Acrylic removable orthodontic appliances are commonly used for myofunctional therapy or simple tooth movements in children and adolescents during the prepubertal or pubertal stage. They can correct some maxillofacial problems by benefitting from the growth potential during this time period. Also, these appliances are used during the maintenance phase after completion of orthodontic treatment to maintain the results and prevent relapse [1]. Long-term daily use of removable orthodontic appliances is imperative to achieve ideal treatment results. However, this pattern of use increases the risk of accumulation of microorganisms on the surface of appliances [2]. Despite the numerous benefits of removable orthodontic appliances, their use can enhance microbial biofilm accumulation on dental surfaces and appliance components such as the clasps, springs, and acrylic base [3]. Evidence shows that use of removable orthodontic appliances can alter the oral microbial flora, increase the salivary count of Streptococcus mutans, and enhance the biofilm formation during the active treatment phase [4, 5]. Moreover, the porosities on the internal and external surfaces of the acrylic resin base of such appliances are covered by pathogenic microorganisms mainly Candida albicans (C. albicans) [6–8].
The acrylic base of removable orthodontic appliances is made of plastic polymers, which contain carbohydrates, and attract several microbial strains such as C. albicans that consume such polymeric materials [7, 9]. Moreover, decomposition of acrylic resin can enhance microbial biofilm accumulation [3]. Microbial biofilm contains different microorganisms that strongly adhere to each other and also to the surface. These microorganisms are located on a network of proteins and polysaccharides [10, 11]. Also, use of removable orthodontic appliances increases the count of pathogenic microorganisms such as Streptococcus mutans, Lactobacillus, and C. albicans in unstimulated saliva of patients. Change in oral microbial flora can increase the risk of caries and periodontal disease [12–14].
Chlorhexidine (CHX) is the gold standard for chemical removal of microbial plaque, which is often prescribed as an adjunct to mechanical plaque removal methods. However, long-term use of chemical agents is not recommended [15–18].
Use of herbal essences for their antimicrobial properties has been previously evaluated [19–21]. Several medicinal plants such as thyme, cloves, lavender and tea leaves have been tested for disinfection of the oral cavity [22–27]. Given that medicinal plants are suitable alternatives to chemical agents, application of chemical agents can be limited to acute cases, and herbal products can be recommended for continuous long-term use by orthodontic patients during their treatment course [18].
Thymus (thyme) is an important medicinal herb that belongs to the Lamiaceae family. Thymus, Ziziphora, and Zataria are the three main genera of the Lamiaceae family. The thymus genus has 14 species in Iran, and Thymus vulgaris (T. vulgaris) is one of the most important species [33]. Thymol and carvacrol are the main constituents of T. vulgaris essence. Also, it contains tannin, flavonoids, and saponins [34]. The T. vulgaris essential oil has several pharmaceutical and therapeutic applications [25]. It also has high chance of acceptance by patients due to its favorable taste and odor, insignificant toxicity and side effects, and low cost [35].
Essential oil is the alcoholic extract with a volatile oil, which can be extracted by different techniques such as the cold-pressed extraction method, distillation, extraction by solvent, distillation under vacuum using a microwave, maceration, or extraction with absorbent oils obtained from herbal products [36]. Distillation is an important method of essential oil extraction, which is based on separating the components or substances in two phases [37]. Evidence shows that Zataria multiflora (Shirazi thyme) has suitable antimicrobial and antifungal properties for irrigation of root canals in endodontic treatment in vitro, compared with chemical irrigating solutions [38, 39]. Also, Zataria multiflora essential oil is effective for disinfection of acrylic plates and orthodontic elastics in vitro [40, 41]. Favorable antifungal activity of T. vulgaris essential oil, compared with CHX, has also been reported for disinfection of removable orthodontic appliances in vitro [42].
Specific objectives and hypotheses
This study aimed to compare the effects of T. vulgaris essential oil and CHX on C. albicans accumulated on removable orthodontic appliances. The null hypothesis was that there was no difference in Antifungal efficacy of T. vulgaris essential oil and CHX.