The impact of substance abuse on overall health is profound, encompassing both physical and psychological dimensions. Among the myriad of health issues faced by individuals with a history of drug abuse, oral and dental health problems are particularly prevalent [1]. Research indicates that drug abuse contributes to a range of oral health complications, including periodontal disease, dental caries, and oral mucosal lesions. These conditions, in turn, can significantly reduce the quality of life of affected individuals, manifesting as pain, discomfort, and functional limitations [2, 3].

The relationship between oral health and quality of life has garnered increasing attention in recent years. Quality of life, particularly in the context of health, is a broad concept that encompasses physical health, psychological well-being, social relationships, and overall life satisfaction. In individuals with a history of drug abuse, the deterioration of oral health not only affects personal comfort and aesthetics but can also lead to social stigma, isolation, and adverse economic consequences. Hence, understanding the interplay of drug abuse, oral health, and quality of life is crucial for developing comprehensive treatment and intervention strategies [4-7].

Several studies have highlighted the factors contributing to poor oral health in drug abusers, including socio-economic status, educational background, and access to dental care. Furthermore, lifestyle choices such as inadequate oral hygiene practices, dietary habits, and the psychosocial consequences of addiction exacerbate these issues. However, a gap remains in the literature regarding the specific examination of how these factors collectively influence the quality of life related to oral health in this vulnerable population [3, 8-11].

Additionally, limited research has specifically examined how socio-demographic characteristics, drug use patterns, and oral hygiene behaviors collectively and independently influence OHRQoL in this vulnerable population, particularly in settings where opium is the predominant substance of abuse.

This cross-sectional, descriptive-analytical study was conducted between March and October 2024 at the Addiction Treatment Center of Imam Reza Hospital in Birjand, Iran. The study was approved by the Ethics Committee of Birjand University of Medical Sciences (Code: IR.BUMS.REC.1402.105) and was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants prior to enrollment.

The findings of this study highlight that older age (>45 years), illiteracy, lack of dental floss use, and early initiation of drug use are the key independent factors associated with impaired OHRQoL among individuals with a history of substance abuse. These results underscore the interplay between socio-demographic vulnerability, behavioral neglect, and the timing of addiction onset in shaping oral health outcomes [4, 13].

Poor oral hygiene practices were alarmingly prevalent, as 55.3% did not use a toothbrush, and 96.5% never used dental floss. Although toothbrush use lost significance in the final model, dental floss use emerged as a robust predictor, suggesting that even minimal interdental cleaning may confer meaningful protection against oral health decline in this population. This finding supports the integration of simple, low-cost hygiene education, particularly flossing, into addiction treatment protocols [8, 16].

The association between early drug initiation (<25 years) and worse OHRQoL aligns with evidence that prolonged substance exposure leads to cumulative oral damage, including xerostomia, caries, and periodontal disease. Similarly, older age may reflect both longer duration of drug use and age-related physiological decline, compounding oral health risks. Illiteracy, as a proxy for low health literacy and limited access to preventive information, further exacerbates vulnerability, consistent with global evidence that links education to oral health outcomes [17, 18].

Interestingly, participants with dentures reported poorer OHRQoL than those without. This likely reflects the severity of prior tooth loss rather than an adverse effect of prostheses per se [19]. In resource-limited settings, dentures may be poorly fitted, inadequately maintained, or provided without follow-up care, factors that can compromise, rather than restore, function and comfort. This underscores the need for comprehensive prosthodontic care, not just appliance provision [20].

All participants in this study used traditional drugs, primarily opium, which limits generalizability to users of synthetic substances (e.g., methamphetamine). However, the identified pathways, such as neglect of hygiene, socioeconomic marginalization, and delayed care, are consistent across substance types, suggesting broader relevance. International studies report similar OHRQoL burdens among heroin and stimulant users, reinforcing the universality of these social-behavioral determinants [18, 21].

From a policy perspective, these findings support the implementation of routine oral health screenings and preventive services within addiction treatment centers. Given that methadone programs provide regular contact with patients, they offer an ideal platform for delivering oral health education, fluoride application, and referrals to dental care. Such integration could significantly reduce the long-term burden of oral disease in this high-risk group.

Notably, while bivariate analyses suggested associations with gender, marital status, self-employment, and toothbrush use, none of these remained statistically significant after multivariate adjustment. This discrepancy likely reflects confounding by stronger predictors (e.g., education and hygiene behaviors), highlighting the importance of multivariate modeling in identifying true independent risk factors. The low representation of women (20.2%) further limits the reliability of gender-based conclusions, a limitation that should be addressed in future studies through targeted recruitment [14, 15].

This study identifies four independent predictors of impaired OHRQoL among individuals with a history of drug abuse, including age over 45 years, illiteracy, lack of dental floss use, and early initiation of drug use. These findings emphasize that oral health in this population is shaped not only by addiction itself but also by educational disadvantage and modifiable hygiene behaviors.

We recommend that oral health promotion, particularly education on interdental cleaning, be systematically integrated into addiction treatment programs. Future research should employ longitudinal, multicenter designs with balanced gender representation, clinical oral examinations (e.g., DMFT, CPI), and assessment of mental health and access-to-care barriers to strengthen causal inference and inform targeted interventions. By addressing these modifiable factors, healthcare systems can significantly improve both oral and overall quality of life for individuals recovering from substance use disorders.