## 4 Discussion
Interestingly, the particle fraction between PM\({}_{0.3-0.5}\) correlated with tooth drilling procedures in a real dental operating room, with no contribution of the particulate matter over 1 \(\upmu\)m [17]. This is consistent with our findings, in which aerosol particles were poorly or not detected over 1 \(\upmu\)m during artificial teeth drilling using standard suction in both vestibular and palatal sides. Nevertheless, the relative humidity was reported 40% [17], in contrast with our settings (average relative humidity: 65%). With a higher relative humidity (70%), another study reported similar findings regarding the increase of ultrafine particles during teeth drilling and grinding [33]. From the biomaterial point of view, we suggest that artificial teeth are a useful tool to reproduce dental tissues. Similarly, an experimental study that drilled and grinded natural teeth detected the highest proportion of dental aerosol particles in the PM\({}_{1}\) fraction, with no significant effect of the vacuum system on the ultrafine particles concentration [16]. The opposite effect was found in our study using high-volume suction, with a significant reduction of the volume fraction of the ultrafine particles in the palatal side (the same side where the tip of the volume evacuator was located). In contrast, this significant reduction in the RDI + HVE group was not observed in the vestibular side (Table 1). This can be explained by the fact that the tip of the high-volume evacuator was not able to suction properly these ultrafine particles, in part because of its location (palatal side) and due to the physical barrier of the tooth. Currently RDI is highly recommended, even during restorative procedures to reduce infection risk [3; 4]. When measured at one and two meters from the patient's mouth, the number of colony-forming units (CFUs) is reduced in two trials during restorative procedures with high-speed handpiece and RDI in children [34; 35]. In contrast, when CFUs were measured in several points of the clinician's head, these were significantly increased when using rubber dam isolation versus control during restorative procedures in adults [14]. Aerosol particle sizes were not reported in these studies. In our study, the DV\({}_{10}\), DV\({}_{50}\), DV\({}_{90}\) and the d\({}_{3,2}\) of RDI group were significantly increased when compared with no rubber dam isolation (SS group) in both vestibular side and palatal side. This result may be explained by the fact that the study that took CFU measurements closer to the mouth of the patient [14] found an increase in this parameter, since larger particles may reach closer surfaces (e.g., clinician's head) but failed to reach longer distances (i.e., one to two meters from the patient's mouth). Because of the lack of previous published studies on the methods implemented here, we were not able to perform a sample size calculation. However, the first results reported here are the basis for the experimental design, including statistical analysis and sample size calculation, of further and larger studies. Therefore, a triplicate experiment per condition was implemented in order to determine the feasibility of the experimental settings when analysing dental aerosol particles using laser diffraction. Taken together, our preliminary results support the effectiveness of the rubber dam isolation combined with high-volume suction to reduce the dental aerosol particles, although not always significantly and not for all particle sizes. Interestingly, the use of rubber dam isolation (with no HVE) reduces the ultrafine particles but increase the DV\({}_{10\text{-}50\text{-}90}\) and the d\({}_{3,2}\) of total aerosol particles, which may increase their precipitation rate but also the surface of contamination in areas close to the patient's mouth. Further studies regarding the potential of infection of dental aerosol particles in the submicron range (under PM\({}_{10}\)) are necessary. RDI is not possible for some procedures like dental surgery or dental hygiene.