Ozone was discovered by Christian Friedrich Schönbein in 1839 [5]. In 1857, Werner von Siemens designed an ozone generator [6]. Ozone was first used in medicine in 1870 [3]. Medication forms of gaseous ozone are somewhat unusual, and that is why special application techniques have had to be developed for its safe use. According to the European Cooperation of Medical Ozone Societies, direct intravenous injections of ozone/oxygen gas may produce air embolisms [7]. In local applications, as in the treatment of external wounds, ozone application in the form of a transcutaneous gas bath has been established as a practical method – for example, at low (subatmospheric) pressures in a closed system guaranteeing no escape of ozone into the ambient air [8].

Apart from rectal insufflation, principally used in the treatment of intestinal conditions, but also applied systemically, autohemotherapy has established itself as a systemic therapy of choice [2]. A corresponding dosage of ozone gas is passed through or, more correctly, transferred (in the form of microbubbles) to 50–100 ml of the patient’s blood in a sealed, pressureless system, thereby assuring the finest possible distribution to reach the greatest possible number of red and white blood cells with the aim of activating their metabolism [1, 2]. In treating pain in the locomotor system, ozone can be applied supportively in the form of intramuscular or intra-articular injections [2]. Ozone can also enhance both lung function and inflammatory airway responses in subjects with preexisting allergic airway diseases [7]. However, its use is contraindicated for the following conditions: acute alcohol intoxication, recent myocardial infarction, hemorrhaging from any organ, pregnancy, hyperthyroidism, thrombocytopenia, and ozone allergy [2–4].

Fisch used ozonated water in dentistry in 1930 for the first time [1]. Following him, the German surgeon Erwin Payr used ozone in surgery and reported his results at the 59th Congress of the German Surgical Society in Berlin [3].

Ozone has been used in various disciplines of dentistry. Ozone is applied to oral tissues in the following forms: ozonated water, ozonated olive oil, and oxygen/ozone gas. Ozonated water and olive oil have the capacity to trap and then release oxygen/ozone which is an ideal delivery system. These forms of application are used singly or in combination to treat dental diseases [8].

Ozone may temporarily arrest the progression of caries by killing bacteria in active carious lesions. This results in preventing or, at the very least, in delaying the need for tooth restorations [8–11]. Our previous systematic review of the applications of ozone in dentistry showed that ozone can be used to manage primary occlusal and root carious lesions [9]. For example, using a KaVo HealOzone device, Baysan et al. [10] showed that ozone exposure for 10–20 s reduced the total levels of Streptococcus mutans and Streptococcus sobrinus in the primary root caries lesions (PRCLs) to <1 % of the control values. Holmes [12] assessed the effect of a KaVo HealOzone device on PRCLs followed by a professionally applied remineralizing solution containing xylitol, fluoride, calcium, phosphate, and zinc and found that after 18 months, 100 % of PRCLs had improved. However, the clinical application has yet to achieve a strong level of efficacy and cost-effectiveness [8]. Filippi [12] observed the influence of ozonated water on the epithelial wound healing process in the oral cavity. It was found that ozonated water applied daily can accelerate the healing rate in the oral mucosa. This effect can be seen in the first two postoperative days. A comparison with wounds without treatment showed that daily treatment with ozonated water accelerates the physiological healing rate. Ozone has also been used to treat TMJ dysfunctions and trismus [4].

Schmidlin et al. [13] showed that, despite a possible retention of surface and subsurface oxide-related substances during high-dose ozone application, shear bond strength was not impaired. Magni et al. [14] indicated that ozone gas did not compromise the mechanical properties of the adhesives. Cadenaro et al. [15] demonstrated that using ozone gas to disinfect the cavity before placing a restoration there had no influence on immediate enamel and dentin bond strength. Cehreli et al. [16] revealed that pretreatment with ozone improved the marginal sealing ability of the fissure sealants. Bojar et al. [17] showed that ozone therapy improved shear bond strength of two root canal sealers (AH26 and EZ-Fill). Gurgan et al. [18] showed that ozone treatment did not impair the shear bond strength of two self-etch adhesives (Clearfil SE Bond and Clearfil Tri-S Bond) used to coronal and radicular dentin. According to Arslan et al. [19] ozone did not significantly affect the dentin bond strength of a silorane-based resin composite, Filtek Supreme. Garcia et al. [20] revealed that ozone gas and ozonated water had no deleterious effects on bond strengths and interfaces. Bitter et al. [21] showed that adhesion of the self-adhesive resin cement RelyX Unicem was significantly reduced after using gaseous ozone. According to Rodriguez et al. [22] ozone decreased the microtensile bond strength of a dentin-composite resin interface. Dalkilic et al. [23] indicated that ozone reduced the initial microtensile bond strength.

In dental surgery, ozonated water was used to promote hemostasis, enhance local oxygen supply, and inhibit bacterial proliferation [4]. One study was found to evaluate the effect of ozone gas in oral and maxillofacial surgery, where ozone therapy was found to be beneficial for the treatment of refractory osteomyelitis in the head and neck in addition to treatment with antibiotics, surgery, and hyperbaric oxygen [4].

Dentin hypersensitivity (DH) is characterized by a short, sharp pain arising from exposed dentin in response to stimuli that are typically thermal, evaporative, tactile, osmotic, or chemical and cannot be ascribed to any other form of dental defect or pathology [25]. The application of ozone as a treatment of dentin hypersensitivity was described more than 50 years ago [26]. Dähnhardt et al. [27] assessed the effect of treatment with gaseous ozone on DH. Findings revealed no significant reduction in pain compared to the placebo group. More recently, in an 8-week, three-visit, triple-blinded, randomized controlled clinical trial with two HealOzone machines (ozone/air), Azarpazhooh et al. [28] confirmed the findings of Dähnhardt et al. [27]. Another study investigated the effect of ozone, with or without the use of desensitizing agents, on the patency and occlusion of simulated hypersensitive dentin. Results indicated that the combined use of ozone/fluoride resulted in a significantly higher percentage of tubular occlusion than fluoride desensitizer alone. However, no significant difference was found between oxalate desensitizer and the combined use of ozone/oxalate [29]. It has been demonstrated that ozonated olive oil as a monotherapy was not efficient in reducing postsurgical root dentin hypersensitivity. However, using it in combination with a mineral wash containing calcium sodium phosphosilicate had a positive impact on the reversal of postsurgical root dentin hypersensitivity [30].

Biofilm is a mode of bacterial growth in which dynamic communities of interacting sessile cells are irreversibly attached to a solid surface, as well as each other, and are embedded in a self-made matrix of extracellular polymeric substances [31]. A microbial biofilm is considered a community when it meets the following criteria: possesses the ability to self-organize (autopoiesis), resists environmental perturbations (homeostasis), is more effective in association than in isolation (synergy), and responds to environmental changes as a unit rather than as single individuals (communality) [31].

A systematic review of the applications of ozone in dentistry showed that there was some evidence that ozone (in both gaseous or aqueous phases) was a potentially effective disinfectant agent for removing the biofilms and related microorganisms such as Legionella pneumophila, Mycobacterium spp., Pseudomonas aeruginosa, and Candida spp. from dental unit water systems and was an effective bactericidal agent for removing S. mutans, methicillin-resistant Staphylococcus aureus, Candida albicans, and E. faecalis from dentures [32]. In endodontics, so far, four in vitro studies investigated the bactericidal effect of ozone as compared to 2.5 % sodium hypochlorite, the standard irrigation solution in endodontics. The results of this outcome are controversial.

While Nagayoshi et al. [33] found nearly the same antimicrobial activity against E. faecalis and S. mutans