# A Novel Method to Measure the Powder Consumption of Dental Air-Polishing Devices
## 3 Results  
The complete powder flowrate over the entire powder chamber was easily obtained for all of the test devices (Figure 3). The Table-top devices had longer autonomy due to their larger powder chambers and more regular flow rates than the handy devices. Table-top E1 had the most regular powder consumption, offering the slowest decreasing slope, and a level allowing the longest autonomy, thanks to its smaller mean powder consumption and larger powder reservoir. All of the Handies had a powder consumption that was strongly dependent on the usage time. Among the Handies, only Handy E1 presented a longer autonomy with a slower decreasing slope. The overall statistical results in terms of the autonomy and mean powder consumption of the ten repetitions are presented in Table 2.  
For each category, the E1 devices had the longest autonomy. Table-top E1 had the lowest powder consumption that was statistically different compared to the other devices. Both Handy E1 and M3 had statistically similar mean powder consumptions. The applied method allowed for a closer analysis of the powder consumption curve. It was possible to observe the details of the powder consumption during a single pedal press. For the Table-tops, this measurement was performed after 7 min of work, in order to ensure a stable device performance (Figure 4). Figure 2: Table-top mean powder consumption (bold line) calculated from 10 repetitions (thin lines). (**a**): Table-top E1, (**b**): Table-top N2; (**c**): Table-top M3. For the Handy devices, the same zoom level for one pedal press was chosen after the sixth pedal press of the sixth repetition, in order to ensure stable device performance (Figure 5). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Device**} & \multicolumn{2}{c}{**Mean Powder**} & \multicolumn{2}{c}{**Mean**} \\  & **Consumption** & \(p\) **Values vs. A1** & **Autonomy** & \(p\) **Values vs. A1** \\  & **(g/min)** & & **(min)** & \\ \hline Table-top E1 & 1.0 \(\pm\) 0.2 & - & 33 \(\pm\) 5 & \\ Table-top N2 & 1.6 \(\pm\) 0.7 & \textless{}0.001 & 18 \(\pm\) 2 & \textless{}0.001 \\ Table-top M3 & 2.9 \(\pm\) 1.7 & \textless{}0.001 & 9 \(\pm\) 1 & \textless{}0.001 \\ Handy E1 & 1.0 \(\pm\) 0.5 & - & 7.5 \(\pm\) 0.5 & \\ Handy N2 & 2.7 \(\pm\) 1.9 & 0.002 & 2.7 \(\pm\) 0.3 & \textless{}0.001 \\ Handy M3 & 1.5 \(\pm\) 0.7 & 0.06 & 2.3 \(\pm\) 0.4 & \textless{}0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Powder consumption and autonomy: the statistical differences are compared between Table-Top E1 for Table-tops and Handy E1 for Handies. Figure 4: Table-top powder consumption during one pedal press of 25 s, and an enlarged view of the first 5 s.  
Figure 3: Powder consumption until complete powder chamber emptying. Only the effective device working time is shown. Notably, because the Handy devices did not have regular powder flow rates, the mean value of one pedal press (Figure 5) could be very different from the overall mean (Table 2). Therefore, one defined pedal press was chosen arbitrarily. The most important function of this pedal press was to understand more precisely the working behavior within the handy powder chamber. Different overall working phases were observed:  
1. Between 0 and 0.5 s, there was a powder burst. The intensity of this burst depended on the device's construction. For example, Table-top M3 had a very high powder burst (>8 g/min) at its start-up, whereas Table-top E1 presented only a very small burst (<2 g/min). This burst has two potential drawbacks: first, it can lead to powder overconsumption if the powder consumption is too high; second, this overconsumption can create a powder residue on the surface, which can reduce the cleaning action over the following seconds of treatment. It was estimated that this burst comes from the residual powder inside the device's tubing. 2. Between 0.5 and 5 s, the powder chamber started working, and the powder consumption reached a steady state.