Antimicrobial or antibiotic agents, which are essential to prevent and treat bacterial infectious diseases, have become one of the most widely used drugs in the world. In the European region, the highest rates of antibiotic consumption are reported in Turkey. There is a nearly fivefold difference between Turkey and the lowest consuming countries.

Studies in dentistry evaluate participants according to the basis of predefined criteria. History of antibiotic consumption is one of the most common exclusion criteria for periodontal trials. However, there is still disagreement on how long the effect of systemic antibiotic agents on the oral mucosa and periodontal tissue lasts. It is unclear whether the timing of antibiotic consumption should be an exclusion criterion for genetic damage and histological studies during the selection of healthy participants.

Periodontal status of participants in study groups is described as with or without periodontitis in many studies, because of the lack of clear definitions of periodontal health and gingivitis. It should be recognized that even the lack of visual signs of inflammation, some mild histopathological changes can be seen in the periodontium. Consequently, for the real diagnosis of the clinically healthy periodontium, clinical findings should be supported and confirmed with histological results.

Micronuclei (Mn) are observed as abnormal nuclear structures and indicators of chromosomal level DNA damage. The oral mucosa epithelium is an immunologic barrier and affected by chemical factors such as antibiotic consumption. The Mn test to exfoliated epithelial cells from the oral cavity is utilized as a non-invasive diagnostic technique for monitoring the status of oral health. To our knowledge, no studies have been conducted on the comparison of the impacts of the timing of antibiotic consumption on human periodontal tissues and oral smear samples. The present study is undertaken to determine whether the different timing of antibiotic (amoxicillin) therapy has effects on the histopathology of gingiva and genetic damage of exfoliated cells from oral mucosa in healthy participants.

Inclusion Criteria:

• Systemically and periodontally healthy participants
• Presence of probing depth (PD) of ≤ 3 mm14 and bleeding on probing (BOP) ˂ 10%15
• No clinical evidence of gingival recession (GR), clinic attachment loss or radiographic evidence of alveolar bone loss
• No periodontal treatment within the last 12 months

Exclusion Criteria:

• Smoking, alcohol or drug abuse
• Any systemic condition would affect the periodontal health (i.e., pregnancy, lactation, ovulation, and diabetes mellitus)
• A history of contagious disease
• Periodontal treatment within the last 12 months

A total of 45 systemically and periodontally healthy participants, who were referred to the clinics of the Department of Periodontology, Faculty of Dentistry, Istanbul Medipol University between 2018 and 2019 for routine periodontal visits, were included in this study. Participants were divided into three groups based on the history of oral antibiotic (1 g amoxicillin bid, two times a day) consumption for upper respiratory tract infection in the previous 12 months: group I (n = 19), participants used antibiotic between 12-6 months before the sampling; group II (n = 13), participants used antibiotic between 6-3 months before the sampling; group III (n = 13), participants used antibiotic within a period of 1-month before to sampling.