patient expectations.

Trial registration

This clinical trial was prospectively registered with ClinicalTrials.gov (Identifier NCT03380702) on December 21, 2017.

Background

The esthetics of teeth play a significant role in facial attractiveness, self-confidence, and social integration [1]. Dissatisfaction with tooth color is a key factor influencing the perceived appeal of a smile and is shaped by cultural, demographic, age-related, gender-based, and educational variables [2–4]. Research consistently identifies tooth color as a primary concern for patients, contributing to the widespread popularity of tooth whitening procedures aimed at enhancing smile aesthetics [5–7].

Traditionally, tooth color has been assessed by dentists using standardized shade guides. However, this method is limited by factors such as an insufficient range of shades, variability in visual perception among practitioners, and poor alignment with the standards of the International Commission on Illumination (CIE) [8, 9]. Instrumental tooth color measurement—particularly spectrophotometry—offers a more objective and reproducible alternative by quantifying color within the CIE Lab* color space. In this system, L* represents lightness, a* measures the red-green axis, and b* the yellow-blue axis. The CIE Lab* model correlates well with human visual perception and has strong clinical relevance [8, 10, 11].

While tooth whitening has proven effective in improving tooth color, its long-term stability is often limited, which may negatively affect patient satisfaction due to perceived color relapse. High lightness and low chroma (i.e., low color saturation) are strong predictors of satisfaction with smile esthetics [12]. However, many studies report a weak or inconsistent relationship between objective measures of smile esthetics and broader quality-of-life outcomes, such as dental self-confidence and psychosocial well-being [13, 14]. Personality traits appear to significantly influence these perceptions: individuals high in neuroticism and low in conscientiousness tend to report more negative impacts of their oral health on daily life [15, 16]. Notably, individuals with higher levels of perfectionism often experience greater short-term gains in dental self-confidence following whitening treatments [17].

This study aimed to evaluate the extent of tooth color change over a one-year period and its impact on patient perception. We hypothesized that short-term whitening would produce a significant color change in the experimental group compared to the placebo group, leading to increased dental self-confidence and reduced esthetic concerns. We also anticipated that long-term discoloration in the experimental group would result in decreased self-confidence and heightened esthetic concerns, with personality traits—particularly perfectionism—modulating these perceptions.

Methods

The initial eligibility assessment sample comprised 95 individuals, including students, who received routine dental treatment at the University Dental Clinic in Rijeka, Croatia, over a 9-month period (November 2015). Of the total number, 35 respondents did not attend the follow-up visit or did not complete the questionnaire in full, and were therefore not included in the study. Sixty participants were assigned to a treatment or placebo group (each group N = 30) using randomization software (http://www.randomization.com). During the one-year follow-up period, 10 participants dropped out, and data from 50 participants were analyzed. The participants were aged between 19 and 28 years (median 21; interquartile range 19–23), with 74% being female. The experimental group consisted of 24 subjects, while the control group included 26.

Inclusion criteria were the presence of a complete anterior segment without caries, fillings, or prosthodontic restorations, without gingivitis, and without pronounced malocclusion. In the experimental group, the anterior teeth of both jaws were bleached using a standardized method with a lamp and bleaching gel (Signal Fast Professional Plus Set and Signal Easy Lamp Plus, Signal, Unilever, Argentina) for 30 min, while the placebo group underwent the same procedure without the active ingredient in the gel (but with the addition of Menthae piperitae aetheroleum to simulate the burning sensation of the whitening procedure).

The sample size was determined based on prior research [18, 19]. To detect a colour change difference of three between the treated and placebo groups,[11] with a standard deviation of three in each group, 80% power, and a 95% significance level, a minimum of 17 subjects in each group was necessary. Similarly, if the pre- and post-intervention difference between the groups was smaller (two units), with a standard deviation of two in both groups, a minimum of 17 subjects per group was still required. Approval for this study was granted by the institutional ethical board (No. 2170-24-01-15-04), and all participants provided written informed consent. The clinical trial is registered under the identifier NCT03380702 on ClinicalTrials.gov on December 21, 2017.

The study was a randomized, double-blind, placebo-controlled trial. Assessments were conducted at three time intervals– before the intervention (T0), one week after the intervention (T1), and one year after the intervention (T2). The colour of the reference tooth (right maxillary central incisor) was assessed using a spectrophotometer (SpectroShade, MHT, Verona, Italy) according to the Lab* system [10]. Lightness was evaluated as the L* value, chroma according to the formula C* = [(a*)² + (b*)²]¹/², and translucency as the difference between the measured values on a white (w) and black (b) background: TL = [(Lw − Lb)² + (aw − ab)² + (bw − bb)²]¹/². The colour differences before and after whitening were calculated using the formula: ΔE* = (ΔL² + Δa² + Δb*²)¹/².

The accuracy and precision of the SpectroShade spectrophotometer have been reported previously.¹³ Participants completed the 23-item Psychosocial Impact of Dental Esthetics Questionnaire (PIDAQ), which assessed dimensions of aesthetic concerns (AC)– such as disliking one’s teeth when seen in the mirror, in photographs, or in video recordings; psychological impact (PI)– including whether individuals believe that others have nicer teeth than they do, feel bad when thinking about their teeth, or envy the attractive teeth of others; social impact (SI)– such as worrying about what people think of their teeth, fearing someone might make a hurtful comment about them, or covering their mouth when speaking in front of others; and dental self-confidence (DSC)– including whether they feel proud of their teeth, believe their teeth are attractive to others, or feel satisfied with the appearance of their teeth [19].

Personality traits were estimated before the tooth whitening procedure (T0) using previously validated Croatian versions of psychometric instruments: the 44-item Big Five Inventory (BFI), the 10-item Rosenberg Self-Esteem Scale (RSS), and the 35-item Multidimensional Perfectionism Scale– Frost (MPS-F) [20–22].

For statistical analysis, repeated measures analysis of variance (ANOVA) with the Bonferroni post hoc test was used to evaluate differences in colour change and psychosocial impacts within each group (treatment and placebo) before (T0) and after the intervention (T1– short-term, and T2– long-term; within-group analysis). Independent samples t-tests were used to evaluate differences between the two groups before and after the intervention and to test the intensity of change (Δ: T1–T0, T2–T1, T2–T0; between-group analysis: treatment vs. placebo). Effect size was calculated using the formula r = √(t² / (t² + df)) for t-tests and η² for ANOVA. Effect size interpretation was based on Cohen’s criteria: 0.1–0.3 = small, 0.3–0.5 = medium, and > 0.5 = large. Eta squared was interpreted as the squared value of r according to Cohen’s criteria.

To analyze whether the impact of tooth whitening on psychosocial improvement depended on personality traits, levels of self-esteem, and perfectionism, moderation models were tested (a total of 84 models). The entered variables were: predictor (X)– delta colour change; outcome (Y)– delta PIDAQ dimensions (AC, PI, SI, DSC); and possible moderators (M)– global perfectionism, self-esteem, personality traits (extraversion, agreeableness, openness, conscientiousness, neuroticism). Twenty-eight models were evaluated for each of the three time intervals: ΔT1–T0, ΔT2–T1, and ΔT2–T0. Moderation was considered significant if the predictor–moderator interaction was statistically significant (unstandardized regression coefficient B, standard error). The proportion of variance explained by the moderation model (X–M interaction) was reported as R². To understand the moderation effect, conditional effects of X on Y were explored for low and high values of the moderator. Low and high values were calculated as the mean ± one standard deviation from the mean. Data analysis was performed using the commercial software IBM SPSS 22 (IBM Corp., Armonk, USA) with PROCESS and Hayes PROCESS Macro extension, while sample size calculations were performed in MedCalc 14.8.1 (MedCalc Software bvba, Ostend, Belgium).

Results

The distribution of colour properties, psychosocial impacts, and personality traits in the entire sample before the intervention is presented in Table 1. Initially, there were no differences between the groups in age, gender, quality of life, personality traits, lightness, or translucency; however, the placebo group had significantly lower chroma (15.86 vs. 17.92; p = 0.001; r = 0.471).

Table 1.

Descriptive statistics of the whole sample before intervention (N = 50). The table presents the mean values, standard deviations, and observed score ranges for dental parameters (lightness, chroma, translucency) and psychological measures including perceived impact of dental aesthetics (PIDAQ subscales), self-esteem, and personality traits

	Mean ± standard deviation	Range (minimum– maximum)
Lightness	75.17 ± 2.22	68.70–79.10
Chroma	16.85 ± 2.21	11.62–20.45
Translucency	2.76 ± 1.68	0.78–7.79
PIDAQ AC	1.8 ± 2.4	0–9
PIDAQ PI	6.3 ± 4.9	0–19
PIDAQ SI	3.3 ± 4.4	0–18
PIDAQ DSC	15.7 ± 4.8	2–24
Self-esteem	43.5 ± 4.9	27–50
Extraversion	29.9 ± 4.0	23–38
Agreeableness	33.8 ± 4.9	23–43
Conscientiousness	34.6 ± 4.8	26–44
Neuroticism	19.8 ± 4.9	12–33
Openness	39.2 ± 4.9	30–47
Global perfectionism	71.7 ± 17.6	46–118

In the active group, lightness increased significantly in the short-term (T1-T0) and decreased in the long-term (T2-T1), ending slightly higher than at the start (T2-T0). The placebo group showed no short-term change in lightness but a long-term decrease. Chroma decreased short-term and increased long-term in the active group, ending lower than initially, while the placebo group saw no short-term change but a long-term decrease. Translucency decreased in both short- and long-term for the active group, but in the placebo group, it increased short-term and decreased long-term. (Figure 1) compares these color properties over time

In the active group, lightness increased significantly in the short term (T1–T0) and decreased in the long term (T2–T1), ending slightly higher than at baseline (T2–T0). The placebo group showed no short-term change in lightness but exhibited a long-term decrease. Chroma decreased in the short term and increased in the long term in the active group, ultimately ending lower than the initial value, while the placebo group showed no short-term change but a long-term decrease. Translucency decreased in both the short and long term for the active group, whereas in the placebo group, it increased in the short term and decreased in the long term. Figure 1 compares these colour properties over time.

Fig. 1.

Comparison of colour properties between tested groups over time

Short-term colour change (ΔE T1–T0) was significantly greater in the active group than in the control group (p < 0.001; r = 0.543), with the difference diminishing in the long term (ΔE T2–T1), as shown in Fig. 2. Ultimately, the overall colour change from baseline (T2–T0) remained significantly higher in the active group (p = 0.025; r = 0.318).

Fig. 2.

Comparison of the degree of colour change between the tested groups (the arithmetic means with 95% confidence intervals are presented)

The intervention reduced psychosocial effects and aesthetic concerns while increasing dental self-confidence in the short term for both groups. However, the active substance showed a long-term relapse, whereas the placebo effect continued to improve. Tooth whitening significantly reduced the psychological and social impact of dental aesthetics (p ≤ 0.004; η² = 0.257–0.283), without significant changes in aesthetic concerns or dental self-confidence. The placebo group also showed a significant reduction in psychological effects (p < 0.001; η² = 0.385). Short-term changes in social impact differed between groups with detectable colour change (ΔE ≥ 3 T1–T0; 0.5 ± 1.3 vs. − 3.1 ± 3.4; p = 0.031; r = 0.441). Psychological impact changes differed significantly between groups with detectable colour relapse (ΔE ≥ 3 T2–T1; 1.7 ± 2.3 vs. − 1.6 ± 3.2; p = 0.015; r = 0.498). The placebo group experienced no colour relapse and reported decreased psychological distress, while the active group with detectable relapse reported increased distress (Fig. 3).

Fig. 3.

Comparison of changes in psychosocial impact of dental aesthetics (PIDAQ) between the tested groups over time

Inter-individual variability prevented significant differences between the active and placebo groups at any time. Changes in quality of life intensity also did not differ between groups (ΔT1–T0, ΔT2–T1, ΔT2–T0). Short-term social impact change was significantly different for those with detectable colour change (ΔE ≥ 3 T1–T0; 0.5 ± 1.3 vs. − 3.1 ± 3.4; p = 0.031; r = 0.441). Psychological impact change differed significantly for those with detectable colour relapse (ΔE ≥ 3 T2–T1; 1.7 ± 2.3 vs. − 1.6 ± 3.2; p = 0.015; r = 0.498). Psychosocial impacts did not differ significantly between groups with detectable and undetectable colour change (T2–T0).

In the active group, short-term colour change (ΔE T1–T0) correlated with social impact change (r = − 0.448; p = 0.028). Across the entire sample, short-term colour change weakly correlated with psychological effects (r = − 0.290; p = 0.041). An increase in short-term colour change was associated with a decrease in short-term psychological effects. Other PIDAQ dimension changes showed no significant linear relationship with colour change (T1–T0, T2–T1, T2–T0).

Introducing personality traits and perfectionism increased the effect of teeth whitening on reducing psychosocial impacts. No difference was observed between the active and placebo groups.

The first moderation model, with neuroticism, showed that short-term whitening reduced aesthetic concerns more in individuals with lower neuroticism (moderation effect = − 0.391; SE = 0.131; p = 0.004). (Fig. 4) This effect was strong in both the placebo and active groups, explaining 13% of the variance in reduced aesthetic concerns (Table 2).

Fig. 4.

Neuroticism and perfectionism moderating the short-term effect of teeth whitening on reduced aesthetic concerns and social impact. In low neuroticism (left), a more pronounced colour change after teeth whitening will lead to more decrease in aesthetic concern (solid line); in high neuroticism colour change will lead to an increase of aesthetic concerns but non-significant (dashed line). In high perfectionism (right), colour change after teeth whitening will lead to a significant improvement in social interactions (solid line); in low perfectionism, that relationship is not significant

Table 2.

Moderation models for the relationship: colour change → change in PIDAQ dimensions. Each row represents a moderated regression model testing the effect of personality change (X) on outcome change (Y), conditional on levels of the moderator (M). B indicates the unstandardized regression coefficient for the X–M interaction. SE is the standard error of B, p is the significance level, and R-sq. (p) is the model R-squared with its significance. The conditional effect represents the effect of X on Y at specific levels of M

Model (X-M→Y)*	B (X-M)	SE	p	R-sq. (p)	Conditional effect X→Y (p)	Values of M
ΔE-neuroticism→ΔAC; T1– T0	0.055	0.020	0.008	0.129 (0.017)	-0.391 (0.004)	low
ΔE-perfectionism→ΔSI; T1– T0	-0.019	0.009	0.047	0.171 (< 0.001)	-0.775 (0.001)	high
ΔE-conscientiousness→ΔPI TT2– T0	-0.131	0.054	0.020	0.132 (0.029)	-1.271 (0.003)	high

*X - predictor, Y– outcome, M - moderator

The second model, with perfectionism, found that teeth whitening improved short-term social interactions more for those with high perfectionism. This model explained 17% of the variance in reduced social impacts (p = 0.047; Table 2). The moderation effect was significant in both groups (moderation effect=-0.775; SE = 0.218; p = 0.001). People with high perfectionistic tendencies are more likely to experience improvement and comfort in social interactions following teeth whitening (Fig. 4).

The third model, with conscientiousness, showed no linear relationship between color change and long-term psychological improvement (ΔPI T2-T0; r=-0.172; p = 0.233), but conscientiousness strongly moderated long-term psychological impacts (Table 2; Fig. 5). The ΔE-conscientiousness interaction was significant (p = 0.020), explaining 13% of the variance in reduced psychological impacts.

Fig. 5.

Conscientiousness moderating the long-term effect of teeth whitening on reduction of psychological impact. In high conscientiousness, long-term colour change will lead to significant improvement of psychological impacts (solid line); in low conscientiousness, that relationship is not significant (dashed line)

Discussion

Present research indicates that patients may not accurately perceive an increase in tooth lightness, and a significant placebo effect in longitudinal color change measurements was observed. However, patients often notice a color relapse after teeth whitening, which is influenced by personality traits affecting the experience of changes in smile aesthetics.

Numerous studies have focused on the efficacy of different whitening techniques, but only a few longitudinal studies have examined the correlation between color change and patient perception, including satisfaction with the results obtained after whitening [23, 24]. Many studies investigate whitening efficacy, yet few assess the link between color change and patient satisfaction [22, 23]. A comparison before (T0) and one week after whitening (T1) in the active group showed a significant short-term color change, associated with a reduction in the psychological and social impact of dental aesthetics. This reduction in psychological effects was also observed in the placebo group, likely due to expectations of change influencing perception and satisfaction. Short-term results suggest a considerable placebo effect, indicating patients may struggle to perceive actual color changes.

Longitudinal measurements (T2–T1) showed a slight reduction in color change difference in the active group compared to the control group. This was followed by a decrease in psychosocial effects related to dental aesthetics in the active group, while effects in the control group remained unchanged. High expectations could explain these results, with younger patients being more critical of their tooth color compared to parents and dentists [25]. Minimal loss of whitening effect could lead to disappointment after high initial expectations.

Comparing short-term color change (ΔE T1–T0) with total change measurements (ΔE T2–T0) showed significant differences within the active group, indicating low color stability after whitening. The long-term decrease in tooth lightness in the placebo group indicates a natural course—teeth become darker over time due to aging and lifestyle factors (food, beverages, smoking, poor oral hygiene) if not professionally cleaned regularly [26]. Various studies report differing degrees of color relapse in long-term observations [27–29].

Short-term results (T1–T0) showed a significant decrease in social impact in the active group, possibly due to an adaptation period. Initial discomfort or adjustment to tooth color change might result in a temporary decrease in social impact. Increased self-confidence about their teeth immediately after the procedure could lead to this short-term decrease. Unrealistic expectations regarding the procedure’s outcome could lead to initial disappointment, influencing social impact. Displaying digital mock-ups may help improve patient satisfaction with tooth color. Young adults, in particular, may compare their smiles to those seen in media and aspire to achieve the specific shade of whiteness often portrayed by celebrities. This desire could have lasting psychological and social effects over time.

In the long term (T1–T2), the control group showed a continuous decrease in psychological stress, while stress increased in the active group due to significant color relapse. The psychological impact of dental aesthetics aims to assess a person’s sense of inferiority [24, 30]. The significant color relapse in the active group may have led to frustration, resulting in increased psychological stress over time. Maintaining the desired tooth color is critical for positive psychological outcomes. Our study aligns with prior research suggesting that a shorter follow-up period may result in less color relapse and fewer psychological effects.

Tooth whitening impacts the quality of life of younger adults by reducing negative emotions and improving social interactions. Preserving tooth color and addressing expectations and adaptation issues are crucial for optimizing psychological outcomes of dental aesthetic procedures. Our study is consistent with previous research showing that tooth color significantly affects self-confidence and social integration [31, 32].

A significant placebo effect was observed in longitudinal measurements of color change, consistent with studies where 30–50% of individuals responded to placebo treatment [33]. Higher placebo response rates were seen in studies where expectations were manipulated [34]. Although subjects may not objectively evaluate the final result, undergoing teeth whitening can create a positive perception.

Moderation analysis revealed that reduced psychosocial impacts following tooth whitening depend on personality traits and perfectionism rather than the objective amount of whitening and color change. Personality characteristics are important for both short- and long-term impacts on perception and satisfaction. Neurotic individuals are more likely to remain concerned about their dental appearance even after treatment. In contrast, emotionally stable and confident individuals are more likely to diminish their aesthetic concerns following improvements [35, 36].

People with perfectionistic tendencies are more aware of their condition and more likely to perceive a greater psychosocial impact of dental aesthetics [37]. They are also more aware of dental aesthetic improvements and can perceive enhanced social contacts following tooth whitening. The complexity of personality determinants and their interrelationships, such as self-esteem mediating the effects of perfectionism, may influence the psychosocial impacts of dental aesthetics [38].

High conscientiousness is linked to strong intrinsic motivation during dental treatment, leading to long-term psychological benefits following tooth whitening. Conversely, spontaneous and procrastinating individuals are less likely to benefit psychologically. Impulsive and less responsible individuals are less affected by dental aesthetics and smile appearance, benefiting less from improvements and having lower expectations and motivation during treatment [39].

Moderation effects were equally strong in experimental and placebo groups, indicating that the impact of color change depends on individual personality characteristics rather than the actual amount of color change. This emphasizes the importance of an individualized approach to satisfy patients’ demands and achieve successful treatment outcomes. Dentists should consider patients’ personality traits and moderate communication to rationalize expectations before treatment begins.

The study’s advantages include a robust design, randomization, focus on long-term outcomes, and use of patient-reported outcome measures. These strengths enhance the study’s reliability and credibility. However, limitations such as a small sample size, participant dropout, and lack of examination of general tooth color hue should be considered. Additionally, the use of a single-episode chairside bleaching technique focused solely on one tooth raises questions about the method’s comprehensiveness and effectiveness. In-office bleaching treatments are known to cause temporary enamel dehydration, which can lead to an initial but misleading increase in tooth lightness. Moreover, reliance on the Spectroshade spectrophotometer for shade evaluation introduces challenges, as accurately measuring the same areas of the tooth repeatedly can be difficult. Finally, both the experimental and control groups experienced temporary whitening likely due to dehydration, leading to similar overall outcomes. Future studies should address these gaps and consider postoperative sensitivity to improve validity and reliability.

Overall, preserving tooth color and addressing patient expectations and adaptation issues are critical for optimizing the psychological outcomes of dental aesthetic procedures. The study emphasizes the significance of personality traits and the need for an individualized approach to achieve successful treatment outcomes.

Conclusion

Participants demonstrated limited ability to accurately perceive improvements in tooth color, with a tendency to notice relapse over time. The psychosocial effects of tooth whitening were influenced by individual personality traits. These findings suggest the value of a personalized approach in cosmetic dental treatments, emphasizing the need for practitioners to consider personality characteristics when managing patient expectations.

Abbreviations

AC

Aesthetic Concern (dimension of PIDAQ)

ANOVA

Analysis of Variance

BFI

Big Five Inventory

CIE

International Commission on Illumination

ΔE*

Color Difference (in Lab* color space)

DSC

Dental Self-Confidence (dimension of PIDAQ)

IBM

International Business Machines

L*

Lightness (component of CIE L*a*b* system)

a*

Red-Green component (CIE color system)

a*

Red-Green component (CIE color system)

b*

Yellow-Blue component (CIE color system)

MHT

Medical High Technologies (SpectroShade manufacturer)

MPS-F

Multidimensional Perfectionism Scale– Frost

PIDAQ

Psychosocial Impact of Dental Aesthetics Questionnaire

PI

Psychological Impact (dimension of PIDAQ)

RSS

Rosenberg Self-esteem Scale

SE

Standard Error

SI

Social Impact (dimension of PIDAQ)

SPSS

Statistical Package for the Social Sciences

T0

Time Point 0– Pre-treatment

T1

Time Point 1– One week post-treatment

T2

Time Point 2– One year post-treatment

TL

Translucency

Author contributions

D. K. P. and S. S. contributed to the conceptualization and methodology. S. S. performed the validation. M. Br. and S. S. conducted the formal analysis. M. Ba. and D. K. P. carried out the investigation. S. S. provided resources. M. Ba. and D. K. P. curated the data. A. S. and M. Br. wrote the original draft of the manuscript. D. K. P., A. S., M. Br., and S. S. reviewed and edited the manuscript. A. S. and M. Br. prepared the visualizations. D. K. P. and S. S. supervised the project. D. K. P. managed the project administration. S. S. acquired funding. All authors have read and approved the final version of the manuscript.

Funding

This research was supported by the University of Rijeka and Faculty of Dental Medicine Rijeka Grants (uniri-biomed-18-22 and FDMRI-IP-2025-1).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was approved by the institutional ethical board of the University Dental Clinic in Rijeka, Croatia (Approval No. 2170-24-01-15-04) in accordance with the Nuremberg Code and the latest revision of the Declaration of Helsinki. All participants provided written informed consent prior to participation.

Consent for publication

All participants provided informed consent for the publication of anonymized data. No identifying information is included in this manuscript.

Competing interests

The authors declare no competing interests.