# A Novel Method to Measure the Powder Consumption of Dental Air-Polishing Devices
## 1 Introduction  
Bacteria play a major role in the development and progression of dental diseases, especially caries, gingivitis, and periodontitis [1]. Most dental prophylaxes and therapeutic procedures, therefore, aim to--mostly nonspecifically--remove bacteria from the non-shedding surfaces of the mouth by mechanical or chemical means. For professional care, the projection of powders onto tooth surfaces with air-polishing devices has been shown to be very efficient [2]. In the past, enamel was predominantly cleaned with sodium bicarbonate, which was effective but also quite aggressive in terms of the intrinsic abrasivity of the material. In response, new small-sized resorbable powders have found widespread clinical use, and have expanded the scope of air polishing from supra-gingival biofilm and stain removal to subgingival maintenance, as well as active therapy, because these surfaces require a gentler treatment based on selective removal. This approach has been proven to be very effective while being gentle to the treated substrates [2; 3; 4]. The enlarged range of applications increases the performance expectations for the device. Indeed, more different types of tissues can now be treated, including exposed dentin and cementum, as well as prosthetic materials like composite resin, ceramics, and titanium. Among thesematerials, dentin is considered to be very critical because it has a low Vickers hardness (60 HV) [5]. In the context of increasing life expectancy, roots become increasingly exposed in the oral cavity [6]. Since exposed cervical roots may be sensitive to caries, erosion, and overall biofilm accumulation and related inflammatory reactions, they represent a delicate predilection site of specific interest. Although there is a need for meticulous cleaning, special care must be taken not to cause iatrogenic damage, including the unnecessary removal of cementum or the opening of tubules [7], as dentinal hypersensitivity may additionally negatively affect this vulnerable area [8]. With respect to these factors, air-polishing devices for the application of new small-sized powders are currently considered the most effective and least abrasive or invasive cleaning method for exposed dentine and other surfaces and materials [9]. However, in order to more selectively clean contaminated areas, biofilm disclosing agents have also been recommended [10]. These allow for a so-called 'guided treatment approach', which has been formalized in a global method called Guided Biofilm Therapy (GBT) [11]. Nonetheless, the device itself plays a key role in this minimally-invasive approach because the mechanical interactions during application include many important aspects, such as the right choice of powder and its delivery quantity. For example, the more powder that is delivered in a given time interval, the more efficient the cleaning becomes. However, more abrasion can also occur on the surface, not only based on the amount but also on the powder's characteristics [12]. Therefore, mastering powder consumption has come into focus for material science, and is necessary to achieve the best and least invasive prophylactic treatment. The development of a better understanding of the exact powder consumption for a given treatment is, therefore, important for any scientific in vitro or in vivo research using air-polishing systems. Ultimately, it is the effectively-used powder amount that determines the amount of abraded material and surface effects [12]. The ability to determine a device's powder consumption is also important for the correct interpretation of clinical outcomes. Measuring powder consumption is a significant challenge, but it has not been considered in many studies yet, despite the important and early work of [PERSON] et al. [13], who characterized different air-polishing systems in terms of their powder consumption. The sampling rate in this study was two minutes, which provided information about general behavior, but no insights into shorter treatment cycles were provided.