A scanning electron microscopy comparison of enamel polishing methods after air-rotor stripping

In the last few years, orthodontic literature has shown particular interest in the interproximal enamel reduction technique described as stripping or slenderizing. Most researchers have shown, by scanning electron microscopy (SEM) studies, the difficulties encountered while attempting to remove coarse abrasions left after stripping with the first instrument. The objective of this SEM study was to compare the different polishing methods proposed in the literature and to assess the efficiency of our own procedure. For this purpose, 48 healthy human teeth (premolars and molars) were used after removal for orthodontic or periodontal reasons. The teeth were divided into eight groups of six teeth each (two molars and four premolars), and mounted on a typodont to simulate a clinical situation. Each group underwent stripping according to one of the following techniques: 16-blade tungsten carbide bur and fine and ultrafine diamond burs; coarse diamond bur and fine and ultrafine diamond burs; coarse diamond disk and Sof-Lex disks (Dental products/3M, St. Paul, Minn.); 16-blade tungsten carbide bur and phosphoric acid on finishing strip; and 8-straight blade tungsten carbide diamond bur and Sof-Lex disks. The SEM investigations demonstrated that it is not possible to eliminate, with normal polishing and cleaning methods, the furrows left on the enamel both by the diamond burs and the diamond disks and the 16-blade tungsten carbide burs. Mechanical and chemical stripping as well did not prove to be effective. By contrast, with the use of a 8-straight blade tungsten carbide bur followed by Sof-Lex disks for polishing the enamel, it is possible to obtain well-polished surfaces that many times appear smoother than the intact or untreated enamel.

Effect of nickel-titanium engine-driven instrument rotational speed on root canal morphology

Thirty-six mesial canals in 18 extracted human mandibular molars were randomly allocated to three experimental groups. Specimens were prepared and evaluated using a modified Bramante technique. Teeth were sectioned at the midroot and apical regions. Canals were prepared with the Lightspeed instruments rotating at 750, 1300, or 2000 rpm. Digitized uninstrumented and instrumented canal images were compared via subtraction software. There was no significant difference (p <0.05) among the three experimental groups in the amount of dentin removed, canal transportation, or the ability of the instrument to remain centered in the canal.

Reducing bacterial aerosol contamination with a chlorhexidine gluconate pre-rinse

The authors compared the effects of chlorhexidine gluconate, an antiseptic mouthwash with essential oils and water on the bacterial aerosol contamination generated by an air polishing device. Patients rinsed with one of the three solutions before treatment. Bacterial counts collected during the treatment indicate that the chlorhexidine pretreatment rinse was significantly more effective than the other solutions in reducing bacterial aerosols.

The influence of bur blade concentricity on high-speed tooth-cutting interactions: a video-rate confocal microscopic study

This study aimed to determine the degree of eccentricity between different tungsten carbide bur manufacturing techniques and to study the effect of bur inaccuracy on dental enamel. Error in bur concentricity may arise from malalignment of the steel shaft and carbide head in a two-piece construction bur. Cutting blades rotate at multiple radii from the shaft axis, potentially producing vibrations and damage to the cut substrate. Techniques now allow for the manufacture of one-piece tungsten carbide burs with strength adequate to withstand lateral loading. A comparison of tungsten carbide dental cutting tools revealed the true extent of concentricity errors. Variation in alignment of the cutting head and shaft in the two-part constructions incurred between 20 and 50 microns of additional axial error. High-speed cutting interactions with dental enamel between carbide burs were studied by means of a video-rate confocal microscope. A cutting stage fitted to a Tandem Scanning Microscope (TSM) allowed for real-time dynamic image acquisition. Images were captured and retrieved by means of a low-light-level camera recording directly to S-VHS videotape. Videotape showing the interactions of high-speed rotary cutting instruments (at 120,000 rpm) were taken under simulated normal wet-cutting environments, and the consequent damage to the tooth tissue was observed as it occurred. Concentrically engineered bur types produced a superior quality cut surface at the entry, exit, and advancing front aspects of a cavity, as well as less subsurface cracking. Imaging of the coolant water film local to recent cutting operations showed regular spherical cutting debris of 6 to 18 microns diameter from the concentric tools, whereas the less-well-engineered burs produced ragged, irregular chips, with 25-40 microns diameter debris, indicating far more aggressive cutting actions. This study has shown that there is reduced substrate damage with high-concentricity carbide burs.

Using air-abrasive technology to diagnose and restore pit and fissure caries

National Institute of Dental Research surveys indicate that the incidence of pit and fissure caries constitutes a higher proportion of the total caries incidence among U.S. teens and children than in the past. Air-abrasive technology may provide a more conservative alternative in the diagnosis and treatment of pit and fissure caries than traditional techniques using handpieces. The authors review characteristics of pit and fissure lesions and discuss methods for diagnosing and treating these lesions using air-abrasive technology.

Cavity preparation with the Nd:YLF picosecond laser

Several laser systems for the removal of hard dental substances are currently under investigation. However, in most cases, such systems have been demonstrated to be inefficient or have led to undesirable thermal side-effects. This paper reports, for the first time, the removal of enamel and dentin by a picosecond laser system, a solid-state Nd:YLF laser. Very precise cavities can be obtained in the enamel and dentin of extracted human molars when laser pulses are distributed onto well-defined areas of the teeth. Scanning electron microscopy shows that the quality of the cavities is superior to that achieved by other laser systems. The cavity walls are very steep, and their surfaces are characterized by a sealed structure. In contrast to laser systems with longer-duration pulses, picosecond laser pulses ablate with less thermal damage to the surrounding substance. The results of dye penetration tests and polarized microscopy show that even mechanical shock-wave effects are negligible. When the Nd:YLF laser is applied to carious enamel, the ablation rate is found to be about ten times higher than for sound molars, thus making the Nd:YLF laser a caries-selective laser system.

Rise in pulp temperature during finishing and polishing of resin composite restorations: an in vitro study

The aim of this study was to establish the effects of the working speed, the use of coolant, and the pressure applied on the temperature of the pulp when resin composite restorations are finished and polished. One hundred eighty teeth with resin composite restorations are finished and polished. One hundred eighty teeth with resin composite restorations were randomly distributed into groups to be finished and polished with violet, blue, or yellow flexible disks. Each group was randomly subdivided into six subgroups of 10 each. Four subgroups were finished and polished, without water cooling, under constant pressure at speeds of 10,000, 8,000, 6,000 or 4,000 rpm. The other two subgroups were finished and polished at 10,000 rpm, one without water cooling while work was carried out intermittently and the the other with water cooling while work was carried out constantly. Results implied that a maximal speed of 4,000 rpm should be applied when polishing is carried out continuously without water coolant. When water cooling is used, flexible disks can safely be used at a speed of 10,000 rpm and with continuous pressure.

A comparison of canal preparation with nickel-titanium and stainless steel instruments

Maintaining the original canal path during instrumentation is a challenge in narrow curved canals. This study compared the maintenance of the original canal path of curved root canals during instrumentation with nickel-titanium (Mac) hand files, nickel-titanium engine-driven files, and stainless steel (K-Flex) files. Canal path maintenance was determined by superimposing instrumentation radiographs over an initial file radiograph and examining for discrepancies. Nickel-titanium hand and engine-driven instruments maintained the original canal path in all cases. The incidence of deviation from the original canal path during instrumentation with stainless steel files increased with file size. The difference between nickel-titanium groups and stainless steel became statistically significant with instruments larger than size 30. In this study, nickel-titanium files were more effective in maintaining the original canal path of curved root canals when the apical preparation was enlarged beyond size 30.

Quantitative and qualitative assessment of enamel surface following five composite removal methods after bracket debonding

The search for an ideal enamel surface finishing method following bracket debonding has met with equivocal response. In this study, four other methods were assessed to determine their effectiveness against the slow speed tungsten carbide bur which is regarded as the established method of removing residual composite. Orthodontic brackets were bonded on 50 premolar teeth extracted for orthodontic purpose. After debonding with a standardized technique, the teeth were randomly divided into five equal groups. Samples in each group were subjected to different finishing procedures: Group A--Ormco band removing plier. Group B--Komet slow speed tungsten carbide bur. Group C--High speed ultrafine diamond bur. Group D--Jet high speed tungsten carbide bur. Group E--High speed white stone finishing bur. For consistency, the finishing procedures were limited to 15 seconds with each particular method. The composite remnants which then remained on the enamel surface were graded by four independent raters using the Composite Remnant Index (CRI). Subsequent to this, the enamel surface was examined in a Scanning Electron Miscroscope at x203 magnification. The photomicrographs were then graded by the same four independent raters using the Surface Roughness Index (SRI). Statistical analysis with the Friedman test indicated that there was no significant difference in inter-examiner variability in both the CRI and SRI assessment, but there existed significant difference among groups (P < 0.01) for both the CRI and SRI. It was found that no single absolute method was considered to be ideal for composite removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Scanning electron micrographic effects of air-abrasion cavity preparation on human enamel and dentin

Recent developments in technology and restorative materials have renewed interest in air abrasion as a means of tooth preparation. The technique, also called kinetic cavity preparation, uses kinetic energy to remove tooth structure. The purpose of this investigation was to use scanning electron microscopy to compare the effects of this technique to those of high-speed burs on extracted human teeth. Class V buccal preparations were made on five teeth with a No. 34 carbide bur used at 400,000 rpm and on 23 teeth with kinetic cavity preparation using differing combinations of aluminum oxide particle sizes and delivery pressures. Features of the specimens prepared at high speed included sharp line angles, chipping of the cavo-surface margin, and striated internal surfaces. Kinetic cavity preparations had rounded cavo-surface margins and internal line angles. The surfaces were microscopically rough and the dentinal tubules were occluded. There was little difference in appearance between specimens treated with various combinations of particle sizes and delivery pressures.

Studies on dental high-speed cutting

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 0.25 s, 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 105 g, while horizontal I-s cut of dentine brought about the minimum (approximately 35 g). 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.

Glass polyalkenoate bond strength to dentine after chemomechanical caries removal

The bond strength of a glass polyalkenoate cement after chemomechanical caries removal of dentine with or without the use of a conditioning agent and the mode of bond failure using scanning electron microscopy was examined. Forty extracted carious human teeth were divided into four groups of ten. Conventional caries removal was carried out on two groups and chemomechanical caries removal on the other two groups. Surface conditioner was applied to the dentine in one conventionally treated and one chemomechanically treated group. Glass polyalkenoate cement was applied via a metal holder to the dentine. The samples were stored for 7 days in a moist environment at 37 degrees C. The samples were subjected to a shearing-type stress at a cross-head speed of 0.5 mm min-1. The mean bond strength for each group, in MPa (standard deviation), was: conventional caries removal alone 1.32 (0.51), conventional caries removal and conditioner application 2.43 (0.47), chemomechanical caries removal alone 2.47 (0.99) and chemomechanical caries removal and conditioner application 2.76 (0.96). Mean bond strengths for both the chemomechanically treated groups and the conventionally treated group, coupled with the use of the conditioning agent, were significantly greater than for the conventionally treated groups alone at the 0.05 level. There was no significant difference between the chemomechanically treated groups or the group conventionally treated with conditioner application. SEM examination revealed a combination of cohesive and adhesive bond failure. Different morphologies between the conventionally and chemomechanically treated surfaces were also evident.

Atmospheric contamination during dental procedures

The aim of this study was to evaluate the level of aerosol pollution following dental procedures performed in 15 sessions with an ultrasound scaler and a bicarbonate cleaner. The air contamination was measured by means of the Surface Air System method and the "plate" method (Air Microbial Index). Each colony-forming unit per cubic meter of air was allotted a unit value for statistical analysis. The data were then compared with the hygienic assessments made in previous studies. The results showed that the initial environmental conditions in a dental office initiated at the level of mediocre, then became very bad during dental procedures, and fell between mediocre and very bad at the end of the procedures.

Evaluating spatter and aerosol contamination during dental procedures

A pilot study evaluated the distribution of spatter and aerosols generated by high-speed instrumentation. In the first phase, fluorescent dye was added to the handpiece water supply. In the second, blood agar culture plates were placed in the operatory. Results show that contamination from spatter and aerosol dissemination remains a significant hazard for dental personnel.

Effect of handpiece pressure and speed on intrapulpal temperature rise

This study determined the effect of handpiece pressure and speed on the intrapulpal temperature rise produced during finishing. Finishing was performed on a class V amalgam restoration with a brown rubber point. The remaining dentin thickness was standardized under the restoration at 2.0 mm. Finishing was done continuously for 60 seconds with temperature rises recorded at the dentin/pulp interface every 15 seconds. All finishing was done dry. Handpiece speed (rpm's) varied from 7000-15,000 rpm's and applied pressure from 20-60 gr force. Increases in either speed or pressure can produce significant intrapulpal temperature increases over these ranges. Doubling either one produces a 50% temperature increase during finishing. Finishing at 15,000 rpm's with 60 gr force is capable of producing damaging temperature rises at the pulp after only 15 seconds finishing time.

Studies on dental high-speed cutting with carbide burs used on bovine dentin

Bovine dentin was cut by hand with carbide burs and two cutting procedures while the rotational handpiece speed and the applied load were simultaneously monitored. It became evident that the maximum applied load during intermittent cutting varied from approximately 30 to 40 gm, whereas that during successive cutting ranged from approximately 20 to 60 gm. It showed that intermittent cutting produced a greater cutting effectiveness (for example, cutting volume per cut contact time) when carbide burs were used on dentin, compared with continuous cutting. It is recommended that the intermittent cutting procedure be used during work on patients.

Pin-retained restorations for severely worn posterior teeth

Restoring severely worn posterior teeth with cast restorations presents a challenge to the dentist. The shortened clinical crowns have insufficient axial wall length for adequate retention and resistance form. Pins, along with other preparation retentive forms, can avoid periodontal support loss created by lengthening procedures. This article describes pin preparation of severely worn mandibular premolars and molar restoration by pin-retained gold castings. These and other teeth are used for retention of a mandibular removable partial denture.

Reducing bacteria in dental aerosols: pre-procedural use of an antiseptic mouthrinse

This study, using a simulated office visit model, showed that the pre-procedural use of an antimicrobial mouthrinse produces a significant reduction in number of viable bacteria in a dental aerosol.

Calculus removal from multirooted teeth with and without surgical access. II. Comparison between external and furcation surfaces and effect of furcation entrance width

The purpose of this study was to evaluate the effect of furcation entrance width on the efficacy of calculus removal from furcation areas as well as to compare this efficacy between external and furcation surfaces after closed root planing, open root planing and use of a rotary diamond for the furcation area. 30 first and second lower molars scheduled for extraction with a calculus index > or = 2 and a degree II or III furcation involvement were divided into 3 groups: 10 molars were scaled and root planed using a closed approach: 10 molars were scaled and root planed using an open approach; 10 molars were scaled and root planed with an open approach and rotary diamond was used for removal of deposits in the furcation area. After extraction, the width of the furcation entrance was measured buccally and lingually 2 mm apical from the bifurcation and furcations were categorized as wide (width > 2.4 mm) or narrow (width < 2.4 mm). The teeth were assessed in a stereomicroscope and the % of residual calculus on external and furcation surfaces was calculated. The width of the furcation entrance influenced the efficacy in root planning in the open group (p = 0.0015). The use of rotary diamond was the most effective method for removing calculus both for narrow and wide furcations. The effectiveness of open root planning in the mesial root was related to the width of the furcation entrance where the % of residual calculus was significantly higher for narrow furcations (p = 0.008).(ABSTRACT TRUNCATED AT 250 WORDS)