Bur Wear Research Articles

Theoretical Notions with Practical Applications Regarding the Statistical Calculation of Dental Bur Wear

This paper presents theoretical notions with practical applications for establishing the lifetime of a dental bur (durability and reliability) based on the wear of the active part and considering a series of statistical indicators. To justify applying theoretical notions in practice, a conical–cylindrical dental bur is studied experimentally to obtain a series of data of the work process necessary for statistical calculation. The parameter taken into consideration in this paper is mass lost through the wear of the dental bur active part, based on testing. This is useful for dental bur lifetime establishment and its extension or even optimization in operation. The loss of mass of the dental bur active part is analyzed in the work process using the results and experimental data obtained and validated by statistical–mathematical numerical calculation. The numerical calculation approximates the mass lost through wear at different rotation speeds and operation times, and based on a comparison with the experimentally determined ones, the lifetime was established. The results show that the dental bur works with high yield in the first 20 h of work, after which it should be replaced with a new one. Theoretically, the studied dental bur can work over 21 h. Practically, it can work up to 18 h without major risk of failure, but the lifetime can be extended up to 20 h, at which point the failure risk can reach 10% and it is recommended to replace the bur.

Analysis of the Pulpal Blood Flow Microdynamics during Prosthetic Tooth Preparation Using Diamond Burs with Different Degrees of Wear.

Pulpal modifications taking place during prosthetic tooth preparation using worn-out burs may represent a risk for the vitality of the dental pulp. The aim of this in vivo study was to evaluate whether the wear of diamond burs has an influence on the vascular microdynamics at the level of the dental pulp, during vertical preparation for zirconia crowns. The study was performed with a split-mouth design and included 32 vital permanent monoradicular teeth (20 maxillary and 12 mandibular), from six subjects, aged between 20 and 50 years. The teeth were randomly assigned to two study groups of 16 teeth each. For prosthetic preparation, new burs were used in the first group, and burs at their 5th use were used in the second group. Four consecutive determinations of the pulpal blood flow by Laser Doppler flowmetry (LDF-laser Doppler MoorLab instrument VMS-LDF2, Moor Instruments Ltd., Axminster, UK) were taken for each tooth included in the study: before the preparation (control values), immediately, at 24 h, and at 7 days after the prosthetic preparation. A four-way ANOVA statistical analysis was applied to analyze the effect of four considered factors (bur wear degree, time of measurement, tooth number, and tooth location) on the pulpal blood flow (PBF). A significant increase in pulpal blood flow compared to the baseline was recorded immediately after preparation (p < 0.01), at 24 h (p < 0.01), and at 7 days (p < 0.05) in both groups, but more pronounced in the case of burs at the 5th use. The blood flow was significantly higher in upper jaw teeth, irrespective of the measurement time. In conclusion, the use of worn-out diamond burs produces lasting modifications in the pulpal blood flow of teeth that undergo prosthetic crown preparation. ISRCTN registry: ISRCTN49594720.

Evaluation of the Pulp Chamber Temperature during Tooth Veneer Preparation Using Burs with Different Degrees of Wear-A Preliminary In Vitro Study.

The heat produced during tooth preparation could be a source of damage for dental pulp, and many variables are involved in this process. The aim of this in vitro study was to evaluate whether the different degrees of wear of the diamond burs significantly influenced the temperature changes in the pulp chamber during tangential veneer preparation. The sample comprised 30 intact permanent monoradicular teeth, randomly assigned to three study groups of 10 teeth each, of which 5 had the pulp tissue preserved and 5 had thermoconductive paste in the pulp chamber. For prosthetic preparation, we used new burs in the first group, burs at their fifth use in the second group, and burs at their eighth use for the third group. The pulp chamber temperature was evaluated at the start, after one minute, and after three minutes of preparation, using a k-type thermocouple. The results of the three-way ANOVA and Tukey post hoc comparisons showed a highly significant effect of the time of measurement, while the pulp condition and the degree of wear of the burs had no effect. In conclusion, the different degrees of wear of conventional diamond burs do not produce statistically significant different changes in the pulp chamber temperature.

Effect of Diamond-like Carbon Coating Applied by the Physical Vapor Deposition Technique on Wear of Diamond and Tungsten Carbide Dental Burs

Background: The methods of increasing the longevity of dental burs by improving the mechanical properties of these surfaces, can increase their longevity. This study assessed the effect of diamond-like carbon (DLC) coating applied by the physical vapor deposition (PVD) technique on wear of diamond and tungsten carbide (TC) burs. Methods: In this in vitro study, 30 diamond and 30 TC burs were evaluated in four groups, including TC burs without coating (control), TC burs with a 3.5-µm DLC coating applied by the PVD technique, diamond burs without coating (control), and diamond burs with a 3.5-µm DLC coating applied by the PVD technique. The burs were weighed by a digital scale, underwent the pin-on-disc wear test, and were weighed again. The weight loss indicated the degree of wear in each group. For qualitative assessments, the surface of the burs was inspected under a stereomicroscope at×4 and×10 magnifications before wear, halfway through the test, and after the test. Finally, the data were analyzed by two-way ANOVA (α=0.05). Results: The effect of DLC coating was significant on the wear of burs (P=0.032), but the effect of the type of bur and their interaction effect on wear were not significant (P=0.151). A significant difference existed in wear among the four groups (P &lt; 0.001), and the wear of coated burs was significantly lower than that of non-coated burs (P=0.012). Stereomicroscopic assessments revealed some residual diamond particles, the impression of dislodged particles and the path of wear on the surface of diamond burs, and the path of wear on the surface of TC burs. Conclusions: Overall, the DLC coating of diamond and TC dental burs by the PVD technique could increase their wear resistance irrespective of the bur type.

A base-line study of the wear of burs used for chairside milling of ceramic crowns of different hardness: effect on internal fit and surface roughness

INTRODUCTION: Wear of milling burs may affect the internal fit and surface roughness of the milled crown. AIM: To assess the wear of diamond and tungsten carbide (TC) burs from milling ceramic materials and the effect on internal fit and surface roughness. METHODS: Thirty crowns of each of the two materials were milled from the same standard preparation. Diamond burs were used for a feldspathic ceramic and TC burs for zirconia. Before and after the 10th, 20th and 30th milling, diamond particle loss was counted and cutting blade changes of the TC burs measured. Internal fit was measured using a silicone replica technique and surface roughness by 3D laser microscope. RESULTS: An average 26% loss of diamond particles occurred after 30 crowns, resulting in a 6% decrease in internal luting space and a 21% decrease in surface roughness. Wear of the TC burs resulted in a 13% decrease in the luting space, and a 16% increase in surface roughness. CONCLUSION: The wear of milling burs reduces the luting space, and the milling parameters must be adjusted to compensate for this. Surface roughness is affected by bur type: with diamond burs it decreased, and increased with TC burs.

Effect of bur selection on machining damage mechanisms of polymer-infiltrated ceramic network material for CAD/CAM dental restorations

The surface and edge quality of polymer-infiltrated ceramic network material (PICN) in CAD/CAM milling and clinical adjusting is crucial to restorative successes. The paper reports on PICN responses to diamond and tungsten carbide machining with respect to machining forces and frictions, material removal mechanisms, surface quality and edge integrity. A force sensor together with a high-speed data acquisition system was used to measure machining forces. Scanning electron microscopy was applied to reveal bur wear and debris adhesion, and machining-induced surface and edge chipping damage. The results show two distinct removal mechanisms of PICN in which tungsten carbide machining was dominated by friction-induced ductile deformation and normal pressing of the material while diamond machining was controlled by the penetration-induced fracture. These mechanisms were reflected by significantly higher tangential (or frictional) forces and coefficients of friction in tungsten carbide machining than in diamond machining (p < 0.05). The ductile removal in tungsten carbide machining yielded more smoother areas and much less edge chipping damage in PICN. The fracture mode in diamond machining broke the ceramic and polymer networks in PICN, resulting in more fractured and pulverized areas with 6–7 times higher roughness and much more severe edge chipping damage in PICN. Thus, for better surface and edge quality, tungsten carbide burs are superior than diamond burs and recommended for surface finishing and adjusting while diamond burs are the good choice for rapid material removal in both CAD/CAM milling and clinical adjusting. However, high material removal rate-induced high tangential (or frictional) forces in tungsten carbide machining limited the bur usage for rapid oral adjusting. This paper also compared the influence of PICN microstructure on the machinability with CAD/CAM glass ceramics.

Influence of Computer-aided Design/Computer-aided Manufacturing Diamond Bur Wear on Marginal Misfit of Two Lithium Disilicate Ceramic Systems.

Marginal misfit of monolithic lithium disilicate ceramic crowns obtained from a chairside computer-aided design/computer-aided manufacturing system is affected after successive millings using a single diamond bur set. This fact can be critical for the longevity of indirect restorations.

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.

Quantifying machining outputs of pristine human teeth relevant to dental preparation procedures

Minimally-assisted tooth repair (MaTR) systems are envisioned to be capable of substituting for the skill of a dentist. If successfully developed, MaTR systems could enable lower-skilled dental technicians to provide dental care at a fraction of the overall medical cost. This paper explores a key initial step towards the development of such systems by quantifying the machining responses of pristine human teeth relevant to dental preparation procedures. The working hypothesis of the study is that such findings will enable the benchmarking of key process planning and control metrics relevant for the future development of MaTR systems. To this end, pristine human cadaver teeth were cut using a computer-controlled motion platform and dental hand-piece. Relevant cutting responses, such as cutting forces, in-process rotational speed of the dental bur, teeth morphology, and bur wear were captured. The trends in cutting forces show the potential for implementing region-specific process parameters for cutting the enamel and dentin regions of the tooth. A feed-per-tooth value of 0.1 µm at rotational speeds of 8 krpm and 50 krpm is seen to cut both the enamel and dentin regions at cutting forces lower than patient discomfort thresholds identified in literature. Cutting force signals were also successfully mapped against the CT-scan data of the tooth. This mapping indicates a clear identification of the enamel/dentin regions, and a transition region that is dependent on cutting parameters, tooth/tool geometry and tool pose. The trends in the in-process rotational speed of the dental bur indicate that stalling of the dental bur occurs at feed per tooth values greater than 0.25 µm. The evidence of stalling can be detected by both a drop in the cutting force signal and by surface morphology changes on the cut surface of the tooth. MaTR systems should be designed to avoid bur stalling regions by either operating at feed per tooth values ≤ 0.25 µm or by the use of dental spindles with higher torque capacity. Lastly, the type of fit present on the shank of the bur is seen to result in differences in the cutting force signals and wear of the cutting edges (flutes) of the dental bur. In general, a right-angle (RA) fit on the shank of the dental bur results in a larger tool runout leading to uneven loads on the flutes and increased tool wear. The friction grip (FG) fit avoids these problems and may be more suited for MaTR systems.

Effects of Polishing Bur Application Force and Reuse on Sintered Zirconia Surface Topography.

Limited information is available on how to polish and finish zirconia surfaces following computer-aided design/computer-aided manufacturing (CAD/CAM), specifically, how differing application forces and reuse of zirconia polishing systems affect zirconia topography. To determine the effect of differing, clinically relevant, polishing application forces and multiple usages of polishing burs on the surface topography of CAD/CAM zirconia. One hundred twenty 220-grit carbide finished zirconia disks were sintered according to manufacturer's directions and divided into two groups for the study of two coarse polishing bur types. Each group was divided into subgroups for polishing (15,000 rpm) at 15 seconds for 1.0 N, 4.5 N, or 11 N of force using a purpose-built fixture. Subgroups were further divided to study the effects of polishing for the first, fifth, 15th, and 30th bur use, simulating clinical procedures. Unpolished surfaces served as a control group. Surfaces were imaged with noncontact optical profilometry (OP) and atomic force microscopy (AFM) to measure average roughness values (Ra). Polishing burs were optically examined for wear. Scanning electron microscopy (SEM) was performed on burs and zirconia surfaces. One-way ANOVA with post hoc Tukey HSD (honest significant difference) tests (α=0.05) were used for statistical analyses. AFM and OP Ra values of all polished surfaces were significantly lower than those of the unpolished control. Different polishing forces and bur reuse showed no significant differences in AFM Ra. However, significant differences in OP Ra were found due to differing application forces and bur reuse between the first and subsequent uses. SEM and optical micrographs revealed notable bur wear, increasing with increasing reuse. SEM and AFM micrographs clearly showed polished, periodic zirconia surfaces. Nanoscale topography, as analyzed with kurtosis and average groove depth, was found dependent on the specific polishing bur type. These in vitro results suggest changes in OP Ra due to bur reuse and polishing application force. Within the parameters of this study, the resultant topography of zirconia polishing is force-dependent and the reuse of coarse polishing burs is possible without statistically significant differences in Ra values after initial use. Nanoscale and microscale topography were shown to depend on specific polishing bur type.

The mechanisms of wear in burs with diamond grits

The aim of the study was to observe changes in dental burs with diamond grits after cutting and elucidate the nature of bur wear.

Effects of Bur Wear during Implant Site Preparation: An in Vitro Study

Few studies have investigated the influence of drilling on bone healing. After the drilling of bone and placement of dental implants a sequence begins of cellular and molecular events which represents a combined response of wound healing. The bone healing around dental implants is a complex phenomenon and influences the proliferation and differentiation of pre-osteoblasts into osteoblasts, together with the activation of periosteal and endosteal lining cells, and initiates the production and mineralization of osteoid matrix followed by the organization of the bone-implant interface. The objective of this study is to quantify the temperature changes in cortical bone and marrow spaces during implant site preparation in bovine rib bone. A total 10 harvested bovine ribs and 6 10.5 x 3.5 new drills for implant insertion with external irrigation (Bone System, Milano, Italy) were used in this study. The implant sites were prepared with 10 mm long drills at 500 rpm under abundant external irrigation with saline solution at 37 degrees C. Each drill was used for 10, 30, 60, 90 and 120 implant site preparations; each drill was then observed under SEM for evaluation of the damage of the cutting edge after 10, 30, 60, 90 and 120 preparations. There was an higher and statistically significant increase in the temperature in the cortical bone; this increase in temperature increases with the number of the times of drill use. The drill wear seemed to play a major role in heat production and could explain the observed increased temperature of the bone.

Effects of bur abrasive particle size and abutment composition on preparation of ceramic implant abutments

Statement of problem Amid increasing use of preparable ceramic implant abutments, there is a lack of quantitative data to show which abrasive particle size of diamond bur yields the fastest reduction and provides the smoothest surface. Purpose The research aim was to determine the effects of diamond bur abrasive particle size and abutment material composition on preparation efficiency, prepared surface roughness, and surface deterioration of diamond burs. Material and methods Fifteen alumina (Cera Base) and 15 zirconia (ZiReal) implant abutments were each machined using a high-speed hand piece with a diamond bur having 1 of 3 abrasive particle sizes (150, 100, or 30 μm) (n=5). Control abutments (n=5) were analyzed without machining. Abutments were weighed before starting and between machining cycles. Three profilometry measurements (root mean square surface roughness) were made for each abutment. Scanning electron micrographs were made of each bur. Lost abrasive particles were then counted on each micrograph through a randomly placed template. Two-way analysis of variance (α=0.05) was used to test for significant effects. Results Bur abrasive particle size and ceramic type had a significant interactive effect on the amount of material removed ( P<.001). Super coarse (150 μm) burs yielded the roughest surfaces for each abutment material ( P<.001), and prepared alumina surfaces were rougher than zirconia surfaces ( P<.001). Super coarse burs showed the highest proportion of lost particles ( P<.001). Abutment composition did not significantly affect bur wear. Conclusion Super coarse burs yielded the most efficient material removal for alumina abutments. All abrasive particle sizes removed a similar amount of material from zirconia abutments. Fine-grained alumina abutments experienced greater material removal and rougher prepared surfaces compared with zirconia abutments. Material was removed by an intergranular fracture mechanism for alumina abutments, in contrast to transgranular fracture for zirconia abutments.

Cutting effectiveness and wear of carbide burs on eight machinable ceramics and bovine dentin

As a first approach in evaluating the feasibility of industrial machinable ceramics in dentistry, we performed weight-load-cutting tests on eight machinable ceramics and bovine dentin, using #1557 carbide burs driven by an air-turbine handpiece. While the transverse load applied to the bur was cyclically varied between 20 and 80 g, we measured the cutting speed ( i.e., the steady-state handpiece speed during cutting) and the cutting volume. The greater the applied load, the more the cutting speed decreased and the cutting volume increased. The degree of this trend, however, differed among the workpieces. When dentin and mica-based glass ceramics were being cut, the cutting speed was moderately reduced, the cutting effectiveness of the bur remained high, and the wear of the bur was small. When other ceramics—such as AIN-based, Si 3N 4-based, and CaO·SiO 2-based ceramics—were being cut, however, the cutting speed was less diminished, and the cutting efficiency of the bur was smaller and decreased rapidly, along with extensive wear of the bur. We speculate that mica-based glass ceramics could be used as the substitute for dentin in the pre-clinical cutting exercise, and that another potential use of machinable ceramics examined might be in the production of future machined dental prostheses.