Questionnaire
Upon arrival for the clinical examination, study subjects completed a multiple-choice questionnaire including demographic items, general health, medication, smoking, oral health/hygiene, and dietary habits. Questions were repeated orally if there were missing answers resulting in a 100% response rate. The questionnaire, tested internally to ascertain that all items were easily understood, was constructed by the research group experienced in the items selected. Participants were classified as either current smokers (had smoked ≥ 100 cigarettes in their lifetime and currently smoked), former smokers (had smoked ≥ 100 cigarettes in their lifetime, not currently smoking), or never smokers (had not smoked ≥ 100 cigarettes in their lifetime) [