To investigate the halitosis level in oral lichen planus (OLP) participants and OLP-free participants.
Methods: This cross-sectional study recruited 70 participants at the New Zealand's National Centre for Dentistry. Halitosis was determined using the objective measurements (parts per billion [ppb] volatile sulphur compounds [VSCs] in the exhaled air) and subjective measurement (self-reported halitosis questionnaire).
Results: The VSCs values of OLP participants (mean ± SD: 144.64 ± 23.85 ppb) were significantly greater than that in the OLP-free participants (105.52 ± 22.31ppb) (mean difference: 39.12 ppb; p < 0.05; 95% CI: 27.95, 50.29). The VSCs value of hyperplastic (mean difference: 34.11; 95% CI: 20.07, 48.15; p<0.05) and erosive/ulcerative (mean difference: 57.47; 95% CI: 34.19, 80.76; p<0.05) OLP participants were statistically greater than that of OLP-free participants. No statistical significance was found between hyperplastic and erosive/ulcerative OLP (p>0.05). "Type (OLP-free/OLP)" has a significant effect on the dependent variable (VSCs). 78.6% of OLP and 90.5% of OLP-free brushed their teeth at least twice daily, with a statistically significant observation (Mean square: 1.61; F: 13.13; p<0.05).
Conclusions: The levels of VSCs were greater in participants with hyperplastic and erosive/ulcerative OLP than that in the OLP-free participants. 
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Keywords: halitosis; oral lichen planus; volatile sulphur compounds.
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