Introduction:
Research has shown that secondhand smoking (SHS) compromises the periodontal health of non-smoking individuals. However, exposure to SHS is difficult to quantitatively measure.

Objectives:
The purpose of this study was to measure exposure to SHS among dental hygiene college students, and to find any association between SHS and oral examination, including gingival melanin pigmentation and inflammation.

Methods:
A sample of 103 female college students (18.2 ± 0.8 years), who had enrolled in April 2014 were selected as subjects. Histories of smoking and SHS exposure were obtained from a questionnaire and oral photos were taken in April of 2014, 2015 and 2016 in order to evaluate gingival melanin pigmentation and inflammation. The questionnaire included the Kano test for social nicotine dependence (KTSND), a ten-question test with 30 possible points. Urinary cotinine was also measured in October of 2014 and assessed as u-SHS cases with more than 5ng/mgCre. Gingival melanin pigmentation and inflammation were evaluated from the oral photos taken in April of 2014, 2015 and 2016.

Results:
There were no smokers in April of 2014 and 2015, but two students started smoking in April 2016. However about 40% of students had been exposed to SHS at home. The u-SHS was positive for only nine students out of the 103 students (9%) and among these, three had gingival pigmentation. The scores of gingival inflammation gradually decreased (1.2 ± 0.3/2014, 1.0 ± 0.2/2015, 0.9 ± 0.2/2016, P < 0.01). The total KTSND score in 2014, 2015 and 2016 were 9.8 ± 0.8, 9.4 ± 9.0 and 10.5 ± 5.2, respectively.

Conclusion(s):
Urinary cotinine was a useful biomarker for identifying exposure to SHS. In non-smoking female students, the u-SHS may depict the effects of the SHS on gingival melanin pigmentation. However, further well-executed studies are required to corroborate these results. This study was supported by Grant-in-Aids (19K10436).