## 4 Conclusions  
* The phenomenon of friction-wear is complex, due to the multitude and interaction in the operation of all factors, both external (load, speed, environment, etc.) and internal (the material of the friction pair with the respective structure and hardness, roughness, temperature, etc.). It is a perfectly objective situation, which is accentuated when  
Figure 14: Probability density plot for the Gaussian (normal) distribution law.  
moving from laboratory research on models to operational real conditions, explaining to some extent the difficulties and the current state of wear calculation.
* The wear statistical calculation starts from the real situation reflected by experimental data as the basis for the analytical calculation relations (regression relations), given the interaction of all influencing factors. It is justified, even from the statistical nature of the friction-wear process.
* It is necessary to find a (statistical-mathematical) model for the studied phenomenon/ process (wear of the dental bur active part) in view of the quantitative extract of the desired information. At the same time, it must not be too complicated for analytical handling but must incorporate its essential characteristics as realistically as possible.
* The solution to this problem is the concept of a random variable (here mass loss of the active part of the dental bur)--a quantity determined by the event resulting from the performance of an experiment (establishing the operating time without failures, in this case). To compare random variables, the distribution function, \(F(x)\), is used.
* When the values come from a normal distribution, some of the main statistical parameters, average, dispersion, mean square deviation, etc., are determined and checked. If these checks do not lead to favorable conclusions regarding the normality of the data distribution, the measurement data from the statistical series will be checked more thoroughly.
* The results showed that the investigated dental burs may operate without failure major risk until 18 h, very close to those determined to be experimental, which validates the correlation between analytical calculation and the experimental test results. Practically, based on the results presented in this paper, it was found that dental burs during the milling operation can easily become decommissioned, resulting in mass loss, and in the first 18 h of work, they operate with high efficiency.
* Over this number of operating hours, to ensure high standards of material processing, the dental burs should be replaced with new ones. Additionally, the methodology applied in this paper showed that it is possible to increase the lifetime by approximately 10% and it allows for investigation of the possibilities of improving or optimizing the working regimes of dental burs.
* The researched parameter of the analyzed dental burs was the mass lost through wear, determined by weighing, taking different random values, between two limits, with each value repeating itself several times (having its frequency), and their scattering can be represented through a distribution law.
* Most experimental data of the mass lost by the wear of the dental bur active part are very close to the Gaussian normal distribution, and the probability density (frequency function) is a normal distribution function, so it is Gaussian.
* In perspective, it is envisaged to expand the analysis of wear behavior by statistical calculation, based on experimental data, and to other types of dental burs, also considering other parameters.  
This research received no external funding.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The author declares no conflicts of interest.