Before discussing our results, we must assume that our study presents some limitations. The selection of subjects without mental disorders for the control group was based on a medical questionnaire and the anamnesis of the patient. This method carries the risks that a questionnaire could be inaccurate or an individual patient could be dishonest. However, the comparison between the two groups seems to indicate that the groups are comparable. The smoking rate among study subjects was high, and this could affect the extrapolation of our results to other populations, especially outside of Spain.
Accepting the above, the clinical findings of this study demonstrate differences in the prevalence and distribution of decayed teeth (DT), missing teeth (MT), filled teeth (FT) and DMFT between patients with schizophrenia and healthy control subjects. Decayed and missing teeth were significantly more prevalent in patients with schizophrenia, suggesting a lack of restorative care with extensive unmet dental treatment needs [6, 16, 23, 24, 27, 28]. In the present study, the DMFT score of the group with schizophrenia was comparable to scores found by other studies concerning non-institutionalised patients with schizophrenia in Mediterranean countries with similar demographic variables [23, 24]. A previous Greek study in outpatients with schizophrenia showed a lower DMFT (16.08) with a DT score of 2.26, MT score of 9.68 and FT score of 2.92 . Also, a recent Spanish study reported a lower DMFT score (13.51) with a DT score of 4.39, MT score of 5.66, and FT score of 3.53 among psychiatric patients with schizophrenia . The main differences may be explained because the combination of decayed teeth and missing teeth in the present study resulted in high DMFT values. The FT scores showed a lower number of filled teeth. The present study reported an MT score of 9.10 ± 8.56 missing teeth among patients with schizophrenia, and 40% of these patients were missing 9-32 teeth. In contrast, the control group had a lower MT score (5.38 ± 5.14) with 22% of subjects missing 9–32 teeth.
The present study indicated significant differences in the number and distribution of decayed teeth. DT scores were higher in patients with schizophrenia compared with controls. Overall, 44% of patients with schizophrenia and 37% of control subjects showed 8 or more decayed teeth. Mental disorders such as schizophrenia may be a risk factor for dental health [3, 4]. A relationship between negative psychopathological states and higher prevalence of decayed teeth has been evidenced [23, 24]. Negative symptoms of schizophrenia impair the ability of patients to exercise preventive oral hygiene . Moreover, chronically hospitalised patients tend to have more severe negative symptoms than patients who live in the community . In fact, long-term hospitalisation causes declines in self- and oral hygiene and dental care, resulting in increased dental caries [10–16]. DMFT scores were higher among hospitalised patients with schizophrenia, but these patients were also older (range of age of 48–58 years) [10, 12, 14–17, 27]. Several studies reporting on hospitalised chronic psychiatric patients with schizophrenia reported high DT scores and MT scores and lower FT scores [12–16]. In addition, one study showed a lower mean DMFT score of 16.08 in outpatients with schizophrenia compared with patients with schizophrenia who had been hospitalised for up to 10 years (18.50) and those hospitalised for more than 10 years (27.17) .
The majority of patients with schizophrenia take psychotropic medications on a regular basis. Relevant medications include conventional and atypical antipsychotics, benzodiazepines and antiparkinsonians [14–16]. Psychotropic medications can contribute to dental caries in patients with schizophrenia, as many of them cause dry mouth due to reduced salivary flow [3, 6, 12, 16]. An American study showed that 99% of smooth surface caries (coronal and root) was associated with low salivary flow . Root surface caries, generally associated with older populations, were notably high in a group of young psychiatric patients with schizophrenia . A Turkish study showed a 39.9% correlation of oral dryness in chronic psychiatric patients with the administration of these medications [mean: 2.3 (number of medications per patient)]. Patients with schizophrenia had the highest incidence of symptoms of oral dryness . These findings were confirmed by another study in Israel, where 94% of inpatient study subjects were taking psychotropic medications [mean 2 (number of medications per patient)] and 22% reported experiencing dry mouth .
The results showed that the prevalence of missing teeth increased significantly with age in both groups. For all age groups, the mean number of missing teeth (MT) was higher in patients with schizophrenia compared with the control subjects. The schizophrenic group showed a significant age-related increase in DMFT with a corresponding significant increase in the MT score and decrease in the DT component. The mean DMFT score in the oldest age group (over 46 years) was approximately twice that of the youngest age group (up to 35 years). These findings are consistent with those seen in similar psychiatric groups demonstrating that age is an important determinant of poor oral health [12, 14, 15, 17, 24, 28]. Among the patients with schizophrenia, the carious disease process seems to progress over time, and teeth are lost rather than being restored. This is indicated by the increases in MT scores over time [12, 14]. The high prevalence of missing teeth with age may be interpreted to suggest that patients with schizophrenia who seek dental care often have their teeth extracted rather than seeking restorative treatment, probably because of the complexity of their dental care needs [10–14].
In the present study, the gender distribution of the patients with schizophrenia (39 males and 11 females) and the control subjects (33 males and 17 females) were similar. In addition, the DMFT scores in this study did not vary greatly between males and females. These results are confirmed by two similar comparative studies of oral health in patients with schizophrenia, also in Spain, which showed that gender did not affect the dental parameters measured in both study and control groups [20, 24]. A study in Taiwan reported the results of DMFT for males and females among inpatients with schizophrenia (13.93 vs. 13.98) and general patients (7.1 vs. 9.73) with no significant differences . Where differences have been reported, men have worse dental disease than women [14–17, 20]. In patients with schizophrenia, males tend to show higher numbers of carious teeth and root remnants caused by negligence of dental care compared with females [14, 16].
Most people suffering schizophrenia smoke heavily. Smoking is associated with medical and dental problems in patients with schizophrenia. A comparative study showed a significantly higher proportion of smokers in patients with schizophrenia (71%) than controls (39%) (24). A similar trend in smoking prevalence is observed in older patients with schizophrenia (52%) compared with older controls (23%) . However, in the present study the prevalence of smoking in the schizophrenia group (56%) was similar to that in the control group (52%). Smoking can contribute to poor dental health as it is associated with increased periodontal disease and higher rates of tooth loss. Smoking has been related to higher DMFT scores in patients with schizophrenia . Higher numbers of missing and decayed teeth have been reported in smokers compared to non-smokers among patients with schizophrenia . These results are confirmed by the present study: analyses of each parameter individually (D, M and F teeth) revealed that smoking affected the number of missing and decayed teeth. The D and M values were higher among smokers compared with non-smokers. Moreover, the mean DT and MT scores were higher in smokers with schizophrenia than in the smokers of the control group.
The overall percentage of smokers in Spain is 40% (one of the highest rates in Europe) . In our sample, the percentage ranged from 50 to 60% in both groups. We do not think this invalidates our conclusions, although they may not be accurately extrapolated to populations with others percentages of smokers, especially given the effect that smoking can have on other habits and behaviours.
Another important finding from this study is the low number of filled teeth (FT). Among patients with schizophrenia the number was 1.38 ± 2.70, while in the control group it was 2.34 ± 3.48. These clinical findings are consistent with those of other studies, which have demonstrated that patients with schizophrenia are in need of preventive and restorative dental treatment [12, 17, 20, 23]. Illness chronicity and psychopathology severity may explain why patients with schizophrenia visit dentists much less frequently than the general population . Negative symptomatology may cause patients to visit the dentist only when they have severe dental problems that are difficult to treat . Schizophrenia may severely interfere with patients seeking dental treatment, delaying restorative treatment until tooth loss is inevitable . Moreover, dental diseases often represent a lower priority in the overall health care of patients with schizophrenia, but these have a negative impact on the general quality of life . The use of a multidisciplinary model involving mental and oral health is fundamental to the development of dental programs. These programmes must educate and sensitise psychiatrists and psychiatric nurses to dental health. Access to skilled dental care can improve most dental problems for patients with schizophrenia .