A comparative study of the cutting efficiency of diamond burs with different grit sizes on zirconia restorations

Abstract

Background: The use of zirconia-based restorations in modern dentistry has increased due to its excellent mechanical properties, superior biocompatibility, and satisfactory aesthetics. This has led to a demand for more efficient machinability thereof. However, little attention has been given to the difficulty experienced by clinicians when cutting zirconia restorations. The cutting of zirconia in dentistry is necessary for the purpose of occlusal reduction, to gain root canal access, or for the removal of restorations. Zirconia used in clinical dentistry is much harder than some other dental prosthetic materials, making it more arduous to cut. It also has an increased susceptibility to fracturing. To date, there is insufficient evidence on which grit size and type of bur is best for the purpose of cutting zirconia. Aim: The aim of the present study was to identify the most efficient diamond bur grit size for cutting zirconia. Efficiency was measured by comparing the cutting depth of each bur into zirconia, analysing zirconia specimens for any surface damage after cutting and measuring bur deterioration. The most efficient bur achieved maximum productivity (cutting depth) with minimum wasted time and expense (bur deterioration and substrate fractures). Hypothesis: Diamond burs with finer grit sizes are more efficient in cutting zirconia than coarser burs due to increased surface area to substrate ratio and decreased damage to the substrate. Method: Zirconia specimens of the same thickness were used as test samples, and cut with burs with different grit sizes, using an electric handpiece with the same amount of force (1.7N) and speed (40 000rpm) for a constant amount of time (1min.) and a constant water flow rate of 25mL/min to produce comparative data. Results: The results obtained revealed the following: 1) The greatest cutting depth was achieved with the fine (F) bur. 2) The most damage to zirconia was done by the coarse (C) and super coarse (SC) burs, with no damage to the super fine (SF), fine (F), and medium (M) burs. 3) The least amount of bur deterioration was found on the super fine (SF) burs, with the most amount of deterioration on the super coarse (SC) burs. Conclusion: Within the limitations of the present study, it can be concluded that the most efficient diamond bur was the fine (F) bur with grit sizes between 40-50 µm. The fine (F) bur group achieved the greatest cutting depth with no detectable macroscopic damage to the zirconia substrate and minimal bur deterioration. The empirical findings in the present study provide a new insight into efficient cutting of zirconia and will aid clinicians in selecting the correct armamentarium when working with zirconia intra-orally.