Introduction
Trust is one of the most important components of relationships between family members, friends and colleagues, especially intimate partners, and the satisfaction with the relationship is highly related to the trust between the partners [1]. Marital satisfaction, which has been investigated in many studies, cannot be a good measure for the long-term romantic relationship quality, but trust can be a better predictor of a satisfied and long-term relationship [2]. Less attention has been paid to the importance of dynamic factors in the relationship between couples [3]. By adopting a dynamic model of trust called “dyadic trust”, we aim to investigate the possible underlying factors such as mentalizing capacity, affecting the trust among Iranian couples. We also investigate that whether conflict resolution styles of couples can play a mediator role between their mentalizing capacity and interpersonal trust. Furthermore, we explore whether internal working model of attachment can moderate the relationship between trust, mentalizing capacity, and conflict resolution styles in our proposed model.

Methods
This is an applied descriptive study using the structural equation modeling (SEM) on 370 married couples who were living in Tehran, Iran, with age 18-45, at least a high school diploma, and a marriage duration of at least 1 year. Sampling was done using a convenience method and based on the entry criteria. The used instruments were the interpersonal relationship scale (IRS), the reflective functioning questionnaire (RFQ), the Rahim organizational conflict inventory, part two  (ROCI-II), and the relationship scales questionnaire (RSQ). At the end, 21 participants were excluded because they had answered less than 20% of questions or to questions. Then, the data were analyzed in SPSS software, version 22 and PLS version 3. To investigate the relationship between variables, Pearson’s correlation test was used.

Results 
The mean age of the participants and the their marriage duration were 34.75±6.69 years and 123.04±86.70 months. The gender and education status of the participants are presented in Table 1.



The mean scores of the study variables are shown in Table 2.



Most of the variables had a significant correlation with each other. The values obtained for the skewness and kurtosis of the variables indicated the normality of data distribution. Mardia’s normalized multivariate kurtosis value was also used to check the multivariable normality [4], whose results showed that the assumption of multivariate normality was also established. At first, the study model was analyzed using analysis of covariance (maximum likelihood estimation) in AMOS. The results showed that the model could not be implemented. Therefore, it was carried out in PLS v.3 software. To assess the fitness of the proposed structural model, standardized root mean squared residual index (SRMR), normalized fit index (NFI) and goodness-of-fit index (GOF) were calculated [5]. The results for showed the good fit of the initial model. After removing the non-significant paths, the values for SRMR (0.017), NFI (0.985), and GOF (0/386) indicated the optimal fit of the final model (Figure 1).




Conclusion
According to the results, the direct and positive relationship of mentalizing capacity with conflict resolution styles of couples was confirmed. The mentalizing capacity in a person is formed in infancy and based on attachment to caregivers. In this way, the person learn how to communicate with self and significant others [6]. The lack of proper communication can create high tension in a child. In this regard, instead of activation of controlled mentalizing, automatic mentalizing is activated, which is associated with impaired self-regulation, emotion dysregulation, and use of inappropriate problem solving methods in future relationships with others [7]. 
On the other hand, the direct and relationship of conflict resolution styles with interpersonal trust between couples was confirmed. Based on dyadic trust model [8], by repeating constructive communication behaviors, couples perceive each other’s behavior as stable and trustworthy [8]. Therefore, it can be said that the conflict situation and how couples resolve it can affect the couples’ trust in each other. 
The results also showed that mentalizing capacity had both direct relationship and indirect relationship (by the mediation of conflict resolution styles) with interpersonal trust between couples. By development of a secure attachment, a controlled mentalizing can be formed [5], which can lead to a more sensitive manner and having a more stable behavior in adulthood in romantic relationships [9]. Therefore, when controlled mentalizing is activated in conflictual relational situations, this can help partners to behave in a way that can increase trust in each other [10, 11].
The attachment system works like a regulatory system in difficult situations. initial Insecure relationships would lead to destructions in managing stressful situations and also the capacity for mentalization [12]. So in times of stressful relational situations changing from controlled mentalization to automatic mentalization can be resulted and effect the problem solving in communications [12-14]. 
In contrast with previous studies, our results showed that only the preoccupied internal working model of attachment had a moderating role in the relationship between mentalizing capacity and conflict resolution of couples. Other attachment styles could not significantly moderate other relations in our model. This non-significant effect may be due to the special nature of attachment styles in adulthood, existence of some questions that may divert people’s minds to people other than their spouse, the change of internal working model components according to current relationships and experiences, and the difference in the methods people with different internal working patterns use to indicate interpersonal problems.

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the ethics committee of Iran University of Medical Sciences (Code: IR.IUMS.REC.1401.501).

Funding
This study was extracted from the thesis of Sara Babaei in clinical psychology approved by the School of Behavioral Sciences and Mental Health, Iran University of Medical Sciences. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Authors contributions
Conceptualization, methodology, data collection, data analysis and writing original draft: Sara Babaei; editing & review, and supervision: Mahmoud Dehghani and Komeil Zahedi Tajrishi

Conflicts of interest
The authors declare no conflict of interest

Acknowledgments
The authors would like to thank all the participants for their cooperation in this study.