Effects of Hawley, Essix, and Vivera® retainers on salivary properties, oral hygiene, and Streptococcus mutans levels: A prospective clinical pilot study

Objectives: The objectives of the study were to investigate the in vitro and in vivo effects of various removable orthodontic retainer materials on clinical and microbiological parameters, specifically on saliva characteristics, oral hygiene, and salivary levels of Streptococcus mutans (S. mutans). Materials and Methods: This study consists of two parts: An in vitro study and in vivo prospective clinical pilot study. The in vitro study measures surface roughness and S. mutans adhesion of three orthodontic retainer materials: Polymethylmethacrylate (PMMA) used in traditional Hawley removable retainers, polypropylene (PP), and polyurethane (PU) used in vacuum-formed retainers. In the clinical pilot study, 20 subjects, on completion of orthodontic treatment were randomized into three groups to receive PMMA, PP, or PU removable orthodontic retainers. They were compared with control subjects with no orthodontic treatment and retainers. Quantitative analysis of salivary S. mutans using real-time polymerase chain reaction was performed to screen for differences during retainer issue (T0) and 8-15 weeks later (T1). Salivary flow rate, pH, buffering capacity, and plaque scores were also recorded at these two periods for comparison. Results: PMMA had significantly greater surface roughness and S. mutans adhesion than PP and PU (P = 0.027). The PMMA group displayed significantly greater amounts of salivary S. mutans count when compared to the PP (0.001) and PU (P = 0.011) groups. Conclusion: PMMA retainers showed increased S. mutans adhesion and intra-oral colonization of S. mutans compared to PP and PU retainers. The results validate further clinical testing for a relationship between caries risk and type of retainer prescribed.