Reducing Gingival Pigmentation Through Workplace Mitigation in Restaurant Oven Workers

This study evaluates an integrated workplace heat and air-pollution mitigation package for restaurant oven workers. Commercial cooking and combustion activities can generate fine particulate matter, carbon monoxide, volatile organic compounds, and substantial heat. The study is designed to determine whether reducing these workplace exposures is associated with changes in gingival pigmentation and biological markers related to oxidative stress, inflammation, aryl hydrocarbon receptor signaling, and melanogenesis.

This is a two-arm, parallel, superiority, cluster-randomized controlled trial. Restaurants are the units of randomization, while individual workers are the units of observation. Twenty restaurants will be allocated in a 1:1 ratio to immediate mitigation or delayed mitigation. Approximately 200 adult workers will be followed for 24 weeks, with assessments at baseline, 12 weeks, and 24 weeks. A 36-week sustainability assessment may be added only through a protocol amendment made before unblinding.

The mitigation package uses a hierarchy of workplace controls. Engineering measures include optimization of local exhaust ventilation, installation of source-capture hoods where feasible, maintenance of cooking equipment to reduce incomplete combustion, and shielding or insulation of radiant heat sources. Administrative measures include work-rest-hydration schedules based on wet bulb globe temperature, task rotation, and worker education about exposure recognition and symptom reporting. Task-appropriate respiratory protection, with a minimum N95 filtering facepiece, will be used during high-exposure activities such as charcoal ignition, deep frying, and oven cleaning. Implementation is planned within six weeks after randomization, with ongoing monitoring of ventilation performance, work-rest procedures, and area particulate matter. Restaurants assigned to delayed mitigation will receive the same package after the 24-week primary comparison period.

The primary clinical assessment is longitudinal change in objective gingival pigmentation measured from calibrated, cross-polarized intraoral photographs. Additional assessments include clinical periodontal measures, personal fine-particulate exposure, carbon monoxide, workplace heat, work-related heat, respiratory and eye symptoms, and intervention fidelity. An embedded mechanistic substudy will examine gene expression in buccal epithelial cells, salivary malondialdehyde, total antioxidant capacity, inflammatory cytokines, urinary 8-hydroxy-2'-deoxyguanosine, and exploratory DNA methylation at the AHRR cg05575921 locus.

An independent statistician will generate the allocation sequence using computer-generated permuted blocks. Allocation will be stratified by dominant fuel type and baseline kitchen particulate-matter category. Restaurant owners, workers, and intervention technicians cannot be blinded to the workplace changes. Image graders, laboratory personnel, outcome adjudicators, and the primary statistician will remain masked to allocation. Statistical analyses will account for clustering by restaurant and repeated measurements within participants.

The study will be conducted in restaurants in Najaf Governorate, Iraq. Participation requires written informed consent. Optional consent covers blood collection, residual specimen storage, exploratory DNA methylation, and future ethically approved analyses. Safety monitoring will include review of heat illness, dizziness, respiratory symptoms, equipment problems, fire or food-safety concerns, and clinically significant oral findings. Serious events will be handled according to institutional and ethics requirements.

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