Effects of Prenatal Nicotine Exposure on the Dental Health of Laboratory Rats (Rattus norvegicus)

Abstract

Nicotine, regarded as the active ingredient in cigarette smoke, is known to directly or indirectly interfere with cellular metabolic pathways including angiogenesis, osteogenesis, and collagen synthesis. Though smoking remains common, relatively little studies focus on nicotine’s role in dental development. The objective of this project was to assess the effect of prenatal nicotine exposure on dental development using rats (Rattus norvegicus) as an animal model. We hypothesized that maternal prenatal exposure to nicotine would have a long lasting negative effects on dental development even after nicotine withdrawal. To test these hypotheses, 12 female and six male Long Evans rats were purchased and bred. Dams were randomly divided into four groups (n=3, per group) and injected subcutaneously with different concentrations of nicotine hydrogen tartrate (Sigma CAS Number 65‐31‐6) as follows; Control Group (saline), Low Dose (1 mg/kg), Medium Dose (2 mg/kg), and High Dose (4 mg/kg). Pups were raised under normal laboratory conditions. We additionally monitored the weights and food intake levels of mothers during pregnancy. Incisor Growth Measurement: Offspring were anesthetized with a 2L/m oxygen flow with 5% isoflurane. Grooves were made above the gum line of mandibular incisors using an electronic dremel. After 7 days, incisor length measurement was made by measuring the distance between the gum tissue boundary and the groove. A new groove was made at the gum line. Measurements were taken every 7 days for eight weeks. Upon completion of the study, the animals were euthanized by carbon dioxide inhalation followed by bilateral thoracotomy. All procedures used on live animals were approved by St. Olaf College Institutional Animal Care and Use Committee. The differences among groups on incisor growth rate, maternal food intake, weight gain and litter size were determined by analysis of variance. P values ≤ 0.05 were considered significant. Nicotine injection during pregnancy is associated with reduced food intake and weight growth of the mothers. Prenatal exposure to nicotine also altered incisor growth rates among their offspring. Our results have shown that the mean dental growth of male offspring in the control, low, medium, and high doses were 4.8 mm, 4.0 mm, 4.4 mm, and 4.4 mm, respectively; the mean dental growth of female offspring in the control, low, medium, and high doses were 4.7 mm, 3.9 mm, 4.1 mm, and 4.4 mm, respectively. According to our two factor ANOVA, the result rejects the hypothesis that there is a correlation between sex and dental growth differences among the groups. On the other hand, the Tukey‐Kramer test suggested that there were statistically significant differences between the control and low groups, control and medium groups, and low and high groups in regard to dental growth rates. However, the correlation between nicotine dosage and dental growth in statistically significant groups is not dosage dependent, In conclusion, maternal nicotine uptake does not affect dental growth rate in a dos...