Dental Cutting with Diamond Burs: Heavy-Handed or Light-Touch?

PURPOSE: The cutting efficiency of diamond dental burs using different handpiece loads was evaluated against simulated enamel, a machinable glass ceramic (Macor). MATERIALS AND METHODS: An ultra-high-speed dental handpiece was mounted in a frictionless bearing so that the pressure applied at the contact interface between the dental bur and the cutting substrate was controlled. One type of coarse- and two types of medium-grit diamond burs were studied. Handpiece loads of 44, 91.5, and 183 g were applied at the bur/Macor interface, and cutting efficiency was determined as the amount of Macor removed in ten 30-second-duration cuts that were 4 mm in length. The data were analyzed by one-way ANOVA and a post-hoc Scheffé test at an a priori alpha = 0.05. RESULTS: Cutting efficiency depended on both the diamond grit of the bur and the load applied to the handpiece. CONCLUSIONS: The pressure used by most dentists, about 100 g at the bur tip, appears to be optimal for medium-grit burs. If the pressure applied to the handpiece is markedly increased, there was no increase in cutting efficiency for medium-grit burs. In contrast, an increased handpiece pressure raises the cutting efficiency of coarse-grit burs but the effect of this enhanced rate of cutting on the pulpal tissues is uncertain. Cutting efficiency also appeared to be dependent on debris accumulation between the diamond chips.     

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, Si3N4-based, and CaO.SiO2-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.     

Effects of the diamond grit sizes of the commercial dental diamond points on the weight-load cutting of bovine enamel and glass-ceramic Typodont teeth

To evaluate the effect of the diamond grit size of commercial dental diamond points on the dental cutting, we conducted weight-load cutting tests on bovine enamel and glass-ceramic typodont teeth using 3 different diamond grit sizes and air-bearing and ball-bearing air-turbine driven handpieces. With the transverse load applied on the diamond point varied between 20 and 80 g, we measured rotational cutting speed and cutting volume. Generally, increases in applied load caused decreases in rotational cutting speed and increases in cutting volume. The intensity of this trend, however, differed between grit sizes. Regular grit diamond points most strongly showed this tendency, while super-fine grit diamond points were least affected. Fine grit diamond points behaved in a manner similar to regular grit points.     

Dental high-speed cutting of four cast alloys

The purpose of this study was to evaluate dental high-speed cutting behaviour of four cast alloys, namely Ag-Pd-Cu-Au alloy, Ag-Zn-In-Sn alloy, Ni-Cr alloy and Ti. Weight-load cutting tests were conducted on four cast alloys, using two rotary cutting instruments, namely a diamond point and a carbide bur, both driven by an air-turbine handpiece. While the constant transverse load of 80 g was applied on the workpiece for 5s, the handpiece speed was measured during cutting as well as the volume of workpiece removal which took place. The cutting tests were repeated 10 times. We found that the cutting volumes of soft Ag-Pd-Cu-Au alloy and Ag-Zn-In-Sn alloy were considerably larger than those of hard Ni-Cr alloy and Ti. It was also clarified that the cutting effectiveness of the carbide bur was generally superior to that of the diamond point. With continuing use, however, the cutting capability of the carbide bur tended to decline while that of the diamond point remained quasi-constant.     

High and low torque handpieces: cutting dynamics, enamel cracking and tooth temperature

OBJECTIVE: The aim of these experiments was to compare the cutting dynamics of high-speed high-torque (speed-increasing) and high-speed low-torque (air-turbine) handpieces and evaluate the effect of handpiece torque and bur type on sub-surface enamel cracking. Temperature changes were also recorded in teeth during cavity preparation with high and low torque handpieces with diamond and tungsten carbide (TC) burs. The null hypothesis of this study was that high torque handpieces cause more damage to tooth structure during cutting and lead to a rise in temperature within the pulp-chamber. MATERIALS AND METHODS: Images of the dynamic interactions between burs and enamel were recorded at video rate using a confocal microscope. Central incisors were mounted on a specially made servomotor driven stage for cutting with a type 57 TC bur. The two handpiece types were used with simultaneous recording of cutting load and rate. Sub-surface enamel cracking caused by the use of diamond and TC burs with high and low torque was also examined. Lower third molars were sectioned horizontally to remove the cusp tips and then the two remaining crowns cemented together with cyanoacrylate adhesive, by their flat surfaces. Axial surfaces of the crowns were then prepared with the burs and handpieces. The teeth were then separated and the original sectioned surface examined for any cracks using a confocal microscope. Heat generation was measured using thermocouples placed into the pulp chambers of extracted premolars, with diamond and TC burs/high-low torque handpiece variables, when cutting occlusal and cervical cavities. RESULTS: When lightly loaded the two handpiece types performed similarly. However, marked differences in cutting mechanisms were noted when increased forces were applied to the handpieces with, generally, an increase in cutting rate. The air turbine could not cope with steady heavy loads, tending to stall. 'Rippling' was seen in the interface as this stall developed, coinciding with the bur 'clearing' itself. No differences were noted between different handpieces and burs, in terms of sub-surface enamel cracking. Similarly, no differences were recorded for temperature rise during cavity preparation. CONCLUSIONS: Differences in cutting mechanisms were seen between handpieces with high and low torque, especially when the loads and cutting rates were increased. The speed increasing handpiece was better able to cope with increased loading. Nevertheless, there was no evidence of increased tooth cracking or heating with this type handpiece, indicating that these do not have any deleterious effects on the tooth.     

Irrigating solution and pressure effects on tooth sectioning with surgical burs.

OBJECTIVE: The purpose of this study was to determine the influence of the applied load on the handpiece, type of cooling agent, and type of tooth on surgical tooth dissection with a tapered crosscut fissure bur. STUDY DESIGN: Cutting studies were performed at handpiece loadings of 295 and 590 g through use of an oral surgery straight handpiece, tapered crosscut fissure burs, and an established cutting regimen. Extracted molars were dissected under irrigation with water, 0.9% saline solution, and lactated Ringer's solution at constant flow rates of 15 and 25 mL/min. Cutting efficiencies were analyzed by 1-way analysis of variance and Scheffé tests. RESULTS: No difference in cutting efficiency was found at low loads under irrigation with water or saline solution, but under irrigation with lactated Ringer's solution, a higher cutting efficiency was found (P < .05). There was no difference in cutting efficiency for lactated Ringer's solution and saline solution at high loads, but both cut more efficiently than water (P < .01). CONCLUSIONS: Saline solution is a useful coolant/irrigant for the dissection of teeth under most conditions, but lactated Ringer's solution might be beneficial with respect to cutting efficiency when lower handpiece loads are required.     

Studies on dental high-speed cutting

summary The primary author, an experienced dentist, cut bovine enamel and dentine horizontally and vertically with diamond points driven by an air-turbine, while the rotational cutting speeds and applied loads were simultaneously monitored. Three cutting techniques employed here were successive cutting with moderate force (S-m); intermittent cutting with moderate force (I-m); and intermittent cutting with a smaller force (I-s). It was found that the cut contact time of S-m, I-m, and I-s cuts were about 10s, 0.4s and 0.25s, respectively. The maximum applied load during cutting varied, depending upon the cutting direction and the cutting technique. Vertical S-m cut of enamel resulted in the largest applied load of around 105g, while horizontal I-s cut of dentine brought about the minimum (approximately 35g). Cutting volumes of dentine tended to exceed those of enamel. It was confirmed that the I-m cut produced larger cutting effectiveness of diamond points on both enamel and dentine compared with the S-m cut.     

Comparing cutting efficiencies of diamond burs using a high-speed electric handpiece

This study sought to compare the cutting efficiency of different diamond burs on initial use as well as during repeated use, alternating with sterilization. Long, round-end, tapered diamond burs with similar diameter, profile, and diamond coarseness (125-150 microm grit) were used. A high-torque, high-speed electric handpiece (set at 200,000 rpm) was utilized with a coolant flow rate of 25 mL/min. Burs were tested under a constant load of 170 g while cuts were made on a machinable ceramic substrate block. Each bur was subjected to five consecutive cuts for 30 seconds of continuous operation and the cutting depths were measured. All burs performed similarly on the first cut. Cutting efficiencies for three of the bur groups decreased significantly after the first cycle; however, by the fifth cycle, all bur groups performed similarly without any significant differences (p > 0.05). A scanning electron microscope revealed significant crystal loss after each use.     

Handpiece coolant flow rates and dental cutting

High-speed handpieces incorporate water coolant sprays to remove cutting debris and minimize thermal insult to the pulp. Little data exists on optimal coolant flow rates during clinical procedures. This study compared the effect of different coolant flow rates on diamond stone cutting efficiency. Cutting studies were performed on Macor machinable ceramic using a previously developed test regimen--a KaVo high-speed handpiece at a cutting force of 91.5 g (0.9 N). Cutting was performed with round end tapered medium grit diamond stones under cooling water flow rates of 15, 20, 25, 30 and 44 ml/min, with cutting rates determined as the time to transect the 13 mm square cross-section of the Macor bar. Each bur was used for five cuts, with six burs used for each flow rate, for a total of 150 measurements. The data were analyzed by one-way ANOVA with a post hoc Scheffé test. The cutting studies indicated that diamond stone cutting rates increased with higher coolant flow rates over the range of 15-44 ml/min. The data suggest that higher coolant flow rates promote cutting efficiency.     

Cutting efficiency of diamond burs operated with electric high‐speed dental handpiece on zirconia

Zirconia‐based dental restorations are becoming used more commonly. However, limited attention has been given to the difficulties experienced, concerning cutting, in removing the restorations when needed. The aim of the present study was to compare the cutting efficiency of diamond burs, operated using an electric high‐speed dental handpiece, on zirconia (Zir) with those on lithium disilicate glass–ceramic (LD) and leucite glass–ceramic (L). In addition, evaluation of the cutting efficiency of diamond burs on Zir of different thicknesses was performed. Specimens of Zir were prepared with thicknesses of 0.5, 1.0, 2.0, and 4.0 mm, and specimens of LD and L were prepared with a thickness of 1.0 mm. Cutting tests were performed using diamond burs with super coarse (SC) and coarse (C) grains. The handpiece was operated at 150,000 rpm with a cutting force of 0.9 N. The results demonstrated that cutting of Zir took about 1.5‐ and 7‐fold longer than cutting of LD and L, respectively. The SC grains showed significantly higher cutting efficiency on Zir than the C grains. However, when the thickness of Zir increased, the cutting depth was significantly decreased. As it is suggested that cutting of zirconia is time consuming, this should be taken into consideration in advance when working with zirconia restorations.     

Cutting efficiency of three diamond bur grit sizes

BACKGROUND: Tooth preparation requires safe, efficient and rapid cutting, and diamond burs routinely are used for extracoronal preparation and gross tooth reduction. Coarser-grit diamond burs often are used for gross tooth reduction, with tooth surface finishes being sacrificed for the presumed greater cutting rates, or CRs, of the coarser diamond burs. The authors compared the CRs of medium-, coarse- and super-coarse-grit diamond burs. METHODS: The authors used a self-contained dental treatment system with digitally controlled handpiece speed, torque and water flow rate to cut a machinable glass ceramic cutting substrate with medium-, coarse- and super-coarse-grit diamond burs from the same manufacturer under a load of 147.5 grams (0.9 kilonewton at the bur tip) and a coolant flow rate of 22 milliliters per minute. They made three cuts through 13-millimeter bars of the cutting substrate with six diamond burs of each grit size. They determined CRs as the transection time per millimeter and analyzed CR data by one-way analysis of variance and post hoc Scheffé tests. RESULTS: The authors found no statistically significant difference in CR (P > .05) between the three diamond bur grit sizes for the first (13 mm) cuts. When they compared the three cuts (39 mm total cut length), they found no difference (P > .05) between CRs for coarse- and super-coarse-grit diamond burs, but they did find that the super-coarse-grit diamond burs cut faster than the medium-grit diamond burs (P < .01). CONCLUSION: Differences in CR for the three diamond bur grit sizes are due to the greater decrease in CR for the medium-grit diamond burs (50 percent) compared with the CRs of the coarse- and super-coarse-grit diamond burs (35 percent and 25 percent, respectively) over the total cutting period. CLINICAL IMPLICATIONS: Coarser-grit diamond burs may be useful for extensive gross tooth preparations, but dental professionals should be aware of the associated effects of the coarser grit on surface finish, heat generation and enamel damage.     

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.     

Micro-cracking of tooth structure

PURPOSE: To determine if the cutting procedure utilized in producing a cavity preparation, i.e., a high speed dental handpiece or an Er:YAG laser may be a factor in initiating the formation of micro-cracks during or after preparation of the cavity and before and after placing and curing the dental composite. METHODS: Class I occlusal and Class II MOD preparations were prepared in extracted third molars using a high speed dental handpiece equipped with a coarse diamond bur or with an Er:YAG laser at 260mJ and 25Hz. Composite was placed into the cavity level with the occlusal surface and bulk cured. The extreme factors of a coarse diamond bur and bulk curing of the composite were utilized to maximize the stresses at the tooth-composite interface. The teeth were vertically sectioned, facio-lingually, and examined, along with resin replicas, under a scanning electron microscope (SEM) to look for the presence of microcracks at the composite/enamel interface and composite/dentin interface. RESULTS: SEM examination indicated that micro-cracking of the tooth structure was not significant or consistent in any of the specimens examined. This study was unable to confirm that micro-cracks form at the composite/tooth interface.     

Evaluation of machinability and flexural strength of a novel dental machinable glass-ceramic

Objectives

To evaluate the machinability and flexural strength of a novel dental machinable glass-ceramic (named PMC), and to compare the machinability property with that of Vita Mark II and human enamel.

Methods

The raw batch materials were selected and mixed. Four groups of novel glass-ceramics were formed at different nucleation temperatures, and were assigned to Group 1, Group 2, Group 3 and Group 4. The machinability of the four groups of novel glass-ceramics, Vita Mark II ceramic and freshly extracted human premolars were compared by means of drilling depth measurement. A three-point bending test was used to measure the flexural strength of the novel glass-ceramics. The crystalline phases of the group with the best machinability were identified by X-ray diffraction.

Results

In terms of the drilling depth, Group 2 of the novel glass-ceramics proves to have the largest drilling depth. There was no statistical difference among Group 1, Group 4 and the natural teeth. The drilling depth of Vita MK II was statistically less than that of Group 1, Group 4 and the natural teeth. Group 3 had the least drilling depth. In respect of the flexural strength, Group 2 exhibited the maximum flexural strength; Group 1 was statistically weaker than Group 2; there was no statistical difference between Group 3 and Group 4, and they were the weakest materials. XRD of Group 2 ceramic showed that a new type of dental machinable glass-ceramic containing calcium-mica had been developed by the present study and was named PMC.

Conclusions

PMC is promising for application as a dental machinable ceramic due to its good machinability and relatively high strength.     

Cutting characteristics of dental diamond burs made with CVD technology

The aim of this study was to determine the cutting ability of chemical vapor deposition (CVD) diamond burs coupled to an ultrasonic dental unit handpiece for minimally invasive cavity preparation. One standard cavity was prepared on the mesial and distal surfaces of 40 extracted human third molars either with cylindrical or with spherical CVD burs. The cutting ability was compared regarding type of substrate (enamel and dentin) and direction of handpiece motion. The morphological characteristics, width and depth of the cavities were analyzed and measured using scanning electron micrographs. Statistical analysis using the Kruskal-Wallis test (p < 0.05) revealed that the width and depth of the cavities were significantly greater when they were prepared on dentin. Wider cavities were prepared when the cylindrical CVD bur was used, and deeper cavities resulted from preparation with the spherical CVD bur. The direction of handpiece motion did not influence the size of the cavities, and the CVD burs produced precise and conservative cutting.     

The present status of dental rotary cutting performance tests*

Appropriate methods of assessing the cutting ability of handpiece and rotary cutting instrument combinations are needed for research into the processes involved in dental cutting. They are also required for the development of improved devices and recommendations on operation as well as for equipment specification and standards testing. In reviewing the literature on dental rotary cutting performance testing to evaluate available methods, the factors which may influence clinical cutting behaviour are identified as those related to characteristics of the operator, handpiece, rotary cutting instrument, coolant/lubricant used and workpiece material. Existing industrial cutting theory is of limited help in understanding dental cutting in view of the differences between the control of relevant variables in the two cases. Consideration is given to the ways in which the important variables have (or have not) been controlled in past studies of dental cutting and thus the clinical relevance of available methods evaluated. Serious problems such as the lack of suitable test workpiece materials, as well as deficiencies in current knowledge of operator behaviour, handpiece characteristics and effects of coolant/lubricant application are noted. It is concluded that before improved, clinically relevant tests can be developed, further fundamental research in these areas is essential and that until this is done, further work under arbitrary experimental conditions would be of little value.     

Enhanced dental cutting through chemomechanical effects

BACKGROUND: Previous studies have shown that certain surface-active agents--compounds that reduce interfacial tension--in a dental handpiece's irrigation water can enhance cutting rates, or CRs. This study evaluated these effects under test conditions simulating dental practice. METHODS: The authors used a self-contained cutting system with a digitally controlled handpiece speed, torque and water flow rate to cut machinable glass ceramic (Macor, Corning Inc.) with medium-grit diamond burs and cross-cut fissure carbide burs under a load of 147.5 grams and 22 milliliters per minute coolant flow rate using water with mouthwash (Scope, Procter & Gamble) additions. They used six burs for each irrigant mixture to make three 5-millimeter edge cuts through 13 mm of Macor; CRs were quantified as the time necessary to transect the Macor cutting substrate. RESULTS: Additions of small amounts of mouthwash to the coolant water accelerated the CR for both carbide and diamond burs. The CRs for carbide burs in millimeters per second were distilled water, 0.21; 1:2.5 mouthwash:distilled water mixture, 0.12; 1:5 mixture, 0.64; and 1:10 mixture, 0.66. The CR differences for the 1:5 and 1:10 mixtures were significant (P < .001). The CRs for diamond burs in millimeters per second were distilled water, 0.09; 1:1 mouthwash:distilled water mixture, 0.13; 1:2.5 mixture, 0.16; 1:5 mixture, 0.21; and 1:10 mixture, 0.18. When it came to the diamond burs, the CR differences between water and the mouthwash:distilled water mixtures were significant (P < .001). The authors found that the mouthwash additions ensured higher CRs compared with those for water alone over the entire cutting regimen; that is, while the CRs for both carbide and diamond burs dropped with prolonged cutting with water irrigation, the addition of mouthwash resulted in the burs' cutting faster and for longer than with water alone. CONCLUSION: Adding small amounts of mouthwash to the coolant water significantly enhanced cutting by diamond and carbide burs and maintained higher CRs with prolonged cutting. CLINICAL IMPLICATIONS: Making low additions of mouthwash (1:5 and 1:10 mouthwash:distilled water mixtures) to the handpiece irrigant system can lead to two- to threefold increase in the dental diamond and carbide bur cutting rate compared with that for water alone.     

Studies on dental high-speed cutting of commercial pure titanium (Ti) and free-machining titanium (DT-2F)

summary Some dental prostheses are formed by machining. The purpose of this study was to evaluate the dental high-speed cutting behaviour of free-machining titanium (Ti), the ease in cutting of which is metallurgically improved. Weight-load cutting tests were performed on commercial pure Ti and free-machining Ti, using a diamond point and a carbide burr. It became evident that the cutting effectiveness of two rotary cutting instruments on free-machining Ti was superior to that on commercial pure Ti due to the formation of accelerated cut debris. Cutting of free-machining Ti resulted in less damage of the carbide burr, compared with the cutting of commercial pure Ti. These results suggest that free-machining Ti is a suitable workpiece for dental Ti-based machined prostheses.     

新型牙科可切削陶瓷材料的硬度

目的：评估所研制的新型可切削陶瓷材料的硬度。方法：采用压痕法测定4组新型陶瓷的维氏硬度。结果：4组陶瓷材料的维氏硬度为（645.6-658.4）kgf.mm^-2。结论：新型陶瓷的硬度与传统的牙科玻璃陶瓷相近。     

Comparison of the cutting efficiencies of electric motor and air turbine dental handpieces

As part of a larger comprehensive performance evaluation to determine whether electric motor handpieces are a suitable substitute for air turbine handpieces in a portable field dental treatment and operating system, the cutting efficiencies of electric motor and air turbine handpieces were compared. A device was made that applies an identical cutting force to a glass ceramic material for each handpiece tested. The laboratory results show that with equal amounts of applied force, the electric motor handpiece cuts a glass ceramic material significantly more efficiently (volume of material removed per second) than does the air turbine. In clinical trials, after minimal experience utilizing the electric motor, the majority of dentists felt that the electric motor cut tooth and amalgam more efficiently than did the air turbine.