Differential scanning calorimetric studies of nickel-titanium rotary endodontic instruments after simulated clinical use.

Differential scanning calorimetric (DSC) analyses have been performed between -130 degrees and 100 degrees C on single-segment specimens obtained from ProFile and Lightspeed nickel-titanium rotary endodontic instruments in the as-received condition and after one, three, and six periods of simulated clinical use in extracted teeth. The DSC analyses showed that both brands of instruments were always in the superelastic condition, although the enthalpy values for the transformation from martensitic NiTi to austenitic NiTi were much smaller for the Lightspeed instruments. Simulated clinical use had no evident effect upon this transformation for both brands, which is attributed to insufficient mechanical deformation of the instruments. There were substantial differences in the enthalpy change associated with the transformation from martensitic NiTi to austenitic NiTi for test segments from different positions along the shafts of the instruments and for as-received instruments from two different batches that were analyzed in this study and a previous study. These differences are attributed to variations in work hardening along the shaft during instrument fabrication and to processing differences during production of the two batches of each instrument brand.

Differential scanning calorimetric studies of nickel titanium rotary endodontic instruments.

Differential scanning calorimetric (DSC) analyses were performed between -130 degrees and 100 degrees C on specimens prepared from nickel-titanium (NiTi) rotary endodontic instruments: ProFile (n = 5), Lightspeed (n = 4), and Quantec (n = 3). The ProFile and Lightspeed instruments were in the as-received condition, whereas the Quantec instruments were randomly selected from a dental clinic and had unknown history. The DSC plots showed that the ProFile and Lightspeed instruments analyzed had the superelastic NiTi property, with an austenite-finish (Af) temperature of approximately 25 degrees C. Differences in DSC plots for the ProFile instruments and the starting wire blanks (n = 2) were attributed to the manufacturing process. The phase transformation behavior when the specimens were heated and cooled between -130 degrees and 100 degrees C, the temperature ranges for the phase transformations, and the resulting enthalpy changes were similar to those previously reported for nickel-titanium orthodontic wires having superelastic characteristics or shape memory behavior in the oral environment. The experiments demonstrated that DSC is a powerful tool for materials characterization of these rotary instruments, providing direct information not readily available from other analytical techniques about the NiTi phases present, which are fundamentally responsible for their clinical behavior.

Wear resistance of cryogenically treated stainless steel files.

Cryogenic treatment, which involves ultra-sub-zero treatment of metal alloys, has been shown to improve the wear resistance of several types of stainless steel. The purpose of this study was to examine the effect of cryogenic treatment on wear resistance of Flex-R and Hedstrom (Union Broach) files. These instruments were attached to an Instron testing machine and underwent 300 push-pull strokes (6-mm movement range, 600-mm/min speed, 1-N loading) against 1.5-mm thick dentin wafers. Their wear was determined by comparing the depth of grooves (without changing file position) cut in acrylic specimens (1.5-mm thick) before and after machining dentin. The mean and standard deviation (n = 20) of the relative change in cutting efficiency was determined for the files. An analysis of variance showed that the cutting efficiency of all files decreased significantly after wearing on dentin (p < 0.0001). However, when comparing the post-/pre-cutting efficiency ratios of the files, it was seen that cryogenic treatment did not affect the wear resistance of the files.

A method to assess rotary nickel-titanium files.

A number of studies have assessed the physical properties and durability of rotary nickel-titanium files. This study proposes a method that will permit this to be done in a controlled manner. Files of 0.04 taper; 25 mm in length; and in ISO sizes 25, 30, and 35 were each used four times in plastic blocks. The canal in the block had a working length of 17 mm; 30 degrees curvature; 15 mm radius of curvature; size 20 at the apex; and the curve began at 8 mm from the orifice of the canal. The irrigant used was Glyde. An electric handpiece was configured to rotate at 200 rpm and secured to the testing device, which also held the plastic block. The testing device controlled the depth of penetration at 17 mm; the load was at 8 N and the rate of penetration was at 120 mm/min. Controls were not subjected to use. Torsional moment (N-cm) and angular deflection (degrees) at failure were determined on a Torsiometer/Memocouple. Data (n = 5) were analyzed by analysis of variance. Tukey-Kramer intervals at the 0.05 significance level were determined. Torsional moment significantly increased with an increase in size. Torsional moment also significantly increased for used instruments, compared with controls. Angular deflection had a range of 480 degrees to 810 degrees for the instruments tested.

Torsional strength of Gates Glidden drills exposed to clinical conditions.

Gates Glidden drills are exposed to a variety of conditions during clinical usage. These usually include canal preparation, endodontic irrigants, and sterilization procedures. All sizes 1 to 6 (n = 5/size) were tested and the torsional fracture strength determined. There were four groups (n = 30/group): group A, control; group B, sterilized 10 times; group C, exposed to 5.25% NaOCl during testing; and group D, sterilized 10 times and exposed to NaOCl during testing. Data were analyzed by ANOVA. Tukey-Kramer intervals at the 0.05 significance level were calculated. No significant differences were noted as a result of simulated clinical conditions. The larger diameter instruments had significantly higher torsional fracture strength.

Effects of simulated clinical conditions on nickel-titanium rotary files.

When rotary nickel-titanium files are used in highly curved canals, there is a significant risk of separation. This study exposed files to saline or 5.25% NaOCl, while freely rotating in axial motion with a range of approximately equal to 6 mm at 150 rpm for 30 s in a 1.5 mm inner diameter, thin-walled metal tube of 15 mm length with a 90 degrees curve and a 5 mm radius of curvature. Files of 0.04 taper; 25 mm length; and in ISO sizes 25, 30, and 35 were each used three times. Groups were sterilized in a Chemiclave at 132 degrees C for 30 min after each use or tested without sterilization. Controls were not subjected to simulated use. Torsional moment (N-cm) and angular deflection (degrees) at failure was determined on a Torsiometer/Memocouple. Data (n = 5) were analyzed by analysis of variance. Tukey-Kramer intervals at the 0.05 significance level were determined. Exposure to cyclic fatigue, irrigants, and sterilization did not consistently affect torsional moment or angular deflection, compared with controls. Torsional moment significantly increased with an increase in size, regardless of condition (unsterilized vs. sterilized) or solution (saline vs. NaOCl).

The hopeless tooth: when is treatment futile?

The decision to place a tooth in the hopeless category is by no means a simple one. There is always the possibility of being wrong, the possibility that this tooth may prove to be the exception and, against all odds, survive as a functioning component of the masticatory apparatus. These are the decisions that make us dentists rather than technicians.

The effect of instrument precurving on transportation in simulated curved canals.

The results of instrumentation studies in small curved canals using various instruments and techniques are not consistent. The amount of instrument precurving and a gradual or abrupt curve of the canal may have influenced the results of these studies. One hundred sixty resin blocks with simulated canals were used. Eighty blocks had gradual (GC) 30 degree curves, the remainder had abrupt (AC) 30 degree curves. Ten blocks for each curvature and for each degree of precurving amount (0, 15, 20, 25, 30, 35, 40, or 45 degrees) were instrumented with a machine that imparted only an in and out motion. The simulated canals were size 30 at the apex, and size 30 stainless steel K-files were used to instrument the canals. A transportation ("t") index was determined at two levels: T1 (1 mm from the apex) and TB (a line bisecting the curve of the canal). For GC at T1 and TB, 40- and 20-degree curved instruments respectively produced significantly less transportation than all other curvatures (p < 0.0001). For AC at T1 and TB, 35 and 25 degree instruments respectively produced significantly less transportation than all other curvatures (p < 0.0001). Comparing GC and AC, the transportation for AC was significantly less (p < 0.0015).

The beginning of the end of the antibiotic era? Part I. The problem: abuse of the "miracle drugs".

The antibiotic era began in the early 1940s with the clinical use of penicillin. Subsequent discovery, development, and clinical use of other antibiotics resulted in effective therapy against major bacterial pathogens. These drugs were so effective that bacterial infectious diseases were considered by many experts to be under complete therapeutic control. However, the scientific community grossly underestimated the remarkable genetic plasticity of these organisms and their ability, through mutations and genetic transfer, to develop resistance to antibiotics. Infectious diseases are now the world's major cause of death. The cause of bacterial reemergence as a threat to human health and life is the abuse of the "miracle drugs." The ubiquitous nature of antibiotics in the human ecosystem foments bacterial resistance and threatens to eliminate antibiotics as effective drugs for human therapeutic use.

The beginning of the end of the antibiotic era? Part II. Proposed solutions to antibiotic abuse.

The bacteria causing diseases that are now becoming serious public health threats are neither strange nor exotic, but rather shockingly familiar. Tuberculosis, typhoid fever, meningitis, pneumonia, and septicemias are emerging global threats. The infectious agents causing these serious threats are the same bacteria identified many decades ago. The only difference is that these and other microorganisms are no longer killed by the "miracle drugs" that have kept them at bay for the past six decades. Antibiotic resistance has made potential killers out of bacteria that previously posed little threat to mankind. The indiscriminate and reckless use of antibiotics has led to a fast-approaching crisis in which human dominance of the planet is threatened by single, elementary cells of the microbial world. Part I of this article detailed the causes of the crisis. Part II addresses the solutions that are recommended by national and international authorities and organizations.

Precurving of nickel-titanium files affects transportation in simulated canals.

Instrumentation studies comparing nickel-titanium with stainless-steel files have been performed without precurving the nickel-titanium files. It is unknown what influence the precurving of nickel-titanium files would have on transportation in small curved canals of varying curvatures. One hundred-sixty resin blocks with simulated canals were used. Eighty blocks had gradual (gradual curve (GC)) 30-degree curves; the remainder had abrupt (abrupt curve (AC)) 30-degree curves. Ten blocks for each curvature and for each degree of precurving (0, 15, 20, 25, 30, 35, 40, and 45) were instrumented with a machine that imparted only an in and out motion. Simulated canals were a size 30 at the apex, and size 30 nickel-titanium files were used to instrument the canals. A transportation "t" index was determined at two levels: T1 (1 mm from the apex) and TB (a line bisecting the curve of the canal). For GC at T1 and TB, 45- and 25-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). For AC at T1 and TB, 35- and 0-degree curved instruments, respectively, produced significantly less transportation (p < 0.0001). Comparing GC and AC, the transportation for GC was significantly less (p < 0.0015).

Hardness and stress-corrosion of rubber dam clamps.

Rubber dam clamps fracture infrequently during use. There are no American National Standards Institute or International Standards Organization standards for their manufacture. The purpose of this study was to measure the hardness of the clamps and test their resistance to a stress-corrosion test. Upper molar, lower molar, and premolar clamps were obtained from two manufacturers (A, B). The Rockwell C hardness at four sites on the bow of each clamp was then determined. Fresh clamps were placed on blocks corresponding to the average buccal-lingual dimension of the tooth on which they would be used. These blocks were then submerged in room temperature 5.25% sodium hypochlorite for 20 min and then allowed to air dry for 30 min. This was repeated 10 times. Rockwell C hardness values ranged from C30 to 38, with the clamps of manufacturer B being significantly harder. None of the clamps from manufacturer B cracked or corroded. When a third batch received from manufacturer A was tested in the same manner, none of the clamps fractured or corroded either.

Analysis of Ni-Ti versus stainless steel instrumentation in resin simulated canals.

This study compared step-back preparations in curved canals of resin blocks using nickel-titanium K-files and stainless steel K-files. Forty canals in resin blocks were cross-sectioned at 3 levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. Time for instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by instrumentation was significantly greater for stainless steel files at the middle level (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05). It took significantly longer to prepare a canal with Ni-Ti K-files in resin blocks compared to stainless steel (p < 0.05). Resin simulated canals showed similar results compared to canals in extracted roots using an identical methodology.

Analysis of nickel-titanium versus stainless steel instrumentation by means of direct digital imaging.

This study compared step-back preparations in curved canals using nickel-titanium (Ni-Ti) K-files and stainless steel K-files. Forty canals in mesial roots of mandibular molars were embedded in casting resin and cross-sectioned at three levels: 1 to 2 mm from the apical foramen, middle of the curve, and coronal. Direct digital computer images were recorded before and after instrumentation. Superimposition of the images combined with digital subtraction computer software allowed direct measurement of area instrumented, distance of transportation, and shape analysis. The computer software calculated absolute center of gravity for each image analyzed to get a full 360-degree interpretation of the canal transport. Time of instrumentation was recorded. Results showed Ni-Ti files to cause significantly less transportation and remain more centered at the apical level (p < 0.05). Area removed by Ni-Ti and stainless steel files was not significantly different (p < 0.05). Time of instrumentation was not significantly different for Ni-Ti and stainless steel instruments (p < 0.05). Cross-sectional shape of the instrumented canal was not significantly different (p < 0.05).

Tensile and tear properties of dental dam.

The tensile and tear properties of highly extensible latex are sensitive to specimen shape. Three specimen shapes (ASTM D412 Die C dumbbell tensile specimen, rectangular tensile specimen with 1.74 mm hole, and ASTM D624 Die C tear specimen) were evaluated for proposed ANSI/ADA specification #90 for dental dams. Fresh and aged dental dams from two manufacturers (Aseptico and Hygenic) in three weights (thin, medium, and heavy) and from two other manufacturers (Ivory and Ivoclar) in one weight (medium) were tested. Means and standard deviations of 10 specimens for tensile strength (MPa), elongation (%), and tear strength (kN/m) are included herein. Data were analyzed by analysis of variance. Means were compared by a Tukey-Kramer interval calculated at the 0.05 significance level. The use of the dumbbell and tear specimens for the evaluation of dental dam should be reconsidered. The rectangular specimen with a hole is recommended for use in the proposed specification because of its sensitivity to condition (fresh versus aged) and manufacturer.

Properties of hand-held spreaders after simulated use.

Root canal spreaders are available in a wide variety of diameters, lengths, and tapers. Proposed ANSI/ADA Specification no. 71 standardizes certain properties of these instruments; however, none of these testing procedures subjects the instruments to conditions of clinical usage. Diameters (D3 and D16) and taper of 40 D11T root canal spreaders from each of three companies [Endeco (EN), Hu-Friedy (HF), and Premier (PR)] were measured. Permanent angular deformation of the instrument tip was measured by a bend test apparatus for four conditions: (group A) as-supplied control, (group B) spreader sterilized in an autoclave for 10 cycles, (group C) spreader inserted 50 times at a rate of 200 mm/min into plastic blocks with a canal curvature of 30 degrees, and (group D) spreader sterilized for 10 cycles and then inserted in blocks as described. All instruments passed the bend test in proposed specifications under all conditions. The EN spreader was more susceptible to permanent deformation than HF or PR. There were no statistical differences among the control and the three simulated clinical conditions.

Continuously infused calcium hydroxide: its influence on hard tissue repair.

To study the ability of calcium hydroxide to promote hard tissue repair, Alza Alzet Osmotic Pumps, implanted in Sprague-Dawley rats, were used to deliver either calcium hydroxide and glycerol, barium hydroxide and glycerol, tetracycline and glycerol, or glycerol only to a standardized round bur defect in a rat femur. The pumps infused one of the reagents into the defects continuously over a 4-wk experimental period. The effects of each reagent on the healing of the bony defects were compared by histological evaluation. The Alza Osmotic Pump proved to be an effective method to deliver an agent to an experimental site. Our preliminary findings from a limited sample size indicated that calcium hydroxide contributed to a more complete osseous repair than either barium hydroxide or tetracycline. Barium hydroxide with a sustained pH equivalent to calcium hydroxide showed no greater healing than the controls. Tetracycline results were also similar to controls.