Effect of wear in rotating diamond instruments on the quality of prepared tooth surface with the use of chemically different conditioners: A nonrandomized experimental controlled study

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Abstract
Background . Modern dental restoration relies on achieving reliable adhesion between dental fillings and hard tissues, which is largely determined by the quality of tooth preparation. Objective . To analyze the effect that the condition of working parts in Diatech and MANI diamond burs, as well as chemically different conditioners, can have on the quality of tooth surface preparation. Methods . A nonrandomized experimental controlled study was conducted using 64 intact molars that had been previously extracted for medical reasons; artificial Class I cavities of the same size were drilled in these teeth (as per G.V. Black’s classification). An air-turbine handpiece, Diatech diamond burs (with a grit size of 64–126 µ), and MANI burs (with a grit size of 106–126 µ) were used to prepare the teeth. These teeth were divided into four groups of 16 teeth each depending on the use of new or previously used diamond burs, as well as eight subgroups of eight teeth each; in half of them, the prepared surfaces were conditioned with Travex37 (Omega Dent, Russia) containing 37% orthophosphoric acid; the other half, with Multi Etchant gel containing an adhesive phosphate monomer (M-TEG-P) (Yamakin, Japan). The enamel and dentin were conditioned for 30 and 15 seconds, respectively, followed by rinsing with a jet of water and air for 60 seconds. The used burs and conditioned tooth surfaces were examined using a scanning electron microscope. The quality of conditioned tooth surfaces was comparatively analyzed through the study of electron diffraction patterns of five dentin areas obtained for each tooth; each examined surface was rated on a scale from 0 to 3. The obtained data were statistically processed using Statistica 12.0 (StatSoft, USA) and Microsoft Office Excel 2017 (Microsoft Corporation, USA). Differences were considered statistically significant at p < 0.05. Results . A comparative analysis of the electron diffraction patterns of tooth surfaces from four experimental groups revealed a relationship between the quality of a diamond bur (the presence of visually and microscopically detectable areas on the bur surface that lack the diamond abrasive layer) and the structural characteristics of a tooth surface after preparation and conditioning. The use of both new (in 62.5% of cases) and previously used (in 100% of cases) MANI burs to prepare the surfaces led to the detection of cracks in the dental hard tissues. According to the analysis of electron diffraction patterns with the use of to the developed scale, Multi Etchant gel was found to ensure better preparation of tooth surfaces for the next stage than 37.0% orthophosphoric acid as it provides a cleaner surface even in the case lower-quality diamond burs. For example, areas of dentin surface prepared with the Mani burs and conditioned with Multi Etchant scored 1 point in 72.5% of cases, while those conditioned with Travex were given a score of 1 in only 37.5% of cases. Conclusion . A microscopic examination of the previously used Diatech burs (ten cycles of use), revealed insignificant wear of the diamond coating, which manifested itself in a partial loss of the abrasive layer on the working surface. Therefore, the effect of bur wear on the quality of tooth surface preparation is insignificant, which contributes to the formation of a smooth surface during tooth preparation and a reduced frequency of crack formation.

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