In this study, a periodontal examination was conducted in a population of UC-subjects and periodontitis defined according to the new classification of periodontal disease. Furthermore, periodontal status was correlated to previous data on disease severity and symptoms of UC (Mayo Score and CAI), and years with UC diagnosis. The majority of subjects presented with periodontitis, of which 34% stage III, 22% stage II and 18% stage I. 26% of the population were diagnosed as non-periodontitis cases. Two patients were diagnosed as periodontally healthy and 11 patients with gingivitis. No correlations were found between previous scores of UC disease severity and symptoms (MAYO and CAI), years with UC diagnosis and the severity of the periodontal disease (stage, grade, BoP, PPD > 6mm).
A recently published article stated there is an emergent need to perform studies on the periodontal disease according to the World Workshop on the Classification scheme for periodontal and peri-implant diseases and conditions 2017 in subjects with IBD ,.
The findings of the present study is in agreement with a recent study on the prevalence of periodontitis in Norway by Stødle et al. . In their sample population of nearly 5000 individuals from Trøndelag county, the prevalence of periodontitis was reported to be 2.3%, 15%, 40% and 12% for stages IV, III, II, and I, respectively, and only 28% were not diagnosed with periodontitis. The present study recorded no case of stage IV and a higher prevalence of stage III. This difference might be explained by the smaller sample size of the present study but also by the diagnostic means. In contrast to Stødle et al., the present study included a more comprehensive examination including clinical assessments of furcation defects and CAL. This most likely led to the diagnosis of more stage III localized cases as compared to the large-population study with a higher percentage of stage II. When summarizing all periodontitis cases regardless of stage the outcome in both populations was similar (74% vs 72.4%). This study shows a higher prevalence of periodontitis compared to other recent studies from Norway [36, 37] and this could be explained by different demographics, inter-observational differences between the examiners and different thresholds for defining periodontitis.
Periodontitis showed no correlation with Mayo and CAI scores (Table 4). This could be explained by the time lapse between the periodontal examination and the historical records of Mayo and CAI. Another explanation is the fact that most patients were medically well-maintained and that the majority (78%) of the patients reported no symptoms of UC at the time of periodontal examination. As pointed out by Vavrica et al., there are very few studies analyzing the effect of IBD medication or disease activity on the periodontal status . This study could not confirm any such association. This may be because the association was too weak to be detected given the small population with limited symptoms.
Based on studies reporting on the symptom-relieving effect of tobacco use among UC patients , information on smoking habits and the use of smokeless tobacco was analyzed to see if this was of significance . A recent study by Kang et al.  reported that periodontitis and smoking increase the risk of UC. Since there were few patients reporting on tobacco use in the current study, no conclusions could be drawn. Interestingly, there were three patients (6%) smoking cannabis as self-medication. This finding is supported by a newly published article which states that approximately 10–20% patients with IBD are active cannabis users .
The OHIP-14 data showed limited negative impact on QoL in this population. This is partly in contrast to studies reporting on the negative influence of UC on health-related quality of life . A recent study by Goldinova et al. , reported a near-significant correlation of the OHIP-14 scores with a simple clinical colitis activity index (SCCAI) and IBD questionnaire (IBDQ-9). In a national cross-sectional Norwegian study from 2011 using the OHIP-14  the proportion of individuals who reported problems ranged from 11–56%, with pain as the most frequently reported item. The most frequently reported problem was physical pain (56%), followed by psychological discomfort (39%) and psychological disability (30%). The most frequently experienced problems were physical pain, such as aching in the mouth (Q3), and discomfort eating food(Q4), which is in agreement with our study and other Scandinavian studies [45, 46]. To our knowledge this is the first study to report on oral-health-related quality of life, periodontitis and UC combined.
The data from this population could not confirm a correlation between periodontitis severity and Mayo score, CAI or years with UC diagnosis.
The use of Mayo score and CAI obtained at a single time point some years before the periodontal examination can be questioned.
This study has other noteworthy limitations with the small number of participants being the most obvious. On the other hand, the recruitment of a high number of participants with long-term UC diagnosis may be challenging. Although the study coincided with the first and second waves of the COVID-19 pandemic in Norway, the majority of invitees (50/63) were willing to participate in the study (78%), which reflects a highly motivated and compliant cohort. The study was conducted in a community hospital in which patients may present with a less aggressive UC than seen in advanced units, as pointed out in the study by Klepp et al . The population examined was a selection of subjects remaining throughout the original study and furthermore agreeing to a periodontal examination years later. It is therefore possible that those with more severe UC did not take part. In general, the population examined were successfully treated as suggested by the OHRQoL-data and patient-reported data reported herein.
The strength of the study is the periodontal diagnostic means according to the new classification and consideration of patients’ OHRQoL with a long duration of UC. In agreement with Lorenzo-Pouso et al. , more evidence of a potential link between periodontitis and UC is needed.