Influence of thermoplastic retainers on Streptococcus mutans and Lactobacillus adhesion C ¸a grı T€ urk€ oz, a Nehir Canig€ ur Bavbek, b Selin Kale Varlik, c and G€ ulc ¸ in Akc ¸a d Ankara, Turkey Introduction: This study was designed to test the hypothesis that thermoplastic retainers influence oral micro- bial flora during the retention period because they prevent the flushing effect of saliva on dental and mucous tissues. Methods: Twenty-four orthodontic patients finished the study. After debonding, the patients were given thermoplastic retainers (Essix ACE 0.040-in plastic, Dentsply International, York, Pa) for both jaws and instructed to wear them all day. Plaque samples from tooth surfaces and saliva samples were collected from each patient just after debonding (T0), and on day 15 (T1), day 30 (T2), and day 60 (T3) of retention. The jaws were divided into 6 regions, and the data for each region were evaluated separately. Total viable Lactobacillus and Streptococcus mutans colonies were counted, and the numbers of the viable microorganisms were calculated. Results: The numbers of Lactobacillus colonies at T3 were higher than at T0, T1, and T2, and the difference between T0 and T3 was statistically significant (P \0.05). The numbers of S mutans colonies at T3 were higher than at T0, T1, and T2, and the differences between T0 and T1, and T1and T2 were statistically significant (P \0.05). Conclusions: Retention with thermoplastic retainers might create oral conditions conducive to S mutans and Lactobacillus colonization on dental surfaces. (Am J Orthod Dentofacial Orthop 2012;141:598-603) R etention is an important phase of orthodontic treatment during which tooth movements after active treatment are stabilized. There are numer- ous types of retention methods for clinical use, and ther- moplastic retainers are widely preferred for their advantages: removable, more esthetic, cost effective, and less time-consuming in the laboratory. Identification of the changes in the oral cavity of pa- tients who have orthodontic therapy, including the re- tention period, is important. Previous data about oral hygiene of orthodontic patients held removable and fixed orthodontic appliances responsible for worsening the oral hygiene 1,2 and promoting the differentiation of microbial flora of the oral cavity 3,4 that might result in caries, white spot lesions, and gingival inflammation. In studies concerning oral hygiene during or after orthodontic treatment, special attention is attributed to cariogenic populations such as Streptococcus mutans and Lactobacillus. Many studies in the literature have evaluated the changes in S mutans and Lactobacillus levels during orthodontic therapy with either acrylic removable appliances or orthodontic bands and brackets. 5-7 Besides, most of these studies concentrated on the active orthodontic treatment phase with fixed or removable appliances. However, microbiologic data during retention period are limited. 8,9 Yet, as far as we know, there is no information about the effects of thermoplastic retainers on oral microbiota, although they are frequently preferred. In addition, there are no data evaluating the oral cavity by separating it into specific zones during retention with thermoplastic retainers. Therefore, the purpose of this study was to test the hypothesis whether thermoplastic retainers influence oral microbial flora during the retention period because they prevent the flushing effect of saliva on dental and mucous tissues. MATERIAL AND METHODS The initial study population comprised 40 subjects with an age range of 14 to 20 years, who had fixed From Gazi University, Ankara, Turkey. a Assistant professor, Department of Orthodontics. b Research assistant, Department of Orthodontics. c Associate professor, Department of Orthodontics. d Assistant professor, Department of Microbiology. The authors report no commercial, proprietary, or financial interest in the prod- ucts or companies described in this article. Reprint requests to: C ¸a grı T€ urk€ oz, Gazi € Universitesi Dis ¸ Hekimli gi Fak€ ultesi Orto- donti, AD 06510 Emek, Ankara, Turkey; e-mail, cturkoz@hotmail.com. Submitted, October 2011; revised and accepted, November 2011. 0889-5406/$36.00 Copyright Ó 2012 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2011.11.021 598 ORIGINAL ARTICLE