Introduction

Early Childhood Caries (ECC) still represents a significant public health burden, affecting primary teeth of more than 530 million children in the world1,2. A recent systematic review and metanalysis revealed that ECC affects approximately 48% of preschool children globally, with Europe falling within this estimate prevalence3. ECC consequences involve medical, social, and economic issues, leading to a challenge of comprehensive well-being at patient and community-level2. Since the introduction of Minimally Invasive Dentistry (MID), a paradigm shift from traditional surgical techniques to more cost-effective and biological approaches for managing ECC has been noted4.

Re-emerged from the early 1970s, Silver Diamine Fluoride (SDF) is an alkaline topical solution that is gaining increasing interest as a suitable tool for arresting cavitated carious lesions in primary teeth5, potentially improving children oral health-related quality of life (OHRQoL)6. The synergic effect of silver and fluoride makes SDF a valuable cariostatic agent. It may perform a re-mineralizing, bacteriostatic and metalloproteinases-inhibitory triple action7,8. Its renaissance in dentistry is supported by the current evidence of umbrella reviews, suggesting that biannual application of 38% SDF reaches caries arrest rates ranging from 53 to 91%4,8. The American Academy of Pediatric Dentistry (AAPD) advocates that SDF is a valuable additional tool in the context of a comprehensive caries management program, and especially indicated in children who exhibit behavioral, economical, and medical barriers to conventional restorative care9.

Despite being recognized as an essential medicine for caries management in children10, this is an ‘off-label’ use of the product. The U.S. Food and Drug Administration (FDA) labeled SDF as a desensitizing agent in 2014. In Italy, Spain and most of European countries SDF is not widely adopted11. National ministerial programs and uniform guidelines regulating and standardizing its clinical application are still required.

The permanent black staining of decayed enamel and dentine surfaces after silver precipitation is a major disadvantage of SDF treatmen12. This staining represents an esthetic concern for parents, and it affects dental professionals’ attitudes and their trends in decision-making13. If our goal is to deliver patient-centered care, it is important to assess SDF aesthetic acceptability among the parents who have to consent for the treatment. For this purpose, Bagattoni et al.14 specifically developed the first Italian validated instrument to measure parental acceptability of the treatment, based on the original ‘Parental Perceptions of SDF Dental Color Changes’ provided by Crystal et al.15. There is a lack of knowledge of whether the acceptability levels are similar between European countries, and the factors that may affect the acceptability.

The aim of this study was to compare aesthetic perceptions and overall acceptance of SDF staining between Spanish and Italian parents. A secondary aim is to study the variables that can affect the acceptability, namely staining location (anterior vs. posterior), child’s behavior and demographic factors.

Materials and methods

Study design and population

This comparative cross-sectional study was approved by the Research Ethic Committee of the International University of Catalunya (UIC), Barcelona, Spain (Approval Reference: ODP-ECL-2022-03) and the Local Bioethics Committee of the Sant’Orsola-Malpighi Hospital, Bologna, Italy (Prot. n. 0041533). The study was registered at ClinicalTrials.gov (NCT, NCT06384326, Registered on 21 April 2024, https://clinicaltrials.gov/study/NCT06384326.) The research project comprised two parts. The first part was carried out in Italy at the Unit of Dental Care for Special Needs Patients and Paediatric Dentistry at the University of Bologna, Bologna, Italy, and the Unit of Paediatric Dentistry at the University of Pisa, Pisa, Italy between September 2020 and March 202216. For the second phase of the study, Spanish parents were recruited at the Department of Paediatric Dentistry of UIC between March 2023 and July 2023.

According to Cappiello et al.16, a minimum sample of 139 Spanish subjects for anterior teeth and 264 Spanish subjects for posterior teeth was required to detect a difference of 12% between anterior and posterior teeth –– considering an acceptability estimate of 10% for anterior teeth and 22% for posterior teeth. To detect a difference in acceptability of 13% between Spain and Italy, a minimum of 227 subjects was required for each population. Alfa level was a priori set at 0.05.

The method protocol detailed in the Italian reference study16 was meticulously applied to the Spanish sample, to ensure a reliable comparison of results between the two populations. Parents waiting for their child’s dental appointment were identified as potential participants in the reception area. During the initial interview parents were approached to assess eligibility. Inclusion criteria were: Spanish and Italian parents of healthy children or children with mild systemic disease (ASA status 1–2), under the age of 12 years, with at least one decayed primary tooth treated by traditional restorative care, and who agreed to participate in the study. In case of both parents accompanying the child, the couple was invited to designate only one parent to be enrolled in the study. Potential participants received a brief explanation of the main characteristics and application of SDF treatment. Parents were then invited to complete an anonymous digital survey designed in Google Forms platform. A specific QR code, scanned using a smartphone or tablet camera, provided a direct link to the questionnaire. Informed consent form ensuring the voluntary and uncompensated enrollment of the participant was properly obtained for all subjects. Access to the questionnaire was possible to achieve only after marking the appropriate consent box on the form. The researcher remained available to the participants for clarifying any questions or concerns. All methods were carried out in accordance with relevant guidelines and regulations17.

Questionnaire and outcome assessment

A 25-item Italian questionnaire validated by Bagattoni et al.14 was adopted as data collection instrument. The Italian version was translated into Spanish using the forward-backward method18, to ensure the accuracy of the translation and internal consistency.

The questionnaire comprised two distinct sections. The first part collected demographic data, including the gender and age of both parent and child, educational level, family income, and residence location. This section also explored parents’ perspectives on the importance of restoring their child’s primary teeth. Information concerning child’s behavior and the need for advanced behavior management techniques during previous dental treatment was also captured within two different items of the questionnaire. Child collaboration scenarios ranged from ‘calm and cooperative’ to ‘upset, but it was possible to restore teeth’, ‘cried’, ‘kicked’, ‘screamed’, ‘it was impossible to restore teeth’, ‘it was impossible to remove decayed tissue’. Advanced methods included ‘physical restraint’, ‘nitrous-oxide oxygen analgesia’ (N2O), ‘oral sedation’, and ‘general anesthesia’ (GA).

The central core of the questionnaire focused on gathering parental perceptions and aesthetic acceptance of SDF treatment. Colored photographs showing both anterior and posterior teeth after SDF application were juxtaposed with images of the same teeth before treatment for comparative analysis. Following this visual examination, parents were invited to respond to closed-ended questions. To assess the overall aesthetic acceptability of SDF staining in both anterior and posterior teeth, parents assigned scores based on a 4-point Likert scale. The scoring ranged from ‘unacceptable’ (scoring 1) to ‘somewhat unacceptable’ (scoring 2), ‘somewhat acceptable’ (scoring 3), and ‘acceptable’ (scoring 4). In a more detailed assessment, aesthetic acceptability of SDF treatment was evaluated by introducing the child behavior variable. Different scenarios of child’s cooperation were prospected within a hypothetical dental restorative treatment. Starting from a positive situation of collaboration, progressively negative scenarios were presented to the parents, with increasing barriers in receiving conventional restorations (child crying; child needs physical restraint; child kicking or screaming; child needs nitrous oxide sedation; child needs oral sedation; child needs general anesthesia). Parents’ willingness to accept SDF treatment in each collaboration scenario was evaluated using 4-point Likert scale, for both anterior and posterior teeth. The scale ranged from ‘extremely unlikely’ (scoring 1) to ‘somewhat unlikely’ (scoring 2), ‘somewhat likely’ (scoring 3), and ‘very likely’ (scoring 4). To evaluate impact of demographic factors on SDF acceptability, parental perceptions of SDF staining were finally assessed according to gender, age, educational level, and family median income.

Statistical analysis

To perform a descriptive analysis, data were treated in three different ways: (1) calculating frequencies and proportions (2) as ordinal variables, by adopting median and interquartilic ranges (3) as function of the central limit theorem, by computing mean and standard deviation. Based on the mean, more complex models were implemented. SDF overall acceptability differences in proportions between anterior and posterior teeth were compared using the McNemar-Bowker test. The Wilcoxon test for paired data was employed to assess the significance of differences in acceptance of SDF staining between anterior and posterior teeth for all the collaboration scenarios. Mann-Whitney test and Wilcoxon test were used to determine potential moderating influences of demographic factors (gender, age, educational level, family income) on parental acceptance levels.

Comparative statistical analysis between Spain and Italy was performed using the Mann-Whitney test for not-related samples, and the Chi-square test for qualitative variables. A linear mixed model was adopted, as function of the following fixed factors: country, location, scenario, and a random intercept represented by the participant.

Statistical analysis was performed using the R Version 4.1.1. (R Foundation for Statistical Computing, Core Team, Vienna) for the tabulation and analysis of the data. A p-value ≤ 0.05 was considered statistically significant.

Results

A total sample of 501 subjects was obtained, with 234 Italians and 267 Spanish parents. All the parents approached for enrollment in the study consented to participate, reaching a 100% participation rate. Most of the parents in both countries were mothers, under the age of 40 years old, with a medium-high family income. The only statistically significant demographic factor was that Spanish parents revealed a higher level of education, compared to Italian parents (p < 0.001). Details of sociodemographic characteristics are described in Table 1.

Table 1 Comparison of parents’ demographic characteristics in Spain (N = 267) and Italy (N = 234).
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Regarding dental experience, although the majority of Spanish and Italian children were calm and cooperative during previous restorative treatment, 19.2% of Spanish children and 23.7% of Italian children required advanced behavior management techniques. Use of GA was significantly higher in Spain compared to Italy (p < 0.001), while use of N2O was higher in Italy than in Spain (p < 0.001).

When assessing overall aesthetic acceptability of SDF staining, it was more accepted among Italian parents compared to Spanish parents, resulting in a statistically significant difference for both anterior and posterior locations (p < 0.001). Only 41.8% (95% CI 32.1 to 53) of Spanish parents, compared to 65.4% (95% CI 59.3 to 71.1) of Italians, considered staining on posterior teeth aesthetically “acceptable” or “somewhat acceptable”. As for anterior teeth, only 17.2% (95% CI 10.7 to 25.6) of Spaniards reported a positive acceptability score, compared to 19.3% (95% CI 14.2 to 24.4) of Italian subjects. These results confirm a statistically significant association, with a higher acceptance level for posterior teeth (p < 0.001) in both populations. Figure 1 shows the percentage of overall SDF acceptability on anterior and posterior teeth in Spain and Italy.

Fig. 1
figure 1

Percentage of overall acceptability on the basis of SDF staining only in Spain and Italy.

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In a more specific analysis, parents’ attitude to choose SDF treatment on anterior and posterior teeth was evaluated according to child’s behavior. Comparative analysis assessed that acceptability was lower in Spain compared to Italy for each scenario of cooperation on both locations (all ps < 0.001), except for the ‘cooperative’ scenario on anterior teeth. Decrease in child cooperation was not clearly related with a progressive increase in SDF acceptability in Spain, since mean acceptability scores remained constant overall. On the other hand, it was observed an evident increase in mean acceptability levels among Italian parents as barriers to conventional treatment increased. Finally, for each scenario of collaboration both Spanish and Italian parents were more likely to choose SDF on less visible location, compared to anterior teeth (p < 0.001). Figure 2 reports acceptability mean scores on anterior and posterior teeth for each collaboration scenario of the child in Spain and Italy.

Fig. 2
figure 2

Acceptability mean scores by tooth location and level of difficulty in receiving conventional treatment in Spain and Italy.

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Linear mixed model corroborated that SDF parental acceptability varied according to country, location, and scenario. Mean acceptability rating decreased − 0.50 score unit from Italy to Spain (p < 0.001). Both Spanish and Italian parents revealed a higher level of acceptance on less visible location, compared to anterior teeth (p < 0.001). Regardless of tooth location, Spanish and Italian parents exhibited a negative trend on SDF acceptability in absence of significative barriers to conventional restorative treatment (child collaborating or at most crying). A positive profile of parental acceptability emerged in case of challenging behavior (child kicking or screaming) and if advanced behavior management techniques would be required (physical restraint, N2O, oral sedation, GA). The level of acceptability increased by 0.49 points from the ‘cooperative’ to the ‘non-cooperative’ scenario (p < 0.001), irrespective of the country variable. Results of multilevel analysis are reported on Table 2.

Table 2 Comparative multilevel results: effects of random intercept, country, location and scenario on overall acceptability score in Spain and in Italy.
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When introducing demographic factors as third covariate, median ratings of acceptability showed a downward trend in Spain compared to Italy. Each demographic sub-group of both populations –– mothers and fathers, ≤ 40 years old and > 40 years old, ≤ secondary school and > secondary school, ≤ 28.000 euros per year and > 28.000 euros per year ––accepted more SDF on posterior teeth, rather than anterior teeth (p < 0.001). Parental acceptability was not significatively affected by demographic factors in Italy. On the other hand, Spanish older parents showed a higher level of SDF acceptability on posterior teeth (p = 0.005). Furthermore, a significant association was observed between family income ≤ 28.000 euros per year among Spanish parents and increased SDF acceptance on anterior teeth (p = 0.009). Table 3 shows results of SDF acceptability stratified by parental gender, age, education, and income in Spain and Italy.

Table 3 Parental acceptability of SDF according to gender, age, education, and income in Spain and in Italy.
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Discussion

The demand for aesthetic solutions in paediatric dentistry is currently increasing. Parents’ concerns about their children’s dental appearance may influence clinical applicability of minimal intervention procedures (MIPs) for managing dental caries in primary teeth19. A typical scenario involves the use of performed metal crowns. Despite the general acceptance of Hall Technique (HT), parents prefer the aesthetic appeal of Atraumatic Restorative Treatment (ART) restorations19. A similar phenomenon has been observed with the permanent black staining that occurs after SDF application12,19. In accordance with recent evidence in the literature13,15,19, the present study demonstrates that Spanish and Italian parents are inclined to accept SDF treatment in less visible locations. Furthermore, they consider it as a secondary option to be implemented in particularly challenging situations that would require advanced behavior guidance techniques to perform conventional restorative treatment. The reluctance against less aesthetic dental solutions could be explained by the concern that their choices could be perceived as a noticeable sign of parental neglect towards their children’s oral health13. This apprehension could be exacerbated by the societal esthetic standards imposed on dental appearance.

Spain and Italy share many similarities at the social and cultural level. Nevertheless, the discrepancy in SDF acceptance between Spanish and Italian parents may be attributed to significant differences in the demographic composition of the two populations. The latest national and international demographic data indicate that Spanish parents have a 20% higher level of education compared to Italians20,21, similar to the demographics in the present study. The difference in educational attainment may affect parental aesthetic perceptions. Al-Batayneh22 noted that university educated parents tend to be more concerned about aesthetic appearance of their children’s teeth and prefer composite restorations over amalgam. This observation aligns with the findings of the present study and other two studies on parental perceptions of SDF23,24, where highly educated parents expressed lower acceptability of SDF treatment. According to Magno et al.12, the correlation observed between elevated educational level and lower acceptability of SDF pigmentation could be explained by the greater impact of perceptions regarding the conventional health-beauty association among parents with higher socio-economic status. Another factor to consider is the higher utilization of GA in Spain compared to Italy. This result is consistent with the study by Brunet et al.25, which reports that approximately 10% of paediatric patients attending the Department of Paediatric Dentistry at the Sant Joan de Déu Hospital in Barcelona annually receive dental treatments under GA. Moreover, Guinot et al.26 and Veloso et al.27 observed that despite being the least favored technique, GA is generally an accepted mode of treatment delivery in Spain. This suggests that, although general anesthesia carries inherent associated risks, the Spanish population might be more accustomed to its use and tends to accept restorative treatment under GA, as it often leads to a satisfactory aesthetic outcome.

The main clinical issue raised by the present study concerns how to guide and present the use of SDF to Spanish and Italian parents. Establishing effective and strategic communication with parents is crucial to promote SDF treatment on patients where it would be of benefit. SDF is a valuable tool for dental caries management in high-risk paediatric patients, as it may reduce or defer the need for general anesthesia28,29. Parents may overcome barriers to SDF application by shifting the paradigm that a treated tooth necessarily means to be white, as suggested by Seifo et al.13. Moreover, SDF can be employed to defer restorative treatment until the child’s cooperation improves and more esthetic restorations can be delivered. A promising advancement in caries management involves the combined use of SDF and ART, known as Silver-Modified Atraumatic Restorative Technique (SMART)30. It could offer an alternative aesthetic solution without the need for GA31. In this context, it seems crucial to embrace a patient-centered approach to care, which entails acknowledging and accommodating parents’ perspectives, preferences, and cultural differences.

The Italian sample may not represent the entire population due to limited geographic sampling and potential clinic-specific demographics. However, the sample’s demographics show no significant differences from those of the overall Italian population16. The Spanish sample may reflect demographic and educational characteristics specific to the regional population analyzed in the present study21. This may restrict extrapolation of the data to wider Spanish population, and constitutes a limitation of this research, as the educational level of parents can play a role in the aesthetic perception of SDF. Furthermore, 6% of Spanish parents and 9% of Italian parents did not respond to the questionnaire item regarding family median income, resulting in missing data. Nevertheless, the assumption of missing completely at random (MCAR) was satisfied. Consequently, likewise deletion was performed, yielding unbiased estimates and conservative results. Moreover, the variability in children’s age and their systemic health conditions (ASA status 1 or 2) may represent a potential confounding factor in determining the level of SDF acceptability among parents. Finally, due to the structure of the study and its aims, other factors beyond aesthetic appearance that could influence the acceptability of SDF treatment were not taken into consideration. Factors such as comfort, dental anxiety, cost-effectiveness, long-term outcomes, and the limitations of anatomic-functional rehabilitation of this therapy may impact the clinical decision-making process by parents.

Conclusions

The current study has provided further evidence that SDF staining represents an aesthetic concern for both Spanish and Italian parents. Nevertheless, SDF could be implemented in less visible areas, especially if a child’s uncooperative behavior presents a significant barrier to conventional restorative treatment.

Spanish parents exhibit lower acceptance of SDF pigmentation compared to Italian parents. This finding underscores the importance of considering cultural and educational factors when implementing SDF treatment in specific populations.