In order to assess self-perception of oral health among in-treatment patients with SUD, we used the OIDP instrument. Although this is a commonly used and theoretically sound instrument to measures the impacts of oral conditions on individuals’ daily activities [10, 13], available evidence on OHRQoL among drug dependents have used the Oral Health Impact Profile-14 instrument [5-8]; leading to less data for comparison. The present study revealed at least one impact of oral conditions on daily performance of a majority of the patients. Patients with higher DMFT and DT reported greater oral impact on their daily performance.
Oral impact on daily performance was much greater among patients with SUD in our study (mean 22.4) than among Iranian general population (mean 4.15) [10]. The prevalence score of OIDP in these patients (74.1%) was also higher than that of the general population (64.9%) [10]. This is in line with other similar studies that OHRQoL among patients with SUD was worse than their counterparts in general population [5, 6]. A great majority of the participants (74.1%) reported at least one performance or daily activity affected by oral problems. This finding is similar to that of a sample of Portuguese in-treatment alcoholic patients that as high as 62.4% reported a negative impact on OHRQoL fairly often or often [19]. In addition to a group of homeless people in Brazil with the prevalence score of 81.9% [12], as high as 74.5% of Brazilian crack users reported a negative impact on OHRQoL at least fairly often [7].
In accordance with the result of the study of Iranian general population [10] and the study of homeless people in Brazil [12], the most prevalent OIDP impact during the previous six months was "difficulty eating". The most prevalent oral conditions affecting daily activities were tooth loss and dental decay. Similarly, the most prevalent oral conditions among Brazilian homeless people were need for jaw prosthesis and dental caries [12].
No significant association revealed between OIDP and patients’ demographic characteristics. This is in contrast with the results of the study of a sample of injecting drug users in Australia which poor OHRQoL was associated with female gender, lower education, and unemployment status [6]. Very few female patients with SUD in our sample (1%), might have resulted to the lack of statistical power to detect any gender difference in OIDP. Furthermore, among Brazilian patients with alcohol and substance use disorder, those with lower income were more likely to have poorer general quality of life [4].
Based on the studies either in general population or among patients with SUD, people with higher socioeconomic status in terms of their income, employment, and/or educational level, are less likely to have poorer oral health and poorer quality of life [4, 6, 14, 20]. In the present study however it seems that other factors might play a more important role in the quality of life of these patients than do their socio-demographic characteristics. This is in line with the results of the study of OHRQoL among drug dependents in South Brazil [8], and the study of Brazilian homeless people in which socio-demographic factors were not associated with OHRQoL of these patients [12].
No significant association existed between OIDP and participants’ drug use profile. In contrast, several studies have reported poorer quality of life among crack users [4, 7, 8]. This difference in findings might be due to the nature of the drugs. Cocaine/crack was the only addictive drug which showed a significant association with the quality of life of patients in the study by Marques et al. [4]. Based on the report of De Souza, among various substances, only the amount of crack consumed per day was associated with worse impacts [8]. Crack is a street name for cocaine in western countries, and is a highly addictive stimulant and a popular drug. However, this same street name in Iran mainly contains heroin, and has no stimulant effects [21].
Among US methamphetamine users, some aspects of OHRQoL were poorer in moderate and heavy users than in light users [5]. In the study of injecting drug users in Australia, poor OHRQoL was associated with injecting drugs for 10 to 20 years, and being in methadone treatment [6]. Very few injecting drug users in our sample (1.9%), might have resulted to the lack of statistical power to detect the effect of injecting route of drug administration on quality of life.
Similar to another study of in-treatment patients with SUD in Iran (mean DMFT 20.3) [14], the mean DMFT of patients in our study was high (21.5). Caries experience among our participants was much higher than that of in-treatment patients with alcohol and substance use disorder in Brazil (mean DMFT 13) [4], Southern Brazilian drug users (mean DMFT 11) [8], Brazilian crack users (median DMFT 7) [7] and a group of homeless people in Brazil (mean DMFT 14.4) [12]. Such difference in caries experience between our participants and those of other similar studies seems to be due to the higher mean age of patients in the present study (55.1 yrs.).
Based on our findings, caries experience was a predictor of poor OHRQoL among patients with SUD. This is in line with the results of the study by De Souza et al. that more impacts were reported by those drug dependents with DMFT>10 [8]. Marques et al. also demonstrated the association between general quality of life of patients with SUD and their caries experience [4]. In the present study, caries experience was the only predictor of poor OHRQoL. Thus, it seems that the effects of drug abuse history on OHRQoL of Iranian drug dependents in our study might be mediated by their clinical oral conditions. In contrast, among Southern Brazilian drug users, in addition to poor dental health status, the higher amount of crack smoked per day was associated with worse OHRQoL [8]. Furthermore, based on the report of Antoniazzi et al., crack use had a negative effect on OHRQoL independently of demographic background and oral health status [7].
Studies on OHRQoL among patients with SUD are scarce. To the best of our knowledge, this is the first study among Iranian patients with SUD in methadone maintenance therapy addressing the issue of OHRQoL. The stratified cluster random sampling method and the high response rate are strength of this study. However, due to the cross-sectional design, it is not possible to infer a causation association. Furthermore, in-treatment patients are not representative of all patients with SUD, thus we cannot generalize the results. Although, OIDP instrument is a commonly used, relatively brief and a theoretically sound measure to assess oral health-related quality of life, the questionnaire nature of the study along with the recall bias due to the report of any problems in daily activities during the previous six months are another limitations. However, we tried to increase the validity of the study by objective data collection via clinical examination.