Comparative Study of the Cutting Efficiency and Working Life of Carbide Burs

In Vitro Study on the Influence of the Buccal Surface Convexity of the Tooth upon Enamel Loss after Bracket Removal

Polishing after the removal of brackets is the final step in orthodontic treatment. It is simple to perform, though some studies have reported that polishing causes damage to the enamel surface. An in vitro study was made of the influence of the buccal surface convexity of the tooth upon possible enamel loss when the remaining resin and adhesive are removed after bracket decementing using two different polishing modes: a tungsten carbide bur at low and high speeds. The convexity of the buccal surface was quantified in 30 incisors and 30 premolars. A stereoscopic microscope was used to obtain photographs of the profile of the crown, and Image J software was used to calculate convexity by dividing the length of a line from the cementoenamel junction to the incisal margin by another line from the mentioned junction to the maximum convexity of the buccal surface. Brackets were cemented on all the teeth and were decemented 24 h later. In both groups, the residual composite was removed with a tungsten carbide bur at a low speed in one-half of the teeth and at a high speed in the other half. The buccal surface of each tooth was then photographed again, and the convexity was calculated and compared against the baseline value. The difference between the two values were taken to represent the enamel loss. The convexity of the premolars was significantly greater than that of the incisors, but this did not result in greater enamel loss when the same polishing mode was used. However, the tungsten carbide bur at a high speed proved more aggressive, causing significantly greater enamel loss than when used at a low speed.

In vitro evaluation of enamel surface roughness and morphology after orthodontic debonding: Traditional cleanup systems versus polymer bur

INTRODUCTION

The primary aim of this randomized in vitro study was to compare the effectiveness of carbide, fibreglass and polymer burs on resinous remnant removal after bracket debonding, by the evaluation of enamel surface roughness and morphology. The secondary objective was to compare the time dispended on the procedures.

METHODS

The buccal surfaces of 28 bovine incisors were analysed by a profilometer to initial roughness measurement (Ra-T1). Brackets were bonded with a light-cured resin and debonded with a debonding plier. The samples were randomly divided into four groups, according to the bur used (n=7): A-Tungsten carbide; B-Fibreglass; C-Polymer; D-Polymer with 75% ethanol pre-treatment. The second roughness measurements were made after resin removal (Ra-T2). Time for removal procedures was also recorded. The third measurements were made after polishing (Ra-T3). Scanning Electronic Microscopy was performed in two samples of each group: after resin removal and after polishing. Results of roughness and time measurements were statically analysed by analysis of variance with post-hoc Bonferroni.

RESULTS

After polishing, tungsten carbide (P=0.1555) and fibreglass burs provided final surface roughness statistically similar to the baseline condition (P=1.0000). Yet, polymer burs, associated (P<0.0001) or not to alcohol (P<0.0001), provided surface roughness significantly higher when compared to baseline values. Polymer burs were more time-consuming on resinous remnant removal than tungsten carbide and fibreglass burs (P<0.05).

CONCLUSION

Polymer burs were less effective and more time-consuming to remove the remaining resin than tungsten carbide and fibreglass burs. The polishing step created smoother surfaces regardless of the burs used for resin removal.

Machinability of high-speed enamel cutting with carbide bur

The cutting of tooth enamel using a high-speed air-turbine handpiece and carbide bur is a key procedure in oral surgeries, such as the minimally invasive extraction. However, presently little is known about the cutting mechanics and material removal mechanism related to tooth enamel machinability. In this study, the machinability of high-speed enamel cutting with carbide bur is studied by a computer-aided numerical control system. The dynamic cutting forces of enamel of the occlusal, buccal/lingual, and proximal surfaces were measured by the force measuring system. The force ratio, cutting torque, rotating speed, specific cutting energy, and bur wear were analyzed. The microstructure of enamel and carbide burs was observed by the scanning electron microscope, and the relationship between enamel microstructures and machinability was further analyzed. The results show that during the high-speed enamel cutting with carbide bur, the chip thickness is on the nano-scale, and the plastic deformation of the machined surface is obvious. With increased material removal rate, the cutting force, torque, specific cutting energy, and bur wear increases accordingly, whereas the rotating speed decelerates (p < 0.05). The different angles between the cutting direction and the axial direction of the enamel rods give rise to the large differences in the cutting mechanics and mechanism of the proximal, buccal/lingual, and occlusal surfaces of the teeth. When the cutting direction is parallel, vertical, and oblique 45° to the axial direction of the enamel rods, the force required for material fracture and crack propagation increases, and the cutting force increases as a consequence. Parallel and oblique 45° cutting are the main modes of tooth segmentation in the minimally invasive extraction. In comparison with the parallel cutting mode, the cutting force, torque, and cutting ratio of the oblique 45° cutting mode can be significantly increased, and the tool wear is obviously accelerated. This is the lowest priority in segmentation surgery, hence the problems of overload and temperature rise need to be considered. The cutting mechanics and cutting mechanism obtained in this study will provide scientific process guidance for dental cutting operations with the air-turbine handpiece driving bur.

Assessing the cutting efficiency of different burs on zirconia substrate

Cutting dental zirconia for endodontic access preparation is difficult. Therefore, this study aimed to determine cutting efficiency of various burs when cutting this material. An air turbine handpiece was used in a customised test rig to cut sintered zirconia specimens, using a conventional blue band diamond, two different zirconia-cutting diamond and a zirconia-cutting tungsten carbide bur. Position and speed of the bur were continuously determined using wireless data acquisition over two successive five-minute runs. Differences in cutting efficiency were statistically analysed. Burs were examined using light and scanning electron microscopy (SEM). All diamond burs cut zirconia more efficiently than the tungsten carbide bur. Overall, all burs showed decreasing cutting efficiency over time. SEM images showed discernible wear and damage to the cutting portion of each bur head. It is concluded that zirconia-cutting burs are advantageous regarding durability, and carbide burs are rather ineffective against carbide substrate.