Approval for this study was obtained from the clinical research ethics committee of West China Hospital of Stomatology, Sichuan University, on 19 February 2025 (approval No. WCHSIRB-D-2025-051). All procedures adhered to the relevant guidelines and regulations, including the Declaration of Helsinki. Informed consent was secured from all participants involved in the study.

The sample size was calculated using the G∗Power statistical software (version 3.1.9.7; Franz Faul, Universität Kiel, Germany). Correlation analysis calculated that a minimum of 96 subjects were required for the study, based on an alpha of 0.05, a power of 0.85, and a correlation coefficient of 0.3. Considering a potential drop-out rate of 10%, the final estimate of the minimum required sample size was approximately 106 patients.

This study was conducted from February 2025 to April 2025 at the Department of Orthodontics of West China Hospital of Stomatology, Sichuan University. The inclusion criteria were as follows: patients aged 6-18 years who underwent treatment with CAs at the Department of Orthodontics of West China Hospital of Stomatology. Parental consent was secured before study participation, and parents were required to complete the questionnaire. The exclusion criteria were as follows: parents who declined study participation, withheld consent, or failed to complete the questionnaire fully and patients who received fixed aligner treatment or were accompanied by nonparental individuals.

Our questionnaire comprised 3 sections. The first section gathered patients’ socio-demographic data. The second section employed the Child-Parent Relationship Scale (CPRS; R Pianta, 1992), a well-established, internationally validated, and widely applied instrument to assess PCR. In this study, the previously translated and validated Chinese version of the CPRS was used, which evaluates 3 dimensions: closeness (10 items), conflict (12 items), and dependence (4 items). Given the low reliability of the dependence dimension in previous studies, only the closeness and conflict dimensions were included in this research. The third section, designed by us based on previous surveys, ^, assesses CA compliance across 8 aspects: adequate wear duration, use chewies, wear elastics, maintain oral hygiene, clean aligners, timely change aligners, appointment adherence, and damage or loss of aligners. The second and third sections both used a 5-point Likert scale ranging from never (1 point) to always (5 points). In the third section, after the scoring of the negative item damage or loss of aligners was reversed, the total score ranged 0-40, with higher values denoting better compliance. As only 58 of the 124 children were required to wear elastics, scores for children not wearing elastics ranged 0-35. The mean compliance score was used to reflect overall compliance, with a higher mean score indicating better overall compliance. The questionnaire used in this study is provided in the Supplementary Material .

Before the main survey, the self-designed third section underwent face validation by an experienced orthodontist and was subsequently pilot tested among 30 patients. The reliability of the third part was assessed using Cronbach Alpha, which yielded a value of 0.751, indicating good internal consistency and acceptability for survey instruments.

A total of 124 children and adolescent participants (53 males and 71 females) were included ( Table I ). Their ages ranged from 6-18 years, with a mean age of 12.35 years (standard deviation = 2.62). The results showed that 66.90% of the participants were the only child, 75.00% had parents with a college degree as the highest education level, and 83.90% were day scholars (ie, did not board at school on weekdays). No significant differences in CA compliance were found between samples with different sociodemographic characteristics ( P >0.05) according to the Mann-Whitney U test and the Kruskal-Wallis H test.

The descriptive data of PCR and compliance demonstrated considerable closeness (40.65 ± 5.42) and an elevated mean compliance score (3.97 ± 0.59) of the samples ( Table II ). The median scores for closeness and conflict were 42.00 and 26.00, respectively. Among compliance indicators, timely change aligners (4.42 ± 0.83) and appointment adherence (4.67 ± 0.70) received the highest scores, whereas use chewies (3.21 ± 1.14) scored lowest.

The heat map demonstrates the Spearman rho correlation coefficients between PCR and compliance indicators ( Fig 1 ). The bottom of the heat map showed the value of the Spearman rho correlation coefficients. Left-sided blue areas denote negative correlations, whereas right-sided red areas denote positive correlations. The color intensity reflects correlation strength, with light and white areas indicating weak or no correlation. Closeness shows a highly significant positive correlation with cleaning aligners and mean compliance score ( P <0.01), whereas conflict has a highly significant negative correlation with cleaning aligners, timely changing aligners, and mean compliance score ( P <0.01). However, with all correlation coefficients <0.39, this indicates a statistically significant, but relatively weak correlation between the high closeness and low conflict scores in PCR and good compliance for CA treatment.

Correlation between PCR and indicators of compliance.

Figure 2 illustrates the proportion of patients with good compliance across each indicator and overall. Pearson chi-square tests indicated that significantly more patients with high closeness showed good compliance in maintaining oral hygiene, cleaning aligners, and timely changing aligners ( P <0.05). Regarding adequate wear duration, 73.44% patients with high closeness showed good compliance, compared with 60.00% of those with low closeness, although not significant ( P = 0.112) ( Fig 2 , A ). Also, significantly more patients with low conflict showed good compliance in adequate wear duration, using chewies, wearing elastics, cleaning aligners, and timely changing aligners ( P <0.05). Specifically, 76.67% patients with low conflict showed good compliance in adequate wear duration, compared with 57.81% of those with high conflict. Significantly more patients with high closeness and low conflict demonstrated a higher mean compliance score of ≥4 ( P <0.01). These suggest that more patients with high closeness and low conflict in PCR demonstrated good compliance, both in most compliance indicators and in the overall level. Furthermore, regardless of the levels of closeness or conflict, a remarkably high and consistent proportion of patients, exceeding 90% and peaking at 95.31%, demonstrated good compliance in appointment adherence ( Fig 2 , B ).

Proportion of good compliance in patients with high or low levels of PCR. A , Closeness; B , conflict.

Binary logistic regression analysis further confirmed that closeness and conflict were significant predictors of compliance for CA treatment ( Table III ). The Hosmer-Lemeshow test ( P = 0.943) indicated that the predicted probability of the model fitted well with the actual probability. It was found that patients with high closeness were 2.2 times more likely to have a high mean compliance score than those with low closeness (odds ratio = 2.238; 95% CI: 1.051-4.764; P = 0.037). Conversely, patients with high conflict were only 0.3 times as likely to have a high mean compliance score as those with low (odds ratio = 0.366; 95% CI: 0.172-0.782; P = 0.009). That is to say, patients with high closeness and low conflict are particularly more likely to have good compliance in CA treatment.

Strict daily compliance is essential for successful CA treatment in young patients, yet reliable assessment remains a challenge because of the predominantly qualitative nature of existing metrics. ^, Our study addresses this gap by introducing a comprehensive, quantitative framework that evaluates 8 key compliance behaviors, which are adequate wear duration, use chewies, wear elastics, maintain oral hygiene, clean aligners, timely change aligners, appointment adherence, and damage or loss of aligners. By employing the CPRS, an internationally validated and widely applied instrument to assess PCR, our study represents the first to systematically examine and confirm the associations between PCR and CA compliance among children and adolescents. Results show that pediatric patients with high closeness and low conflict in PCR tend to exhibit better compliance during CA treatment, both in the most compliance indicators and in the overall level. Thus, assessing PCR via observation, inquiry, or brief questionnaires during orthodontic treatment planning may offer valuable prognostic information. In particular, low closeness or high conflict can serve as a warning that CA treatment may be at an increased risk of poor compliance and suboptimal outcomes, thereby encouraging the need for additional motivational or behavioral management and more careful consideration of tooth movement design. Such a proactive approach could help mitigate various adverse outcomes (eg, treatment prolongation and unsatisfactory outcomes) associated with noncompliance.

This study examined the association between sociodemographic factors and compliance in CA treatment. The results indicated no significant differences in CA compliance across sociodemographic variables, including sex, age, only-child status, parental education, family income, and boarding status. Regarding gender, Al-Abdallah et al found that female patients aged 12-18 years were more compliant during fixed orthodontic treatment. Schäfer et al reported that females aged 7-15 years were more compliant with removable appliances. Consistently, 2 additional studies focusing on children and adolescents under the age of 18 years also reported better compliance with fixed appliances in females. ^, Regarding age, studies have reported that orthodontic compliance with removable appliances decreases with age in children and adolescents aged 6-15 years, which may be associated with the onset of puberty. ^, Regarding boarding status, previous research indicates that boarding can lead to unstable relationships and reduced attachment among children and adolescents, potentially affecting CA compliance indirectly. The discrepancies between our findings and those of previous studies may stem from differences in the types of orthodontic appliances used, as well as the specific sample characteristics arising from nonrepresentative and convenience sampling. Further research with more diverse, cross-regional samples is needed to confirm the association of gender, age, and boarding status with CA compliance.

Building on previous research, ^, we incorporated a broader set of compliance indicators for CA treatment, including adequate wear duration, usage of chewies, wear of elastics, and incidence of aligner damage or loss, to promote a more comprehensive assessment. Adequate aligner wear duration (22 hours daily) is fundamental to maintaining continuous and stable orthodontic forces for efficient tooth movement. Insufficient wear duration disrupts force application, thereby compromising treatment efficiency and prolonging the overall treatment duration. Orthodontic chewies critically enhance aligner-tooth adaptation by eliminating interfacial gaps, thereby optimizing force transmission fidelity. However, our study found that the usage of chewies scored lowest among the 8 indicators, which may result in force decay and an increased risk of tracking failures, consequently necessitating more midcourse corrections. To enhance patient compliance with chewies usage and achieve better treatment outcomes, strategies, such as daily records and timely reminders from parents, could be adopted. Elastics supplement directional forces for complex tooth movements, such as reducing midline deviation and achieving Class I molar relationships. ^, Damage or loss of aligners can interrupt the application of orthodontic force, leading to stagnation of tooth movement or even rebound. Our results indicated that for adequate wear duration, usage of chewies, and damage or loss of aligners, no statistically significant associations were found between closeness and any of the 3 compliance indicators. In contrast, conflict demonstrates a significantly negative association with adequate wear duration and chewies usage, as evidenced by both the Spearman rho correlation coefficients and the proportion of patients with good compliance. In addition, regarding the usage of elastics, the results of the correlation analysis and proportion analysis are inconsistent, which may stem from the limited number of patients using elastics (58 of 124). Further research with larger sample sizes is needed to clarify how PCR relates to elastics usage compliance and, consequently, to final treatment outcomes.

Our results suggest that among the compliance indicators, cleaning aligners and timely aligner change show the strongest associations with PCR. Spearman correlation coefficients revealed that cleaning aligners and timely aligner change were statistically significantly, although weakly, positively correlated with closeness and negatively correlated with conflict. Similarly, the proportion of patients with good compliance in these 2 indicators was significantly higher among those with high closeness and low conflict. The findings suggest that enhancing PCR may yield particularly marked effects on these 2 specific compliance behaviors, thereby optimizing treatment outcomes. In addition, closeness exhibited a significant positive association with maintaining oral hygiene, as demonstrated by both Spearman rho correlation coefficients and the proportion of patients with good compliance, whereas conflict showed a marginal association. Maintaining oral hygiene through practices, such as brushing teeth and using dental floss, can prevent the accumulation of dental plaque on the tooth surface. Cleaning the aligners helps prevent the adhesion of harmful bacteria and the formation of plaques, while preserving the transparency and esthetic appeal of the aligners. Given that CAs can cause prolonged plaque retention or even sugary fluid buildup on the tooth surface, which may lead to disastrous consequences, cleaning both teeth and aligners is essential to reduce the risk of oral diseases, including gingivitis, periodontitis, white spot lesions, caries, and halitosis. Timely aligner change prevents material fatigue and ensures proper force application. Recent research shows that a 7-day changing interval for CAs achieves similar clinical accuracy to the conventional 14-day interval regardless of extraction. Delayed aligner change doesn’t improve treatment outcomes and instead prolongs the treatment duration. ^,

In this study, appointment adherence served as the most consistent and compliant behavior among 8 indicators, with rates exceeding 90% and reaching a peak of 95.31% across varying PCR level cohorts. Moreover, this high level of adherence showed no significant variation across patients with different levels of PCR. Similarly, other research incorporating appointment adherence as a compliance indicator also found no significant differences among patients with varying economic status, communication strategies, or types of invisible appliance (CAs or lingual braces). ^, Better appointment adherence allows the dentist to address orthodontic emergencies and make timely adjustments to the treatment plan to ensure that the orthodontic process stays on track.

Previous studies have shown that parental motivation, higher parental education levels, parental self-efficacy, and a positive orthodontist-patient-parent relationship are associated with children’s better cooperation in orthodontic treatment, highlighting parents’ crucial role in pediatric orthodontic compliance. Our study on PCR further extends this understanding, particularly regarding CA treatment. These findings collectively suggested that family-centered interventions may be beneficial in promoting orthodontic compliance among children and adolescents. Evidence-based family interventions, such as role-playing exercises and family discussions among parents, have shown efficacy in strengthening PCR. Hence, family psychoeducation and targeted interventions appear to represent promising strategies for supporting compliance during long-term orthodontic treatment and ultimately improving clinical outcomes in children and adolescents.

Though meticulously planned, this research has several limitations. First, the relatively modest correlation coefficients between PCR and CA compliance suggest that other confounding variables, such as oral health–related quality of life and the orthodontist-patient relationship, may also be associated with CA compliance. Therefore, PCR should be considered as a complementary factor, rather than the sole determinant, in predicting CA compliance. Second, the cross-sectional design precludes causal inference; thus, the observed associations should not be interpreted as direct causation. Third, although the CPRS is a widely validated and cross-culturally applied tool, its applicability may be affected by cultural bias and reduced sensitivity in adolescents. Fourth, assessing CA compliance via questionnaires may introduce subject-reported and social desirability biases, as overreporting of appliance wear has been noted in a previous review. Finally, as data were collected from a single-center sample, the generalizability of the findings may be limited. Sociocultural and economic variations across regions could further influence the observed associations. Despite these limitations, this study provides valuable preliminary insights into the relationship between PCR and CA compliance among children and adolescents. Future multicenter, cross-regional studies with more diverse and representative samples are warranted.