Premixed Mineral Trioxide Aggregate Setting Reaction in Primary Molar Pulpotomies.

Purpose: To assess the setting of premixed mineral trioxide aggregate (NuSmile NeoPUTTY) when used as a pulpotomy agent in primary molars, restored in a single visit, and to compare the effect of overlying materials, including zinc oxide eugenol (ZOE), resin-modified glass ionomer cement (RMGIC) and stainless steel crowns (SSC), on the microhardness of the NeoPUTTY.
Methods: Forty-eight extracted primary molars were prepared with the standard pulpotomy technique. Approximately three mm of NeoPUTTY were placed on the pulpal floor of each tooth. The teeth were divided into four groups according to restorative material: (1) control group-none; (2) RMGIC; (3) ZOE; and (4) ZOE and SSC. Groups 2, 3 and 4 specimens were placed in artificially simulated oral cavity conditions. After 24 hours, all teeth were sectioned mesiodistally and polished. Microhardness was then measured in Knoop scales (HK) at one mm, two mm and three mm away from the NeoPUTTY-overlying material interface following the application of a 25-gf load force for 30 seconds at each site. One-way analysis of variance was used to compare the NeoPUTTY microhardness values between groups at each depth as well as between the three different depths within each group (P <0.05).
Results: No statistically significant differences in mean HK values (57.9 to 62.3 range) were found between groups at each depth, or between depths within each group (Group 1,P =0.328; Group 2, P =0.74; Group 3, P =0.293; Group 4, P =0.788).
Conclusion: The setting reaction of NeoPUTTY, as a function of microhardness, was not affected by the presence or type of overlying material used in a single-visit pulpotomy. This in vitro study found no evidence against the immediate restoration of primary molar pulpotomies done with NeoPUTTY.

C5a complement receptor modulates odontogenic dental pulp stem cell differentiation under hypoxia.

AIM: Alterations in the microenvironment change the phenotypes of dental pulp stem cells (DPSCs). The role of complement component C5a in the differentiation of DPSCs is unknown, especially under oxygen-deprived conditions. The aim of this study was to determine the effect of C5a on the odontogenic differentiation of DPSCs under normoxia and hypoxia. MATERIAL AND METHODS: Human DPSCs were subjected to odontogenic differentiation in osteogenic media and treated with the C5a receptor antagonist-W54011 under normal and hypoxic conditions (2% oxygen). Immunochemistry, western blot, and PCR analysis for the various odontogenic differentiation genes/proteins were performed. RESULTS: Our results demonstrated that C5a plays a positive role in the odontogenic differentiation of DPSCs. C5a receptor inhibition resulted in a significant decrease in odontogenic differentiation genes, such as DMP1, ON, RUNX2, DSPP compared with the control. This observation was further supported by the Western blot data for DSPP and DMP1 and immunohistochemical analysis. The hypoxic condition reversed this effect. CONCLUSIONS: Our results demonstrate that C5a regulates the odontogenic DPSC differentiation under normoxia. Under hypoxia, C5a exerts a reversed function for DPSC differentiation. Taken together, we identified that C5a and oxygen levels are key initial signals during pulp inflammation to control the odontogenic differentiation of DPSCs, thereby, providing a mechanism for potential therapeutic interventions for dentin repair and vital tooth preservation.

Prevalence of Radiographically Identifiable Dental Anomalies in Children and Association with Health Status.

Purpose: The purpose of this study was to describe the prevalence of radiographically identifiable developmental dental anomalies (DDA) in a university-based pediatric dental clinic and to assess for associations between DDA and health status. Methods: Retrospective data, obtained from the electronic dental records of a three-year pediatric patient cohort, were evaluated by two trained and calibrated examiners. Strict inclusion/ exclusion criteria were applied. A validated image quality grading system was used for radiograph assessment, and the physical status classification of the American Academy of Anesthesiology was utilized. A chi-square test and bivariate logistic regression were used for statistical analysis. The inter- and intraexaminer reliability was assessed using Cohen's Kappa. Results: A total of 1,478 subjects (69 percent medically healthy) were enrolled. DDA were identified in 25 percent of the subjects, with hyperdontia, hypodontia, and microdontia being more common. A statistically significant association was found between the presence of DDA and health status (P<0.001) and between DDA and asthma (P=0.035). Patients with systemic disturbances showed 2.12 times greater odds of having DDA (P<0.001, 95 percent confidence interval equals 1.7-2.7). Conclusions: The prevalence of developmental dental anomalies was high, with one in four patients affected. DDA in number were the most common. Patients with systemic disturbances had greater odds of having DDA.

A Randomized Controlled Trial Comparing the Success of Mineral Trioxide Aggregate and Ferric Sulfate as Pulpotomy Medicaments for Primary Molars.

Purpose: To evaluate and compare the clinical and radiographic performance of a new type of mineral trioxide aggregate (MTA, NuSmile® NeoMTA®) and ferric sulfate (FS) as pulpotomy medicaments for primary molars over 12 months.
Methods: Fifty participants (25 per group) were enrolled, according to specific inclusion criteria. Each participant received a single primary molar pulpotomy either with MTA or FS, depending on random digit table method allocation. Fifteen pediatric dental residents completed all pulpotomies, supervised by specialist faculty. Two calibrated examiners performed outcome assessments according to standardized criteria. Every six months, the study teeth were evaluated clinically and every 12 months radiographically. The inter- and intraexaminer reliability was assessed using Cohen's kappa, and the chi-square test was used for statistical analysis.
Results: At six months, 42 participants (21 in each group) returned for evaluation. The FS group showed 95.2 percent clinical success compared to 100 percent for the MTA group. At the 12-month clinical and radiographic evaluation, the return sample consisted of 29 participants (14 in the MTA group, 15 in the FS group). FS had 86.6 percent clinical success and 60 percent radiographic success, while MTA showed 100 percent clinical and radiographic success. At 12 months, MTA showed a statistically significantly higher success rate compared to FS (P = 0.008). Examiner reliability was excellent with a kappa score greater than 0.88.
Conclusion: At 12 months, MTA showed superior success as a pulpotomy medicament in primary molars compared to FS.

Effect of Overlying Material on Final Setting of Biodentine ® in Primary Molar Pulpotomies.

Purpose: The purpose of this study was to evaluate and compare in vitro the effect of overlying materials, including zinc oxide eugenol (ZOE), resin-modified glass ionomer cement (RMGIC), and stainless steel crowns (SSC) cemented with glass ionomer cement (GIC), on the setting of Biodentine ® (BD) used as a pulpotomy agent in primary molars that were restored definitively in a single visit. Methods: Forty extracted primary molars were prepared to replicate pulpotomy procedures. The teeth were randomly allocated to four restorative groups: (1) BD, ZOE, SSC; (2) BD, RMGIC, SSC; (3) BD, SSC; (4) BD only (control). All samples were incubated for 24 hours, sectioned mesial-distally, and polished. BD setting was measured as a function of Knoop hardness value (HK) using a Leco Microhardness Tester. Each sample was tested in three zones with 50 gf load force and 30 seconds dwell time and at one, two, and three mm distance from the BD-material interface. A one-way analysis of variance was used to determine statistical significance between groups (P<.05). Results: There was no statistically significant difference between the mean HK value among the four groups and three zones. Conclusions: Overlying materials, including zinc oxide eugenol, resin-modified glass ionomer, and stainless steel crowns cemented with glass ionomer cement, showed no effect on the BD final set. This in vitro study found no evidence against immediate definitive restoration of Biodentine ® pulpotomies.

Poly(Adenosine Phosphate Ribose) Polymerase 1 Inhibition Enhances Brain-derived Neurotrophic Factor Secretion in Dental Pulp Stem Cell-derived Odontoblastlike Cells.

INTRODUCTION: The nuclear enzyme poly(adenosine phosphate ribose) polymerase 1 (PARP-1) has been implicated in the maintenance and differentiation of several stem cells. The role of PARP-1 in dental pulp stem cell (DPSC) differentiation, especially in the context of its ability to modulate nerve regeneration factors, has not been investigated. Regeneration of neuronal components in pulp tissue is important for the assessment of tooth vitality. Brain-derived neurotrophic factor (BDNF) is known to play an integral signaling factor during nerve regeneration. In this study, we identified the role of PARP-1 in the modulation of BDNF in DPSC differentiation into odontoblastlike cells. METHODS: Human DPSCs were prepared from healthy molars and cultured in regular and osteogenic media treated with PARP-1 antagonist and PARP-1 exogeneous protein. Polymerase chain reaction and immunohistochemistry analysis for BDNF and various differentiation markers were performed. RESULTS: Our polymerase chain reaction results showed that differentiated cells show odontoblastlike properties because they express odontogenic markers such as dentin sialophosphoprotein and dentin matrix protein 1. Both PARP-1 inhibitor and protein did not affect odontogenic differentiation and proliferation because the number of the differentiated cells was unaffected, and the expression of dentin sialophosphoprotein and dentin matrix protein 1 was not significantly changed. There is the possibility that PARP-1 treatment induces DPSCs into the unique cell lineage. Some differentiated cells show a very unique morphology with large irregular cytoplasm and an oval nucleus. Moreover, PARP-1 inhibition significantly increased BDNF secretion in DPSC-derived odontoblastlike cells. This observation was also confirmed by immunohistochemistry. CONCLUSIONS: Taken together, our results indicate PARP-1 as a negative regulator in BDNF secretion during odontogenic DPSC differentiation, showing its potential application for translational nerve regeneration strategies to improve dental pulp tissue vitality assessments.

Wear characteristics and inhibition of enamel demineralization by resin-based coating materials.

In this study, wear and inhibition of enamel demineralization by resin-based coating materials were investigated. Seven commercially available coating materials, with and without fillers, were used. A mechanical wear test was performed, and the specimens were then examined with a scanning electron microscope. Hardness and elastic modulus measurements for each material were obtained by nanoindentation testing. Thin layers of each material were applied on human enamel surfaces, which were subjected to alternating immersion in demineralizing and remineralizing solutions. The inhibition ability of enamel demineralization adjacent to the coating was estimated with depth-dependent mechanical properties using the nanoindentation test. The non-filled coating material showed significantly lower hardness, lower elastic modulus, and higher weight loss. There were no significant differences in weight loss among the six filled coating materials. After the alternating immersion protocol, the enamel specimens having application of coating materials with ion-releasing ability were harder than those in the other groups in some locations 1-11 µm from the enamel surface and within 300 µm from the edge of the coating materials. In conclusion, clinical use of the resin-based coating materials with ion-releasing ability may prevent demineralization of exposed enamel adjacent to the coating during treatment.

Mechanical changes in human dental pulp stem cells during early odontogenic differentiation.

INTRODUCTION: Cell adhesion and migration in bioactive scaffolds require actin cytoskeleton remodeling and focal adhesion formation. Additionally, human dental pulp stem cells (hDPSCs) undergo several changes in their mechanical properties during odontogenic differentiation. The effect of factors essential for odontogenesis on actin stress fiber elasticity and focal adhesion formation is not known. METHODS: Live hDPSCs cultured in odontogenic media were imaged for cytoskeleton changes using an atomic force microscope. The Young's modulus (kPa) of the cytoskeleton was recorded as a function of culture medium for 10 days. Focal adhesion formation was assessed using immunofluorescence. Cultured hDPSCs were incubated with a monoclonal vinculin antibody, and filamentous actins were visualized using 0.5 µmol/L phalloidin. RESULTS: Cytoskeletal elasticity significantly increased in response to odontogenic media. Both the number and physical size of focal adhesions in hDPSCs also increased. Up-regulation of vinculin expression was evident. The increase in the formation of focal adhesions was consistent with actin remodeling to stress fibers. CONCLUSIONS: Our findings suggest that hDPSCs firmly attach to the glass substrate in response to odontogenic media. Successful regeneration of pulp-dentin tissue using biomimetic scaffolds will likely require cell-extracellular matrix interactions influenced by biochemical induction factors.

Effect of coating on properties of esthetic orthodontic nickel-titanium wires.

OBJECTIVE: To determine the effect of coating on the properties of two esthetic orthodontic nickel-titanium wires. MATERIALS AND METHODS: Woowa (polymer coating; Dany Harvest) and BioForce High Aesthetic Archwire (metal coating; Dentsply GAC) with cross-section dimensions of 0.016 × 0.022 inches were selected. Noncoated posterior regions of the anterior-coated Woowa and uncoated Sentalloy were used for comparison. Nominal coating compositions were determined by x-ray fluorescence (JSX-3200, JOEL). Cross-sectioned and external surfaces were observed with a scanning electron microscope (SEM; SSX-550, Shimadzu) and an atomic force microscope (SPM-9500J2, Shimadzu). A three-point bending test (12-mm span) was carried out using a universal testing machine (EZ Test, Shimadzu). Hardness and elastic modulus of external and cross-sectioned surfaces were obtained by nanoindentation (ENT-1100a, Elionix; n  =  10). RESULTS: Coatings on Woowa and BioForce High Aesthetic Archwire contained 41% silver and 14% gold, respectively. The coating thickness on Woowa was approximately 10 µm, and the coating thickness on BioForce High Aesthetic Archwire was much smaller. The surfaces of both coated wires were rougher than the noncoated wires. Woowa showed a higher mean unloading force than the noncoated Woowa, although BioForce High Aesthetic Archwire showed a lower mean unloading force than Sentalloy. While cross-sectional surfaces of all wires had similar hardness and elastic modulus, values for the external surface of Woowa were smaller than for the other wires. CONCLUSIONS: The coating processes for Woowa and BioForce High Aesthetic Archwire influence bending behavior and surface morphology.

Impact energy absorption of three mouthguard materials in three environments.

The objective of this study was to compare the impact energy absorption of three mouthguard materials in three environments. Thirty specimens with 12.7 cm x 12.7 cm x 4 mm dimensions were prepared for each material: ethylene vinyl acetate (EVA, T&S Dental and Plastics), Pro-form (Dental Resources Inc), and PolyShok (Sportsguard Laboratories). Ten specimens of each material were conditioned for 1 h at 37 degrees C in three environments: dry (ambient) condition, deionized water and artificial saliva. Specimens were impacted at 20 mph by a 0.5-inch diameter indenter containing a force transducer (Dynatup Model 9250 HV, Instron Corp), based upon ASTM Standard D3763. Energy absorption was determined from the area under the force-time curve during impact (approximately 5 or 7 ms depending on the material). Groups were compared using anova and the Tukey test. Energy absorption values, normalized to specimen thickness (mean +/- SD in J mm(-1)), were: (i) Dry: EVA 4.73 +/- 0.27, Pro-form 3.55 +/- 0.25, PolyShok 6.32 +/- 0.24; (ii) DI water: EVA 4.82 +/- 0.40, Pro-form 3.78 +/- 0.33, PolyShok 5.87 +/- 0.38; (iii) Artificial saliva: EVA 5.63 +/- 0.49, Pro-form 4.01 +/- 0.54, PolyShok 6.37 +/- 0.55. PolyShok was the most energy-absorbent material in all three environments. EVA was significantly more impact resistant than Pro-form in all three environments. EVA and Pro-form performed significantly better after saliva conditioning than dry or water conditioned, but PolyShok did not show any difference in energy absorption when conditioned in any of the three environments. Characteristic deformation patterns from impact loading were observed with an SEM for each material. The superior energy absorption for PolyShok is attributed to the polyurethane additive.

Metallurgical characterization of a new nickel-titanium wire for rotary endodontic instruments.

INTRODUCTION: A novel thermomechanical processing procedure has been developed that yields a superelastic (SE) nickel-titanium (NiTi) wire (M-Wire) that laboratory testing shows has improved mechanical properties compared with conventional SE austenitic NiTi wires used for manufacture of rotary instruments. The objective of this study was to determine the origin of the improved mechanical properties. METHOD: Specimens from 2 batches of M-Wire prepared under different processing conditions and from 1 batch of standard-processed SE wire for rotary instruments were examined by scanning transmission electron microscopy, temperature-modulated differential scanning calorimetry, micro-x-ray diffraction, and scanning electron microscopy with x-ray energy-dispersive spectrometric analyses. RESULTS: The processing for M-Wire yields a microstructure containing martensite, that the proportions of NiTi phases depend on processing conditions, and that the microstructure exhibits pronounced evidence of alloy strengthening. CONCLUSIONS: The presence of Ti(2)Ni precipitates in both microstructures indicates that M-Wire and the conventional SE wire for rotary instruments are titanium-rich.

Micro-XRD and temperature-modulated DSC investigation of nickel-titanium rotary endodontic instruments.

OBJECTIVES: Employ Micro-X-ray diffraction and temperature-modulated differential scanning calorimetry to investigate microstructural phases, phase transformations, and effects of heat treatment for rotary nickel-titanium instruments. METHODS: Representative as-received and clinically used ProFile GT and ProTaper instruments were principally studied. Micro-XRD analyses (Cu Kalpha X-rays) were performed at 25 degrees C on areas of approximately 50 microm diameter near the tip and up to 9 mm from the tip. TMDSC analyses were performed from -80 to 100 degrees C and back to -80 degrees C on segments cut from instruments, using a linear heating and cooling rate of 2 degrees C/min, sinusoidal oscillation of 0.318 degrees C, and period of 60s. Instruments were also heat treated 15 min in a nitrogen atmosphere at 400, 500, 600 and 850 degrees C, and analyzed. RESULTS: At all Micro-XRD analysis regions the strongest peak occurred near 42 degrees , indicating that instruments were mostly austenite, with perhaps some R-phase and martensite. Tip and adjacent regions had smallest peak intensities, indicative of greater work hardening, and the intensity at other sites depended on the instrument. TMDSC heating and cooling curves had single peaks for transformations between martensite and austenite. Austenite-finish (A(f)) temperatures and enthalpy changes were similar for as-received and used instruments. Heat treatments at 400, 500 and 600 degrees C raised the A(f) temperature to 45-50 degrees C, and heat treatment at 850 degrees C caused drastic changes in transformation behavior. SIGNIFICANCE: Micro-XRD provides novel information about NiTi phases at different positions on instruments. TMDSC indicates that heat treatment might yield instruments with substantial martensite and improved clinical performance.

Application of plasma immersion ion implantation for surface modification of nickel-titanium rotary instruments.

By means of X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC), this study set out to investigate the application of plasma immersion ion implantation (PIII) for the surface modification of ProTaper NiTi rotary instruments. This study was undertaken because the PIII method was perceived to have the potential of developing into a standard surface modification technique that improves clinical quality and outcome. Specimens received nitrogen ion or nitrogen plus argon ion implantation. XPS analyses with and without argon ion etching were obtained for all specimens. In addition, DSC analysis was performed to investigate the phase transformation behavior of the bulk material. Results indicated that the surfaces of NiTi instruments were successfully modified by nitrogen PIII, whereby a light golden TiN layer was yielded. Moreover, the PIII technique did not alter the superelastic character of NiTi instruments because it was carried out at near-room temperature. We thus concluded that nitrogen PIII is a promising surface modification technique to improve the surface characteristics of NiTi rotary instruments.

Differential scanning calorimetry (DSC) and temperature-modulated DSC study of three mouthguard materials.

OBJECTIVES: Employ differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) to investigate thermal transformations in three mouthguard materials and provide insight into their previously investigated energy absorption. METHODS: Samples (13-21mg) were obtained from (a) conventional ethylene vinyl acetate (EVA), (b) Pro-form, another EVA polymer, and (c) PolyShok, an EVA polymer containing polyurethane. Conventional DSC (n=5) was first performed from -80 to 150 degrees C at a heating rate of 10 degrees C/min to determine the temperature range for structural transformations. Subsequently, TMDSC (n=5) was performed from -20 to 150 degrees C at a heating rate of 1 degrees C/min. Onset and peak temperatures were compared using ANOVA and the Tukey-Kramer HSD test. Other samples were coated with a gold-palladium film and examined with an SEM. RESULTS: DSC and TMDSC curves were similar for both conventional EVA and Pro-form, showing two endothermic peaks suggestive of melting processes, with crystallization after the higher-temperature peak. Evidence for crystallization and the second endothermic peak were much less prominent for PolyShok, which had no peaks associated with the polyurethane constituent. The onset of the lower-temperature endothermic transformation is near body temperature. No glass transitions were observed in the materials. SEM examination revealed different surface morphology and possible cushioning effect for PolyShok, compared to Pro-form and EVA. SIGNIFICANCE: The difference in thermal behavior for PolyShok is tentatively attributed to disruption of EVA crystal formation, which may contribute to its superior impact resistance. The lower-temperature endothermic peak suggests that impact testing of these materials should be performed at 37 degrees C.

Fatigue limits and SEM/TEM observations of fracture characteristics for three Pd-Ag dental casting alloys.

The fatigue limits and fracture characteristics for three Pd-Ag dental casting alloys (Super Star, Heraeus Kulzer; Rx 91, Pentron; W-1, Ivoclar Vivadent) were studied. Specimens meeting the dimensions for ADA Specifications No. 5 and 38, and having the as-cast surface condition, were subjected to heat treatment simulating dental porcelain firing cycles and fatigued in air at room temperature under uniaxial tension-compression at 10 Hz. A ratio of compressive stress amplitude to tensile stress amplitude (R-ratio) of -1 was used. Alloy microstructures and fracture surfaces were examined with a scanning electron microscope and a transmission electron microscope. Fatigue limits for the three alloys had low values of approximately 15% of the yield strength for 0.2% permanent tensile strain. Complex fracture surfaces with characteristic striations were observed for all three fatigued alloys. Planar slip of dislocations occurred in the Pd solid solution matrix, along with dislocation-precipitate interactions and dislocation networks in the interfaces between the precipitates and surrounding matrix. Twinning occurred in the Pd solid solution matrix of Rx 91, and within discontinuous precipitates in Super Star and Rx 91. The low fatigue limits for these alloys are attributed to their complex microstructures and perhaps to casting defects.

Micro-XRD study of beta-titanium wires and infrared soldered joints.

OBJECTIVE: The purpose of this study was to investigate the metallurgical phases in beta-titanium soldered joints prepared by infrared soldering, using the Micro X-ray diffraction technique (Micro-XRD), and to characterize the Vickers hardness in the soldered beta-titanium wires. METHODS: Beta-titanium wires with cross-section dimensions of 0.032in.x0.032in. (TMA, Ormco), and both titanium-based solder (Ti-30Ni-20Cu, Selec) and silver-based solder (Ag-22Cu-17Zn-5Sn, Tomy) were selected. Soldering was performed using infrared radiation (RS-1, Morita) under argon atmosphere. Micro-XRD analyses were performed at room temperature. Micro-XRD spectra were obtained for the boundary region of the soldered beta-titanium wires using 50microm and 10microm diameter analysis regions. Hardness was measured at 30microm intervals from boundary of the diffusion layer and beta-titanium wire. The Kruskal-Wallis test with the Bonferroni and Wilcoxson Mann-Whitney tests for nonparametric means were employed as statistical methods (P<0.05). RESULTS: For both types of soldered beta-titanium samples, the Micro-XRD spectra contained four major peaks for body-centered cubic (bcc) beta-titanium. Additional peaks at about 41 and 45 degrees are attributed to Cu-Ti intermetallic phase(s), which may be metastable under soldering conditions. The diffusion layer had greater hardness than bulk beta-titanium for both types of soldered specimens (P<0.05). SIGNIFICANCE: Soldering of beta-titanium orthodontic wire by infrared radiation may be acceptable for clinical use, since Micro-XRD spectra revealed that both types of soldered specimens largely retained the bcc beta-titanium structure. Further research is needed to investigate the mechanical properties and corrosion behavior of infrared-soldered beta-titanium wire.

Vickers hardness investigation of work-hardening in used NiTi rotary instruments.

A contributing mechanism for clinical failure of NiTi rotary instruments might be excessive work hardening. Vickers hardness was measured with 300 gm load near the flutes in three regions (D2-D4, D6-D10, and D14 towards the shank) for nine representative clinically used ProFile GT instruments that had been axially sectioned (10 measurements in each region). Consistent values could not be obtained at D1. Minimum hardness occurred at D2 to D4, with means from 313 to 324 (SD from 7 to 16). Maximum hardness with means ranging widely from 330 to 481 was found beyond D14. Mean hardness at D2 to D4 was 320 for an as-received ProFile instrument. Because a mean Vickers hardness of 326 has been reported for a shape-memory NiTi orthodontic wire product, it can be concluded that the NiTi instruments did not experience substantial work hardening at D2 to D4 during clinical use, in agreement with previous differential scanning calorimetric analyses.

Microstructures of beta-titanium orthodontic wires joined by infrared brazing.

The microstructures and interdiffusion in brazed beta-titanium orthodontic wires were investigated by scanning electron microscopy and electron probe microanalysis, respectively. Beta-titanium wire (Ti-11Mo-6Zr-4Sn) with cross-section dimensions of 0.032 in. x 0.032 in., titanium-based braze alloy (Ti-30Ni-20Cu), and silver-based braze alloy (Ag-22Cu-17Zn-5Sn) were selected for the study. Brazing was performed using infrared radiation (RS-1) under an argon atmosphere. Specimens were etched with two solutions (2.5% HF + 2.5% HNO(3) + 95% H(2)O; 25% HN(4)OH + 30% H(2)O(2) + 45%H(2)O). It was found that the silver-based braze alloy has a eutectic structure. In the diffusion layer between the beta-titanium wire and this silver-based braze alloy, Cu and Ti were enriched on the wire side, and Sn and Ti were enriched on the braze alloy side. The titanium-based braze alloy has a dendritic structure. Beta-titanium wire specimens brazed with the titanium-based braze alloy had a thicker intermediate area compared to the silver alloy; Ti in the diffusion layer had an irregular concentration gradient, and the braze alloy side had higher Ti concentration. The original microstructure of the beta-titanium wire was not altered with the use of either braze alloy. Infrared brazing of beta-titanium orthodontic wire is acceptable for clinical use, since the wire microstructure did not deteriorate with either the titanium-based or silver-based braze alloy. The differing microstructures of the joint regions for the two braze alloys suggest that the joint strengths may also differ.

Bending fatigue study of nickel-titanium Gates Glidden drills.

ProFile nickel-titanium Gates Glidden drills were tested in bending fatigue to simulate clinical conditions. Ten samples each in sizes #1 through #6 were placed in a device that deflected the drill head 4 mm from the axis. The drill head was placed inside a ball bearing fixture, which allowed it to run free at 4000 rpm, and the total number of revolutions was recorded until failure. Fracture surfaces were examined with a scanning electron microscope to determine the initiation site and nature of the failure process. Mean +/- SD for the number of revolutions to failure for the drill sizes were: #1: 1826.3 +/- 542.5; #2: 5395.7 +/- 2581.5; #3: 694.4 +/- 516.8; #4: 261.0 +/- 138.0; #5: 49.6 +/- 14.9; #6: 195.9 +/- 78.5. All drills failed in a ductile mode, and fracture initiation sites appeared to be coincident with machining grooves or other flaws, suggesting the need for improved manufacturing procedures.

SEM observations of nickel-titanium rotary endodontic instruments that fractured during clinical Use.

Numerous discarded ProFile GT, ProFile, and ProTaper nickel-titanium rotary instruments obtained from two graduate endodontic clinics were examined by scanning electron microscopy. These instruments had an unknown history of clinical use and had fractured or experienced considerable permanent torsional deformation without complete separation. The failure processes generally exhibited substantial ductile character, evidenced by a dimpled rupture fracture surface. Crack propagation at grain boundaries and cleavage surfaces indicative of transgranular fracture were observed for some specimens. It appeared that oxide particles from the manufacturing process served as nucleating sites for the microvoids, leading to dimpled rupture. A previously unreported fracture mode also was observed, in which crack propagation, approximately parallel to the local flute orientation, connected pitted regions on the surface. Combining present and previous scanning electron microscopy observations of clinically failed instruments, suggestions are offered for improving their fracture resistance.