Abstract: The invention relates to a method of decreasing the risk of injury from mercury in conjunction with dental treatment. The invention is characterized by passing an effective air flow immediately outside the oral cavity in which the dental treatment is effected. The air flow, together with air removed by suction from the oral cavity when sucking saliva therefrom is passed through a first filter in which solid and liquid particles are extracted from the air flow. The air is then passed through a second filter which is capable of taking up essentially all of the mercury vapor present in the air. This filter is preferably a selenium filter.