4.2. Data Interpretation and Comparisons with Previous Studies
The severity (mean OHIP-14 score) and prevalence of low OHRQoL in medical and dental students in the present study (4.6 and 53.6%) are similar to that reported in Brazilian dental students (4.5 and 45.0%) [
17] and Chinese young adults (6.3 and 50.6%) [
15]. By contrast, an Indian study found a mean OHIP-14 score of 13.4 and 10.7 in dental students in their first and fourth year of education, respectively [
18], while a Japanese study reported a mean OHIP-14 score of 1.9 in first-year university students [
10]. Direct comparison of these results with our data must be done with caution. Evaluation of quality of life, including OHRQoL, depends on an individual’s expectations and experiences, which vary according to social, psychological, socioeconomic, demographic, and other cultural factors [
28]. Someone with poor OH and low expectations may not consider themselves to have low OHRQoL and report being satisfied. By contrast, individuals who have good OH and high expectations may experience low OHRQoL, due to even minor oral problems and report being dissatisfied [
28]. Previous studies showed that 80.0% of Brazilian dental students were satisfied with their mouth and teeth [
17]; only 15.1% of Chinese young adults [
15] and 36.8% of Japanese university students [
10] reported good OH, while 44.4% and 63.8% of our medical and dental students were satisfied with their mouth and teeth and reported good OH, respectively. To compare these results, we need to know the frames of reference, i.e., the expectations and experiences these people used, when assessing their OH, satisfaction, and OHRQoL. Qualitative research should be designed to answer these questions [
29]. Nevertheless, in the present study, we found that the OHIP-14 dimensions of physical pain and psychological discomfort were the biggest drivers of low OHRQoL, which is in line with all aforementioned studies [
10,
15,
17,
18]. Therefore, one may assume a similar pattern of OHRQoL exists in young adults in different countries.
We found that the strongest factors associated with low OHRQoL were poor self-reported OH characteristics. This was expected and is in line with results from other studies [
10,
15,
17,
18]. One obvious explanation is that the concept of OHRQoL is based on outcome measures from the patients’ perspective, rather than from a dental professional’s viewpoint [
1,
2,
3]. Indeed, dissatisfaction with mouth and teeth and poor self-assessed dental aesthetic may best reflect the OHIP-14 dimensions of psychical pain and psychological discomfort, which were the biggest drivers of low OHRQoL in our study. Physical pain is often considered easy to remember [
17]. Psychological discomfort may result from poor dental aesthetic and dissatisfaction with mouth and teeth; a Malaysian study showed that psychological discomfort had the highest reported impact on OHRQoL in young adults with malocclusion [
13]. These findings may have important implications in dental practice by allowing dentists to assume the OHRQoL of young adults asking them about their dental aesthetic and satisfaction with their mouth and teeth.
In our study, a higher DMFT index was associated with low OHRQoL. In contrast, a Swedish study did not find any differences in OHRQoL between young adults at high risk (DMFT > 8) and low risk (DMFT = 0) of caries [
11]; nor were differences in DMFT index found in young adults in China [
15]. Nevertheless, Japanese university students with a higher DMFT index had lower OHRQoL [
10]. In the present study, the mean DMFT index was 7.5, while in China and in Japan, the corresponding values were 1.4 [
15] and 2.0 [
10], respectively. At present, the mechanisms of the relationship between dental caries experience and OHRQoL are unclear [
10]. Given that physical pain was the OHIP-14 dimension most frequently reported, one may assume that the dental caries experience in our medical and dental students was likely associated with pain in mouth. Public health measures, as well as dental practitioners, should focus on the prevention of dental diseases to decrease dental pain and DMFT index and improve OHRQoL in young Russian adults.
Our study also showed that students who lived in rural places during childhood had higher odds of reporting low OHRQoL compared to those who lived in urban places. Geographical remoteness, socioeconomic deprivation, and limited access to OH services have been discussed by other researchers to explain these differences [
30]. Indeed, the European North-West of Russia has a low population density, covering an area of approximately 1.5 million km
2, but with a population of only 4.6 million (78.9% urban in 2016) [
31]. In addition, the inhabitant-to-dentist ratio in North-West Russia is high; much higher, for example, than in the neighbouring Nordic countries (2294 inhabitants per dentist in North-West Russia vs. 1262 in Norway and 1101 in Sweden) [
32]. The corresponding figure in rural areas of North-West Russia is even higher (~3700 inhabitants per dentist in the Arkhangelsk Region) [
33].
Female students showed higher odds of having low OHRQoL than male students. One possible explanation is that women are more likely to report more severe and frequent pain than men, although mechanisms behind this phenomenon remain understudied [
34]. Moreover, one may speculate that women are more concerned about their appearance, and thus may describe their psychological discomfort more openly than men. Nevertheless, other studies found no sex differences in OHRQoL in young adults [
13,
14,
15,
16,
17,
19].
4.4. Limitations of the Study
Due to the cross-sectional study design, no causal relationships in the association between OHRQoL and the factors studied or trends in the prevalence of low OHRQoL over time can be determined. Only medical and dental students from the NSMU participated in the study, which may limit the generalization of our findings to the young Russian population at large in North-West Russia. One may speculate that medical and dental students are a fortunate group of young adults in terms of SES and general and oral health-related issues. Nevertheless, in the present study, the subjective SES values students reported were close to average (median was 6.0 on the MacArthur Scale). In addition, one-third of the students reported skipping tooth-brushing, which, to some extent, may reflect poor oral health behaviour. The OHIP-14 scores may be positively overestimated due to the 64.9% response rate for Stage 2. Moreover, students who were excluded due to missing data in the OHIP-14 (9.7%) more often had poor self-assessed dental aesthetic, dissatisfaction with their mouth and teeth, and poor clinically-assessed OH, which might have biased our ORs, resulting in an underestimation of the OR estimates. Only visual and tactile methods were applied during the clinical dental examination; radiographs were not taken, which could lead to an underestimation of dental caries. Information on SES and dental aesthetic was self-reported; thus, the possibility of social desirability bias due to under- or over-reporting cannot be ruled out.