Tooth sectioning for coronectomy: how to perform?

OBJECTIVES: The aim of this study was to determine the increase in heat production, preparation time, and cutting surface quality of conventional, high-speed rotating instruments and piezoelectric preparation for coronectomy procedures. MATERIALS AND METHODS: One hundred intact extracted molars were sectioned horizontally, sub-totally, 1 mm under the cemento-enamel line with five methods: (1) tungsten carbide torpedo (TcT), (2) round (TcR) drills using a conventional speed surgical straight handpiece (< 40,000 min-1), (3) tungsten carbide fissure (TcF), (4) diamond torpedo (DT) drills using a surgical high-speed, contra-angle handpiece (~ 120,000 min-1), or (5) a saw-like piezoelectric tip (PT). Temperatures, preparation times, and cutting surface irregularities were registered and the differences were analyzed with ANOVA, Tukey's HSD post hoc test (temperature, time) and with chi-square test (irregular surface). RESULTS: Rotating instruments produced a maximal temperature increase of less than 1 °C. TcF produced the least heat (ΔT = - 3.92 °C to the baseline), while PT produced significantly the highest temperature increases (ΔT = 12.38 °C, p < 0.001). Tungsten carbide drills were the fastest for coronectomy (from 55.9 to 64.3 s), while DT (169.7 s) while PT (146.8 s) were significantly slower. TcT and TcR drills produced an irregular root surface more frequently. CONCLUSIONS: During coronectomy, rotating instruments produced entirely acceptable heat, while PT produced unacceptable temperatures. Tungsten carbide drills performed coronectomies effectively, but the diamond torpedo and PT seemed clinically questionable. Considering heat, speed, and the cutting surface quality simultaneously, TcF in a surgical high-speed handpiece seems to be the best choice for coronectomy. CLINICAL RELEVANCE: The correct insert can significantly reduce excessive heat and operation time during coronectomy procedures.

Fracture Forces of Dentin after Surface Treatment with High Speed Drill Compared to Er:YAG and Er,Cr:YSGG Laser Irradiation.

Dental tooth restorative procedures may weaken the structural integrity of the tooth, with the possibility of leading to fracture. In this study we present findings of coronal dentin strength after different techniques of surface modification. The fracture strength of dentin beams after superficial material removal with a fine diamond bur high speed drill hand piece, Er:YAG (2.94 µm, 8 J/cm(2)), and Er,Cr:YSGG (2.78 µm, 7.8 J/cm(2)) laser irradiation slightly above the ablation threshold was measured by a four-point bending apparatus. Untreated dentin beams served as a control. A total of 58 dentin beams were manufactured from sterilized human extracted molars using the coronal part of the available dentin. Mean values of fracture strength were calculated as 82.0 ± 27.3 MPa for the control group (n = 10), 104.5 ± 26.3 MPa for high speed drill treatment (n = 10), 96.1 ± 28.1 MPa for Er,Cr:YSGG laser irradiation (n = 20), and 89.1 ± 36.3 MPa for Er:YAG laser irradiation (n = 18). Independent Student's t-tests showed no significant difference between each two groups (p > 0.05). Within the parameter settings and the limits of the experimental setup used in this study, both lasers systems as well as the high speed drill do not significantly weaken coronal dentin after surface treatment.

Comparative study of the cutting efficiency and working life of carbide burs.

PURPOSE: The aim of this study was to establish the wear and cutting efficiency of tungsten carbide burs from different manufacturers by performing cutting tests with machinable glass ceramic. MATERIALS AND METHODS: Cutting tests were performed with 70 tungsten carbide burs from seven manufacturers: (A) Coltene/Whaledent, (B) CEI, (C) Meisinger, (D) Axis, (E) Komet, (F) Kerr, (G) Edenta. All groups were examined under scanning electron microscope (SEM) before and after the cutting efficiency test for similarities and differences. A specially designed cutting device was used. An electric handpiece was operated at 200,000 rpm with a 120 ml/min coolant water supply rate. The burs were tested under a 165 g constant load using 3 mm wide Macor ceramic as substrate. For each bur the cutting procedure involved a total of five cuts of 3 minutes on every cut, with a total cutting time for each bur of 15 minutes. Data were analyzed using one-way ANOVA at 95.0% confidence level. RESULTS: Significant differences (p < 0.05) were found in the mean cutting rates of the different groups. Groups A and B showed the highest cutting rates. Higher cutting rates were associated with a longer bur lifespan. SEM photomicrographs of the burs and substrates revealed significant changes on the surfaces after the cutting process. CONCLUSIONS: The morphology characteristics of tungsten carbide burs are related to their effectiveness. The group that presented the worst working life also showed substantial wear on its surface according to the results of SEM.

Topography and presence of a smear layer in deciduous molars prepared with high-speed cutting and ultrasonic abrasion: an in-vitro study.

OBJECTIVE: The aim of this in-vitro study was to compare the effect of high-speed cutting (HS) with ultrasonic abrasion (US) concerning the internal topography and the presence of a smear layer in a cavity preparation performed in healthy deciduous molars. MATERIAL AND METHODS: Seven first deciduous molars were used. Two occlusal cavity preparation were done, one in the medial fossula and another in the distal fossula, which were chosen randomly. One preparation was carried out with a diamond point adapted to the HS system (GI), while a chemical vapor deposition (CVD) point adapted to a US device (GII) was used for the other preparation. Subsequently, all samples (n = 14) were cleaved to observe the inside and then prepared for evaluation using scanning electron photomicroscopy. The internal topography of the prepared cavities was descriptively analyzed. In order to assess the presence of a smear layer, scores were tabulated using the 2000 GMC program and analyzed using the Mann-Whitney test. RESULTS: Concerning the internal topography, the presence of striae was verified in both groups. In the GI group they were finer, found in a greater number, and with narrower spaces between them. In the GII group, the striae were undulating, similar to the effect of wheels on sand, and with wider spaces between them. As regards the presence of a smear layer, there was no statistically significant difference between the groups (P > 0.05). CONCLUSIONS: In view of the methodology employed, it may be concluded that cavity preparation with a CVD point in a US abrasion system led to the formation of fewer striae and both devices promoted the marked presence of a smear layer, obstructing dentinal tubuli.

Use of coolant for high-speed tooth preparation: a survey of pediatric dentistry residency program directors in the United States.

PURPOSE: To determine current teaching policies regarding the use of coolant type during tooth preparation with high-speed hand-pieces in pediatric dental residency programs in the US. METHODS: A 17-question survey was electronically mailed to 63 program directors with one follow-up. Multiple-choice questions asked about school and program teaching of cavity preparation with or without water coolant, including hypothetical clinical situations. RESULTS: Fifty-two (83%) program directors returned the survey. Fifty-two percent taught both dry and water coolant methods, 6% taught dry cutting exclusively, and 42% did not teach the dry method and always used water coolant. Dry techniques were used primarily for special needs patients with poor swallow reflexes (50%) and for young children undergoing sedation (41%). Air coolant was taught more frequently in programs in the Midwest (77%) and South (85%) vs. the Northeast (32%) and West (50%) (P<.01). Forty-four percent of combined programs and 60% of hospital programs taught water spray use exclusively, while all university programs taught the dry cutting technique (P<.01). CONCLUSIONS: A majority of program directors teach the use of air coolant alone for high-speed preparation of teeth. University and combined programs were more likely to teach the method compared with hospital based ones.

Avaliação da resistência à fadiga por flexão de instrumentos rotatórios do sistema protaper universal / Evaluation of the fatigue strength of rotatory instruments from the protaper universal system

O objetivo deste estudo foi avaliar a resistência a fratura por fadiga de instrumentos rotatórios de níquel titânio, por meio de um ensaio estático de resistência a flexão. Foram avaliados instrumentos F1, F2 e F3 pertencentes ao Sistema ProTaper Universal (Dentisply/Maillerfer). O estudo utilizou 60 instrumentos, divididos em três grupos com 20 instrumentos de cada diâmetro. Todos os instrumentos foram submetidos a um ensaio estático de flexão usando um dispositivo especialmente desenvolvido para este estudo. O dispositivo era composto por um canal radicular artificial com ângulo de curvatura de 45º e raio de 5mm, fabricado com aço inoxidável temperado. Um motor elétrico X-Smart (Dentisply/Maillefer) com um contra-ângulo redutor de 16:1 foi programado para funcionar em velocidade constante de 300rpm e torque de 2N.cm. Cada instrumento ProTaper Universal foi encaixado no contra-ângulo e então introduzido no canal artificial onde girava livremente até ocorrer a fratura. O tempo ocorrido até a fratura estática dos instrumentos foi cronometrado e registrado; o número de rotações foi calculado a partir dessa medida. Os resultados deste estudo não mostraram diferenças significantes no número de rotações até ocorrer a fratura. Instrumentos submetidos a velocidade constante em ensaio estático de resistência a flexão, dentro de canais radiculares curvos artificiais, apresentaram número de ciclos até a fratura semelhantes, independente do diâmetro.

The aim of this study was to evaluate the fracture strength under cyclic fatigue load of Nickel-Titanium rotatory endodontic instruments by means of a static flexure strength test. The F1, F2 and F3 instruments from the ProTaper Universal System (Dentisply/Maillerfer) were evaluated. The study used 60 samples, divided in three groups with 20 samples of each diameter. All instruments were submitted to the flexure strength test using a device specially developed for this study. The device was composed by a 45º sloped artificial root canal, made with tempered stainless steel, with radius of 5mm. An X-Smart (Dentisply/Maillefer) electric engine that had a contra-angle with rotatory reduction of 16:1 was stated to work with a constant speed of 300rpm and with a torque of 2N.cm. Each ProTaper Universal Instrument was individually attached to the contra-angle and then introduced into the artificial root canal where rotate freely until failure. The time elapsed until static fracture of the instruments was chronometrically measured and registered; then, the number of rotations was calculated from this measurement.The results of this study showed no statistically significant differences in the mean number of cycles until failure. Instruments submitted to constant speed in static flexure strength test, inside artificial curved canals, presented the same number of cycles to fracture, no matter the diameter.

Human teeth versus bovine teeth: cutting effectiveness of diamond burs

Aim: In this study, a mass-loss method was used to verify whether bovine enamel has the same wear pattern as human enamel in cutting efficiency tests of diamond burs. Methods: Seventy-two teeth were used: 36 human molars (HT) and 36 bovine mandibular central incisors (BT). The enamel of the teeth was cut using diamond bur #1092 attached to a high-speed handpiece under controlled pressure (50-80 g). Each bur (n=12) cut for a total of 72 min, divided into 6 periods of12 min each (12-min, 24-min, 36-min, 48-min, 60-min, and 72-min). The amount of enamel removed was determined by the difference between pre- and post-cut tooth masses. Results:The mean amounts (g) of enamel removed were: HT- 12-min=0.11; 24-min=0.12; 36-min=0.11; 48-min=0.11; 60-min=0.10; 72-min=0.12; BT- 12-min=0.12; 24-min=0.15; 36-min=0.15; 48-min=0.13; 60-min=0.16; 72-min=0.14. Data were analyzed using ANOVA followed by Tukey’s test, and the results showed statistically significant differences between human and bovine teeth (p<0.001) and among the cutting periods (p<0.001).Conclusions: It was concluded that the cutting efficiency of the burs was different between the tested substrates, and that bovine enamel underwent greater mass loss than did human enamel.

In vitro comparison of the cutting efficiency and temperature production of 10 different rotary cutting instruments. Part I: Turbine.

STATEMENT OF PROBLEM: Standards to test the cutting efficiency of dental rotary cutting instruments are either nonexistent or inappropriate, and knowledge of the factors that affect their cutting performance is limited. Therefore, rotary cutting instruments for crown preparation are generally marketed with weak or unsupported claims of superior performance. PURPOSE: The purpose of this study was to examine the cutting behavior of a wide selection of rotary cutting instruments under carefully controlled and reproducible conditions with an air-turbine handpiece. MATERIAL AND METHODS: Ten groups of rotary cutting instruments (n=30) designed for tooth preparation were selected: 9 diamond rotary cutting instruments (7 multi-use, 2 disposable) and 1 carbide bur. One bur per group was imaged with a scanning electron microscope (SEM) at different magnifications. Macor blocks (n=75) were used as a substrate, and 4 cuts were made on each specimen, using a new rotary cutting instrument each time, for a total of 300 cuts. The cuts were performed with an air-turbine handpiece (Midwest Quiet Air). A computer-controlled, custom-made testing apparatus was used to monitor all sensors and control the cutting action. The data were analyzed to compare the correlation of rotary cutting instrument type, grit, amount of pressure, cutting rate, revolutions per minute (rpm), temperature, and type of handpiece, using 1-way ANOVA and Tukey's Studentized Range test (alpha=.05). RESULTS: Compared to the baseline temperature, all rotary cutting instruments showed a reduction of temperature in the simulated pulp chamber. The Great White Ultra (carbide bur) showed a significantly higher rate of advancement (0.15 mm/s) and lower applied load (106.46 g) and rpm (304,375.97). CONCLUSIONS: Tooth preparation with an adequate water flow does not cause harmful temperature changes in the pulp chamber, regardless of rotary cutting instrument type. The tested carbide bur showed greater cutting efficiency than all diamond rotary cutting instruments.

An in vitro investigation of the effectiveness of bioactive glass air-abrasion in the 'selective' removal of orthodontic resin adhesive.

The process of clinically debonding orthodontic brackets causes histomorphological damage to enamel that needs to be quantified and minimized. This study compared three methods for removing residual resin adhesive following bracket debonding. The surface finish following removal of residual adhesive using a slow-speed eight-bladed tungsten carbide bur (group 1), alumina air-abrasion (group 2), and bioactive-glass air-abrasion (group 3) and following polishing, was examined using scanning electron microscopy imaging of resin replicas. Contact profilometry was used to image surfaces before and after debonding for quantifiable volumetric analysis of enamel damage. Surface scarring was seen on scanning electron micrographs from group 1, a sharp pitted surface was identified in group 2, while group 3 exhibited similar, but subjectively smoother, pits. The surface finish following polishing was similar for groups 2 and 3 but did not completely remove the scarring evident from group 1. Quantifiable enamel lost was as follows: group 1, 0.285 mm(3); group 2, 0.386 mm(3); and group 3, 0.135 mm(3); statistical differences were observed between groups 2 and 3. From these results, bioactive-glass air-abrasion more consistently caused less physical damage to enamel and achieved a clinically smooth surface finish following polishing and is therefore to be recommended for clinical use.

In vitro rapid intraoral adjustment of porcelain prostheses using a high-speed dental handpiece.

In vitro rapid intraoral adjustment of porcelain prostheses was conducted using a high-speed dental handpiece and diamond bur. The adjustment process was characterized by measurement of removal forces and energy, with scanning electron microscopic (SEM) observation of porcelain debris, surfaces and subsurface damage produced as a function of operational feed rate. Finite element analysis (FEA) was applied to evaluate subsurface stress distributions and degrees of subsurface damage. The results show that an increase in feed rate resulted in increases in both tangential and normal forces (analysis of variance (ANOVA), P<0.01). When the feed rate approached the highest rate of 60mm min(-1) at a fixed depth of cut of 100microm, the tangential force was nearly seven times that at the lowest feed rate of 15mm min(-1). Consequently, the specific removal energy increased significantly (ANOVA, P<0.01), and the maximum depth of subsurface damage obtained was approximately 110 and 120microm at the highest feed rate of 60mm min(-1) using SEM and FEA, respectively. The topographies of both the adjusted porcelain surfaces and the debris demonstrate microscopically that porcelain was removed via brittle fracture and plastic deformation. Clinicians must be cautious when pursuing rapid dental adjustments, because high operational energy, larger forces and severe surface and subsurface damage can be induced.

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.

Use of CVDentUS diamond tips for ultrasound in cavity preparation.

AIM: The aim of this study was to evaluate the use of CVDentUS tips for preparing cavities with ultrasound by dentists certified to use the Chemical Vapor Deposition (CVD) system. METHODS AND MATERIALS: One thousand sixty (1060) questionnaires were sent via e-mail inquiring about the use of the system with regard to the indication for use, need for anesthesia, final form of cavity preparation, and tip wear. RESULTS: Of the valid answers, 81.4% of the dentists used this system for tooth preparation in up to 60% of cases treated. For these procedures, 17.8% did not require use of local anesthesia while using the system. The final form of preparation compared to high speed diamond tips was considered to be more conservative by 48.3% of the certified professionals. With regard to wear, tip and/or adapter fractures, and low cutting speed, 44.4% of users reported problems. DISCUSSION: The CVD system seems to be used for tooth cavity preparation by the majority of the certified dentists. This is due to the resultant conservation of tooth structure despite the necessity of anesthesia and the limitations with regard to the lack of cutting efficiency of CVDentUS and tip wear. CLINICAL SIGNIFICANCE: The CVD system seems to present limitations with regard to cutting efficiency, wear, and the use of anesthesia in a majority of restorative procedures.

Effect of rotary instrumentation on composite bond strength with simulated pulpal pressure.

This study evaluated the effect of cutting teeth with different types of burs at various speeds on shear bond strength using Prime and Bond NT (Dentsply/DeTrey). A simulated pulpal pressure of 25-mmHg, equivalent to 34 cmH2O, was created in a false pulpal chamber filled with distilled water and maintained for seven days. The human teeth were divided into six groups of 10 teeth each: fine grit straight fissure diamond bur in air rotor (DA), fine grit straight fissure diamond bur in micromotor (DM), crosscut fissure carbide bur in air rotor (CCA), crosscut fissure carbide bur in micromotor (CCM), plain fissure carbide bur in micromotor (CM) and #600-grit silicon carbide paper (SiC). The tooth surfaces in these groups were cut under copious air-water spray and treated with Prime and Bond NT after etching with 38% phosphoric acid. Composite restorations were then prepared with TPH spectrum (Dentsply/ DeTrey). After soaking in water at 37 degrees C for 24 hours, the specimens were loaded at a 45 degrees angle to their longitudinal axes by using a Z 010 Universal Testing Machine (Zwick), and shear bond strengths were determined at a crosshead speed of 2 mm/minute. All of the specimens were then observed under Stereomicroscope at 10x. Statistical analysis was made using one-way and two-way ANOVA and t-test (p < 0.05). The bond strengths achieved with a fine grit straight fissure diamond bur, a crosscut fissure carbide bur in air rotor and a crosscut fissure carbide bur in micromotor, were significantly higher than a fine grit straight fissure diamond bur, a plain fissure carbide bur and #600-grit silicon carbide abrasive paper in the micromotor. Therefore, selecting an appropriate bur and its speed may improve bonding for adhesive systems, although crosscut fissure carbide burs produced high bond strengths at either speed used.

Cutting characteristics of dental diamond burs made with CVD technology

O objetivo deste estudo foi determinar a habilidade de corte das pontas de diamante obtidas pelo processo de deposição química a vapor (CVD) associadas ao aparelho de ultra-som no preparo cavitário minimamente invasivo. Uma cavidade padronizada foi preparada nas faces mesial e distal de 40 terceiros molares, utilizando-se pontas de diamante CVD cilíndrica e esférica. A habilidade de corte foi comparada quanto ao tipo de substrato (esmalte e dentina) e quanto à direção do movimento realizado com a ponta. As características morfológicas, a largura e profundidade das cavidades foram analisadas e medidas em microscopia eletrônica de varredura. A análise estatística pelo teste de Kruskal-Wallis (p < 0,05) revelou que a largura e profundidade das cavidades foram significativamente maiores em dentina. Cavidades mais largas foram obtidas quando se utilizou a ponta de diamante CVD cilíndrica, e mais profundas quando a ponta esférica foi empregada. A direção do movimento da ponta não influenciou o tamanho das cavidades, sendo os cortes produzidos pelas pontas de diamante CVD precisos e conservadores.

[The effect of root canal preparation with nickel-titanium rotary instruments in reducing post-operative pain].

OBJECTIVE: To examine the effect of nickel-titanium rotary instruments in reducing post-operative pain. METHODS: 95 molars with pulpal and/or periapical involvement were randomly assigned to two groups for root canal preparation. One group was treated with ProFile nickel-titanium rotary instruments; the other was treated by using stainless steel hand files-FlexoFile. The incidence and degree of post-operative pain after root canal preparation in the two groups were recorded. RESULTS: In ProFile group, the incidence of post-operative pain was 27.7%, while 62.5% of the teeth developed post-operative pain after hand preparation. The difference between two groups was statistically significant (P < 0.01). CONCLUSION: Root canal preparation on molars with stainless steel hand files resulted in relatively high incidence of post-operative pain. Mechanical preparation using ProFile nickel-titanium instruments generated less post-operative pain and discomfort.

The effect of three types of rasps on the occlusal surface of equine cheek teeth: a scanning electron microscopic study.

Two hand rasps (tungsten chip blade, solid carbide blade) and an electrically-driven solid carbide axial bur were used to treat the cheek teeth of 2 horses immediately postmortem. All teeth were normal and were rasped to a standard considered satisfactory in practice. Six teeth from each horse served as untreated controls. Following treatment, the teeth were extracted and the clinical crown removed and prepared for scanning electron microscopy. Teeth were also extracted and examined from a horse that had excessive dental treatment previously. Dental debris created by the procedures was collected and examined. All three rasp techniques resulted in amputation of odontoblast processes. The solid carbide blade cut deep gouges and grooves into the surface of the dentin, chipping the enamel and peripheral cement. No smear layer was created. Rasping with a tungsten chip blade created a partial smear layer and a smoother surface than the solid carbide blade. The electrically-driven bur produced a complete smear layer and removed all dental tissues to a smooth layer. The enamel had also been damaged by the electric bur. Crown particles collected after the procedures were larger following hand rasping compared with particles produced by the electric bur. The extent of damage to sensitive and vital dentin tissue was of concern. Further studies are required to establish the optimum technique for rasping equine cheek teeth.

Surface roughness and bond strength of enamel to composite.

OBJECTIVES: The aim of the study was to assess the influence of pretreating enamel by different rotary instruments on shear-bond strength of composite to enamel after the acid etch technique. METHODS: Ninety human enamel specimens with transversely and longitudinally sectioned prisms were ground flat, and half of the enamel area of each specimen was prepared with one of the eight different rotary instruments: a 120 microns diamond bur, three finishing diamonds (30, 15 and 8 microns), two tungsten carbide finishing instruments (8- and 30-fluted) and two stones (Dura green and Dura white). The other half of the enamel area was left untreated. Enamel roughness was measured by laser-stylus profilometry. Two cylinders filled with the hybrid composite Pertac were adhesively fixed on each enamel surface, one on the prepared side and the other on the untreated side. After seven days of water storage, shear-bond strength was measured with a Universal testing machine. RESULTS: Rz values of the treated enamel surfaces were between 4.14 and 17.75 microns. The shear-bond strength data varied between 16.8 and 29.4 MPa and were similar for transversely and longitudinally orientated prisms. The different roughness data had no significant influence on shear-bond strength of composite to enamel. Additional SEM investigation showed that the surface geometry caused by the rotary instruments largely persisted after acid etching. SIGNIFICANCE: With regard to shear-bond strength, there was no advantage in using a special bur for finishing enamel surfaces prior to the acid etch technique. Burs causing extreme roughness should not be used for this purpose.

Step-by-step description of a rotary root canal preparation technique.

CLINICAL TECHNIQUE: Since the introduction of nickel-titanium in endodontics, several canal preparation techniques involving the use of rotary instruments have become popular. Such engine-driven rotary instruments rotate between 150 and 2000 r.p.m. and may be high or low torque orientated. This paper describes one such engine-driven system called the ProFile technique. The instruments are of a different specification to that used for conventional endodontic files and reamers. This paper describes a technique employed by the Division of Endodontology, Zurich Dental School, in a step-by-step procedure using primarily photographs of radiographs. The intention is to give any interested clinician a better idea of the technique using radiographs taken from both the buccolingual (clinical) perspective and the mesiodistal projection. Basically, the technique involves preparing the coronal portion of the root canal using Gates-Glidden burs and the ProFile instruments. Only when any constricting coronal parts of the canals have been removed is the working length established using conventional files. Finally, the apical part of the canal is prepared using only the ProFile instruments. Three clinical cases are also briefly described, in order to illustrate the potential of the technique in cases treated generally by clinicians.

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.