Nicotine is a risk factor for dental caries: An in vivo study

Abstract

Background/purpose: Streptococcus mutans is an important pathogen in the development of dental caries. Many studies have focused on the relationship between nicotine and S. mutans in vitro. The aim of this study was to investigate the effect of nicotine on the growth of S. mutans and its cariogenic potential in vivo.

Materials and methods: Sixteen male Specific-pathogen-free Wistar rats were divided into 2 groups (nicotine-treated and nicotine-untreated group) and infected with S. mutans. The S. mutans suspension was treated with 1 mg/mL nicotine in the nicotine-treated group. The Keyes method was used to evaluate sulcal caries of rats, and dental plaque on molar teeth was observed by scanning electron microscopy (SEM).

Results: Incidence of sulcal caries was higher in nicotine-treated group compared to nicotine-untreated group (42.7 ± 1.7 vs 37.3 ± 4.9, P = 0.009). Severity of caries increased with nicotine treatment. The slightly dentinal caries scores and moderate dentinal caries scores were higher in the presence of nicotine (P < 0.001). Increased number of S. mutans cells attached to dental surface was observed under SEM in the nicotine-treated group.

Conclusion: Nicotine would promote the attachment of S. mutans to dental surface, and further increase the incidence and severity of dental caries. Therefore, nicotine might be a risk factor for smoking-induced caries.

Keywords: Dental caries; Nicotine; Rats; Streptococcus mutans.

Figure 1

Challenge schedule of rats. Rats were fed with antibiotics for the first three consecutive days and then were challenged with a S. mutans suspension for next three consecutive days and sterile BHI (with or without 1 mg/mL of nicotine) every four days until the rats were sacrificed.

Figure 2

Representative caries lesions were detected by stereo microscopy. Caries progressed to moderate dentine (Dm) and extensive dentine (Dx) in the nicotine-treated group. Dm & Dx caries were seldom seen in the other group.

Figure 3

Statistical analysis of Keyes scores. (A) Scores for enamel caries (E), slightly dentinal caries (Ds), and moderate dentinal caries (Dm) caries were significantly higher in nicotine-treated group (P < 0.05), while no statistical difference in extensive dentinal caries (Dx) was seen between the two groups (P > 0.05). *P < 0.05, ***P < 0.001, ns, not significant. Error bars represent SD. (B) Values denote means ± SD (n = 7), nd, not detectable. There was an obvious increase in the incidence and severity of sulcal caries.

Figure 4

Representative bacterial plaques on tooth surfaces were observed by scanning electron microscopy. The two groups of nicotine treated (the upper) and nicotine untreated (the lower) samples were detected at least three times on randomly selected positions at 2000×, 5000×, 10000× magnification. More cells were observed in the nicotine-treated group, and cells formed clumps and aggregates.